Homoleptic dithiolenes transition metals

Potentially coordinatively unsaturated dithiolene-metal complexes are rare,298-306 and 1 1 dithiolene-transition-metal complexes with no other ligands are, to our knowledge, unprecedented.307 The neutral complex [PdS2C2(COOMe)2]6,308 is homoleptic containing one dithiolene unit for each palladium atom and no other ligands. Electrochemical reduction of the compound depicted in Figue 21 proceeds in four reversible steps. 

Figure 7. Plot showing the inverse correlation between average MSC and SCC angles within homoleptic bis(dithiolene) transition metal complexes.

Dichalcogenolene ligands form complexes with main group and d transition metal ions.103 Bis( 1,2-dithiolene) complexes have been obtained for metals, such as Cr, Mn, Ni, Cu, Zn, for the first row, Pd, Ag, and Cd for the second row, and Pt, Au, and Hg for the third row. Homoleptic /ra(l,2-dithiolcnc) complexes have been obtained for Ti, V, Cr, Zr, Nb, Mo, Tc, Ru, Ta, W, Re, and Os. Fe and Co have been found both in bis and /ra(l,2-dithiolene) complexes, although /ra(l,2-dithiolene) complexes containing these metal ions... 

A. Transition Metal Homoleptic Tris(dithiolene) Complexes / 80... 

There are roughly 421 reports of homoleptic bis(dithiolene) units based on transition metal elements. The approximate tally of the structures as a function of central metal atom is outlined in Fig. 2. The examples predominantly contain late transition metals. The majority of complexes are Ni based, partially because of interest in these complexes for materials applications. Other common central elements are Cu, Pd, Pt, Au, and Zn. There are also a few Fe and Co complexes and a small number of structures based on Cr, Mn, Ag, Cd, and Hg. 

There are roughly 50 homoleptic tris (dithiolene) complexes reported in the CSDC (5). The elemental distribution of these structures is outlined in Fig. 15. As opposed to bis(dithiolene) complexes, tris(dithiolene) complexes are based predominantly on early transition metal elements. Many of the tris(dithiolene) complexes are centered on V, Mo, and W. There are also complexes of Ti, Zr, Nb, Ta, Cr, Tc, Re, Ru, and Os. In addition, there are tris(dithiolene) complexes of Fe and Co, elements that also form homoleptic complexes with two dithiolene ligands. A detailed listing of the structural units along with references and geometrical parameters (to be discussed) is given in Table IV. 

A great amount of research has focused on the electronic structure, spectroscopy, redox properties, and conductivity of homoleptic bis(l,2-dithiolene) complexes of c transition metal ions (51). The compounds are often highly... 

Average bond length and angle parameters for the homoleptic tris(dithiolene) complexes are less sensitive to the identity of the transition metal or dithiolene ligand than those of bis(dithiolene) structures. Ranges of values are summarized in Fig. 22. Average M—S bond lengths cluster between 2.263 and 2.543 A, with values for two [Fe(mnt)3]2 units (2.263 and 2.269 A) (18), Co CAlCO),, 3... 

Some homoleptic unsymmetrical (dmit/mnt, dmit/tdas) dithiolene nickel complex-based D-A compounds with D = TTF and EDT-TTF also exhibit metal-like conductivity (see Table I) (101). Their molecular structure is shown in Scheme 3. The unsymmetrical tetraalkylammonium salts [MLjLJ- (M = Ni, Pd, Pt) have been prepared by ligand exchange reaction between tetraalkylammonium salts of MLj and ML21 (128, 129) and the D-A compounds have been synthesized by electrooxidation. Among these complexes, only the Ni derivatives exhibit metallic-like properties, namely, TTF[Ni(dmit)(mnt)] (metallic down to --30 K), a-EDT-TTF[Ni(dmit)(mnt)] (metallic down to 30 K), TTF[Ni(dmit)(tdas)] (metallic down to 4.2 K), and EDT-TTF[Ni(dmit)(tdas)] (metallic down to --50 K) (see Table I). The complex ot-EDT-TTF-[Ni(dmit)(mnt)J is isostructural (130) to a-EDT-TTF[Ni(dmit)2)] [ambient pressure superconductor, Section II.B.2 (124)]. Under pressure, conductivity measurements up to 18 kbar show a monotonous decrease of the resistivity but do not reveal any superconducting transition (101). 

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