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

Three isonicotinamide (isn) copper(II) complexes with different bridging ligands, azide, thiocyanate and sulfate, have been prepared. The molecular structure of [Cu2(μ-1,1-N3)2(μ-1,3-N3)2(isn)2]n (1) is composed of binuclear species, Cu2(μ-1,1-N3)2(isn)2, inter-connected by additional four azide bridges in the end-to-end mode (1,3). This gives a CuN4N square-pyramidal coordination sphere around each copper(II) ion. A trans mononuclear octahedral coordination sphere CuN4S2 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’-SO4)(H2O)(isn)2]·2H2O}n (3) completes the CuO2N2O square-pyramidal coordination sphere, and thus enables bridging between the mononuclear Cu(H2O)(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 (J1) for the FM interaction. Additionally, the inter-binuclear pathway in 1 gives another contribution (J2) to the whole FM interaction seen herein (J1 = 18.5 cm–1, J2 = 4.9 cm–1).

The copper(II) isonicotinamide complexes with different bridging ligands [Cu2(μ-1,1-N3)2(μ-1,3-N3)2(isn)2]n (1), [Cu(μ-N,S-NCS)2(isn)2]n (2) and {[Cu(μ-O,O′-SO4)(H2O)(isn)2]·2H2O}n (3) have been prepared, structurally characterized and their magnetic properties described. The compounds 1 and 2 comprise 2D, while compound 3 1D polymeric units. In all three complexes catemeric amide–amide hydrogen bonds are established, in 1 and 2 between adjacent sheets, while in 3 by involving amide neighbouring groups within a particular chain. The temperature dependant magnetic susceptibility data show ferromagnetic coupling in 1, while complexes 2 and 3 reveal paramagnetic behaviour.Figure optionsDownload as PowerPoint slide