Three Unique Barium Manganese Vanadates from High-Temperature

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Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines Tiffany M. Smith Pellizzeri, Colin D. McMillen, Yimei Wen, George Chumanov, and Joseph W. Kolis* Department of Chemistry and Center for Optical Materials Science and Engineering Technologies, Clemson University, Clemson, South Carolina 29634-0973, United States S Supporting Information *

ABSTRACT: Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V2O7]4− groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl2/Ba(OH)2 mineralizer, and the third compound was prepared from BaCl2 mineralizer. An interesting structural similarity exists between two of the compounds, Ba2Mn(V2O7)(OH)Cl and Ba4Mn2(V2O7)(VO4)2O(OH)Cl. These two compounds crystallize in the orthorhombic space group Pnma, Z = 4, and are structurally related by a nearly doubled a axis. The first structure, Ba2Mn(V2O7)(OH)Cl (I) (a = 15.097(3) Å, b = 6.1087(12) Å, c = 9.5599(19) Å), consists of octahedral manganese(II) edge-sharing chains linked by pyrovanadate [V2O7] groups, generating a three-dimensional structure. Compound II, Ba4Mn2(V2O7)(VO4)2O(OH)Cl (a = 29.0814(11) Å, b = 6.2089(2) Å, c = 9.5219(4) Å), is composed of manganese(III) edge-sharing chains that are coordinated to one another through pyrovanadate groups in a nearly identical way as in I, forming a zigzag layer. A key difference in II is that these layers are capped on either end by two monomeric [VO4] groups that directly replace one [V2O7] group in I. The third compound, Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III), crystallizes in the trigonal space group R32 (a = 9.7757(4) Å, c = 22.4987(10) Å) and is composed of manganese(II) trimeric units, [Mn3O12(OH,Cl)], coordinated to one another through pyrovanadate [V2O7] groups to form a three-dimensional structure. The unusual manganese trimers are built of three square pyramids all linked by a central (OH/Cl) atom. The key factor directing the formation of the different structures appears to be the identity and concentration of the halide brine mineralizer fluid. The ability of such brines to induce the formation of interpenetrated salt lattices in the present study is suggestive of a versatile realm of descriptive synthetic inorganic chemistry.

1. INTRODUCTION The use of tetrahedral oxyanions as structural building blocks with cationic transition-metal ions is an excellent route to an enormous range of extended solids, especially since the (MO4)z− oxyanion groups can adopt a wide variety of bridging formats. Of the various tetrahedral oxyanions, the vanadate group (VO4)3− has proven to be especially versatile in terms of its ability to adopt an assortment of bridging arrangements with other structural building blocks.1−5 The combination of extensive structural flexibility, possible threefold symmetry, and presence of empty d-orbitals in the tetrahedral building block also leads to transition-metal vanadates with interesting magnetic behavior.6−14 The structural complexity can also be increased considerably by the formation of polyvanadates that can adopt even more complicated bridging arrangements.1,4 Recently we found that high-temperature hydrothermal solutions (550−600 °C, 1−2 kbar) are excellent conditions for the growth of transition-metal vanadates.15,16 The resultant products are stable in the hydrothermal fluids and grow reasonably large single crystals suitable for subsequent physical property measurements.17,18 The descriptive chemistry is rich and varied with many interesting new phases emerging. Clearly, © XXXX American Chemical Society

the identities of the phases are highly sensitive to the reaction conditions, and the role of the mineralizer is very important in the formation of the final products. Traditionally we employed hydroxide as the mineralizer for the metal oxide starting materials. The hydroxide enables the solubility and transport of the oxides, leading to formation of single crystals that can sometimes be quite large.19,20 As we explored the phase space of these new materials, we began to move beyond simple hydroxide mineralizers and started to explore other small nucleophiles as mineralizers. We are now beginning to focus our attention on halides, either alone or in conjunction with added hydroxide.21 There are three reasons to examine halide mineralizers: (1) the chemistry often appears to be substantially different when halides are used instead of, or in addition to, hydroxide; (2) the halide may replace or inhibit the introduction of the OH− group in the crystal lattice of the final product; (3) concentrated halide solutions may serve as geomimetic environments to model the chemistry of geothermal brines in natural geological solReceived: January 25, 2017

A

DOI: 10.1021/acs.inorgchem.7b00229 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Structure Refinement Data for Ba2Mn(V2O7)(OH)Cl (I), Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II), and Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III) Ba2Mn(V2O7)(OH)Cl

Ba4Mn2(V2O7)(VO4)2O(OH)Cl

I

II

III

Ba2MnV2O8HCl 595.96 298(2) orthorhombic Pnma (No. 62) 15.1549(7) 6.1889(3) 9.6233(4) 902.59(7) 4 4.386 0.710 73 12.257 1060 0.20 × 0.10 × 0.10 2.507 to 30.487 11 296/1487/1408 0.0261 81 R1 = 0.0209a wR2 = 0.0431b R1 = 0.0233a wR2 = 0.0437b 1.299

Ba4Mn2V4O17HCl 1171.46 298(2) orthorhombic Pnma (No. 62) 29.0814(11) 6.2089(2) 9.5219(4) 1719.31(11) 4 4.526 0.710 73 12.719 2080 0.34 × 0.22 × 0.08 2.250 to 26.500 14 973/1956/1848 0.0318 159 R1 = 0.0241a wR2 = 0.0550b R1 = 0.0266a wR2 = 0.0567b 1.287 0.000 90(7)

