FORMATION OF A HIGHLY-ORDERED POLYMERIC, SUPERSANDWICH METALLOCENE - THE 1ST X-RAY CRYSTAL-STRUCTURE OF A BASE-FREE LITHIUM CYCLOPENTADIENIDE, ([MU-MU-5, ETA-5-C5H4(SIME3)]LI)N

Crystals of {[mu-eta5:eta5-C5H4(SiMe3)]Li}n form in the space group P1BAR with a = 8.402 (2) angstrom. b = 11.778 (3) angstrom, c = 14.740 (4) angstrom, alpha = 81.25 (2)-degrees; beta = 80.76 (2)-degrees, gamma = 77.30 (2)-degrees, V = 1394.1 (5) angstrom3, and D(calcd) = 1.03 g cm-3 for Z = 2. Least-squares refinement of the model based on 2902 reflections (\F(o)\ > 3.0sigma\F(o)\) converged to a final R(F) = 5.44%. The structure consists of parallel chains of LiC5H4SiMe3 units which extend along the b-axis. In each chain, lithium atoms alternate with the C5H4SiMe3 rings to form a continuous polymeric sandwich structure. Within a chain, the dihedral angles between cyclopentadienyl planes are 5.1-8.1-degrees and the Li-(ring centroid distances range from 1.957 to 1.982 angstrom. The orientation of the SiMe3 substituents in the trimetallic (LiC5H4SiMe3)3 repeat unit found in the chains generates a highly ordered interchain structure.