Nitrosyl complexes of rhenium. Crystal and molecular structures of the tetraethylammonium salts of tetrabromo(ethanol)nitrosylrhenate-(II) and of acetonitriletetrabromonitrosylrhenate(II)

Abstract

The crystal and molecular structures of the title compounds, [NEt₄][Re(NO)Br₄(EtOH)](I) and [NEt₄][Re(NO)-Br₄(MeCN)](II), have been determined by the heavy-atom method from three-dimensional X-ray data collected by counter methods. Both compounds are orthorhombic. Compound (I) crystallizes in space group Pbca, Z= 8, with cell constants a= 16.41 (2), b= 1 3.81 (1), and c= 16.91 (2)Å; compound (II) is in space group Pn2₁a, Z= 4, with cell constants a= 13.12(1), b= 8.71(1), and c= 17.25(2)Å. Least-squares refinements gave R 0.038 (I) and 0.030 (II), based on 837 and on 930 independent reflections. The anions display distorted octahedral geometry, with solvent molecules co-ordinated trans to nitrosyl groups. Mean Re–Br distances are 2.516 (I) and 2.511 Å(II). The nitrosyl groups are linked in an essentially linear manner, as NO⁺ ligands. The Re–O(EtOH)[2.161(15)Å] and Re–N(MeCN)[2.153(11)Å] distances are longer than expected for single bonds, and this together with distortions of the octahedral geometry is discussed in comparison with the structures of similar compounds.