Structure, Physical, and Photophysical Properties of Platinum(II) Complexes Containing Bidentate Aromatic and Bis(diphenylphosphino)methane as Ligands

• Published in: Inorganic chemistry Vol. 39; no. 9; pp. 1955 - 1963
• Main Authors: DePriest, J, Zheng, G. Y, Goswami, N, Eichhorn, D. M, Woods, C, Rillema, D. P
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01-05-2000
• Subjects: AROMATICS; LUMINESCENCE; MATERIALS SCIENCE; ORGANIC PHOSPHORUS COMPOUNDS; PHYSICAL PROPERTIES; PLATINUM COMPLEXES; SYNTHESIS; TEMPERATURE DEPENDENCE
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic991306d

This study focuses on a series of PtII(L−L‘)(dppm) n + complexes, where dppm is bis(diphenylphosphino)methane and L−L‘ are C∧C‘ (n = 0), C∧N (n = 1), and N∧N‘ (n = 2) aromatic ligands. Structural characteristics are as follows:  for [Pt(phen)(dppm)](PF6)2, a N∧N‘ derivative, monoclinic, C2/c, a = 33.583(6) Å, b = 11.399(2) Å, c = 22.158(4) Å, Z = 8; for [Pt(phq)(dppm)](PF6), a C∧N derivative, triclinic, P1̄, a = 11.415(3) Å, b = 13.450(3) Å, c = 14.210(4) Å, Z = 2; for [Pt(phpy)(dppm)](PF6), a C∧N derivative, triclinic, P1̄, a = 10.030(3) Å, b = 13.010(2) Å, c = 15.066(4) Å, Z = 2; and for [Pt(bph)(dppm)], a C∧C‘ derivative, P21/c, a = 17.116(7) Å, b = 21.422(6) Å, c = 26.528(6) Å, Z = 12, where phen is 1,10-phenanthroline, phq is 2-phenylquinoline, phpy is 2-phenylpyridine, and bph is 2,2‘-biphenyl. Structural features indicate that the Pt−C bond distance is shorter than the Pt−N bond distance in symmetrical complexes and that the Pt−P bond distance trans to N is shorter than the Pt−P bond trans to C. This is consistent with the 31P NMR spectra where the chemical shift of the P trans to C is ∼10 ppm less than found for P trans to N. The energy maxima of the metal-to-ligand charge-transfer band for the complexes containing various L−L‘ ligands occur in the near-UV region of the spectrum and fall into the energy series bpy > bph > phen > 2-phpy > 2-ptpy > 2-phq > 7,8-bzq, where bpy is 2,2‘-bipyridine, 2-phpy is 2-phenylpyridine, 2-ptpy is 2-p-tolylpyridine, and 7,8-bzq is 7,8-benzoquinoline. The emission energy maxima, ascribed to variance in metal-perturbed triplet ligand centered emission, commence near 500 nm and follow the series phen > bpy > 7,8-bzq > 2-phpy > 2-ptpy > bph > 2-phq. In general, emission is observed at 77 K and in solution at low temperatures, but the temperature dependence of the emission lifetimes indicates thermal activation to another state occurs with an energy of ∼1800 cm-1 for the complexes, with the exception of [Pt(bph)(dppm)], which has an activation energy of ∼2300 cm-1.