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 cm1 compared with the nearest excited doublet state, is close to 5cm 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=9.35cm 1, J23=3.95cm 1, for CASPT2 J12, 13=6cm 1, J23=2cm 1 and for DFT-BS J12, 13=11.31cm 1, J23=4.20m 1. The methodological comparison is briefly discussed.

Magnetic exchange interaction for the μ-hydroxo bridged vanadium (IV) dimers is investigated based on calculations of density functional theory combined with the broken-symmetry approach. It is found that there is an exponential correlation between the V-O (hydroxo)-V angle, the V-O (hydroxo) distance and the exchange coupling constants J. Meanwhile, the calculated results reveal that the deprotonation of the bridging hydroxo ligand causes a sharp increase of the exchange coupling interaction, but the magnetic coupling constant J is insensitive to the deprotonation of the bridging aquo ligand. Moreover, simplifying each 1,2-bridging squarate ligand with two OCH2 groups almost does not influence magnetic exchange behavior between the two vanadium (IV) ions, and the principle of the shortest superex-change pathway is available for the multiplicity of the bridging ligand in the μ-hydroxo bridged vanadium (IV) di-mers.

Two new complexes, 1 and 2, with halo acetate ligands have been prepared from the reaction of ClCH2CO2H or BrCH2CO2H with the precursor Mn12Ac, and their structures and magnetic properties studied. The structures of complexes 1 and 2 consist of a central cubane-like [Mn4O4]8 unit held within a non-planar ring of eight Mn4 by eight µ3-O ions, sixteen XCH2CO2 units and four terminal water molecules, as well as included CH2Cl2 and H2O. Dierent arrangements of the four Mn4 relative to the eight Mn4 comparable complexes could play a role in the observed magnetic properties. Five and three periodic steps in the magnetic hysteresis loops are observed for both 1 and 2 at 2.2 and 2.6K, respectively.χmT values for complexes 1 and 2, where χm is the in-phase component of the AC magnetic susceptibility, exhibit a plateau in the 6-20K region, below which there is an abrupt decrease in χmT. Their χm signals measured at different frequencies are observed in the region 2-10 K, and exhibit a frequency dependency on the χm AC peaks, with a predominant peak in the 4-10K region. For these complexes, there is a difference between the zero-field-cooled (ZFC) and the field-cooled (FC) magnetization due to slow relaxation of the magnetization.

The synthesis, structures, and magnetic properties of four cyano-bridged MIIRuIII 2 compounds prepared from the paramagnetic RuIII building blocks, trans-[Ru(salen)(CN)2]- 1 [H2salen) N, N¢-ethylenebis(salicylideneimine)] and trans-[Ru(acac)2(CN)2]-(Hacac) acetylacetone), are described. Compound 2, {Mn(CH3OH)4[Ru(salen)(CN)2]2}‚ 6CH3OH‚2H2O, is a trinuclear complex that exhibits antiferromagnetic coupling between MnII and RuIII centers. Compound 3,{Mn(H2O)2[Ru(salen)(CN)2]2 H2O}n, has a 2-D sheetlike structure that exhibits antiferromagnetic coupling between Mn and Ru, leading to ferrimagnetic-like behavior. Compound 4,{Ni(cyclam)[Ru(acac)2(CN)2]2}‚ 2CH3OH‚2H2O (cyclam ) 1,4,8,11-tetraazacyclotetradecane), is a trinuclear complex that exhibits ferromagnetic coupling. Compound 5,{Co[Ru(acac)2(CN)2]2}n, has a 3-D diamond-like interpenetrating network that exhibits ferromagnetic ordering below 4.6 K. The density functional theory (DFT) method was used to calculate the molecular magnetic orbitals and the magnetic exchange interaction between RuIII and MII (MnII, NiII) ions.

The effect of magnetic exchange, double exchange, vibronic coupling, and asymmetry on magnetic properties of d2-d3 systems is discussed. The temperaturedependent magnetic moment was calculated with the semiclassical adiabatic approach. The results show that the vibronic coupling from the out-of-phase breathing vibration on the metal sites (Piepho, Krausz, and Schatz [PKS] model) and the vibronic coupling from the stretching vibration between the metal sites (P model) favor the localization and delocalization of the "extra" electron in mixed-valence dimers, respectively. The magnetic properties are determined by the interplay among magnetic exchange, double exchange, and vibronic coupling. The results obtained by analyzing d2-d3 systems can be generalized to other full delocalized dinuclear mixed valence systems with a unique transferable electron.