Electronic structure comparisons of isostructural early d- and f-block metal() bis(cyclopentadienyl) silanide complexes

• Published in: Chemical science (Cambridge) 2023-01, Vol.14 (3), p.621-634
• Main Authors: Gransbury, Gemma K, Réant, Benjamin L. L, Wooles, Ashley J, Emerson-King, Jack, Chilton, Nicholas F, Liddle, Stephen T, Mills, David P
• Format: Article
• Language: English
• Subjects: Absorption spectra; Anisotropy; Bonding strength; Cerium; Chemical analysis; Congeners; Electronic structure; Electrostatic bonding; Lanthanum; Ligands; Magnetic measurement; Mathematical analysis; Metals; NMR; Nuclear magnetic resonance; Silicon; Single crystals; Superconducting quantum interference devices; Titanium; Zirconium
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d2sc04526e

We report the synthesis of the U( iii ) bis(cyclopentadienyl) hypersilanide complex [U(Cp′′) 2 {Si(SiMe 3 ) 3 }] (Cp′′ = {C 5 H 3 (SiMe 3 ) 2 -1,3}), together with isostructural lanthanide and group 4 M( iii ) homologues, in order to meaningfully compare metal-silicon bonding between early d- and f-block metals. All complexes were characterised by a combination of NMR, EPR, UV-vis-NIR and ATR-IR spectroscopies, single crystal X-ray diffraction, SQUID magnetometry, elemental analysis and ab initio calculations. We find that for the [M(Cp′′) 2 {Si(SiMe 3 ) 3 }] (M = Ti, Zr, La, Ce, Nd, U) series the unique anisotropy axis is conserved tangential to ; this is governed by the hypersilanide ligand for the d-block complexes to give easy plane anisotropy, whereas the easy axis is fixed by the two Cp′′ ligands in f-block congeners. This divergence is attributed to hypersilanide acting as a strong σ-donor and weak π-acceptor with the d-block metals, whilst f-block metals show predominantly electrostatic bonding with weaker π-components. We make qualitative comparisons on the strength of covalency to derive the ordering Zr > Ti > U > Nd Ce La in these complexes, using a combination of analytical techniques. The greater covalency of 5f 3 U( iii ) vs. 4f 3 Nd( iii ) is found by comparison of their EPR and electronic absorption spectra and magnetic measurements, with calculations indicating that uranium 5f orbitals have weak π-bonding interactions with both the silanide and Cp′′ ligands, in addition to weak δ-antibonding with Cp′′. We report an isostructural series of early metal complexes containing cyclopentadienyl (Cp)-supported M-Si bonds. Differences in the extent of metal-ligand covalency causes a magnetic anisotropy switch between d- and f-block metals.