title: From solution to the solid state: control of niobium oxide-fluoride [NbOxFy]n- species.
abstract: In this study, we describe the crystallization of specific niobium oxide-fluoride anions (either [NbOF4](-) or [NbOF5](2-)) by increasing the fluoride concentration with the appropriate use of organic bases with varied corresponding pKa values to create suitable equilibria for the formation of each anion. HpyNbOF4 (I; py = pyridine) contains the [NbOF4](-) anion, while [H2(4,4'-bpy)]NbOF5] (II; 4,4'-bpy = 4,4'-bipyridyl) contains the [NbOF5](2-) anion; their identity is correlated with reagent ratios. The increase of basic species (proton acceptors) results in an increase in the fluoride concentration and high fluoride-containing anions. The crystallization of [NbOF4](-) in [NbO2/2F4]∞ chains in I was controlled with the use of weak base pyridine (pKa = 5.23), while isolated [NbOF5](2-) crystallized in II with strong base 4,4'-bipyridyl (pKa = 10.5). This approach can be broadly applied to target-specific basic building units for fundamentally new and potentially functional solid-state materials.
authors: State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , 127 Youyixilu Road, Xi'an 710072, China.
authors: Hongcheng
authors: H
authors: Lu
authors: Romain
authors: R
authors: Gautier
authors: Martin D
authors: MD
authors: Donakowski
authors: Zhengtang
authors: Z
authors: Liu
authors: Kenneth R
authors: KR
authors: Poeppelmeier