Ba5Mn3V6O21.75H0.75Cl3.25 1621.13 298(2) trigonal R32 (No. 155) 9.7757(4) 9.7757(4) 22.4987(10) 1862.02(17) 3 4.337 0.710 73 11.829 2169 0.35 × 0.10 × 0.06 2.571 to 26.483 6361/864/852 0.0279 63 R1 = 0.0249a wR2 = 0.0709b R1 = 0.0251a wR2 = 0.0710b 1.153

empirical formula FW (g/mol) temperature (K) crystal system space group a (Å) b (Å) c (Å) volume (Å3) Z D(calcd) (Mg/m3) wavelength (Å) μ, mm−1 F(000) crystal size 2θ range, deg reflections coll/ind/obs (I > 2σ(I)) Rint No. of parameters final R indices (obs. data) R indices (all data) goodness-of-fit (S) extinction coefficient Flack parameter a

Ba5Mn3(V2O7)3(OH,Cl)Cl3

0.034(14)

R1 = ∑||F0| − [Fc||/∑|F0|. wR2 = {∑[w(F0 − b

2

Fc2)2]/∑[wF02]2}1/2.

utions.22,23 In this paper we describe a continuation of our study of high-temperature hydrothermal reactions involving alkaline earth manganese vanadates, in this case using brine mineralizers. Our initial work with hydroxide fluids led to the discovery of a series of low-dimensional manganese vanadates with interesting magnetic properties.15−18 Preliminary efforts with fluoride as a mineralizer led to the discovery of several interesting new manganese vanadate fluorides,21 so extension to other halide mineralizers is logical. The present study is an initial investigation using a variety of barium chloride and mixed barium chloride/hydroxide mineralizers. The investigations presented herein when using mixed BaCl2/Ba(OH)2 mineralizer led to the synthesis of two new structures, Ba2Mn(V2O7)(OH)Cl (I) and Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II), that share an interesting structural relationship. The use of pure BaCl2 as mineralizer with no hydroxide leads to formation of a third new solid, Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III), containing an unusual manganese trimer consisting of three square pyramids joined by a mixed hydroxide/chloride site in the apical position. The synthesis and unusual structural aspects of these three new solids, as well as the role of the mineralizer in product formation, will be discussed. Specifically, the role of barium chloride hexagonal nets in the structure determination is highlighted as well as the relationships of these barium chloride nets to the previously reported salt inclusion structures (SIS) formed from molten salts.24−30

2. EXPERIMENTAL METHODS 2.1. Hydrothermal Synthesis: General Procedures. The hydrothermal reactions were conducted in 2.75 in. long silver ampules with an outer diameter of 0.25 in. The reactants (∼0.19−0.22 g total) were loaded into the silver ampules along with 0.4 mL of either mixed barium chloride/barium hydroxide or barium chloride mineralizer. The silver ampules were then welded shut and placed in a Tuttle-seal autoclave filled with an appropriate amount of water to provide suitable counter pressure (ca. 80% fill). The autoclaves were then heated for 4 d at 580 °C by ceramic band heaters at 1.4 kbar of pressure, after which the autoclaves were allowed to cool to room temperature naturally. The crystalline product was then retrieved from the silver ampules through vacuum filtration, and the entire product was washed with deionized water. All of the chemical reagents utilized in these reactions were used as received from the supplier. The chemicals used in this study were: V2O5 (Alfa Aesar, 99.6%), V2O3 (Alfa Aesar, 95%), Mn2O3 (Strem Chemicals, 98%), MnO2 (Strem Chemicals, 99%), BaCl2 (Spectrum Chemicals, 98%), Ba(OH)2 (Alfa Aesar, 94−98%). 2.2. Synthesis of Ba2Mn(V2O7)(OH)Cl. A mixture of BaCl2 (0.091g, 0.437 mmol), Mn2O3 (0.0384g, 0.243 mmol), and V2O5 (0.082g, 0.451 mmol) in a mole ratio of ∼1.8:1:1.9 were added to a silver ampule along with 0.4 mL of a mixed 3 M Ba(OH)2/1 M BaCl2 mineralizer and reacted under the hydrothermal conditions described above. When the product was filtered from the reaction, dark red polyhedra identified as Ba2Mn(V2O7)(OH)Cl, (I), were isolated. During an initial synthesis of I, 1 M Ba(OH)2/3 M BaCl2 was used as the mineralizer, but the crystals produced were not of suitable quality to provide an adequate structure solution. Once the mineralizer was changed to 3 M Ba(OH)2/1 M BaCl2, the same compound was synthesized, but the crystal quality was much higher and, therefore, provided crystals from which the structure could be determined. B


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Inorganic Chemistry

Table 2. Selected Interatomic Distances (Å) and Angles (deg) for Ba2Mn(V2O7)(OH)Cl (I), Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II), and Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III) Ba2Mn(V2O7)(OH)Cl

Ba4Mn2(V2O7)(VO4)2O(OH)Cl

I

II

III

[Mn(II)O6]

[Mn(III)O6]

[Mn(II)O5]

