초록
1H NMR spectra of pyridine, α-, β-, and γ-picoline coordinated to the paramagnetic heteropolyanion [Ni3(PW9O34)2]12- (P2Ni3) are reported. NMR lines are assigned to [Ni3(ptl)n(PW9O34)2]12- (n=1, 2 or 3; ptl=pyridine-type ligand) on the basis of their [P2Ni3]/[ptl] dependence. The formation constants for γ-picoline complexes at 25 ℃ are K1=80, K2=610, and K3=190 L mol-1. The monopicoline complex has greater affinity for γ-picoline than P2Ni3. A degradation product, [Ni2(WO2)(PW9O34)2]12-, was also identified at low pH by measuring the NMR spectrum of pyridine coordinated to it. The isotropic NMR shifts come mainly from the contact interaction due to σ-electron delocalization.