Studies on α-C 3S 52− (dmit 2−) and its dinuclear Ni(II) complex: spectroscopic and structural characterization

Abstract

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: λ max=504 (H 2O), 514 (MeOH), 568 (MeCN), and 632 nm (DMF). With a shift in absorption maximum of 4000 cm −1 (DMF versus H 2O), dmit 2− is possibly the most solvatochromic species known. The dianion is monoprotonated by NH 4 + and binds CS 2 to form a thioxanthate (C 3S 5·CS 2 2−). 13C NMR measurements of 13C-enriched dmit 2− demonstrated that C 3S 5·CS 2 2− exchanges with free CS 2 via an associative pathway involving binding of a second molecule of CS 2. Titration with acid showed that the M 2dmit (M=Na, Cs) dissolves to give the dianion in protic solvents, rather than Hdmit −. The conversion of α-C 3S 5 2− to its β-isomer (‘Steimecke rearrangement’) occurs very slowly with purified Na 2dmit, in contrast to the literature method. The salt (NBu 4) 2[Ni(dmit) 2] is also highly solvatochromic but its behavior does not follow any simple pattern. Treatment of (NBu 4) 2[Ni(dmit) 2] with 1/3 equiv. of [Ni(NCMe) 6](BF 4) 2 gave the dinuclear compound (NBu 4) 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 2Cl 2 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 Å.