Synthesis, spectroscopy and magnetism of transition-metal complexes with pyridylmethylphosphonate ligands

The compounds [ML2(H2O)2]X2[M = Co, Ni or Cu; L = diethyl 4-pyridylmethylphosphonate (4-pmpe) or diethyl 2-pyridylmethylphosphonate (2-pmpe); X = NO3 or ClO4] have been prepared. Two types of complexes, [M(4-pmpe)2(H2O)2]X2 with the N-bonded monodentate ligand and [M(2-pmpe)2(H2O)2]X2 where 2-pmpe acts as a didentate N,O-bonded chelate ligand, were obtained. The complexes of CoII and NiII are isomorphous. The new complexes were identified and characterized by elemental analysis, magnetic measurements and by infrared, electronic and some 1H NMR spectral studies. The crystal and molecular structure of [Co(4-pmpe)2(H2O)2][ClO4]2·2H2O has been determined: space group P, a= 8.159(1), b= 9.860(1), c= 11.262(1)A, α= 78.44(1), β= 75.11(1), γ= 84.30(1)°, Z= 2, R= 0.0485, R′= 0.0445, for 3078 reflections. The cobalt ion is octahedrally surrounded by two pyridine nitrogens with distances 2.133(3)A and two oxygens of the phosphoryl groups from two organic ligands at distances of 2.100(2)A. Two water molecules occupy the fifth and the sixth co-ordination sites trans with Co–O bond distances of 2.101(2)A. The ligand bridges the cobalt ions, thereby forming infinite chains (Co ⋯ Co 8.159 A). The spectroscopic and magnetic data are consistent with an octahedral geometry for all the studied complexes, e.g. mono- and poly-nuclear for the 2- and 4-pmpe ligands, respectively.