(R)- and (S)-[C8H10NO3]2[NbOF< sub>5]: noncentrosymmetric niobium oxyfluorides with large optical anisotropy

초록

Huge crystals of noncentrosymmetric (NCS) organic-inorganic hybrid niobium oxyfluorides, (R)-[C8H10NO3](2)[NbOF5] [(R)-Nb] and (S)-[C8H10NO3](2)[NbOF5] [(S)-Nb], have been easily grown via a slow evaporation method in high yields through the systematic driving of chiral structure-directing agents, 4-hydroxy-d-(-)-2-phenylglycine [(R)-HPG] and 4-hydroxy-l-(+)-2-phenylglycine [(S)-HPG], respectively. Both (R)-Nb and (S)-Nb crystallizing in the NCS nonpolar space group, P2(1)2(1)2, exhibit pseudo-three-dimensional structures assembled via multiple hydrogen bonding interactions between distorted [Nb(O/F)(2)F-4](2-) octahedra and the respective protonated HPG cations. Interestingly, crystals of (R)-Nb and (S)-Nb exhibit large birefringence (Delta n(exp)) of 0.19-0.199@589.3 nm attributable to the strong pi-pi interactions arising from the stacked benzene rings in HPG cations. The reported materials exhibit strong stability in most solvents in a wide range of polarities. Detailed characterization studies, including thermal properties, various spectroscopic analyses, second-harmonic generation measurements, and electronic structure calculations on the reported materials, are also described.

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