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-SO 3 H), which were designed for nonlinear optical materials. The cocrystals are colorless, and the melting points are fairly high, at around 200 °C. Both components are commonly crystallized in 1:1 ionic forms of 2A5NP + · Ar-SO 3 - . The crystal of 2A5NP and 3-methyl-4-nitrobenzenesulfonic acid belongs to chiral space group P 2 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 Pna 2 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.