Analysis of supramolecular interactions in alendroniate alkali metal salts: synthesis, structure, and properties of novel sodium alendronate polymorph

Abstract

A new polymorph of anhydrous sodium alendronate, C4H12NO7P2Na, has been synthesized and characterized by single crystal X-ray diffraction as well as infrared spectroscopy and thermal analysis. The title compound crystallizes in the monoclinic P21/c space group. Asymmetric unit consists of one alendronic anion and one sodium cation. An interplay of classical strong O-H…O, N-H…O and non-classical weak C-H…O hydrogen bonds creates 3D framework in the crystal. Contrary to previously reported sodium alendronate salts, in which Na+ cation is surrounded by six-coordinated sphere, in compound (1), the Na+ cation is five-coordinated in a distorted trigonal-bipyramidal geometry. In order to provide a detailed investigation of the molecular arrangement in view of intermolecular interactions, the title compound was compared with alendronic acid and other known alkali metal alendronate salts, retrieved from the Cambridge Crystal Structure Database. The intercontacts were qualitatively and quantitatively compared using Hirshfeld surface analysis. It highlights that strong O…H/H…O and subtle H…H contacts play an influential role in the total surface area. The Me+…H/H…Me+ and Me+…O/O…Me+ contacts are meaningful as well. These evidently simple systems show a diverse complexity. Moreover, the powder X-ray diffraction, DSC, thermogravimetry/derivative thermogravimetry, and FT-IR results are also reported.