Mn1−O4 × 2 Mn−O6 × 2 Mn−O5 × 2

2.0580(17) 2.2196(19) 2.2348(19) [V2O7]

V1−O3 V1−O6 × 2 V1−O1 V2−O2 × 2 V2−O5 V2−O1

1.671(3) 1.6991(19) 1.789(3) 1.680(2) 1.713(3) 1.812(3)

Ba1−Cl1 Ba2−Cl1 Ba2−Cl1 × 2

3.1485(10) 3.2429(11) 3.4702(5)

V1−O1−V2 Mn1−O4−Mn1 Mn1−O5−Mn1 Cl1−Ba2−Cl1 × 2 Cl1−Ba2−Cl1

156.29(18) 97.49(11) 87.63(9) 116.910(16) 126.18(3)

Mn1−O7 Mn1−O5 Mn1−O9 Mn1−O6 Mn1−O8 Mn1−O3

2.003(3) 2.013(3) 2.026(4) 2.125(4) 2.159(4) 2.264(4) [V2O7]

V1−O3 V1−O6 x2 V1−O1 V2−O2 × 2 V2−O5 V2−O1

1.650(5) 1.710(4) 1.786(5) 1.676(4) 1.728(5) 1.810(5) [VO4]

V3−O11 V3−O10 V3−O9 × 2 V4−O12 V4−O13 V4−O8

1.662(6) 1.679(6) 1.751(4) 1.664(6) 1.704(4) 1.773(5)

Ba1−Cl1 Ba2−Cl1 Ba2−Cl1 × 2

3.1721(18) 3.205(2) 3.4730(9)

V1−O1−V2 Mn1−O4−Mn1 Mn1−O5−Mn1 Mn1−O7−Mn1 Mn1−O8−Mn1 Cl1−Ba2−Cl1 × 2 Cl1−Ba2−Cl1

159.7(4) 100.1(2) 87.14(18) 102.3(2) 91.32(19) 116.63(3) 126.73(6)

2.3. Synthesis of Ba4Mn2(V2O7)(VO4)2O(OH)Cl. Compound II was synthesized utilizing a similar procedure as above; however, in this synthesis vanadium(III) oxide was used in place of vanadium(V) oxide, and manganese(IV) oxide was used in place of manganese(III) oxide. Single crystals of Ba4Mn2(V2O7)(VO4)2O(OH)Cl were produced utilizing a mixture of BaCl2 (0.088g, 0.423 mmol), MnO2 (0.0383g, 0.441 mmol), and V2O3 (0.0684g, 0.456 mmol) in a mole ratio of ∼1:1:1. These reactants were added to a silver ampule along with 0.4 mL of a mixed 1 M Ba(OH)2/3 M BaCl2 mineralizer. After hydrothermal treatment as described above, dark red polyhedral crystals of II were obtained. Note that, when starting with vanadium(III) oxide and manganese(IV) oxide in the synthesis of the Ba4Mn2(V2O7)(VO4)2O(OH)Cl compound, vanadium(III) is oxidized during the reaction to vanadium(V), and manganese(IV) is reduced to manganese(III). 2.4. Synthesis of Ba5Mn3(V2O7)3(OH,Cl)Cl3. Compound III was synthesized using the same procedure as for compound I with the exception of the mineralizer choice. Compound I was synthesized from a 3 M Ba(OH)2/1 M BaCl2 mineralizer, whereas compound III was synthesized using only 1 M BaCl2 mineralizer. A mixture of BaCl2 (0.091g, 0.437 mmol), Mn2O3 (0.0384g, 0.243 mmol), and V2O5 (0.0882g, 0.485 mmol) were treated as above, and dark red rods identified as Ba5Mn3(V2O7)3(OH,Cl)Cl3 were isolated. 2.5. X-ray Diffraction. Single-crystal X-ray diffraction was performed on well-formed single crystals. For compounds I−III, diffraction images were obtained at room temperature from ϕ- and ωscans using a Bruker D8 Venture Photon 100 diffractometer equipped

Ba5Mn3(V2O7)3(OH,Cl)Cl3

Mn1−O4 × 2 Mn1−O2 × 2 Mn1−O5/Cl3

2.087(5) 2.091(5) 2.1254(12) [V2O7]

V1−O3 V1−O4 V1−O2 V1−O1

1.653(6) 1.692(6) 1.692(6) 1.7869(16)

Ba1−Cl2 Ba1−Cl1 × 2

3.2491(5) 3.2646(3)

V1−O1−V1 Mn1−O5−Mn1 O4−Mn1−O4 O4−Mn1−O2 × 2 O4−Mn1−O2 × 2 O2−Mn1−O2 O4−Mn1−O5 × 2 O2−Mn1−O5 × 2 Cl1−Ba1−Cl1 Cl2−Ba1−Cl1 × 2

