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Studies on the ligand properties of phosphonitrilic derivatives Calhoun, Harry P.

Abstract

Complexes of dodeca(dimethylamino)cyclohexaphosphonitrile with, divalent first series transition metal ions manganese through zinc have been studied. Previous X-ray work has established that N₆P₆ (NME₂)₁₂ forrns five-coordinate complexes with transition metal chlorides in which the phosphonitrile donates to the metal through four ring nitrogen atoms and the metal atom is close to the centre of the phosphonitrilic ring. In the present work, the complexes with metal nitrates have been shown to have the formulae (M(N₆P₆ (NMe₂)₁₂)N0₃+)N0₃~, with M = Mn,Co,Ni,Cu, and Zn, on the basis of conductivity measurements and the electronic spectra of the Co, Ni, and Cu complexes. Magnetic susceptibility measurements indicate that the nitrate complexes with M = Mn,Co, and Ni are high spin complexes. For the copper nitrate complex the above formulation is probably correct in the solid state, but in solution coordination evidently depends on the solvent. The electronic spectra are best interpreted in terms of D₃[sub h] symmetry about the metal, and the crystal field parameters derived from published energy level diagrams are similar to corresponding values derived for five-coordinate complexes formed with N (CH₂CH₂N(CH₃)₂)₃ • a saturated tetradentate amine ligand. Infrared spectra of N₆P₆(NMe₂)₁₂ and its complexes are also discussed. In order to investigate changes in -the ligand geometry-occurring when other phosphonitrilic derivatives coordinate to transition metals or interact with other acceptor groups the crystal structures of (N₄P₄Me₉⁺)(Cr(CO)₅I⁻), ((NPMe₂)₅H₂²⁺)(CuCl₄²⁻)•H20, and (N₄P₄ (NMe₂)₈-W(CO)₄ have been determined. For all three structures intensity data were collected on a diffractometer and the positional and thermal parameters were refined by full-matrix least-squares methods. In (N₄P₄ (NPME⁺)(Cr(CO)₅l⁻) a ring nitrogen atom is bonded to a methyl group, and the N₄P₄ ring has an unusual 'distorted tub' conformation, most likely a result of steric requirements The P-N bond lengths are not equal around the ring, and the observed pattern of bond length variation agrees qualitatively with the pattern predicted by a simple Hiickel M.O. calculation The geometry of the Cr(CO)^I~ ion closely approaches the expected C4v symmetry. In ((NMe₂)₅ H₂²⁺)( CuCl₄²⁻)•H20 the 10-membered phosphonitrilic ring is protonated at two sites, and the P-N bond lengths show a variation which is explained in terms of perturbation of a homomorphic ring π-system. The conformation of the N₅P₅, ring is influenced primarily by hydrogen 2-bondmg considerations. The CuCl₄ ion has a distorted tetrahedral geometry. In N₄P₄(NMe₂)₈-W(CO)₄ the phosphonitrile acts as a bi-dentate ϭ-ligand, coordination occurring through a ring nitrogen atom and an exocyclic nitrogen atom on an adjacent phosphorus atom. The observed variation in the ring P-N bond lengths is understood in terms of perturbations of the ring π systems at two sites. The conformation of the phospho-nitrilic ring is different from that in N₄P₄(NMe₂)₈, the ring being formed from two nearly planar segments making an angle of 48°. The coordination geometry about W is distorted octahedral, the NWN angle being 65.4°.

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