Novel phosphorescent cyclometalated organotin(IV) and organolead(IV) complexes of 2,6-bis(2′-indolyl)pyridine and 2,6-bis[2′-(7-azaindolyl)]pyridine

Four novel five-coordinated Sn(IV) and Pb(IV) complexes of 2,6-bis(2′-indolyl)pyridine (H₂-bip) and 2,6-bis[2′-(7-azaindolyl)]pyridine (H₂bap) were synthesized. These four complexes have the formulas Sn(bip)Ph₂ (1), Sn(bap)Ph₂ (2), Pb(bip)Ph₂ (3), and Pb(bap)Ph₂ (4), respectively. The structures were determined by single-crystal X-ray diffraction. In the complexes, the metal centers are tridentately chelated by the bip or the bap ligand and further coordinated by two phenyl groups, resulting in a distorted-trigonal-bipyramidal geometry. These complexes display interesting extended π-π stack structures in the solid state. Complexes 1 and 2 are luminescent at room temperature in solution and the solid state. At 77 K in THF solution, all four complexes display both blue-green fluorescent and orange-red phosphorescent emissions, which originate from ligand-centered π → π* transitions. The Sn(IV) and Pb(IV) centers play a key role in enhancing phosphorescent emission of the bip and bap ligands.