Crystal and molecular structure of tetrakis(trifluoroacetato)bis(dimethyl-d6 sulfoxide)dirhodium(II): a structural deuterium isotope effect in an oxygen-bonded sulfoxide adduct

In a previous study the authors prepared the perdeuterated compound Rh/sub 2/(O/sub 2/CCF/sub 3/)/sub 4/(Me/sub 2/SO-d/sub 2/) to aid in the assignment of the infrared spectrum of the Me/sub 2/SO adduct. Earlier studies have noted that the advantage derived from recording the infrared spectra of both Me/sub 2/SO and Me/sub 2/SO-d/sub 6/ compounds stems from the near degeneracy of the S-O stretching and methyl rocking vibrations in the normal Me/sub 2/SO complex while in the Me/sub 2/SO-d/sub 6/ analogue these vibrations are well separated. Since the preparaton of Rh/sub 2/(O/sub 2/CCF/sub 3/)/sub 4/sup -//(Me/sub 2/SO-d/sub 6/)/sub 2/ afforded a crystalline product, several of the crystals were examined on an x-ray diffractometer. Unexpectedly, all of the crystals examined possessed a triclinic cell which was not the same as that for the corresponding Rh/sub 2/sup -//(O/sub 2/CCF/sub 3/)/sub 4/(Me/sub 2/SO)2 complex. In this paper the structure of the Me/sub 2/SO-d/sub 6/ adduct of Rh/sub 2/(O/sub 2/CCF/sub 3/)/sub 4/, which has been refined with the inclusion of all deuterium atoms is described. This structure is compared to that of the undeuterated adduct which has been further refined with the inclusion of all hydrogen atoms. The two structures represent the first example of a crystal packing modification in a transition-metal complex effected solely by the substitution of deuterium for hydrogen.