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Systematic centricity control using a chiral template: novel noncentrosymmetric polar niobium oxyfluorides and tantalum fluorides directed by chiral histidinium cations, [(L-hisH(2))NbOF5], [(D-hisH(2))NbOF5], [(L-hisH(2))TaF7], and [(D-hisH(2))TaF7]

Choi, HeeJung|Ok, Kang Min (서강대학교 화학과)

INORGANIC CHEMISTRY FRONTIERS, 2021, 8(16)

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Enantiomorphic histidinium cation-driven niobium and tantalum (oxy)fluoride compounds have been systematically synthesized through a slow evaporation method. Single-crystal X-ray diffraction indicates that all four reported chiral materials crystallize in the noncentrosymmetric polar space group, P2...
Enantiomorphic histidinium cation-driven niobium and tantalum (oxy)fluoride compounds have been systematically synthesized through a slow evaporation method. Single-crystal X-ray diffraction indicates that all four reported chiral materials crystallize in the noncentrosymmetric polar space group, P2(1). While [NbOF5](2-) distorted octahedra are templated by enantiopure histidinium cations in [(L-hisH(2))NbOF5] (L-Nb) and [(D-hisH(2))NbOF5] (D-Nb), monocapped trigonal prismatic [TaF7](2-) units are aligned by the acidified amino acid cations in [(L-hisH(2))TaF7] (L-Ta) and [(D-hisH(2))TaF7] (D-Ta). The frameworks of the title compounds exhibit thermal stability up to ca. 180 degrees C. While the band gaps of L-Nb and D-Nb were found to be ca. 4.45 and 4.47 eV, respectively, those of L-Ta and D-Ta turned out to be higher, with values of 5.07 and 5.06 eV, respectively. Clearly reversed signals observed in the solid-state circular dichroism spectra confirm the chirality of the reported materials. Powder second-harmonic generation (SHG) measurements indicate that the title compounds are type-I phase-matchable and reveal an SHG efficiency that is ca. 0.4-0.6 times that of KH2PO4.