Hydrogen bond-assisted crystallization: structure, growth and characterization of a new mixed-anion transition metal fluoride Na3NH4(TiF6)(SO4)·H2O

Abstract

The first mixed-anion transition metal (TM) fluoride with a [MF₆]^x− (M = TM cation) anion group, Na₃NH₄(TiF₆)(SO₄)·H₂O (NTS), was synthesized by a facile hydrothermal method. The structure of NTS features hydrogen-bonded layers constructed by four kinds of building blocks, i.e., [NH₄]⁺, [TiF₆]²⁻, [SO₄]²⁻, and H₂O, and four categories of hydrogen bonds, i.e., N–H⋯O, N–H⋯F, O–H⋯O and O–H⋯F, and the layers are further connected by Na⁺ forming a three-dimensional framework. A transparent crystal with a size up to 5.0 × 2.5 × 1.0 mm³ has been grown just by controlling the hydrothermal conditions. The crystal morphology, electronic structure, and optical and thermal properties of NTS were analyzed.