H-1-NMR STUDY OF PYRIDINE-TYPE LIGANDS COORDINATED TO THE PARAMAGNETIC [NI-3(PW9O34)(2)](12-) ANION

H-1 NMR spectra of pyridine, alpha-, beta-, and gamma-picoline coordin ated to the paramagnetic heteropolyanion [Ni-3(PW9O34)(2)](12-) (P2Ni3 ) are reported. NMR lines are assigned to [Ni-3(ptl)(n)(PW9O34)(2)](12 -) (n=1, 2 or 3; ptl=pyridine-type ligand) on the basis of their [P2Ni 3]/[ptl] dependence. The formation constants for gamma-picoline comple xes at 25 degrees C are K-1=80, K-2=610, and K-3=190 L mol(-1). The mo nopicoline complex has greater affinity for gamma-picoline than P2Ni3. A degradation product, [Ni-2(WO2)(PW9O34)(2)](12-), was also identifi ed 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 sigma-electron delocalization.