Crystal structures and spectroscopic properties of platina-β-diketones — a new mode of stacking in platinum complexes

Platina-β-diketones [Pt2{(COR)2H}2(μ-Cl)2] (R=Me 1a, Et 1b, n-Pent 1c, n-Hex 1d, (CH2)4Ph 1e) are prepared by reaction of hexachloroplatinic acid in n-butanol with silyl-substituted acetylenes R′CCSiMe3 (R′=RCH2). Complexes 1 are characterized by NMR, IR and UV–vis spectroscopies. The crystal structures of complexes 1a, b, e reveal discrete dinuclear molecules linked via Pt⋯Pt interactions [d(Pt⋯Pt)=3.318(1)–3.352(1) Å] in such a way that polymeric chain-like structures are formed. These complexes exhibit only an emission in the solid state (λmax 555 nm) that is ascribed to a d8–d8 electronic excited state. No emission is observed in solution. The distinct differences in the absorption and emission spectra in solution and in the solid state, as well as the lack of photoconductivity, are ascribed to the columnar structures in the solid state with the mode of stacking of the platinum centers with alternating Pt⋯Pt interactions and PtClPt bridges.