Low co-ordination numbers in lanthanoid and actinoid compounds. Part 2. Syntheses, properties, and crystal and molecular structures of triphenylphosphine oxide and peroxo-derivatives of [bis(trimethylsilyl)amido]lanthanoids

The preparation, properties, and n.m.r. spectra of 1:1 triphenylphosphine oxide adducts of [M{N(SiMe₃)₂}₃] (M = La Eu, or Lu) and dimeric peroxo-species [M₂{N(SiMe₃)₂}₄(O ₂)(PPh₃O)₂] (M = La, Pr, Sm, Eu, or Lu) are described. The crystal and molecular structures of [La{N(SiMe₃)₂}₃(PPh₃O)] (1) and [La₂{N(SiMe₃)₂}₄(O ₂)(PPh₃O)₂] (2) have been determined bysingle-crystal X-ray diffraction methods from data measured on a manual diffractometer and refined by least-squares to R 0.116 for 2 770 observed reflections for (1) and to R 0.113 for 2 153 data for (2). Both species crystallise in space group P1 with cell parameters: (1); a = 19.92, b = 12.64, c = 12.48 Å, α = 120.5, β = 87.3, γ = 102.7°, Z = 2; (2); a = 13.55, b = 18.54, c = 12.54 Å α = 90.8, β = 121.7, γ = 115.3°, Z = 1. Complex (1) is monomeric and the lanthanum atom has slightly distorted L_aN₃O tetrahedral geometry. The La-O-P unit is almost linear, with La-O 2.39(2) Å; La-N distances are 2.38(2)-2.41(2) Å. Complex (2) is a peroxo-bridged centrosymmetric dimer in which the peroxo-function acts as a symmetrical doubly bidentate bridge linking two La{N(SiMe₃)₂}₂(PPh₃O) units. The metal atom can again be considered to have distorted tetrahedral co-ordination if the O₂ function is assumed to occupy one co-ordination site. The La-O(O₂) distances are both 2.33(3) Å, whilst La-O(PPh₃O) is 2.42(2) and La-N 2.37(2) and 2.49(3) Å. The O-O separation is 1.65(4) Å, but this may be artificially lengthened by the effects of crystal decomposition.