Structures and characterization of m-nisoldipine polymorphs

Abstract

m-Nisoldipine, a dihydropyridine calcium ion antagonist, first synthesized in the School of Pharmaceutical Sciences, Hebei Medical University, exhibits two polymorphs A and B with different colors and morphologies. The single-crystal X-ray structure analysis reveals that polymorph A crystallizes in a monoclinic P2₁/c space group with a = 9.3045(2) Å, b = 16.5991(5) Å, c = 13.0018(3) Å, β = 91.539(2)° and Z = 4, while B crystallizes in a triclinic space group of P with a = 7.4965(2) Å, b = 11.4692(4) Å, c = 12.3648(5) Å, α = 68.093(2)°, β = 88.655(2)°, γ = 81.853(2)° and Z = 2. The m-nisoldipine molecules are connected through N–H⋯O hydrogen bonds between the carbonyl group and the amine group to form either a wavy chain for A or a linear chain for B. The two polymorphs show distinct physicochemical properties as characterized by IR, Raman, DSC and terahertz pulse spectroscopy. DFT theoretical calculations are also used to simulate the terahertz spectroscopy of the two polymorphs.