Dithiocarboxylates in the synthesis of metal complexes

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DITHIOCARBOXYLATES IN THE SYNTHESIS OF METAL COMPLEXES

Emilia Niittyviita

MASTER’S THESIS Inorganic Chemistry Kemistin koulutusohjelma

634/2019

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Dithiocarboxylates in the Synthesis of Metal Complexes Emilia Niittyviita, 267313

University of Eastern Finland, Department of Chemistry

Supervisors: docent Sirpa Jääskeläinen and docent Pipsa Hirva Joensuu 23.9.2019

Abstract

Dithiocarboxylates are sulphur rich organic ligands, that contain the group -CSS^-. They are formed by deprotonation from dithiocarboxylic acids (RCSSH, where R is a hydrocarbon). The dithiocarboxylic acids are strong organic acids, that are usually colourful, foul smelling, highly reactive and instable. Because of the instability of the precursor, the complexes have not been extensively studied. However, the dithiocarboxylates are versatile ligands, that can coordinate to a metal ion in several different ways, commonly as a bidentate donor forming a four-membered ring with the metal. The dithiocarboxylates are usually resonance stabilized, with the negative charge distributed throughout the -CSS^- group. This leads to the ability of the group to coordinate to a wide range of metal ions. Hence, a range of metal complexes have been previously synthesised and reported. The complexes are often colourful substances and they can be used in chemical and material manufacturing for example as catalysts and reactants. Dithiocarboxylates can also form larger structural units with metals such as coordination polymers and clusters.

The practical work consists of evaluating different synthesis methods of producing complexes of one dithiocarboxylate ligand (4-imidazoledithiocatboxylate) with coinage metals. Seven different synthesis methods (one-pot, two-phase, solvothermal, UV-, and gel synthesis as well as mechano- and sonochemical synthesis), with varying reaction conditions and reactant ratios were used in order to gain information about the reactions. In addition, several crystallization techniques were used. The products were analysed with various spectroscopic methods (NMR, IR, Raman, UV-VIS) as well as with scanning electron microscopy, single crystal x-ray crystallography, elemental analysis and melting point measurements.

Based on the analysis of 60 syntheses performed, the ligand is reactive with all the metals used and the synthesis methods influence the product. The products of each metal have similar properties still maintaining unique characteristics. The limited use of solvent in one form or other produces interesting results, by minimizing ligand degradation.

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Dithiocarboxylates in the Synthesis of Metal Complexes Emilia Niittyviita, 267313

Itä-Suomen yliopisto, Kemian laitos

Ohjaajat: dosentti Sirpa Jääskeläinen and dosentti Pipsa Hirva Joensuu 23.9.2019

Tiivistelmä

Ditiokarboksylaatit ovat rikkipitoisia orgaanisia ligandeja, jotka sisältävät -CSS^- -ryhmän. Ne muodostuvat ditiokarboksyylihapoista (RCSSH, jossa R on hiilivety) deprotonoitumalla.

Ditiokarboksyylihapot ovat voimakkaita orgaanisia happoja, jotka ovat yleensä värikkäitä, pahanhajuisia, reaktiivisia ja epävakaita. Ditiokarboksyylihappojen epävakaudesta johtuen ditiokarboksylaattien komplekseja on tutkittu vähän. Ditiokarboksylaatit ovat kuitenkin monipuolisia ligandeja, jotka voivat koordinoitua metalleihin monella eri tavalla. Yleisin koordinaatiotapa on nelijäseninen rengas metallin kanssa. Ditiokarboksylaattianionille on tyypillistä resonanssirakenne, jossa varaus tasaantuu vakauttaen niin anionin kuin kompleksin rakennetta. Tämä johtaa ryhmän kykyyn sitoa monenlaisia metalli-ioneja. Useiden metallien ditiokarboksylaattikomplekseja onkin syntetisoitu ja raportoitu. Ne ovat usein värillisiä yhdisteitä, ja niitä voidaan hyödyntää kemikaali- ja materiaalituotannossa mm. katalyytteinä ja lähtöaineina. Molekulaaristen kompleksien lisäksi ditiokarboksylaatit voivat muodostaa suurempia rakenneyksiköitä, eli rypäleyhdisteitä ja koordinaatiopolymeerejä.

Työn käytännön osuudessa valmistetiin ditiokarboksylaattikomplekseja erilaisia synteesimenetelmiä käyttäen. Synteeseissä käytettiin yhtä ditiokarboksylaattiligandia (4-imidatsoliditiokarboksylaatti) kolmen eri metallin (kupari, hopea ja kulta) kanssa. Synteeseissä käytettiin kaiken kaikkiaan seitsemää eri synteesimenetelmää (liuos-, geeli-, kaksifaasi-, autoklaavi- ja mekanokemiallinen synteesi, sekä ultraääni ja UV-säteily –avusteinen synteesi). Eri menetelmien lisäksi reaktio- olosuhteita ja lähtöaineiden suhteellisia määriä muunneltiin, jotta menetelmistä saataisiin mahdollisimman monipuolinen kuva. Synteesimenetelmien lisäksi erilaisia kiteytysmenetelmiä testattiin laajalti. Tuotteiden analysointiin käytettiin useita spektroskooppisia menetelmiä (NMR, IR, Raman, UV-VIS) sekä pyyhkäisyelektronimikroskopiaa, yksikideröntgenkristallografiaa, alkuaineanalyysia ja sulamispistemittauksia.

Synteesejä tehtiin yhteensä 60, ja niistä syntyneiden tuotteiden perusteella voidaan sanoa ligandin olevan reaktiivinen kaikkien käytettyjen metallien kanssa, ja synteesimenetelmän vaikuttavan syntyvään tuotteeseen. Kunkin metallien tuotteet ovat keskenään samankaltaisia, mutta eivät identtisiä. Menetelmistä lupaavimpia ovat ne, joissa liuottimien käyttö on rajattua, jottei ligandi ala hajota.

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Abbreviations

BP = boiling point

DMF = N,N-Dimethylformamide DMSO = dimethyl sulfoxide EA = elemental analysis IR = infrared

LMCT = ligand to metal charge transfer MLCT = metal to ligand charge transfer MP = melting point

NMR = nuclear magnetic resonance SEM = scanning electron microscope TMS = tetramethylsilane

UV = ultraviolet

UV-VIS = ultraviolet-visible

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1. Introduction

Dithiocarboxylates are a group of organic molecules with general chemical formula RCSS^-.¹ The anions can act as ligands in metal complexes. Dithiocarboxylates belong to a ligand group called dithioacids. Dithioacids in general, contain the CSS- functional group.¹ Dithiocarboxylates have been known since the 19^th century, but have not been extensively researched so far, because of the instability of their precursors, the dithiocarboxylic acids.^1,2 Other dithioacids are more stable and have therefore been more broadly investigated than dithiocarboxylates.¹ However, the examples of metal complexes with a range of metals, and with several coordination modes for dithiocarboxylates have been presented.³ Based on the literature the dithiocarboxylate moiety is versatile.

