Effective core potential studies of lanthanide complexes

Abstract

A recently developed compact effective core potential (ECP) scheme for lanthanides [T. R. Cundari and W. J. Stevens, J. Chem. Phys. 98, 5555 (1993)] is applied to molecular species—the lanthanide trihalides (LnX3, Ln=Ce to Lu; X=F, Cl, Br, I). This research is the first ECP study of lanthanide trihalides in which 4f electrons are explicitly included in the lanthanide valence space. The high-spin 4fn configuration of Ln(III) is described using multiconfiguration (MC) and unrestricted Hartree-Fock (UHF) wave functions. Both methods give excellent agreement with experiment for Ln–X bond lengths, although UHF is faster with no evidence of extensive spin contamination. There is no loss of accuracy from early to late members of the lanthanide series and from the lightest to heaviest halogen for the MC calculations. The root-mean-square difference between MC/ECP Ln–X bond lengths and those estimated from gas-phase experiments is only 0.05 Å (≊2%). The UHF calculations on LnF3 yield only three nonplanar minima (CeF3, PrF3, and PmF3). For the three complexes with pyramidal minima, the planar transition states are very close in energy (ΔEUHF<100 cm−1), suggesting these complexes will probably be fluxional at ambient conditions.

Theoretical Study on the f−f Transition Intensities of Lanthanide Trihalide Systems

“…Full geometry optimization and vibrational analysis of PrBr 3 were carried out, and the equilibrium structure and six normal coordinates Q i 's were obtained as shown in Figure 4. The optimized bond lengths of Pr-Br and the symmetry were 5.20 (Bohr) and D 3h , respectively, in good agreement with previously obtained results by Cundari et al 47 This bond length is also in reasonable agreement with a recent theoretical one, 5.15 (Bohr) with CASPT2, 48 and with the experimental one, 35 5.08 (Bohr). The frequency of each normal vibration, as shown in Table 4, is also in reasonable agreement with the experimental one.…”

How an Inert‐Gas Matrix Can Modify the Molecular Properties of Lanthanide Trifluoride

“…[5,6,7,8,9] Recent advances in quantum chemistry have provided a complementary and independent tool to probe molecular properties of lanthanide halide compounds. [10,11,12,13,14,15] All calculations so far reported agree in predicting a pyramidal equilibrium structure for the isolated LnF 3 molecules with a very shallow minimum, in agreement with most of the molecularbeam electric deflection data. [16] Recently, we showed that for the LnF 3 ·IG and LnF 3 ·IG 2 (IG = Ne, Ar, Kr, Xe and N 2 ) model complexes, LnF 3 -IG interactions are strong, and a possible LnF 3 planar structure may be found in contrast to the results on isolated molecules.…”

The molecular structure of TbI3, DyI3, HoI3 and ErI3 as determined by synchronous gas-phase electron diffraction and mass spectrometric experiment assisted by quantum chemical calculations

“…Calculations at B3LYP/ECP D ,MIDIX and MP2/ECP D ,MIDIX levels (see Table 4) overestimate essentially the equilibrium distances r e (Ln-I) as compared with the experimental values. Despite using the ECP s [20] which does not include 4f-electrons into the core, the MCSCF/ ECP s ,CEP s d calculations [21] also resulted in overestimated values. Basis set ECP D ,MIDIX augmented by polarization functions 3f2g [13] for Ln atom improves the results for both, MP2 and B3LYP, methods and led to the r e (Ln-I) values which are very close to the experimental r g -values.…”