Complexation induced chemical shifts

The NMR investigation is presented in two parts the first covers i3C 99rpc ancj i5N studies where protonations of the dioxo complexes induce chemical shift changes but where line-broadening effects due to exchange are not observed. The second part covers 170 studies which produce more complicated spectra due to protonation and simultaneous exchange with bulk water. 

Fig. 4 Continuous variation plots for (a) ( )-CL//3-CD and (b) ( )-CL/HDAS-/3-CD complexes. The complexation-induced chemical shifts of aromatic protons were used for the construction of Job s plots in the case of ( )-CL//3-CD complex and the protons of ten-butyl moiety in the case of ( )-CL/HDAS-/3-CD complex. (Reproduced with permission from Ref. 65.)... 

The complex was characterized by thermogravimetric analysis (TGA) and solid state NMR. Low temperature X-ray crystal structure analysis of the compound indicated the inclusion of CS2 in the calixarene cavity to be highly symmetrically oriented directly on the C4 axis of the host. The CP/MAS experiment showed significant complexation-induced chemical shift (CIS=... 

CIS=complex-induced chemical shift=A8=6(complex)-8 (free guest). 

GIAO-DFT calculated and experimentally derived complexation-induced chemical shifts of calix[4]arene-solvent inclusion complexes, A. C. Backes, J. Schatz and H. U. Siehl, J. Chem. Soc., Perkin Trans. 2, 2002, 484. 

This NMR technique has been applied to a series of alkanediammonium ions, and the results (induced shifts of proton resonances) are summarized in Fig. 2. It may be seen that the shielding region extends for approximately 4.5 methylene units, or 6 A, which coincidentally is the interatomic distance axially spanning the cavity of cucurbituril. Similar induced chemical shift effects are found in CNMR spectra, and UV spectral perturbations are noted upon encapsulation of certain aromatic-ring bearing ammonium ions (particularly 4-methyl-benzylamine). Conclusive evidence for internal complexation with cucurbituril has been secured by crystallography [3]. 

Ethylene-W -diacctic acid (EDDA) and similar ligands form well-characterized octahedral complexes in aqueous solution where C-13 coordination-induced chemical shifts, 51V and nO NMR spectroscopy has been utilized in their study [40], X-ray crystal structure analysis showed formation of the (3-cis isomer, whereas NMR studies clearly showed two complexes in solution. The nO NMR studies [40] were fully consistent with retention of octahedral coordination by both of the isomers, and these two compounds were assigned as the a- and p-cis isomers, which are depicted in Scheme 4.11. The study of these isomers in water (a-cis, -514 ppm 13-... 

Chiral complexes have been prepared174 and tested for their utility in inducing chemical shifts between corresponding resonances of enantiomeric species. The complex (10) was the most effective for resolution of enantiotopic resonances, but while (11) and (12) were less effective, they were more easily synthesized. 

Kinetics of adduct formation between Ni complexes of the type referred to under interactions via donor atom and Eu(fod)3 were studied which showed changes in line-widths of the proton resonances in addition to induced chemical shifts. From the concentration dependence of the chemical shifts and line-width, the lifetime of the adduct and kf (formation rate constant), kT (revere rate constant) can be determined using the relationship... 

Two dioxa-trithia- and two trioxa-dithiacrown ethers connected to one calix[4]arene unit have been prepared by Sim et al. <2002BKC879>. Macrocycles 165 and 166 have an Ag+ selectivity in metal picrate extraction, but the percentage extractability was lower than those of corresponding monocrown derivatives 155 and 156 due not only to electrostatic repulsion between the two metal ions, but also to an induced conformation change that does not favor binding of the second metal. The extractability is consistent with the result of silver ion-induced chemical shift change upon the complexation. 

The five-coordinate complexes of type 421 possess a rigid structure, which is retained in solution as indicated by comparing the Sn NMR in solution and in the solid state . For 421a-c, isotope-induced chemical shifts A ( C( Sn) were determined for the first time for five-coordinate tin nuclei at natural abundance of A positive sign of 1 Ai2/i3c(ii Sn) was found, in contrast with most tetracoordinate organotin compounds. 

Alkali metal NMR in conjunction withcryptand complexation finally led to the sensational discovery of alkali metal anions by Dye and coworkers. (14) The complexing power of the cryptands is such that the ionophore is capable of extracting the cation from alkali metal in solutions of THF, methylamine, and ethylamine. The electron left behind is conclusively proved to form the anion M (M = Na, Rb, Cs) leading to a separate resonance line at low temperature. The corresponding shielding is close to the theoretical value computed for the metal anion. A most striking feature of this resonance is its solvent independence. The absence of solvent-induced chemical shifts for Na ... 

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