Preparation of cocrystals of 2-amino-3-nitropyridine with benzenesulfonic acids for second-order nonlinear optical materials

Noncentrosymmetic and chiral cocrystals were prepared from 2-amino-3-nitropyridine (2A3NP) and achiral benzenesulfonic acids (Ar-SO3H), which were designed for second-order nonlinear optical materials. Both components are commonly crystallized in 1:1 ionic forms of 2A3NPH(+)-Ar-SO3-. The molecular packings of cocrystals are controlled by the aromatic-aromatic interactions as well as multidirectional ionic and hydrogen bonds between the 2A3NPH(+) cations and the sulfonate anions. The crystal of 2A3NP with p-toluenesulfonic acid belongs to acentric space group Pna2(1), in which 2A3NPH(+) cations and anions are alternately stacked with some dihedral angle due to the large sulfonate anions to form two independent column structures in a perpendicular direction to each other. The crystal of 2A3NP with p-nitrobenzenesulfonic acid crystallizes into chiral space group P2(1)2(1)2(1). The 2A3NPH(+) cations and the anions are also alternately stacked to give herringbone network of 2A3NPH(+) cations. The crystal of 2A3NP with 2,5-dimethylbenzenesulfonic acid belongs to acentric space group Pn, in which two independent stacking structures are formed in perpendicular directions. Second-harmonic generation (SHG) power measured with an evanescent wave technique revealed the relatively high SHG efficiency of cocrystal of 2A3NP with p-toluenesulfonic acid, 2-fold larger than that of well-known m-nitroaniline.