Solid-state 25Mg QCPMG NMR of bis(cyclopentadienyl)magnesium

Application of the quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) sequence permits the first natural abundance solid-state Mg-25 NMR study of an organometallic magnesium compound, bis(cyclopentadienyl)magnesium. Analytical and numerical simulations of both static and magic-angle spinning QCPMG NMR spectra beget an axially symmetric Mg-25 electric field gradient (EFG) tensor (quadrupolar asymmetry parameter, eta(Q) = 0.0 1 (1)) with a nuclear quadrupole coupling constant of C-Q = 5.80(5) MHz. Restricted Hartree-Fock and hybrid density functional theory (B3LYP) calculations are in good agreement with experimental EFG values and predict a chemical shielding anisotropy of about 40-50ppm, which we attempt to elucidate by numerical simulations. The parameters and orientation of the Mg-25 EFG tensor are rationalized from examination of the crystal structure and molecular symmetry. The NMR properties of the cyclopentadienyl rings are examined by C-13{H-1} CPMAS NMR, RHF and hybrid-DFT (B3LYP) calculations, and simulations of the effects of chemical exchange on the C-13 powder pattern. (C) 2003 Elsevier Inc. All rights reserved.