Comparative X-ray crystallographic characterization of the mono- and bimetallic complexes of rhenium(I) tricarbonyl chloride with 2,3-bis(2-pyridyl)pyrazine

Comparative X-ray crystallographic characterization of [Re(dpp)(CO)(3)Cl] and [Re(CO)(3)Cl](2)dpp, where dpp is 2,3-bis(2-pyridyl)pyrazine, has been conducted to examine the structural consequences resulting from sequential coordination of two [Re(CO)(3)Cl] molecular fragments to dPP Addition of one metal center results in the coordinating portion of dpp adopting a relatively planar configuration. The dihedral angle between the pyrazine ring and the coordinated N(1)-pyridyl ring is 15.3(4)degrees, while the dihedral angle between the pyrazine ring and the uncoordinated N(2)-pyridyl ring is 45.8(3)degrees. The dpp ligand in the bimetallic complex is found to twist to accommodate the second metal center as manifested by a two-fold increase in the N(1)pyridyl and pyrazine dihedral angle [29.7(4)degrees] and a decrease for the N(2)-pyridyl and pyrazine dihedral angle [31.6(3)degrees]. The direct structural consequence is an increase in the distortion of the central pyrazine moiety upon addition of each [Re(CO),Cl] fragment. This observation confirms previously reported spectroscopic results that inferred the differences in electronic structure between [Re(dpp)(CO)(3)Cl] and [Re(CO)(3)Cl],dpp were due to the dpp ligand adopting a nonplanar geometry in the bimetallic complex. (C) 1998 Elsevier Science Ltd. All rights reserved.