Interaction of SbCl₅²⁻ and Thioether Groups at the Open Coordination Sites of Platinum(II) Diimine Complexes

In the solid-state, the approximately square planar cation in orange crystals of [Pt(NO2phen)(ttcn)](PF6)2 (NO2phen = 5-nitro-1,10-phenanthroline; ttcn = 1,4,7-trithiacyclononane) has a short apical Pt···S(ttcn) distance (2.9415(15) Å). In acetonitrile solution, the electronic spectrum shows a long-wavelength absorption band (412 nm; 2200 M−1 cm−1), consistent with the notion that the axial Pt···S(ttcn) interactions stabilize states having metal-to-ligand charge-transfer (MLCT) character. Reaction with the hexachloroantimonate(V) salt of tris(4-bromophenyl)aminium (TBPA+) results in complex redox chemistry, involving the platinum complex, SbCl52− and TBPA+. In the case of Pt(bpy)(ttcn)2+, orange-yellow crystals of [Pt(bpy)(ttcn)]2(Sb4Cl16) were isolated from the reaction, whereas the reaction with Pt(NO2phen)(ttcn)2+ consistently yielded red crystals of [Pt(NO2phen)(ttcn)](SbCl5)·2CH3CN. In the latter case, the geometry of the cation, including the apical Pt···S(ttcn) distance (2.9390(12) Å), is very similar to that of the PF6− salt. However, the basal plane of each square pyramidal SbCl52− opposes the nearly parallel coordination plane of an adjacent Pt(NO2phen)(ttcn)2+ complex, resulting in an unusually short intermolecular Pt···Sb distance of 3.4259(3) Å. The longest wavelength maximum in the diffuse reflectance spectrum and the solid-state emission maximum are shifted by ∼1200 cm−1 and ∼700 cm−1, respectively, to the red of those of the PF6− salt, consistent with perturbation of the complex’s electronic structure because of the Pt···Sb interaction.