Crystal supramolecular motifs for [Ph4P]+ salts of [M(mnt)2]2−, [M(mnt)2]−, [{M(mnt)2}2]2−, [M(mnt)3]3− and [M(mnt)3]2− (mnt2− = maleonitriledithiolate)

Abstract

The crystal structures of [Ph₄P]₂[M(mnt)₂] (M = Zn 1, Cu 2 or Ni 3), [Ph₄P][M(mnt)₂] (M = Cu 4 or Ni 5), [Ph₄P]₂[{M(mnt)₂}₂] (M = Co 6 or Fe 7), [Ph₄P]₂[M(mnt)₃] (M = Fe 8 or Cr 10) and [Ph₄P]₃[Cr(mnt)₃] 9 {mnt = maleonitriledithiolate, [S₂C₂(CN)₂]²⁻} have been determined to investigate the packing and supramolecular motifs in crystals containing [Ph₄P]⁺ cations and [M(mnt)_n]^z− anions. Seven different crystal packings are described. Crystals 2 are isomorphous with 3, as are 4 with 5, and 6 with 7, and two dimorphs of 8 were identified (orthorhombic α-8 and monoclinic β-8). The lattices of all compounds with planar (2, 3, 4, 5) or approximately planar (6, 7) anions contain segregated parallel stacks of anions (canted to the stack axis) and columns of embracing [Ph₄P]⁺ cations. The structures of 2 and 3 contain approximately linear sequences of alternating sixfold phenyl embraces (6PE) and offset-face-to-face (OFF) motifs between cations, while the structures of 4, 5, 6 and 7 contain linear chains of cations engaged in translational fourfold phenyl embraces (4PE). Where the anions are not planar (tetrahedral 1 or octahedral 8–10), OFF interactions between planar subsections of the anions (i.e. mnt ligands) and planar subsections of the cations (i.e. phenyl rings) occur, as a concerted motif involving four ions (1), or as a new sandwich motif (α-8, β-8). This sandwich motif, Ph⋯mnt⋯Ph, occurs for one mnt ligand per anion in α-8, and two mnt ligands per anion in β-8. Calculated energies are reported. Weak C–H⋯S and C–H⋯N hydrogen bonds occur in all structures, and appear to control the details of the commensurability between chains of cations and stacks of anions. Edge-to-face (EF) motifs between phenyl rings and mnt ligands do not occur. All crystals except one (9) are devoid of solvent, implying an absence of shape awkwardness in crystals of this type. The crystal packing of the related compound [MePh₃P][Ni(mnt)₂] contains columns of stacked parallel fourfold phenyl embracing cations, parallel to stacked anions.