Broken symmetry density functional study of biomimetic models for Purple Acid Phosphatases of the type Fe(III)-M(II) (M = Fe, Cu, Ni, Co and Mn)

Density Functional Theory (OFT) calculations using the hybrid meta-GGA TPSSh functional, were carried out for mixed valence compounds Fe(III)-M(II)(M = Fe, Cu, Ni, Co and Mn) which are structural and functional biomimetic models for Purple Acid Phosphatases. The broken symmetry (BS) formalism was used to compute the magnetic coupling constant which shows that all complexes exhibit weak antiferromagnetic coupling. The effect of the geometry on the accuracy of the BS calculations is evaluated and it is shown that the TPSSh functional provides accurate results with errors in the range of 10-19%, as long as the geometry around the transition metal ions is well described. All complexes show one magnetic exchange sigma/pi pathway involving the in-plane p-orbitals of the phenoxo bridge and the metal d-orbitals. Additionally, a correlation between the computed coupling constant and the M-II-O(bridge) bond distance is found, in agreement with the experimental findings. (C) 2011 Elsevier B.V. All rights reserved.