Unusual supramolecular assembly and nonlinear optical properties of l-histidinium hydrogen malate

A new nonlinear optical material, l-histidinium hydrogen malate, has been synthesized. The crystal structure was determined at 90 K by single-crystal X-ray diffraction in order to analyze its supramolecular structure. A new building block type has been found. The malate anions form head-to-side infinite chains parallel to [100], via O–H⋯O interactions, instead of the usual head-to-tail infinite chains found in other hydrogen malate salts. The l-histidine cations form chains parallel to [100] via N–H⋯O hydrogen bonds, with cations of adjacent chains in anti-parallel way. The compound shows a good optical second-harmonic generation capability with an effective second-order susceptibility estimated to be 0.70 of that for potassium dihydrogen phosphate.