Multifrequency ESR study of dimeric molecular conformation determined from exchange and dipolar magnetic spin-spin interactions

Characterization of a stable ruthenium complex with an oxyl radical

The ruthenium oxyl radical complex, [Ru(II)(trpy)(Bu(2)SQ)O(.-)] (trpy = 2,2':6',2"-terpyridine, Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) was prepared for the first time by the double deprotonation of the aqua ligand of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2) is reversibly converted to [Ru(III)(trpy)(Bu(2)SQ)(OH-)](+) upon dissociation of the aqua proton (pK(a) 5.5). Deprotonation of the hydroxo proton gave rise to intramolecular electron transfer from the resultant O(2-) to Ru-dioxolene. The resultant [Ru(II)(trpy)(Bu(2)SQ)O(.-)] showed antiferromagnetic behavior with a Ru(II)-semiquinone moiety and oxyl radical, the latter of which was characterized by a spin trapping technique. The most characteristic structural feature of [Ru(II)(trpy)(Bu(2)SQ)O(.-)] is a long Ru-O bond length (2.042(6) A) as the first terminal metal-O bond with a single bond length. To elucidate the substituent effect of a quinone ligand, [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) (4ClSQ = 4-chloro-1,2-benzosemiquinone) was prepared and we compared the deprotonation behavior of the aqua ligand with that of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). Deprotonation of the aqua ligand of [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) induced intramolecular electron transfer from OH- to the [Ru(III)(4ClSQ)] moiety affording [Ru(II)(trpy)(4ClSQ)(OH.)]+, which then probably changed to [Ru(II)(trpy)(4ClSQ)O(.-)]. The antiferromagnetic interactions (J values) between Ru(II)-semiquinone and the oxyl radical for [Ru(II)(trpy)(Bu(2)SQ)O(.-)] and for [Ru(II)(trpy)(4ClSQ)O(.-)] were 2J = -0.67 cm(-1) and -1.97 cm(-1), respectively.

Drug-metal interactions: copper(II) complex of the antidiabetic drug acetohexamide and pyridine

The preparation, spectral properties, and crystal structure of a copper(II) complex of 4-acetyl-N-[(cyclohexylamino)carbonyl]benzenesulfonamide, which is known as acetohexamide, and pyridine are reported. The complex Cu(AH)2(py)2, where AH = acetohexamide and py = pyridine, was prepared and characterized by X-ray and ESR. The complex is monoclinic, space group P2(1)/a, with a = 17.412(6), b = 9.039(2), c = 26.531(10) A, beta = 102.24(2) degrees, and Z = 4. The final refinement used 3892 unique reflections and gave an R value of 0.0646. The copper atom is surrounded by four nitrogen atoms in a square-planar arrangement, two from the acetohexamide ligands (Cu-N = 2.009 A) and two from the pyridine molecules (Cu-N = 2.016 A) in a trans geometry. The ESR data support a similar coordination behavior of the copper (g parallel greater than g perpendicular greater than ge) with the unpaired electron in the dx2-y2 orbital.