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Dec 19, 2016 - Weak ferromagnetic interlayer interactions cause a small tilt (∼1.5°) of the magnetic moments, resulting in canted antiferromagnetis...
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Canted Antiferromagnetism in Two-Dimensional Silver(II) Bis[pentafluoridooxidotungstate(VI)] Zoran Mazej,*,† Tomasz Gilewski,‡,§ Evgeny A. Goreshnik,† Zvonko Jagličić,∥ Mariana Derzsi,‡ and Wojciech Grochala*,‡ †

Department of Inorganic Chemistry and Technology, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia CENT, University of Warsaw, Ż wirki i Wigury 93, 02-089 Warsaw, Poland § Faculty of Chemistry, University of Warsaw, Pasteur 1, 02-093 Warsaw, Poland ∥ Faculty of Civil and Geodetic Engineering, and Institute of Mathematics, Physics and Mechanics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia ‡

S Supporting Information *

ABSTRACT: By slow reaction between colorless AgIW2O2F9 and elemental F2 in liquid anhydrous HF, violet platelike single crystals of Ag(WOF5)2 were grown. The crystal structure of Ag(WOF5)2 consists of layers built from Ag2+ cations bridged by [WOF5]− anions and not, as previously assumed, from infinite [AgII−F]+∞ chains and [W2O2F9]− anions. A majority (97%) of the disordered AgII cations are found with square-planar coordination of F/O ligands within the same layer, and they form additional long contacts with O/F atoms originating from the neighboring layers. The remaining 3% the of Ag(II) ions are coordinated only by F atoms in a square-planar fashion. The magnetic moments of Ag2+ from the same layer are almost perfectly antiferromagnetically aligned. Weak ferromagnetic interlayer interactions cause a small tilt (∼1.5°) of the magnetic moments, resulting in canted antiferromagnetism. Because of the lowering of the symmetry of [WOF5]− in the solid state, the vibrational spectra show more bands than expected for regular C4v symmetry. The electronic spectrum of Ag(WOF5)2 is reported and analyzed.

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work, we describe the crystal structure of AgII(WOF5)2 and the results of a detailed examination of its vibrational and electronic spectra as well as its thermal and magnetic properties.

INTRODUCTION In the literature there are many reports about the ternary Ag(II) fluorides that consist of infinite −[F−Ag−F−Ag−]n (i.e., [AgII−F]+∞) chains, such as AgFBF4 and AgFMF6 (M = As, Ir, Au, etc.1). The [AgII−F]+∞ chains may be kinked, with the Ag−F−Ag angles varying from 127° to 176°, or linear (180°).1 Most of these substances were previously reported to exhibit temperature-independent paramagnetism.1 Two decades ago it was reported2−4 that fluorination of AgIW2O2F9 in anhydrous hydrogen fluoride (aHF) yielded a compound with the elemental composition of AgW2O2F10. Two isomers, AgII[WOF5−]2 and [AgIIF]+[W2O2F9−], are formally possible for such a stoichiometry. On the basis of vibrational spectra2−4 and magnetic properties3 it was proposed that the prepared compound corresponded to the AgIIFW2O2F9 formulation. If true, this would be the only example of an oxofluoride material containing infinite [AgII−F]+∞ chains.1 Although the crystal structure of the compound was not known, it was later assumed, on the basis of its chemical behavior, that oxygen atoms most probably do not bind directly to the Ag centers.1 To learn whether the reported compound indeed corresponds to AgFW2O2F9 and not to Ag(WOF5)2, we decided to grow single crystals and determine the crystal structure. Surprisingly, our study shows that the previously proposed formulation is incorrect, i.e., the compound contains the [WOF5]− anion rather than [W2O2F9]−.2−4 In the present © XXXX American Chemical Society

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RESULTS AND DISCUSSION

Preparation of Ag(WOF5)2 and Growth of Corresponding Single Crystals. The example of the growth of single crystals of AgSb2F11 had already shown how the insolubility of a compound in aHF can be taken into advantage for its single-crystal growth.5 Similarly, the fluorination of AgW2O2F9 with F2 in aHF, which started at 77 K and continued during warming to ambient temperature, was slow enough to result in violet-blue single crystals of Ag(WOF5)2 instead of a powdered material. In the previous work on AgW2O2F10, the growth of crystals of the same violet color was also reported, thus suggesting that the two products are identical.2,4 Those authors2,4 assumed that the crystals correspond to AgFW2O2F9, but there have not been any reports about the crystal structure determination of this phase. Interestingly, when the violet-blue crystals are powdered, the resulting fine powder is bluish-gray. Larger quantities of powdered Ag(WOF5)2 were also synthesized. The reaction was done in a similar manner as crystallization, with the main differences being that the reaction mixture was warmed to Received: August 22, 2016

A

DOI: 10.1021/acs.inorgchem.6b02034 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ambient temperature much more quickly and that it was stirred all the time. After 1 day, the gray material was obtained. Although AgF2 could not be detected using X-ray powder diffraction analysis, the magnetic measurements showed that Ag(WOF5)2 was contaminated with a tiny amount of AgF2. As reported before, the reaction of AgF2 and 2 equiv of WOF4 in aHF did not proceed.2−4 Crystal Structure of Ag(WOF5)2. The title compound was found to crystallize in the monoclinic unit cell (P21/c). There are two crystallographically distinct Ag atoms in the structure, with partial occupancies of Ag(1) = 0.966(4) and Ag(2) = 0.034(4), and also two crystallographically independent [WOF5]− anions inside the irreducible cell. The crystal structure of Ag(WOF5)2 may be described as a layered one in which each puckered layer is built from Ag(II) cations interconnected via [WOF5]− anions (Figure 1). The buckled

Figure 2. Packing of the puckered layers in the crystal structure of Ag(WOF5)2. Long interlayer Ag···F contacts (>2.5 Å) have been omitted for clarity.