Dithiocarboxylates are analogues of carboxylates and therefore comparing the two, dithiocarboxylates and carboxylates, and their complexes are of interest.¹ Carboxylates also show a range of metal complexes and they are more widely studied than the dithiocarboxylates, since they are more stable and well-known species.^{2,4- 20} The ligands have great similarity, but also notable differences in their properties, due to the different nature of oxygen and sulfur.^3,21-24 The chalcogens (O, S, Se, Te) in general have noticeable variety in their properties as one goes down the group 16.

Even though having the same valence-electron structure does create similarities among them, oxygen is the odd one out in the group. Among the chalcogens, oxygen has the highest electronegativity and ionization energy. These properties decrease as one moves to the heavier chalcogens. In general, sulphur and the heavier elements of group 16 favour to interact with soft elements, where oxygen prefers hard ones.²³ Elements that are large and easy to polarize are called soft elements, whereas hard ones have the opposite qualities.²⁴ This creates differences among the analogies with the preference of metals and oxidation states. Similarities include having anionic resonance stabilized ligands from corresponsive acids with versatile coordination and capability to form larger structures.3,7,8,21,22,25-38

In the experimental section of this thesis the focus will be on synthesising new complexes using 1H- imidazole-4-carbodithioic acid, or 4-imidazoledithiocarboxylic acid and group 11 metals (Cu, Ag, Au). Different synthesis methods and conditions were used during the work exploring what methods are suitable with the somewhat sensitive ligand. The solid products formed were analysed with an array of analytical methods (H¹-NMR, UV-VIS, Raman and IR spectroscopy, SEM, single crystal X- ray crystallography, elemental analysis and melting point measurements).

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2. General properties of dithiocarboxylates

Figure 1. The general structure of dithiocarboxylic acid.¹

Dithiocarboxylates are organic anions formed from dithiocarboxylic acids (Figure 1) by deprotonation. These anions can function as ligands and they belong to the ligand group dithioacids.

Dithioacids are organic acids that have a general formula of RnXCSS^- (n=1 or 2), where R is an aryl or alkyl group and X depends on the type of molecule. X is N for dithiocarbamates, O for xanthates, S for thioxanthates and C for dithiocarboxylates. All dithioacids have a charge of -1. The dithioacid ligands are formed by deprotonation of corresponsive dithiocarboxylic acids. The general structures of dithiocarbamates, xanthates and thioxanthates are shown in Figure 2.¹

Figure 2. General structures of dithiocarbamates, xanthates and thioxanthates.¹

The common attributes of dithiocarboxylic acids are instability, unpleasant smell, solubility to organic solvents, colourfulness and reactiveness. Instability of the dithiocarboxylic acids makes them hard to handle and they easily oxidize to disulphides, thiocarboxylic acids and their disulphides, mixed disulphides of dithio- and thiocarboxylic acids, trithianes and hexathiaadamantanes.^1,2 Because of the instability of the acids, their salts or esters are often used instead.² As acids dithiocarboxylic acids are quite strong. The strength of the acidity of dithiocarboxylic acids can be seen as a result of the stabile resonance form of the deprotonated species and the dithiocarbonyl groups high electron- withdrawing ability.³⁷

The dithiocarboxylate moiety can be attached to many kinds of aryl of alkyl groups. The aryl and alkyl groups can have other functional groups within them.^1-3 The additional functional groups can add sites of coordination in the molecule. These sites can have different properties than the dithiocarboxylate moiety. An example of a R group with further functional groups is the imidazole ring. 4-imidazoledithiocarboxylate, formed from 1H-imidazole-4-carbodithioic acid by

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deprotonation, is a dithiocarboxylate containing an imidazole ring. The aromatic ring adds new properties to the ligand. With the ring, there is a conjugated system throughout the molecule. The aromatic ring also adds coordination sites and reactivity with the nitrogen atoms in it.²⁶ The molecule is a tautomeric species with two forms, 4- and 5-imidazoledithiocarboxylate, which can change to one another. The structures of 4- and 5-imidazoledithiocarboxylate are presented in Figure 3 with the numbering of the atoms.

Figure 3. Structures of a) 4-imidazoledithiocarboxylic acid and b) 5-imidazoledithiocarboxylic acid.

The dithiocarboxylates are analogues of carboxylates, which form from carboxylic acids via deprotonation. In the dithiocarboxylates in place of the two oxygen atoms of the carboxylate group there are two sulphur atoms. Because the species have similar structures it is of interest to compare the two with each other. Further comparison can be made with thiocarboxylic acids. Thiocarboxylic acids, or monothiocarboxylic acids, are analogues of carboxylic acids, with one of the oxygen atoms replaces by a sulphur atom.³⁸

The different qualities of sulphur and oxygen have an effect on the qualities of carboxylic acids and their sulphur derivatives. A noticeable effect is on the acidity of these species.³⁷ In terms of acidity the more sulphur in the compound, the more acidic the compound is. This means that the dithiocarboxylic acids are the most acidic and the carboxylic acids the least acidic of the three, when comparing acids with structures that are the same besides the acid moiety (Table 1). The dithiocarboxylic acids being the strongest of the acids is to some extent due to the strongest resonance stabilization of the deprotonated form among the three species.³⁷ Besides acidity the reactivity of dithiocarboxylic acids is high in comparison to corresponsive carboxylic acids.

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Table 1. Examples of dithio-, thio- and carboxylic acids presented with their pKa values, where values marked with * are predicted values.^{37,39, 40}

Compound pKa Compound pKa Compound pKa

CH3CS2H 2.55³⁷ CH3COSH 3.33³⁷ CH3COOH 4.78³⁷

CH3CH2CS2H 2.52³⁷ CH3CH2COSH 4.20±0.10³⁹ * CH3CH2COOH 4.87⁴⁰

PhCS2H 2.00±0.20³⁹ * PhCOSH 2.48³⁷ PhCOOH 4.21³⁷

3. Dithiocarboxylates as ligands

3.1. Ligand properties

Ligand properties like ligand type, donor ability, hardness or softness of the ligand can tell a lot about the ligand and its behaviour during complextion. Dithiocarboxylates, like carboxylates are formally a LX type ligand. This means that the ligand has an anionic and a neutral donor atom in the structure.

