Syntheses, crystal structures and autoreduction behavior of antiferromagnetically coupled dicopper(II) oximato complexes

Four dicopper(II) oximato complexes of 2-[2-(alpha-pyridyl)methyl]imino-3-b utanone oxime (pmiboH) and 2-[2-(alpha-pyridyl)ethyl]imino-3-butanone oxime (peiboH), [Cu-2(pmibo)(2)](ClO4)(2) (1), [Cu-2(pmibo)(2)](NO3)(2). CH3OH, (2), [Cu-2(peibo)(2)](ClO4)(2). CH3OH (3) and [Cu-2(peibo)(2)(H2O)(2)](ClO4 )(2) (4), were prepared and characterized structurally and magnetically. Al l the dicopper(II) oximato complexes have a common cationic structure in wh ich the two Cu atoms are bridged through two N-O bridges of the oximato lig and to afford a dinuclear structure. The cation moieties of 1 and 2 consist of one six-membered Cu2N2O2 chelate ring and four five-membered (CuN2C2 an d CuNC2N) chelate rings, providing a planar configuration. The cation moiet ies of 3 and 4 are also composed of three six-membered (Cu2N2O2 and CuNC3N) chelate rings and two five-membered CuN2C2 chelate rings, giving a twisted -boat configuration. The -2J values (H = -2JS(1)S(2)) are 835, 825, 550 and 510 cm(-1) for 1, 2, 3 and 4, respectively, indicative of a strong antifer romagnetic interaction in the solid state. All the dicopper(II) oximato com plexes show seven H-1 NMR signals at 23 degrees C in the range of -0.5 to 3 0 ppm with the linewidths at half-height, Delta v(1/2) of 60-1500 Hz, which is characteristic of antiferromagnetic species and indicates that the dinu clear structure is kept in solution. The -2J values reflect the degree of d istortion from the planarity of the Cu-2 framework. The -2J values roughly correlate with the H-1 NMR parameters; the larger the -2J values, the small er the chemical shifts and linewidths. Complexes 1 and 2 were found to unde rgo an autoreduction reaction in dimethyl sulfoxide (DMSO), N,N-dimethylfor mamide (DMF) and N,N-dimethylacetamide (DMA), and their behaviors were firs t monitored by UV-Vis and H-1 NMR methods. (C) 1999 Elsevier Science S.A. A ll rights reserved.