Carbonyl complexes of noble metals with halide ligands II. Palladium(II): preparation of Pd2Br4(CO)2 and -: crystal structures of (X=Cl or Br)

Article abstract of DOI:10.1016/0022-328X(88)80662-4

The previously elusive Pd2Br4(CO)2 has been isolated, mixed with PdBr2, from the reaction of PdBr2 with CO under pressure.A centrosymmetric structure is suggested for it on the basis of IR spectral data in solution.Attempts to prepare the corresponding iodo carbonyl complex of palladium(II) failed.The anion ^- rapidly undergoes decarbonylation both in solution and in the solid state.The stabilities of the halocarbonyl complexes relative to those of the corresponding halides (PdX2 or Pd2X6^2-) appear to decrease in the sequence Cl > Br > I.The crystal and molecular structures of the ^- anions (X=Cl, Br) with ⁺ as counter-cation have been determined by X-ray diffraction.Crystal data for : monoclinic; space group, P2₁/n; a 18.231(10); b 8.889(4); c 14.978(8) Angstroem; β 104.88(2) deg; U 2346(2) Angstroem³; Z=4; D_c 1.368 g cm^-3; μ(Mo-K_α) 11.29 cm^-1; R=0.0397.Crystal data for *C2H2Cl4: triclinic; space group, P/1; a 16.667(10); b 10.376(8); c 9.644(7) Angstroem; α 74.27(3) deg; β 75.12(3) deg; γ 83.27(4) deg; U 1549(2) Angstroem³; Z=2 D_c 1.681 g cm^-3; μ(Mo-K_α) 47.84 cm^-1; R=0.0886.In both anions, which are essentially planar, the Pd-X bond trans to the CO ligand is not significantly different in length from the other two Pd-X distances.The overall idealized symmetry of the ⁺ cation changes from D_2d to S₄ when the counter-anion is changed from ^- to ^-.