ORGANOLANTHANOIDS .19. THE X-RAY CRYSTAL-STRUCTURES OF DI[MU-(ACETATO-O,O-O')BIS(DIPHENYLPHOSPHINO-ETA(5)-CYCLOPENTADIENYL)YTTERBIUM(III)] AND DI[MU-(ACETATO-O,O-O')BIS(ETA(5)-CYCLOPENTADIENYL)YTTERBIUM(III)]-UNEXPECTED EXAMPLES OF FORMAL 9 COORDINATION IN LANTHANOID ORGANOMETALLICS

Treatment of bis(diphenylphosphinocyclopentadienyl)ytterbium(II) with mercury(II) acetate in tetrahydrofuran (THF) gave Yb(C(5)H(4)PPh(2))(2)(O2CCH3) as a fractional (0.75) THF solvate. Crystallization from toluene gave the THF-free dimer [Yb(eta(5)- C(5)H(4)PPh(2))(2)(mu-O2CCH3)](2), the structure of which was determined by X-ray crystallography (monoclinic; P2(1)/n; a = 9.615(2), b = 13.665(5), and c = 23.209(9)Angstrom; beta = 91.47(3)degrees; Z = 2(dimers); R = 0.034 for 3996 ''observed'' data). Unexpectedly, the bridging acetate groups are unsymmetrically chelating to one ytterbium atom and bonded by one oxygen atom to the other, and each ytterbium atom is formally nine coordinate with two eta(5)-C(5)H(4)PPh(2) groups (Ct-Yb-Ct, 130.7 degrees; Ct = centroid), two oxygen atoms from one bridging acetate (Yb-O, 2.454(4), and 2.339(4)degrees, and one (Yb-O, 2.282(4) Angstrom from the other. For comparison, the structure of YbCp(2)(O2CCH3) (Cp = cyclopentadienyl) was determined (orthorhombic; Pbam; a = 13.16(1), b = 12.98(1) and c = 13.376(4) Angstrom; Z = 4 (dimers); R = 0.058 for 1745 ''observed'' data) and showed the presence of two crystallographically different acetate-bridged dimers (A and B) with some variation between their geometries. Again, ytterbium is nine coordinated with two eta(5)-Cp groups (Ct-Yb-Ct, 132.1 degrees (A) or 123.3 degrees (B)), two nearly symmetrically bonded oxygen atoms from one acetate (cf. Yb(C(5)H(4)PPh(2))(2)(O2CCH3))(Yb-O 2.38(1) and 2.39(1) Angstrom (A) or 2.42(1) and 2.39(1) A (B)) and one more tightly bound oxygen atom (Yb-O, 2.25(1) Angstrom (A) or 228(1) Angstrom (B)) from the other acetate.