Inorganic Salts of N-phenylbiguanidium(1+)—Novel Family with Promising Representatives for Nonlinear Optics

Seven inorganic salts containing N-phenylbiguanide as a prospective organic molecular carrier of nonlinear optical properties were prepared and studied within our research of novel hydrogen-bonded materials for nonlinear optics (NLO). All seven salts, namely N-phenylbiguanidium(1+) nitrate (C2/c), N-phenylbiguanidium(1+) perchlorate (P-1), N-phenylbiguanidium(1+) hydrogen carbonate (P21/c), bis(N-phenylbiguanidium(1+)) sulfate (C2), bis(N-phenylbiguanidium(1+)) hydrogen phosphate sesquihydrate (P-1), bis(N-phenylbiguanidium(1+)) phosphite (P21), and bis(N-phenylbiguanidium(1+)) phosphite dihydrate (P21/n), were characterised by X-ray diffraction (powder and single-crystal X-ray diffraction) and by vibrational spectroscopy (FTIR and Raman). Two salts with non-centrosymmetric crystal structures—bis(N-phenylbiguanidium(1+)) sulfate and bis(N-phenylbiguanidium(1+)) phosphite—were further studied to examine their linear and nonlinear optical properties using experimental and computational methods. As a highly SHG-efficient and phase-matchable material transparent down to 320 nm and thermally stable to 483 K, bis(N-phenylbiguanidium(1+)) sulfate is a promising novel candidate for NLO.