178.2(5) 120.0 158.7(3) 85.0(2) 91.5(2) 160.9(3) 100.68(15) 99.52(14) 119.739(15) 120.130(8)

with Mo Kα radiation (λ = 0.710 73 Å) and an Incoatec I\ms source employing the APEXIII software suite. The structures were determined by intrinsic phasing with refinement on F2 using fullmatrix least-squares methods. These refinements were performed using the SHELX software suite.31,32 All atoms were first refined using isotropic thermal displacement parameters, followed by anisotropic refinement on all non-hydrogen atoms. Table 1 summarizes the structural refinement data for I−III, and selected interatomic bond distances and angles are provided in Table 2. Powder X-ray diffraction (PXRD) measurements were obtained utilizing a Rigaku Ultima IV diffractometer equipped with Cu Kα radiation (λ = 1.5406 Å). The powder diffraction patterns were collected in 0.02° increments over a 2θ range from 5° to 65° at a scan speed of 0.5° min−1. Experimental PXRD patterns of the overall reaction products compared favorably to those calculated on the basis of the single-crystal structure refinement (Supporting Information, Figures S1−S5). 2.6. Spectroscopic Characterization. Infrared (IR) and singlecrystal Raman spectra were collected on the compounds of this study. IR spectra were collected from ground single-crystal samples Ba2Mn(V2O7)(OH)Cl (I), Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II), and Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III). The IR spectra were obtained by mixing each respective ground sample with KBr and grinding thoroughly to form a uniform mixture. Each mixture was then pressed into a pellet, and the infrared spectra were collected on a Nicolet Magna IR Spectrometer 550, in the frequency range from 400 to 4000 cm−1, with a resolution of 4 cm−1. C


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Inorganic Chemistry Single-crystal Raman measurements were performed using an Olympus IX71 inverted microscope with a 20× objective lens coupled to a TRIAX 552 spectrometer equipped with a thermoelectrically cooled CCD detector (Andor Technology, Model DU420A-BV) operating at −60 °C. An argon ion laser (Innova 100, Coherent) was used to excite the Raman signal with 514.5 nm light in a 180° backscattering geometry. A PR-550 broadband polarization rotator (Newport Corp.) was used to rotate the polarization of the incident laser source. All spectra were processed, and figures were prepared with Spectra-Solve for Windows software (LasTek Pty. Ltd.). Data were collected with a laser output power from 100 to 200 mW with a 2 min integration time.

(V2O7)(OH)Cl (orange crystals) and Ba2Ni(V2O7)(OH)Cl (green crystals) were structurally analogous to I (Supporting Information, Tables S1 and S2). In all three structures the Ba2+ and Cl− ions perform a similar important structural function in that they form hexagonal nets that separate the manganese vanadate layers. These hexagonal Ba−Cl layers have been observed before both from hydrothermal reactions as well as from the broad class of salt inclusion solids that form from reactions in molten halides.29,30,33 In the case of the pioneering work on salt inclusion complexes by Hwu et al.24−28 the products were isolated from molten salt solvent environments, making it likely that the salts also elect to adopt lattice sites in the metalcontaining product. In contrast, in the hydrothermal brine environments, the salts have the choice of remaining solvated in the aqueous hydrothermal fluid or taking part in the crystalline lattice. Thus, the relative solubility of the ionic halides is an important parameter in the final product formation, and we feel it is no coincidence that the salt inclusion complexes we observe are all Ba−Cl salts, since BaCl2 has a very low solubility in aqueous phases. Similar hydrothermal reactions using strontium chloride brines, which have a much higher solubility in water, lead to a very different series of solids, thus far showing a reduced frequency to form structures containing Sr− Cl features.34 This is not a rigorous limitation across all hydrothermal systems, as we recently observed alkali and alkaline earth chloride salt chains templated with other oxyanions in the structures of NaSr2V3O3(Ge4O13)Cl and KSr2V3O3(Ge4O13)Cl,35 but has so far held for the manganese vanadate systems. 3.2. Crystal Structures of Ba 2 Mn(V 2 O 7 )(OH)Cl, Ba4Mn2(V2O7)(VO4)2O(OH)Cl, and Ba5Mn3(V2O7)3(OH,Cl)Cl3. The three compounds are thematically related by a common salt inclusion lattice of hexagonal barium chloride nets (vida infra) interpenetrated with manganese vanadate frameworks. Compounds I and II show additional interesting similarities to one another, and their structures can be described in similar context. Both compounds crystallize in the orthorhombic space group Pnma, with I having lattice parameters of a = 15.1549(7) Å, b = 6.1889(3) Å, c = 9.6233(4) Å and II having lattice parameters of a = 29.0814(11) Å, b = 6.2089(2) Å, c = 9.5219(4) Å. We note that the a-axis length of II is not strictly a doubling of that of I, and indeed, the empirical formula of II is not entirely obtained as a twofold multiple of I. However, there is an obvious correlation between the b and c lattice parameters of the two compounds, as well as the ratios of barium, manganese, and vanadium atoms in the formulas. The departure of oxygen and hydroxide from this relationship suggests there is a subtle difference in oxygen atom bridging in the manganese vanadate networks of I and II, particularly directed along the a-axis, that can be tied to the manganese oxidation states of Mn(II) in I and Mn(III) in II. Compound I has a similar structure to that of the recently reported Ba2Cu(V2O7)(OH)Cl that was prepared from a lowtemperature (ca. 200 °C) hydrothermal reaction.33 The structure consists of octahedral manganese(II) edge-sharing chains that run parallel to the b axis and are coordinated to one another through corner-sharing pyrovanadate [V2O7] groups (Figure 1a). The pyrovanadates also link neighboring chains together, forming a three-dimensional structure. The linking of the Mn(II) chains through the pyrovanadate groups is such that 12-membered rings are formed within the structure (Support-

