Homoleptic dithiolenes ligand structures

To underpin the syntheses, properties, and applications of dithiolene molecules, this chapter presents a comprehensive discussion of structurally characterized homoleptic dithiolene complexes. That is, the structural unit must contain dithiolene ligands as the only ligand type, and there must be only one type of dithiolene ligand. Emphasis is placed on structural aspects such as coordination geometries, bond distances and angles, and on identifying trends related to the specific dithiolene ligand and the identity and formal oxidation... 

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. 

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... 

Bertrand, J. A. and Eller, P. G., Polynuclear Complexes with Aminoalcohols and Iminoalcohols as Ligands Oxygen-Bridged and Hydrogen-Bonded Species Beswick, Colin L., Structures and Structural Trends in Homoleptic Dithiolene... 

Despite the diversity of ligand types, more than one-half of all structurally characterized homoleptic bis(dithiolene) complexes contain the mnt or dmit ligands (Table II A and B, Entries 1 and 30 Fig. 1). Extended packing arrangements of some mnt complexes are addressed by Lewis and Dance (18). Investigations of the dmit ligand and associated derivatives with a wide range of different cations account for the numerous examples. 

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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