A comparison of the angular-overlap and crystal-field models in interpreting the magnetic properties of hexakis(pyridine N-oxide)nickel(II) tetrafluoroborate

Abstract

The angular-overlap model (a.o.m.) has been applied to the title complex where the local metal symmetry is S₆. A.o.m. parameters have been obtained which fit the magnetic anisotropy and average magnetic susceptibility and the results are compared with those from a crystal-field model. General expressions are presented which relate the a.o.m. parameters to an ‘effective crystal field’ expressed in terms of coefficents of spherical harmonics. The NiO₆ core has almost exact octahedral symmetry and in this case the a.o.m. increases the effective symmetry from S₆ to D₃. From the X-ray crystal structure, the Ni–O–N angle is 119° and, if one assumes that the oxygen atom is sp² hybridized, it is possible to obtain values for all the three a.o.m. parameters. These are found to be e_σ= 4 393, e_πx= 830, and e_πy= 1 660 cm^–1.