Phosphonitrilic derivatives. Part XVIII. Ionisation potentials, orbital symmetry, and π-electron interactions

Abstract

The ionisation potentials of the phosphonitrilic fluorides (NPF2), (n = 3-8) have been measured by photoelectron spectroscopy, and those of other phosphonitrilic derivatives (NPX2)n [X = CI, n = 3-7; X = OCH,*CF,, OMe. OPh, NMe,, or Me, n = 3 or 41 by electron impact. All the 6-membered cyclic compounds have first ionisation potentials which are higher than those of their 8-membered analogues, and in the fluorides the first ionisation potentials alternate as the size of the ring increases beyond 8 atoms. These results, and also the relative energies of a number of states of ( NPF2),+, are interpreted by use of the orbital approximation and a model of a dual r-system which involves 3d-orbitals at phosphorus and valence-shell orbitals of nitrogen and which supplements the underlying o-framework. Comparison of the results with simple molecular orbital calculations suggest that the highest r-system is of the homomorphic type, involving mainly the 3dz~-y:-orbital, and that it is accompanied by a lower and partly overlapping heteromorphic system, to which the 3dzz-orbital makes the major contributions. Ionisation spotential are also assigned to molecular orbitals which span the P-N and P-F a-bonds, and the fluorine lone pairs.

Organophosphazenes. 24. Ultraviolet Photoelectron Spectra of Selected Alkenyl- and Alkynylfluorocyclotriphosphazenes1

“…The ionization energy data for compounds 1-7 are summarized in Table 1. The assignments of the spectra are based on the composite molecule approach using the previously assigned spectrum of N 3 P 3 F 6 6,15 and those of the alkenyl and alkynyl substituents. 20 The results of an investigation of the photoelectron spectra of the series of phenylfluorocyclotriphosphazenes N 3 P 3 F 6-n (C 6 H 5 ) n (n ) 1-4) 16 provide a valuable guideline for assignment of the spectra and evaluation of the results.…”

“…The out-of-plane π orbital ionization in N 3 P 3 F 6 is observed at 11.4 eV, and the in-plane π ionization, at 13.1 eV. 6,15 Replacement of the fluorine atoms by phenyl groups results in a decrease in the phosphazene ionization potentials. 16 On the basis of the variations in the phenylphosphazene ionization potentials and the fact that the substituents in this study are also π-electron-rich organic moieties, the I 1 set (Table 1) is assigned to the organic π system and the I 2 set to the in-plane phosphazene π ionization.…”

“…13,14 Surprisingly, few reports of determination of valence shell ionization energies, the most direct probe of electronic structure, have appeared. 15,16 In this paper, we report selected vertical ionization potentials of a series of alkenyl-and alkynylfluorocyclotriphosphazenes as determined by ultraviolet photoelectron spectroscopy (UPS), to probe the interaction between the cyclophosphazene and the unsaturated organic centers.…”

Conjugative interactions in 1-methylpyrrol-2-yl derivatives of the cyclic phosphazenes (NPF2)n (n = 3–6): the crystal and molecular structure of 1-methylpyrrol-2-ylheptafluorocyclotetraphosphazene

“…The spectra show another interesting feature, in the small but significant oscillations in A , , , of the longer wavelength band. They show the same type of variation with ring size as the ionization energies of the fluorophosphazenes themselves (30) . 3 Since the oscillation is small, the conjugative perturbation induced by the pyrryl group may not extend far beyond the phosphorus atom to which it is attached.…”

The molecular and electronic structure of 1-pyrazolylphosphazenes

“…Crystallographic analyses of [1][2][3][4][5][6] Crystallographic data for the six compounds appear in Table 1. Final unit-cell parameters were obtained from least-squares refinement of 2 sin 8/h values for 25 reflections with 28 = 22-3 1, 50-83, 35-44, 35-40, 35-41, and 64-84" for 1-6, respectively.…”