Variable Dimensionality, Valence, and Magnetism in Fluoride-Rich

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Variable Dimensionality, Valence, and Magnetism in Fluoride-Rich Iron Phosphates BaxFex(PO4)Fy (1 ≤ x ≤ 3, 2 ≤ y ≤ 12) Jianhua Jiang,† Suheon Lee,‡ Bei Zhu,† Yang Yu,∥ João Carlos Waerenborgh,§ Kwang-Yong Choi,‡ and Minfeng Lü*,†

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF RHODE ISLAND on 12/14/18. For personal use only.

†

School of Environmental & Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, Jiangsu, China ‡ Department of Physics, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea § Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal ∥ State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China S Supporting Information *

ABSTRACT: We report the synthesis and characterization of three fluoride-rich barium iron phosphates BaxFex(PO4)Fy (1 ≤ x ≤ 3, 2 ≤ y ≤ 12), which exhibited abundant structural chemistry, exhibiting diverse frameworks and connecting modes between [FeOnF6−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 cornersharing 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 edgesharing oxygen or fluorine atoms of cis-FeF4O2 octahedra. Ba3Fe3(PO4)F12 (III) contained one-dimensional columns of 6− infinite sections built from cis-FeF4O2 and ∞[Fe3(PO4)F12] FeF5O octahedra and tetrahedral PO4 linkers. The magnetic characterization of BaxFex(PO4)Fy 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).

1. INTRODUCTION Oxides and oxyfluorides containing oxyanion building groups, such as [VO4]3−, [CO3]2−, [PO4]3−, and [BO3]3−, have been investigated intensively during the past decade. These studies gave rise to many compounds exhibiting important physical properties, such as nonlinear optical (NLO) second-harmonic generation, ionic conductivity, electrical conductivity, lithium insertion/extraction, and novel magnetism. For example, BaFe2(PO4)2 showed two-dimensional (2D) Ising ferromagnetism with a magnetically driven reentrant transition.1 Cu7(TeO3)6F2 revealed a mixed dimensionality, where spin chain fragments were weakly coupled with single Cu S = 1/2 magnetic moments.2 FeSeO3F is characterized by alternating antiferromagnetic S = 5/2 chains.3 KBe2BO3F2 is the solely available NLO material that could practically produce deepUV coherent light.4,5 LiFePO4, LiVPO4F, and LiFePO4F are up-and-coming electrode materials for rechargeable Li batteries.6−8 Crystal chemistry in oxides can be categorized primarily in consideration of the connection between MOx polyhedra around the metal and various polyhedral oxyanion building © XXXX American Chemical Society

blocks that form zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) frameworks.9 However, the structural diversity of oxyfluorides involves not only the varied [MOxFy]z− building units containing the metal M but also the ability of these units to connect one, two, or more oxygen or fluorine atoms of oxyanion or fluoro-oxyanion groups via corner-, edge-, or facesharing arrangements.10 The intergrowth of various [MOxFy]z− units and oxyanion building blocks in varying sequences can give birth to new structures of increasing complexity. Fluorine insertion into oxides is frequently achieved by gas− solid reactions11 or solid−solid reactions via a two-step process.12 Recently, various hydrothermal methods successfully incorporated low concentrations of fluoride into framework structures. Much work has been devoted to the synthesis of 3d transition metal fluoride phosphates, fluoride selenites, and fluoride tellurites at low temperature (T < 250 °C), where the transition-metal-containing starting material coordinated fluoReceived: July 15, 2018

A

DOI: 10.1021/acs.inorgchem.8b01982 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Table 1. Crystal Data, Measurement Parameters, and Structural Refinement Parameters of BaFe(PO4)F2, Ba2Fe2(PO4)F6, and Ba3Fe3(PO4)F12 molar weight (g/mol) symmetry space group Z a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) T (K) μ (mm−1) R(int) (%) indep all (I > 3σ(I)) indep obsd (I > 3σ(I)) number of refined parameters R(F)a [I > 3σ(I)/all data, %] Rw(F2)b [I > 3σ(I)/all data, %] max/min residual electronic density (e/Å3)

BaFe(PO4)F2

Ba2Fe2(PO4)F6

Ba3Fe3(PO4)F12

326.2 monoclinic P21/n 4 5.2440(2) 12.7889(5) 7.1765(2) 90 102.142(2) 90 470.52(3) 293 11.717 5.95 1154 865 55 2.89/4.52 2.74/2.99 0.83/−0.80

595.3 monoclinic P21/n 4 9.3242(13) 7.2827(9) 12.7017(17) 90 99.220(7) 90 851.4(2) 293 12.746 8.07 2096 1376 81 5.50/8.62 5.67/6.07 2.70/−1.57

902.5 triclinic P1̅ 2 7.5665(2) 7.7044(2) 12.4694(3) 74.3210(13) 79.3925(13) 85.7554(13) 687.67(3) 293 4.3586 4.17 3341 2768 128 3.19/4.10 3.78/3.97 1.33/−1.23

R = ∑∥Fo| − |Fo∥/∑|Fo|. bRw = [∑w(|F2o| − |F2c |)2/∑w|F2o|2]1/2].

a

ride.2,3,13 A number of gallium fluoride phosphate and iron fluoride phosphate materials14,15 were also prepared by the hydrothermal reaction under subcritical conditions using HF as a mineralizer. Hydrothermal growth under supercritical conditions mainly led to fluoride oxysalts.16−18 Due to their strict preparation conditions, very little work has been done on fluoride-rich oxysalts. Recently, high concentrations of fluoride stemming from the hydrolysis of HPF610 were mainly applied to the synthesis of fluorophosphates. However, the resulting networks were frequently associated with PO2(OH, F)2−, PO3F2−, or M(O, OH, F)n (n = 4, 6) groups (it should be noted that compounds with PO3F2− and PO2(OH, F)2− anions were strictly categorized as f luorophosphates, whereas those containing the [PO4]3− anion as f luoride phosphates).19 In this article, we report the synthesis and structural characterization of three fluoride-rich barium iron phosphates, BaxFex(PO4)Fy (1 ≤ x ≤ 3, 2 ≤ y ≤ 12), derived from phosphoric and fluorophosphoric acids through fluoride-rich hydrothermal routes.10 However, with the aid of hydrazine to adjust the pH of hydrothermal solutions, we successfully found an alternative method to synthesize the fluoride oxysalts without high-temperature supercritical conditions. BaxFex(PO4)Fy (1 ≤ x ≤ 3, 2 ≤ y ≤ 12) possessed a rich structural chemistry, exhibiting diverse frameworks and connecting modes between [FeOnF6−n]m− octahedra surrounding the Fe2+ or Fe3+ ions. Remarkably, the different structures host distinct magnetic properties at low temperature.

