Structures, photoluminescence, and reversible vapoluminescence properties of neutral platinum(II) complexes containing extended π-conjugated cyclometalated ligands

Reacting K2PtCl4 with the tridentate R-C boolean AND N boolean AND C-H-2 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 boolean AND N boolean AND C) Pt(DMSO)] (2a-d). In the crystal structures of 2a-c, the molecules are paired in a head-to-tail orientation with Pt center dot center dot center dot Pt separations > 6.3 angstrom, and there are extensive close C-H center dot center dot center dot pi (d = 2.656-2.891 angstrom), pi center dot center dot center dot pi (d = 3.322-3.399 angstrom), and C-H center dot center dot center dot O=S (d = 2.265- 2.643 angstrom) contacts. [(Ph-C boolean AND N boolean AND C)Pt(PPh3)] (3) was prepared by reacting 2b with PPh3. Reactions of 2a-d with bis(diphenylphosphino)-methane (dppm) gave [(R-C boolean AND N boolean AND C)(2)P(t)2(mu-dppm)] (4a-d). Both head-to-head (syn) and head-to-tail (anti) conformations were found for 4a center dot 3CH(2)Cl(3)center dot C5H12, whereas only one conformation was observed for 4b center dot 2CHCl(3) (syn), 4c center dot 3CH(2)Cl(2) (syn), and 4d center dot 2CHCl(3) (anti). In the crystal structures of 4a-d, there are close intramolecular Pt center dot center dot center dot Pt contacts of 3.272-3.441 angstrom in the syn conformers, and long intramolecular Pt center dot center dot center dot Pt separations of 5.681-5.714 angstrom in the anti conformers. There are weak C-H center dot center dot center dot X (d = 2.497-3.134 angstrom) and X center dot center dot center dot X (X = Cl or Br; d = 2.973-3.655 angstrom) interactions between molecules 4a-d and occluded CHCl3/CH2Cl2 molecules, and their solvent channels are of varying diameters (similar to 9-28 angstrom). 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 center dot 6CHCl(3)center dot C5H12.