(2.075(7) Å), and one short W(1)O bond (1.729(8) Å). As the two previously reported compounds containing [WOF5]− anions exhibited the O/F disorder (with average W−O/F distances of 1.82(1) and 1.842 Å6,7), the substitutional disorder of O and F atoms in [W(1)OF5]− cannot be excluded. A residual electron density of 5.1 e/Å3 was observed at 0.27 Å from the other tungsten site, W(2), which allowed the tungsten site to be split into two positions W(2a) and W(2b) (with an 0.8715:0.1285 occupancy ratio). After the split model had been used, there was immediate improvement in the fit. The observed W(2) splitting must be also connected with the random distribution of Fax and trans-O atoms, as suggested for the FeO5F octahedra in the crystal structure of Sr2FeO3F.8 The F(1d)/O(1d) and F(2d)/(O2d) sites of the W(2)OF5 unit were randomly distributed according to the ratio of the corresponding tungsten site occupancies. In such a way, the [W(2)OF5]− anion shows two possible orientations of Fax/O atoms, one of them being 7 times more probable than the other (Figure S1). Further attempts to introduce additional disorder of O and Feq atoms were unsuccessful. More details about the O/F substitutional disorder could be gained from the neutron diffraction studies. Vibrational Spectra of Ag(WOF5)2. The infrared and Raman spectra of Ag(WOF5)2 were acquired on powdered samples. Additionally, Raman spectra were recorded on randomly orientated single crystals that were checked first on a diffractometer. The spectra are shown in Figure 3, and numerical data are given in Table 1. Interestingly, they are in complete disagreement with the previously reported data for “AgFW2OF9”,2,4 although the X-ray powder patterns of the compounds (refs 2−4 and this work) are practically the same. The possible reason for this discrepancy will be discussed below. The assignment of the spectra was made on the basis of a comparison with the literature data9−11 and additionally supported by our theoretical calculations (see the Supporting Information). Because of the reduction in the symmetry of WOF5 units upon transition from the gas phase to the solid state, there are more bands in the spectra than expected for [WOF5]− anions with C4v symmetry. However, many of the additional bands in

Figure 1. Puckered layer in the crystal structure of Ag(WOF5)2.

layers are mostly formed of Ag−F/O−W chains interconnected by Ag(1) with an overall metal:anion ratio of 1:2 and a topology resembling that of the [CuO2] sublattice of layered oxocuprates. It should be noted that the observed Ag(1)/Ag(2) disorder could in fact correspond to the disorder of the packing of the layers, with 3% staggered and 97% eclipsed ones. The first coordination sphere of Ag(1) consists of four short bonds (Ag(1)−F(5) = 2.083(7) Å, Ag(1)−O(1) = 2.098(8) Å, Ag(1)−F(2d)/O(2d) = 2.091(8) Å, Ag(1)−F(1d)/O(1d) = 2.073(7) Å; “d” stands for disorder) that are arranged in a nearly square-planar geometry within the layer and three additional long contacts (Figure 2) to the F(1) and F(5) atoms (2.700(8) and 2.895(8) Å) located in the first neighboring layer and F(7) (2.507(7) Å) in the second one. Ag(2) is squareplanar-coordinated by four F atoms (Ag(2)−F(1) = 2.26(3) Å, Ag(2)−F(3) = 2.12(3) Å, Ag(2)−F(8) = 2.17(3) Å, and Ag(2)−F(10) = 2.15(3) Å) within the layer, and additionally, it forms one contact with the F(4) atom (2.51(3) Å) originating from the first neighboring layer and two long contacts with F(8) (2.83(3) Å) and F(1d)/O(1d) (2.91(3) Å) originating from the second one. In the [W(1)OF5]− anion there are four longer W(1)−Feq bonds (Feq = a fluorine atom in an equatorial position) (1.826(7)−1.873(7) Å), one elongated W(1)−Fax bond (Fax = fluorine atom in an axial position, i.e., trans to the O atom) B

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bands based on the C4v local symmetry model, while in the Supporting Information we have presented more complex assignments based on the assumption of the lower-symmetry C2h model (corresponding to the observed space group P21/c). With 15 atoms in the formula unit and four formula units in the unit cell, there are 120 vibrational degrees of freedom, only three of which correspond to IR-active acoustic modes; the other 117 correspond to optical phonons. The acoustic modes were predicted by our DFT calculations to fall very close to the expected null wavenumbers, i.e., within −2.4 cm−1 (Supporting Information); thus, the error of diagonalization of the Hessian matrix supposedly does not exceed 3 cm−1. Moreover, the calculated and observed band wavenumbers (Supporting Information) are in excellent agreement (and without any scaling factor for the calculated values), the largest discrepancy not exceeding 12 cm−1. The correlation coefficient between the calculated and measured wavenumbers is 1.0032 with a goodness of fit of R2 = 0.9997 (Supporting Information). Thus, all 42 bands (out of 117) observed in the experiment may be reliably assigned to fundamentals using the spinpolarized calculations for the C2h model (the antiferromagnetic ground state; see below). The IR absorption spectrum of Ag(WOF5)2 was obtained here both in the mid-IR (MIR) and far-IR (FIR) regions. It is predominated by a group of very strong bands with the

Figure 3. (top) Infrared absorption and (bottom) Raman scattering spectra of Ag(WOF5)2.

the IR and Raman spectra have weak intensities, which suggests that symmetry breaking is not substantial. Therefore, in Table 1 we have kept the assignments of the IR- and Raman-active

Table 1. Wavenumbers Appearing in the IR and Raman Spectra of Ag(WOF5)2 and Literature Data for A(WOF5) (A = Cs+, [NF4]+, [NO]+) Ag(WOF5)2a IRf 1012(vs) 984(vs) 964(sh) 714(m) 696(sh) 681(s) 667(vs) 649(s) 622(w) 609(s) 477(m) 442(ms) 432(sh) 346(w) 329(sh) 317(m) 272(m) 258(m) 238(m) 215(w) 195(w) 175(w) 116(w) 101(w)

Ramanf 1025(sh) 1002(100) 980(50) 964(25) 725(40) 710(30)

AgWOF5b IR

NF4WOF5d Raman

IR

Raman

992(s,br)

989(vs)

987(vs)

989(vs)

991(vs)

996(10)

1003(s)

1001(10)

ν1(A1)

692(ms,sh)

690

686(w)

689(m)

688(vs)

690(5.4)

680(sh)

684(3.5)

ν2(A1)

620(vs,br)

610(vs,br)

515(vs)

455(ms)

594(vw) 445(vs)

440(w)

507(m)

348(42)

330(m)

329(w)

311(m)

329(6.8)

316(24) 280(20)

291

286(m) 242(s)

287(vw)

285(0.5)

Raman

assign.g

IR

608(vs)

IR

NOWOF5e

Raman

632(s,br) 624(sh) 603(8) 479(25) 449(22)

CsWOF5c

ν8(E) 591(0.4)