mL), 13.6 mmol of HPF6 (0.2 mL), 8.23 mmol of hydrazine monohydrate (0.4 mL), and 4.1 mL of deionized water were mixed. The mixture was transferred into a stainless steel autoclave (23 mL) with a Teflon liner. After being sealed tightly, the reactor was heated to 220 °C for 72 h and then cooled down to room temperature (2.5 °C/h). After the mixture was washed with water and then filtered, single crystals and polycrystalline samples of (I) were extracted in 45% yield (based on Fe). The purity of the precursors was checked using standard laboratory X-ray diffraction (XRD). Calculated from the pure powder diffraction pattern utilizing the program Unitcell,20 the lattice parameters were obtained, leading to a monoclinic cell with a = 5.2441(2) Å, b = 12.7891(5) Å, c = 7.1766(3) Å, and β = 102.142(4)°, consistent well with the results from single-crystal data (see Table 1). Ba2Fe2(PO4)F6 (II): Red brick crystals were obtained from hydrothermal reactions. FeCl2·4H2O (2.45 mmol, 0.487 g), 1.00 mmol (0.197 g) of BaCO3, 1.31 mmol of H3PO4 (0.09 mL), and 33.9 mmol of HPF6 (0.5 mL) were transferred into a 23 mL Teflon-lined autoclave with hydrazine monohydrate (0.4 mL). The autoclave was filled to 5 mL with 4.0 mL of deionized water and heated to 220 °C for 72 h. The autoclave was cooled down to room temperature at a rate of 2.5 °C/h after heating. The autoclave was opened, and the reaction products were obtained by filtration. After washing with distilled water, a pure phase of (II) was obtained in 35% yield (based on Fe). The lattice parameters refined from the powder diffraction pattern are a = 9.3244(4) Å, b = 7.2828(3) Å, c = 12.7020(5) Å, and β = 99.22 (1)°, in good agreement with the results from single-crystal data (see Table 1). Ba3Fe3(PO4)F12 (III): This was obtained from hydrothermal reactions. FeCl2·4H2O (2.45 mmol, 0.487 g), 1.00 mmol (0.197 g) of BaCO3, 1.46 mmol of H3PO4 (0.1 mL), 54.2 mmol of HPF6 (0.8 mL), and 8.23 mmol of hydrazine monohydrate (0.4 mL) were introduced into a stainless steel autoclave (23 mL) with a Teflon liner. The autoclave was filled to 5 mL with deionized water, heated to 220 °C (70 °C/h) for 72 h, and cooled to room temperature (2.5 °C/h). Transparent brick-shaped crystals of (III) were collected after washing with distilled water. A pure phase of (III) was obtained in 28% yield (based on Fe). After refinement of the powder diffraction pattern, the lattice parameters suggest a primitive triclinic unit cell with a = 7.563(4) Å, b = 7.698(5) Å, c = 12.452(8) Å, α =

2. EXPERIMENTAL SECTION 2.1. Synthesis. BaCO3 (Sinopharm Chemical, 99%), FeCl2·4H2O (Acros Organics, 99%), HPF6 (Alfa Aesar, 60%), phosphoric acid (H3PO4, Energy Chemical, 85 wt % in H2O), fluorophosphoric acid (HPF6, 60 wt % in H2O), and hydrazine monohydrate (Alfa Aesar, >99%) were used. BaFe(PO4)F2 (I): Polycrystalline phases and single crystals of (I) were grown via hydrothermal reactions. FeCl2·4H2O (2.10 mmol, 0.418 g), 1.40 mmol (0.276 g) of BaCO3, 4.37 mmol of H3PO4 (0.3 B


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Inorganic Chemistry

Figure 1. (a) Projection of the structure of BaFe(PO4)F2 along the a-axis. [Fe3+OnF6−n]m−1 octahedra are drawn in sky blue, and PO4 tetrahedra are highlighted in light orange. (b) Views of a slab of [Fe(PO4)F2]2− in the ac-plane. (c) Views of a chain of ∞[Fe2O6F4]10−along the c-axis observed in the ac-plane. (d) Coordination environment of the Ba cation with O/F atoms for BaFe(PO4)F2. 74.378(7)°, β = 79.461(6)°, and γ = 85.831(8)°, although it suffered from severe preferred orientation. 2.2. Single-Crystal X-ray Diffraction (SCXRD). SCXRD data of all of the samples were collected using a Bruker SMART BREEZE diffractometer equipped with a 1k CCD area detector and monochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature. A narrow-frame method was used to acquire the data with a scan width (ω) of 0.30° and an exposure time of 10 s/frame. The program SAINT was used to integrate the obtained data.21 Absorption corrections were performed by the multiscan method using the program SADABS.22 The collected and pertinent data of the refinements are outlined in Table 1 for all single crystals investigated in this work. 2.3. Scanning Electron Microscopy/Energy-Dispersive X-ray Spectroscopy (SEM/EDX). EDX analyses of the isolated crystals were qualitatively carried out using a Hitachi S-3400N instrument. EDX analyses under the similar process are reported elsewhere.23,24 BaFe(PO4)F2, Ba2Fe2(PO4)F6, and Ba3Fe3(PO4)F12 exhibited approximate Ba/Fe/P/F ratios of 0.98:1.00:1.02:2.54, 2.37:2.00:1.04:6.27, and 3.14:3.00:1.35:11.5, respectively. Surplus P ratios in Ba3Fe3(PO4)F12 were found because of overlapped peaks of P and Au. 2.4. Electron Paramagnetic Resonance (EPR) Measurements. EPR measurements were conducted using a commercial spectrometer (JEOL, model JES-FA200) operated at an X-band frequency of ν = 9.445 GHz at T = 295 K. The obtained EPR spectra provided information about the crystal environments of the Fe3+ ions. 2.5. Mössbauer Spectroscopy Measurements. 57Fe Mössbauer measurements were recorded in the range of 4−298 K in transmission mode using a conventional constant-acceleration spectrometer and a 25 mCi 57Co source in a Rh matrix. The velocity scale was calibrated using an α-Fe foil at room temperature. Isomer shift (IS) values are given relative to this standard. A homogeneous powder sample was gently packed into a perspex holder. The absorber thickness was calculated on the basis of the corresponding electronic mass absorption coefficient for 14.4 keV radiation according to the method of Long et al.25 Low-temperature measurements were performed with the sample immersed in liquid He in a bath cryostat for measurements at ≤4.1 K and in He exchange gas in the same

cryostat for temperatures >4.1 K. The spectra were fitted to Lorentzian lines using a nonlinear least-squares method.26 2.6. Static Magnetization Measurements. The dc magnetic susceptibilities of polycrystalline BaFe(PO4)F2, Ba2Fe2(PO4)F6, and Ba3Fe3(PO4)F12 were measured by a superconducting quantum interference device (SQUID) magnetometer. Zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibilities were recorded in the temperature range 2−300 K with a measuring field of 1000 Oe. Magnetization versus applied field data was collected using a SQUID magnetometer in a field range of −7 to 7 T at T = 2 K.