Neutral donors are ligands or ligands parts, which have no charge, and which interact through lone- pairs or bonds like double bonds, in the ligand.⁴¹ As LX type ligand one of the sulphur atoms in dithiocarboxylate motif formally has a double bond and lone-pairs, functioning as the neutral donor.

The other sulphur atom is the anionic X type, with a formal charge of -1. However, the charge is often equally distributed throughout the group via resonance when coordinated or deprotonated, stabilizing the ligand (Figure 4). Because of the resonance stabilization of the dithiocarboxylate group, the sulphur atoms can support a wide range of metal oxidation states.³

Figure 4. The resonance stabilization of dithiocarboxylate.²⁵

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Both dithiocarboxylates and carboxylates have a double bond and lone pairs, which are considered properties of soft ligands. Soft ligands are ligands that have a tendency to form covalent bonding and they often prefer to interact with soft metals which also favour covalent bonding, whereas hard ligands and metals tend to form ionic bonds. In general, comparing oxygen and sulphur ligands, ligands containing oxygen are considered to be harder and sulphur ligands to be softer ligands.⁴¹ In 4(5)-imidazoledithiocarboxylate, there is additional donor ability from the aromatic imidazole ring.

The nitrogen atom with no hydrogen can act as a further contact point as a neutral donor, enabling connectivity to other metal centres or molecules and different chelating i.e. ring formation possibilities. The other nitrogen can also be deprotonated, adding anionic nature. Nitrogen atoms are harder donors compared to sulphur atoms. The hardness adds new character to the molecule, this can be of use when coordinating to harder metals, since they prefer harder ligands.⁴¹

3.2. Coordination modes

Dithiocarboxylates have several modes of coordination, the typical one being a four-membered ring, chelating to the metal through the sulphur atoms acting as bidentate ligand.^3,38 The resonance stabilization of the dithiocarboxylate moiety results in quite strong bonding between the metal centre and the ligand.³ The anionic sulphur atoms enable versatile coordination to one or several metal centres. Different coordination modes of dithiocarboxylates are shown in Figure 5, these include both coordination to single metal and bridging modes.³ The typical four-membered ring noted as mode B.

Figure 5. Coordination modes of dithiocarboxylates, where R is aryl or alkyl. A) Monodentate B) chelating C) bridging D) chelating and bridging and E) bridging of three metals.³

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If other heteroatoms or binding parts, like π-bonds, are added to the R group they may take part in the coordination. This can be seen in the coordination of 4(5)-imidazoledithiocarboxylate, which besides chelating through the sulphur atoms, can chelate through nitrogen and sulphur as well as form bridging modes through the nitrogen. Five possible coordination modes of 4(5)- imidazoledithiocarboxylate have been suggested in literature (Figure 6). Modes I-III are for 4- imidazoledithiocarboxylate and IV and V for 5-imidazoledithiocarboxylate. I and II are chelating through nitrogen and sulphur, forming a five-membered ring. The imidazole nitrogen at mode II is further connected to a second metal centre. III and IV are modes that chelate through the sulphur atoms, forming the four-membered rings common to dithiocarboxylates. Mode IV is also bridging to a second metal centre through nitrogen. Mode V is the only mode that does not form a ring when coordinated, the mode only bridges two metal centres through one of the sulphur atoms and one of the nitrogen atoms.²⁶

Figure 6. Coordination modes of 4-imidazoledithiocarboxylate and 5-imidazoledithiocarboxylate.²⁶

Dithiocarboxylates and carboxylates have several common coordination modes.^3,21,22 However, comparing the strength of bonding between the metal and ligand as well as coordination of specific analogous ligands between ditiocarboxylates and carboxylates proves difficult, because of the lack of comparable complexes available. Despite this, when comparing coordination modes in general they do not appear to have much of a difference, all modes seen in Figure 5 also apply to carboxylate ligands.^21,22 Outside of those presented in Figure 5, there are further modes of coordination that can be found for carboxylates, these are shown in Figure 7.^21,22

Figure 7. Coordination modes of carboxylates, where R is aryl or alkyl. F) Bridging, G) bridging of three metals, H) chelating and bridging with three metals, I) bridging with both oxygen atoms and J) chelating and bridging with five metals.^21,22

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4. Metal complexes of dithiocarboxylates

Wide range of transition metals as well as some of the main group metals, lanthanides and actinides have been studied with dithiocarboxylate ligands.3,25,26,42-51 Popular transition metals include groups 10^3,51 and 12^44-46, as well as metals iron⁴⁷, ruthenium^{50, 52} and copper^47,27. In the reviewed literature a variety of metals and oxidation states can be found, showing that the dithiocarboxylate motif is a versatile ligand, with no apparent preferences on a metal. 3,25,26,42-51 Examples of metal complexes in the coordination modes A and B are presented in Figure 8.⁴⁵

Figure 8. Complexes a) CdL4 (L=2-(1,3-dimethylimidazolidinio) dithiocarboxylate), b) ZnL^’3 (L^’=2,2- dimorpholino-2-ethylium-1-dithioate).⁴⁵

The only known complexes with 4(5)-imidazoledithiocarboxylate as a ligand are complexes of tin and copper.^26,53 For tin, there are two crystallographic structures presented in the literature and one structure can be found for copper. The copper complex (Figure 9) is the only complex with of 4(5)- imidazoledithiocarboxylate as sole ligand.⁵³ For tin several different structures with 4(5)- imidazoledithiocarboxylate with different second ligands have been presented.²⁶ All the complexes show coordination through both sulphur and nitrogen atoms, forming a five-membered chelating ring of modes I or II. The tin complexes with studied crystallographic structures can be seen in Figure 10.²⁶

Figure 9. Complex CuL2 (L=4-imidazoledithiocarboxylate).⁵³

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Figure 10. Examples of 4(5)-imidazoledithiocarboxylate tin complexes a) SnLMe2Cl (L=4- imidazoledithiocarboxylate) and b) SnPh2L2, and a coordination polymer of c) SnL²Me2 (L²=5- imidazoledithiocarboxylate).²⁶

For 4(5)-imidazolecarboxylate complexes with Fe¹⁵, Mg⁴, Mn⁵, Ni^6,16, Ca⁷, Cd⁸, Co^6,9,10, Cu^10,11,53, Pt^6,10, Ru^12,20, Zn^4,10,19, V^13,17,18 and several lanthanides¹⁴ have been previously presented. Structures are not available for all the complexes in an accuracy that determines the coordination mode of the ligand, and some of the structures have been deduced from only infrared measurements and elemental analysis. Those complexes that have suggested structures are usually coordinated to the metal through mode I. Large part of the complexes have other ligands in addition to the 4(5)-imidazolecarboxylate, the second ligand is often water. Common type of complex of 4-imidazolecarboxylate is pictured in Figure 11. The common complexes have trans and cis isomers. Regardless of the isomer, the coordination mode of the 4-imidazolecarboxylate is I and the complexes have water as a second ligand.^4-20

