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

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posted on 28.06.2006, 00:00 by Steven C. F. Kui, Stephen Sin-Yin Chui, Chi-Ming Che, Nianyong Zhu
Reacting K2PtCl4 with the tridentate R-CNC-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-CNC)Pt(DMSO)] (2ad). In the crystal structures of 2ac, 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···OS (d = 2.265−2.643 Å) contacts. [(Ph-CNC)Pt(PPh3)] (3) was prepared by reacting 2b with PPh3. Reactions of 2ad with bis(diphenylphosphino)methane (dppm) gave [(R-CNC)2Pt2(μ-dppm)] (4ad). 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 4ad, 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 4ad and occluded CHCl3/CH2Cl2 molecules, and their solvent channels are of varying diameters (∼9−28 Å). Complexes 2ad, 3, and 4ad 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.