Andrew L. Porte

Chlorine-35 nuclear quadrupole resonance spectra of the chlorocyclodiphosphazanes (Cl3PNR)2 and of the chlorooxocyclodiphosphazanes (ClOPNR)2

Abstract Chlorine-35 NQR frequencies, ν, for (Cl 3 PN R ) 2 , where R = CH 3 , C 2 H 5 , or Ph, and for (ClOPNCH 3 ) 2 have been measured over the temperature range 77 ⩽ T ⩽ 350 K. Chlorine-35 asymmetry parameters have been measured for (Cl 3 PNCH 3 ) 2 at 295 K, and they show that π-character cannot contribute any more than 1–2% to the nature of the PCl bonds in this molecule. Chlorine-35 NQR frequencies for (Cl 3 PN R ) 2 , where R = CH 3 or Ph, also have been measured over the pressure range 1 ⩽ P ⩽ 1500 Kg cm −2 , at 295 K. These measurements enable three methods to be used to distinguish axial from equatorial chlorine atoms. Their resonance frequencies are different, the temperature coefficients of these frequencies are different, and the pressure coefficients of these frequencies are different. The partial differential coefficients have been evaluated for (Cl 3 PN R ) 2 , where R = CH 3 and Ph. Bayer-type analyses show that the characteristic effects of temperature and pressure on these compounds originate in the typical ionic characters of the PCl bonds and in the characteristic 64 cm −1 PCl 3 torsional-bending modes in these solids. The analyses also indicate that it should be possible to distinguish between different kinds of PCl systems by measuring the effects of applied pressures or changes in temperature on their chlorine-35 NQR frequencies.

Chlorine-35 nuclear quadrupole resonance studies of some chlorocyclotriphosphazatrienes

Abstract Chlorine-35 NQR frequencies, v (MHz), in the chlorocyclotriphosphazatrienes are related to the corresponding PC1 bond lengths, d ( A ): d = −0.012 8 v + 2.355. v is also related to θCl, the valence shell electronic population localized on the chlorine atom: θCl = −0.0345v + 8. Chlorine-35 NQR frequencies discriminate between the positional isomers of N3P3C13(NMe2)3. Chlorine-35 NQR frequencies in N1P3Cl6, N3P3Cl5NHPri, N3P3Cl5NC5H10, cis-N3P3Cl4(NMe2)2, and trans-N3P3Cl4(NMe2)2 are linear functions of the applied pressure, P, within the range 1 to 700 kg cm−2. N3P3CI5NC5H10, cis-N3P3Cl4(NMe2)2 and trans-N3P3Cl4(NMe2)2 undergo minor phase changes at about 150 K. The partial differential coefficients (ϖv ϖP) T=293 K′ (ϖv ϖT) P=1kgcm −2 , T=293 K′ and (ϖv ϖT) V,T=293K have been evaluated for each of the resonance frequencies in N3P3Cl6, N3P3Cl5NHPri, N3P3Cl5NC5H10, cis-N3P3Cl4(NMe2)2, and trans-N3P3Cl4(NMe2)2. The pressure derivatives, (ϖv ϖP) T , discriminate between geometric isomers. The temperature derivatives, (ϖv ϖT) , and the pressure derivatives together discriminate between molecular conformers and give detailed information about molecular dynamics in these solids.

Chlorine-35 nuclear quadrupole resonance spectra of the chlorocyclotriphosphazatrienes N3P3Cl6 and N3P3Cl5NHPri

Abstract Chlorine-35 nuclear quadrupole resonance frequencies, ν, in N 3 P 3 Cl 6 and in N 3 P 3 Cl 5 NH Pr i are linear functions of the applied pressure, P , within the range 1 to 1000 kg·cm −2 . Chlorine-35 nuclear quadrupole resonance frequencies in N 3 P 3 Cl 5 NH Pr i , examined over the temperature range 100 to 320 K, have revealed that this solid undergoes a sharp phase change over the temperature range 220 to 235 K. Values of the partial differential coefficients. have been evaluated for each of the resonance frequencies in N 3 P 3 Cl 6 and in N 3 P 3 Cl 5 NH Pr i . The applied pressure discriminates between the two kinds of chlorine atoms in the PCl 2 groups in N 3 P 3 Cl 5 NH Pr i . The effects of pressure on the chlorine-35 nuclear quadrupole resonance frequencies of nine chlorine nuclei in similar environments in these two molecules are similar and appear to be characteristic of the functional groups involved.

A correlation between p–cl bond lengths and 35Cl nuclear quadrupole resonance frequencies in some cyclophosphazenes; the use of 35Cl nuclear quadrupole resonance spectroscopy for structural assignments in cyclodiphosphazanes

The 35Cl n.q.r. spectra of a series of chlorocyclophosphazenes have been obtained and are discussed in the light of their known crystal structures. An approximately linear relationship exists between 35Cl n.q.r. frequencies and P–Cl bond lengths in closely related structures. The 35Cl n.q.r. spectra of the cyclodiphosphazanes, (Cl3PNR)2(R = Me, Et, or Ph), are reported. The axial and equatorial chlorine atoms in the trigonal bipyramidal distribution of atoms about phosphorus in the latter class of compound can be identified by their frequency ranges, and by relative changes in frequency with temperature.