Figure 11. General structure of a common type of complex ML2L^’2 (L=4(5)-imidazolecarboxylate, L’=H2O), a) cis conformation, b) trans conformation.^4,5,9,16

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5. Dithiocarboxylates in clusters and coordination polymers

A cluster can be defined in two ways, here both are used. Therefore, clusters discussed are species containing several metal ions with and without metal-metal bonds. This is because examples of both types of clusters can be found.⁴¹ In general, clusters can be viewed as large molecules or small pieces of bulk material, having properties of both, but also unique features of their own.⁵⁴ Coordination polymers, on the other hand are structures where metal ions are bridged together by ligands to from large polymers ranging from 1D to 3D structures of infinite dimension.⁵⁵ Clusters and coordination polymers of 4(5)-imidazoledithiocarboxylate and its derivatives can be found. A range of metals can form either clusters or coordination polymers with dithiocarboxylates. The metals include groups 10 and 11, Fe, Li, Mn, Re, Ru, Sn and Zn. The number of metal ions in these larger structures range from two to the infinite arrays of coordination polymers.^3,26-33

Clusters with metal-metal -bonds can be found for example for copper one such cluster is pictured in Figure 12a. The cluster is built up from four copper atoms and four dithiocarboxylate ligands. Each ligand is bridging three metals together via the sulphur atoms in coordination mode E. The copper atoms are then further connected to other copper atoms to form a square amongst them.³² There are also clusters of copper, where the dithiocarboxylate simply works as a link between the metals, these types of species are examples of clusters with no metal-metal -bonds. An example of this kind of cluster is presented in Figure 12b. In this cluster as well, the coordination mode of two of the dithiocarboxylate groups is E. In addition to that the remaining three ligands are in coordination mode C.³¹ The clusters presented in Figure 12 only contain dithiocarboxylatelate ligands, but clusters with dithiocarboxylates with auxiliary ligands exist.^27-29,31

Figure 12. Schemes of cluster a) Cu4L4 (L=n-butyldithiocarboxylate),³² and b) Cu3L^’5 (L^’=N,N-dibenzyl-2- imidazoliumdithiocarboxylate)³¹.

Coordination polymers can also either have or not to have metal-metal interactions. Interesting examples of coordination polymers with metal-metal interactions can be found for gold where the gold atoms form continuous chains. These chains can be bridged together in different ways by the dithiocarboxylate ligands, one example is shown in Figure 13a. In the presented chain of dimers, the dithiocarboxylate ligands are attached to the gold atoms by mode C and the chain is formed by

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continuous gold-gold interaction in and between the dimers.³⁰ As an example of a coordination polymer with both metal-metal interactions and ligand bridging a dimeric silver chain with intramolecular silver-silver interaction is presented in Figure 13b. The dimers are connected to each other through silver-sulphur -bonds. The dithiocarboxylate in the silver chain is in coordination mode E.³³ An example of structures without direct metal-metal interaction can be found for copper, where dithiocarboxylates bridge copper ions together in coordination mode C (Figure 13c).³¹

Figure 13. Schemes of coordination polymers a) (Au2L2)n (L=dithioasetate),³⁰ b) (Ag2L2)n,³³ and c) CuL^’L^’’

(L^’=chloride and L^’’=N,N-dibenzyl-2-imidazoliumdithiocarboxylate)³¹.

One coordination polymer containing 4(5)-imidazoledithiocarboxylate with crystallographic structure can be found. In the chain, each penta coordinated tin ion is connected to the ones either side through the 4(5)-imidazoledithiocarboxylate ligands. The ligands are alternatingly connected to the tin ions by chelating with sulphur and nitrogen to one tin and connected to the next tin with the other nitrogen atom in the imidazole ring. The 4(5)-imidazoledithiocarboxylate is coordinating in mode II in the polymer. Each tin ion also has two methyl groups attached to them. Structure of the chain is presented in Figure 14.²⁶

Figure 14. Structure of coordination polymer of tin, (SnLMe2)n (L=5-imidazoledithiocarboxylate).²⁶

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For 4(5)-imidazolecarboxylate both clusters and coordination polymers exist. Clusters of rhodium, manganese, cobalt, nickel and zinc have been presented. In all of these clusters there are no metal- metal interactions, nor is the 4(5)-imidazolecarboxylate the only ligand. Coordination modes of the ligand varies, but only modes I and II are found. For manganese, cobalt, nickel and zinc clusters of polyoxometalates have been presented. A tetranuclear species of manganese can also be found. In the clusters of manganese, cobalt, nickel and zinc coordination mode is I and the metals are connected by other ligands in the systems, but with a tetranuclear rhodium cluster (Figure 15) the rhodium atoms are bridged by the 4(5)-imidazolecarboxylate ligands in coordination mode II.^34-36

Figure 15. Cluster Rh4L4L^’4 (L=4-imidazolecarboxylate and L^’=1,2,3,4,5-Pentamethylcyclopentadiene).³⁵

Two 4(5)-imidazolecarboxylate coordination polymers have been introduced. A 1D chains of calcium with water and 4-imidazolecarboxylate ligands, and a 2D lattice of cadmium with oxalate, water and 4-imidazolecarboxylate ligands can be found. The repeating unit of the 1D chain is shown in Figure 16a and the equivalent of the 2D lattice in Figure 16b. In both structures there is a 4(5)- imidazolecarboxylate coordinated to the metals in modes that were not introduced in Figures 5, 6 or 7. However, one of the 4(5)-imidazolecarboxylates in the 1D chain is coordinated to the metals through mode D. The two other modes found in these structures involve a nitrogen atom from the imidazole ring and can be seen as the combinations of the coordination modes previously presented.

For the other 4(5)-imidazolecarboxylate in the lattice the coordination mode is a combination of C and I, and in the 1D polymer of A and I.^7,8

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Figure 16. Coordination polymers a) [CaL2L^’]n (L=4-imidazolecarboxylate and L^’=H2O)⁷, and b) [CdLL^’L^’’0.5]n (L^’=H2O and L^’’= C2O42-8.

