P—N stretching vibrations

In compounds in which resonance of this kind is not possible a P=N band can be found at higher frequencies in the 1400— 

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The nickel chloride complex(X) of the spiro-cyclic phosphazene(V) is diamagnetic suggesting a square planar coordination around nickel. The P=N stretching vibration for the complex appears as two split bands(1215 and 1183 cm-1) compared to a single band at 1200 cm-1 observed for the ligand. The phosphorus chemical shifts move upfield compared to those of the ligand the spiro phosphorus atom is the one most affected [complex SpR 21.9 Sp(spir0) 25.5 ... 

The infrared spectra of trimer to heptamer have been published (46) though so far complete interpretation is restricted to the two lowest members (24). There is a common feature, however, in the very strong absorption in the 1200-1360 cm- region, principally contributed by the P-N stretching vibration. Daasch and Smith (25) examined the infrared absorption spectra of the phosphonitrilic esters, and showed that the... 

The bicyclic phosphazene III forms colorless crystals that are stable in air and melt sharply at 124°. The compound is readily soluble in petroleum, benzene, chloroform, and dichloromethane but insoluble in water. The IR spectrum of the compound shows a broad absorption band at 1195 cm" attributable to ring P=N stretching vibration. The H NMR spectrum is discussed in the literature,The P H NMR spectrum is that of an A2BC spin system (8 18-24). The structure of the compound has been established by X-ray crystallography. The crystals are monoclinic with space group C2/c, a = 10.81, b = 17.52, c = 28.48 A, p = 94.8° with eight molecules in the unit cell. 

The shortness and equality of the P-N bonds in the trimeric and in the tetrameric chloride have been demonstrated in Section IV,B. The thermochemical evidence for a bond order greater than unity in the trimeric chloride is confirmed by the high value of the observed P-N stretching frequency, which is maintained or even increased as the series is ascended. The effect of mass on ring vibration frequencies is not large m, 25), so that the higher and lower infra-red absorption frequencies characteristic of the phosphonitrilic fluorides and bromides, respectively, are indications of their relative bond strengths, and are consistent with the aromatic theory. 

Stretching and bending vibrations (for cross-linking) -P=N— stretching... 

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