Density-functional computation of ⁹³Nb NMR chemical shifts.

93Nb chemical shifts of NbX6 (X = Cl, F, CO), NbXCl4 (X = O, S), Nb2(OMe)10, Cp2Nb(κ2-BH4), (CpNb)2(µ-B2H6)2, CpNb(CO)4, and Cp2NbH3 are computed at the GIAO (gauge-including atomic orbitals)-, BPW91- and B3LYP-, and CSGT (continuous set of gauge transformations)-CAM-B3LYP, -ωB97, and -ωB97X levels, using BP86-optimized or experimental (X-ray) geometries. Experimental chemical shifts are best reproduced at the GIAO-BPW91 level when δ(93Nb) values of inorganic complexes are referenced directly relative to NbCl6 and those of organometallic species are first calculated relative to Nb(CO)6. An inadvertent error in the reported δ(93Nb) values of cyclopentadiene borane complexes (H. Brunner et al., J. Organomet. Chem.1992, 436, 313) is corrected. Trends in the observed 93Nb NMR linewidths for anionic niobates Nb(CO)5, Nb(CO)5H, and Nb(CO)5(NH3) are rationalized in terms of computed electric field gradients at the metal.