A computational study of Sb nF 5 n ( n = 1–4) : Implications for the fluoride ion affinity of nSbF 5

Abstract

This contributions shows with a series of ab initio MP2 and DFT (BP86 and B3-LYP) computations with large basis sets up to cc-pVQZ quality that the literature value of the standard enthalpy of depolymerization of 1 4 Sb 4F 20(g) to give SbF 5(g) (+18.5 kJ mol −1) [J. Fawcett, J.H. Holloway, R.D. Peacock, D.R. Russell, J. Fluorine Chem. 20 (1982) 9] is by about 50 kJ mol −1 in error and that the correct value of Δ r H depoly . ° ( 1 4 Sb 4F 20(g)) is +68 ± 10 kJ mol −1. We assign Δ r H depoly . ° , Δ r H ° , Δ r G ° and Δ r G ° values for Sb n F 5 n with n = 2–4 and compare the results to available experimental gas phase data. Especially the MP2/TZVPP values obtained in an indirect procedure that rely on isodesmic reactions or the highly accurate compound methods G2 and CBS-Q are in excellent agreement with the experimental data, and reproduce also the fine experimental details at temperatures of 423 and 498 K. With these data and the additional calculation of [Sb n F 5 n+1 ] − ( n = 1–4), we then assessed the fluoride ion affinities (FIAs) of Sb n F 5 n(g) , nSbF 5(g), nSbF 5(l) and the standard enthalpies of formation of Sb n F 5 n(g) and [Sb n F 5 n+1 ] − (g): FIA(Sb n F 5 n(g) ) = 514 ( n = 1), 559 ( n = 2), 572 ( n = 3) and 580 ( n = 4) kJ mol −1; FIA( nSbF 5(g)) = 667 ( n = 2), 767 ( n = 3) and 855 ( n = 4) kJ mol −1; FIA( nSbF 5(l)) = 434 ( n = 1), 506 ( n = 2), 528 ( n = 3) and 534 ( n = 4) kJ mol −1. Error bars are approximately ±10 kJ mol −1. Also the related Gibbs energies were derived. Δ f H°([Sb n F 5 n+1 ] − (g)) = −2064 ± 18 ( n = 1), −3516 ± 25 ( n = 2), −4919 ± 31 ( n = 3) and −6305 ± 36 ( n = 4) kJ mol −1.