Isostructurality in amino molecular salts of two dicarboxylic acids driven by noncovalent synthons

Abstract

Six molecular salts of 2,6-naphthalene dicarboxylic acid (ndc-H2) and 4-carboxycinnamic acid (cca-H2) with 4-aminopyridine (4apy), 2-aminobenzimidazole (2abi) and 2-aminopyridine (2apy) have been synthesized. In the crystal structures of molecular salts with 4apy-H and 2abi-H, ndc and cca showed isostructurality attributed to the centrosymmetric disorder in cca. In the case of molecular salts with 2apy-H, ndc and cca did not show the same packing due to the presence of different quantities of water molecules; however, the disorder in cca can be observed and is very similar to other salts. These molecular salts can also be synthesized from solvent assisted mechanical grinding. The solid solutions prepared by varying the ratio of ndc and cca by keeping the amines constant were characterized by PXRD analysis. The fluorescence intensity of these compounds can be controlled by varying the ratio of ndc and cca in the solid solutions without changing the crystal structure of the compounds. Thus, ndc and cca pairs join the family of isomorphous crystals.