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] a nd [Re(CO)(3)Cl](2)dpp, where dpp is 2,3-bis(2-pyridyl)pyrazine, has been c onducted to examine the structural consequences resulting from sequential c oordination of two [Re(CO)(3)Cl] molecular fragments to dPP Addition of one metal center results in the coordinating portion of dpp adopting a relativ ely planar configuration. The dihedral angle between the pyrazine ring and the coordinated N(1)-pyridyl ring is 15.3(4)degrees, while the dihedral ang le 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 decreas e for the N(2)-pyridyl and pyrazine dihedral angle [31.6(3)degrees]. The di rect structural consequence is an increase in the distortion of the central pyrazine moiety upon addition of each [Re(CO),Cl] fragment. This observati on confirms previously reported spectroscopic results that inferred the dif ferences in electronic structure between [Re(dpp)(CO)(3)Cl] and [Re(CO)(3)C l],dpp were due to the dpp ligand adopting a nonplanar geometry in the bime tallic complex. (C) 1998 Elsevier Science Ltd. All rights reserved.