Polymorphs and salts of 4-nitro-N-(quinolin-8-yl)benzamide

Three polymorphs (I-III) of 4-nitro-N-(quinolin-8-yl)benzamide (L) arising from differences in their packing patterns are characterized. Out of the three polymorphs, two polymorphs (I and II) have extended chain of R22(10) type of hydrogen bonds involving oxygen atom of carbonyl and nitro group through C-H⋯O interactions. These two polymorphs have head to head arrangements of molecules in their respective crystal lattice. One polymorph has two layers of molecules which are held by π⋯π interactions; whereas another polymorph is devoid of π-interactions. The third polymorph (III) has head to tail arrangement of molecules and have C-H⋯O interactions involving carbonyl groups of amides. The polymorph I shows two melting points resembling liquid crystalline property. The powder X-ray diffraction studies performed on the crystals obtained from solutions of different mixed solvents showed the independent role of each solvent to guide crystallization of mixture of polymorphs. The structure of the salts of L having ethylsulphate (IV), bromide (V) and nitrate (VI) anions were determined and conformational differences are established. The nitrate salt is an isomorphic desolvate, which has a porous structure, with voids of dimension 114.8 Å3 (13.5%) per unit cell having volume of 853.4 Å3. It is found that the projection of carbonyl group with respect to the nitrogen atom of the quinoline in LH+ part in the structure of ethylsulphate salt (IV) with respect to bromide salt (V) is opposite.