Theoretical study of the harmonic and anharmonic force fields of phosphorus pentafluoride

Breidung, Jürgen; Thiel, Walter

doi:10.1016/0022-2860(93)08003-m

Cited by 6 publications

(1 citation statement)

References 40 publications

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“…The similarity between the NF 5 and the PF 5 harmonic force field − was stressed by Michels and Montgomery . The softest normal mode of PF 5 , , the e‘ equatorial bend ω 7 = 180 cm -1 , was found to be an in-phase combination of the equatorial and axial bending symmetry coordinates and it transforms one D 3 h symmetric trigonal-bipyramid into another, thus enabling an exchange between axial and equatorial atoms.…”

Section: Resultsmentioning

confidence: 87%

NF₅Viable or Not?

1998

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The structure, bonding, harmonic vibrational frequencies, and decomposition reactions of NF 5 were studied employing complete active space SCF (CASSCF), multireference configuration interaction (MRCI), hybrid Hartree-Fock/density functional theory (B3LYP), second-order perturbation theory (MP2), and the coupled-cluster method with single, double (CCSD), and perturbative triple excitations [CCSD(T)] in conjunction with basis sets of up to triple-quality. The overall NF 5 f NF 3 + F 2 reaction is exothermic by 42 kcal mol -1 at the CCSD(T)/cc-pVTZ//CCSD/DZP level. Nevertheless, the trigonal-bipyramidal form of NF 5 (D 3h ) is found to be a minimum at all levels of theory employed for harmonic vibrational frequency analysis [up to CCSD(T)/DZP]. The C 4V NF 5 stationary point is a 4 kcal mol -1 [CCSD(T)/cc-pVTZ// CCSD/DZP] higher lying transition structure for Berry rotation. No C 3V NF 4 + F -ion pair minimum could be found at correlated levels of theory. A natural bond orbital comparison of NF 5 and PF 5 revealed the much greater polarity of the PF than the NF bonds. NF 5 has one well-developed three center-two electron and three two center-two electron bonds. The weak ionic character and the relatively short FF separations, within the sum of the van der Waals radii, are responsible for the metastable nature of NF 5 . The lowest energy transition state found, 16 to 23 kcal mol -1 above NF 5 at MRCI/cc-pVTZ//CASSCF(4,3)/DZP, MRCI/cc-pVTZ//UB3LYP/cc-pVTZ, or CCSDT-1/TZ2P//UHF-CCSD/DZP, corresponds to the 8.5 kcal mol -1 exothermic [CCSD(T)/cc-pVTZ//CCSD/DZP + ZPVE] decomposition into C 3V symmetric NF 4 and F radicals.

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