Steven Creve

Properties of phosphorus compounds by density functional theory: CH3P species as a test case

A comparison of different density functional theory (DFT) and molecular orbital (MO) methods for calculating molecular and energetic properties of low‐coordinated phosphorus compounds is reported. While DFT methods include both Becke–Lee–Yang–Parr (BLYP and B3LYP) nonlocal functionals, MO methods involve second‐order perturbation theory (MP2), quadratic configuration interaction [QCISD(T)], and coupled‐cluster theory [CCSD(T)], in conjunction with the 6‐31G(d,p), 6‐311++G(3df,2p), and 6‐311++G(3df,3pd) basis sets. Properties examined include geometrical parameters of the different CH3P equilibrium structures (phosphaethene, phosphinocarbene, methylphosphinidene, and a phosphacarbyne) and relevant transition structures for isomerisations and rearrangements in both the lowest‐lying singlet and triplet states, vibrational wave numbers, relative energies, barrier heights, and singlet–triplet energy gaps. In addition, the heat of formation, ionization energy, and proton affinity of phosphaethene are also evaluated. Overall, the B3LYP method, when employed with a large basis set, yields energetic results comparable to the CCSD(T) results. Nevertheless, both DFT methods fail to predict the behavior of the addition/elimination reactions of the hydrogen atom in the triplet state.A comparison of different density functional theory (DFT) and molecular orbital (MO) methods for calculating molecular and energetic properties of low‐coordinated phosphorus compounds is reported. While DFT methods include both Becke–Lee–Yang–Parr (BLYP and B3LYP) nonlocal functionals, MO methods involve second‐order perturbation theory (MP2), quadratic configuration interaction [QCISD(T)], and coupled‐cluster theory [CCSD(T)], in conjunction with the 6‐31G(d,p), 6‐311++G(3df,2p), and 6‐311++G(3df,3pd) basis sets. Properties examined include geometrical parameters of the different CH3P equilibrium structures (phosphaethene, phosphinocarbene, methylphosphinidene, and a phosphacarbyne) and relevant transition structures for isomerisations and rearrangements in both the lowest‐lying singlet and triplet states, vibrational wave numbers, relative energies, barrier heights, and singlet–triplet energy gaps. In addition, the heat of formation, ionization energy, and proton affinity of phosphaethene are also evalu...

Phosphinidene Transition Metal Complexes: A Combined Ab Initio MO-DFT Study of Cr(CO) 5 -PR

Ab initio MO and DFT calculations have been performed on phosphinidene complexes of the type Cr(CO)5–PR, with R = H, CH3, SiH3, NH2, PH2, OH, and SH. The formation of the Cr–P bond essentially arises from a ligand-to-metal charge transfer. While a significant π backdonation is also observed for the Cr(CO)5–PH, Cr(CO)5–PCH3, and Cr(CO)5–PSiH3 complexes, this is less the case for Cr(CO)5–POH, Cr(CO)5–PSH, and Cr(CO)5–PNH2, and the backbonding almost disappears for Cr(CO)5–PPH2. In both the lowest lying singlet and triplet states, all complexes exhibit a staggered conformation. CASSCF/CASPT2 calculations performed with the ANO basis sets indicate a closed-shell singlet ground state along the whole series. The binding energy between Cr(CO)5 and PR ranges from 216 kJ/mol for Cr(CO)5–PNH2 to 127 kJ/mol for Cr(CO)5–PSiH3 (B3LYP values). In general, the B3LYP-DFT scheme yields reasonable qualitative and quantitative results when compared with CASPT2(12/12).

Stabilization of phosphinidenes by metal complexation: A theoretical study of Cr(CO)5–PH

Abstract Ab initio MO and DFT calculations have been performed on the Cr(CO) 5 –PH complex to probe the interaction between a phosphinidene ligand and a transition-metal fragment. The formation of a Cr–P bond essentially arises from a ligand → metal charge transfer. In the lowest-lying singlet and triplet states, the complex exhibits a staggered conformation. CASSCF/CASPT2 calculations, performed with ANO basis sets, indicate a closed-shell singlet ground state for Cr(CO) 5 –PH, which lies about 35 kJ/mol below the triplet state. The binding energy between Cr(CO) 5 and PH is 172 kJ/mol as calculated by CASPT2 (138 kJ/mol by DFT/B3LYP). While HF and MP2, either in restricted or unrestricted formulation, CASSCF(2/2) and CASPT2(2/2) fail to predict a correct qualitative picture, B3LYP-DFT yields reasonable qualitative and quantitative results as compared to CASPT2(12/12).

On the formation of the CH2CH2CH = NH2+ distonic radical cation upon ionization of cyclopropylamine and allylamine

Abstract Ab initio molecular orbital and density functional theory calculations have been applied to determine the relative stability of the cyclopropylamine 1 and allylamine (CH 2 =CHCH 2 NH 2 +· 2 ) radical cations and their isomers. It is confirmed that, upon ionization, 1 undergoes barrier-free ring-opening giving the distonic species · CH 2 CH 2 CH=NH 2 + 3 . 2 also rearranges by a 1,2-H-shift to the more stable 3 (by 70 kJ/mol) which is, however, less stable than the 1-aminopropene ion (CH 3 –CH=CH–NH 2 +· 4 ) by 60 kJ/mol. The transition structure TS 2/3 lies 40 kJ/mol higher in energy than TS 3/4 . Although QCISD and B3LYP calculations of isotropic hyperfine coupling constants agree reasonably with observed values, supporting the presence of the distonic 3 in ESR matrix experiments, the exclusive observation of 3 , but not 4 , is intriguing. This emphasizes the role of the matrix in stabilizing 3 .

A Density Functional Study of the Dimerization of Phosphaalkynes in the Presence of Transition Metal Fragments

The dimerization of phosphaalkynes (R–C;P, R = H, Me, tBu) [H2C2P2] systems. In an attempt to address the exciting controversy and uncertainty about phosphaalkyne without and with the presence of transition metal fragments, including CpCo (Cp = cyclopentadienyl) and COT–Ti (COT = dimerization, a number of dimer formation mechanisms proposed in the literature have been examined. Some new cyclooctatetraene), has been probed using density functional theory calculations (B3LYP with different basis sets). MP2 and plausible intermediates have also been identified. and CCSD(T) calculations were also performed for the

On the geometry and inversion process of PF3+· (X̃ 2A1)

Abstract Geometries of PF 3 , PF 3 +· and the respective energy barriers to inversion are calculated using both MO (MP2, QCISD(T) and CISD) and DFT (B3LYP) methods. Various points on the potential energy surfaces are explored by means of vibrational analyses. Similar to the neutral species, PF 3 +· has, in its ground state X 2 A 1 , a pyramidal geometry and undergoes inversion following an edge-inversion mechanism through T-shaped C 2v structures. Our calculations suggest the barrier heights of 225 kJ/mol for PF 3 and 168 kJ/mol for PF 3 +· . Although these barriers to inversion are significantly smaller than those recently reported in the literature, the barrier of PF 3 +· is still greater than the value of the v 2 frequency of this cation, supporting this pyramidal character.