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Two novel semi-organic salts of tetra- n-propylammonium (1+) and tetra- n-butylammonium (1+) hydrogen selenate have been prepared and characterised. Tetra- n-propylammonium (1+) hydrogen selenate ( a = 15.7949(6) Å, b = 15.3876(6) Å, c = 40.4384(17) Å, V = 9828.4(7) Å, Z = 8 for 8775 observed reflections) and tetra- n-butylammonium (1+) hydrogen selenate ( a = 15.0870(3) Å, b = 15.3380(4) Å, c = 17.4750(4) Å, V = 4043.79(16) Å, Z = 8, R = 0.0432 for 3335 observed reflections) crystallise in the centrosymmetric space groups Pbcn and Pccn of the orthorhombic system, respectively. Both salts were also characterised by the methods of vibrational spectroscopy (IR and Raman). The interpretation of the vibrational spectra is based on ab initio calculations of the isolated cations. The crystal structure of the third analogous compound, tetra- n-ethylammonium(1+) hydrogen selenate was redetermined at 150 K ( a = 8.2109(17) Å, b = 9.072(2) Å, c = 9.431(3) Å, α = 77.13(3)º, β = 74.43(2)º, γ = 63.62(3)º, V = 601.89(3) Å, Z = 2, R = 0.0167 for 2237 observed reflections). This compound crystallises in centrosymmetric space group P-1 of the triclinic system and was previously studied only at room temperature. Graphical Abstract: The preparation and detailed characterisation (using the combination of diffraction and spectroscopic methods) of salts of tetra- n-alkylammonium hydrogen selenates (alkyl = propyl, butyl). [ABSTRACT FROM AUTHOR]

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, 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 = 13.4183(3) Å, β = 92.375(2)°, V = 1168.00(5) Å, Z = 2, R = 0.0367 for 4761 observed reflections) belong to the monoclinic space group P2. They are stable, non-hygroscopic, colorless and exhibit non-zero SHG efficiency for powdered samples. Graphical Abstract: Two novel non-centrosymmetric salts of 2,4-diaminoquinazolinium(1+) were prepared and thoroughly characterized during the search for materials for the second harmonic generation. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]