3. RESULTS AND DISCUSSION 3.1. Structural Descriptions. BaFe(PO4)F2 (I) crystallizes in the centrosymmetric space group P21/n with lattice parameters a = 5.2440(2) Å, b = 12.7889(5) Å, c = 7.1765(2) Å, and β = 102.142(2)°, which was proved early.27 The crystal structure was solved by a charge-flipping program28 and refined using Jana 2006.29 The refinement was carried out using F values by full-matrix least-squares minimization with anisotropic thermal parameters, yielding 4.98% R1 (all 1154 refl.) and 3.38% R1 (865 obs. refl. with I > 3σ(I)). At this stage of the refinement, the chemical formula was BaFePO6. However, the bond valence sum (BVS) calculation30 gave charges of 2.26, 3.26−3.47, 4.83, 1.29−1.46, and 1.86−2.05 for Ba, Fe1−Fe2, P, O5−O6, and O1−O4, respectively, which indicated the presence of Fe3+ and F−. After reassignment of fluorine atoms, the charge balanced according to the formula BaFe(PO4)F2, in agreement with the results of EDX analysis. The final refined model yielded 4.52% R1 (all 1154 refl.) and 2.89% R1 (865 obs. refl. with I > 3σ(I)). The refined anisotropic displacement parameters and atomic positions are summarized in Tables S1 and S2, respectively. The pertinent angles and distances are listed in Table S3. The crystal structure consists of polyhedral BaO7F3, octahedral trans-FeO4F2, octahedral trans-FeO2F4, and tetrahedral PO4 building units (Figure 1a). A slab of the 2D C


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Inorganic Chemistry Table 2. BVS Calculation Results for BaFe(PO4)F2, Ba2Fe2(PO4)F6, and Ba3Fe3(PO4)F12a BaFe(PO4)F2 atom

VBa*

Ba(1) Fe(1) Fe(2) P(1)

2.03(1)

VFe*

Ba2Fe2(PO4)F6 VP*

2.84(1) 2.97(1) 4.85(3)

atom

VF*

F(1) F(2) O(1) O(2) O(3) O(4)

−1.10(1) −0.98(1)

VO*

−1.92(1) −2.06(2) −1.87(2) −1.86(2)

atom

VBa*

Ba(1) Ba(2) Fe(1) Fe(2) P(1)

2.04(2) 1.84(1)

VFe*

Ba3Fe3(PO4)F12 VP*

3.07(3) 1.98(2) 4.93(7)

atom

VF*

VO*

F(1) F(2) F(3) F(4) F(5) F(6) O(1) O(2) O(3) O(4)

−1.17(1) −1.10(1) −0.95(1) −0.94(1) −1.03(1) −1.02(1) −1.78(4) −1.91(4) −2.02(4) −1.93(4)

atom

VBa*

Ba(1) Ba(2) Ba(3) Fe(1) Fe(2) Fe(3) P(1) atom

2.16(1) 2.10(1) 1.79(1)

F(1) F(2) F(3) F(4) F(5) F(6) F(7) F(8) F(9) F(10) F(11) F(12) O(1) O(2) O(3) O(4)

VFe*

VP*

2.98(2) 3.09(2) 3.01(2) 4.95(3) VF*

VO*

−1.04(1) −1.02(1) −0.94(1) −0.95(1) −1.10(1) −0.98(1) −1.03(1) −0.92(1) −0.89(1) −1.15(1) −1.02(1) −1.08(1) −2.11(2) −2.12(2) −1.96(2) −1.76(2)

a (R, b) parameters for Ba2+−O (2.285, 0.37), Ba2+−F (2.188, 0.37), Fe3+−O (1.759, 0.37), Fe3+−F (1.679, 0.37), Fe2+−O (1.734, 0.37), Fe2+−F (1.734, 0.37), and P5+−O (1.617, 0.37).

2− ∞[Fe(PO4)F2]

sheet isolated by [BaO7F3]15− units in the acplane is shown in Figure 1b. The sheet is formed by linear 10− moieties along the c-axis that are connected by ∞[Fe2O6F4] 3− tetrahedra at intervals (see Figure 1b). The PO 4 [Fe2O6F4]10− unit is formed by FeO4F2 and FeO2F4 octahedra that are linked to each other through corner-sharing fluorine atoms. Each PO4 group shares oxygen atoms with two FeO4F2 units and one FeO2F4 unit (see Figure 1b). A remarkable structural feature is the distinct nature of the two iron sites. Fe(1)3+ is characterized by trans-FeO2F4 octahedra with four equatorial fluorine atoms and two vertex oxygen atoms, whereas Fe(2)3+ in the trans-FeO4F2 octahedra is coordinated by two vertex fluorine atoms and four equatorial oxygen atoms. In addition, Fe(1)3+ possesses four normal Fe− F bond distances ranging from 1.927(4) to 1.964(3) Å and two Fe−O bonds of length 2.003(4) Å (see Table S3). For comparison, the Fe−F bond lengths in (NH4)3Fe4F9(PO4)2 are 1.907−2.002 Å and the Fe−O bond lengths are 1.982 Å.31 The cis bond angles around Fe(1) range from 85.6(2) to 94.4(2)°. Fe(2)3+ exhibits two short Fe−O bond lengths of 1.950(4) Å, two long Fe−O bond distances of 2.023(4) Å, and two elongated Fe−F bond distances of 1.991(3) Å. The observed interatomic distances in the trans-FeO4F2 octahedra are well consistent with the ranges in other examples of FeO4F2 units in the literature (e.g., Fe−F = 1.944−1.997 Å and Fe−O = 1.947−2.000 Å in [CH3NH3]FeFPO4).31 The cis bond angles around Fe(2) are between 85.3(2) and 94.7(2)°, consistent with the data for Fe(1). Despite the complexity of the distorted octahedral environments around Fe3+, the linear ∞[Fe2O6F4]10− moieties show relatively high symmetry with all of the iron atoms sitting on

