Photoluminescent cyclometallated diplatinum(II,II) complexes: Photophysical properties and crystal structures of [PtL(PPh(3))]ClO4 and [Pt(2)L2(mu-dppm)][ClO4](2) (HL=6-phenyl-2,2'-bipyridine, dppm=Ph(2)PCH(2)PPh(2))

The complexes [PtL(Cl)] 1, [PtL(PPh(3))]ClO4 2 and [Pt(2)L(2)(mu-dppm)][ClO4](2) 3 (HL = 6-phenyl-2,2-'bipyridine, dppm = Ph(2)PCH(2)PPh(2)) 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 (1)m.m.l.c.t. (1)[d(sigma*)--> sigma(pi*)], where d(sigma*) arises from the antisymmetric combination of the two platinum d(z2) orbitals and sigma(pi*) from the symmetric combination of pi* orbitals of the two L ligands. All the complexes show luminescence in both the solid state and in solution. Both 1 and 2 display (3)m.l.c.t. emission in solution at room temperature. The solid-state emission oft and both the solid-state and fluid-state emission of 3 are assigned to the (3)m.m.l.c.t. (3)[(d(sigma*)){sigma(pi*)}] state. The crystal structure of 2 shows an intermolecular pi-pi interaction between two L ligands as evidenced by the intermolecular ligand plane separation of 3.35 Angstrom. The solid-state emission of 2 is suggested to arise from a pi-pi excimeric interaction of the L ligands. The crystal structure of 3 shows discrete [Pt(2)L(2)(mu-dppm)](2+) units with an intramolecular Pt-Pt separation of 3.2703 Angstrom.