Ionic Isomerism. 3. Estimation of Enthalpies of Formation of the Gaseous Tetrachlorophosphonium Ion, Δ_fH°(PCl₄⁺,g), and of the Gaseous Hexachlorophosphate Ion, Δ_fH°(PCl₆^-,g). Lattice Enthalpy Calculations for Bis(tetrachlorophosphonium) Hexachlorophosphate Halides, [PCl₄]₂[PCl₆]X, Where X = Cl or Br. Bond Enthalpies of Phosphorus(V) Chloro Compounds

Abstract

Recent structural and synthetic work on phosphorus−halo compounds over the past 3 years has provided a means of estimating associated thermochemical data. The lattice energy of Me4NPCl6 and the stability criteria for the existence of CsPCl6 as the only stable alkali metal hexachlorophosphate at ambient temperature are used to predict values for Δf H°(PCl6 -,g) while, in parallel, the rigorous calculation of the lattice potential energy of normal PCl5 (phase II, PCl5 as [PCl4 +][PCl6 -]) provides a functional thermodynamic relationship between Δf H°(PCl6 -,g) and Δf H°(PCl4 +,g) and hence enables estimation of Δf H°(PCl4 +,g). The total lattice potential energies of the [PCl4]2[PCl6]X (X = Cl (phase III, PCl5) and Br) salts are computed using a rigorous computational procedure designed to model lattices possessing complex anions and cations. These calculations lead to values of 1038 ± 5 kJ mol-1 for the lattice potential energy of [PCl4]2[PCl6]Cl and 1013 ± 5 kJ mol-1 for [PCl4]2[PCl6]Br and to estimates for the enthalpies of formation of the gaseous complex ions, Δf H°(PCl4 +,g) and Δf H°(PCl6 -,g) of 384 ± 10 kJ mol-1 and −813 ± 10 kJ mol-1, respectively. The above values differ from our previous estimates, which were based on speculative structures. Bond enthalpy estimates are made for phosphorus(V) chloro compounds. A brief consideration of the recent Glasser extension of the Kapustinskii equation is made with respect to these salts.

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

“…The lattice energy estimate [6] f H 298 (PCl 4 + ) = 384 ± 10 compares well to the experimental result, being well inside the combined error limits. The other estimated value, 430 ± 40 kJ mol −1 , is in moderate agreement considering the substantial uncertainty ascribed to the value.…”

“…for over 80 years [4], and have been developed into more generalized techniques, such as Volume-Based Thermodynamics (VBT) [5]. In 1996, Jenkins and coworkers [6] predicted the enthalpies of formation for PCl 4 + and PCl 6 − to be 384 ± 10 and −813 ± 10 kJ mol −1 , respectively, through a detailed analysis of crystals such as (PCl 4 + ) 2 (PCl 6 − )(Cl − ). Jolly and Gin also estimated f H(PCl 4 + ) = 430 ± 40 kJ mol −1 by comparison to the isoelectronic SiCl 4 [7].…”

Unique thermodynamic relationships for Δf H o and Δf G o for crystalline inorganic salts. I. Predicting the possible existence and synthesis of Na2SO2 and Na2SeO2

“…Their investigation of the likely stability of MPCl 6 compounds (M = alkali metal) and their prediction (ahead of synthesis) that CsPCl 6 would be the only stable alkali metal salt was proven following the synthesis of this salt by Muir (1993), after several abortive attempts at doing so. Recently Hao et al (2007), using energy-resolved, collision-induced, ion-beam mass spectrometry, have determined experimentally Á f H o (PCl 4 + , g) and the result agrees well with the theoretical predictions made earlier (Jenkins et al, 1994(Jenkins et al, , 1996. A similar result for Á f H o (PCl 4 + , g) -again in agreement with the experimentally determined value (Hao et al, 2007) -can be generated very simply using VBT (Jenkins et al, 1999;Jenkins, 2008Jenkins, , 2009Glasser & Jenkins, 2011b).…”

“…Indeed it was the topic of Bill Dasent's excellent book (Dasent, 1965) 'Non-Existent Compounds' which sparked much exploratory work. Secondly we would point to a study made by Finch, Gates and Jenkins in a series of papers (Finch et al, 1980;Jenkins et al, 1982Jenkins et al, , 1994Finch et al, 1993;Jenkins et al, 1996) of the thermodynamics of the PCl þ 4 and PCl À 6 gaseous ions. Their investigation of the likely stability of MPCl 6 compounds (M = alkali metal) and their prediction (ahead of synthesis) that CsPCl 6 would be the only stable alkali metal salt was proven following the synthesis of this salt by Muir (1993), after several abortive attempts at doing so.…”

A Density Functional and Thermochemical Study of M−X Bond Lengths and Energies in [MX6]2- Complexes: LDA versus Becke88/Perdew86 Gradient-Corrected Functionals

“…The net charge on many Werner complexes leads to large environmental effects in solution and the solid state, and it is difficult to make direct thermochemical measurements on the isolated complexes themselves. However, there is a combined experimental/computational approach, originally developed by Jenkins and Pratt, which uses thermochemical considerations and total lattice potential energy calculations 8 to derive heterolytic bond energies E (M−X) .…”