RUTHENIUM(II) AND OSMIUM(II) COMPLEXES WITH NEW TERDENTATE POLYQUINOLINE AND CYCLOMETALATING LIGANDS - SYNTHESIS, NMR CHARACTERIZATION, LUMINESCENCE PROPERTIES, AND ELECTROCHEMICAL-BEHAVIOR

A series of Ru(ll) and Os(ll) complexes with new polyquinoline and cyc lometalating terdentate ligands has been synthesized and fully charact erized by H-1 and C-13 NMR. The new ligands are 2,6-bis(7'-methyl-4'-p henyl-2'quinolyl)pyridine (bmpqpy) and its N-C--N cyclometalating homo log, 1,3-bis(7'-methyl-4'-phenyl-2'-quinolyl)benzene (bmpqb-H);the com plexes studied are [Ru(bmpqpy)(2)](PF6)(2) (1), Ru(bmpqpy)Cl-3 (2), [R u(bmpqpy)(bmpqb)](PF6) (3, bmpqb(-) is the anion of bmpqb-H), [Ru(bmpq b)(terpy)] (PF6) (4, terpy = 2,2':6',2 ''-terpyridine), [Ru(bmpqpy) (t ppz)](PF6)(2) (5, tppz = 2,3,5,6-tetra(2'-pyridyl)pyrazine), [Os(bmpqp y)(2)](PF6)(2) (6), Os(bmpqpy)Cl-3 (7), and [Os(bmpqpy)(bmpqb)](PF6) ( 8). The absorption spectra, redox behavior, and luminescence propertie s (both at 77 K in a rigid butyronitrile matrix and at room temperatur e in a fluid acetonitrile solution) of the bis-terdentate complexes ha ve been investigated. The complexes have noticeable absorption propert ies throughout the visible region, due to spin-allowed metal-to-ligand charge-transfer (MLCT) transitions. In the Os-containing complexes, s pin-forbidden MLCT transitions contribute significantly to the visible light absorption. The complexes undergo metal-centered oxidation proc esses and ligand-centered reduction processes in the potential window investigated (-2.0 to +1.6 V vs. SCE). All the bis-terdentate complexe s exhibit luminescence at 77 K and 1, 4, 5, 6, and 8 also exhibit lumi nescence at room temperature in the near-IR. The luminescence originat es in all cases from triplet MLCT excited states. The lack of room tem perature luminescence of 3 (as well as the very weak room temperature luminescence of 1) is attributed to the presence in 3 (and in 1) of tw o terdentate polyquinoline ligands, which leads to increased steric hi ndrance around the metal with respect to the terdentate polypyridine l igands in octahedral complexes. Because of their properties, these com plexes are interesting species in terms of light-harvesting compounds and can be regarded as useful energy traps when inserted into supramol ecular arrays.