ν5(B1) ν3(A1)

327(5.9)

ν9(E)

292(sh)

208(10) 181(4) 159(1) 135(1) 106(20)

ν4(A1) ν10(E) 200(sh) 163(1.1)

lattice vibrations

a

This work. bReference 4 cReference 9. dReference 10. eReference 11. fValues in parentheses denote relative Raman intensities (%). Abbreviations: sh = shoulder, vs = very strong, m = medium, w = weak, vw = very weak, br = broad. gVibrational bands of [WOF5]− anions: MO stretching vibrations (v1), in-plane symmetric stretching vibrations of the MF4 moiety (v2), M−Fax stretching vibrations (v3), bending of the MF4 moiety, i.e., the umbrella mode (v4), out-of-phase symmetric stretching vibrations of the MF4 moiety (v5), in-plane asymmetric stretching vibrations of the MF4 moiety (v8), MOF4 bending (v9), and π(MF4) or π(MF3O) bending (v10). The assignment for Ag(WOF5)2 was done for the regular C4v symmetry, although the actual local symmetry in the solid state is lower; for assignments corresponding to the observed P21/c space group, see the Supporting Information. C

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Inorganic Chemistry maximum at 1012 cm−1; this band is assigned to the WO stretching.12 As a result of symmetry lowering in the solid state, O/F substitutional disorder, and group factor splitting, this band has several components (from 1025 to 964 cm−1). Some of them are Raman-active, with the most preeminent band at 1002 cm−1. Interestingly, the strongest IR- and Raman-active bands from this family are slightly blue-shifted (by ca. 13−20 cm−1) compared with those found for AgWOF5, despite the supposedly stronger binding of the terminal O of the anion to the AgII cation rather than the AgI cation. Elucidation of the crystal structure of AgIWOF5 should help to explain this feature (which may also arise from group factor splitting). The second group of very strong IR-active bands appears between 667 and 714 cm−1, with their Raman-active counterparts at 710 and 725 cm−1. These bands are assigned to the symmetric stretching vibrations of the MF5 moiety, i.e., of the four W−Feq bonds and one W−Fax one (eq stands for equatorial, ax for axial). The departure of the MF4 unit from perfect square-planar coordination generates a substantial dipole moment and renders the symmetric stretching vibrations IR-active. The third group of bands is found between 622 and 649 cm−1. They are mostly IR-active. They have been assigned to the doubly degenerate asymmetric stretching vibrations of the MF4 moiety.12 The fourth set of bands seen nearby, between 603 and 609 cm−1, has been assigned to the out-ofphase symmetrical stretching vibrations of the MF4 moiety.12 The W−Fax stretching bands are found at 442−479 cm−1 in the spectra. The higher-frequency components are markedly upshifted (by ca. 32−39 cm−1) with respect to the respective bands found for AgWOF5, and again, the reason for that remains to be elucidated. The bands found in the IR and Raman spectra below 350 cm−1 but above 220 cm−1 have been assigned to various deformation modes, including the O−W−F and F−W−F bending modes, and the characteristic π(MF4) umbrella deformation at 258 cm−1 (Table 1).12 Last but not least, bands below 220 cm−1 may be associated with the butterfly mode of the MF4 moiety as well as various lattice modes and hindered rotations of the WOF5− anions. In this way, the entire spectral range measured has been analyzed. Among the 42 assigned bands, 24 appear in the IR spectrum and the remaining 18 in the Raman spectrum. Among the Raman-active modes, 11 are totally symmetric ones (Ag), and the remaining seven have Bg symmetry; it cannot be excluded that the spectrum has resonance- or at least preresonance-Raman character, as is customary for compounds of AgII.13−16 The last point that requires comment is the discrepancy between our Raman spectra and those of “AgFW2OF9” described previously.2,4 We anticipate that enormous sensitivity of Ag(WOF5)2 to the laser beam intensity (with a too-high intensity resulting in photochemical and/or thermal decomposition of the compound; cf. the Experimental Section) is a possible reason for this discrepancy. Indeed, if the laser power used is too high, spots appear on the surface, their spectra corresponding to that of WOF4 (Supporting Information). Electronic Spectrum of Ag(WOF5)2. Electronic spectra in conjunction with electron spin resonance (ESR) spectra and quantum-mechanical calculationshave proven in the past to be very useful for analysis of chemical bonding in Ag(II) systems.17−20 Here we studied the electronic spectra of the samples of AgII(WOF5)2 in the NUV−vis−NIR range (10000− 42000 cm−1 or ca. 1.2−5.0 eV). The measured spectrum is

shown in Figure 4. The electronic spectrum of AgII(WOF5)2 is characterized by an usually broad band centered at 20 200 cm−1

Figure 4. Electronic absorption spectrum of AgII(WOF5)2 in the UV− vis−NIR region.

(2.5 eV), which is responsible for the color of the compound, as well as two structured bands in the UV region, at 35 600 cm−1 (4.4 eV) and 39 200 cm−1 (∼4.9 eV).21 The latter two may be identified as charge-transfer (CT) transitions involving equatorial F atoms, Feq → AgII, as they should indeed fall in the spectral region 35000−41000 cm−1,21,23 as observed previously for Ag(SbF6)2.22 However, the assignment of the major broad band is troublesome; judging from its energy and using the previously computed orbital scheme21,23 and selection rules, as well as the occurrence of a similar absorption for Ag(SbF6)2,25 one might be tempted to assign this band to the CT transition involving axial F atoms (2eg → 3b1g assuming the first coordination sphere in the form of an elongated octahedron with D4h symmetry). Indeed, one F ligand in the first coordination sphere apically coordinates AgII at 2.507(6) Å, and another one is found at 2.700(7) Å, although it is not collinear with the first F atom and Ag. However, the unusually large width of the discussed band (fwhm >10 000 cm−1) suggests that its presence may be connected also with the presence of diverse coordination spheres around AgII centers due to the presence of O/F substitutional disorder in the crystal structure (in other words, the acceptor centers of the CT transition are found in diverse ligand environments, such as [AgOF3], [AgO2F2], and [AgO3F]). The d−d transitions are either covered by this broad band, extend further into NIR, or are too broad to be seen (for the same reason as that described above), and hence, the value of the ligand field splitting energy, 10Dq, cannot be determined from the measured spectrum. The presence of 3% of additional AgII sites surrounded only by fluoride ligands further contributes to the complexity of the electronic excitations in this system. Magnetochemistry of Ag(WOF5)2. The susceptibility χ(T) and (inset) effective magnetic moment μeff(T) between 2 and 300 K are shown in Figure 5. The susceptibility was measured according to two experimental regimes. The zerofield-cooled (zfc) susceptibility was measured upon heating the sample from 2 to 300 K in a magnetic field of 1 kOe after the sample was precooled in zero magnetic field. The field-cooled (fc) susceptibility was taken while the sample was cooled from 300 to 2 K in a magnetic field of 1 kOe. A difference between D

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Figure 5. Temperature-dependent susceptibility χ and (inset) effective magnetic moment measured in a magnetic field of 1 kOe. The arrow at 163 K in the inset denotes the Curie temperature of AgF2.

