Magneto–structural correlation of dimeric copper(II) carboxylates with pyridyl-substituted nitronyl nitroxides

Abstract

The synthesis, crystal structure and magneto–structural correlations of three new paddle-wheel type dicopper(II) carboxylate complexes with pyridyl-substituted nitronyl nitroxides, [Cu 2(μ-Me 3CCO 2) 4(NITpPy) 2](C 6H 6) ( 1), [Cu 2(μ-CH 3CO 2) 4(NITpPy) 2] ( 2), and [Cu 2(μ-C 6H 6CH 2CO 2) 4(NITmPy) 2] ( 3) (NITpPy=4,4,5,5-tetramethyl-2-(4-pyridyl)-2-imidazoline-N 1-oxyl N 3-oxide, NITmPy=4,4,5,5-tetramethyl-2-(3-pyridyl)-2-imidazoline-N 1-oxyl N 3-oxide) are reported. Structures of complexes 1–3 consist of a symmetrical dimeric Cu(II) carboxylate paddle-wheel core and pyridyl nitrogen atoms of radical ligands at the apical position. Cryomagnetic susceptibilities were measured in the temperature range 4–300 K. According to the structural results, the magnetic data are discussed in terms of four S=1/2 spin units involving one strong coupled dicopper(II) unit plus two monomer nitroxyl radicals. It is found that two paddle-wheel copper(II) ions are strongly coupled antiferromagnetically with J=−192, −172, and −160 cm −1 for complexes 1, 2, and 3, respectively, while the interactions between copper(II) and the radicals are very weak. The magneto–structural correlations for complexes 1, 2, and 3 are discussed on the basis of the structural parameters and magnetic data for the complexes