Crystal structures and thermal properties of Ba(1,2,4-t-Bu3C5H2)2 and Sr(1,2,4-t-Bu3C5H2)2:: Precursors for atomic layer deposition

Sterically hindered Lewis base free his(1,2,4-tri-tert-butylcyclopentadienyl)strontium (1) and his(1,2,4-tri-tert-butylcyclopen tadienyl)barium (2) were synthesized using the common metathesis route and characterized with NMR, MS, TGA/SDTA and XRD. Compound 1 crystallized as a monomer with typical bent structure. Asymmetric unit contains two independent slightly different Sr(t-Bu3C5H2)(2) molecules with Cp(centroid)-Sr-Cp(centroid) angles of 165.1 degrees and 169.4 degrees. Depending on the way of crystallization two polymorphs (2a and 2b) were observed for Ba(t-Bu3C5H2)(2). On sublimation Ba(t-Bu3C5H2)(2) crystallizes as chains in which one methyl group of each Ba(t-Bu3C5H2)(2) unit interacts with neighboring Ba(t-Bu3C5H2)(2) unit's barium atom. Slow crystallization of waxy evaporation residue of toluene solution results in monoclinic crystals (2b) whose asymmetric unit contains four slightly different individual Ba(t-Bu3C5H2)(2) molecules with Cp(centroid)-Ba-Cp(centroid) angles of 161.3-164.9 degrees. Both compounds prepared are volatile, thermally stable and reactive and thus suitable precursors for atomic layer deposition of thin films. (c) 2007 Elsevier B.V. All rights reserved.