3. RESULTS AND DISCUSSION 3.1. Synthesis of Ba2Mn(V2O7)(OH)Cl, Ba4Mn2(V2O7)(VO4)2O(OH)Cl, and Ba5Mn3(V2O7)3(OH,Cl)Cl3. Our initial investigations into the synthesis of new transition-metal vanadates using chloride-based mineralizers employ either chloride or mixed chloride/hydroxide mineralizers at high temperatures and pressures (ca. 580 °C/2 kbar) in silver-lined reaction vessels. This is part of a systematic program to determine the role of increasing the amount of halide ions (brines) in the synthesis of new oxyanion-based solids. The use of BaCl2 in significant concentrations, either alone or in combination with Ba(OH)2 as mineralizer, leads to a series of new metal vanadate materials that also incorporate Cl− into the structure. The use of a mineralizer with mixed chloride and hydroxide (1 M BaCl2/3 M Ba(OH)2) generated crystals of Ba2Mn(V2O7)(OH)Cl (I), containing both chloride and hydroxide in the final product. This result led us to examine a variation of the mineralizer identities and concentrations. When the chloride/hydroxide ratio was varied slightly (1 M Ba(OH)2/3 M BaCl2), and the oxidation states of the starting materials were altered somewhat, the product generated was Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II), which has a very complex arrangement in the unit cell but has an interesting structural relationship to I (see below). Finally, when no hydroxide is included in the mineralizer and only BaCl2 is employed, a different product is isolated, Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III), which appears to exhibit some substitutional disorder of Cl− and OH− as a capping group on the Mn(II) ions to form an unusual trimer. Energydispersive X-ray (EDX) examination of all three products indicates the presence of Ba, Mn, V, and Cl in appropriate ratios consistent with the crystallographic determinations (Supporting Information, Figures S6−S10). Also the IR spectra of the products all contain sharp bands in the region from 3300 to 3600 cm−1, supporting the presence of coordinated hydroxide groups (see below). The role of the manganese oxidation state is curious and deserves mention, since it appears to have structural implications as described below. In the cases of I and III, the final product contains Mn(II) when a Mn(III) starting material (Mn2O3) was used. In contrast, compound II contains Mn(III), and it was synthesized utilizing a Mn(IV) starting material (MnO2). We have not yet determined the definitive role of the oxidation state in the starting materials versus final product nor the overall stability of the manganese oxidation states in the various reaction conditions. In general, the hydrothermal reactions seem to provide a reducing environment with respect to manganese. In the case of compound I, syntheses were also performed using transition metals partial to divalent oxidation states, where NiO and Co2O3 were used as starting materials instead of Mn2O3. As expected, the resulting crystals Ba2CoD


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Inorganic Chemistry

Figure 2. Structures of I (a) and II (b) along [010] showing aligned regions of manganese chains and vanadate linkers. Note the presence of the [VO4] groups acting as a “broken” [V2O7] group in II (b), which requires elongation of the unit cell along the a-axis relative to I (a). Manganese, vanadium, oxygen, barium, and chlorine atoms are shown in blue, orange, red, gray, and green, respectively (hydrogen atoms omitted for clarity).

Figure 1. Manganese vanadate frameworks of I and II displaying the coordination of the manganese edge-sharing chains to the vanadate groups in Ba2Mn(V2O7)(OH)Cl, I (a), and Ba4Mn2(V2O7)(VO4)2O(OH)Cl, II (b). Part (a) is shown along [001], and part (b) is tilted slightly off [001] to show the separation of the [VO4] units in II. Color scheme: manganese, vanadium, and oxygen atoms are shown as blue octahedra, orange tetrahedra, and red spheres, respectively; hydrogen, barium, and chlorine atoms are omitted for clarity.

The structure of Ba4Mn2(V2O7)(VO4)2O(OH)Cl, II, is built from similar structural concepts to those in I, namely, edgesharing infinite chains of [MnO6] units connected through bridging equatorial oxygen atoms, as well as vanadates that link the chains of octahedra through several bridging motifs. As in I, two chains are joined together through pyrovanadate [V2O7] groups to extend the dimensionality of the structure. The connection pattern of the pyrovanadate is identical to I in that one end of a pyrovanadate shares a single edge-bridging oxygen atom of the Mn chain, while the other end uses two oxygen atoms to bridge consecutive apical sites on the manganese octahedra of the neighboring chain. Again the void spaces created by the linked chains provide sufficient space for both the barium cations and chloride anions to reside, and the chlorides are not ligated to the manganese. Compound II, however, also contains two unique monomeric [VO4] units in the structure identified as V3 and V4. Interestingly, each lone vanadate performs one function that each end of the pyrovanadate also performs (Figures 1b and 3b). Vanadate V3 links two apical sites (O9) of the manganese oxide chain, and it also has two terminal V−O oxide bonds. Vanadate V4 bridges two manganese octahedra at one edge sharing site via O8 and contains three terminal V−O bonds. The [VO4] tetrahedra are pointed toward each other and could almost be superimposed along the c-axis on the corresponding [V2O7] group in I (Figure 2b). Thus, the structures are almost identical except that one pyrovanadate is clipped into two orthovanadates. This has the overall result of having only two chains linked together in II with the other side of each chain capped by [VO4] groups, whereas all chains are linked by pyrovanadates in I. Because of orthovanadate [VO4] units acting as capping groups, as opposed to another pyrovanadate [V2O7] group tethering to the next manganese chain, a zigzag

