Studies on α-C3S52- (dmit2-) and its dinuclear Ni(II) complex:: spectroscopic and structural characterization

The optical properties of the dmit(2-) ion (dmit(2-) = 4,5-dimercapto-1,3-dithiol-2-thiolate) have been characterized under a range of conditions. The oxidatively sensitive anion is highly solvatochromic: lambda(max) = 504 (H2O), 514 (MeOH), 568 (MeCN), and 632 nm (DMF). With a shift in absorption maximum of 4000 cm(-1) (DMF versus H2O), dmit(2-) is possibly the most solvatochromic species known. The dianion is monoprotonated by NH4+ and binds CS2 to form a thioxanthate (C3S5. CS22-). C-13 NMR measurements of C-13-enriched dmit(2-)demonstrated that C3S5. CS22- exchanges with free CS2 via an associative pathway involving binding of a second molecule of CS2. Titration with acid showed that the M(2)dmit (M = Na, Cs) dissolves to give the dianion in protic solvents, rather than Hdmit(-). The conversion of alpha-C3S52- to its beta-isomer ('Steimecke rearrangement') occurs very slowly with purified Na,dmit, in contrast to the literature method. The salt [(NBu4])(2)[Ni(dmit)(2)] is also highly solvatochromic but its behavior does not follow any simple pattern. Treatment of (NBu4)(2)[Ni(dmit)(2)] with 1/3 equiv. of [Ni(NCMe)(6)](BF4)(2) gave the dinuclear compound (NBu4)(2)[Ni-2(dmit)(3)], the first Ni-dmit(2-) complex with a Ni/dmit(2-) ratio that is not 1:2. The binuclear salt crystallizes as the CH,CI, solvate as dark purple prisms. The planar Ni(dmit)(2)(2-) is bridged to Ni(dmit) via two sulfur atoms; the anion features a short Ni-Ni distance of 2.71 Angstrom. (C) 2000 Elsevier Science Ltd All rights reserved.