6. Optical properties

The colourful dithiocarboxylic acids are interesting from the viewpoint of optics, since they can form colourful complexes.2,42,43,45,47,48,52 Besides the colourfulness of the substances, there is little information available about the UV-VIS absorption of dithiocarboxylic acids.² However, more information is available of the dithiocarboxylate complexes. In general, colour and absorption of UV- VIS region are often reported in literature.42,43,45,47,48,52 For some complexes, further optical properties like luminescence have been noted.⁵⁶

A range of colours can be found in the complexes of dithiocarboxylates.42,43,45,47,48,52 As examples 4(5)-imidazoledithiocarboxylate tin complexes presented in Figure 10 are red and the cadmium complex of Figure 8a is orange.^26,45Naturally these colourful complexes display absorbance in UV- VIS region. The absorbance of UV-VIS light is caused by different types of charge transfer, or electron transition, in the system, like a molecule or a complex. The types of transfers include d–d transitions and charge transfers in the system.⁵⁷ Charge transfer is an electronic transition from one part of a molecule to another or from one molecule to another, where a part of an electronic charge is relocated. This transfer allows an exited state to be created.⁵⁸ d–d transitions are electron transitions between d-orbitals.⁵⁷

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7. Applications

The dithiocarboxylate complexes and complexation of the ligands can be used in many applications.

In production of chemicals and materials dithiocarboxylates can be used as catalysts or as reactants or precursors.44,48,49,59,60 Use of dithiocarboxylate complexes in catalysis has been suggested for the synthesis of enol esters.⁵⁹ Some complexes can be utilized in material manufacturing, for instance during vulcanization in rubber production.⁶⁰ As a precursor, the dithiocarboxylate complexes can be used in producing metal sulphur nanoparticles and films. 44,48,49,60 Sulphur metal nanoparticles of zinc, cadmium and mercury have been synthesized from their dithiocarboxylate complexes.⁴⁴ Complexes of dithiocarboxylates can also be used to make mixed-metal sulphur nanomaterials, like AgBiS2.⁴⁹ An example of sulphur metal film made from dithiocarboxylate complexes is sulphur indium film.⁴⁸ Super conductors are also a possible application of the complexes.⁶¹

Complexes of dithiocarboxylates can be used in several medical applications. In medicine, complexation of dithiocarboxylates can be used as antimicrobial and antitumor agents and complexes of dithiocarboxylates in modelling the metal containing sites of biomolecules.^27,60,62 Antimicrobial properties include antifungal and -bacterial properties.^60,62 Dithiocarboxylate complexes can be used to model sulphur containing the active sites of proteins, to study and understand how they function.²⁷ Environmental applications of dithiocarboxylates and their complexes include separation of metals and metal detection, as well as their usage as pesticides.^43,51,60 Dithiocarboxylates can be used to sort nuclear waste, by creating selective ligands in order to remove more active actinides from lanthanides.⁴³ Detection of trace amount of metals can also be counted as a health-related application as well as an environmental one. The detection techniques are based on the strongly coloured complexes formed when the dithiocarboxylates coordinate to metal ions in samples.⁵¹ Deduction of trace amounts of metals is an application which takes advantage of the optical properties of dithiocarboxylates. Other potential applications of the optical properties of dithiocatboxylate complexes are photosensitive sensors.⁶¹

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8. Aims of the work

The aim of this work was to study different methods of synthesis of complexes with a dithiocarboxylate ligand, using coinage metals (Cu, Ag, Au). Different synthesis methods and environments were tested to gain insight to the complexation of the ligand and how it behaves with different environments, like solvents. The coinage metals were chosen because they have previously been used in syntheses resulting in interesting larger scale structures (clusters and CPs) with ligands containing the dithiocarboxylate group. Copper has also been used in synthesis to create a complex ligand (4-imidazoledithiocarboxylate) used in the experimental work.

9. Synthesis and study of properties of complexes of 4- imidazoledithiocarboxylate and coinage metals

9.1. Synthesis of complexes

Several different synthesis methods were attempted and 60 different syntheses (65 syntheses including all repeat syntheses) were made during the experimental work. A complete listing of the syntheses can be found in the appendices in table form (Appendix 1. Synthesis table). General methods used with example syntheses are presented below. Some notable syntheses are discussed separately later in the analysis section. In general, all the metals acted uniquely and consistently with the ligand. Typically, the copper syntheses resulted in a precipitate, where both silver and gold syntheses in clear coloured solutions. The silver syntheses formed dark blood red and gold syntheses formed orange to red solutions. Chemicals used in all the syntheses and analyses are presented bellow at Table 2 and Table 3.

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20 Table 2. Liquid chemicals used in the experimental work.

Name of the chemical Chemical Formula

Molar Weight CAS number Manufacturer Purity (%)

Acetonitrile C2H3N 41.05 75-05-8 VWR Chemicals 99.9

Dichloromethane CH2Cl2 84.93 75-09-2 VWR Chemicals Analytical reagent, 100.0

N,N-Dimethylformamide HCON(CH3)2 73.09 68-12-2 Merck 99.8

BDH Laboratory Supplies 99.9

Dimethyl sulfoxide C2H6OS 78.13 67-68-5 Sigma-Aldrich ≥99.5

Dimethyl sulfoxide-D6 C2D6OS 84.17 2206-27-1 VWR Chemicals 99.80

Ethanol C2H6O 46.07 64-17-5 Altia 99.5

Ethylene glycol (CH2OH)2 62.07 107-21-1 VWR Chemicals 99

Glycerine C3H8O3 92.09 56-81-5 VWR Chemicals 87

Hydrobromic acid HBr 80.91 10035-10-6 Merck 47

Hydrochloric acid HCl 36.46 7647-01-0 VWR Chemicals 37

Methanol CH3OH 32.04 67-56-1 VWR Chemicals Analytical reagent, 100.0

Nitric acid HNO3 63.01 7697-37-2 Merck p.a., 65

Propylene glycol C3H8O2 76.10 57-55-6 VWR Chemicals 99

Tetraethyl orthosilicate C6H20O4Si 208.33 78-10-4 Sigma-Aldrich Reagent grade. 98

Tetrahydrofuran C4H8O 72.11 109-99-9 Merck 99.8

Tetramethylsilane Si(CH3)4 88.22 75-76-3 Sigma-Aldrich ≥99.5

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21 Table 3. Solid chemicals used in the experimental work.

