Decoding hydrogen-bond patterns. The case of iminodiacetic acid

Abstract

The hydrogen-bond patterns of three polymorphs of iminodiacetic acid are evaluated and compared using a recently developed form of analysis based on graph theory. The results of the analysis are compared with several previous analyses of these structures which are noted for their hydrogen-bond complexities. Graph-set analysis provides a way of abstracting hydrogen-bond patterns as recognizable motifs which are easily compared and contrasted among related structures. It is shown that there are five hydrogen-bond motifs present in different combinations in these polymorphs. Two structures are indistinguishable on the basis of these characteristic motifs alone, and higher-order networks involving multiple hydrogen-bond types are used to define their differences. The two metastable polymorphs are shown to lack a particular cyclic pattern involving hydrogen bonds between two carboxylate and two iminium ions found only in the stable form.