The Crystal and Molecular Structure of Bis(cyclopentadienyldicarbonylchromium) (Cr[triple bond]Cr)

Abstract

The crystal structure of bis(cyclopentadienyldicarbonyl-chromium) has been determined by x-ray diffraction. The compound crystalizes in the triclinic system, space group P (C1i, No. 2) with unit cell parameters: a, 7.829(3); b, 14.543(6); c, 6.588(2)A; [alpha], 94.67(3), [beta], 110.70(3); [gamma], 104.04[deg](3); V, 699.1(4)A3; Z=2. There are two independent molecules per unit cell located at the inversion centers at O,O,O and O, , O. The Cr---Cr bond distances are, respectively 2.200(3) and 2.230(3), thus supporting their formulation as triple bonds. The Cp---Cr---Cr--- angles in the two molecules are 165.0[deg] and 158.7[deg], respectively. The structural features are compared with those of Cp2Mo2(CO)4, which has a linear Cp---Mo---Mo---Cp axis; and the differences rationalized in terms of electronic interactions of the Cp-ligand with the orbitals of the M2 unit. The differences observed in the structures of the two independent molecules are also related to the proposed bonding model and to packing considerations.