The asymmetric unit of the title compound, (C4H6N3O)2[InCl5(H2O)], comprises two independent cytosinium cations and an aquapentachloridoindate anion. The InIII ion is in a slightly distorted octa­hedral coordination geometry. In the crystal, alternating layers of cations and anions are arranged along [010] and are linked via inter­molecular N—H⋯O, O—H⋯Cl and N—H⋯Cl hydrogen bonds, forming sheets parallel to (001). Additional stabilization within these sheeets is provided by weak inter­molecular C—H⋯O inter­actions.

The asymmetric unit of the title compound, (C4H12N2)3[InCl6]2·4H2O, consists of one and half independent piperazinium cations, an hexa­chloridoindate anion and two mol­ecules of water. The InIII ion is six-coordinated and forms a quasi-regular octa­hedral arrangement. In the crystal, alternating layers of cations and anions are arranged parallel to (10) and are linked with the water mol­ecules via intra- and inter­molecular N—H⋯O, O—H⋯Cl, C—H⋯O and N—H⋯Cl hydrogen bonds, forming a complex three-dimensional network. Additional stabilization within the layers is provided by weak inter­molecular C—H⋯Cl inter­actions.

The crystal structure of the title compound, C14H15N2O4 +·Cl−, can be described as being composed of layers containing both cations and anions that are staggered along [010]. Two types of the hydrogen bonds are observed, viz. cation–anion and cation–cation. The chloride anions are acceptors of the strong hydrogen bonds donated by the secondary amine and the hy­droxy groups. The packing is also stabilized by weak C—H⋯O inter­molecular hydrogen bonds. An intra­molecular N—H⋯O inter­action also occurs.

hydrogen bonds of the type C-H⋅⋅⋅O/N and weaker interactions of the type C-H⋅⋅⋅F and C-H⋅⋅⋅π are also considered to have important role in the building of a crystal lattice in the presence of strong hydrogen bonds [3]. Different altered modes of hydrogen bonds and weak interactions are known to generate a number of polymorphs of many compounds [4]. Polymorphism is a phenomenon of immense importance in pharmaceutical industry [5] and generation of new polymorphs, [5] cocrystals [6] and salts [7] of known APIs are possible using different modes of hydrogen bonds and weaker interactions. Study of polymorphism and cocrystal formation have gained momentum in recent years in the view of intellectual property rights (IPR) as well as in the enhancement of physicochemical properties of the drug molecules for their batter formulations [8]. We are interested to investigate the possibility of the formation of new polymorphs and cocrystals of a number of well-known Active Pharmaceutical Ingradients (APIs). Our recent experiments using Fluconazole, Ciprofloxacin, Lamivudine, Lamotrigine and Voriconazole revel that these APIs form new polymorphs or cocrystals or salts when crystallized in the presence of stoichimetric amount of a cocrystal former. The cocrystallization screening experiments have been performed by using both single crystal and powder X-ray diffraction techniques and solid state Raman spectroscopy. We shall highlight our recent results of these experiments and elucidate the crystal structures of new polymorphs of Fluconazole and Lamivudine, new salts of Fluconazole, Ciprofloxacin, Lamivudine and Lamotrigine and a new cocrystal of Voriconazole. Our studies indicate that the presence of a number of weak hydrogen bonds or weaker intermolecular interactions collectively can alter the mode of strong hydrogen bonds and generate new polymorphs, cocrystals and salts of the known APIs.

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