Molecular co-crystals of 2,6-di-t-butyl-4-nitrophenol

The single-crystal structures of 2,6-di-^tbutyl-4-nitrophenol (dbpH), guanidinium 2,6-di-^tbutyl-4-nitrophenolate, piperidinium 2,6-di-^tbutyl-4-nitrophenolate, 1,8-diazabicyclo-(5,4,0)-undec-7-enium 2,6-di-^tbutyl-4-nitrophenolate and 4-(dimethylamino)pyridinium 2,6-di-^tbutyl-4-nitrophenolate are reported. The structure of dbpH is non-centrosymmetric and an ungraded powder sample exhibits five times the second-order nonlinear optical intensity of an ungraded urea sample when irradiated with infrared light. The four salt co-crystals all associate via hydrogen-bonding interactions to the phenolate oxygen atom while two of these also involve hydrogen-bonding associations to the nitro oxygen atoms. The presence of the 2,6-disubstituted t-butyl groups hinder the rotation of the plane of the associated base molecules to >60° with respect to the plane of the phenolate ring, thus introducing limited controllability over the approach and association of these molecules.