Name of the chemical Chemical Formula Molar Weight CAS number Manufacturer Purity (%)

Copper(II) bromide CuBr2 223.35 7789-45-9 Sigma-Aldrich 99

Copper(II) chloride CuCl2 134.45 7447-39-4 Sigma-Aldrich 99

Copper(II) sulphate CuSO4 159.60 7758-98-7 Merck p.a. 99

Gold(III) bromide AuBr3 436.69 10294-28-7 Alfa Aesar 99

Gold(III) chloride AuCl3 303.33 13453-07-1 Alfa Aesar 99.99

Hydrogen tetrachloroaurate(III) trihydrate HAuCl4 ·3 H2O 393.83 16961-25-4 Alfa Aesar 99.99 4-imidazoledithiocarboxylic acid C4H4N2S2 144.22 84824-76-0 Sigma-Aldrich 70

Potassium bromide KBr 119.00 7758-02-3 Merck ≤100

Potassium carbonate K2CO3 138.21 584-08-7 Merck ≥99

Silver nitrate AgNO3 169.88 7761-88-8 Alfa Aesar 99

Silver trifluoromethanesulfonate AgCF3SO3 256.93 2923-28-6 Alfa Aesar 98

Sodium carbonate Na2CO3 105.99 497-19-8 VWR Chemicals 98

Sodium tetrachloroaurate(III) dihydrate NaAuCl4 ·2 H2O 397.80 13874-02-7 Alfa Aesar 99.99

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22 9.1.1. The ligand 4-imidazoledithiocarboxylate

The ligand, or its precursor 4-imidazoledithiocarboxylic acid, was tested in several ways during the experimental work. The acid is in a form of dark red powder, which is only 70% pure. The first test done, before the syntheses, was to test the solubility with normal solvents. Some solvents were tested later as their use became timely. All in all, eleven solvents were tested (acetonitrile, dichloromethane, diethyl ether, DMF, DMSO, glycerine, hydrochloric acid, methanol, tetrahydrofuran, toluene and water). The precursor only dissolved in methanol, DMF, DMSO, HCl and glycerine, of which fully only to methanol, DMF, DMSO and HCl. To 5M HCl and methanol the solubility is noticeably lower than to DMF and DMSO. The poor solubility was a surprising discovery since the rather small polar molecule was thought to be soluble in polar solvents, like water.

The ligand precursors’ durability in moisture and under mechanical work was also tasted, as well as the melting point was measured. For moisture durability some of the powder was placed in an analysis bottle with a moist surface and sealed with a cap and left alone in the refrigerator, to see whether its appearance would change. The appearance stayed the same even after a week in the moist vessel. The effect of mechanical work was also tested using a pestle and a mortar. The appearance did not change and based on the IR spectrum measured the acid did not change during the mechanical manipulation.

The melting point was measured with Stuart Melting Point Apparatus SMP10. According to the manufacturer, the acid starts to disintegrate after 145 °C. During the measurement the powder started to darken after 130 °C and melted to black liquid between 139-145 °C.

9.1.2. One-pot syntheses

One-pot synthesis is a form of direct synthesis method, where an in situ reaction between the metals and ligands takes place in one vessel. These syntheses can include many subdivisions like direct coordination, metal exchange and ligand substitution. Direct coordination reaction is a synthesis method where ligand and metal halides, oxides, hydrides etc. are placed in solvent and allowed to coordinate to each other. In metal exchange the ligands of pre-existing metal complex transfer to another metal ion. Ligand substitution is a method where the ligands of pre-existing metal complexes are replaced by new ligands.⁶³ In the experimental work the direct coordination reaction method is used.

Experimental work started with one-pot syntheses. Several different solvents and environments were used to see how they would affect the syntheses. The simplified process consisted of dissolving the ligand and the metal salt separately, mixing the solutions from 5 minutes up to an hour. After the reagents had been dissolved, they were filtered if needed and then the solutions were combined and mixed together for a few minutes. Then in general, the bottles were sealed with a septum and placed in the refrigerator with a ventilation needle. In case precipitation occurred the solid formed was filtrated, and the solid and filtrate were placed in separate vessels in the refrigerator. Different

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variations of environments were used: different solvents, acidity and basicity of the media, nitrogen atmosphere, cold solutions and adding agents to slow hydrogen bond formation. The majority of the syntheses (36 with the repeat syntheses) were made using these different variations of one-pot synthesis, in most of them ligand was dissolved in either DMF or methanol. Different subcategories of syntheses prepared in the previously presented method are further discussed below.

Syntheses in organic solvents

The syntheses using organic solvents were done with the earlier described method at ambient temperature and pressure. Since the ligand (4-imidazoledithiocarboxylate) only dissolved in methanol, DMF and DMSO for the available organic solvents, methanol and DMF as well as their mixtures were mainly used in the syntheses with organic solvents. As the ligand was more easily dissolved in DMF, and the reactions in methanol often lead to instantaneous precipitation, DMF was the main solvent used. For dissolving the metal salts, both DMF and methanol were used. Besides the two main solvents, in one synthesis the metal salt was dissolved in dichloromethane.

The molar ratio of ligand to metal used for all the syntheses was 1:1. With one synthesis adding of potassium carbonate to the solution was tested (molar ratio 1:1:1), the silver synthesis did not act differently from ones without the carbonate. Several, mainly copper syntheses, produced precipitates.

Most of the syntheses, however, yielded clear coloured solutions. Only one crystalline product was gained from the 14 syntheses from a filtrate of EN2.

Syntheses in water

Performed in ambient temperature and pressure, the water syntheses were done in several solvent media using either neutral, acidic and basic conditions. The ligand was dissolved in either organic solvents (DMF or methanol) or non-neutral water solution since the ligand is not water soluble. The metal salts were dissolver in water solutions. Seven different syntheses were made, one with neutral solvent, three in acidic solvent and three in basic solvent. 1:1 molar ratio of ligand and metal salts were used. Acidic solvent used was hydrochloric acid solutions and the syntheses in basic media sodium carbonate was added to the solvent.

The three acidic media syntheses were done by dissolving the metal salts in hydrochloric acid solutions. The solvents used for the ligand were DMF, methanol and HCl. For the acidic syntheses gold and silver salts were experimented with. Silver was used in the neutral water synthesis and all coinage metals were used in the basic media syntheses. In all basic synthesis the base was added in 1:1 ratio to the ligand. The basic syntheses were made using sodium carbonate, that was added to the ligand solutions and mixed for a half an hour before combining. The metal salts were dissolved in water and the ligand in water, DMF or their mixture depending on the synthesis. All syntheses

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precipitated as the metal salt and ligand solutions were combined. The solids were saved for analysis, no crystallization occurred in the filtrates.

Syntheses in nitrogen atmosphere

Four syntheses were performed under nitrogen atmosphere. Two syntheses using gold and two using silver. Syntheses with and without sodium carbonate were performed with both metals. The sodium carbonate was added in the reaction mixture, to see whether it would help with the crystallization of the product by boosting the reactivity of the ligand. The idea is that the basic media helps to form a stabile sodium salt of the 4-imidazoledithiocarboxylic acid, preventing the decomposition of the ligand. This was done because signs of decomposition in solvent media had been discovered with previous syntheses. DMF was used in all the syntheses and was prepared by bubbling the solution with nitrogen for 20 minutes before using. Ligand to metal to sodium carbonate molar ratio used was 1:1:1.

