Dark green-black crystals of [Ru(bpy),](PF,), (111) were obtained from [Ru(bp )3](PF6)2 (11) by oxidation with Mn02 in 7 M H2S04. The X-ray crystal structures of I11 (trigonal R k , a = 17.846 (7) 1, c = 19.915 (7) A, Z = 6) and I1 (trigonal P31c, u = 18.338 (7) A, c = 16.216 (13) A, Z = 6) were determined at 105 K. The low temperature structure of I1 shows the a-and b-axis increased by a factor of 47 relative to the room temperature structure and has three distinct Ru sites (phase transition at 190 ( 5 ) K). This explains many recent spectroscopic observations. The Ru-N distances of I1(2.053 (2) A) are virtually indistinguishable from those of I11 (2.057 (3) A). This is compatible with the high electron self-exchange rate between I1 and 111. The pattern of differences in intra-bpy bond lengths seems in contradiction to the conventional a-backbonding model. Changes of bpy distances in [M(bpy),], bpy, Hbpy', and H2bpy2+ are examined by a principal component analysis, which yields two main factors: The first factor is related to the temperature of measurement, the crystal packing pattern or the model used to interpret the diffraction data. The second factor can be characterized as electronic in nature and confirms that there are as yet unresolved contradictions in the model of a-backbonding as applied to the ligand geometry of [M(bpy),]"+ complexes.

We have prepared a new family of ruthenium complexes containing the bpea ligand (where bpea stands for N,N-bis(2-pyridyl)ethylamine), with general formula [Ru(bpea)(bpy)(X)](n+) (2, X = Cl(-); 3, X = H(2)O; 4, X = OH(-)), and the trisaqua complex [Ru(bpea)(H2O)(3)](2+), 6. The complexes have been characterized through elemental analyses, UV-vis and (1)H NMR spectroscopy, and electrochemical studies. For complex 3, the X-ray diffraction structure has also been solved. The compound belongs to the monoclinic P2(1)/m space group, with Z = 2, a = 7.9298(6) A, b = 18.0226(19) A, c = 10.6911(8) A, and beta = 107.549(8) degrees. The Ru metal center has a distorted octahedral geometry, with the O atom of the aquo ligand placed in a trans position with regard to the aliphatic N atom of the bpea ligand so that the molecule possesses a symmetry plane. NMR spectra show that the complex maintains its structure in aqueous solution, and that the corresponding chloro complex also has a similar structural arrangement. The pH dependence of the redox potential for the complex [Ru(bpea)(bpy)(H2O)](PF(6))(2) is reported, as well as the ability of the corresponding oxo complex to catalyze the oxidation of benzylic alcohol to benzaldehyde in both chemical and electrochemical manners.

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Complexes Ru(DMF)6n+ ( = 2, 3; DMF = A,A-dimethylformamide) are prepared by a direct and simple synthesis from commercially available RuCls-xHaO and characterized by UV-vis, NMR, and cyclic voltammetry. Crystal and molecular structures are presented for [Ru(DMF)6](CF3SOa)3 (I) and [Ru(DMF)6](CF3S03)2 (II). I is monoclinic, of space group P2\/c, with a = 18.28(1) Á, b = 18.62(1) Á, c = 13.29(1) X, ß = 100.8(1)°, V = 4443(5) Á3, Z = 4, dCaic = 1.495 g cm"3, and d0bs = 1.49 (25 °C) g cm"3. R = 0.061 (Rw = 0.061) for 4506 independent observed reflections with I > 3 ( ). II is triclinic, of space group , with, a = 8.799(2) Á, b = 9.557(2) Á, c= 11.627(2) Á, a = 76.11(2)°, ß = 84.73(2)°, y = 85.12(2)°, V= 943.1(3)Á3, Z = 1, dcaic = 1.475 g cm-3, and dobs = 1.477 (25 °C) g cm-3. R = 0.061 (Rw = 0.058) for 5189 independent observed reflections with I > 3 a{I). Metal to ligand coordination is through the oxygen atom with average Ru-O distances of 2.02(1) Á (I) and 2.088( 9) Á (II) in the octahedral units. The reduction potential for I measured by cyclic voltammetry is 0.28 V vs NHE.

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