NMR investigation of bis(2,3-alkanedione dioximato)-bis(pyridine)cobalt(III) iodide complexes: 1H and 13C NMR spectra and 13C spin-lattice relaxation time measurements

Abstract

The complexes of trans-[Co(III)(R,CH 3-dioxH) 2(py) 2]I† (R = CH 3, C 2H 5, n-C 3H 7 and n-C 4H 9) were investigated in solution by 1H and 13C NMR spectra and 13C spin-lattice relaxation time measurements. The 1H and 13C-resonances of the R = C 2H 5, n-C 3H 7 and n-C 4H 9) groups were shifted to higher field than those of the free ligands by the complexation; it was attributable to the ring current shielding due to the axial pyridine ligands of the complexes. 13C spin-lattice relaxation times were interpreted as due to movement of the axial pyridine ligands as if they twist around the CoN (pyridine nitrogen) bond axis and the above R groups were moving segmentally. These segmental movements allowed the R groups to approach closely toward the axial pyridine ring plane to experience the ring current shielding.