Figure 6. Magnetization M(H) for Ag(WOF5)2 at 30, 5, and 2 K.

approximately 0.024 μB/molecule and a coercive field of Hc = 1.1 kOe at 2 K. The magnetization in the largest magnetic field of 50 kOe (5 T) is only 0.07 μB/molecule, and it still increases with increasing field. This value is much smaller than the expected saturation magnetization S·g·μB ≈ 1 μB/molecule for the S = 1/2 spin of the Ag2+ ion. On the basis of this observation, we tentatively propose a canted antiferromagnetic model of a magnetic ground state. The AgII magnetic moments are almost perfectly antiferromagnetically aligned in the sheetsthis antiferromagnetic interaction is seen as a negative Curie−Weiss temperaturewith a small tilt of the magnetic moments out of the collinear direction. A rough estimate of the canting angle (∼1.5°) in zero magnetic field can be obtained by comparing the measured remnant magnetization of only 0.024 μB/formula unit to the full magnetic moment of 1 μB/Ag2+ ion. Magnetic Properties and Electronic Structure of Ag(WOF5)2 from Theoretical Calculations. Theoretical DFT+U calculations have been used to describe the crystal, electronic, and magnetic structure of Ag(WOF5)2. Since this compound shows disorder at both cationic and anionic sites, an assumption of the ordered model was a necessary compromise. Various magnetic models were considered. The AFM model hosting two-dimensional (2D) AFM intrasheet interactions (Supporting Information) was predicted to be energetically favored over both nonmagnetic and FM ones by 417 and 13.5 meV/FU, respectively. Within the AFM model, each AgII cation with spin up is surrounded by four nearest Ag cations with spin down. Silver cations with the same spin orientation are stacked along the a axis (Figure S2). Most of the calculated properties of the AFM model are in agreement with the experimental observations, which justified it as a reliable ordered simplification of the Ag(WOF5)2 structure. The volume of ordered nonmagnetic model is overestimated by 6.3% with respect to the experimentally refined one, while inclusion of AFM ordering reduces this discrepancy to 4.8% (Supporting Information). In view of the 5% limit of DFT methods on the volume discrepancy and the artificially forced structural order, the obtained volume mismatch can be considered as very small. Additionally, spin polarization results in elongation of the Ag− O and contraction of the Ag−F bonding distances with respect to the nonmagnetic solution, leading to a better agreement with the observed bonding distances. While the two magnetic solutions (AFM and FM) result in comparable crystal structures and carry similar absolute values of the spin densities on atoms, their electronic properties differ significantly (Tables 2 and 3).

the zfc and fc susceptibilities below 15 K is a clear demonstration of some kind of magnetic order in the studied system. The effective magnetic moment at room temperature is 1.7 μB. This value corresponds to a magnetic moment of an ion with the spin quantum number S = 1/2 as expected for AgII cations.23 With decreasing temperature, the effective magnetic moment decreases. At T = 163 K, the fc susceptibility exhibits a small increase (a “bump”) indicating a ferromagnetic-like transition. As this bump is very small and coincides very well with the known weak ferromagnetic transition of AgF2,24,25 we attribute this feature to a minute amount of AgF2 in the parent compound. At 30 K the effective magnetic moment reaches a minimum of 0.9 μB. A nearly 2-fold decrease in the effective magnetic moment from room temperature down to 30 K (from 1.7 to 0.9 μB) is an indication of prevailing antiferromagnetic (AFM) interactions in the system. This was additionally proven by fitting the high-temperature susceptibility (T > 200 K) to the Curie−Weiss law, χ = C/(T − θ). The obtained Curie constant, C = 0.42 emu K/mol, is in agreement with the expected value for the spin-only S = 1/2 Ag2+ ions, while the negative paramagnetic Curie−Weiss temperature, θ = −63 K (or −5.4 meV), reflects the predominating AFM interactions between the nearest-neighbor AgII centers. According to the crystal structure of Ag(WOF5)2, the in-plane AgII ions bridged by [WOF5] units at a ca. 155° Ag−W−Ag angle constitute these nearest neighbors, which should be prone to AFM interactions. More discussion of the strength of the intrasheet interactions is given in the section devoted to the theoretical calculations. Below 30 K the susceptibility abruptly increases with decreasing temperature, indicating a ferromagnetic-like transition. The transition temperature, Tc = 20.7 K, was determined from the maximum of −dχ/dT. Below the transition temperature a small difference between the zfc and fc susceptibilities can be detected, indicating long-range order in three dimensions (Figures S4 and S5). In order to obtain deeper insight into the magnetic structure at low temperature, the isothermal magnetization curves were measured above and below the transition temperature. The magnetization M(H) at three different temperatures is shown in Figure 6. Above the transition temperature Tc, at 30 K, the magnetization is linear with magnetic field with no remnant magnetization or coercivity. Below the transition temperature, at 5 and 2 K, the magnetizations are practically identical. Clear hysteresis loops are visible with a remnant magnetization of E

