Ladder-like heteropolynuclear assemblies cyanido bridges and platinum(II)-thallium(I) bonds: structural and photophysical properties.

We describe the mononuclear anionic cyanido-pentafluorophenyl complexes, (NBu)[Pt(C^N)(CF)(CN)] [C^N = 7,8-benzoquinolate (bzq) 1, 2-(2,4-difluorophenyl)pyridinate (dfppy) 2] and the heteropolynuclear derivatives [{Pt(C^N)(CF)(CN)}Tl] (C^N = bzq 3, dfppy 4). These complexes were synthesized a two-step modular synthesis by reaction of the corresponding potassium salts K[Pt(C^N)(CF)(CN)], prepared from [Pt(C^N)(CF)(DMSO)] and KCN in acetone/HO, with TlPF. The structures of {[Pt(bzq)(CF)(CN)Tl]·THF} (3·THF) and [{Pt(dfppy)(CF)(CN)}Tl]·dioxane [4]4·dioxane, determined by X-ray crystallography, confirm the presence of Pt(II)-Tl(I) bonds [2.9795(6)-3.0736(3) Å], but in the dfppy complex, the incorporation of dioxane, causes a significant structural change. Thus, whereas [3·THF] achieves a bent-ladder shape extended double chain Tl⋯[Pt⋯Tl]⋯Pt supported by lateral bridging Pt[Tl] ligands, [4]4·dioxane is formed by discrete PtTl rectangular aggregates stabilized by Pt[Tl] and Pt⋯Tl bonds, which are connected by dioxane bridging molecules through Tl⋯O(dioxane) additional contacts. Solid state emissions are redshifted compared with the mononuclear derivatives 1 and 2 and have been assigned, with the support of theoretical calculations on PtTl models, to metal-metal'-to-ligand charge transfer (MM'LCT [d/s σ*(Pt, Tl) → π*(C^N)]) for 3 and mixed MM'LCT/IL for 4. In fluid THF solution, the complexes are not emissive. At 77 K, 3 and 4 exhibit bright emissions attributed to the formation of bimetallic [{Pt(C^N)(CF)(CN)}Tl(THF)], and anionic [Pt(C^N)(CF)(CN)] fragments. Furthermore, both 3 and 4 exhibit a reversible mechanochromism with a red shift of the emissions upon crushing, suggesting some degree of shortening of metal-metal separation. Finally, complex 3 shows solvatochromic behavior with color/luminescence changes by treatment with a drop of MeOH, CHCl, THF or EtO, with shifts from 583 in 3-MeOH to 639 nm in 3-THF. However, 4 only demonstrates a bathochromic response to MeOH.