Magneto-structural correlation in di-μ-oxo bridged dicopper complexes -: Predictability of isotropic exchange-coupling constant from structure

The relation between isotropic exchange-coupling constant and their structural parameters was examined using 117 compounds containing di-mu-oxo dicopper (CuO2Cu) moiety. The Cu-O bond distances should be in the range of covalent bonding region, preferably 1.93 Angstrom and should be less than 2.25 Angstrom for the superexchange path. The scatter plot between the Cu-O-Cu angle (phi) versus Cu...Cu distance (r) suggests that large number of molecules have a Cu-O bond length of 1.93 Angstrom, and their Cu...Cu distances are determined by phi. The atoms attached to bridging oxygen and ligands of copper can influence the exchange-coupling constant to a larger extent when compared to other distortions like deviation from planarity and ideal bond lengths and angles. It is suggested that the superexchange pathway is ineffective at Cu-O distances greater than 2.25 Angstrom resulting into | 2J|< 50 cm(-1) and no magnetostructural correlation for these systems could be given. The magneto-structural correlations are given by 2J [cm(-1)] = - 99.1 φ [°]+ 9587=- 4600 r [&ANGS;]+ 13 226. A study including only four-coordinate copper atoms indicate that 2J =(2/r(Cu-O))(- 74.8φ+ 7126+ B) where r(Cu-O) is the Cu-O bond length and B is a correction term applied based on distortions and atoms attached to bridging oxygen and copper atoms. The above least-squares fit lines indicate continuity between antiferromagnetic and ferromagnetic regions crossing the 2J = 0 value at around 97°.