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predominated by the contribution from F and slightly smaller contribution from Ag atoms just below the Fermi level (the highest occupied states), while the lowest unoccupied states are strongly dominated by the contribution from Ag atoms (Figure 7). This result suggests that the electronic band gap of Ag(WOF5)2 is of the p(F)/d(Ag) charge-transfer type, which is typical for Ag(II) in a F ligand field.27 The energy preference for the AFM solution additionally supports the interpretation of the magnetic susceptibility and magnetization measurements for this compound: the observed features originate from the predominating AFM interactions. The average spin-up component of the absolute magnetic moment for the AFM solution is 0.75 μB, which is close to the experimental effective magnetic moment minimum of 0.9 μB observed at 30 K. According to the DFT+U calculations, the magnetic density resides mostly on Ag atoms (±0.608 μB), but considerable density is found also at O (±0.065 and ±0.069 μB), F (±0.057 and ±0.059 μB), and W (±0.013 and ±0.014 μB) atoms that are involved in mediation of AFM superexchange interactions within the puckered sheets.28 For the terminal F atoms and the F atoms that axially coordinate Ag atoms from successive layers, the calculated magnetization approaches zero (0 to ±0.003 μB). These results suggest very weak superexchange between successive AFM-ordered layers, which may easily be overcome by very small spin canting (spin canting, though, is not taken into account in our simple model). The theoretical DFT+U intrasheet interaction parameter J = −6.4 meV estimated considering the two above-mentioned magnetic models (AFM and FM) agrees fairly well with the experimental value of −5.4 meV, which is based on the value of the Curie−Weiss temperature, θ, of −63 K. The small discrepancy may be due to either inherent deficiencies of theoretical method or the presence of 3% of the AgII cations at another crystal site (which is not taken into account in the simplified model used for the calculations). The spin at this additional AgII site is frustrated between four neighboring (mutually antiferromagnetically aligned) spins, and it presumably slightly decreases the measured intrasheet superexchange constant, J.

Table 2. Magnetic Moments Calculated for the FM and AFM Models of Ag(WOF5)2 within DFT+U Calculations and Listed Per Atom Type (Fb = Bridging F Atom, Ft = Terminal F Atom) magnetic moment (μB) model

Ag

O

Fb

Ft

W

AFM

±0.608

±0.065 ±0.069

±0.057 ±0.059

±0.013 ±0.014

0.608

0.070 0.076

0.076

0 ±0.001 ±0.003 0 ±0.001 0.002

FM

0.015 0.016

Table 3. Electronic Band Gaps at the Fermi Level Calculated for All Models Considered in the DFT+U Calculations; For Magnetic States the Band Gaps in the α and β States Are Also Listed, and Results from DFT Calculations Obtained for the Nonmagnetic Model Are Shown for Comparison model

ΔFermi (eV)

ΔαFermi (eV)

ΔβFermi (eV)

EFermi (eV)

AFM FM nonmagnetic nonmagneticDFT

2.000 0.000 0.035 0.053

2.000 0.000 − −

2.000 2.000 − −

−3.052 −3.390 −2.155 −1.925

Within both the DFT and DFT+U approaches, the nonmagnetic model is predicted to be a small-gap semiconductor with a band gap of 0.053 and 0.035 eV, respectively. The AFM ordering leads to broadening of the electronic band gap to ca. 2 eV, which is in line with the violet-blue color of the synthesized Ag(WOF5)2 crystals and reminiscent of the 2.5 eV absorption detected in the electronic spectrum. On the other hand, the FM ordering opens the 2 eV-wide band gap only in the minority β spin states, while the band gap is closed in the majority α ones.26 It should be noted here that accumulation of the electronic density at the Fermi level for the FM solution is connected with a surprisingly small energy increase (13.5 meV/ formula unit) with respect to the AFM one. Considering electronic density of states in the AFM model, it is

Figure 7. Atomic projections of electronic density of states calculated for the AFM model of Ag(WOF5)2 at the DFT+U level of theory. The plot on right side focuses on the highest occupied and lowest unoccupied states just below and above the Fermi level, which is positioned at E = 0 eV. F

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Table 4. Comparison of the Values of Several Key Parameters Related to the Magnetic Properties of Three 2D AFM Materials Based on AgII property

AgF2

Ag(WOF5)2

Ag(pyz)2(S2O8)

Ag(nic)2

intrasheet superexchange pathway the shortest Ag−Ag separation [Å]a Ag−ligandb−Ag angle [deg] Curie−Weiss temperature θ [K] intrasheet superexchange constant J [meV] FM component of the magnetic moment [μB] canting angle [deg] 3D ordering temperature [K]

−F− 3.78 130 −715 NDc 0.01 0.5 163−165

−F/O−W−F/O− 7.5 155 −63 −5.4 0.024 1.5 20.7

−N−C−C−N− 7.11/7.15 177/180 −66 −5.7 0.0 NAd 7.8

−N−C−C−C−O− 8.21 133.6 −46 −2.6 ND ND 11.8

a Neglecting the minority (3%) Ag(2) site. bF for AgF2, W for Ag(WOF5)2, and N for Ag(pyz)2(S2O8) and Ag(nic)2. cND = not determined. dNA = not applicable.

of the Ag−N bonding result in a nearly square-planar AgII sublattice. The Ag−Ag separations exceed 7 Å. This compound is characterized by moderately strong AFM interaction, as measured by J = −5.7 meV, which leads to the appearance of a maximum in the magnetic susceptibility at ca. 49 K. This suggests the absence of spin canting and a lack of the uncompensated ferromagnetic component.33 The moderate strength of magnetic superexchange comes from the fact that the superexchange pathway involves four nonmetal atoms (i.e., as many as five chemical bonds), and it is transmitted via the σ/ σ* orbital manifold of the organic ligand. Ag(WOF5)2 resembles Ag(pyz)2(S2O8) as far as the strength of magnetic superexchange and the shortest Ag−Ag separations are concerned. However, the superexchange pathway now involves three atoms (two O/F and one W) with a Ag−W−Ag angle of 155°, thus departing from linearity somewhat less than for AgF2. The substantial iconicity of the W−F bonding is one possible reason for the relatively modest J value. The small canted component of the spin on the AgII center equals 0.024 μB, with a canting angle of ca. 1.5°. The possibility of chemical doping of layered antiferromagnetic materials is a key factor for achieving superconductivity. Our previous experiments have shown that AgF2 cannot be doped with either inorganic or organic compounds, as full reduction of AgII to AgI usually takes place.34,35 Moreover, a quasi-binary Ag(I)/Ag(II) fluoride (which formally corresponds to a high doping level) is not known. Likewise, we were unable to dope Ag(pyz)2(S2O8),36 and we have failed to obtain similar systems with other counterions (e.g., NO3−, ClO4−, SO42− etc.), which seems to suggest that the presence of the S2O82− is necessary to stabilize the structure. Hence, it remains to be seen whether Ag(WOF5)2 can be chemically doped, and such experiments are currently underway in our laboratories.

