Magnetic exchange of trinuclear spin frustration system: CASPT2 and density functional theory study on hydroxo-bridged chromium complex [Cr3(NH3)10(OH)4] · Br5

The theoretical calculations on magnetic exchange of the title complex are carried out by using multiconfigurational second-order perturbation theory, CASPT2, and density functional theory combined with broken-symmetry approach, DFT-BS. The CASPT2 calculated quartet ground state, stabilized by 8.02 cm−1 compared with the nearest excited doublet state, is close to 5 cm−1 of the experimental measurement. The dependence of energy levels on the ratio J23/J12,13 validates occurrence of the spin frustration phenomenon. Both CASPT2 and DFT-BS calculations reproduce well experimentally coupling constants of J12,13 = −9.35 cm−1, J23 = −3.95 cm−1, for CASPT2 J12,13 = −6 cm−1, J23 = −2 cm−1 and for DFT-BS J12,13 = −11.31 cm−1, J23 = −4.20 m−1. The methodological comparison is briefly discussed.