VCl₄ Revisited:  ESR and Photolysis in Solid Hydrogen, Neon, and Argon; Formation of VH₄

Abstract

Electron -spin-resonance (ESR) spectra of the VCl4 molecule were observed at low concentrations at 2−4 K in solid H2, D2, Ne, and Ar. As previously observed in other matrixes, the spectra of an axial molecule were obtained in H2, D2, and Ne, indicative of a Jahn−Teller (JT) distorted molecule with compressed tetrahedral D 2 d symmetry. However, in argon, a composite of an axial and a near-isotropic spectrum was observed, and annealing yielded only the isotropic at 4 K. This surprising result is discussed relative to JT dynamic vibronic interaction. Photolysis of VCl4 in H2 (and D2) matrixes yielded a new spectrum assigned to VH4 (or VD4), indicating that the tetrahydride is also a JT-distorted 2E ground-state molecule, in accord with earlier ab initio theory.

Matrix-Isolation Infrared and Theoretical Study of the Reaction of VCl4 with CH3OH

“…The separation between the upper band (509 cm -1 ) and the lower bands (473 cm -1 ) was calculated to be 36 cm -1 , which is in good agreement with the observed separation of 27 cm -1 . Thus, the observed spectrum is well-explained by an axially distorted structure, as proposed by Weltner et al…”

“…For each system, a sequence of intermediate species was observed, from the initially formed 1:1 molecular complex to the thermally or photochemically induced HCl elimination product. In addition, a recent matrix isolation electron spin resonance (ESR) study of VCl 4 in several different matrices was performed, in search of indications of Jahn−Teller distortion as a consequence of the lone unpaired electron . No infrared studies have been conducted on VCl 4 in cryogenic matrices, and no recent theoretical studies have been conducted.…”

Jahn–Teller Effect in VCl4

“…Taking account of the dependence of the electronic magnetic moment integrals on the nuclear coordinates gives little change to g θ and a noticeable change to g ϵ . g θ = 1.983 goodbreak0em2em⁣ g ϵ = 1.877 The average value of 1.93 agrees with the experimental average value in a large variety of host systems, but the individual values differ from the average more than the experimental values do: , g ∥ = 1.95 ± 0.01 goodbreak0em2em⁣ g ⊥ = 1.91 ± 0.01 The 1.93 average value is consistent with measured values of the magnetic susceptibility …”

“…These g values are observable, in principle, for a static JTE with a distortion along the z axis, but not for a dynamic JTE because the vibronic coupling must be taken into account. With somewhat different data, one study felt that the data did not distinguish between static and dynamic effects, a second study preferred a static JTE interpretation, and further studies − supported a dynamic JTE.…”

“…The vanadium tetrachloride molecule has one unpaired electron and is a liquid at room temperature with enough vapor pressure to make it a candidate for gas-phase experiments bearing on the Jahn–Teller (JT) effect (JTE), but many experiments were done in the liquid and in solution as well. The electronic absorption spectrum, − vibrational spectrum, − photoelectron spectrum (PES), − magnetic deflection spectrum, electron paramagnetic resonance (EPR) spectrum, − nuclear magnetic resonance spectrum, electric deflection, electric dipole moment, electron diffraction, − and magnetic susceptibility ,,,, have all been studied, sometimes with respect to the JTE, sometimes not.…”