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Mn-55 NMR; density functional calculations; chemical shift computations; electric field gradients; NMR line widths
Abstract:
Gradient-corrected (GGA) and hybrid variants of density functional theory are used to compute geometries and Mn-55 chemical shifts of MnO4-, Mn(CO)(6)(+), Mn-2(CO)(10), Mn(CO)(5)X [X=H, Cl, C(O)Me], Mn(CO)(5)(-), Mn(NO)(3)(CO), and Mn(C5H5)L-x [L-x = (CO)(3), C6H6, C7H8]. For this set of compounds, substituent effects on delta(Mn-55) are significantly underestimated with the pure GGA functional BPW91 and are well described with hybrid functionals such as mPW1PW91 and, in particular, B3LYP. The computed data provide evidence for solvent and counterion effects on delta(Mn-55) of MnO4- and Mn(CO)(6)(+), respectively. The latter, in the presence of Cl-, may be described as highly fluxional Mn(CO)(5)C(O)Cl. Electric field gradients computed with the B3LYP functional can be used for a qualitative rationalization of observed trends in 55 Mn NMR line widths. Electronic supplementary material to this paper can be obtained by using the Springer INK server located at http://dx.dol.org/10.1007/s00214-002-0338-x.
