Resumen de NMR Spectroscopy in an Advanced Inorganic Lab: Structural Analysis of Diamagnetic and Paramagnetic Ni(II) Schiff Base Complexes
In a two-step synthesis starting with Ni(CH3COO)2·4H2O and salicylaldehyde, students prepare N-ethyl and N-isopropyl Ni(II) Schiff base (imine) complexes. After isolation and recrystallization, the products are characterized by room-temperature magnetic susceptibility measurements, FTIR spectroscopy, and 1H, 13C{1H}, and 13C DEPT-135 or 13C APT NMR spectroscopy. The results are analyzed by considering the steric requirements of the ethyl and isopropyl groups and the subsequent effect on the preferred geometries, either the diamagnetic square-planar geometry, as expected for a Ni(II) d8 complex, or the paramagnetic tetrahedral geometry. Students are challenged to explain why the spectra for these similar complexes are so different and what this difference reveals about steric requirements in determining geometry.
