NMR Crystallography, Hydrogen Bonding and Optical Properties of the Novel 2D Hybrid Oxyfluorotitanate [H 2 taz ] 2 ·(Ti 5 O 5 F 12 )

Abstract : The new 2D hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12), where [H2taz]+ represents 1,4-diH-1,2,4-triazolium cation ([C2N3H4]+), has been prepared, and its structure has been refined from powder X-ray diffraction data. It is built up from ∞(Ti5O5F12)2– inorganic layers separated by [H2taz]+ cations and adopts the same space group (Cmm2) and, considering the inorganic part, the same structure as [H2gua]2·(Ti5O5F12), where [H2gua]+ represents guanidinium cation ([C(NH2)3]+). The substitution of [H2gua]+ by [H2taz]+ was aimed at reduction of the refractive index, while a high optical band gap was maintained. The substitution effect is small, but [H2taz]2·(Ti5O5F12) could also allow a high UV protection with a good aesthetic effect. In [H2taz]2·(Ti5O5F12), a 50% site occupancy is attributed to one H atom site and two mirror symmetry related positions have a mixed C and N composition, preventing DFT calculations from being performed for the structural cell and preventing the cation configuration from being determined. Three ordered structures have then been constructed by using a double cell in the Cmc21 space group and their geometries DFT optimized. The resulting calculated 1H NMR parameters are in good agreement with experimental values for the structure that involves the most stable 1,4-diH+ tautomer. 1H and 19F solid-state NMR and DFT modeling of NMR parameters of [H2gua]2·(Ti5O5F12) have been also achieved for the sake of comparison. Moreover, it is demonstrated that for hybrid materials, in the same way as for molecular solids, the comparison of the 1H chemical shielding values calculated from the full crystal structure, from the cations alone, and from an isolated cation provides a quantitative way of assessing hydrogen bonding, between organic and inorganic parts and between organic cations, as well as intercationic ring current effects.