A solid-state Mn-55 NMR spectroscopy and DFT investigation of manganese pentacarbonyl compounds

Kirk W. Feindel, Kristopher J. Ooms, Roderick E. Wasylishen

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Central transition Mn-55 NMR spectra of several solid manganese pentacarbonyls acquired at magnetic field strengths of 11.75, 17.63, and 21.1 T are presented. The variety of distinct powder sample lineshapes obtained demonstrates the sensitivity of solid-state Mn-55 NMR to the local bonding environment, including the presence of crystallographically unique Mn sites, and facilitates the extraction of the Mn chemical shift anisotropies, CSAs, and the nuclear quadrupolar parameters. The compounds investigated include molecules with approximate C-4v symmetry, LMn(CO)(5) (L = Cl, Br, I, HgMn(CO)(5), CH3) and several molecules of lower symmetry (L = PhCH2, Ph3-nClnSn (n = 1, 2, 3)). For these compounds, the Mn CSA values range from <100 ppm for Cl3SnMn(CO)(5) to 1260 ppm for ClMn(CO)(5). At 21.1 T the Mn-55 NMR lineshapes are appreciably influenced by the Mn CSA despite the presence of significant Mn-55 quadrupolar coupling constants that range from 8.0 MHz for Cl3SnMn(CO)(5) to 35.0 MHz for CH3Mn(CO)(5). The breadth of the solid-state Mn-55 NMR spectra of the pentacarbonyl halides is dominated by the CSA at all three applied magnetic fields. DFT calculations of the Mn magnetic shielding tensors reproduce the experimental trends and the magnitude of the CSA is qualitatively rationalized using a molecular orbital, MO, interpretation based on Ramsey's theory of magnetic shielding. In addition to the energy differences between symmetry-appropriate occupied and virtual MOs, the d-character of the Mn MOs is important for determining the paramagnetic shielding contribution to the principal components of the magnetic shielding tensor.

Original languageEnglish
Pages (from-to)1226-1238
Number of pages13
JournalPhysical Chemistry Chemical Physics
Issue number10
Publication statusPublished - 2007
Externally publishedYes


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