title: To bend or not to bend: experimental and computational studies of structural preference in Ln(Tp(iPr)2)2 (Ln = Sm, Tm).
abstract: The synthesis and characterization of Ln(Tp(iPr2))2 (Ln = Sm, 3Sm; Tm, 3Tm) are reported. While the simple (1)H NMR spectra of the compounds indicate a symmetrical solution structure, with equivalent pyrazolyl groups, the solid-state structure revealed an unexpected, "bent sandwich-like" geometry. By contrast, the structure of the less sterically congested Tm(Tp(Me2,4Et))2 (4) adopts the expected symmetrical structure with a linear B-Tm-B arrangement. Computational studies to investigate the origin of the unexpected bent structure of the former compounds indicate that steric repulsion between the isopropyl groups forces the Tp ligands apart and permits the development of unusual interligand C-H···N hydrogen-bonding interactions that help stabilize the structure. These results find support in the similar geometry of the Tm(III) analogue [Tm(Tp(iPr2))2]I, 3Tm(+), and confirm that the low symmetry is not the result of a metal-ligand interaction. The relevance of these results to the general question of the coordination geometry of MX2 and M(C5R5)2 (M = heavy alkaline earth and Ln(II), X = halide, and C5R5 = bulky persubstituted cyclopentadienyl) complexes and the importance of secondary H-bonding and nonbonding interactions on the structure are highlighted.
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, AB, Canada T6G 2G2.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Momin
authors.forename: Lee
authors.initials: L
authors.lastname: Carter
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Robert
authors.initials: R
authors.lastname: McDonald
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Essafi Labouille
authors.forename: François
authors.initials: F
authors.lastname: Nief
authors.forename: Iker
authors.initials: I
authors.lastname: Del Rosal
authors.forename: Andrea
authors.initials: A
authors.lastname: Sella
authors.forename: Laurent
authors.initials: L
authors.lastname: Maron
authors.forename: Josef
authors.initials: J
authors.lastname: Takats