Transition metal thioether complexes comprise

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es of thioether (R₂S) ligands. The inventory is extensive.

Dimethylsulfide complexes

As the simplest thioether,

dimethyl sulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula . It is the simplest thioether and has a characteristic disagreeable odor. It is a flammable liquid that boils at . It is a component of the smell produc ...

forms complexes that are illustrative of the class. Well characterized derivatives include ''cis''- iCl₄L₂ VCl₃L₂, NbCl₅L, NbCl₄L₂, Cr(CO)₅L, CrCl₃L₃, RuCl₂L₄, RuCl₃L₃, RhCl₃L₃, ''cis''- and ''trans''- rCl₄L₃sup>−, ''cis''-MCl₂L₂ (M = Pd, Pt), tCl₃Lsup>−, ''cis''- and ''trans''- tCl₄L₂(L = SMe₂). With respect to donor properties, dimethyl sulfide is a soft ligand with donor properties weaker than phosphine ligands. Such complexes are generally prepared by treating the metal halide with the thioether. Chloro(dimethyl sulfide)gold(I) can however be prepared by redox reaction of elemental gold and

DMSO Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula . This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is ...

in the presence of

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

Stereochemistry

Thioether complexes feature

pyramidal A pyramid () is a structure whose visible surfaces are triangular in broad outline and converge toward the top, making the appearance roughly a pyramid in the geometric sense. The base of a pyramid can be of any polygon shape, such as triangu ...

sulfur centers. Typical C-S-C angles are near 99° in both free thioethers and their complexes. The C-S distance in dimethylsulfide is 1.81 Å, which is also unaffected in its complexes. The stereochemistry of thioether complexes have been extensively studied. Unsymmetrical thioethers, e.g., SMeEt, are

prochiral In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step, such as changing one atom. An achiral species which can be converted to a chiral in two steps is called proprochiral. A molecule ha ...

ligands, and their complexes are chiral. One example is u(NH₃)₅(SMeEt)sup>2+. The complex ''cis''-VOCl₂(SMeEt)₂ exists as meso- and a pair of enantiomers. In complexes of thioethers of the type S(CH₂R)₂ (R ≠ H), the methylene protons are

diastereotopic In stereochemistry, topicity is the stereochemical relationship between substituents and the structure to which they are attached. Depending on the relationship, such groups can be ''heterotopic'', ''homotopic'', ''enantiotopic'', or ''diastereotopi ...

. Examination of the NMR spectra of such complexes reveal that they undergo

inversion Inversion or inversions may refer to: Arts * ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas * Inversion (music), a term with various meanings in music theory and musical set theory * ''Inversions'' (novel) by Iain M. Bank ...

at sulfur, without dissociation of the M-S bond.

Thioether as a bridging ligand

Unlike ethers, thioethers occasionally serve as

bridging ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually r ...

s. The complexes Nb₂Cl₆(SMe₂)₃ is one such example. It adopts a face-sharing bioctahedral structure with a Nb(III)=Nb(III) bond, spanned by two chloride and one dimethylsulfide ligands. The complex Pt₂Me₄(μ-SMe₂)₂ is a source of "PtMe₂".

Complexes chelating thioether ligands

File:Ag(18-ane-S6) dication.png, Structure of g(18-ane-S6)sup>2+. The Ag-S distances are 2.62 Å. File:Ru(15-ane-5)Cl+ (ORIZIZ).png, Structure of u(15-ane-S5)Clsup>+. File:(DTCO)PdCl2 (VIVXUT).png, Structure of ( DTCO)PdCl₂. Thiacrown ligands are analogous to

crown ether In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups (). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., . Impor ...

s. The best studied thiacrown ligands have the formula (SCH₂CH₂)_n (n = 3,4,5,6). The tridentate tri-thioether 9-ane-S3 forms extensive families of complexes of the type M(9-ane-S3)L₃ and (9-ane-S3)₂sup>2+. Examples of Cu(II)-thioether complexes were prepared from 14-ane-S4 and 15-ane-S5. The hexadentate ligand 18-ane-6 also forms extensive family of complexes, including unusual examples of Pd(III) and Ag(II). Examples of homoleptic complexes (SR₂)₆sup>n+ are otherwise rare.

Occurrence

Thioether complexes in nature arise from coordination of the sulfur substituent found in the amino acid

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine play ...

. One of the axial ligands in cytochrome c is illustrative. Methionine sulfur weakly binds to copper in

azurin Azurin is a small, periplasmic, bacterial blue copper protein found in ''Pseudomonas'', ''Bordetella'', or ''Alcaligenes'' bacteria. Azurin moderates single-electron transfer between enzymes associated with the cytochrome chain by undergoing oxida ...

References

{{Coordination complexes Coordination complexes