2D Antiferromagnetism of Ag(WOF5)2 Compared with Those of AgF2 and Ag(pyz)(S2O8)2 (pyz = Pyrazine). Ag(WOF5)2 is a rather rare example of 2D antiferromagnetism based on a transition metal cation other than CuII. Three other examples of AgII-based systems are known, namely, AgF2,28 Ag(pyz)2(S2O8), where pyz stands for pyrazine, p-N2C4H4,29 and Ag(nic)2, where nic stands for nicotinate anion.30 Such systems have long been sought as they are analogues of layered oxocuprates(II), such as La2CuO4 and CaCuO2. Therefore, it was anticipated thatif dopedthey could become hightemperature superconductors, similar to copper oxides.1,31 Hence, it is instructive to compare the four layered compounds of AgII that are characterized by strong intrasheet AFM interactions (Table 4). AgF2, a prototypical binary AgII fluoride, is characterized by a very short superexchange pathway consisting of one fluorine atom only; the shortest Ag−Ag separation is 3.78 Å. The Ag− F−Ag angle is far from linear (close to 130 °C), despite the fact that the magnetic superechange is very strong, as judged from the large negative value of the paramagnetic Curie−Weiss temperature (θ = −715 K).32 It is possible that the θ value is even larger than that because the extrapolation was done by those authors from temperatures slightly exceeding 500 K, in discordance with the rule that the fit to the Curie−Weiss law should be performed at sufficiently high temperatures corresponding to the paramagnetic regime (i.e., at which the magnetic interactions within the material are negligible). One likely reason for performing experiments up to 500 K only is the immensely high chemical reactivity of AgF2 toward quartz containers at temperatures exceeding 400 K. The value of the magnetic intrasheet superexchange constant, J, for AgF2 has never been properly evaluated from the experimental data. The theoretical DFT+U calculations yield values ranging from −40 meV (for U = 6 eV) to −58 meV (for U = 3 eV),31 which are on the same order as the measured paramagnetic Curie−Weiss temperature θ. It is thus likely that J is around −50 to −60 meV. Indeed, even higher absolute values of J exceeding 100 meV were measured and calculated for KAgF3, a system with fluoride bridges much closer to linearity.33 AgF 2 exhibits incomplete quenching of the angular momentum and spin canting due to the Dzyaloshinskii− Moriya interaction.27 The net component of the canted magnetic moment is about 0.01 μB, with a canting angle of ca. 0.5°. On the other hand, Ag(pyz)2(S2O8) is very close to a perfect 2D AFM material. The superexchange pathway is complex, as it involves the pyrazine ring, but its rigidity and the directionality

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CONCLUSIONS

The crystal structure determination of violet single crystals grown by the reaction between AgW2O2F9 and F2 in aHF shows that the product is a genuine [WOF5]− salt of Ag(II), i.e., Ag(WOF5)2 and not AgFW2O2F9 as previously suggested.2−4 This work thus expands our knowledge of fluorooxotungstates, as the crystal structure determinations of [WOF5]− salts37 have to date been limited only to [Cs(15crown-5]2[WOF5] and AsPh4[WOF5],6,7 and the recently reported [(CH3)4N][WOF5].38 The crystal structure of Ag(WOF5)2 consists of slightly puckered [Ag(WOF5)2] sheets that are linked with one another via weak Ag···F contacts. G

DOI: 10.1021/acs.inorgchem.6b02034 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

for Ag(WOF5)2 were collected at 150 K on an Agilent Gemini A diffractometer equipped with an Atlas CCD detector using graphitemonochromatized Mo Kα radiation (λ = 0.71069 Å). The data were treated using the Crysalis software suite.40 The structures were solved with the charge-flipping method using the Superflip41 program (Olex crystallographic software42) and refined with the SHELXL-201443 software implemented in the program package WinGX.44 The refinement of the W/O/F ordered model resulted in R = 0.047, wR2 = 0.129, and a residual electron density of 5.1 e/Å3, located close to the W(2) atom. This, together with a noticeably elongated thermal ellipsoid of W(2), stimulated us to split the position of this atom. Consequently, the positions of the axial F(10) and O(2) atoms (bound to W(2)) were also modeled assuming the F/O disorder to get a physically reasonable model of the W(2)OF5 unit. This procedure lowered the values of R factors and the value of the highest electron density peak (0.045, 0.123, and 3.4 e/Å 3, respectively). In the last step, the highest peak of electron density found in the middle of the square built of four F atoms was interpreted as the Ag atom with the small partial occupancy, with its distances to F atoms falling in the typical range expected for AgII. The final refinement led to the 0.966:0.034 ratio of occupancies of the two Ag centers and further decreases in the R factors and the highest electron density peak. The figures were prepared using the DIAMOND 3.1 program.45 The corresponding crystal data and refinement results are as follows: chemical formula Ag(WOF5)2; FW = 697.55 g/mol; space group P21/c; a = 10.0226(3) Å, b = 9.5464(2) Å, c = 9.8641(3) Å, β = 110.533(3)°, V = 883.84(5) Å3; Z = 4; Dcalc = 5.242 g/cm3; T = 150 K; R1 = 0.0442 (R1 is defined as ∑||F0| − |Fc||/∑|F0| for I > 2σ(I)), wR2 = 0.1197 (wR2 is defined as {∑[w(F02 − Fc2)2]/∑w(F02)2}1/2). More details about the crystal-structure investigations may be obtained from Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: (+49)7247-808-666; e-mail: crysdata@fizkarlsruhe.de; web: http://www.fiz-karlsruhe.de) by quoting the deposition number CSD-431737. Thermal Analysis. Our experimental setup has been described in detail elsewhere.13 The analysis was performed for the powdered sample of Ag(WOF5)2 with a mass of 13.874 mg using a heating rate of 5 K/min and an Ar (N6.0) gas flow of 80 mL/min. Electronic Spectra. Our experimental setup has been described in detail elsewhere.25 The measurement was performed in transmission mode on a powdered sample of Ag(WOF5)2 placed between the SiO2 (infrasil quality) windows of a standard airtight liquid cell, with a 125 μm thick separator between the windows. A CaF2 beamsplitter was used. Raman Spectra. Raman spectra were recorded using a Horiba Jobin Yvon LabRam-HR Raman microspectrometer with a 632.8 nm He−Ne laser excitation beam. The power of the beam varied from 0.0017 to 17 mW. It should be noted that using a laser power above 0.17 mW led to decomposition of Ag(WOF5)2, as in the case of many other thermally fragile AgII compounds. Infrared Spectra. Infrared spectra with a resolution of 4 cm−1 were recorded (10 scans) on a PerkinElmer Spectrum GX FTIR spectrometer on a powdered sample between AgCl windows in a leaktight brass cell and a Bruker VERTEX 80 V spectrometer on a powdered sample between AgCl and polyethylene windows for the mid- and far-IR ranges, respectively. Merging of the FIR and MIR spectra was done with supplied software (OPUS 7) with an overlap of the spectra in the 600−400 cm−1 range. Magnetic Investigations. Magnetic properties were studied with a Quantum Design MPMS-XL-5 SQUID magnetometer. Susceptibility as a function of temperature T was measured between 2 and 300 K in a constant magnetic field of 1 kOe. The isothermal magnetization was measured between −50 and +50 kOe at temperatures of 2, 5, and 30 K. The data were corrected for the experimentally determined contribution of the sample holder and the diamagnetic response of the compound due to closed atomic shells as obtained from Pascal’s tables.46 Theoretical Calculations. Periodic density functional theory (DFT) calculations with plane-wave basis sets were performed with the VASP package. 47 Both spin-polarized and nonmagnetic

