Solid-state NMR spectroscopy is a powerful technique to determine structure and to assess bonding. In solution NMR, rapid tumbling results in an averaging of chemical shift tensors, and only the isotropic chemical shift can be measured. In rigid solids, chemical shift tensors can be measured directly. The magnitude of the chemical shift tensor relates near frontier filled and empty orbitals, which correlates electronic structure to this measurement. DFT methods model these interactions, and allows these orbitals to be “read out” to determine how various bonding and antibonding combinations contribute to the chemical shift tensor. This is invaluable when assigning the presence of weak secondary interactions in situations where X-ray crystallography provides ambiguous results. For example, we will show how the coupling of σ(Cα-Cβ) to π*(Sc…HCβ) in Cp*2ScCH2CH3 unambiguously reveals the b-agostic alkyl interaction in Cp*2ScCH2CH3. This molecule was previously studied by variable temperature solution NMR spectroscopy and diffraction methods, though these methods led to ambiguous assignments about the secondary interaction of this compound. We will also describe how this technique can be applied to the analysis of 11B NMR chemical shift tensors to describe the interactions between a metal and Z-type boryl ligands. Extensions of this method to related systems will also be discussed.

Solid-state NMR and density functional theory approaches for the elucidation of structure for inorganic complexes

2019 Fall National Meeting

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