ing Information, Figure S11), which provide sufficient space for the barium and chloride ions to reside (Figure 2a). Note that the Cl− ions do not act as ligands to the manganese or vanadium centers but rather bond to the barium atoms, forming a hexagonal net that interpenetrates the manganese chains and the pyrovanadate groups (see below). There is only one unique Mn(II) ion in the structure, coordinated by six oxygen atoms, in an approximately octahedral geometry. Equatorial oxygen atoms are shared between manganese atoms to propagate the Mn(II) chains along the b axis. Of the two unique bridging oxygen atoms in the chain, one is a bridging hydroxide group (O4), while the other is an oxygen atom that links to a pyrovanadate group. Each axial oxygen site is also shared by one of the vanadium atoms of the pyrovanadate group. Typical Mn(II)−O bond lengths (2.0580(17) to 2.2348(19) Å) are observed, with the shortest bonds occurring to the bridging hydroxide group. The pyrovanadate linkers serve two structural functions (Figures 1a and 3a). First, they provide additional bridging along the length of the b-axis Mn chains by connecting axial oxygen atoms on consecutive [MnO6] groups. They also link neighboring Mn chains to extend the structure along the a and c axes, connecting the axial oxygen atoms of two [MnO6] groups on one chain to one equatorial bridging oxygen atom on the neighboring chain. The vanadium−oxygen bonds in the structure range from 1.671(2) to 1.812(3) Å in length, which is typical for pyrovanadates, with the longest bond occurring to the V−O−V bridging oxygen atom within the pyrovanadate.29,30,33,36,37 This range was consistent for the pyrovanadates in II and III as well, with their V−O bond lengths ranging from 1.650(5) to 1.810(5) Å and from 1.653(6) to 1.7869(16) Å, respectively (see below). E


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Inorganic Chemistry

corresponding bridging oxygen atoms in the Mn chains (Mn− O5 = 2.264(4) Å in II vs Mn−O5 = 2.2348(19) Å in I) and a somewhat shorter bond length to the apical oxygen atoms of the Mn chain (Mn−O6 = 2.125(4) Å in II vs Mn−O6 = 2.2196(19) Å in I). While on average, these latter bonds in II are shorter to account for Mn(III), they are not shortened to the degree of the Mn−O9 bonds, which have the effect of cleaving a [V2O7] group into [VO4] groups. The other unique [VO4] group in II, which connects to the bridging oxygen atom O8 in the Mn(III) chain, is also pulled closer to the chains by Mn(III), exhibited by a contracted Mn−O8 bond length (Mn− O8 = 2.159(4) Å in II vs the corresponding Mn−O5 = 2.2348(19) Å in I). The extra layer established by the orthovanadate groups and Mn(III) in II also influences the OH− group behavior in the structure. In I, the Mn atom sits on a special position, and each Mn(II) octahedron can be described as [MnO4(OH)2], where O4−H4···Cl hydrogen bonding occurs on both sides of the Mn(II) chains. In II, the Mn atom sits on a general position, and there are two unique bridging oxygen atom sites that can support a hydrogen atom as a hydroxide group. Both provide suitable hydrogen-bonding geometries: O4−H4···Cl, which is comparable to O4−H4···Cl in I, and O7−H7···O12, which is completed by a terminal oxygen atom of one of the capping orthovanadates from a neighboring Mn(III) chain. Test refinements with hydrogen atoms fully adopting either arrangement showed no significant differences in R1 and wR2 values, as may be expected. Thus, the hydrogen atoms were chosen to be equally disordered on both sites in half occupancy, creating a [MnO5(OH)] unit. Establishing full hydrogen occupancy at both sites in II would direct the Mn oxidation state to be 2.5, and such crystals might be expected to be dark brown or black due to intervalence transfer effects, rather than the red color that is observed.38,39 Such mixed oxidation-state manganese complexes in these types of chains are not typically observed from our hydrothermal reactions. The structure of Ba5Mn3(V2O7)3(OH,Cl)Cl3, III, is considerably different in its manganese vanadate network. It crystallizes in the trigonal space group R32 and contains only [V2O7] vanadate building blocks. However, the manganese component consists of the very unusual square pyramidal [MnO4(OH,Cl)] unit with the disordered hydroxide/chloride ion in the apical position on the Mn(II) center. Furthermore, the apical anion site (O5, Cl3) serves as a common cap for three square pyramids to form an unusual [Mn3O12(OH,Cl)] trimer as a discrete structural unit (Figure 3c). More often, the Mn3O13 unit built of three [MnO5] groups is merely a substructure of a larger Mn−O−Mn network.40−42 Attempting to refine the Mn3-μ3 anion site as a fully occupied oxygen atom resulted in nonpositive definite anisotropic displacement parameters (ADPs), while a fully occupied chlorine atom produced larger ADPs with a shorter than ideal bond length for Mn to Cl. Modeling the site as a substitutional disorder primarily with oxygen character (75% O5, 25% Cl3) improved the refinement statistics and results in good ADPs. Also, this degree of chlorine content is consistent with the elemental analysis (Supporting Information Figure S8). This Mn3-μ3X arrangement is planar in the ab plane. The Mn−O bond lengths in III are comparable to the sum of the Shannon radii for five-coordinate Mn(II) and oxygen.43 Of course fivecoordinate complexes are well-known among transition metals and are found to adopt both trigonal bipyramidal and square pyramidal coordination.44,45 Typically however the trigonal

