N-glycoside complexes of Nickel(II); Probing carbohydratetransition 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) ₂2H₂O 1 and [Ni(en-l-ara)₂](ClO ₄)₂2H₂O 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 dd 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 -C₂-helical configuration around the metal centre. The arabinose ring adopts the rare -¹C₄ chair conformation and the carbohydratechelate ring conformation is.