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

Abstract Four dicopper(II) oximato complexes of 2-[2-(α-pyridyl)methyl]imino-3-butanone oxime (pmiboH) and 2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime (peiboH), [Cu 2 (pmibo) 2 ](ClO 4 ) 2 ( 1 ), [Cu 2 (pmibo) 2 ](NO 3 ) 2 ·CH 3 OH ( 2 ), [Cu 2 (peibo) 2 ](ClO 4 ) 2 ·CH 3 OH ( 3 ) and [Cu 2 (peibo) 2 (H 2 O) 2 ](ClO 4 ) 2 ( 4 ), were prepared and characterized structurally and magnetically. All the dicopper(II) oximato complexes have a common cationic structure in which the two Cu atoms are bridged through two NO bridges of the oximato ligand to afford a dinuclear structure. The cation moieties of 1 and 2 consist of one six-membered Cu 2 N 2 O 2 chelate ring and four five-membered (CuN 2 C 2 and CuNC 2 N) chelate rings, providing a planar configuration. The cation moieties of 3 and 4 are also composed of three six-membered (Cu 2 N 2 O 2 and CuNC 3 N) chelate rings and two five-membered CuN 2 C 2 chelate rings, giving a twisted-boat configuration. The −2 J values ( H =−2 JS 1 S 2 ) are 835, 825, 550 and 510 cm −1 for 1 , 2 , 3 and 4 , respectively, indicative of a strong antiferromagnetic interaction in the solid state. All the dicopper(II) oximato complexes show seven 1 H NMR signals at 23°C in the range of −0.5 to 30 ppm with the linewidths at half-height, Δ ν 1/2 of 60–1500 Hz, which is characteristic of antiferromagnetic species and indicates that the dinuclear structure is kept in solution. The −2 J values reflect the degree of distortion from the planarity of the Cu 2 framework. The −2 J values roughly correlate with the 1 H NMR parameters; the larger the −2 J values, the smaller the chemical shifts and linewidths. Complexes 1 and 2 were found to undergo an autoreduction reaction in dimethyl sulfoxide (DMSO), N , N -dimethylformamide (DMF) and N , N -dimethylacetamide (DMA), and their behaviors were first monitored by UV–Vis and 1 H NMR methods.