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An Unusual Carbonyl Chemical Shift in a Carbonylhexairidium Cluster: A Combined Solid‐State NMR and DFT Approach
Author(s) -
Chierotti Michele R.,
Garlaschelli Luigi,
Gobetto Roberto,
Nervi Carlo,
Peli Giulia,
Sironi Annalisa,
Della Pergola Roberto
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200601040
Subject(s) - chemistry , chemical shift , nuclear magnetic resonance spectroscopy , crystallography , solid state nuclear magnetic resonance , ligand (biochemistry) , carbon 13 nmr , density functional theory , computational chemistry , stereochemistry , nuclear magnetic resonance , biochemistry , physics , receptor
The 13 C NMR spectrum of TMBA 2 [Ir 6 (CO) 15 ] [TMBA =(CH 3 ) 3 N(CH 2 C 6 H 5 )] shows, at low temperatures, an unprecedented μ 2 ‐bridging carbonyl low‐frequency shift, with the resonances of the terminal μ 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 13 C MAS data of Ir 6 (CO) 16 where μ 3 ‐CO ligands are present. Further evidence for the assignment and for the peculiar chemical shift value of bridging carbonyl ligands in TMBA 2 [Ir 6 (CO) 15 ] has been obtained by the DFT calculation of the NMR 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 ( δ = 26.6 ppm) to the μ 2 ‐bridging CO ligand 13 C chemical shifts accounts for the position of the experimentally observed resonance.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)