Noncentrosymmetric Crystals with Marked Nonlinear Optical Properties

The crystal structures and optical properties of the novel (1R,2R)-(−)-1,2-diammoniumocyclohexane squarate trihydrate (1) and bis(hydrogen squarate) (2) were elucidated and reported. Physical methods, single crystal X-ray diffraction, UV−vis−NIR, polarized IR spectroscopy of oriented colloids, mass spectrometry, and thermal methods were used. Quantum chemical DFT calculations were performed with a view to predict the optical and NLO properties of the systems (1) and (2). Both compounds are characterized with the noncentrosymmetric orthorhombic space groups C2221 (1) and P212121 (2), indicating nonlinear optical properties in the bulk. These organic salts are thermal stable up to 400 °C and transparent over the range from 270 to 1100 nm.