special positions (see Table S1). The Fe(1) and Fe(2) centers share F(1) atoms along the length of the chain with an Fe(1)− F(1)−Fe(2) bridging bond angle of 130.2(2)°. However, the PO43− groups show slight distortion, with the P−O bond distance varying from 1.523(4) to 1.573(5) Å. Finally, the BVS calculations30 for Ba2+, Fe3+, and P5+ cations gave values of 2.03(1), 2.84(1)−2.97(1), and 4.85(3), respectively, as shown in Table 2. We already stated in the Experimental Section that the BaFe(PO4)F2 powder was successfully prepared using the hydrothermal method. The powder diffraction pattern is shown in Figure 2 and is in good agreement with the results from the single-crystal data. Ba2Fe2(PO4)F6 crystallizes in a monoclinic unit cell (a = 9.3242(13) Å, b = 7.2827(9) Å, c = 12.7017(17) Å, and β = 99.220(7)°). The crystal structure was solved and refined in the P21/n space group, as suggested by the XPREP program.32 Two crystallographically unique Fe atoms are located in two distinct sites. The coordination of both Fe(1) and Fe(2) is characterized by cis-FeF4O2 octahedra. Coupled with the results of BVS calculations,30 the Fe(1) atom is formally Fe3+, whereas the Fe(2) atom is in the Fe2+ state. Similar discrete Fe2+ and Fe3+ coordination environments have been previously observed in Fe 2 F 5 ·2H 2 O. 33 Unlike the iron sites in Ba2Fe2(PO4)F6, those in Fe2F5·2H2O are composed of FeF6 octahedra and trans-FeF4(H2O)2 octahedra. Ba2Fe2(PO4)F6 consists of BaF7O2 and BaF8O3 polyhedra, cis-FeF4O2 octahedra, and PO4 seesaws. A projection view of (II) is shown in Figure 3a. The structure may be described as an Fe4O6F12 tetramer (Figure 3b) formed by edge-sharing oxygen or fluorine atoms of cis-FeF4O2 octahedra (see Figure 3c). One Fe4O6F12 unit is connected to another by two bridging PO4 groups via shared oxygen corners, forming a D


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Inorganic Chemistry

the Fe4O6F12 tetramer, whereas the gap between two crosslinked chains is occupied by only a single PO4 unit. The 3D structure with mixed-valence iron is quite distinct from those reported, i.e., mixed-valence iron fluoride hydrate and iron fluorophosphate phases. The chains in Ba2Fe2(PO4)F6 can be described as Fe22+O2F8 dimers alternately isolated by Fe23+P2O8F8 units, whereas the Fe3+ ions are coupled to each other through Fe−O−O−Fe paths. However, Fe2F5·2H2O33 was formed by vertex-sharing octahedral Fe3+F6 chains, where the four fluorine atoms of an Fe2+F4(H2O) octahedron linked the chains. Charge-ordered RbFe2+Fe3+F6 exhibited a 3D pyrochlore-related architecture formed by corner-sharing Fe3+F6 and Fe2+F6 octahedra.34 (NH4)2Fe2+Fe3+(PO3F)2FCl2 contains sheets of Fe2+O2Cl4 octahedra linked by chains of Fe3+O4F2 octahedra via edge-sharing PO3F tetrahedra with fluoride.31 Two different types of edge connections are present in Ba2Fe2(PO4)F6, and their respective roles of bridging two Fe2+ groups or linking Fe2+ and Fe3+ atoms may be recognized from the metal−oxide or metal−fluoride bond lengths. The average Fe(1)−F bond length of 1.982 Å and Fe(1)−O bond length of 1.921 Å are significantly shorter than the corresponding Fe(2)−F bond length of 2.107 Å and the Fe(2)−O bond distance of 2.117 Å, in accordance with the formal oxidation state assignments of Fe3+ and Fe2+, respectively. However, the average Fe3+−F distances in FeF335 and BaFeF536 are 1.93 and 1.92 Å, respectively, whereas the Fe2+−F distances in FeF237 and Fe2F5·2H2O33 are 2.07 and 2.06 Å, respectively, where the fluoride atoms function as a trans vertex in the FeF6 octahedra. The long Fe−F bond lengths in Ba2Fe2(PO4)F6 suggest that the cis-FeF4O2 octahedra are more distorted than those of the above examples. More evidence for this possibility is that the

Figure 2. Experimental (black) and calculated (red) X-ray powder patterns for (a) BaFe(PO4)F2, (b) Ba2Fe2(PO4)F6, and (c) Ba3Fe3(PO4)F12.

chain running parallel to the cell c-axis. These parallel chains are cross-linked with adjacent parallel chains through bridging PO4 tetrahedra, which produces an unusual 3D framework. The distance between two parallel chains is half the length of

Figure 3. (a) Projection of the structure of Ba2Fe2(PO4)F6 along the b-axis. [Fe(1)3+OnF6−n]m−1 octahedra, [Fe(2)2+OnF6−n]m− octahedra, and PO4 tetrahedra are drawn in sky blue, light green, and light orange, respectively. Fe(1) and Fe(2) atoms are highlighted in blue and teal, respectively. (b) Views of a slab of ∞[Fe2(PO4)F6]4− in the bc-plane. (c) Views of a chain of ∞[Fe2O2F6]5− along the [110] direction. (d) Coordination environment of the Ba cations by O/F atoms for Ba2Fe2(PO4)F6. E


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Inorganic Chemistry

Figure 4. (a) Projection of the structure of Ba3Fe3(PO4)F12 along the b-axis. [Fe3+OnF6−n]m−1 octahedra are drawn in sky blue, and PO4 tetrahedra are highlighted in light orange. (b) Projection of a slab of a part of ∞[Fe3(PO4)F12]6− blocks along the b-axis in the ac-plane. [Fe3F12O4]11− chains are highlighted in circles. (c) Coordination environment of the Ba cations with O/F atoms for Ba3Fe3(PO4)F12.

