The C-13 NMR spectrum of TMBA(2)[Ir-6(CO)151 [TMBA = (CH3)(3)N(CH2C6H5)] shows, at low temperatures, an unprecedented mu(2)-bridging carbonyl low-frequency shift, with the resonances of the terminal mu(1)-carbonyl ligands placed at higher frequencies. The chemical shift tensors and the shielding anisotropies of the carbonyl ligands, obtained from solid-state NMR analysis, allow us to determine the nature of the M-CO interaction. The results have been compared with the C-13 MAS data of lr6(CO)16 where mu(3)-CO ligands are present. Further evidence for the assignment and for the peculiar chernical shift value of bridging carbonyl ligands in TMBA(2)[Ir-6(CO)15] has been obtained by the DFT calculation of the NNIR parameters. The scalar and spin-orbit (SO) relativistic two-component zero-order regular approximation (ZORA) methods were employed in the geometry optimization and NMR chemical shift calculations, respectively. The large SO contribution (delta = 26.6 ppm) to the mu(2)-bridging CO ligand C-13 chemical shifts accounts for the position of the experimentally observed resonance. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).

An unusual carbonyl chemical shift in a carbonylhexairidium cluster: A combined solid-state NMR and DFT approach

CHIEROTTI, Michele Remo;GOBETTO, Roberto;NERVI, Carlo;
2007

Abstract

The C-13 NMR spectrum of TMBA(2)[Ir-6(CO)151 [TMBA = (CH3)(3)N(CH2C6H5)] shows, at low temperatures, an unprecedented mu(2)-bridging carbonyl low-frequency shift, with the resonances of the terminal mu(1)-carbonyl ligands placed at higher frequencies. The chemical shift tensors and the shielding anisotropies of the carbonyl ligands, obtained from solid-state NMR analysis, allow us to determine the nature of the M-CO interaction. The results have been compared with the C-13 MAS data of lr6(CO)16 where mu(3)-CO ligands are present. Further evidence for the assignment and for the peculiar chernical shift value of bridging carbonyl ligands in TMBA(2)[Ir-6(CO)15] has been obtained by the DFT calculation of the NNIR parameters. The scalar and spin-orbit (SO) relativistic two-component zero-order regular approximation (ZORA) methods were employed in the geometry optimization and NMR chemical shift calculations, respectively. The large SO contribution (delta = 26.6 ppm) to the mu(2)-bridging CO ligand C-13 chemical shifts accounts for the position of the experimentally observed resonance. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).
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DENSITY-FUNCTIONAL CALCULATIONS; EFFECTIVE CORE POTENTIALS; ORDER REGULAR APPROXIMATION; NUCLEAR-MAGNETIC-RESONANCE; SPIN COUPLING-CONSTANTS; MOLECULAR CALCULATIONS; IRIDIUM CARBONYL; MAGIC-ANGLE; IR4(CO)12; SPECTROSCOPY
M. R. Chierotti; L. Garlaschelli; R. Gobetto; C. Nervi; G. Peli; A. Sironi; R. Della Pergola
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2318/44633
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