Ferromagnetic Coupling Behavior in Oxo-Bridged Binuclear Bis(η5-cyclopentadienyl)titanium(III) Complex (Cp2Ti)2(μ-O): A Density Functional Theory Combined with Broken-Symmetry Approach

Abstract

The ferromagnetic coupling behavior in oxo-bridged bis(bis(cyclopentadienyl)titanium(III)) complex (Cp 2Ti)2(I-O) is investigated on the basis of calculations of density functional theory combined with the brokensymmetry approach. The magnetic coupling constants calculated for the experimental and optimized geometries are 11.41 and 1.29 cm -1 , respectively, comparable with the experimentally measured J value (8.3 cm -1 ). The calculated results show that the magnetic coupling constant J slightly decreases with the increase of the Ti-(I-O)-Ti angle and decreases exponentially with the increase of the Ti-(I-O) distance. In variation of the dihedral angle ‚ between the two Cp2Ti fragments the transition of the magnetic coupling property occurs near ‚ ) 45°. For ‚ > 45°, the coupling is ferromagnetic, and it is antiferromagnetic for ‚ < 45°. The ferromagnetic coupling interaction between the magnetic centers is almost not affected by the protonation of the oxo-bridge ligand. Molecular orbital analysis reveals that, because of the nonbonding character and electronic location character of the single-occupied molecular orbitals (SOMO), there is no antiferromagnetic coupling pathway through superexchange via the bridging atom. However, when ‚ varies from 90° to 0°, the throughspace interaction between the two magnetic centers in the SOMOs occurs, leading to a gradually increscent antiferromagnetic contribution, JAF. As soon as the antiferromagnetic contribution exceeds the ferromagnetic contribution, JF, the transition of the magnetic coupling properties for the molecule occurs. The spin population analysis is briefly discussed.