Association of copper(II) isonicotinamide moieties via different anionic bridging ligands: Two paths of ferromagnetic interaction in the azide coordination compound

Abstract

Three isonicotinamide (isn) copper(II) complexes with different bridging ligands, azide, thiocyanate and sulfate, have been prepared. The molecular structure of [Cu 2(μ-1,1 -N 3) 2(μ-1,3 -N 3) 2(isn) 2] n ( 1) is composed of binuclear species, Cu 2(μ-1,1 -N 3) 2(isn) 2, inter-connected by additional four azide bridges in the end-to-end mode (1,3). This gives a CuN 4N square-pyramidal coordination sphere around each copper(II) ion. A trans mononuclear octahedral coordination sphere CuN 4S 2 is present in [Cu(μ- N, S-NCS) 2(isn) 2] n ( 2), with thiocyanato ligands serving as bridges between the adjacent Cu(isn) 2 moieties. The third anionic ligand, i.e. sulfate, in {[Cu(μ- O, O’-SO 4)(H 2O)(isn) 2]·2H 2O} n ( 3) completes the CuO 2N 2O square-pyramidal coordination sphere, and thus enables bridging between the mononuclear Cu(H 2O)(isn) 2 moieties. The ligands that bridge the principal building blocks, i.e. binuclear in 1 and mononuclear in 2 and 3, connect the axial ligands with the equatorial positions of the copper(II) coordination spheres in all three cases. A ferromagnetic interaction FM is found for 1, while 2 and 3 are paramagnetic. Therefore, the key structural difference between 1 on one hand, and 2 and 3 on the other, is found in the anionic ligand, serving in 1 also as the intra-binuclear bridge, showing the main path ( J 1) for the FM interaction. Additionally, the inter-binuclear pathway in 1 gives another contribution ( J 2) to the whole FM interaction seen herein ( J 1 = 18.5 cm –1, J 2 = 4.9 cm –1).