New C∧N∧C bis-cyclometalated platinum(II) complexes: Synthesis, structures, and photophysical properties

摘要

The reaction of a new ligand, ethyl 2,6-diphenylisonicotinate (EtO _2C-C∧N∧C-H _2), with K _2PtCl _4 in acetic acid affords the monocyclometalated complex [{(EtO _2C- C∧N∧C-H)-Pt(μ-Cl)} _2] (1), which transforms to the bis-cyclometalated derivative [Pt(EtO _2C-C∧N∧C)(DMSO)] (2) when heated in hot DMSO. Complex 2 is the precursor for preparing a new series of neutral mononuclear bis-cyclometalated complexes [Pt(EtO _2C- C∧N∧C)(L)] (L = tht (3), PPh _3 (4), CN- ~tBu (5), py (6), py- ~tBu (7), py-NH _2 (8), py-CN (9), py-CONH _2 (10)). These new complexes have been characterized spectroscopically, and structures of 2-10 have been determined crystallographically. Within each crystal structure the individual molecules pack in a head-to-tail arrangement. Noncovalent interactions, including ππ, C-HO, C-HN, N-HPt, N-Hπ, C-Hπ, and N-HO, contribute significantly to the supramolecular structures displayed by these complexes in the solid state. All complexes display UV-vis absorptions in dichloromethane solution. Excitation and emission studies as well as lifetime measurements are described and can be correlated to the solid-state structures of the complexes. DFT and TDDFT computational studies have been performed on 5 and 8 which support the conclusions drawn from the photophysical studies.