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)₄Cl₂]Cl·6H₂O, mer-[Co(py)₃Cl₃] and mer-[Co(py)₃(CO₃)Cl] were studied by UV-Vis, far-IR and ¹H, ¹³C, ¹⁵N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of ¹H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands. ¹³C nuclei were deshielded upon Co(III) coordination, while ¹⁵N 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). ¹³C and ¹⁵N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)₄Cl₂]Cl·6H₂O and mer-[Co(py)₃Cl₃], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)₄Cl₂]Cl → mer-[Co(py)₃Cl₃] + py reaction was monitored by ¹H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)₃Cl₃] preparation.      

Cyclovoltammetric and spectroscopic characterization of optically active cobalt(II) and copper(II) complexes with the Schiff base derived from (N,N′)-(1R,2R)-(−)-cyclohexylenediamine and 2-hydroxyacetophenone

The Schiff base prepared by reacting (–)-(1R,2R)-1,2-cyclohexanediamine with 2-hydroxyacetophenone was used as a ligand for Co^II and Cu^II. The coordination compounds were studied by u.v.–vis. absorption and by circular dichroism (c.d.) spectroscopy in solution. The complexes are four-coordinated in a slightly distorted square planar symmetry. The distortion from planarity is a main factor influencing the chiral surroundings of the metal ion. The d–d and c.t. transitions are consistent with the observed distortion, which arises from intramolecular interactions between the methyl groups attached to the Schiff base imine carbon and hydrogen atoms of the cyclohexane ring. The electrochemical properties of the Co^II and Cu^II complexes were observed in MeCN but investigations revealed weaker oxygen activation than of Co^II analogue with salicylaldehyde. The Cu^II complex is reduced in H₂O to Cu^I which disproportionates to Cu^II and Cu⁰.     

Optically active cobalt(II) and copper(II) complexes with tetradentate Schiff bases derived from (N,N′)-(1R,2R)-(−)-cyclohexylenediamine and salicylaldehyde, 2-hydroxynaphthaldehyde or 2-hydroxyacetophenone

The Schiff bases obtained from (1R,2R)-1,2-cyclohexanediamine and salicylaldehyde, 2-hydroxynaphthaldehyde or 2-hydroxyacetophenone have been used as ligands for copper(II) and cobalt(II). The coordination compounds have been studied by u.v.–vis. absorption and by circular dichroism spectroscopy in solution. The complexes are four-coordinated in a slightly distorted square-planar geometry. The distortion from planarity is a main factor influencing the chiral surroundings of the metal ion. The d–d and c.t. transitions are consistent with the observed distortion which arises from intramolecular interactions between substituents at the Schiff base imine carbon and hydrogens of the cyclohexylene ring. Distortion is more pronounced in Co^II than in Cu^II complexes. In the Schiff base chelates the cyclohexane ring is trans-fused to the central chelate ring, forming a rigid structure in which the chelate ring is locked stereospecifically in the conformation.