Lanthanide induced variability in localised CoII geometries of four triangular L3Co3IILnIII complexes

Abstract

Four tetranuclear heterobimetallic triangle complexes [L₃Co₃Dy(NO₃)₂(H₂O)(MeOH)₅](NO₃) (C1), [L₃Co₃Gd(NO₃)₃(MeOH)₄] (C2), [L₃Co₃La(NO₃)₂(H₂O)₆](NO₃)(H₂O) (C3), and [L₃Co₃TbCl(NO₃)₂(H₂O)_0.5(MeOH)_3.5] (C4), where H₂L = 1,4-bisformylnaphthalene-2,3-diol, have been synthesised and structurally characterised. Each complex crystallises with a complete molecule in the asymmetric unit (Z′ = 1) and displays near perfect octahedrality in two out of three Co^II centres. The third Co^II ion assumes a different coordination geometry in each complex: six-coordinate octahedral in C1, six-coordinate with a distortion towards trigonal prismatic in C2, five-coordinate trigonal bipyramidal in C3, and five-coordinate square pyramidal in C4; which has been attributed to increasing lanthanide cation size, coupled with a non-macrocyclic coordination environment. Continuous Shape Measurement (CShM) calculations and octahedral distortion parameter calculations were performed, using the SHAPE and OctaDist software packages, respectively, in order to aid in the assessment of each metal centre's local coordination geometry. The preliminary magnetic investigation of C3 found χ_mT = 9.4 cm³ K mol⁻¹ at 300 K and M = 7.1 μ_B at 1.8 K, which are approximately two thirds the maximum theoretical values for three Co^II ions and indicates the presence of a relatively large zero-field splitting parameter (D/k_B = 65 K) operative in each Co^II ion rather than exchange coupling between the Co^II centres.