Abstract

The salts [ML₂]₂[{M′(mnt)₂}₂] {M = Co, L = Cp; M = Fe or Co, L = Cp* (Cp* = η-C₅Me₅); M′ = Fe or Co; mnt = [S₂C₂(CN)₂]²⁻} have been prepared and structurally characterised to investigate the effects of cation size, metal d-electron configuration and the packing of pseudo-spherical cations with ellipsoidal dianions. By comparing the structures of [CoCp₂]₂[{M′(mnt)₂}₂] (M′ = Fe 1 or Co 2) with those of [FeCp*₂]₂[{M′(mnt)₂}₂] (M′ = Fe 3 or Co 4) the effect of cation size and magnetic character on the crystal lattice is investigated. Two polymorphs of 3 were identified, α-3 and β-3, both of which crystallise in the space group P2₁/n. The structures of 1, 2, and α-3 are similar with columns of anion dimers separated by cations lying perpendicular to the anion stacks, whereas β-3 comprises mixed, face-to-face ⋯cation⋯cation⋯anion⋯ stacks. Two forms of 4 were characterised, namely the polymorph α-4, which is isostructural with α-3, and the dichloromethane-solvated pseudo-polymorph 4S2. The structure of 4S2 is analogous to that of β-3 in comprising face-to-face stacks of mixed ions. Three related structures are known, namely [FeCp*₂]₂[{Co(mnt)₂}₂] [denoted γ-4 (CSD refcode ZAXJAJ)] and the two pseudo-polymorphs [FeCp*₂]₂[{M′(mnt)₂}₂]·MeCN [M′ = Fe 3S1 (ZAXJEN) or Co 4S1 (ZAXHUB)]. These are included for comparison with the structures determined here. The packing coefficients, k, varied in the range 0.59(3) (for 4S2) to 0.73(1) (for β-3).