Radical cations in mixtures of phosphorus trichloride and dimethyl sulfide. A combined ESR and quantum chemical study

Abstract

been neglected. For these compounds it has been shown that the latter "memory effects" may cancel the nearest neighbor control. Such processes have to be expected in compounds with "unstable" local electronic configurations in the absence of "memory effects". VII. Final OutlookThe many-particle nature of a electron bonding in alternant hydrocarbon systems has been investigated by the method of the local approach supplemented by rather simple model Hamiltonians. The present authors believe that it is most convenient for the reader to review the principal findings in the form of characteristic catchwords. (i) The A electrons in annulenes and linear polyenes are sizably localized. It seems to be necessary to substitute widely accepted traditional models for a compounds. (ii) Bond alternation leads throughout to an increase in the A electron delocalization. (iii) The respective enhancement of the charge fluctuations is probably the microscopic origin for the distortive nature of A networks. (iv) An enhancement of the charge fluctuations (decreasing electronic correlation-strength Ai) and increasing interatomic A correlation energies caused by bond dimerization are not mutually exclusive in larger hydrocarbons. The out-of-phase modulation is obviously the rule. (v) Cyclic 67 electron structures allow for the optimum possible a delocalization in alternant hydrocarbons; but even this takes place far from the "free-electron" limit. The latter process may lead to the situation that extended a systems prefer to form more or less decoupled spatially localized 6 r subunits. (vi) Extension of linear monocyclic or polycyclic A systems is frequently not coupled to an increasing delocalization of the A electrons (effects due to the end atoms neglected); their fluctuations saturate quite early. Exceptions have been discussed in the above sections. (vii) The interatomic A correlation energy is one driving force for the bond length alternation in linear and monocyclic hydrocarbons exceeding a certain threshold dimension. (viii) Strong electronic correlations tend to attenuate Jahn-Teller or Peierls instabilities. The attenuation is maximized with increasing correlation strength; see the series C4H4, CsHs, CI2Hl2. (ix) The latter effect may be of some influence in "metastable" solids, i.e. solids where the instability is scarcely suppressed. In these compounds superconductivity under strong coupling conditions may become possible.Exposure of phosphorus trichloride (C13P) and dimethyl sulfide (Me#) dissolved in halocarbons (CFC13, CF3CC13, CF2C1CFCl2, and CH2Clz) to X rays at 77 K results in the corresponding parent cations and several cationsubstrate adducts. The radicals are detected and identified by ESR spectroscopy. In dilute solution exclusive formation of the parent C13P.+ and Me2S'+ radical cations is observed. In CFC13, Me2S'+ exhibits superhyperfine interactions due to chlorine and fluorine nuclei of the matrix molecule(s). At increased concentration, or on warming the sample, the parent radical cations readily react with d...

The gas-phase thermochemistry of PCl4+: A test of lattice energy calculations

“…The calculations indicate that PCl 4 + has tetrahedral symmetry, while PCl 3 + and PCl 3 have C 3v symmetry, in agreement with experiment [21,32]. The bond angles are in good agreement, while the B3LYP method gives slightly long bond lengths, as observed previously [33].…”

“…The reactant ion has no excited electronic states with a significant population at room temperature. The main product ion PCl 3 + has a 2 A 1 ground state [21], with no important excited states. However, the main neutral product (the chlorine atom) has a 2 P 3/2 ground state and a 2 P 1/2 excited level that is 10.6 kJ mol −1 higher in energy [22].…”

Methyl Substituent Effects in [HnX∴XHn]+ Three-Electron-Bonded Radical Cations (X = F, O, N, Cl, S, P; n = 1−3). An ab Initio Theoretical Study

“…Two-center three-electron (2c-3e) bonds have attracted considerable attention in recent years. In this type of bonding, first described by Linus Pauling in the 1930s, two electrons occupy the σ orbital of a dimer and one single electron occupies the corresponding σ* one, hence the alternative name of σ*-bond for this interaction. − Such species have been the subject of considerable recent experimental and theoretical interest, and their importance as major intermediates is nowadays well recognized. ,− They can be encountered in many different areas such as free-radical chemistry 7-11 or biochemistry, − organic reactions, − radiation studies, − intrazeolite photochemistry, , and bioinorganic enzymology. , Three-electron bonds are preferentially observed in cations but can also be detected in neutral 12,19,23a,26,27,34 and anionic 11,15,19,23b,24,26,30-32 adducts. Here we will restrict ourselves to cationic radicals, which are by far the most frequently observed.…”

F4+: A Stable Three-Electron Bonded Complex and a Challenge for Standard ab Initio Computational Methods

“…A growing interest has been noted for a decade in the nature and stability of three-electron (3-e) bonds that consist of two bonding σ electrons and one antibonding σ* electron. Among the various species that owe their stabilities to such bonds, the radical cation dimers of the type A∴A + form an important subclass, with bonding energies often ranging from 20 to 50 kcal/mol. , Particularly well known are the noble gas dimer cations, which all are experimentally observed, and some disulfur or diphosphorus radical cations of the types R 2 S∴SR 2 + and R 3 P∴PR 3 + . , However, the ab initio computational studies of Clark 1 and Radom 2 have shown that all compounds of the H n X∴XH n + type (X = N, O, F, P, S, Cl; n = 1 to 3), which are isoelectronic to the noble gas dimer cations, are bound relative to the separate XH n and XH n + dissociation products.…”