Structures, Photoluminescence, and Reversible Vapoluminescence Properties of Neutral Platinum(II) Complexes Containing Extended π-Conjugated Cyclometalated Ligands

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Abstract
Reacting K2PtCl4 with the tridentate R-C∧N∧C-H2 ligands 2,6-di-(2‘-naphthyl)-4-R-pyridine (R = H, 1a; Ph, 1b; 4-BrC6H4, 1c; 3,5-F2C6H3, 1d) in glacial acetic acid, followed by heating in dimethyl sulfoxide (DMSO), gave complexes [(R-C∧N∧C)Pt(DMSO)] (2a−d). In the crystal structures of 2a−c, the molecules are paired in a head-to-tail orientation with Pt···Pt separations >6.3 Å, and there are extensive close C−H···π (d = 2.656−2.891 Å), π···π (d = 3.322−3.399 Å), and C−H···OS (d = 2.265−2.643 Å) contacts. [(Ph-C∧N∧C)Pt(PPh3)] (3) was prepared by reacting 2b with PPh3. Reactions of 2a−d with bis(diphenylphosphino)methane (dppm) gave [(R-C∧N∧C)2Pt2(μ-dppm)] (4a−d). Both head-to-head (syn) and head-to-tail (anti) conformations were found for 4a·6CHCl3·C5H12, whereas only one conformation was observed for 4b·2CHCl3 (syn), 4c·3CH2Cl2 (syn), and 4d·2CHCl3 (anti). In the crystal structures of 4a−d, there are close intramolecular Pt···Pt contacts of 3.272−3.441 Å in the syn conformers, and long intramolecular Pt···Pt separations of 5.681−5.714 Å in the anti conformers. There are weak C−H···X (d = 2.497−3.134 Å) and X···X (X = Cl or Br; d = 2.973−3.655 Å) interactions between molecules 4a − d and occluded CHCl3/CH2Cl2 molecules, and their solvent channels are of varying diameters (∼9−28 Å). Complexes 2a − d, 3, and 4a−d are photoluminescent in the solid state, with emission maxima at 602−643 nm. Upon exposure to volatile organic compounds, 4a shows a fast and reversible vapoluminescent response, which is most intense with volatile halogenated solvents (except CCl4). Powder X-ray diffraction analysis of desolvated 4a revealed a more condensed molecular packing of syn and anti complexes than crystal 4a·6CHCl3·C5H12.