Nickel dithiolene complexes

In one seminal work on dithiolene compounds, Schrauzer and Mayweg (37) considered three possible structures for neutral dithiolene nickel complexes in which the oxidation state of nickel may be Ni(0), Ni(II), or Ni(IV) [Scheme 8 ... 

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). 

DITHIOLENE NICKEL COMPLEXES AS ABSORBERS IN RECORDING LAYER IN THE DRAW DISC... 

The dithiolene nickel complexes have the first allowed n—n,... 

DITHIOLENE NICKEL COMPLEXES AS SINGLET OXYGEN QUENCHER... 

Singlet Oxygen Quenching Mechanisms of Dithiolene Nickel Complexes in Solution... 

Ohta, K. Discotic Liquid Crystals of Transition Metal Complexes. 4 1 Novel Disco tic Liquid Crystals Obtained from Substituted Bis(dithiolene)nickel Complexes by a New Method. Mol. Cryst. Liq. Cryst.,1987 Gordon and Breach Science Publishers S.A., Vol 147, pp 15-24. 

Several transition metal ions form stable complexes with aliphatic 1,2-dithiols, which absorb in the near-lR. Known as dithiolenes, their nickel complexes in particular have been found to have valuable properties. The physical properties of dithiolenes can be readily tailored by variations on the substituents attached to the dithiols, see (4.13). Although they have low molar absorption coefQcients, when compared to cyanines etc., they do have one big advantage in that they show very little absorption in the visible region." Stracturally analogous dyes can be made from aromatic dithiols and oxothiols (4.14), and the much more bathochromic naphthalene derivatives (4.15), but they are much weaker absorbers. 

The chemistry of bis(l,2-dithiolene) complexes of nickel has stimulated considerable investigations over the past 20 years, owing to the peculiar and unusual electronic and electrochemical properties which the complexes exhibit both in the solid state and in solution. A number of articles cover the early reports up to 19701923 1925 1927 2108 on nickel complexes having general formulas (287) and (288). The formulas of representative complexes together with die synthetic routes and some physicochemical properties are summarized in Table 91. 

The more recent work includes two detailed studies on tetramethylphenylenediamine (TMPD) complexes of Ni- and Pt-mnt180,181 and an example of a complex in which both the donor and the acceptor are nickel complexes.182 However, most recent activity has been devoted to materials in which the strict one-dimensionality of the dithiolene salts and complexes has given way to interstack coupled systems with lesser degrees of anisotropy. 

The group 8 (VIII) metals comprise almost 80% of the structurally characterized homoleptic bis(dithiolene) units. Nickel complexes alone account for... 

Redox non-innocent ligands have also been employed in other kinds of processes. For example, a nickel-based system has been used in the purification of ethene gas streams [41]. The two forms (reduced and oxidized) of the dithiolene complex have different affinities for olefin, leading to separation of ethene from gas mixtures (Scheme 14). Intermediate 47 is obtained after electrochemical oxidation of the anionic nickel complex 46. The oxidized complex 47 reacts selectively with ethylene to form the adduct 48, thus the non-olefinic contamination of the multi-component stream... 

Figure 2.16 Transformation of N-Ni bonded dimers to Ni-S bonded dimers in bis[l,2-bis(4- -alkoxyphenyl)ethane-l,2-dithiolene]nickel(II) complexes...

D. O Hare),many new findings have appeared in this field. First of all, new superconducting phases based on [M(dmit)2] complexes have been isolated, and the first neutral metallic conductors based on nickel complexes of the TTF (tetrathiafulvalene)-extended dithiolene... 

Another unusual optical property is solvatochromism (27, 28). Most inorganic complexes have small solvent-dependent absorption spectra. Pronounced solvatochromism has not been extensively characterized for inorganic complexes in solution with the exception of a recent report on the electronic spectra of a variety of dipolar dithiolene a-diimine nickel complexes (29). 

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