Zhida Chen

Synthesis and structure of a one-dimensional cobalt(II) coordination polymer with 1,3-bis(1,2,4-triazol-1-yl)propane

A novel 1D-coordination polymeric Co(II) complex [Co(btp)2(NCS)2]n [1, btp = 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.

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.

Synthesis, crystal structures and magnetic properties of [Co3(NCS)6(admtrz)6].CH3OH.H2O and [Ni3(NCS)6(admtrz)6]. 1.5H2O (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole)

Abstract Two linear trinuclear complexes [Co3(NCS)6(admtrz)6]·CH3OH·H2O (1) and [Ni3(NCS)6(admtrz)6]·1.5H2O (2) containing 1,2,4-triazole and NCS anion as bridging ligands have been isolated, and characterized by X-ray diffraction methods. The two complexes are the isostructural neutral linear trimers, in which the central and terminal metal(II) ions are linked by two N1,N2-1,2,4-triazole ligands and one N-bridging NCS anion, while the terminal metal ions complete their octahedral coordination with one monodentate triazole and two N-bonded NCS anions. The magnetic behavior was investigated in the temperature range 5–300 K. The magnetic susceptibility measurements show that the Co(II) ions are weakly antiferromagnetically coupled with J=−2.8 cm−1, while Ni(II) ions are ferromagnetically coupled with J=10.45 cm−1. The nature and the magnitude of the magnetic-exchange of the two complexes have been discussed on the basis of the structural features.

Magnetic exchange interaction in the μ-hydroxo bridged vanadium(IV) dimers: a density functional theory combined with broken-symmetry approach

Abstract 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 –OCH 2 groups almost does not influence magnetic exchange behavior between the two vanadium(IV) ions, and the principle of the shortest superexchange pathway is available for the multiplicity of the bridging ligand in the μ-hydroxo bridged vanadium(IV) dimers.

Theoretical study on the magnetic coupling mechanism in alkoxo-bridged Cu(II) dimers

A useful parameter, which is the square of the overlap integral between the magnetic orbitals in the broken symmetry (BS) state, has been suggested as a measure of the magnetic coupling interaction. The effect of electronegativity of the ligands (including the bridging and terminal ligands) on the magnetic interaction has been investigated. The calculations for the model molecules derived from bis-[bromo-(N,N-diethylaminoethanolato)]copper(II) have been performed using the density functional method and the BS approach to inspect the conclusions drawn. The results show that the parameter can properly describe the magnetic coupling interaction, and the magnitude of electronegativity of the ligands is the important factor that can affect the magnetic interaction.

Theoretical investigation of glycine–2Ben+ (n=0,1,2) complexes in gas phase: Origin of negative dissociation energies

The negative dissociation energies (or positive binding energies) have first been found in seven different glycine–2Be2+ conformers, one glycine–Be2+Be+ complex, and one glycine–2Be2+ complex. For the seven glycine–2Be2+ conformers, the negative dissociation energies originate from the contributions of electrostatic, dipolar, charge transfer and deformed terms. All of these terms play important roles for the negative dissociation energy during separating one Be2+ from the corresponding complex. Also two dissociation energy barriers have been observed in the course of separating each of the two Be2+ ions from the most stable glycine–2Be2+ conformer. One barrier derives from the deformed effect and another is mainly from electronic effect. For the glycine–Be2+Be+, the positive binding energy (or negative dissociation energy) is also observed when Be+ ion interacts with the oxygen end of zwitterionic glycine. Binding energy contribution analysis (BECA) shows that it mainly stems from the electrostatic effect...