Figure 3. Comparison of the vanadate (orange) binding modes between manganese (blue) units present in (a) Ba2Mn(V2O7)(OH)Cl (I), (b) Ba 4 Mn 2 (V 2 O 7 )(VO 4 ) 2 O(OH)Cl (II), and (c) Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III). In I, both sides of the Mn chain are decorated by and linked through [V2O7] groups. In II, Mn chains are decorated by [V2O7] and [VO4] groups on opposite sides of the chain, such that the linking of chains is broken by the [VO4] groups. In III, [V 2 O 7 ] groups provide a linking function between [MnO12(OH,Cl)] trimer units.

manganese vanadate layer is formed in II, rather than a threedimensional manganese vanadate structure, as is seen in I. Thus, the 12-membered ring of I is a broken ring in II. The structural similarity is highlighted by the fact that the unit cell dimensions are nearly equal on the b and c axes in both crystals but nearly doubled along a in II versus I. This is also seen in Figure 2, where insertion of the extra region involving the [VO4] groups requires the extended a axis in II. An important consequence of clipping a [V2O7] group into two [VO4] groups is that it produces an extra oxygen atom that must be accounted for by electroneutrality. Thus, Mn is trivalent in II compared to divalent in I, and II exhibits correspondingly shorter average Mn−O bond lengths (2.098(4) vs 2.1708(19) Å). This is most apparent in the corresponding nonbridging (axial, apical) bonds within the Mn chains, namely, the Mn−O9 bond length of II (2.026(4) Å, where O9 connects to the [VO4] group) compared to the Mn− O6 bond length of I (2.2196(19) Å, where O6 connects to the [V2O7] group). Thus, the oxygen atoms are drawn closer to Mn(III) in II, effectively pulling the [V2O7] group apart. Interestingly, the one unique [V2O7] group that remains intact in II results in a comparable Mn−O bond length for the F


Article

Inorganic Chemistry bipyramidal environment is more common among the fivecoordinate species for low to midvalent d-block ions.46 There are several examples of square pyramidal Mn(III) complexes,47−49 but fewer square pyramidal Mn(II) complexes are known.50,51 Although it appears to be a densely packed structure when viewed along the c-axis (Figure 4a), there are three layers of

There are three layers of trimers and corresponding pyrovanadates that comprise the c-axis of the unit cell of III. The long c-axis here (22.4987(10) Å) provides an interesting comparison to the a-axes of I (15.1549(7) Å), built of two layers of Mn chains and corresponding pyrovanadates, and II (29.0814(11) Å), built of four layers of Mn chains and corresponding pyrovanadates and orthovanadates. On the basis of this, the sizes of individual manganese vanadate features correlate to ∼7.58 Å in I, 7.27 Å in II, and 7.50 Å in III, which are self-consistent with the trends expected for Mn(II) versus Mn(III) and [MnO6] versus [MnO5] structural units. The Ba−Cl interactions play an important function in the formation of the structures and deserve mention. In all three examples in the present study the barium and chloride ions form a planar, pseudohexagonal net, and the [V2O7] groups of the manganese vanadate frameworks interpenetrate the hexagonal holes in the nets (Figure 5a). The Ba−Cl distances

Figure 5. Planar pseudohexagonal Ba−Cl net of I, II, and III with interpenetrating pyrovanadate groups. Figures shown are derived from the structure of I: (a) along [100], (b) along [010]. Color scheme as denoted in Figure 2.

comprising the net are 3.2429(11) and 3.4702(5) Å for I, 3.205(2) and 3.4730(9) Å for II, and 3.2491(5) and 3.2646(3) Å for III. The bridging oxygen atoms of the pyrovanadate groups are centered in the plane of the salt lattice (Figure 5b). This particular type of hexagonal barium chloride net and the pyrovanadate groups seem to be ideally templated to one another. Similar two-dimensional arrays have been observed previously in the salt inclusion lattices of Ba5(V2O7)2Cl2 and KBa2(V2O7)Cl,28,29 as well as the aforementioned Ba2Cu(V2O7)(OH)Cl similar to I,33 all of which are based on pyrovanadate building blocks. The preference of the barium chloride net and pyrovanadate groups for one another is particularly evident when compounds I, II, and III are considered as a group (Figure 6). There is a mutual presence of the barium chloride nets with [V2O7] groups in all three structures. However, in the regions of II where the [VO4] groups are instead present, the [BaCl] salt lattice is not sustained (center of Figure 6b). Here, there is only a barium

Figure 4. Structure of Ba5Mn3(V2O7)3(OH,Cl)Cl3, III, viewed along [001] (a) and [010] (b). Color scheme as denoted in Figure 2.

