Phosphonitrilic Halides Research Articles

Gas-phase on-line generation and infrared spectroscopic investigations of polyphosphazenes, (NPX 2) 3 where X = F, Cl and Br

Gas-phase infrared spectra of polyphosphazenes (phosphonitrilic halides trimer), (NPX 2) 3 where X = F, Cl and Br have been recorded. The molecules were generated for the first time by an on-line process using solid (NPCl 2) 3 as a precursor passed over heated sodium fluoride and potassium bromide at about 550 and 700 °C for (NPF 2) 3 and (NPBr 2) 3 production, respectively. The products were characterized by the infrared spectra of their vapors. The low-resolution gas-phase Fourier transform infrared spectra reported for the first time show strong bands centered at 1295, 1215 and 1200 cm −1, assigned to ν 7( E′), in plane P N stretching mode of (NPX 2) 3, where X = F, Cl and Br, respectively.

The evaluation of α′-elements for the knowledge of forms of molecular vibrations

Abstract Elements of the tensors of molecular polarizability changes in the single vibrations (the α′-elements) may be obtained from single crystal Raman work if the “oriented gas hypothesis” is applicable. From work on phosphonitrilic halides, relations between some of the α′ in the normal vibrations of triatomic groups have been extracted. Certain relations derived for p-chloroaniline are in accord with calculated values for benzene, but they require new concepts about the forms of the normal vibrations connected with the substituents. The apparent absence of interpretations of the α′ in most single crystal work is regretted.

The Reactions of N,N′-Dimethylethylenediamine with Cyclic Phosphonitrilic Halides

The reactions of N,N′-dimethylethylenediamine with the cyclic phosphonitrilic halides N3P3F6, N4P4F8, N3P3Cl6, and N4P4Cl8 lead to spiro halogenophosphonitrilic imidazolidines of the type[Formula: see text](n = 3, 4; x = 1, 2; X = Cl, F) together with polymeric materials. Structure[Formula: see text]has also been prepared by fluorination of the corresponding chloride with KSO2F and from N3P3F6 and[Formula: see text]The 1H and 19F n.m.r., i.r., and mass spectra of the phosphonitrilic imidazolidines are discussed.

Vibrational assignments of some phosphonitrilic halides

Vibrational assignments of some phosphonitrilic halides

3d Orbitals and bonds of second-row atoms. Part III. The cyclic phosphonitrilic halides

The five 3d orbitals of phosphorus in cyclic phosphonitrilic halides are compared both in relation to overlap with orbitals on neighbouring atoms, and by the effects of the perturbations caused by the molecular environment. Energy-minimised exponents are estimated for the valence shell orbitals of phosphorus in the planar molecules (F2PN)3, (F2PN)4, and (Cl2PN)3; each 3d orbital is treated separately assuming that 3d interactions are involved predominantly in the ring bonds. The main conclusions are that the 3dxz and 3dx2–y2 orbitals of phosphorus are compact and available for bonding, but that the 3dz2, 3dyz, and 3dxy orbitals are diffuse and have high energies. These results are consistent with the model which emphasises cyclic electron delocalisation in two π systems: one symmetric and one antisymmetric to reflection in the molecular plane.

New Types of Aromaticity

RECENTLY it has been shown1 that the two ideas of aromatic character and the aromatic sextet, which are generally associated in current theory, are not necessarily connected and that in addition to the well-known pπ–pπ bonding of the cyclic polyenes and aromatic hydrocarbons there is a second type, dπ–pπ bonding, which is exemplified notably by the phosphonitrilic halides. The two types have been termed2 ‘homomorphic’ and ‘heteromorphic’, respectively, and it has been demonstrated1,2 that, in terms of the site-symmetry of the atomic orbitals combined to form molecular π-orbitals, there are only these two forms of cyclic π-bonding.

The relative rates of reaction of trimeric and tetrameric phosphonitrilic halides with n-propylamine

A conductimetric kinetic analysis of the aminolysis of the phosphonitrilic halides (NPF 2) 3 and 4, (NPCl 2) 3 and 4, and (NPBr 2) 3 and 4 by n-propylamine in acetonitrile at 25° indicates a second-order rate-determining step in each instance. From data for the second-order constants ( k 2) and the pseudo first-order constants ( k′ 1), the comparative order of reactivity is (NPBr 2) 4 > (NPBr 2) 3 ∼ (NPCl 2) 4 > (NPCl 2) 3 ∼ (NPF 2) 4 > (NPF 2) 3.

Bond Alternation in Heterocyclic Ring Systems

IN a recent communication Davies1 has made an interesting extension of Longuet-Higgins and Salem's treatment2 of bond alternation to the case of mono-cyclic ring compounds of the type (AB)n such as the phosphonitrilic halides. The total energy is separated into ζ- and π-parts: E = Eζ + Eπ. He shows that: for ‘homomorphic’ systems3, where the combining orbitals on A and B have the same site symmetry, and that: for ‘heteromorphic’ systems, where the site symmetries are different4. The following symbols have been used in equations (1) to (4) : alternate bonds are of length r1 = r0 + x, r2 = r0 − x; the resonance integral is5: (note that we write a where ref. 2 has 1/a); δ is the difference between the Coulomb integrals for atoms A and B; and l takes the values 0, ±1, … ± (m − 1),m, where m = ½n for n even, and m = ± ½ (n − 1) for n odd. Furthermore6: where f(r) is the energy of one ζ-bond. Davies stated1 that Eπxx is finite whatever n, and he concluded that : (a) for the infinite heterocyclic polyene, the stable configuration always has equal bonds, whatever the value of δ (other than zero); (b) for the finite polyene, and for sufficiently small δ, there may be a critical value of n below which bond alternation should occur.

The crystal structure of trimeric phosphonitrilic bromide

The results of an X-ray two-dimensional analysis of the crystal structure of trimeric phosphonitrilic bromide are reported. The compound is isomorphous with trimeric phosphonitrilic chloride, as found by Bode. The refinement of the structure has been carried out by means of Fourier differential synthesis on the projections (100) and (001). On the basis of the results obtained the most important aspects of the molecular geometry are discussed with reference to the other phosphonitrilic halides thus far investigated.

Infra-red spectra and vibration assignment of phosphonitrilic halides—I: Trimeric phosphonitrilic chloride

The infra-red spectra of (NPCl 2) 3, have been measured in the vapour phase, in solution and in KBr pellets, between 3000 and 300 cm −1. Using the Raman spectra given in the literature, a new vibrational assignment is given on the basis of a D 3 h molecular symmetry. The assignment of the infra-red active modes is confirmed from the measurement of their dichroic ratios in the crystal.

Vibrational spectra of phosphonitrilic halides—II: The crystal spectra of (NPCl 2) 3 in polarized light

1N the preceding paper by one of us, (1) the infra-red spectra o f (NPCI2)3 in different states of agregation have been discussed. The assignment of many of the observed bands to the proper symmetry species was however not unambiguous, due to the unresolved rotational shape of the vapour phase bands. In addition to this, the solid phase spectrum shows some interesting features which point out the existence of appreciable crystal field effects. In order to investigate these effects and to furnish more definitive evidence for the vibrational assignment, the crystal spectra in polarized light have been studied. Some of the results obtained have been already anticipated in the first paper of this series and will be discussed in detail.

Remarks on the electronic structure of phosphonitrilic halides

Remarks on the electronic structure of phosphonitrilic halides