Magnetic exchange cooperative effect of the bridges in μ-hydroxo and μ-acetato bridged chromium(III) dimers: a density functional theory coupling the broken-symmetry approach

Abstract The magnetic exchange behaviour for μ-hydroxo and μ-acetato double-bridged chromium(III) dimer is investigated based on calculations of density functional theory combined with the broken-symmetry approach. It is demonstrated that there is a magnetic exchange cooperative effect of the two bridging ligands in a double-bridged dimer systems with approximate equal coupling intensity. Meanwhile, the calculated results reveal that the deprotonation of the μ-hydroxo ligand causes a sharp increase of the magnetic exchange interaction between the chromium centers. Replacing either the μ-hydroxo bridging ligand by one water bridging ligand or the μ-acetato bridging ligands by two terminal water ligands produces a relatively reasonable model to examine the contribution on the magnetic exchange interaction of another individual bridging ligand.

Ab initio multireference configuration-interaction theoretical study on the low-lying spin states in binuclear transition-metal complex: Magnetic exchange of [(NH3)5Cr(μ-OH)Cr(NH3)5]5+ and [Cl3FeOFeCl3]2−

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 [(NH(3))(5)Cr(mu-OH)Cr(NH(3))(5)](5+) and [Cl(3)FeOFeCl(3)](2-). 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.

Unusual magnetic properties of mixed-valence system: Multiconfigurational method theoretical study on Mn2+ cation

The geometry structure, dissociation energy, vibrational frequencies, and low-lying spin-state energy spectrum of Mn2+ are investigated by using ab initio CASSCF/ECP10MDF, complete active space self-consistent field/atomic natural orbital basis sets (CASSCF/ANO-s), CASPT2/ECP10MDF, and second-order perturbation theory with CASSCF reference function/atomic natural orbital basis sets (CASPT2/ANO-s) levels of theory. For the ground state the dissociation energy of 1.397 eV calculated at the CASPT2/ANO-s level supports Jarrlods experimental value of 1.39 eV. The equilibrium bond length and vibrational frequency are 2.940 A calculated at the CASPT2/ANO-s level of theory and 214.4 cm-1 calculated at the CASSCF/ANO-s level of theory, respectively. On the basis of the mixed-valence model, the Heisenberg exchange constant J(-71.2 cm-1) and the double-exchange constant B(647.7 cm-1) are extracted explicitly from the low-lying energy spectrum calculated at the higher levels of theory. The magnetic competition between the weaker Heisenberg exchange interactions and the stronger double-exchange interactions makes the ground state a 12Sigmag+ state, consistent with electron paramagnetic resonance experimental observation, which explains unusual magnetic properties of Mn2+, quite different from the antiferromagnetic ground state of Mn2 and Cr2. On the other hand, the results calculated at the higher levels of theory show the consistent antiferromagnetic Heisenberg exchange interactions between 3d-3d for Cr2, Mn2+, and Mn2.

Structure, Magnetism and Spin Coupling Mechanism of Cyano-Bridged LnIII-FeIII Binuclear Metal Complexes

A series of binuclear metal complexes [Ln(L)4(H2O)3Fe(CN)6]·nH2O (Ce(1), Pr(2), Nd(3), Sm(4), Eu(5), Gd(6), Tb(7), Dy(8), Er(9), L=2-pyrrolidinone) were prepared and the X-ray crystal structures of complexes 4, 6, and 8 were determined. All the compounds consist of an Ln–CN–Fe unit, in which an octahedral coordinated FeIII is bridged to an LnIII ion located in square antiprism environment by a cyano group. The magnetic properties of 3, 4, 5, 6, 7, 9 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of complex 6 gave g=1.99, J=0.735 cm−1, zJ′=−0.080 cm−1 on the basis of a binuclear spin system (SGd=7/2, SFe=1/2), revealing a ferromagnetic intra-molecular Gd–Fe interaction and an antiferromagnetic inter-molecular interaction. Results on the quantum chemical density functional theory (DFT) calculation for 6 showed that the calculated magnetic coupling constant is 8.1 cm−1, supporting the occurrence of weak ferromagnetic intra-molecular interaction in 6. The spin density maps for 6 in the high spin ground state and broken symmetry state were obtained, and the spin–spin coupling mechanism is discussed.