NF₅Viable or Not?

Abstract

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.

Domain-averaged Fermi holes - a new means of visualization of chemical bonds. Bonding in hypervalent molecules

“…This dierence in the character of the bonding is also re¯ected at NF bond lengths where consistent with what was observed for SF 4 ,``hypervalent'' axial NF bonds are considerably longer than the``normal'' axial ones. It is interesting that the same conclusions about the dierent nature of axial and equatorial NF bonds was reported also in the recent study [59].…”

Tutorial review: Bohr circular orbit diagrams for some fluorine-containing molecules

“…The results of more recent MO studies [12] are in accord with this rationalisation. It is to be noted that in orbital theory, the singlet diradical structure of type 9, as well as the ionic structures of types 7 and 8, is also considered to make a substantial contribution to the ground-state resonance scheme for each of NF 5 and PF 5 [7 (b),13,14-16], but because of the above ionisation potential differences, the singlet diradical structure should be more important for NF 5 than it is for PF 5 .…”

“…The results of molecular orbital (MO) studies [11,12] suggest that trigonal bipyramidal NF 5 could be structurally stable, but unstable thermodynamically with regard to dissociation into each of NF 4 + F, NF 3 + 2F and NF 3 + F 2 .…”

Solid‐State Structural Study of the Charge‐Transfer Complexes of 5,7,9‐Trimethyl‐ and 2,11,20‐Trithia[33](1,3,5)cyclophanes

“…We have performed conformational analyses [16] of [3.3]meta- [17,18] and [3.3]para-cyclophanes, [19,20] and also of (11) 3.137(4), C(3)ϪC (12) 3.087(4), C(4)ϪC (13) 3.173(4), C(5)ϪC (14) 3.097(4), C(6)ϪC (15) multibridged [3 n ]cyclophanes (n ϭ 3Ϫ6), [14,21,22] by the variable-temperature (VT) 1 H and 13 C NMR methods. A flipping process of the bridges similar to that in [3 3 ](1,3,5)CP 2 was observed in the 1 H NMR spectrum of 1 in CD 2 Cl 2 .…”