Unique structural topologies involving metal–metal and metal–sulfur interactions: salts of [Ni(C3S5)2]x− with cis-anti-cis-dicyclohexyl-18-crown-6 complexed counter ions

Abstract

Preparation by electrocrystallisation has been carried out for the salts [Rb(anti-dchyl-18c6)]₂[Ni(dmit)₂] 1, [Rb(anti-dchyl-18c6)][Ni(dmit)₂] 2, [Cs(anti-dchyl-18c6)]₂[Ni(dmit)₂] 3 and [Cs(anti-dchyl-18c6)_1.5][Ni(dmit)₂]₆4 (anti-dchyl-18c6 = cis-anti-cis-dicyclohexyl-18-crown-6, dmit = C₃S₅). Salts 1 and 3 involve the planar dianionic nickel complex sandwiched by two metal–crown units. This leads to short Rb⁺ ⋯ Ni and Rb⁺ ⋯ S interactions in 1 and the shortest recorded Cs⁺ ⋯ Ni distance of 3.47 Å in 3, presumably stabilised by the four surrounding S atoms at 3.73–4.44 Å. DFT calculations on the dianionic salts 1 and 3 indicate an essentially electrostatic interaction between the [Ni(dmit)₂]²⁻ complex and the Rb⁺ or Cs⁺ ion and show frontier orbitals qualitatively similar to those previously derived from EHMO calculations on molecular conductors containing [Ni(dmit)₂]. Salt 2 consists of non-stacked nickel complexes arranged in chains linked by S ⋯ Rb⁺ interactions through the terminal sulfurs with the Rb⁺ ion placed exactly within the plane of the crown oxygens. Magnetic susceptibility measurement indicated weak antiferromagnetic interactions. Salt 4 shows a 2-D sheet of nickel complexes stacked in a herringbone arrangement separated by layers of counter ions complexed by the crowns in a disordered manner with the anion ∶ cation ratio of 6 ∶ 1 uniquely high among [Ni(dmit)₂]^x− salts. Salt 4 displays semiconductor behaviour with σ_RT = 10⁻² S cm⁻¹.