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 Pna21, 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 P212121. 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.