Development and Application of a Complete Active Space Spin-Orbit Configuration Interaction Program Designed for Single Molecule Magnets.

We present a spin-orbit configuration interaction program which has been tailored for the description of the magnetic properties of polynuclear metal complexes with partially filled d- and f-shells. The spin-orbit operators are directly included in the configuration interaction program based on Slater-determinants. The lowest states are obtained by a Block-Davidson-type diagonalisation. The usage of localised active orbitals enables the construction of start vectors from tensor products of single-center wave functions that already include spin-orbit interaction. This allows for an analysis of the role and the interplay of the different metal centres. Furthermore, in case of weak coupling of the metal centres these tensor products are already close to the final wave functions ensuring fast convergence. In combination with a two-layer hybrid parallelisation, this makes the program highly efficient. Based on the spin-orbit coupled wave functions, magnetic D-tensors, g-tensors and temperature-dependent susceptibilities can be calculated. The applicability and performance of the program is shown exemplarily on a trinuclear transition metal (CoII VII CoII ) complex.

Analyzing Anisotropic Exchange in a Pentanuclear Os2 Ni3 Complex.

Spin Hamiltonian parameters of a pentanuclear Os 2 III Ni 3 II cyanometallate complex are derived from ab initio wave function based calculations, namely valence-type configuration interaction calculations with a complete active space including spin-orbit interaction (CASOCI) in a single-step procedure. While fits of experimental data performed so far could reproduce the data but the resulting parameters were not satisfactory, the parameters derived in the present work reproduce experimental data and at the same time have a reasonable size. The one-centre parameters (local g matrices and single-ion zero field splitting tensors) are within an expected range, the anisotropic exchange parameters obtained in this work for an Os-Ni pair are not exceedingly large but determine the low-T part of the experimental χT curve. Exchange interactions (both isotropic and anisotropic) obtained from CASOCI have to be scaled by a factor of 2.5 to obtain agreement with experiment, a known deficiency of such types of calculation. After scaling the parameters, the isotropic Os-Ni exchange coupling constant is J = - 4 . 2  cm-1 and the D parameter of the (nearly axial) anisotropic Os-Ni exchange is D = J ∥ - J ⊥ = 18 . 8 c m -1 , so anisotropic exchange is larger in absolute size than isotropic exchange. The negative value of the isotropic J (indicating antiferromagnetic coupling) seemingly contradicts the large-temperature behaviour of the temperature dependent susceptibility curve, but this is caused by the negative g value of the Os centres. This negative g value is a universal feature of a pseudo-octahedral coordination with t 2 g 5 configuration and strong spin-orbit interaction. Knowing the size of these exchange interactions is important because Os(CN) 6 3 - is a versatile building block for the synthesis of 5 d / 3 d magnetic materials.

Solvents effects on the mechanism of cellulose hydrolysis: A QM/MM study.

This article reports a combined quantum mechanics/molecular mechanics (QM/MM) investigation on the acid hydrolysis of cellulose in water using two different models, cellobiose and a 40-unit cellulose chain. The explicitly treated solvent molecules strongly influence the conformations, intramolecular hydrogen bonds, and exoanomeric effects in these models. As these features are largely responsible for the barrier to cellulose hydrolysis, the present QM/MM results for the pathways and reaction intermediates in water are expected to be more realistic than those from a former density functional theory (DFT) study with implicit solvent (CPCM). However, in a qualitative sense, there is reasonable agreement between the DFT/CPCM and QM/MM predictions for the reaction mechanism. Differences arise mainly from specific solute-solvent hydrogen bonds that are only captured by QM/MM and not by DFT/CPCM.

Structure-reactivity relationships in the hydrogenation of carbon dioxide with ruthenium complexes bearing pyridinylazolato ligands.

Pyridinylazolato (N-N') ruthenium(II) complexes of the type [(N-N')RuCl(PMe3)3] have been obtained in high yields by treating the corresponding functionalised azolylpyridines with [RuCl2 (PMe3)4] in the presence of a base. (15)N NMR spectroscopy was used to elucidate the electronic influence of the substituents attached to the azolyl ring. The findings are in agreement with slight differences in the bond lengths of the ruthenium complexes. Furthermore, the electronic nature of the azolate moiety modulates the catalytic activity of the ruthenium complexes in the hydrogenation of carbon dioxide under supercritical conditions and in the transfer hydrogenation of acetophenone. DFT calculations were performed to shed light on the mechanism of the hydrogenation of carbon dioxide and to clarify the impact of the electronic nature of the pyridinylazolate ligands.