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

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).