Ligand chemical shifts

While DFT may or may not be more accurate than MP2 for absolute shielding calculations is debatable, the strength of the DFT method in calculations of shieldings is in the ability of DFT to provide a consistent picture over a wide range of chemical systems, since calculations can be done at a very modest computational cost compared to MP2. Among the successes of the method is in ligand chemical shifts in transition metal complexes. For example, 13C, 170,31P and H chemical shifts for oxo (12,14,15), carbonyl (16-19), interstitial carbide (20), phosphine (21,22), hydride (23), and other ligands have been successfully reproduced to within tens of ppm in... 

Schreckenbach et al. [92-94] investigated ligand chemical shifts in uranium compounds (ZORA DFT). Nonhybrid ZORA DFT computations were not able to reproduce the trends for 19F shifts of UF6 C1 though the correct magnitudes between 750 and 790 ppm were obtained. Spin-orbit effects were found to be of minor importance for the 19 F shifts. ZORA DFT computations were successfully... 

Bisalkyne d4 monomers, with N = 3 by symmetry, exhibit proton and carbon chemical shifts at higher fields than those of monoalkynes with N = 4. The proton chemical shift of 10.45 ppm for Mo(PhC=CH)2-(S2CNEt2)2 (52) falls nicely between the four-electron donor Mo(CO)-(PhC=CH)(S2CNEt2)2 case (12.6 ppm) and the two-electron donor (7r-C5H5)2Mo(HC=CH) case [7.68 ppm (Table II)]. Additional data for bisalkyne complexes, including pyrrole-N-carbodithioate derivatives, support a correlation of H chemical shifts with alkyne ttj donation, with three-electron donors typically near 10.0 0.5 ppm. Similar H values are found for cyclopentadienyl bisalkyne complexes with terminal alkyne ligands. Chemical shifts between 8.5 and 10.5 ppm characterize all the neutral and cationic bisalkynes listed in Table V except for [CpMo-(RC=CH)2(MeCN)]+ where one isomer has S near 11 ppm for the acetylenic proton (72). 

The P coordination chemical shifts for both the L2PtX2 and L3PtX2 complexes (Table 10) are related to the free ligand chemical shifts in a fashion analogous to those found for the palladium complexes. Likewise, for platinum phosphole complexes the coordination chemical shifts are less than those found for similar platinum phosphine complexes also indicating some platinum phosphole back donation. 

Table 10 <5 V) ligand chemical shifts (ppm) and coordination shifts (ppm) in Cr, Mo, and W complexes containing P-donor molecules...

Table 6. Ligand Chemical Shifts (ppm) and Coordination Shifts (ppm)"" in Cr, Mo, W, and Pt Complexes...

In principle, any type of NMR spectroscopy may be used to detect the chemical shift changes upon ligand binding. For very small proteins, 1D-NMR might even... 

P]0 is the total molar concentration of the protein and [L]0 is the total molar concentration of ligand. X is the molar concentration of the bound species determined according to the chemical shift change ... 

---