A theoretical study of the nearest Cu•••Cu antiferromagnetic exchange coupling interactions in [LaCu6] and [YCu6]

A density functional study of the exchange coupling interactions between the two nearest Cu-II centers in [LaCU6] and [YCu6] is presented. Two approaches show that the (CuCu)-Cu-... antiferromagnetic interactions increase with a decrease of the ionic radius of the diamagnetic central La-III and Y-III ions. However, the influence of the central ions on the (CuCu)-Cu-... interactions is small compared to that of their structures according to our calculations. We therefore conclude that the stronger antiferromagnetic interactions between the two nearest Cu-II centers in [LaCu6] than in [YCu6] are not a result of the central La-III ion but the structure. The antiferromagnetic contributions of the direct overlap between the two nearest Cull magnetic orbitals also play a major role according to the calculations of the overlap integral S-ij based on Kahn's theory. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)