1H NMR spectra of pyridine and α-, β-, and γ-picoline coordinated to the paramagnetic heteropolyanion [HmSiW9O37Cu3](10-m)- (SiW9Cu3) are reported. NMR lines are assigned to [HmSiW9O37Cu3(ptl)n] (10-m)- (n = 1, 2 or 3; m = 0, 1 or 2; ptl = pyridine-type ligands) on the basis of their pH and [SiW9Cu3]/[ptl] dependence. The isotropic NMR shifts come mainly from the contact shifts, which for some protons exceed 70% of those in analogous nickel complexes. The nuclear longitudinal relaxation times are 0.006, 0.06, and 0.1 s for α-, β-, and γ-H in pyridine coordinated to SiW9Cu3. The electronic correlation time calculated from the T1 values is in the order of 10-11 or 10-12 s, which is two or three orders of magnitude smaller than those of ordinary copper complexes. It is suggested that spin frustration causes rapid electronic relaxation in these complexes in which the three Cu2+ ions form an equilateral triangle.
ASJC Scopus subject areas
- Colloid and Surface Chemistry