Structural evidence in 2-amino-5-nitropyridinium halides (Cl^–, Br^–) of herringbone motifs favourable to efficient quadratic non-linear optical properties

Abstract

2-Amino-5-nitropyridinium halides have been synthesized and their crystal structures determined. The structures of acentric phases reveal networks of non-linear chromophores arranged in herringbone motifs. Their secondharmonic generation responses vary in magnitude between that of 3-methyl-4-nitropyridine N-oxide and 2-methyl-2,4-dinitrophenyl aminopropanoate molecular compounds. Chained anions screen favourably the interactions between the non-linear cations in acentric phases, while the reverse situation is observed in the centric phase of 2-amino-5-nitropyiridinium bromide built up with open pseudo-hexagonal anionic layers.