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Schiff bases obtained from (1R,2R)-(−)-cyclohexanediamine and 5-chloro- (1) or 5-bromosalicylaldehyde (2) are used as ligands for Zn(II) resulting in [(1R,2R)-cyclohexylenebis(5-chlorosalicylideneiminato)]zinc(II) (1a) and (1R,2R)-[cyclohexylenebis-(5-bromosalicylideneiminato)]zinc(II) (2a). In the presence of pyridine, 1a and 2a turned out into (1R,2R)-[cyclohexylenebis(5-chlorosalicylideneiminato)pyridine]zinc(II) (1b) and (1R,2R)-[cyclohexylenebis(5-bromosalicylideneiminato)pyridine]zinc(II) (2b). Coordination sphere of Zn(II) atoms in both pyridine adducts is a slightly distorted square pyramid, with N2O2 chromophore units and axially bonded pyridine as it is evident from single crystal X-ray analyzes of 1b and 2b. The asymmetric unit of 1b and 2b contains two molecules of complexes. The observed distances of Zn–O in both molecules indicate the rigidity of the tetradentate ligand as a main factor influencing the geometry of coordination sphere. Obtained complexes were characterized by 1H NMR in solution and 13C CP MAS NMR. NOE differential experiments revealed significant steric interactions between C(6)–H in the phenyl ring, cyclohexyl C(1)–H and imine hydrogen. Significant coordination shifts of carbons in the closest proximity to the coordination center were noted as well. |
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