Solid-state C-13 and Co-59 NMR spectroscopy of C-13-methylcobalt(III) complexes with amine ligands

Kristopher J. Ooms, Guy M. Bernard, Anders Kadziola, Pauli Kofod, Roderick E. Wasylishen

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    Five octahedral Co(III) cations, [trans-Co(en)(2)(X)((CH)-C-13)(3)](n+) where en = ethylenediamine, X = CN-, N-3(-), NH3, NO2- or H2O and n = 1 or 2, well as [Co(NH3)(5)(CH3)-C-13](2+), have been investigated by solid-state C-13 Co-59 NMR spectroscopy. We show that the determination of the Co-59 nuclear quadrupolar parameters both directly via Co-59 NMR and indirectly via C-13 NMR provide complementary information that is unavailable if one investigates only one nucleus. Specifically, (1)J(Co-59, C-13) and the orientation of the largest component of the EFG were determined via C-13 NMR spectroscopy, which also established the negative sign of C-Q(Co-59). Cobalt-59 NMR spectroscopy was used to characterize the cobalt magnetic shielding tensor, to verify the magnitudes of C-Q(Co-59) and to establish the value of eta(Q), which is difficult to determine indirectly. The measurements show that the EFG tensors are either axially symmetric or close to being so but there is a wide range of C-Q values, from -40 MHz for the complex with X = H2O to -105 MHz with X = CN-. The Co chemical shift tensors are approximately axially symmetric with the spans. delta(11) - delta(33), ranging from 3700 to 5600 ppm for X = H2O and CN-, respectively. The latter measurements also established the relative orientations of the Co EFG and chemical shift tensors. Density functional theory calculations of the Co-59 EFG and magnetic shielding tensors as well as of (1)J(Co-59, C-13) for the NO2- and N-3(-) complexes were undertaken. These calculations confirm the experimental observation that the sign of C-Q is negative and that the largest component of the EFG is along the Co-methyl-carbon bond.
    TidsskriftPhysical Chemistry Chemical Physics
    Udgave nummer15
    Sider (fra-til)2690-2699
    StatusUdgivet - 2009

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