Haiquan Hu

Influence of structural parameters of Cu2O2 core on magnetic coupling in alkoxo-bridged Cu(II) binuclear system

Abstract The influence of the structural parameters of Cu 2 O 2 core on magnetic coupling is studied in model alkoxo-bridged Cu(II) dimers using the density functional method and the broken symmetry approach. The effect of the hinge distortion of the bridge and the out-of-plane displacement of alkoxo group is also analyzed. A small Cu–O–Cu angle, a large Cu–O distance, the hinge distortion and the out-of-plane displacement are all the factors that can enhance the ferromagnetic character. The asymmetry at the Cu 2 O 2 backbone affects the magnetic coupling slightly. Spin polarization may exist in weak antiferro- or ferromagnetic systems.

Theoretical investigation on second-order nonlinear optical properties of (dicyanomethylene)-pyran derivatives

Abstract On the basis of the ZINDO program, we have designed a program to calculate the second-order nonlinear polarizabilities β ijk , β 0 and β μ according to the sum-over-states (SOS) expression. A series of new 4-(dicyanomethylene)-2-methyl-6-( p -dithylamino-styryl)-4 H -pyran (DCM) derivatives were designed and their electron spectra and nonlinear optical properties were studied. It is proposed that these compounds possess two important excited states close to each other in energy, both contributing to hyperpolarizability in an additive fashion; 4-(dicyanomethylene)-2,6-bis-( p -donor-styryl)-4 H -pyran derivatives are more nonlinear than 4-(dicyanomethylene)-2,6-bis-( p -donor-phenyl)-azo-4 H -pyran derivatives. The high nonlinearities, good thermal stability and high transparency make them attractive candidates for second-order nonlinear applications such as electro-optic modulators and frequency doublers.

Effect of structural and chemical parameters on magnetic coupling in hydroxo-bridged Cu(II) dimer

Abstract The influence of various structural and chemical parameters on magnetic coupling in model hydroxo-bridged Cu(II) dimers has been analyzed using the density functional theory and the broken symmetry approach. These parameters, such as the environment around copper atom, the electro negativity of the nonbridging ligands, the Cu–O–Cu angle, the Cu–O distance, the out-of-plane displacement of hydroxo group and the hinge distortion of the bridge, are all the factors that can affect magnetic coupling. The change of antiferromagnetic coupling strength does not depend on the Cu⋯Cu distance simply. In antiferromagnetic complexes, the spin delocalization from magnetic centers towards their neighbors is remarkable and weakens with ferromagnetic coupling strengthening. The effect of asymmetry at the Cu2O2 core has been studied also.

Magnetic coupling mechanism in singly bridged binuclear systems

Abstract The magnetic coupling mechanism in HHeH and OFe 2 Cl 6 2− systems has been investigated using the density functional theory with the broken symmetry approach. The approximately linear relationship between the coupling constant and the square of the energy difference of the singly occupied molecular orbitals (MOs) can be expected for the slight change of structural parameters. By analyzing the magnetic interaction one conclusion has been drawn that the σ-like interaction between the magnetic centers and bridging atom plays an important role in the magnetic coupling.

Theoretical study on magnetic coupling interaction for Cu(II) binuclear systems with extended bridging groups

Abstract The magnetic coupling interaction for Cu(II) binuclear systems with bridging groups C 2 O 4 2− , C 2 O 2 ( NH ) 2 2− ( cis ), C 2 O 2 ( NH ) 2 2− ( trans ) and C 2 S 2 ( NH ) 2 2− ( trans ) was studied by the broken symmetry (BS) approach within the framework of the density functional theory (DFT). The influence of different coordination atoms and geometry on magnetic coupling interaction was theoretically analyzed. Both of the calculated and experimental results were compared. The variation trends of coupling interaction calculated are in agreement with experimental ones.

The electron-transfer reaction for Co(H2O)62+/3+

Abstract A theoretical scheme is presented to study the rate of the electron-exchange reaction between transition metal complexes in aqueous solution. In the scheme the activation energy is obtained via an activation model and ab initio technique, and the coupling matrix element at the transition state is determined by using perturbation theory and a numerical integral method. The electron-transfer (ET) reactivity of Co(H 2 O) 6 2+/3+ , a prototype system of the ET reactions between transition metal complexes in solution, is determined by employing this scheme. The theoretical results are compared with the corresponding experimental values and good agreement is found. The further extension of the scheme is also discussed.