cis-(O, F)−Fe(1)−(O, F) bond angle ranges from 78.2(3) to 100.2(4)°, whereas the cis-(O, F)−Fe(2)−(O, F) bond angle ranges from 69.1(3) to 115.2(4)°. These data are far from 90°. The crystal structure of Ba3Fe3(PO4)F12 was solved in the P1̅ space group (a = 7.5665(2) Å, b = 7.7044(2) Å, c = 12.4694(3) Å, α = 74.3210(13)°, β = 79.3925(13)°, γ = 85.7554(13)°, and V = 687.67(3) Å3) with final reliability factors of R1 = 3.19% and wR2 = 3.78%. The structure of Ba3Fe3(PO4)F12 contains 1D columns of ∞[Fe3(PO4)F12]6− infinite sections along the b direction (Figure 4a). The surrounding Ba(1)F9O and Ba(2)F9 polyhedra form parallel layers along the a direction, whereas Ba(3)F6O2 polyhedra form parallel channels along the b direction. The [Fe3(PO4)F12]6− 1D columns comprise circular [Fe3F12O4]11− chains linked by corner-sharing PO4 tetrahedra (see Figure 4b), whereas each [Fe3F12O4]11− chain is formed by one cis-FeF4O2 octahedron that bridges two FeF5O octahedra via cis cornersharing fluorine atoms. Selected bond distances and angles are summarized in Table S9. The Fe(1)−F bond lengths fall in the range of 1.926(5)− 2.037(4) Å, and the Fe1−O bond lengths range from 1.944(4) to 1.995(4) Å, which are comparable to those for Fe3+ in Ba2Fe2(PO4)F6. The average Fe(2)−F bond distance of 1.937 Å compares quite favorably with the value of 1.93 Å calculated for Fe3+ with bridging fluoride from the effective ionic radii suggested by Shannon and Prewitt, whereas the average Fe(3)−F bond distance of 1.950 Å deviates from the ideal range.38 The BVS calculations27 for Ba2+, Fe3+, and P5+ cations gave values of 1.79(1)−2.16(1), 2.98(2)−3.09(2), and 4.95(3), respectively, as shown in Table 2. 3.2. EPR and Mössbauer Spectra. To elucidate the crystal environments of the Fe ions, an EPR technique was employed. Figure 5 compares the room temperature EPR spectra of the BaFe(PO 4 )F 2 , Ba 2 Fe 2 (PO 4 )F 6 , and Ba 3 Fe 3 (PO 4 )F 12 samples. For the BaFe(PO 4 )F 2 and Ba2Fe2(PO4)F6 samples, the EPR signals are described by

Figure 5. Derivative of the EPR absorption of the BaFe(PO4)F2, Ba2Fe2(PO4)F6, and Ba3Fe3(PO4)F12 samples measured at ν = 9.445 GHz and at room temperature. For the former two samples, the red solid lines are fits to a sum of two Lorentzian profiles and the dashed lines represent the Lorentzian components. For Ba3Fe3(PO4)F12, the EPR spectrum is described by a single Lorentzian profile.

the convolution of two Lorentzian absorption lines. In contrast, a single Lorentzian profile sufficiently describes the EPR spectrum of the Ba3Fe3(PO4)F12 sample, implying that it has negligible magnetic anisotropy. By virtue of fast electronic fluctuations induced by the strong exchange interaction between Fe ions, the exchange-narrowed EPR lines are found. From the Lorentzian fits, the g factors were determined to be g// = 1.96(3) and g⊥ = 1.96(7) for BaFe(PO4)F2, g// = 1.95(4) and g⊥ = 1.96(1) for Ba2Fe2(PO4)F6, and g// = g⊥ = 1.98(6) for Ba3Fe3(PO4)F12. The determined values are in line F


Article

Inorganic Chemistry with a typical g-factor expected for high-spin Fe3+ ions (d5; S = 5/2, g ≈ 2.003), which reside in an octahedral environment. Some comment on the mixed-valence system Ba2Fe2(PO4)F6 is in order. Although Ba2Fe2(PO4)F6 contains distinct Fe3+ and Fe2+ ions, the EPR signal stemming from the Fe2+ ions could not be probed by X-band EPR. Therefore, 57Fe Mössbauer spectra of Ba2Fe2(PO4)F6 were collected at several temperatures between 4 and 293 K to obtain the local structural information about the iron ions. As shown in Figure 6, the Mössbauer spectra obtained at T = 20 and 298 K consist of two quadrupole doublets. The

magnetic transition occurs between 20 and 4 K. Strong magnetic correlations are observed at 4 K, and considering the narrow well-defined peaks in the Mössbauer spectrum taken at 4 K, long-range magnetic ordering most likely occurs. Further information concerning the direction of the spin moments with respect to that of the electric field gradient axes may be deduced in the case of Fe2+. In fact, fitting of the spectrum recorded at 4 K lead, in the case of Fe2+, to the following value of the asymmetry parameter of the electric field gradient, η, of 0.35, the value of the angle θ between Bhf and the main axis of the electric field gradient, Vzz, θ = 66°, and the angle between Vxx and the projection of Bhf on the xy plane of 5°.40 The angle between Vzz and the spin moment of Fe2+, μFe2, is therefore ∼24° because μFe2 is antiparallel to Bhf.39 In the case of Fe3+, however, no information on the direction of the spin moment is obtained. When the electric quadrupole interaction is much lower than the magnetic interaction, only a six-peak pattern (with peak relative areas 3:2:1:1:2:3) is observed as is the case of Fe3+ in Ba2Fe2(PO4)F6 and the angles θ and φ are not determinable from the spectrum.39 3.3. Magnetic Properties. We further measured the magnetic susceptibilities (χ(T)) of three samples to understand their underlying magnetism. Figure 7 exhibits the temperature dependence of χ(T) of BaFe(PO4)F2 measured under an applied field of 1 kOe in ZFC and FC processes. We found no difference between the ZFC and FC data, ruling out

Figure 6. Mössbauer spectra of the Ba2Fe2(PO4)F6 sample taken at different temperatures. Above the magnetic ordering temperature, the lines over the experimental points are the sum of two doublets, and below this temperature, they are the sum of two magnetic splittings: a sextet for Fe3+ and an octet for Fe2+ (see the text and Table S10).

doublets with the lowest values are calculated by the fitting procedure for the isomer shifts (ISs) at 298 K, and quadrupole splittings (QSs) are compatible with Fe3+, having a spin state of S = 5/2 (see Table S10). The doublets with the highest IS and QS values are consistent with Fe2+, having a spin state of S = 2.39 As expected, the QS values of Fe3+ do not depend on the temperature within the experimental error, whereas the QS of Fe2+ decreases as the temperature increases. The decrease in IS with the increasing temperature is due to the second-order Doppler shift. Thus, it is suggested in a clear manner by the Mössbauer spectra that half of the Fe cations in Ba2Fe2(PO4)F6 are Fe3+ (S = 5/2), whereas the other half are Fe2+ (S = 2). A spectrum consisting of two magnetic splittings was observed at 4 K. The magnetic hyperfine field (Bhf) ∼ 55.4 T of the sextet confirms the presence of Fe3+ with a spin state of S = 5/2. The shape of the magnetically split signal of Fe2+ shows that the quadrupole hyperfine interaction is not small enough to be considered a perturbation to the magnetic hyperfine interaction. To estimate the peak positions and intensities, the Hamiltonian for the hyperfine interactions was solved following the method described in ref 40. The estimated IS, QS, and Bhf values (see Table S10) are consistent with those obtained for the spectra measured for temperatures above 20 K, confirming that approximately half of the total Fe in Ba2Fe2(PO4)F6 is Fe2+ with a spin state of S = 2.39 Moreover, in agreement with the magnetization data, a

