Organic salts of biguanide – An attempt to crystal engineering of novel materials for second harmonic generation

Three organic salts of biguanide with oxalic, succinic and l-tartaric acids have been prepared and X-ray structural analysis has been performed. Biguanidium(1+) oxalate hemihydrate (a = 6.8330(2) Å, b = 10.0430(2) Å, c = 14.6230(4) Å, α = 90.236(1) , β = 90.333(1) , γ = 105.605(2) , V = 966.46(4) Å3, Z = 1, R = 0.0393 for 3704 observed reflections) and biguanidium(1+) hydrogen succinate (a = 6.4600(1) Å, b = 6.7670(2) Å, c = 11.4150(3) Å, α = 91.822(1) , β = 105.312(1) , γ = 90.922(1) , V = 480.89(2) Å3, Z = 2, R = 0.0357 for 1880 observed reflections) belong to the triclinic space group P 1 ¯ . Their crystal structures are based on biguanidium(1+) pairs connected by intermolecular N–H⋯N hydrogen bonds. The remaining ions (eventually water molecules) form a 3D structural network with these pairs. Furthermore, the formation of the cationic and anionic layers interconnected by intermolecular N–H⋯O hydrogen bonds was observed in the crystal structure of biguanidium(1+) hydrogen succinate. idium(2+) l-tartrate crystallizes in the orthorhombic space group P 212121 (a = 6.7170(2) Å, b = 9.2740(2) Å, c = 16.1500(4) Å, V = 1006.04(4) Å3, Z = 4, R = 0.0432 for 2193 observed reflections). The crystal structure is based on l-tartrate chains, which are interconnected by isolated biguanidium(2+) cations via several types of N–H⋯O hydrogen bonds. The formation of l-tartrate chains is mediated by two types of intermolecular O–H⋯O hydrogen bonds connecting the hydroxyl and carboxylate groups. IR and FT Raman spectra of all the compounds were recorded and discussed. eoretical values of the first hyperpolarizability components were calculated for biguanidium(1+) and biguanidium(2+) cations at the B3LYP level with the 6-311G(d,p) basis set. Quantitative measurements of the second harmonic generation of powdered biguanidium(2+) l-tartrate at 800 nm were performed and a relative efficiency of 2% (compared to KDP) was observed. ermal behaviour of all the prepared compounds was studied by the DSC method in the temperature interval from 90 K up to a temperature close to the melting points of the crystals. The FTIR and FT Raman spectra of biguanidium(2+) l-tartrate were investigated down to 130 K.