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)]ClO₄2 and [Pt₂L₂(µ-dppm)][ClO₄]₂3(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[d_σ*→σ(π*)], where d_σ* arises from the antisymmetric combination of the two platinum d_z² 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[(d_σ*){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.