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Crystal and molecular structures of some cyclic phosphonitriles Marsh, Wayne Clifford


Single crystal X-ray diffraction methods have been used to determine the structures of four cyclic phosphonitriles: 1,1,5,5-tetrafluoro-3,3,7,7-tetramethylcyclotetra- phosphonitrile, N(4)P(4)F(4)Me(4) ; 1,1,3,3,5,5-hexafluoro-7,7-dimethyl- cyclotetraphosphonitrile, N(4)P(4)F(4)Me(2); hexaphenoxycyclotriphosphonitrile, [NP(OPh)2](3) and dodeca(dimethylamino)-cyclohexaphosphonitrilechlorocopper (II) dichlorocuprate (I), [formula omitted]. Intensity measurements were made on a Datex automated General Electric diffractometer using a scintillation counter; Cu-K [symbol omitted], radiation being used for the first three structure determinations and Mo-K [symbol omitted] radiation for the fourth. The structure of N(4)P(4)F(4)Me(4) has been determined by Patterson and Fourier methods and refined by full-matrix least-squares. The molecule is situated on a C(2) axis, and the phosphonitrilic ring has the 'saddle' conformation. Different electronegativities of the substituent groups result in two distinct P-N bond lengths, 1.53 and 1.59 Å explicable in terms of π -bonding theories. Patterson, Fourier, and full-matrix least-squares methods have been used to determine the structure of N(4)P(4)F(6)Me(2). This molecule is also situated on a C(2) axis and has the 'saddle' conformation, but tends strongly towards planarity. The most interesting features of the ring are four distinct P-N bond lengths (1.584, 1.470, 1.532, and 1.487 Å), and large valency angles (145°) at nitrogen, which are explicable in terms of π -bonding theories. The structure of [NP(CPh)2]3 was determined from Patterson and Fourier syntheses, and refinement of positional and thermal parameters of the atoms by block-diagonal least-squares. The phosphonitrilic ring is slightly non-planar, with two nitrogen atoms displaced by 0.15 Å in opposite directions from the plane of the other four (3P and 1N) atoms. The conformations of the phenoxy groups are different at the three phosphorus atoms, and there are small deviations among chemically-equivalent angles; these differences are probably a result of intra- and intermolecular steric effects. There are no differences among chemically equivalent bond lengths, the mean distances being P-N 1.575(2), P-O 1.582(2), 0-C 1.406(3) Å. The structure of [formula omitted] was determined by Patterson, Fourier, and full-matrix least-squares methods. The structure is ionic with the cation and anion each situated on a C(2) axis. The cation consists of a Cu(II) bonded to four nitrogens of the phosphonitrilic ring (N-Cu 2.07 Å) and a chlorine (Cℓ-Cu 2.28 Å) in a distorted square pyramid. The Cu(I)Cℓ2¯ anion is linear with a Cu-Cℓ bond length of 2.11 Å. There are two distinct P-N bond lengths in the phosphonitrilic ring, 1.62 and 1.55 Å, explicable by π -bonding theory. The overall shape of the structure is determined primarily by steric effects and the distortion of the phosphonitrilic ring caused by the bonding to copper.

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