This paper offers the first series of state-of-the-art quantum chemical calculations (CASSCF, CASPT2, MS-CASPT2) and analytical models for the well-known problem of quasi-general ferromagnetic coupling in copper-gadolinium complexes. A system chosen from the chemical report of Costes et al. was taken as prototype. At the CASSCF level, calculated results for the experimental structure reproduced the magnetic coupling constant well (J(calcd)( )()= +7.67 cm(-)(1) vs J(exp)( )()= +7.0 cm(-)(1)). For more insight, the study molecule was further idealized by geometry optimization to C(2)(v)() symmetry. Systematic ab initio computation experiments were designed and performed. Owing to specific problems related to the non-aufbau ground configuration of the [CuL-Gd] complexes, the calculations were conducted in a nonstandard manner. We found that the qualitative mechanism of Kahn, assigned to the electron jump from 3d of Cu(II) to 5d shell of Gd(III), can be presented effectively as the cause of the phenomenon, if CASPT2 MOs are taken as magnetic orbitals. We showed that the ferromagnetic coupling is also matched and magnified by spin polarization effects over the ligand, in line with the early assumption of Gatteschi. To be distinguished from the initial hypothesis of Gatteschi, which assumed the role of 6s AO of Gd(III), we found that one 5d-type AO is actually involved in the polarization scheme. In fact, the Gatteschi and Kahn mechanisms are not mutually contradictory, but are even interconvertible with appropriate changes of the magnetic orbitals. Within C(2)(v)() symmetry of complexes, the ferromagnetic coupling can be qualitatively regarded as the preponderant influence of interaction channels exhibiting orbital orthogonality (four 3d-4f contacts) over the nonorthogonal ones (two 3d-4f contacts). The effective preponderance from ferromagnetic pathways is supported by CASPT2 results. One may explain the generality of Cu(II)-Gd(III) ferromagnetic coupling as being correlated with the large occurrence of approximate pseudo-C(2)(v)() geometry of complexes. The observed orbital regularity is lost in lower symmetries. Thus, the antiferromagnetic exceptions occur when the molecular asymmetry is advanced (e.g., owing to strong chemical nonequivalence of the donor atoms).

We report on the performance of the third-order Douglas–Kroll ab initio model potential (DK3-AIMP) method-based electron-correlated spin–orbit calculations. Our treatment assumes that the problem can be separated into a spin–free correlation treatment and a spin–orbit calculation. The correlation effects were calculated using the multistate complete active space second-order perturbation method, and the spin–orbit effects were treated by means of the restricted active space state interaction spin–orbit method, where the spin–orbit effects were approximated by the Douglas–Kroll type of atomic mean-field spin–orbit method. We used our method for illustrative calculations on the ground and low-lying electronic states of thorium monoxide. For a proper description of the inner core region in the spin–orbit calculations, an auxiliary spin–orbit basis set was introduced. The DK3-AIMP-based electron-correlated spin–orbit calculations on ThO yield good agreement with corresponding all-electron results and with the available experimental data. This confirms that the DK3-AIMP method can be easily combined with highly accurate correlation treatments and relativistic effects, both of which are vital for studying the actinides. To our knowledge, the literature contains no references to AIMP calculations on the low-lying states of ThO.

The U + O chemi-ionization reaction has been investigated by quantum chemical methods. Potential-energy curves have been calculated for several electronic states of UO and UO + .Comparison with the available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemi-ionization reaction U + O → UO + + e − is proposed. The U + O and Sm+ O chemi-ionization reactions are the first two metal-plus-oxidant chemi-ionization reactions to be studied theoretically in this way.

Density functional theory based global and local electrophilicity descriptors are used to study the reliability of local electrophilicity values of the strongest electrophilic sites in generating global intermolecular electrophilicity trends. The evaluated values on 15 different organic chlorides show that, for systems having more than one comparatively strong electrophilic site, the local electrophilicity value of the strongest site does not produce a reliable global intermolecular electrophilicity trend. But for systems having one distinctly strong electrophilic site it does. The analytical explanation in favor of the above observation is also provided. Thus, what was argued in an earlier study (Roy, R. K. J. Phys. Chem. 2004, 108, 4934) is established strongly by numerical demonstrations as well as analytical reasoning in the present one.