Crystal structure of (18-crown-6) potassium(I) [(1,2,3,4,5-η)-cycloheptadienyl][(1,2,3-η)-cyclo-heptatrienyl]cobalt(I)

The reaction of bis(anthracene) cobaltate(- I) with excess cycloheptatriene, C₇H₈, resulted in a new 18-electron cobaltate containing two different seven-membered ring ligands, based on single-crystal X-ray diffraction. The asymmetric unit of this structure contains two independent cation-anion pairs of the title complex, [K(18-crown-6)][Co(η³ -C₇H₇)(η⁵ -C₇H₉)], where 18-crown-6 stands for 1,4,7,10,13,16-hexaoxacyclooctadecane (C₁₂H₂₄O₆), in general positions and well separated. Each (18-crown-6) potassium cation is in contact with the η³-coordinating ligand of one cobaltate complex. Each η³-coordinating ligand behaves as an allylic anion whose exo-diene moiety is bent away from the allylic plane, and thus is not involved directly in the bonding. The metal-coordinating portions of the anionic η⁵ ligands are planar and one of these ligands is modeled as disordered over two positions, with occupancy ratio 0.699 (5):0.301 (5), such that one orientation is rotated by one carbon atom with respect to the other. The diffraction intensities were integrated according to non-merohedral twin law [100/010/0.06401], a 180° rotation about reciprocal lattice axis [001], and the masses of the twin domains refined to equal amounts. As both ligands are formally coordinated as anions, the cobalt atom is best considered to be Co^I. This compound is of interest as the first to possess cycloheptatrienyl and cycloheptadienyl ligands in an anionic metal complex.