Crystallographic and thermal investigation of coordination and ionic compounds of metal halides and 4-aminobenzoic acid and related molecules

Abstract

In organic-inorganic hybrid compounds an organic and an inorganic component are combined to form either a coordination or an ionic material. Relevant to the current study are hybrid materials composed of an organic part that contains one or more functional groups, for example amine, amide or carboxylic acid functional groups, and a metal halide inorganic portion. These functional materials display a range of interesting and desired properties, as evidenced from numerous literature reports on their properties. In order to utilise these properties in applications, a detailed understanding of the way that the crystal structure influences the properties of a material is required. However, before this step can be achieved, it is necessary to obtain information on the structural trends of the materials, and to use the approach of crystal engineering to identify robust supramolecular synthons that may afford structural control and prediction. The aim of the current study was to investigate the synthesis and crystal structures of hybrid materials, both ionic and coordination, composed of divalent transition metal halides and the organic components 4-aminobenzoic acid, 4-aminobenzamide and isonicotinic acid, and to identify the structural trends and crystal engineering synthons displayed by these materials. A secondary objective was the preliminary identification of properties exhibited by selected materials, in order to decide on the suitability of the materials for detailed future property investigations. Part of the work describes the investigation of the structural characteristics of coordination materials prepared by the combination of the organic and inorganic components. Five novel crystal structures of coordination materials were determined, and these are compared with six related coordination structures reported in the literature. Two of the novel structures display interesting one-dimensional coordination polymers, one of which has never been reported previously in the literature. The molecular and structural characteristics of both the novel and the literature coordination structures are presented in detail, and this discussion includes a description of the coordination geometry, the molecular geometry, packing trends, hydrogen bonding interactions and aromatic interactions. A comparison study across the three families of organic components in which the structural trends, hydrogen bonding interactions, aromatic interactions, ligand geometry and coordination modes are compared, is included. The results of the synthesis of the coordination materials by means of a mechanochemical method are presented, and the products afforded by this method are compared with those prepared via solution crystallisation. Finally, the results of preliminary studies of the thermal and electronic propertries of the materials are presented and interpreted. The combination of the hybrid components as cations and anions to form ionic materials yielded nine novel structures, and these were compared with five related ionic structures reported in the literature. The novel structures include three polar structures that contain the 4-ammoniumbenzamide cation, and to our knowledge no structures containing this cation have ever been reported in the literature, hence a significant contribution to the structural knowledge of perhalometallate salts of 4-ammoniumbenzamide is made by this study. In addition two novel structures display interesting one-dimensional and two-dimensional polymeric anions, respectively, are reported. The discussion of the novel and literature ionic structures includes a description of the molecular geometry of each of the components, the identification of packing trends, and an analysis of the hydrogen bonding and aromatic interactions occurring in the structures. The structures of all three families of organic components are compared, and trends in structural type, anion geometry, water inclusion, hydrogen bonding and functional group recognition are presented. In addition, a detailed analysis of robust crystal engineering synthons occurring in these structures is presented. Lastly the results of preliminary property investigations of the thermal and electronic properties of the materials are presented and discussed