Bromine nuclear quadrupole resonance studies of some bromocyclotriphos-phazatrienes: N3P3Br6, N3P3Br5NHPri and cis-

Abstract Bromine NQR frequencies, v (MHz), for N 3 P 3 Br 6 , N 3 P 3 Br 5 NHPr i and for cis -N 3 P 3 Br 4 (NMe 2 ) 2 have been examined over the temperature range 77⩽=T⩽=300K. Bromine-81 resonance frequencies in these compounds are approximately linearly related Co the chlorine-35 resonance frequencies observed in the corresponding chloro-derivatives: v ( 81 Br) ≈ 8.121 v ( 35 Cl) - 29.4. Bromine nuclei are more sensitive monitors of physical and chemical change than chlorine nuclei. In the cyclotriphosphazatrienes, bromine is more electronegative than amino-nitrogen. Asymmetry parameters for N 3 P 3 Br 6 show that π-character cannot contribute any more than about 0.2% to the nature of the P-Br bonds in this molecule. One phase change, at 125K, has been detected for N 3 P 3 Br 6 and two, at 135K and 215K, for N 3 P 3 Br 5 NHPr i . In cis -N 3 P 3 Br 4 (NMe 2 ) 2 bromine-81 spectra fade out at 215K. Bromine NQR spectra for N 3 P 3 Br 5 NMe 2 have not been detected in the temperature range 77⩽=T⩽=300K. The NQR data enable conformations to be assigned to these molecules.

Chlorine-35 nuclear quadrupole resonance studies of some six-membered ring systems containing nitrogen, sulphur, and/or phosphorus : α-(NSClO)3, cis-(NSClO)2(NPCl2), and (NSClO)(NPCl2)2

Chlorine-35 n.q.r. spectra for α-(NSClO)3, cis-(NSClO)2(NPCl2), and (NSClO)(NPCl2)2 have been recorded in the temperature range 77–300 K. Spectra have also been examined for these substances at 293 K when subjected to pressures within the range 1–700 kg cm–2 : the chlorine-35 resonance frequencies are linear functions of pressure. The partial differential coefficients (∂ν/∂P)T at 293 K, (∂ν/∂T)P, at 1 kg cm–2 and 293 K, and (∂ν/∂T)v, at 293 K have been evaluated for each resonance frequency and are related to the molecular conformers present in these solids. At 165 K (NSClO)(NPCl2)2 undergoes a phase change in which the conformation of the six-membered ring changes. The chlorine resonance frequencies, ν/MHz, are related to the corresponding bond lengths, d/A: these relationships are d=–0.0152ν+ 2.4166 for P–Cl bonds and d=–0.0172ν+ 2.636 for S–Cl bonds. The NSClO group is more electronegative than the NPCl2 group. Chlorine valence-electron populations, ϕ, can be deduced from the corresponding chlorine-35 n.q.r. frequencies at 77 K. The appropriate relationships are ϕ=–0.0345ν+ 8 for P–Cl bonds and ϕ=–0.0265ν+ 8 for SClO groups.

Chlorine-35 nuclear quadrupole resonance studies of some chlorine-containing phosphorus–nitrogen compounds

The 35Cl n.q.r. spectra of a series of chlorine-containing phosphorus–nitrogen compounds including [Cl(X)PNR]2(X = lone pair, R = But; X = O, R = But or Me), PCl2(NButH)O, Cl2P·NBut·PCl2, Cl2P·NMe·P(O)Cl2, Cl2(X)P·NMe·P(X)Cl2(X = O or S), Cl2(O)P·NR·P(S)Cl2(R = Me or Ph), the heterocycle C17H20ClN2OP (see Table 1), and Cl2(O)P·N:PPh3 have been recorded at ambient temperatures and/or 77 K. The results are discussed in terms of the structures, where known, and a linear correlation between P–Cl bond lengths and n.q.r. frequencies has been deduced for phosphoryl compounds : this is different from the correlation previously deduced for cyclophosphazenes. Data for Cl2(O)PCH2P(O)Cl2 are also included. The n.q.r. results enable some comparisons to be made of the relative electron supply of some common substituents encountered in phosphorus chemistry.

Use of chlorine-35 nuclear quadrupole resonance spectroscopy for structural assignments in chlorocyclotriphosphazatrienes

The 35Cl nuclear quadrupole resonance spectra of a series of aminochlorocyclotriphosphazatrienes N3P3Cl6–nRn(R = NMe2, n= 1–4; R = NC5H10, n= 1–3) have been recorded at 77 and/or 273 K. These data show that positional isomers may be distinguished, but that unambiguous structural assignments to geometrical isomers are not generally possible. Similar conclusions may be drawn for other aminochloro- and phenylchloro-cyclotriphosphazatrienes. Resonance frequencies diagnostic of PCl2, PCl·NR2, and PClPh groups fall in the ranges 26–29, 22–25, and 23–25 MHz respectively, but the last two groups cannot be distinguished by this technique.