1H, 13C, 15N NMR and 13C, 15N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py→Cl substitution in trans-[Co(py)4Cl2]Cl, and a new synthesis of mer-[Co(py)3Cl3]

trans-[Co(py)(4)Cl-2]Cl center dot 6H(2)O, mer-[Co(py)(3)Cl-3] and mer-[Co(py)(3)(CO3)Cl] were studied by UV-Vis, far-IR and H-1, C-13, N-15 NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of H-1 NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands. C-13 nuclei were deshielded upon Co(III) coordination, while N-15 NMR studies exhibited ca. 85-110 ppm shielding effects (ca. 15-25 ppm more expressed for nitrogens trans to N than trans to Cl or O). C-13 and N-15 CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)(4)Cl-2]Cl center dot 6H(2)O and mer-[Co(py)(3)Cl-3], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)(4)Cl-2]Cl -> mer-[Co(py)(3)Cl-3] + py reaction was monitored by H-1 NMR and UV-Vis. This process of py -> Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)(3)Cl-3] preparation.