1 research outputs found
To Bend or Not To Bend: Experimental and Computational Studies of Structural Preference in Ln(Tp<sup>iPr</sup><sub>2</sub>)<sub>2</sub> (Ln = Sm, Tm)
The synthesis and characterization of LnĀ(Tp<sup>iPr2</sup>)<sub>2</sub> (Ln = Sm, <b>3Sm</b>; Tm, <b>3Tm</b>) are reported.
While the simple <sup>1</sup>H NMR spectra of the compounds indicate
a symmetrical solution structure, with equivalent pyrazolyl groups,
the solid-state structure revealed an unexpected, ābent sandwich-likeā
geometry. By contrast, the structure of the less sterically congested
TmĀ(Tp<sup>Me2,4Et</sup>)<sub>2</sub> (<b>4</b>) adopts the expected
symmetrical structure with a linear BāTmāB 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 CāHĀ·Ā·Ā·N
hydrogen-bonding interactions that help stabilize the structure. These
results find support in the similar geometry of the TmĀ(III) analogue
[TmĀ(Tp<sup>iPr2</sup>)<sub>2</sub>]ĀI, <b>3Tm</b><sup><b>+</b></sup>, and confirm that the low symmetry is not the result of a
metalāligand interaction. The relevance of these results to
the general question of the coordination geometry of MX<sub>2</sub> and MĀ(C<sub>5</sub>R<sub>5</sub>)<sub>2</sub> (M = heavy alkaline
earth and LnĀ(II), X = halide, and C<sub>5</sub>R<sub>5</sub> = bulky
persubstituted cyclopentadienyl) complexes and the importance of secondary
H-bonding and nonbonding interactions on the structure are highlighted