Norman L. Paddock

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

The ionisation potentials of the phosphonitrilic fluorides (NPF2)n(n= 3–8) have been measured by photoelectron spectroscopy, and those of other phosphonitrilic derivatives (NPX2)n[X = Cl, n= 3–7; X = OCH2·CF3, OMe, OPh, NMe2, or Me, n= 3 or 4] 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)n+, are interpreted by use of the orbital approximation and a model of a dual π-system which involves 3d-orbitals at phosphorus and valence-shell orbitals of nitrogen and which supplements the underlying σ-framework. Comparison of the results with simple molecular orbital calculations suggest that the highest π-system is of the homomorphic type, involving mainly the 3dx2–y2– orbital, and that it is accompanied by a lower and partly overlapping heteromorphic system, to which the 3dxz-orbital makes the major contributions. Ionisation spotential are also assigned to molecular orbitals which span the P–N and P–F σ-bonds, and the fluorine lone pairs.

Xα scattered wave calculations of the ionisation energies of N3P3F6 and N4P4F8

Abstract Ionisation energies have been calculated for N 3 P 3 F 6 and N 4 P 4 F 8 with the overlapping sphere version of the Xα scattered wave method and with the inclusion of a vacacy sphere for the interior of each PN ring. Experimental energies are calculated to within 1 eV on average for both sets of calculations, but the spacings of the levels are reproduced better with the vacancy sphere model.

Reaction of N-methylphosphazenium halides with bases: a phosphazene–phosphorin rearrangement

On deprotonation by a sufficiently strong base, N-methylphosphazenium iodides NnPnMe2n+ 1I (n= 3,4) rearrange to phosphorins with exocyclic methylamino-groups.

Crystal and molecular structure of tetraphenylcyclotetraphosphine monosulphide

The title compound, (C6H5P)4S, has been structurally characterised by a single crystal X-ray study, and contains a 5-membered P4S ring.

Dodeca(dimethylamido)cyclohexaphosphonitrile as a macrocyclic ligand

In the compound [N6P6(NMe2)12CuCl]+CuCl2–, a 5-co-ordinated cupric ion is situated inside the 12-membered ring, the slight weakening of the ring bonds to the co-ordinating nitrogen atoms being partially compensated by increased electron release.

Helium I photoelectron spectrum of disulphur dinitride

The photoelectron spectrum of disulphur dinitride has been determined and tentatively assigned.

Crystal and molecular structure of hexadeca (dimethylamino) cyclooctaphosphazene

Crystals of the title compound are monoclinic, a= 17.383(5), b= 24.167(7), c= 14.637(6)A, β= 111.16(2)°, space group C2/c. The structure was determined by direct methods from diffractometer X-ray data and refined by full-matrix least-squares methods to R 0.038 for 1 920 observed reflexions. The molecule occupies a crystallographic centre of symmetry. Mean endo- and exo-cycli P–N bond lengths are 1.548(9) and 1.651(7)A P–N–P angles range from 145.9(4) to 170.2(5)°, mean 156.5°, and endocyclic N–P–N angles range from 114.8(3) to 119.2(3)°, mean 116.8° Three exocyclic N–P–N angles are nearly equal, mean 101.5(7)°, the fourth being significantly larger, 106.1(3)°. Mean N–C is 1.43(2)A, and mean C–N–C angle 113.9(8)°. The molecular confirmation is very similar to that of [NP(OMe)2]8; structural comparisons are also made with the dimethylamides [NP(NMe2)2]3,4,6.

Preparation and donor properties of the cyclic methylphosphazenes

The cyclic methylphosphazenes (NPMe2)3–5 form simple salts such as N3P3Me6,HCl. N4P4Me8,2HClO4, and N5P5Me10H2CuCl4,H2O, and complexes such as N4P4Me8,2HgCl2, N4P4Me8,4AgNO3 and N4P4Me8,HCl,CuCl2. All three phosphazenes form quaternary salts NnPnMe2n,Rl (n= 3–5; R = Me or Et) with alkyl iodides. The iodide can be exchanged for other anions such as Cl– Or Hgl3–; the tetramer forms a dipositive cation in N4P4Me9–HZn(NCS)4. The phosphorus d-orbitals are less electronegative than they are in the halogenophosphazenes, the ring bonds are consequently weakened, and π-charge is concentrated on nitrogen. The molecular structures of N4P4Me8H+, N4P4Me9+, and N5P5Me10H22+ show that localisation of two electrons by an acceptor induces substantial bond length inequalities, with patterns expected for the perturbation of an otherwise delocalised π-system. The methylphosphazenes begin to absorb strongly near 190 nm, the band being attributable to a ring transition. Its large energy shows that the electronegativities of the phosphorus and nitrogen orbitals are appreciably different, and, as a consequence, methylphosphazenes make no significant use of antibonding orbitals in complexes with transition metals.

Phosphazene carbanions as synthetic intermediates: silicon, germanium, and tin derivatives

The tetra-carbanion formed from methyl-lithium and octamethylcyclotetraphosphazene reacts with methyl iodide and with the chlorides Me3XCl(X = Si, Ge, Sn) to give N4P4Me4(CH2R)4(R = Me, XMe3).

Crystal and molecular structure of [octakisdimethylaminocyclotetraphosphazene]tetracarbonyltungsten

Crystals of the title compound are monoclinic, a= 18·274(22), b= 18·594(24), c= 10·533(14)A, β= 90·39(10)°, Z= 4, space group P21/n. The structure was determined from diffractometer data by Patterson and Fourier methods, and refined by full-matrix least-squares methods to R 0·071 for 2372 observed reflexions. The phosphonitrile is co-ordinated to tungsten through a ring nitrogen atom and an exocyclic dimethylamido-nitrogen atom. The co-ordination geometry about tungsten is distorted octahedral with the nitrogen atoms of the phosphonitrile occupying cis-positions and N–W–N angle 65·4°. The bond-length variations in the phosphonitrilic ring caused by co-ordination are explained in terms of π-bonding theory.