THE INFRARED-SPECTRA OF COMPLEXES WITH PLANAR DITHIOOXAMIDES .10. THECU(LH(2))(2)X(1) COMPLEXES

In this article, the preparation, X-ray powder results and vibrational properties of a new type of complex with planar dithiooxamides are di scussed. In acetonitrile, Cu(I) can form complexes with the formula Cu (LH(2))(2)X(1) (X = Cl, Br) where LH(2) is an N,N'-disubstituted dithi ooxamide. Complexes with N,N'-dimethyldithiooxamide and N,N'-diethyldi thiooxamide have been prepared. A thorough vibrational analysis with i nfrared and Raman techniques was performed, assisted by H/D and Cu-63/ Cu-65 isotope substitution. The vibrational study indicates the presen ce of an inversion centre in the structure. This leads to the proposal of a very unusual six-coordinate structure for these compounds, with the two dithiooxamide ligands, having S-cis conformation, coordinated to the same copper and with the halogens bridged between two different copper atoms. Confirmation of this result was attempted by X-ray anal ysis, but although several methods were tried to obtain crystals, only powder X-ray data could be obtained, which could not give a definitiv e answer. Since such six-coordinate Cu(I) has never been described bef ore, a less rigourous interpretation of the vibrational data was follo wed, leading to a square-pyramidal five-coordinate structure, with a r ather weak bond between Cu(I) and a terminal halogen. The latter struc ture, with the data available up to now, seems a bit more likely, sinc e five-coordination for Cu(I) has already been described.