There is some positional and substitutional disorder in the structure. Ag(WOF5)2 is a rare example of a quasi-2D antiferromagnet containing 4d-row transition metal spin-1/2 centers. The strength of the intrasheet AFM superexchange mediated by the [WOF5]− anions is similar to that observed before for Ag(pyz)2(S2O8), although Ag(WOF5)2 shows some spin canting, which results in a small ferromagnetically ordered canted component. Such a ferromagnetic component is absent for Ag(pyz)2(S2O8) but has been observed for AgF2. The synthesis and characterization of Mo and Te analogues of the title compound constitute an interesting target for future research.

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EXPERIMENTAL SECTION

Caution! Anhydrous HF (aHF) is highly corrosive, and most f luorides are toxic; they must be handled using appropriate apparatus and protective gear. Reagents. AgNO3 (Fisher Chemical, 99.8%) and AgF (Aldrich, 99.9%) were used as supplied. AgF2 was obtained by fluorination of AgNO3 in anhydrous aHF. WOF4 was prepared from WF6 and SiO2 in aHF as described previously.39 AgW2O2F9 was prepared by a reaction between AgF and 2 equiv of WOF4 in aHF according to the literature.2,4 Synthetic Apparatus. The volatile materials (aHF, F2, WF6) were handled in an all-PTFE vacuum line equipped with PTFE valves. The manipulation of moisture-sensitive nonvolatile materials was done in a drybox (mBraun, Germany) in which the residual water in the atmosphere never exceeded 0.5 ppm. The reactions were carried out in tetrafluoroethylene−hexafluoropropylene (FEP) reaction vessels (length 250−300 mm, i.d. 16 mm, o.d. 19 mm) equipped with PTFE valves and PTFE-coated stirring bars. Prior to use, all of the reaction vessels were passivated with elemental fluorine. Fluorine was used as supplied (Solvay). Anhydrous aHF (Linde, 99.995%) was treated with K2NiF6 (Advanced Research Chemicals, Inc.) for several hours prior to its use. Synthetic Procedures. Successful Reaction between AgW2O2F9 and Elemental Fluorine in Liquid aHF. AgW2O2F9 (0.61 mmol) was loaded into a reaction vessel in a drybox. Anhydrous HF (2 mL) was condensed onto the reaction mixture, and the reaction vessel was warmed to ambient temperature. Elemental fluorine was slowly added until the final pressure in the reaction vessel reached 3 bar. After 30 min of intense stirring, the insoluble colorless solid started to change its color to gray. After 3 days the volatiles were pumped off at ambient temperature. Unsuccessful Reaction between AgF2 and WOF4 in Liquid aHF. AgF2 (0.58 mmol) and WOF4 (1.16 mmol) were loaded into an FEP reaction vessel in a glovebox. Then aHF (∼3 mL) was condensed on them at 77 K, and the mixture was warmed to room temperature. The reaction was left to proceed for 3 weeks. According to Raman spectroscopy and X-ray powder diffraction analysis, only starting materials were detected in the isolated solid. Growth of Single Crystals of Ag(WOF5)2. Around 250 mg of AgW2O2F9 was loaded into a reaction vessel in a drybox. aHF (∼2 mL) and elemental fluorine (10 mmol) were then condensed onto the starting material at 77 K. The bottom part of the reaction vessel was placed in a Dewar vessel filled with 1 L of liquid nitrogen. With slow evaporization of the N2, the reaction mixture slowly warmed to ambient temperature and was left for 10 days without stirring or shaking. Very thin platelike violet crystals were grown. Selected single crystals of Ag(WOF5)2 were placed inside 0.3 mm quartz capillaries in a drybox, and their Raman spectra were recorded. Some of the crystals were powdered, and magnetic measurements and powder X-ray diffraction were performed. Crystal Structure Determination of Ag(WOF5)2. Single crystals were immersed in perfluorinated oil (perfluorodecalin; Fluorochem, Hadfield, U.K.) in the drybox, selected under a microscope, and transferred into the cold nitrogen stream of the diffractometer. Data H

DOI: 10.1021/acs.inorgchem.6b02034 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry calculations were performed within the generalized gradient approximation48 with projector augmented waves49 and the PBEsol functional.50 The plane-wave cutoff was set to 520 eV, and the k-mesh was set to 2 × 2 × 2 for optimization and calculation of Brillouin zonecentered frequencies and 5 × 5 × 5 for total energy and electronic density of states (eDOS) calculations. The thresholds for electronic and ionic convergence were set to 10−7 and 10−5 eV, respectively. The forces per atom (for the Γ-frequency calculations) were converged to the maximum value of 0.0009 eV/Å. DFT+U calculations51 with Hubbard U = 5 eV and J = 1 eV (values used in previous calculations for AgII systems) were performed for two spin-polarized models (an FM model and an AFM model using a broken-symmetry approach) as well as for a nonmagnetic state. One ordered nonmagnetic model of P21/c symmetry and Z = 4 was considered as a starting point for all of the calculations (Supporting Information). It was constructed from the experimentally refined structure by omitting all atoms of minor occupancies: Ag(2) (occ. = 0.034), W(2b) (occ.= 0.1285), O(1D) (occ. = 0.1285), and F(2D) (occ. = 0.1285). The unit cells of the FM and AFM models considered in our calculations are equivalent to the unit cell of the ordered P21/c structure, while the AFM ordering lowers the monoclinic P21/c symmetry to the triclinic P1̅ one. The magnetic intrasheet superexchange constant, J, was derived from the energy difference between the AFM and FM solutions, ΔE = EAFM − EFM, where EFM was computed in a single-point calculation (vertical excitation) using the geometry optimized previously for the AFM solution, while taking into account the number of superexchange interactions in the unit cell. Throughout this article, we have assumed a Heisenberg Hamiltonian of the form Hij = −Jijsi·sj.

