H-1-NMR STUDY OF AZIRIDINE DERIVATIVES COORDINATED TO THE PARAMAGNETIC UNDECATUNGSTOCOBALTO(II)SILICATE AND UNDECATUNGSTONICKELO(II)SILICATE ANIONS

H-1 NMR spectra of D2O solutions containing 2,2-dimethylaziridine (1) or 2-methylaziridine (2) and [SiW11-(CoO39)-O-II](6-) (SiW11-Co) or [( SiW11NiO39)-O-II](6-) (SiW11Ni) exhibit separate signals for the free ligand and the complex, indicating that the ligand exchange is slow on the NMR time scale. Identified are two linkage isomers with the methy l group of 2 at trans or cis position with respect to the metal. The i sotropic shifts of 1 and 2 coordinated to SiW11Ni originate mainly fro m the contact shifts, and they agree reasonably with the relative valu es reported for similar ligands coordinated to bis(2,4-pentanedionato) nickel(II). The isotropic shifts for the SiW11Co complexes were separa ted into contact and pseudocontact contributions. The pseudocontact sh ifts show that ((chi(parallel to)-chi(perpendicular to)) is positive, while that for the SiW11Co complexes of pyridine derivatives is negati ve. This result indicates that the ordering of d(xy) and d(xz) d(yz) o rbitals in SiW11Co complexes can be reversed by ligands.