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of Health under Grant No. 5-R01-GM32296-03 for support of this research.Registry No. [(bpy)2Ru(H20)]204+, 56110-87-3; [(bpy)2Ru-(H20)]2Os+, 96364-22-6; (bpy)2(H20)Rum0Ru1 11*IV(0H)(bpy)24+, 86045-59-2; m-(bpy)2Ru(H20)2+, 72174-10-8; cii-(bpy)2Rum(H20)-(OH)2+, 85027-43-6; (bpy)2(H20)Ru0Ru(bpy)20Ru(H20)(bpy)24+, 101695-59-4; [(bpy)20s(H20)2](C104)2, 84988-26-1; riwii-(bpy)2Ru-(H20)2+, 72174-09-5; [(bpy)2Os(H20)]204+, 99626-17-2; (bpy)2Ru-(OH2)ORu(OH)(bpy)23+, 100570-91-0; [ [(bpy)20s(H20)]20] (C104)4, 101695-60-7; [[(bpy)2Ru(H20)]20](C104)4, 56110-88-4; [(bpy)2Ru-(H20)2](C104)

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Abstract.[CuBr(C18H 12N4 Mo Ka, A = 0-71073/~, /z = 14.04 cm-1, F(000) = 4456, T = 294 K, R = 0.0523 for 3418 observed reflections. The title compound is the product of a side reaction in the bromo-induced oxidation of a copper/dpq system. Two dpq ligands are bonded to copper in a bidentate fashion; one is bonded only through pyridyl N atoms, while the other bonds through one pyridyl and one quinoxaline N atom. A third dpq molecule is not involved in bonding to copper nor in any other intermolecular or ionic interactions. The coordination sphere of the Cu atom has a distorted square pyramidal geometry, with the ligand N atoms forming the basal plane and the Br atom occupying the apical position.)Experimental. Green parallelepiped crystal of (1) obtained by slow evaporation of an ethanol solution, dimensions 0.20 x 0.25 x 0.38 mm. Data collected at room temperature, graphite-monochromated Mo Ka radiation, Nicolet R3mV diffractometer, to scans of 2-15°min -1, 20max =45 °, h= -29 to 29, k=0 to 15, l = 0 to 30, 6892 measurements, 6131 unique (Ri,t = 0.076), 3418 observed [I> 3or(/)]. Unit-cell dimensions determined by least-squares fit to settings for 29 reflections (16 < 20 < 30°). Empirical absorption correction (/z --14.04 cm-~), transmission factors 0.88-1.00; three standards monitored ( _+ 2%), 66.9 h of X-ray exposure. Solved by the Patterson method; full-matrix least-squares refinement on F, R =

As the counterion is varied, the emission quantum yield of *Cu(dmp)2+ (dmp is 2,9-dimethyl-1,10-phenanthroline) varies by as much as 30% in fluid CH2C12 while the lifetime is unchanged. These results are explained in terms of a static quenching mechanism that occurs within ion pairs present in solution. Anions do not quench the emission of the corresponding complex of 2,9-diphenyl-1,10-phenanthroline, and BPh4" does not quench the emission of *Cu(dmp)2+, even though significant ion pairing occurs. On the basis of these observations and related studies involving Lewis bases, the quenching is associated with inner-sphere coordination of the anion to copper in the excited state.