Crystal structures and electrochemical properties of two phases of tetrabutylammonium bis(1,3-dithiole-2-thione-4,5-diselenolato)nickelate(III)

Abstract

The crystal structures of two phases (α and β) of [Bu 4N] 2[Ni(dsit) 2] 2 are reported (dsit=1,3-dithiole-2-thione- 4,5-selenolate). The compound crystallises either in blocks (α-phase) or needles (β-phase). The α-phase crystallises in the triclinic space group P 1 , with a=12.381(3), b=14.009(2), c=9.571(1) Å, α=94.43(1), β=99.61(2), γ=81.32(2)° and Z=1 with the asymmetric unit having the formula Ni 2C 44H 72N 2S 12Se 8. The β-phase crystallises in the triclinic space group P 1 , with a=11.820(1), b=14.998(1), c=9.517(1) Å, α=96.980(8), β=100.251(9), γ=76.926(8)° and Z=1 with the asymmetric unit having the formula Ni 2C 44H 72N 2S 12Se 8. The structures were solved by direct methods, and refined by Fourier and least-squares techniques. Both crystal structures differ only marginally. They consist of anionic dimers made up of two chemically bound Ni(dsit) 2 units. The Ni atom is square pyramidally coordinated by five selenium donor atoms, with the apically bridging NiSe distances (2.48 and 2.47 Å for α- [Bu 4N] 2[Ni(dsit) 2] 2 and β-[Bu 4N] 2[Ni(dsit) 2] 2, respectively) being significantly longer than the equatorial distances (2.316–2.347 Å). In the β-phase one of the thionyl groups and three of the four butyl chains of the cations are in disorder. Because of the bulky nature of the cations, no short interdimer contacts are present in the lattices. Cyclic voltammety studies of [Bu 4N] 2[Ni(dsit) 2] 2 in acetone show a first reversible 2[Ni(dsit) 2] −⇌[Ni(dsit) 2] 2 2− couple at E 1/2=−0.12 V (versus Ag/AgCl), and a second quasi-reversible couple involving a single anodic peak at 0.18 V and two reduction peaks at 0.08 and −0.01 V.