Crystalline Phase Selections in a [Pt(mnt)₂]⁻ Ion-Pair Compound Using Solvents

Three crystalline phases of [4′-CH₃-Bz-NH₂Py]­[Pt­(mnt)₂] (1) (4′-CH₃-Bz-NH₂Py⁺ = 1-N-(4′-methylbenzyl)-4-aminopyridinium and mnt^2– = maleonitriledithiolate) were isolated, identified, and characterized. The pure 1α·solvent and 1β phases can be obtained by the evaporation of 1 in CH₃CN/CH₂Cl₂ (V:V = 1:5) and CH₃CN/CH₃OH (V:V = 1:1) mixed solvents at ambient temperature, respectively; the pure 1γ phase is easily formed via the evaporation of 1 in CH₃OH or mixed solvent of CH₃OH/CH₂Cl₂ at room temperature. 1α·solvent and 1β phases crystallize in the triclinic space group P1̅ and possess quite similar cell parameters and packing structures. The anions and cations form the segregated and regular stacks in both 1α·solvent and 1β phases; moreover, the cations show the same orientation in a stack. The phase 1γ with monoclinic space group P2₁/c exhibits the separated and non-equidistant stacks of anion and cation, and the neighboring cations are aligned in a chair-type conformation in a stack. Charge-assisted intermolecular hydrogen-bonds exist between the anions and cations in three different crystalline phases. Dramatically different magnetic properties were observed for three crystalline phases, a spin-Peierls-type transition occurred around 260 K for 1α·solvent, while it did not appear over the temperature range 1.8–300 K for 1β, although two crystalline phases show rather analogous crystal structures. The phase 1γ shows the magnetic behavior of an S = ¹/₂ Heisenberg alternating-exchange antiferromagnetic linear chain.