STRUCTURES OF ORGANO-F-ELEMENT COMPOUNDS DIFFERING IN THE OXIDATION-STATE OF THE CENTRAL METAL - CRYSTAL-STRUCTURES OF BIS([8]ANNULENE) COMPLEXES OF CERIUM(IV), YTTERBIUM(III), AND URANIUM(III)

Crystal structures of bis(methyl[8]annulene)cerium(IV) (5), [(diethylene glycol dimethyl ether)potassium] [bis([8]annulene)ytterbate(III)] (14), and [(diethylene glycol dimethyl ether)potassium] [bis(methyl[8]-annulene)uranate(III)] (12) are reported. These include the first structures of an organocerium(IV) compound and of a reduced uranocene. Crystals of 5 are orthorhombic, P2(1)2(1)2(1), with a = 11.690 (3) angstrom, b = 14.315 (3) angstrom, c = 8.977 (2) angstrom, Z = 4, and R(F) = 2.9%. Crystals of 14 are also orthorhombic, Pbca, with a = 16.611 (4) angstrom, b = 14.219 (5), angstrom, c = 9.257 (4) angstrom, Z = 4, and R(F) = 3.6%. Crystals of 12 are monoclinic, P2(1)/c, with a = 13.833 (4) angstrom, b = 9.989 (3) angstrom, c = 17.581 (3) angstrom, beta = 95.87 (3)degrees, Z = 4, and R(F) = 3.8%. These structures are compared to the previously reported structures of [(diethylene glycol dimethyl ether)potassium] [bis([8]annulene)cerate(III)] (13), bis[(dimethoxyethane)potassium] [bis([8]annulene)ytterbate(II)] (15), and uranocene (1). A comparison of the structural parameters of several additional [8]annulene metal complexes is also presented. The effect of coordination number on metal ligand distances in ionic complexes is discussed in terms of electrostatic interactions among the ligands.