For both syntheses with and without sodium carbonate, the ligand and metal solutions were mixed separately for a half an hour under nitrogen flow. The sodium carbonate was placed with the ligand in solvent before dissolving. The sodium carbonate did not completely dissolve in the ligand solution, and so the metal solution was added in with the ligand solution and the mixture was mixed for a half an hour. For the gold synthesis with sodium carbonate dissolved in the mixture completely after combining, but in the silver synthesis it did not. All syntheses yielded clear coloured solutions and were placed sealed in the freezer for crystallization. No crystals were obtained.

Syntheses at low temperature

Cold solutions, cooled with an ice-salt bath, were used with three copper synthesis since the copper salts were very reactive with the ligand. In addition, one gold synthesis was made. With these cold solutions it was possible to make clear solution with no solid formation. The effect of ligand and metal salt (CuBr2) ratio was also tested with these syntheses, as the ratios of amount of substance were 1:1, 1:2 and 1:3 (metal salt to ligand ratio). The process began by dissolving the salt and ligand separately to DMF at room temperature and then cooling the solutions in the ice-salt bath for 20 minutes, after which the solutions were combined, sealed with a septum and placed in a freezer. The solutions are of different colour: 1:1 a reddish brown, 1:2 a dark red and 1:3 brown red. Further the 1:2 synthesis does not precipitate, where the two others do within days of preparation. However, no crystallization was observed for any of the syntheses.

Syntheses with added glycerol, ethylene glycol and propylene glycol

Another method used to prevent precipitation was the addition of glycerol, ethylene glycol or 1,3- propanediol to the reaction mixture. Glycerol can be used to prevent hydrogen bond formation, and

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so hopefully slow down the formation of precipitation ⁶⁴. The glycols are very similar in structure to glycerol and should therefore function alike. Six different syntheses were made to see what concentrations and which reagent would be the most effective. First three copper syntheses in the glycerol DMF mixtures of varying volume ratios (with 1:10, 3:10 and 1:2) with copper to ligand ratio 1:2. The glycerol was added to both ligand and salt solution before combining the solutions. Based on these three syntheses, the 3:10 ratio was enough to prevent precipitation.

Next two new reagents (ethylene glycol and propylene glycol) along with the glycerol were used in three gold (AuBr3:L was 1:3)syntheses. The volume ratio was 1:3 for all the liquid chemicals to DMF.

These syntheses with gold were done to observe the differences of the substances. With glycerol, the red solutions (ligand and metal salt solutions) turned to reddish brown when combined. Ethylene glycol synthesis acted the same. For both syntheses, no precipitation was observed. The 1,3- propanediol variant however, formed at first a red solution, which slowly turned to the same reddish brown as the previous ones, in a course or a few minutes. Drops of each solution were placed on a Petri dish and observed as the solvent evaporated, to all a flaky solid started to appear, and no crystallization was observed with the drops nor the bulk liquids.

9.1.3. Two-phase synthesis

Two-phase synthesis is a form of synthesis where interfaces are utilized. The interface provides a space where the species on both sides can interact and crystal growth is enabled. The different phases are liquids that do not mix, like water and organic solvent, where the components are dissolved separately.⁶⁵ This can solve problems like finding a common solvent for the reactants. As the ligand used was soluble in very few solvents, it was hard to find two solvents that had difference in density so that the layering could be achieved and were not miscible.

Figure 17. Pictures of syntheses a) EN11 and b) EN13, showing phase separation.

b)

a)

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Two different two-phase syntheses were made, one with gold and one with silver. Both syntheses were made by preparing dilute solutions separately dissolving the ligand and a metal salt in different solvents with different density. The heavier solution was then placed in the reaction vessel and the lighter carefully added on top of it, avoiding the mixing of the layers. For both syntheses, the denser solvent was dichloromethane, in which the metal salt was dissolved, and the less dense solvent used for ligand was DMF. Unfortunately, the layers mixed in time of day or two to clear solutions. The syntheses were done and kept in room temperature for the period of the layer mixing, and then divided in three parts for crystallization one open vessel in room temperature and one open and one closed in the refrigerator. The gold synthesis (EN11) yielded needle like colourless crystals.

9.1.4. Solvothermal synthesis

Solvothermal synthesis is a method of synthesis where reactions occur in elevated temperatures and under pressure in a solvent. If water is used as the solvent, the method can also be called hydrothermal synthesis. This technique can be used in a wide range of material synthesis from minerals to nanomaterials. Reactions are generally performed in autoclaves, where the temperature and pressure are controlled to have conditions around the critical point of the solvent. The synthesis and crystallization happen at the reaction vessel. In the elevated temperature and pressure properties of the solvent, like viscosity and density change. In these conditions organic solvents act as more than the mere reaction medium: they dissolve reactants, form complexes with them and influence their concentration.⁶³

Considering solvents besides water it is possible that they take part in the reactions, aiding them to desired outcomes, but also as ligands themselves as is or as new ones formed during the synthesis.

Using this technique, the purification of the product usually consists of just washing the product with a solvent. The solvothermal synthesis has also been found to be effective for the growing crystals and it can be used to synthesize crystalline metal clusters. This is because of the superheated solvent induces reactivity by better solvation and increased mobility of the reactants. This in turn improves diffusion and can resolve in faster crystal growth.⁶⁶

The solvothermal syntheses were done in an autoclave with 3 ml of solvent to which the metal salt and the ligand were added. The mixture was then heated to 100 °C for about a 20-hour time period and slowly cooled down from there to room temperature. Five syntheses were made, using both gold and silver salts in either methanol, DMF or their mixture. Two crystalline products were gained (one from gold and one from silver synthesis), both colourless or white crystals. The gold crystals with a needle like and the silver with a helix shape.

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27 9.1.5. UV-synthesis

Ultraviolet light can be used in the synthesis of organometallic compounds. Use of light as an energy source for syntheses is called photochemical synthesis. In photochemical synthesis ultraviolet or visible light can be used. The light irradiation causes exited states in the reactants. In the syntheses, these exited species react, creating selective products that depend on the unique way of absorption of the reactants.⁶³

Two syntheses were made, one gold and one silver. For both dilute solutions were prepared adding all reagents in the reaction mixture, after which the mixture was placed under an UV-lamp for a week.

The silver synthesis was done in methanol and produced a fine precipitated solid and a clear colourless filtrate. DMF was used in the gold synthesis and it resulted in a clear orange solution. The solution from the gold synthesis was then divided in three parts for crystallization one open and one closed vessel kept in room temperature and one closed vessel placed in the refrigerator. No crystallization occurred.

