Far-Infrared Spectra of Complexes of Rhodium And Iridium With.Π-Bonding Ligands

Abstract

The infrared spectra of the following square-planar rhodium(I) and iridium(I) halógeno complexes have been measured in the range 460-200 cm-1: [RhXL2]2 (L = CO, C2H4, or cyclooctene or L2 = norbornadiene or 1,5-cyclooctadiene; X = Cl or Br); RhX(CO)(MR3)2 (M = P or As; R = alkyl or aryl; X = Cl or Br); RhCl(C7H8)(p-toluidine) and RhCl(C7H8)-{M(C6H5)3} (C7H8 = norbornadiene;M = P, As, or Sb); RhX{ P(C)3}3 (X = Cl or Br) and [RhCl{P(C6H5)3}2]2; [Ir-(C8H12)Cl]2 (C8H12 = 1,5-cyclooctadiene); IrX(CO){P(C6H5)3}2 (X = Cl or Br). Strong bands due to metal-chlorine stretching vibrations appear in the range 310-250 cm-1 and the frequencies of bridging metal-chlorine stretching vibrations are about 20-40 cm-1 lower than those of terminal metal-chlorine stretching vibrations. Similar measurements have been made on the following octahedral rhodium (III) and iridium (III) complexes: RhX3{M(C2H5)3}3 and [RhX3{M(C2H6)3}2]2 (X = Cl or Br; = P or As); RhClX2(CO)(MR3)2 (X = Cl, Br, or I; = P or As; R = C2H5or C6H5); IrClXY(CO)-{P(C6H5)3}2 (XY = Cl2, Br2, I2, H2, HCl.orCHal) and IrBrX2(CO){P(C6H5)3}2 (X = Cl or Br). Bands due to metal-chlorine stretching vibrations appear in the range 350-250 cm-1, the frequencies depending mainly on the ligand trans to the chlorine atom in the complex. Ligands can be ordered according to their effect on y(M-Cltrans) as follows: Cl > Br > I ∼ CO > CHs ∼ PRa ∼ AsRs > H (decreasing metal-chlorine stretching frequency along this series). From the pattern and frequencies of the -Cl absorption bands, it is concluded that the octahedral adducts of IrCl(CO){P(C6H5)3}2 with halogens, hydrogen, hydrogen chloride, and methyl iodide contain the addend atoms in cis positions. Show more