N-glycoside complexes of nickel(II) : probing carbohydrateââ"šÂ¬Ã¢â‚¬Å“transition metal interactions

Nickel(ii) complexes prepared from d- and l-arabinose (d-ara and l-ara) and 1,2-diaminoethane (en), [Ni(en-d-ara)2](ClO4)2ââ"šÂ¬Ã‚¢2H2O 1 and [Ni(en-l-ara)2](ClO4)2ââ"šÂ¬Ã‚¢2H2O 2 (where en-d-ara is 1-((2-aminoethyl)amino)-1-deoxy-d-arabinose) were synthesized and characterized by absorption spectroscopy, circular dichroism (CD), and X-ray crystallography. The CD spectra of 1 and 2 in the dââ"šÂ¬Ã¢â‚¬Å“d transition region indicate a C2 chiral configuration around the metal centre. X-ray crystallography of 1 revealed that two 1-((2-aminoethyl)amino)-1-deoxy-d-arabinose ligands coordinate to the nickel atom in nearly C2 symmetry, through the C(2) hydroxy group of the arabinose moiety and two nitrogen atoms of the diamine in a meridional mode. This results in a Λ-C2-helical configuration around the metal centre. The arabinose ring adopts the rare α-1C4 chair conformation and the carbohydrateââ"šÂ¬Ã¢â‚¬Å“chelate ring conformation is δ.