Modeling the coordination chemistry of chitosan: Synthesis and characterization of a nickel(II) complex with a 2-aminoglucose Schiff-base ligand

Based on the sugar-modified Schiff-base ligand derived from salicylaldehyde and benzyl 2-deoxy-2-amino-α-d-glucopyranoside (H2salagluc) the new mixed-ligand nickel(II) complex [Ni(Hsalagluc)(tptz)]ClO4 has been synthesized (tptz = 2,4,6-tri-(2-pyridyl)-1,3,5-triazine). The X-ray crystal structure reveals a distorted octahedral geometry at the nickel(II) center with the rare 2,3-chelation of the trans-configured donor atoms of the carbohydrate backbone. Intermolecular hydrogen bonding leads to dimeric units of the complex cations. The supramolecular assembly of these units by π-stacking of the tptz coligands affords one-dimensional chains along the two fold screw axis. O–H⋯π(Ar) hydrogen bonding is observed for a methanol molecule of crystallization. Magnetic susceptibility measurements are consistent with a high-spin nickel(II) ion with a zero-field-splitting of D = −11.5 cm−1 (g = 2.311).

The first nickel(II) complex with a 2-aminoglucose Schiff-base ligand representing a monomeric chitosan model with trans-configured 2,3-chelation by the sugar backbone is reported. The complex shows extensive hydrogen bonding and π-stacking in the crystal lattice. The distorted octahedral geometry at the nickel(II) ions leads to a rather large zero-field-splitting.Figure optionsDownload as PowerPoint slide