Photoluminescent cyclometallated diplatinum(II,II) complexes: Photophysical properties and crystal structures of [PtL(PPh3)]ClO4 and[Pt2L2(μ-dppm)][ClO4]2(HL = 6-phenyl-2,2′-bipyridine, dppm = Ph2PCH2PPh2)

Abstract

The complexes [PtL(Cl)] 1, [PtL(PPh3)]ClO4 2 and [Pt2L2(μ-dppm)][ClO4]2 3 (HL = 6-phenyl-2,2′-bipyridine, dppm = Ph2PCH2PPh2) have been prepared and their spectroscopic and emission properties studied. Complex 3 shows a broad and intense absorption at 420-510 nm which is tentatively assigned to a metal-metal to ligand charge-transfer transition 1m.m.l.c.t. 1[dσ*→σ(π*)], where dσ* arises from the antisymmetric combination of the two platinum dz2 orbitals and σ(π*) from the symmetric combination of π* orbitals of the two L ligands. All the complexes show luminescence in both the solid state and in solution. Both 1 and 2 display 3m.l.c.t. emission in solution at room temperature. The solid-state emission of 1 and both the solid-state and fluid-state emission of 3 are assigned to the 3m.m.l.c.t. 3[(dσ*){σ(π*)}] state. The crystal structure of 2 shows an intermolecular π-π interaction between two L ligands as evidenced by the intermolecular ligand plane separation of 3.35 Å. The solid-state emission of 2 is suggested to arise from a π-π excimeric interaction of the L ligands. The crystal structure of 3 shows discrete [Pt2L2(μ-dppm)]2+ units with an intramolecular Pt-Pt separation of 3.2703 Å.