title: Effect of crystal packing on the structures of polymeric metallocenes.
abstract: The pressure dependencies of the crystal structures of the polymeric metallocenes lithium cyclopentadienide (LiCp) and potassium cyclopentadienide (KCp) have been determined by synchrotron X-ray powder diffraction. The decrease of the volume of LiCp by 34% up to a pressure of p = 12.2 GPa and of KCp by 23% at p = 5.3 GPa as well as the bulk moduli of K = 7.7 GPa for LiCp and 4.9 GPa for KCp indicate a high compressibility for these compounds. The crystal structures of KCp have been determined up to p = 3.9 GPa. An increase of the bend angle is found from 45 degrees at p = 0 GPa up to 51 degrees at p = 3.9 GPa. This variation is completely explained by a model invoking attractive K+ Cp- interaction and repulsive nonbonded carbon-carbon interactions. It is proposed that the bend angle in the polymeric alkali metal metallocenes is the result of the optimization of the crystal packing.
authors.affiliation: Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany. r.dinnebier@fkf.mpg.de
authors.forename: R E
authors.initials: RE
authors.lastname: Dinnebier
authors.forename: Sander
authors.initials: S
authors.lastname: van Smaalen
authors.forename: F
authors.initials: F
authors.lastname: Olbrich
authors.forename: S
authors.initials: S
authors.lastname: Carlson