Metal complexes of 3-pyridazinecarboxylic acid (Hpdc). The x-ray crystal structure of [Mn(pdc) 2(H 2O) 2].2H 2O and a structural comparison between equivalent pyridine and pyridazine systems

Abstract

An X-ray structure determination is reported for the complex [Mn(pdc) 2(H 2O) 2]·2H 2O of 3-pyridazinecarboxylic acid (Hpdc). The complex is triclinic, P 1 , with a = 5.356(1), b = 7.433(2), c = 9.800(2) Å; α = 79.79(2), β = 88.92(2), γ = 71.74(2)° and Z = 1. Centrosymmetric octahedral molecules of [Mn(pdc) 2(H 2O) 2] are linked by hydrogen bonds involving the two lattice waters. The chelating 3-pyridazinecarboxylate ligands are present in a trans-planar arrangement, with each ligand coordinating via a carboxylate oxygen and the 2-nitrogen. Two water molecules coordinate in the axial positions. The structure differs from that of the corresponding 2-pyridinecarboxylic acid (Hpic) complexes [M(pic) 2(H 2O)2]·2H 2O (M = Co, Ni, Zn) only in terms of the hydrogen bonding network. This enables the first structural comparison between equivalent pyridine and pyridazine systems to be made. Magnetic susceptibility measurements to 89 K, and electronic, infrared and X-ray powder diffraction spectra are reported for the complexes M(pdc) 2·4H 2O (M = Mn, Co, Ni, Zn) and Cu(pdc) 2. The Co and Ni complexes are isomorphous, with [Mn(pdc) 2(H 2O) 2]·2H 2O. The Cu complex is probably six-coordinate with bridging carboxylate groups.