Theoretical Studies on the Hydrogen-bonding and π-Stacking Interactions in the m-Nisoldipine Polymorphism Dimers

The intermolecular interactions in the dimers of m-nisoldipine polymorphism were studied by B3LYP calculations and quantum theory of ＂atoms in molecules＂ （QTAIM） studies. Four geometries of dimers were obtained： dimer I （a：dimer, O…H--N）, dimer II （b-dimer, O…H--N）, dimer III （b-dimer, n-stacking-c）, and dimer IV （b-dimer, n-stacking-p）. The interaction energies of the four dimers are along the sequence of II〉I〉III〉IV. The intermolecular distance of the interactions follows the order： I （O…H--N）〈II （O…H--N）, and III （n-stacking）〈 IV （n-stacking）. Both the O…H--N hydrogen-bonding and n-stacking interactions belong to weak non-covalent interactions. The O…H--N hydrogen-bonding interactions with more electrostatic characters are stronger than the n-stacking interactions. The strength of the weak interactions decreases in the order： I〉II〉III〉IV, and the electrostatic character decreases along the sequence： I〉II〉III〉IV.