Figure 7. (a) Temperature dependence of the magnetic susceptibility of BaFe(PO4)F2 measured in an external field of H = 1000 Oe. The black solid line is a fit to the modified Bonner−Fisher model. The vertical arrows mark two magnetic transitions at TN = 21.5 K and T* = 12.6 K. The inset plots the temperature dependence of the reciprocal magnetic susceptibility with the Curie−Weiss fit. (b) Isothermal magnetization curve M(H) measured at T = 2 K. The solid lines represent the linear dependence of M(H), allowing identification of a spin−flop field at Bsf = 3.1 T, as marked by vertical arrows. G


Article

Inorganic Chemistry the presence of site disorders and magnetic anisotropy. With a decrease in temperature, χ(T) shows a broad maximum at approximately 74 K, indicative of the development of lowdimensional, short-range spin correlations. Upon further cooling, χ(T) displays two successive small kinks at TN = 21.5 K and T* = 12.6 K [marked by vertical arrows in Figure 7a]. The higher-temperature anomaly is ascribed to the onset of antiferromagnetic long-range ordering, judging from the clear observation of a λ-like peak in the heat capacity (Figure S4). However, the heat capacity shows no discernible peak at T* = 12.6 K. Thus, the lower-temperature anomaly may be due to either a hidden order involving tiny entropy or structural defects. For temperatures above TN, χ(T) is well described by the modified Bonner−Fisher model for an S = 5/2 spin chain41 χ (T ) = χ0 +

NAS(S + 1) 2 2 1 + u(K ) g μB 3kBT 1 − u(K )

where u(K ) = coth K −

1 K

and K =

2JS(S + 1) . kBT

(1)

Here, χo is the

temperature-independent contribution stemming from the diamagnetism of the core electron shells and the van Vleck paramagnetism of the open shells of the Fe3+ ions, kB is the Boltzmann constant, g is the Landé factor, and J is the nearestneighbor exchange interaction. As seen from the solid line in Figure 7a, the S = 5/2 uniform antiferromagnetic chain model provides a reasonable description of BaFe(PO4)F2 despite the presence of interchain interactions and a zigzag-type modulation. The fit to the data yields the following magnetic parameters: JBF/kB = −8.9 ± 0.2 K and χo = (1.64 ± 0.04) × 10−3 cm3/mol. In the fitting procedure, the g-factor is fixed to the experimental value of g = 1.96 determined directly from the EPR signal (see above). We further analyzed the high-temperature χ(T) in terms of the Curie−Weiss law χ(T) = C/(T − θCW) + χo, where C is the molar Curie constant and θCW is the Curie−Weiss temperature. As shown in the inset of Figure 7a, the Curie−Weiss fitting of 1/χ(T) above 200 K gives the effective magnetic moment (μeff) = 6.36 ± 0.23 μB and θCW = −216.7 ± 2.4 K. The estimated μeff value is larger than the spin-only value of μeff of 5.92 μB. In the mean-field theory, the intrachain exchange interaction is evaluated to be JMF ≈ −37 K by taking the number of nearest neighbors z = 2. This value is roughly four times larger than JBF/kB = −8.9 ± 0.2 K. This discrepancy is ascribed partly to the presence of appreciable interchain interactions and partly to a limited temperature window. Figure 7b displays the isothermal magnetization curve (M(H)) collected at 2 K. M(H) shows a linear increase with a slope change at Bsf = 3.1 T. This change is due to a spin−flop transition, which is characteristic of antiferromagnets. Next, we turn to χ(T) of Ba2Fe2(PO4)F6, which is presented in Figure 8a. Upon cooling to TN = 14.2 K, χ(T) shows a steep increase, suggesting the presence of weak ferromagnetism. As is evident from the inset of Figure 8a, at temperatures above 50 K, χ(T) exhibits a Curie−Weiss behavior. Fitting the data to the Curie−Weiss law yields μeff = 5.67 ± 0.17 μB and θCW = −29.34 ± 1.2 K. Compared to those of BaFe(PO4)F2, the estimated μeff value of Ba2Fe2(PO4)F6 is close to the spin-only value and the Curie temperature is reduced by almost one order of magnitude. This result suggests an extensive alteration of the exchange paths between the two systems. Figure 8b displays M(H) collected at 2 K. M(H) shows a steep increase with an increase in the field up to 0.6 T and,

Figure 8. (a) Magnetic susceptibility of Ba2Fe2(PO4)F6 measured with a measuring field of 1000 Oe as a function of temperature. The vertical arrow marks a magnetic transition at TN = 14.35 K. The inset plots the temperature dependence of the reciprocal magnetic susceptibility with the Curie−Weiss fit. (b) Isothermal magnetization curve M(H) measured at T = 2 K. The inset reveals magnetic hysteresis, showing a small remnant magnetization.

subsequently, a linear increase with a further increase in the field. The high-field linear component with no obvious hysteretic behavior arises from the presence of sizable antiferromagnetic interactions, consistent with the negative θCW value. The low-field, ferromagnetic-like component of the magnetization with 0.2 μ B may be due to canted antiferromagnet or weak ferrimagnet. Finally, Figure 9a shows χ(T) of Ba3Fe3(PO4)F12 for the FC and ZFC processes measured in an external field of 1 kOe. With a decrease in temperature, χ(T) displays a steep increase, followed by a sharp peak and finally a drop to two-thirds of the maximum χ(T) value at approximately 15 K. In addition, the ZFC−FC curves bifurcate at TN = 11.1 K. At this temperature, the sharp peak observed in the heat capacity (Figure S5) confirms the second-order transition to the antiferromagnetic state. The inverse susceptibility data shown in the inset of Figure 9a show two linear regimes within the temperature range. Application of a linear fit to the high-temperature data above 120 K reveals strong antiferromagnetic correlations with θCW = −104.78 ± 2.3 K and μeff = 6.11 ± 0.13 μB/Fe. For temperatures below 70 K, a second low-temperature Curie− Weiss fit yields θCW = 13.89 ± 1.2 K and μeff = 6.02 ± 0.11 μB/ Fe. The positive value of θCW suggests the development of ferromagnetic correlations, which is consistent with the steep growth of χ(T) in the corresponding temperature range. Figure 9b displays M(H) measured at 2 K. M(H) first shows a linear increase with an increase in the field up to 0.6 T and, subsequently, a steep increase to saturation with a further increase in the field up to 3.0 T. The low-field linear increase in H


