Theoretical study on the structural aspects of CuII Hybrid-Spin complexes

Theoretical approaches to hybrid-spin systems aim at clarification of the nature of spin exchange between the metal ion and the organic radicals. This aids the molecular design, of novel materials based on studies of the relevant molecular fragments. The current investigations were focused on two isomeric complexes of CuII with acetylacetonate and organic radicals (3- and 4-N-oxyl-tretbutylaminopyridine), whose geometry and magnetic properties were known from, experimental data. A DFT approach based on the UB3LYP functional and basis sets of different size and quality were used in order to elaborate a computational protocol providing a reliable quantitative estimate of the spin-spin interaction. The computational scheme allows the elucidation of the role of various structural factors on the type and magnitude of the spin coupling, such as symmetry, spatial orientation of the radicals and type of the magnetic orbital of the metal ion. Proper symmetry assignment of the wavefunction proved to be critical for correct description of the magnetic behaviour of the complexes. The introduction, of extended basis sets did not justify the computational cost, as the 6-31G* results were sufficiently accurate for the purpose of the study. Detailed analysis of the energies, the natural orbitais and the spin density distribution, upon conformational changes was carried out. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA