Inorganic salts of biguanide – Searching for new materials for second harmonic generation

Abstract

Five inorganic salts of biguanide with carbonic, nitric, phosphoric and phosphorous acids were prepared and X-ray structural analysis has been performed for three novel compounds. Biguanidium(1+) phosphite trihydrate crystallizes in the triclinic space group P 1 ¯ , a = 7.1470(1) Å, b = 9.6530(2) Å, c = 11.3140(2) Å, α = 70.094(1)°, β = 75.688(1)°, γ = 86.099(1)°, V = 713.71(2) Å 3, Z = 2, R = 0.0350 for 3031 observed reflections. The crystal structure is based on a network of phosphite anions and water molecules. Biguanidium(1+) cations form pairs through two intermolecular hydrogen bonds of the N–H…N type and fill the network with anions and water molecules. Biguanidium(2+) phosphite monohydrate crystallizes in the triclinic space group P 1 ¯ , a = 6.9690(2) Å, b = 7.3500(3) Å, c = 8.1730(3) Å, α = 82.518(2)°, β = 83.015(2)°, γ = 82.811(2)°, V = 409.44(3) Å 3, Z = 2, R = 0.0308 for 1779 observed reflections. The structure is formed of a network of alternating biguanidium(2+) cations, phosphite anions and pairs of water molecules interconnected by a system of intermolecular hydrogen bonds. Biguanidium(2+) hydrogen phosphate monohydrate crystallizes in the triclinic space group P 1 ¯ , a = 7.0630(2) Å, b = 7.8740(3) Å, c = 8.1120(3) Å, α = 102.706(2)°, β = 104.976(2)°, γ = 92.632(3)°, V = 422.61(3) Å 3, Z = 2, R = 0.0337 for 1827 observed reflections. The crystal structure is formed by pairs of anions that are mutually connected in chains through two water molecules. These chains are interconnected by biguanidium(2+) cations to form a three-dimensional network. The FTIR and FT Raman spectra of all five compounds were recorded, calculated (HF, B3LYP and MP2 methods) and discussed. Quantitative measurements of second harmonic generation of powdered biguanidium(2+) nitrate and novel biguanidium(2+) carbonate monohydrate at 800 nm were performed and a relative efficiency (compared to KDP) of 87% and 20% was observed, respectively.