Article

Inorganic Chemistry

framework with mixed-valence iron contains Fe 4 O 6 F 12 tetramers formed by the edge-sharing oxygen or fluorine atoms of cis-FeF4O2 octahedra. Finally, (III) shows coupled spin-trimers that contain [Fe3F12O4]11− chains formed by one cis-FeF4O2 octahedron that bridges two FeF5O octahedra via cis corner-sharing fluorine atoms. In addition, a unique ordered Fe2+/Fe3+ pattern was found in Ba2Fe2(PO4)F6 and confirmed by Mössbauer spectroscopy. This pattern was formed by edgesharing octahedral Fe22+O2F8 dimers alternately isolated by edge-sharing [Fe3+O4F2]7− units, in contrast to normal cornersharing [Fe2+OnF6−n]m− and [Fe3+OnF6−n]m−1 octahedra.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01982. Detailed structural parameters; BVS, TG, and Mössbauer spectroscopy; deposition numbers CCDC 1855914, 1855915, and 1855916 for BaFe(PO4)F2, Ba2Fe2(PO4)F6, and Ba3Fe3(PO4)F12, respectively (PDF) Accession Codes

CCDC 1855914−1855916 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Figure 9. (a) Magnetic susceptibility of Ba3Fe3(PO4)F12 measured by applying an external field of 1000 Oe as a function of temperature. The vertical arrow marks a magnetic transition at TN = 11.1 K. The inset plots the temperature dependence of the reciprocal magnetic susceptibility with the Curie−Weiss fit. (b) Isothermal magnetization curve M(H) measured at T = 2 K, showing a one-third magnetization plateau.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Minfeng Lü: 0000-0003-2576-3840

M(H) is linked to antiferromagnetic ordering, whereas the intermediate-field quick saturation is due to ferromagnetic correlations. It is remarkable that the saturation magnetic moment of 1.67μB/Fe amounts to one-third of the full saturation magnetization MS = gSμB ≈ 5 μB. Here, we note that the basic magnetic building block of Ba3Fe3(PO4)F12 is a spintrimer consisting of a strong antiferromagnetic interaction J1 between Fe1 and Fe2 ions and a weak ferromagnetic interaction J2 between Fe1 and Fe3 ions (see Figure 4b). The coupled spin-trimers adopt an antiferromagnetic arrangement below TN = 11.1 K. Application of a small field first leads to polarization of the ferromagnetically coupled spin, whereas the antiferromagnetically coupled spins remain robust.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21671185). The authors at C2TN/IST gratefully acknowledge the support from FCT through the UID/Multi/04349/2013 project.

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REFERENCES

(1) Kabbour, H.; David, R.; Pautrat, A.; Koo, H.-J.; Whangbo, M. H.; André, G.; Mentré, O. A Genuine two-dimensional ising ferromagnet with magnetically driven re-entrant transition. Angew. Chem., Int. Ed. 2012, 124, 11915−11919. (2) Hu, S.; Mace, A.; Johnsson, M.; Gnezdilov, V.; Lemmens, P.; Tapp, J.; Möller, A. Crystal structure and magnetic properties of the S = 1/2 quantum spin system Cu7(TeO3)6F2 with mixed dimensionality. Inorg. Chem. 2014, 53, 7661−7667. (3) Hu, S.; Johnsson, M.; Law, J. M.; Bettis, J. L., Jr.; Whangbo, M.H.; Kremer, R. K. Crystal structure and magnetic properties of FeSeO3F alternating antiferromagnetic S = 5/2 chains. Inorg. Chem. 2014, 53, 4250−4256. (4) Xia, Y. N.; Chen, C. T.; Tang, D. Y.; Wu, B. C. New nonlinearoptical crystals for UV and VUV harmonic-generation. Adv. Mater. 1995, 7, 79−81. (5) Cyranoski, D. China’s crystal cache. Nature 2009, 457, 953−955. (6) Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. J. Electrochem. Soc. 1997, 144, 1188−1194.

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CONCLUSIONS We have successfully synthesized fluoride-rich barium iron phosphates BaxFex(PO4)Fy (1 ≤ x ≤ 3, 2 ≤ y ≤ 12) using a fluoride-rich hydrothermal method derived from phosphoric and fluorophosphoric acids with the aid of hydrazine to balance the pH of the hydrothermal solutions. The successful synthesis allowed us to examine the magnetic properties of BaxFex(PO4)Fy (1 ≤ x ≤ 3, 2 ≤ y ≤ 12) and the frameworks and connection modes between [FeOnF6−n]m− octahedra. (I) shows an interesting spin−flop transition at low temperature, stemming from the antiferromagnetic ordering of an S = 5/2 spin chain formed by linear ∞[Fe2O6F4]10− moieties consisting of fluorine corner-sharing FeO4F2 and FeO2F4 octahedra. (II) is a canted antiferromagnet or weak ferrimagnet whose 3D I


