Synthesis, structure, and second-harmonic generation of noncentrosymmetric cocrystals of 2-amino-5-nitropyridine with achiral benzenesulfonic acids

A series of noncentrosymmetric cocrystals were prepared from 2-amino-5-nitropyridine (2A5NP) and achiral benzenesulfonic acids (Ar-SO3H), which were designed for nonlinear optical materials. The cocrystals are colorless, and the melting points are fairly high, at around 200degreesC. Both components are commonly crystallized in 1:1 ionic forms of 2A5NP(+).Ar-SO3-. The crystal of 2A5NP and 3-methyl-4-nitrobenzenesulfonic acid belongs to chiral space group P2(1)2(1)2(1), in which the 2A5NP(+) cation and the anion are alternately stacked with a dihedral angle due to the large sulfonic anion to form column structures. Crystals of 2A5NP with both p-toluenesulfonic acid and p-chlorobenzenesulfonic acid are crystallized into noncentrosymmetric space group Pc and are isomorphic with each other. The 2A5NP+ cation and anion in each crystal are also alternatively stacked to form independently elongated zigzag and layer arrays in perpendicular directions. The crystal of 2A5NP and p-phenolsulfonic acid belongs to acentric space group Pna2(1), in which herringbone networks of 2A5NP(+) cations are arranged in the lattice. The feature of these organic-organic crystals is that the molecular packings are controlled by the aromatic-aromatic interactions as well as multidirectional hydrogen bondings between the 2A5NP(+) cations and anions. Second-harmonic generation (SHG) powers measured by the SHEW (second-harmonic generation with evanescent wave) technique revealed the high SHG efficiencies of cocrystals of 2A5NP with p-toluenesulfonic and p-phenolsulfonic acid, comparable to those of the well-known m-nitroaniline and 4-(dimethylamino)-3-acetamidonitrobenzene (DAN), respectively.