Stereochemistry of coordination polyhedra vs. single ion magnetism in penta- and hexacoordinated Co(ii) complexes with tridentate rigid ligands.

A tridentate ligand L (2,6-bis(1-(3,5-di-tert-butylbenzyl)-1H-benzimidazol-2-yl)pyridine) was synthesized and used for the preparation of three pentacoordinated Co(ii) complexes of formula [Co(L)X] (where X = NCS for 1, X = Cl for 2 and X = Br for 3) and one ionic compound 4 ([Co(L)]Br·2CHOH·HO) containing a hexacoordinated Co(ii) centre. Static magnetic data were analysed with respect to the spin (1-3) or the Griffith-Figgis (4) Hamiltonian. Ab initio calculations enable us to identify the positive axial magnetic anisotropy parameter D accompanied by a significant degree of rhombicity in the reported complexes.