First published as an Advance Article on the web 25th October 2002 A novel 1D-coordination polymeric Co (II) complex [Co(btp)2(NCS)2]n [1, btp ¼ 1,3-bis(1,2,4-triazol-1-yl)propane] was synthesized and characterized. The coordination geometry of the cobalt ions is distorted octahedral, with the equatorial plane formed by the four nitrogen atoms of the four triazole groups and the axial sites occupied by two terminal trans thiocyanato ligands. The Co (II) ions are linked by the btp ligands, building up coordination polymers of infinite 1D-neutral chains.

In order to theoretically study on the magnetic coupling interaction in the Mn-Mn dimer, quantum chemical calculations on the equilibrium Mn-Mn distance Re, total energy ET, binding energies Be and exchange interaction energies EðSÞ under dierent spin multiplets were performed at CASPT2 level of theory. It is found that the calculated Re, ET, and Be values are correlated with the spin multiplet, and with increasing the total spin S, Re increases, but ET and Be exhibit a decrease trend. The exchange interaction energies EðSÞ "deviate significantly from the Lande interval rule". This unusual magnetic phenomenon is primarily attributed to the biquadratic jðSa SbÞ2 term contribution in spin Hamiltonian for the Mn-Mn dimer.

The magnetic exchange interaction behavior and energy spectrum of low-lying spin states are investigated by using ab initio multireference configuration-interaction method for the representative binuclear transition-metal complexes fsNH3d5Crs m-OHdCrsNH3d5g5+ and fCl3FeOFeCl3g2−. Our calculations for the nonmodeling real title complexes found that under the appropriate basis sets and active space, ab initio method at multireference configuration-interaction level of theory is able to give accurate energy spectrum of low-lying spin states within reachable computation demand nowadays and the deviation of magnetic exchange interaction to Lande interval rule can be described by the biquadratic correction in terms of Heisenberg spin Hamiltonian. As a methodology comparison, density-functional theory combined with broken-symmetry approach provides an alternative yet efficient approach to produce accurate numerical results, but there are dependences on the particular chosen exchange-correlation functionals and system dependent. The spin population analyses at complete active space self-consistent-field level of the theory provide an instructively understanding and prediction for the magnetic interaction mechanism.

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.

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.