Search

Abstract: The two-state mechanism of the reaction of Nb(NH2)3 with N2O on the singlet and triplet potential energy surfaces has been investigated at the B3LYP level. Crossing points between the potential energy surfaces have been located using different methods. Analysis of the strain model shows that the singlet state of the four-coordinate (N2O)Nb(NH2)3 complex with N2O bonded via terminal N atom coordination (1 2) is more stable in the initial stage of reaction, since the bending of the N2O fragment [E def(N2O) = 86.1 kcal mol−1] results in an energy splitting of the doubly degenerate LUMO; the low-energy LUMO can now strongly couple with the occupied Nb-localized d orbitals, forming a back-bond and transferring charge (q = 0.82 e) from Nb(NH2)3 to the N2O ligand. Going from 3 2 to 1 2, the reacting system changes spin multiplicity near the MECP (minimal energy crossing point) region, which takes place with a spin crossing barrier of 9.6–10.0 kcal mol−1. Analysis of spin-orbit coupling (SOC) indicates that MECP will produce a significant SOC matrix element. The value of SOC is 111.52 cm−1, due to the electron shift between two perpendicular ϕ orbitals with the same rotation direction, and the magnitude of the spin-multi-plicity mixing increases in the small energy gap between high- and low-spin states, greatly enhancing the probability of intersystem crossing. The probabilities of single (P 1ISC) and double (P 2ISC) passes estimated at MECP (SOC = 111.52 cm−1) are approximately 1.17×10−2 and 2.32×10−2, respectively.

Abstract: The optimized geometries of the three complexes between MeH n (Me=Na, Mg, Be; n=1 or 2) and SiH4 have been calculated at the B3LYP/6-311++g**, MP2/6-311++g(3df,3pd) and MP2/aug-cc-pvtz levels, respectively. The red-shift inverse hydrogen bonds (IHBs) based on Si-H, an electron donor, were reported. The calculated binding energies with basis set super-position error (BSSE) correction of the three complexes are −5.98, −8.65 and −3.96 kJ mol−1 (MP2/6-311++g(3df, 3pd)), respectively, which agree with the results obtained via MP2/aug-cc-pvtz (−6.18, −9.12 and −4.28 kJ mol−1, respectively). The relative stabilities of the three complexes are in the order of SiH4…MgH2 > SiH4…NaH > SiH4…BeH2. Natural bond orbital theory (NBO) analysis and the chemical shift calculation of the related atoms revealed that the charges flow from SiH4 to MeH n and the chemical shifts of the interacting H shift to downfield. Here, the Si1-H3 of SiH4 acts as both a bond hydrogen donor and an electron donor. Therefore, compared with conventional hydrogen bonds, they formed IHB complexes. Atoms in molecules (AIM) theory have been used to investigate the topological properties of the critical points in the three IHB structures.