Crystal structures and thermal properties of Ba(1,2,4- t-Bu 3C 5H 2) 2 and Sr(1,2,4- t-Bu 3C 5H 2) 2: Precursors for atomic layer deposition

Abstract

Sterically hindered Lewis base free bis(1,2,4-tri- tert-butylcyclopentadienyl)strontium ( 1) and bis(1,2,4-tri- tert-butylcyclopentadienyl)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-Bu 3C 5H 2) 2 molecules with Cp(centroid)–Sr–Cp(centroid) angles of 165.1° and 169.4°. Depending on the way of crystallization two polymorphs ( 2a and 2b) were observed for Ba( t-Bu 3C 5H 2) 2. On sublimation Ba( t-Bu 3C 5H 2) 2 crystallizes as chains in which one methyl group of each Ba( t-Bu 3C 5H 2) 2 unit interacts with neighboring Ba( t-Bu 3C 5H 2) 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-Bu 3C 5H 2) 2 molecules with Cp(centroid)–Ba–Cp(centroid) angles of 161.3–164.9°. Both compounds prepared are volatile, thermally stable and reactive and thus suitable precursors for atomic layer deposition of thin films.