Adenine complexes with divalent 3d metal chlorides

Upon refluxing 2:1 mixtures of adenine (adH) and divalent 3d metal chloride hydrates in a 7:3 (v/v) mixture of ethanol-triethyl orthoformate for several days, partial substitution of ad^? for Cl^? ligands occurs, and solid complexes of the M(ad)Cl· 2H₂0 (M = Mn, Zn), Fe₂(ad)(adH)₂Cl₃·2H₂O, M(ad)- (adH)Cl·H₂O (M = Co, Cu) and Ni₂(ad)₃Cl·6H₂O types are eventually isolated [1]. It is probably of interest that during analogous previous synthetic work, involving interaction of ligand and salt in refluxing ethanol, no substitution reactions between Cl^? and ad^? took place, and MCl₂ adducts with neutral adH were reportedly obtained. Characterization studies suggest that the new complexes reported are linear chainlike polymeric species, involving single adenine bridges between adjacent M²⁺ ions. Terminal chloro, adenine and aqua ligands complete the coordination around each metal ion. The new Ni²⁺ complex is hexacoordinated, whilst the rest of the complexes are pentacoordinated. Most likely binding sites are considered to be N(9) for terminal unidentate and N(7), N(9) for bridging bidentate adenine [1].