Variable Dimensionality, Valence, and Magnetism in Fluoride-Rich Iron Phosphates Ba_xFe_x(PO₄)F_y (1 ≤ x ≤ 3, 2 ≤ y ≤ 12)

Abstract

We report the synthesis and characterization of three fluoride-rich barium iron phosphates Ba x Fe x (PO4)­F y (1 ≤ x ≤ 3, 2 ≤ y ≤ 12), which exhibited abundant structural chemistry, exhibiting diverse frameworks and connecting modes between [FeO n F6–n ] m – octahedra surrounding Fe2+ or Fe3+ ions. BaFe­(PO4)­F2 (I) consisted of two-dimensional [Fe­(PO4)­F2]2– sheets built from linear ∞[Fe2O6F4]10– moieties formed by fluorine corner-sharing FeO4F2 and FeO2F4 octahedra with linking PO4 tetrahedra. Mixed-valence Ba2Fe2(PO4)­F6 (II) possessed a three-dimensional framework containing Fe4O6F12 tetramers formed by the edge-sharing oxygen or fluorine atoms of cis-FeF4O2 octahedra. Ba3Fe3(PO4)­F12 (III) contained one-dimensional columns of ∞[Fe3(PO4)­F12]6– infinite sections built from cis-FeF4O2 and FeF5O octahedra and tetrahedral PO4 linkers. The magnetic characterization of Ba x Fe x (PO4)­F y unveiled diverse magnetism: an S = 5/2 spin chain for (I), a weak ferrimagnet or canted antiferromagnet for (II) thanks to the presence of distinct Fe2+ and Fe3+ sites identified by Mössbauer spectroscopy, and coupled spin-trimers for (III).

Transition-Metal Monofluorophosphate Ba2M2(PO3F)F6 (M = Mn, Co, and Ni): Varied One-Dimensional Transition-Metal Chains and Antiferromagnetism

“…Single crystals of I were obtained from several experiments using improved fluoride-rich phosphoric and fluorophosphoric acids via hydrothermal routes . In one experiment, a mixture of 3.50 × 10 –3 mol (0.304 g) of MnO 2 , 1.75 × 10 –3 mol (0.345 g) of BaCO 3 , 0.1 mL of H 3 PO 4 , 0.8 mL of HPF 6 , 0.5 mL of hydrazine monohydrate, and 0.8 mL of deionized water, with a molar ratio of Ba:Mn:P:F = 1:2:31.8:186.0, was homogenized by vigorous stirring with 0.8 mL of deionized water and transferred to a 23 mL Teflon-lined stainless steel autoclave.…”

“…12 Ba x Fe x (PO 4 )F y hosts diverse magnetism: an S = 5 / 2 spin chain for BaFe(PO 4 )F 2 and coupled spin trimers for Ba 3 Fe 3 (PO 4 )F 12 . 13 In this context, we are interested in organizing [MO n F 6−n ] m+ units into [PO 4−p F p ] q− -containing frameworks. Strictly speaking, Li 2 FePO 4 F, containing isolated PO 4 3− tetrahedral and F − anions, belongs to the class of f luoride phosphates, while the compounds containing tetrahedral (PO 3 F) 2− and (PO 2 F 2 ) − anions are designated as f luorophosphates.…”

“…A new diamond-chain compound Cu 2 FePO 4 F 4 (H 2 O) 4 exhibits a noncollinear spin order and possible successive phase transitions . Ba x Fe x (PO 4 )­F y hosts diverse magnetism: an S = 5 / 2 spin chain for BaFe­(PO 4 )­F 2 and coupled spin trimers for Ba 3 Fe 3 (PO 4 )­F 12 …”

Cycloidal Magnetic Order Promoted by Labile Mixed Anionic Paths in M2(SeO3)F2 (M = Mn2+, Ni2+)

“…Fmay procure a playground for destabilizing the standard collinear spin order into exotic ones, and provide a nice platform for spin-induced multiferroicity. 6 Only few examples of selenium-oxofluorides have been reported due to hard control of the reactive fluorine ions [7][8][9] using HF (or else) as a dual mineralizer and strong acid, suitable for the formation of metal ions. In fact, reacting SeO2, metal halide and HF acid is a suitable strategy to grow single crystals of M2(SeO3)F2 (M = Co, Cu).…”

“…On the other hand, the smaller fluoride anion may act as a bridging species between transition-metal cations, forming there by sizable dimensionalities in phases such as the 1D-Fe­(SeO 3 )­F or the 3D-M 2 (SeO 3 )­F 2 (M = Co, Cu). , Here, the contrasting magnetic exchanges mediated by O 2– vs F – may create a playground for destabilizing the standard collinear spin order into exotic orders and provide a nice platform for spin-induced multiferroicity . Only few examples of selenium oxofluorides have been reported due to difficult control of the reactive fluorine ions − using HF (or others) as a dual mineralizer and strong acid suitable for the formation of metal ions. In fact, reacting SeO 2 , a metal halide, and the acid HF is a suitable strategy to grow single crystals of M 2 (SeO 3 )­F 2 (M = Co, Cu). , The realization of polycrystalline mixed (Mn,Zn) 2 (SeO 3 )­F 2 by fine adjustment of the pH environment using NH 4 OH was achieved, but the crystal growth was hampered by the reduction of Se­(IV) to Se(0) above 120 °C, which remains a chemical challenge.…”