Magneto-structural correlations in a family of di-alkoxo bridged chromium dimers

Abstract

A series of di-alkoxo bridged Cr(III) dimers have been synthesised using pyridine alcohol ligands. The structures fall into four general categories and are of formula: [Cr₂(OMe)₂(pic)₄]·½MeOH·½Et₂O (1), [Cr₂(hmp)₂(pic)₂X₂] (where X = Cl (2), Br (3)), [Cr₂(L)₂Cl₄(A)₂]·2S (where L = hmp, A = H₂O and S = Et₂O (4); L = hmp, A = pyridine and S = pyridine (5); L = hmp, A = 4-picoline and no S (6); L = hep, A = H₂O and S = MeCN (7)), and [Cr(hmp)(hmpH)Cl₂]·MeCN (8). Direct current (DC) magnetic susceptibility measurements show relatively weak antiferromagnetic exchange interactions between the Cr(III) centres with J values <|15| cm⁻¹ in all of the complexes measured. DFT calculations performed on complexes 1–8 reproduce both the sign and strength of the exchange interactions found experimentally, and confirm that the magnitude and sign of the J value is strongly dependent upon the orientation of the dihedral angle formed between the bridging Cr₂O₂ plane and the O–R vector of the bridging group (θ), and the Cr–O–Cr–O dihedral angle (ψ).