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Inorganic Chemistry (7) Huang, H.; Faulkner, T.; Barker, J.; Saïdi, M. Y. Lithium metal phosphates, power and automotive applications. J. Power Sources 2009, 189, 748−751. (8) Ramesh, T. N.; Lee, K. T.; Ellis, B. L.; Nazar, L. F. Tavorite lithium iron fluorophosphate cathode materials: phase transition and electrochemistry of LiFePO4F−Li2FePO4F. Electrochem. Solid-State Lett. 2010, 13, A43−A47. (9) Clearfield, A. Recent advances in metal phosphonate chemistry. Curr. Opin. Solid State Mater. Sci. 1996, 1, 268−278. (10) Armstrong, J. A.; Williams, E. R.; Weller, M. T. Fluoride-Rich, Hydrofluorothermal Routes to Functional Transition Metal (Mn, Fe, Co, Cu) Fluorophosphates. J. Am. Chem. Soc. 2011, 133, 8252−8263. (11) Atuchin, V. V.; Molokeev, M. S.; Yurkin, G. Y.; Gavrilova, T. A.; Kesler, V. K.; Laptash, N. M.; Flerov, I. N.; Patrin, G. S. Synthesis, Structural, Magnetic, and Electronic Properties of Cubic CsMnMoO3F3 Oxyfluoride. J. Phys. Chem. C 2012, 116, 10162−70. (12) Galven, C.; Legein, C.; Body, M.; Fourquet, J.-L.; Buzaré, J.-Y.; Le Berre, F.; Crosnier-Lopez, M.-P. New Oxyfluoride Pyrochlores Li2−xLa (1+x)/3□(2x−1)/3B2O6F (B = Nb, Ta): Average and Local Structure Characterization by XRD, TEM and 19F Solid - State NMR. Eur. J. Inorg. Chem. 2010, 5272−5283. (13) Rouse, J.; Redrup, K. V.; Kotsapa, E.; Weller, M. T. Controlling dimensionality in templated layer, chain and framework structures by combining metal fluorides with oxotetrahedra. Chem. Commun. 2009, 46, 7209−11. (14) Bonhomme, F.; Thoma, S. G.; Rodriguez, M. A.; Nenoff, T. M. Ga4(PO4)4F·N2C7H11·1/2H2O: A Three-Dimensional Open Framework with 12-Membered Pores and “Bowl-Shaped” Building Units. Chem. Mater. 2001, 13, 2112−2117. (15) Riou-Cavellec, M.; Riou, D.; Férey, G. Magnetic iron phosphates with an open framework. Inorg. Chem. Acta 1999, 291, 317−325. (16) Leblanc, M.; Collin-Fèvre, I.; Férey, G. The magnetic structures of Mn2PO4F and Co2PO4F at 1.2 K. J. Magn. Magn. Mater. 1997, 167, 71−79. (17) Ben Ali, A.; Maisonneuve, V.; Kodjikian, S.; Smiri, L. S.; Leblanca, M. Synthesis, crystal structure and magnetic properties of a new fluoride carbonate Ba2Co(CO3)2F2. Solid State Sci. 2002, 4, 503− 506. (18) Sanjeewa, L. D.; McGuire, M. A.; Smith Pellizzeri, T. M.; McMillen, C. D.; Ovidiu Garlea, V.; Willett, D.; Chumanov, G.; Kolis, J. W. Synthesis and Characterization of New Fluoride-Containing Manganese Vanadates A2Mn2V2O7F2 (A = Rb, Cs) and Mn2VO4F. J. Solid State Chem. 2016, 241, 30−37. (19) Weil, M.; Baran, E. J.; Kremer, R. K.; Libowitzky, E. Synthesis, crystal structure, and properties of Mn(PO3F)·2H2O. Z. Anorg. Allg. Chem. 2015, 641, 184−191. (20) Holland, T. J. B.; Redfern, S. A. T. Unit cell refinement from powder diffraction data: the use of regression diagnostics. Mineral. Mag. 1997, 61, 65−77. (21) SAINT: Area-Detector Integration Software; Siemens Industrial Automation, Inc.: Madison, 1996. (22) SADABS: Area-Detector Absorption Correction; Siemens Industrial Automation, Inc.: Madison, 1995. (23) Yahia, H. B.; Shikano, M.; Kobayashi, H. Single crystal growth of the novel Mn2(OH)2SO3, Mn2F(OH)SO3, and Mn5(OH)4(H2O)2[SO3]2[SO4] compounds using a hydrothermal method. Dalton Trans 2013, 42, 7158−7166. (24) Fedotov, S. S.; Khasanova, N. R.; Samarin, A. S.; Drozhzhin, O. A.; Batuk, D.; Karakulina, O. M.; Hadermann, J.; Abakumov, A. M.; Antipov, E. V. AVPO4F (A = Li, K): A 4 V Cathode Material for High-Power Rechargeable Batteries. Chem. Mater. 2016, 28, 411−415. (25) Long, G. J.; Cranshaw, T. E.; Longworth, G. The ideal Mössbauer effect absorber thicknesses. Moessbauer Eff. Ref. Data J. 1983, 6, 42−49. (26) Waerenborgh, J. C.; Rojas, D. P.; Shaula, A. L.; Mather, G. C.; Patrakeev, M. V.; Kharton, V. V.; Frade, J. R. Phase formation and iron oxidation state in SrFe(Al)O3‑δ perovskites. Mater. Lett. 2005, 59, 1644−1648.

(27) Le Meins, J.-M.; Hémon-Ribaud, A.; Laligant, Y.; Courbion, G. A new fluorophosphate with a laueite-type structural unit:synthesis, TEM study and crystal structure of SrFePO4F2. Eur. J. Solid State Inorg. Chem. 1997, 34, 391−404. (28) Palatinus, L.; Chapuis, G. SUPERFLIP−a computer program for the solution of crystal structures by charge flipping in arbitrary dimensions. J. Appl. Crystallogr. 2007, 40, 786−790. (29) Petricek, V.; Dusek, M.; Palatinus, L. The Crystallographic Computing System, Jana2006; Institute of Physics: Praha, Czech Republic, 2006. (30) Brese, N. E.; O’Keeffe, M. Bond-valence parameters for solids. Acta Crystallogr., Sect. B: Struct. Sci. 1991, 47, 192−197. (31) Keates, A. C.; Armstrong, J. A.; Weller, M. T. Iron fluorophosphates. Dalton Trans. 2013, 42, 10715−10724. (32) Sheldrick, G. M. SHELXTL NT, Program Suite for solution and Refinement of Crystal Structure, version 5.1, Bruker Analytical X-ray Systems: Madison, WI. (33) Hall, W.; Kim, S.; Zubieta, J.; Walton, E. G.; Brown, D. B. Structure of a mixed-valence iron fluoride, Fe2F5·2H2O. Inorg. Chem. 1977, 16, 1884−1886. (34) Ferey, G.; LeBlanc, M.; De Pape, R. Crystal structure of the ordered pyrochlore NH4FeIIFeIIIF6 structural correlations with Fe2F5· 2H2O and its dehydration product Fe2F5·H2O. J. Solid State Chem. 1981, 40, 1−7. (35) Hepworth, M. A.; Jack, K. H.; Peacock, R. D.; Westland, G. J. The crystal structures of the trifluorides of iron, cobalt, ruthenium, rhodium, palladium and iridium. Acta Crystallogr. 1957, 10, 63−69. (36) Von der Mühll, R.; Anderson, S.; Galy, J. Sur quelques fluométallates alcalino-terreux. I. Structure cristalline de BaFeF5 et SrAlF5. Acta Crystallogr., Sect. B: Struct. Sci. 1971, 27, 2345−53. (37) Baur, W. H.; Khan, A. A. Rutile-type compounds. IV. SiO2, GeO2 and a comparison with other rutile-type structures. Acta Crystallogr., Sect. B: Struct. Sci. 1971, 27, 2133. (38) Shannon, R. D.; Prewitt, C. T. Effective ionic radii in oxides and fluorides. Acta Crystallogr., Sect. B: Struct. Sci. 1969, 25, 925−46. (39) Greenwood, N. N.; Gibb, T. C. Mössbauer Spectroscopy; Chapman and Hall, Ltd. Publishers: London, 1971. (40) Ruebenbauer, K.; Birchall, T. A computer programme for the evaluation of Mössbauer data. Hyperfine Interact. 1979, 7, 125−133. (41) Dingle, R.; Lines, M. E.; Holt, S. L. Linear-Chain Antiferromagnetism in [(CH3)4N] [MnCl3]. Phys. Rev. 1969, 187, 643−647.

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Variable Dimensionality, Valence, and Magnetism in Fluoride-Rich

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