The electronic structure and energetics of V+-benzene half-sandwiches of different multiplicities: Comparative multireference and single-reference theoretical study

Abstract

Multireference [complete active space self-consistent field (CASSCF) and multiconfigurational quasidegenerate perturbation theory (MCQDPT)] and single-reference ab initio (Moller-Plesset second order perturbation theory (MP2) and coupled clusters with singles, doubles and noniterative triples [CCSD(T)]) and density functional theory (PBE and B3LYP) electronic structure calculations of V(C(6)H(6))(+) half-sandwich in the states of different multiplicities are described and compared. Detailed analyses of the geometries and electronic structures of the all found states are given; adiabatic and diabatic dissociation energies are estimated. The lowest electronic state of V(C(6)H(6))(+) half-sandwich was found to be the quintet (5)B(2) state with a slightly deformed upside-down-boat-shaped benzene ring and d(4) configuration of V atom, followed by a triplet (3)A(2) state lying about 4 kcal/mol above. The lowest singlet state (1)A(1)(d(4)) lies much ( approximately 28 kcal/mol) higher. MCQDPT calculated adiabatic dissociation energy (53.6 kcal/mol) for the lowest (5)B(2)(d(4)) state agrees well with the current 56.4 (54.4) kcal/mol experimental estimate, giving a preference to the lower one. Compared to MCQDPT, B3LYP hybrid exchange-correlation functional provides the best results, while CCSD(T) performs usually worse. Gradient-corrected PBE calculations tend to systematically overestimate metal-benzene binding in the row quintet<triplet<singlet.

Effect of Metal Cluster-Cap Interactions on the Catalyzed Growth of Single-Wall Carbon Nanotubes

“…To account for quantum effects in the nanotube growth, ab initio calculations using DFT with the three-parameter Becke , gradient-corrected exchange functional in conjunction with the Lee−Yang−Parr correlation functional (B3LYP) were carried out using the Gaussian 03 software . The B3LYP functional has been widely used to describe similar interactions. − In particular, Polestshuk et al reported a very detailed study of metal−benzene interactions involving a comparative analysis of the electronic structure and diabatic and adiabatic dissociation energies using a series of multiconfigurational methods such as multiconfigurational quasidegenerate perturbation theory (MCQDPT) and complete active space self-consistent field (CASSCF) among others, as well as a group of single-configuration methods including Moller−Plesset second-order perturbation theory (MP2) and two DFT methods: B3LYP and PBE. It was concluded that B3LYP offers the best representation among the single configuration methods, outperforming both MP2 and the PBE functional, and yielding dissociation energies close to those of the best multiconfigurational method.…”

Coordination versus Solvation in Al+(benzene)nComplexes Studied with Infrared Spectroscopy

“…Spectroscopy studies have included tunable laser electronic photodissociation − ,, and photoelectron spectroscopy. − Perhaps the most informative data about structures and bonding come from infrared photodissociation studies of mass-selected ions. − Free electron lasers (FELs) have generally been employed for resonance-enhanced multiphoton dissociation (REMPD) studies in the fingerprint region, − whereas IR optical parametric oscillator (OPO) laser systems have investigated the C–H stretching region, ,− usually using the method of tagging with rare gas atoms. Computational work has complemented many of these spectroscopic studies. − Unfortunately, the infrared spectrum of isolated benzene in the C–H stretching region is complicated by the occurrence of a Fermi triad in the vibrational structure . This feature and its response to metal cation binding are not handled with standard harmonic computational methods, limiting the insight that can be gained in this region.…”

Quantum Monte Carlo Study of π-Bonded Transition Metal Organometallics: Neutral and Cationic Vanadium–Benzene and Cobalt–Benzene Half Sandwiches

“…The missing dynamical correlations move the minimum to significantly larger V + −Bz distance of ≈2.6 Å, which QMC optimization with CASSCF nodal hypersurfaces reduces back to 2.41 Å, almost identical to the QMC-optimized values with other nodal hypersurfaces and MCQDPT value. 29 CASSCF nodal hypersurfaces yield DMC geometry similar to that of MCQDPT. However, the QMC energies, irrespective of DFT nodal hypersurface used, result in V + −Bz binding energy significantly higher by 0.26 eV than those obtained with DFT nodal hypersurfaces; see the SI.…”

“…Electronic and Atomic Structure of VBz + and CoBz + . The VBz + cation has extensively been studied by Polestshuk and collaborators, 29 who found, using MCQDPT technique, that the system ground-state has a quintet spin multiplicity and spontaneously reduces its symmetry from C 6h ( 5 A 2 (d 3 s 1 ) state) to the so-called "up-side-down-boat-shaped" (UDBS) geometry of C 2v symmetry ( 5 B 2 (d 4 ) state), see Figure 2. Quintet spin multiplicity was also found by Bauschlicher et al 27 using MCPF method, who considered C 6v symmetry.…”