Protonated Adenine and Cytosine Ribbons Stabilized by Dipicolinato Metal Frameworks

Abstract

Stabilization of protonated adenine (ade) and cytosine (cyt) ribbons through hydrogen bonding interactions in a series of bis-dipicolinato metal(II) (metal = manganese, copper, zinc at +2 oxidation state) complexes are studied. Protonated assemblies of adenine as infinite chains in [1<i>H</i>, 9<i>H</i>-ade][3<i>H</i>, 7<i>H</i>-ade][MnL₂]·3H₂O and [1<i>H</i>, 9<i>H</i>-ade][3<i>H</i>, 7<i>H</i>-ade][CuL₂]·3H₂O (L = dipicolinato anion) are structurally characterized. The one-dimensional (1D) zigzag ribbons are comprised of alternate nonequivalent [1<i>H</i>, 9<i>H</i>-ade] and [3<i>H</i>, 7<i>H</i>-ade] adeninium cations. Protonated cytosinium cation aggregates with neutral cytosine to form pairs, and such pairs form tetrameric units with a length of 33.45 Å in the lattice of the seven coordinated manganese(II) complex [1<i>H</i>, 3<i>H</i>-cyt]₂[MnL₂(H₂O)]·2cyt·6H₂O. The discrete cations of cytosine stabilized by electrostatic, hydrogen bond, and stacking interactions within the inorganic layers build the closely packed organic−inorganic hybrid materials in the crystal lattice of the complexes [1<i>H</i>, 3<i>H</i>-cyt]₂[CuL₂]·5H₂O and [1<i>H</i>, 3<i>H</i>-cyt]₂[ZnL₂]·5H₂O.