Syntheses, crystal structures, and magnetic properties of first row transition metal coordination polymers containing dicyanamide and 4,4′-bipyridine

Abstract

The complexes of formulae M(dca)₂(bipy) (M = Fe 1, Co 2, Ni 3; dca = dicyanamide, N(CN)₂⁻; bipy = 4,4′-bipyridine) and M(dca)₂(bipy)(H₂O)·0.5MeOH (M = Mn 4, Fe 5, Co 6), have been synthesized and characterized by single crystal and powder X-ray diffraction. Compounds 1–3 contain two interpenetrating 3D α-Po related networks. Bidentate dca ligands bridge the octahedral metal atoms to form square-grid like M(dca)₂ sheets, with the bipyridine ligands linking these sheets together to form the α-Po-like 3D networks. The large amount of space within a single 3D network allows the interpenetration of the second 3D network. Compounds 4–6 contain 1D ‘tubes’ packing together in a parallel interdigitated fashion. Water ligands coordinated to the octahedral metal ions and intercalated methanol molecules occupy the inside of the M(dca)₂ tubes while protruding monodentate bipyridine ligands participate in both π-stacking and hydrogen bonding interactions between adjacent tubes. Co(dca)₂(bipy)·0.5H₂O·0.5MeOH 7 and Cu(dca)₂(bipy)·H₂O 8 consist of inclined interpenetrating 2D sheets of M(dca)₂(bipy), while Cu(dca)₂(bipy)·MeOH 9 and Cu(dca)₂(bipy)·2H₂O 10 contain 2D zigzag sheets of Cu(dca)₂(bipy) with parallel packing. Fe(dca)₂(bipy)(H₂O)₂·(bipy) 11 contains 1D chains of Fe(bipy) with hydrogen bonding extending the topology to that of two 3D interpenetrating α-Po related networks. Compounds 7 and 11 contain octahedral metal ions, while 8 and 9 have five-coordinate Cu atoms. Variable temperature magnetic susceptibility studies (2–300 K; H = 1 T) have shown that these framework compounds generally display very weak antiferromagnetic coupling because of the long bipy and μ_1,5 bridging pathways. Consequently no long-range magnetic order occurs.