The chloride and L-tartrate salts of the 2,4-diaminoquinazolinium(1+) were prepared and characterized by both X-ray diffraction and infrared spectroscopy. The potential of the 2,4-diaminoquinazolinium(1+) cation as a building block for materials for nonlinear optics was assessed using quantum mechanical computations. Both 2,4- diaminoquinazolinium(1+) chloride dihydrate (a = 7.2121 (1) Å, b = 8.0105(2) Å, c = 18.6157(5) Å, β = 92.493(1)°, V = 1074.46(4) Å 3, Z = 4, R = 0.0305 for 4605 observed reflections) and 2,4-diaminoquinazolinium(1+) L-tartrate dihydrate (a = 7.2899(2) Å, b = 11.9508(2) Å, c = 13.4 183(3) Å, β = 92.375(2)°, V = 1168.00(5) Å 3, Z = 2, R = 0.0367 for 4761 observed reflections) belong to the monoclinic space group P2 1. They are stable, nonhygroscopic, colorless and exhibit non-zero SHG efficiency for powdered samples. © Springer Science+Business Media, LLC 2012.