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

Abstract

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 Co^II and Ni^II 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)Å, 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)Å and two oxygens of the phosphoryl groups from two organic ligands at distances of 2.100(2)Å. Two water molecules occupy the fifth and the sixth co-ordination sites trans with Co–O bond distances of 2.101(2)Å. The ligand bridges the cobalt ions, thereby forming infinite chains (Co ⋯ Co 8.159 Å). 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.