A Comparison of 4f vs 5f Metal−Metal Bonds in (CpSiMe3)3M−ECp* (M = Nd, U; E = Al, Ga; Cp* = C5Me5): Synthesis, Thermodynamics, Magnetism, and Electronic Structure

Autor: John Arnold, Tolek Tyliszczak, Jeffrey D. Rinehart, Markus Janousch, Stefan G. Minasian, David K. Shuh, Roy Copping, Jamin L. Krinsky
Rok vydání: 2009
Předmět:
Zdroj: Journal of the American Chemical Society. 131:13767-13783
ISSN: 1520-5126
0002-7863
DOI: 10.1021/ja904565j
Popis: Reaction of (CpSiMe(3))(3)U or (CpSiMe(3))(3)Nd with (Cp*Al)(4) or Cp*Ga (Cp* = C(5)Me(5)) afforded the isostructural complexes (CpSiMe(3))(3)M-ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E = Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature (1)H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV-visible-NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature (1)H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters DeltaH and DeltaS obtained by (1)H NMR titration methods revealed a much stronger U-Ga interaction in 2 than the Nd-Ga interaction in 4. Competition reactions between (CpSiMe(3))(3)U and (CpSiMe(3))(3)Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 degrees C and 96:4 at -33 degrees C. For 1 and 3, comparison of (1)H NMR peak intensities suggests that Cp*Al also achieves excellent U(III)/Nd(III) selectivity at 21 degrees C. The solution electronic spectra and solid-state temperature-dependent magnetic susceptibilities of 1 and 2, in addition to X-ray absorption near-edge structure (XANES) measurements from scanning transmission X-ray microscopy (STXM) of 1, are consistent with those observed for other U(III) coordination complexes. DFT calculations using five different functionals were performed on the model complexes Cp(3)M-ECp (M = Nd, U; E = Al, Ga), and empirical fitting of the values for Cp(3)M-ECp allowed the prediction of binding energy estimates for Cp*Al compounds 1 and 3. NBO/NLMO bonding analyses on Cp(3)U-ECp indicate that the bonding consists predominantly of a E--U sigma-interaction arising from favorable overlap between the diffuse ligand lone pair and the primarily 7s/6d acceptor orbitals on U(III), with negligible U--E pi-donation. The overall experimental and computational bonding analysis suggests that Cp*Al and Cp*Ga behave as good sigma-donors in these systems.
Databáze: OpenAIRE
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