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Technology. W.G. thanks the Polish National Science Center (NCN) for the OPUS Grant “AgCENT” UMO-2011/01/B/ ST5/06673. CEPT-funded apparatus was used (POIG.02.02.00-14-024/08-00). The authors are grateful to Dr. Paweł Szarek (CeNT) for performing of the DFT calculations for an isolated WOF5− anion. The theoretical research was carried out at the Interdisciplinary Center for Mathematical and Computational Modeling using OKEANOS (Cray XC40) supercomputer, within the ICM grant GA65-26 ‘ADVANCE’.

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DEDICATION This work is dedicated to Dr. Piotr Leszczyński, chemist and friend, at his 50th birthday.

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(1) Grochala, W.; Hoffmann, R. Real and Hypothetical IntermediateValence AgII/AgIII and AgII/AgI Fluoride Systems as Potential Superconductors. Angew. Chem., Int. Ed. 2001, 40, 2742−2781. (2) Katayama, Y. A Study on Acid−Base Reactions of Halides and Oxide Halides in Anhydrous Hydrogen Fluoride. Ph.D. Thesis, Kyoto University, Kyoto, Japan, 1996; http://repository.kulib.kyoto-u.ac.jp/ dspace/handle/2433/77802 (accessed June 19, 2016). (3) Shen, C. Preparations and Characterizations of Novel Graphitelike Materials and Some High Oxidation State Fluorine Chemistry. Ph.D. Thesis, University of California, Berkeley, CA, 1992; http:// www.osti.gov/scitech/servlets/purl/10174522-8k0XZi/native/ (accessed June 19, 2016). (4) Katayama, Y.; Hagiwara, R.; Ito, Y. Acid-base Reactions of Tungsten and Uranium Oxide Fluorides in Anhydrous Hydrogen Fluoride. J. Fluorine Chem. 1995, 74, 89−95. (5) Mazej, Z.; Benkič, P. Silver(I) Undecafluorodiantimonate(V). Inorg. Chem. 2003, 42, 8337−8343. (6) Massa, W.; Hermann, S.; Dehnicke, K. Reaktionen von Chloronitrenkomplexen des Molybdäns und Wolframs mit Silberfluorid Die Kristallstruktur von AsPh4(WOF5]. Z. Anorg. Allg. Chem. 1982, 493, 33−40. (7) Nuszhär, D.; Weller, F.; Dehnicke, K.; Hiller, H. Synthesen und Kristallstrukturen von [Na(15-Krone-5)]-[NbF 5 (NPPh 3 )], (PPh3NH2)[NbF5(NPPh3)] und [Cs(15-Krone-5)2](WOF5). J. Alloys Compd. 1992, 183, 30−44. (8) Tsujimoto, Y.; Matsushita, Y.; Hayashi, N.; Yamaura, K.; Uchikoshi, T. Anion Order-to-Disorder Transition in Layered Iron Oxyfluoride Sr2FeO3F Single Crystals. Cryst. Growth Des. 2014, 14, 4278−4284. (9) Beuter, A.; Sawodny, W. Die Schwingungsspektren und Kraftkonstanten der Anionen MoOF5−, MoOF52−, MoF6− und WOF5−. Z. Anorg. Allg. Chem. 1976, 427, 37−44. (10) Wilson, W. W.; Christe, K. O. Perfluoroammonium and Cesium Fluorotungstates. Inorg. Chem. 1981, 20, 4139−4143. (11) Bougon, R.; Bui Huy, T.; Charpin, P. Acid Properties of the Oxytetrafluorides of Molybdenum, Tungsten, and Uranium toward some Inorganic Fluoride Ion Donors. Inorg. Chem. 1975, 14, 1822− 1830. (12) According to our DFT calculations for an isolated WOF5− anion (B3LYP functional, 6-31++G** basis set for O and F, SDD or LanLTZ+f pseudopotentials and valence functions for W). (13) Malinowski, P. J.; Derzsi, M.; Gaweł, B.; Łasocha, W.; Jagličić, Z.; Mazej, Z.; Grochala, W. AgIISO4: A Genuine Sulfate of Divalent Silver with Anomalously Strong One-Dimensional Antiferromagnetic Interactions. Angew. Chem., Int. Ed. 2010, 49, 1683−1686. Also see the Supporting Information. (14) Malinowski, P.; Mazej, Z.; Derzsi, M.; Jagličić, Z.; Szydłowska, J.; Gilewski, T.; Grochala, W. Silver(II) Triflate with One-dimensional [Ag(II) (SO3CF3)4/2]∞ chains hosting antiferromagnetism. CrystEngComm 2011, 13, 6871−6879.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02034. Crystal structure of the AFM model that corresponds to the lowest-energy state in the DFT calculations; lattice parameters and bond lengths calculated by DFT for various magnetic models of Ag(WOF5)2; IR- and Ramanactive modes as calculated by DFT+U for the AFM model and compared with those measured for Ag(WOF5)2; assignment of the IR- and Raman-active modes measured for Ag(WOF5)2 while assuming the C2h model; correlation between the calculated and measured wavenumbers for the IR- and Raman-active modes for Ag(WOF5)2; estimate of the content of the AgF2 impurity from magnetic susceptibility measurements; low-field and ac magnetic measurements; thermal decomposition profile; and powder X-ray diffraction (PDF) Crystallographic data for Ag(WOF5)2 (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Zoran Mazej: 0000-0003-3085-7323 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Z.M. and E.A.G. gratefully acknowledge the Slovenian Research Agency (ARRS) for financial support of the present study within the research program P1-0045 Inorganic Chemistry and I

DOI: 10.1021/acs.inorgchem.6b02034 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.6b02034 Inorg. Chem. XXXX, XXX, XXX−XXX