Spin Spin Interactions in Polynuclear Nickel(II) Complexes. a Magnetic and Structural Study of Binuclear Nickel(II) Complexes of Enolic 1,3,5-Triketonates

Abstract

The bulk magnetic susceptibilities of the binuclear nickel(II) complexes of the 1,3,5-triketonates from diethyl (2-oxocyclopentane- 1,3-diyl) bisglyoxylate (H₂ecg) (1) and diethyl 2,4,6-trioxoheptanedioate (H₂decg) (2) have been measured over the temperature range 6-300 K. Antiferromagnetic spin-spin coupling is observed in each case with Neel temperatures in the range 45-65 K. The X-ray crystal structure of [Ni( ecg )( py )2]2.( py ) has been solved. The complex crystallizes with one pyridine of solvation in the space group Pī [a 10.507(1), b 13.384(1), c 9.992(1) Ǻ, α 103.004(9), β 115.867(9), β 86.857(10)°, Z = 1]. The molecule is binuclear with two coplanar triketonate dianions bridging the two six-coordinate nickel atoms through a di-μ-oxo linkage [Ni-O_b-Ni angle 102.0(1)°]. Two pyridine molecules and four triketonate oxygen atoms are bound to each nickel atoms.

Magnetostructural correlations are presented in comparison with binuclear copper(II) 1,3,5-triketonates. The marked decrease in spin-spin interaction in the nickel complexes is attributed to increasing metal-bridging oxygen bond lengths that decrease the efficacy of the σ antiferromagnetic pathway xy||O_b||xy and contributions from the ferromagnetic xy||O_b||z² pathway.