Dmit ligand metal derivatives

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). 

A close structural relationship with I IF derivatives, especially BEDT-TTF, is exhibited by dddt metal complexes [dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate (63)]. The most interesting feature of this dithiolene ligand is the ability of its metal complexes to form not only anionic salts like dmit, but also cationic salts like TTF derivatives [89], to afford non-stoichiometric IR salts of type [M(dddt)2]mX . Thus the cyclic voltam-mogram of [Bu4N][Ni(dddt)2], after its initial oxidation, exhibits the reduction of neutral [Ni(ddt)2]° to anion [Ni(ddt)2]" at 0 V, and its further reduction to the dianion [Ni(dddt)2]2 , as well as the oxidation of [Ni(dddt)2]° to the cation [Ni(dddt)2] + at 0.8 V (MeCN versus Ag/Ag/Cl). The feasible synthesis of conducting donor-acceptor complexes involving dddt metal derivatives as donors and dmit metal derivatives as acceptors has also been demonstrated [90]. 

NIOS salts or CT-complexes, which contain donors of various types, such as Per or TTF (Chapter 12.1). More than one-half are again Ni-, Pd-, or Au- complexes based on the dmit ligand, but recent literature also reports many examples of Z)Zj (l,2-dithiolene) complexes deriving from mnt (with metals such as Au, Co, Cu, Fe, Ni, Pd, Pt), tfd , dddt , dmise , dcit , and dmbit (Ni and pd).n>i8,19,199,200,231 examples of CT salts containing... 

The well-known synthesis of the dmit ligand (40) was first reported in 1975 from carbon disulphide and sodium in dimethylformamide (DMF) [63]. The dmit ligand can be separated of the sodium trithiocarbonate (39) obtained in the reaction by precipitating the zinc complex (41), formed in aqueous ammonia, with methanol (Scheme 1.11). This procedure was later improved [64] and the dmit ligand better protected by converting the tetraalkylammonium zinc complex (41) into the benzoyl derivative (42) by reaction with benzoyl chloride. The dmit dianion (40) can be regenerated from the benzoyl derivative by treating with sodium methoxide. Fmfher treatment with the metal salt (M = Ni, Pd, Pt, Fe, Au, Cu, Rh) affords the dmit complex [61]. 

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