Speciation in solution, solid state spectroscopy and vapochromism of [Pt(trpy)(NCS)]SbF6 where trpy = 2,2′:6′,2′′-terpyridine

Abstract

Treatment of [Pt(trpy)Cl]SbF₆ with AgSCN in a metathesis reaction affords after work-up yellow crystals of [Pt(trpy)(NCS)]SbF₆·CH₃CN where trpy is 2,2′:6′,2′′-terpyridine. A single crystal structure determination of the solvate shows that the SCN⁻ ion is N-bound to the Pt atom, and that the planar cations stack as Pt₂ dimers with a Pt⋯Pt separation of 3.293(1) Å. The crystals rapidly de-solvate under ambient conditions to give a polycrystalline maroon material characterised as [Pt(trpy)(NCS)]SbF₆ (1). A ¹⁵N NMR spectroscopic study of a solution of isotopically labeled [Pt(trpy)(¹⁵N¹³CS)]SbF₆ in CD₃CN shows that both linkage isomers of the SCN⁻ ion co-exist in solution with the N-bound isomer dominant, and the S-bound isomer present at a much lower concentration. Compound 1 exhibits temperature dependent ³MMLCT emission in the solid state; at 280 K the emission maximises at 692 nm, but red-shifts systematically on cooling to reach 762 nm at 80 K. Compound 1 shows vapochromic behaviour that is selective and reversible for vapours of acetonitrile, DMF and pyridine. The colour change is from maroon for 1 to yellow for all three solvates. The emission spectra recorded for the solvates maximise at wavelengths that are all significantly blue-shifted compared to λ_em^max recorded for 1: the blue-shifts measured at 77 K are 90, 115 and 155 nm for the acetonitrile, DMF and pyridine solvates respectively. The origin of the vapochromic properties of compound 1 is likely to do with the breaking and making of metallophilic Pt⋯Pt interactions in the solid state.