Application of 2,6-Diphenylpyridine as a Tridentate [C∧N∧C] Dianionic Ligand in Organogold(III) Chemistry. Structural and Spectroscopic Properties of Mono- and Binuclear Transmetalated Gold(III) Complexes

The synthesis of a series of mono- and binuclear cyclometalated gold(III) complexes containing the tridentate C∧N∧C ligand (HC∧N∧CH = 2,6-diphenylpyridine) was developed using K[AuCl4] and the organomercury(II) compound Hg(C∧N∧CH)Cl as precursors. The molecular structures of [Au(C∧N∧C)(Spy-2)] (Spy-2 = 2-mercaptopyridine), [Au(C∧N∧C)PPh3]ClO4, [Au2(C∧N∧C)2(μ-dppm)](ClO4)2, and [Au2(C∧N∧C)2(μ-dppe)](ClO4)2 have been determined by X-ray crystallography. In the crystal lattice of [Au2(C∧N∧C)2(μ-dppm)](ClO4)2 and [Au2(C∧N∧C)2(μ-dppe)](ClO4)2, interplanar separations of 3.4 Å are observed between the intramolecular [Au(C∧N∧C)] moieties, which imply the presence of weak π−π interactions. The torsion angle between the two [Au(C∧N∧C)] units in the former is 8.7°, while a larger angle (34.2°) is observed in the latter. In the absorption spectra, the binuclear complexes show a red shift for the absorption band in the near-visible region compared to the mononuclear analogues. This is attributed to π−π interactions between the intramolecular C∧N∧C ligands in solution. The new complexes are emissive at low temperatures (77 K) in acetonitrile.