9.1.6. Sonochemical synthesis

Sonochemical synthesis is based on using ultrasound as a mean to introduce energy to the system to ease reactions. The syntheses are performed in solution with liquid or solid reagents. The basic mechanism through which the synthesis works is the formation and collapse of gas bubbles in the solution. This process created turbulence in the solution mixing the solution effectively.⁶⁷

Five syntheses were performed in ultrasound, three gold and two silver syntheses. In the syntheses, the reagents were first mixed in the ultrasound for 30 minutes separately and then combined while mixing for an hour further. The first synthesis using silver salt was done in methanol solution, to see whether the solubility of the ligand could be enhanced through the method. Both substances dissolved in the methanol within the 30-minute mixing period. The salt solution was added to the ligand solution, with the ultrasound on, resulting in blood red solution, typical for the silver syntheses previously performed. After the one hour mixing period a dark brown precipitate had been formed in reddish brown solution. Since the ligand was fully soluble in a relatively small quantity of methanol in comparison to previous syntheses, solvents that did not dissolve the ligand where then tested as a reaction medium with this synthesis method. The second silver synthesis was done using dichloromethane as solvent for both metal salt and ligand. Both silver syntheses were done with molar ratios 1:1.

The gold syntheses used acetonitrile, dichloromethane and DMF respectively as the solvents. With acetonitrile the metal salt was dissolved fully, but the ligand solution still had solid in it. Despite the solid, the ligand solution was added to the salt solution without filtering while mixing with ultrasound.

The solution slowly turned from orange to brown and had in the end small amount of red precipitate, which seemed by eye to be just the remainder of the solid ligand, which had not reacted in the

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synthesis. For the syntheses in dichloromethane neither the metal salts nor the ligand fully dissolved in the solvent. As the solutions were combined, both mixtures reacted, resulting in precipitates. The one using DMF as a solvent was done to see whether this synthesis method would yield better results when it came to crystallization. However, no crystal material was gained from the syntheses, solution nor filtrates.

9.1.7. Gel synthesis

Different gels can be used in the crystallization and synthesis of metal complexes. Gels are liquid rich semi-solid two component systems with a three-dimensional network when set. Wet gels have liquid in the network, whereas dry gels do not. Agar, gelatine, silica and polyvinyl alcohol can be used to create gels. General idea of crystallizing in a gel is that the specimen to be crystallized is placed over the gel in a solvent and it slowly diffuses into the gel. The crystals then start to grow in the gel as the concentration rises. Synthesis in gel can be done by adding one component of the reaction in the gel beforehand, and then adding the second component on top of it in solvent.⁶⁸

Figure 18. Formation of solid and crystalline material in the liquid phase in a) EN29-EN31 respectively and a) EN30.

In the experiments, silica gel was prepared from tetraethyl orthosilicate (TEOS). The silica gel preparation from silicates is a hydrolysis process where water is added to the silicate and the reaction between them is catalysed either by an acid or a base. Several different ratios of water and TEOS were tested, to achieve a tolerable setting time. For actual synthesis three different gel ratios were used to prepare altogether 13 gels. First batch of gels was prepared according to experiment

a) b)

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instructions with mixing 15,5 ml of ethanol with 15 ml of TEOS, to this mixture a mixture of 19 ml of water with three drops of concentrated HCl was added.⁶⁹ The mixtures pH was checked to be acidic, and the solution was then mixed until it cleared up. The solution was then divided into five approximately equal parts and the metal salts were added to them. After the salts had been added the gels were allowed to set in open vessels.

Two silver (AgCF3SO4), two gold (HAuCl4) and one copper (CuCl2) gel were prepared from the first solution. The gold and silver gel pairs had different amounts of metal in them, so that the effects of different solvents (methanol and DMF) could be studied. The amounts needed to be different in order to achieve complete dissolving of the ligand into methanol in reasonable liquid volumes that would fit in the test tubes used. The silver gel preparation failed as small amounts of HCl was used as a catalyst in the gel formation reaction. The solution turned white after a while (as the silver salt and HCl reacted), and then further on blueish grey sediment was formed at the bottom of the vessels. The gold and copper gels took between 20 and 25 days to set properly. These gels can be seen in Figure 18, with the ligand solutions already placed on top of the gels and left to react for a week in the refrigerator. Solid formation on top of the gel can clearly be seen, and even crystal formation in the liquid in observable. In the gel however, no change in appearance besides the slight colour gradient near the top can be observed.

The second batch of gel was prepared with gold (HAuCl4). The gel prepared was divided into two equal parts to see how the temperature would affect the crystal formation. Since the hydrolysis of TEOS results in silica and ethanol, to speed up the setting ethanol was left out of the gel mixture. The gel was prepared by mixing the metal salt and 10 ml of water, then adding 1 ml of TEOS and mixing until the solution cleared. The gel was then divided into two 5,5ml portions and allowed to set in open vessels. The gels set in a month. After this, equal amounts of ligand were placed on top of the gels in DMF and the tubes were sealed with rubber caps, one then placed in room temperature (EN32B) and one in refrigerator (EN32A) to react (Figure 19).

Figure 19. Pictures of syntheses EN32A and EN32B respectively a) right after adding ligand solution and b) after three days from adding the ligand solution.

Dithiocarboxylates in the synthesis of metal complexes

DITHIOCARBOXYLATES IN THE SYNTHESIS OF METAL COMPLEXES

Emilia Niittyviita

MASTER’S THESIS Inorganic Chemistry Kemistin koulutusohjelma

634/2019

Dithiocarboxylates in the Synthesis of Metal Complexes Emilia Niittyviita, 267313

University of Eastern Finland, Department of Chemistry

Supervisors: docent Sirpa Jääskeläinen and docent Pipsa Hirva Joensuu 23.9.2019

Abstract

Dithiocarboxylates in the Synthesis of Metal Complexes Emilia Niittyviita, 267313

Itä-Suomen yliopisto, Kemian laitos

Ohjaajat: dosentti Sirpa Jääskeläinen and dosentti Pipsa Hirva Joensuu 23.9.2019

Tiivistelmä

Contents

Abbreviations

1. Introduction

2. General properties of dithiocarboxylates

3. Dithiocarboxylates as ligands

3.1. Ligand properties

3.2. Coordination modes

4. Metal complexes of dithiocarboxylates

5. Dithiocarboxylates in clusters and coordination polymers

6. Optical properties

7. Applications

8. Aims of the work

9. Synthesis and study of properties of complexes of 4- imidazoledithiocarboxylate and coinage metals

9.1. Synthesis of complexes

b)

a)

a) b)

a) b)