trimers that are staggered as the structure extends in this direction (Figure 4b). Each end of the pyrovanadate groups bridges the corners of two of the square pyramids in a trimer, and the whole [V2O7] group then provides connectivity between staggered trimer units along the c-axis (Figures 3c and 4b). The trimers within a given layer are not directly connected to one another through single pyrovanadate linkers, though a three-dimensional manganese vanadate framework is still established by the staggered arrangement between layers. G


Article

Inorganic Chemistry

Figure 6. Relationships of the interpenetrating manganese vanadate frameworks with the barium chloride nets viewed down the sides of the salt lattice nets: (a) I off [010], (b) II off [010], and (c) III off [100]. Color scheme as denoted in Figure 2.

oxide network, which also has pseudohexagonal character (Supporting Information Figure 12). The two unique [VO4] groups then interact with the center of the net and its oxygen vertices. The lack of the chloride salt lattice in this region of the structure accounts for why the chemical formulas of I and II both have the same number of chlorine atoms, while II has twice as many Ba, V, and Mn atoms as I and further supports the need for an elongated a-axis in II. In all three structures, barium atoms also extend off the chloride ions of the planar nets into gaps in the Mn regions of the structure. In III, the extending Ba−Cl distances are much longer (∼3.6−3.8 Å) than those in I and II (∼3.1−3.2 Å). Barium atoms also coordinate oxygen atoms throughout all three structures over an approximate range of 2.65−3.30 Å for Ba−O bonds. All three compounds reported here have different long-range arrangements of the pyrovanadates (Supporting Information, Figure S13). The materials prepared previously by molten salt methods, KBa2(V2O7)Cl and Ba5(V2O7)2Cl2, contain eclipsed [VO4] tetrahedra comprising the pyrovanadate groups, but each individual pyrovanadate group is staggered with respect to those in layers above and below it.29 This is similar to the arrangement in I and in the related Ba2Cu(V2O7)(OH)Cl.33 In the case of the copper compound, however, the authors report disorder with regard to the rotation of the pyrovanadate groups within the Ba−Cl lattice. We observe no such disorder in the manganese complex I, and the pyrovanadate groups are wellaligned in the hexagonal nets. In the case of compound II, the individual pyrovanadates are all eclipsed, but the intermediate layers of [VO4] groups provide a separation (the broken 12membered ring) that causes the alignment of the pyrovanadates to shift relative to those in other layers. The groups still remain staggered relative to the next layer, but they are offset along the c-axis. Finally, in III the tetrahedra are eclipsed within each individual pyrovanadate group, and the entire groups are also eclipsed with respect to each other. The pyrovanadate group in III is considerably more linear (V−O−V = 178.3(6)°) than those in I (156.29(18)°) and II (159.7(4)°). 3.3. Infrared and Raman Spectroscopy. The Raman spectra of I−III from 300 to 1300 cm−1 are shown in Figure 7. Previous work indicated that vibrational frequencies of vanadates are affected by the presence of alkali, alkaline earth, and transition-metal ions, oxidation state, and the complexity of

Figure 7. Raman spectra of Ba 2 Mn(V 2 O 7 )(OH)Cl (I), Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II), and Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III), displayed from 300 to 1300 cm−1 with the polarization indicated by arrows.

the crystal symmetry, all of which can introduce ambiguity in the vibrational band assignments.14,20,52 Indeed, we observe similar metal ion sensitivity in the Raman spectra of I and its Ni(II) and Co(II) analogues (Supporting Information, Figure S14). In general, the V−O terminal and V−O−V stretching vibrations originating from [V2O7] groups appear in the 770− 1050 cm−1 and 500−800 cm−1 spectral ranges, respectively, whereas the V−O−V bending modes appear around 150−400 cm−1.33,53,54 The Raman bands of I in the V−O and V−O−V stretching region are nearly identical to those reported for the Ba2Cu(V2O7)(OH)X (X = Br, Cl) series.33 Compound II exhibits additional bands in the V−O stretching region, particularly the bands at 880 and 760 cm−1. These bands correlate well with V−O stretching bands observed in other compounds having [VO4] groups, which are an additional feature of II.6,14 The Raman spectrum of III appears simpler than those of I and II, since III only contains the [V2O7] group, H


Article

Inorganic Chemistry

interesting new structure types using a variety of chloride mineralizers. It appears that the identity of final products is a strong function of the concentration of BaCl2 as well as the presence or absence of Ba(OH)2 comineralizer. All three products reported contain planar hexagonal nets of Ba−Cl ions. These form layers that separate the chains or layers of the manganese vanadate complexes. In all the cases the hexagonal holes in the layers are interpenetrated by well-ordered pyrovanadate groups, which link the metal complexes in a variety of ways. This arrangement of Ba−Cl hexagonal nets interpenetrated by pyrovanadate groups has been observed previously in a range of products and seems to be a uniquely common structural feature regardless of whether the synthetic procedure is a molten salt, low-temperature hydrothermal, or high-temperature hydrothermal brine reaction. The pyrovanadate groups in the compounds reported here are always eclipsed themselves, but they have an interesting eclipsedversus-staggered relationship with the other interpenetrating pyrovanadate groups. This work also demonstrates the high sensitivity of the product formation to the reaction conditions, whereby altering the oxidation state of the transition-metal center leads to formation of different products. When a mixed Cl−/OH− mineralizer is used, chains of edge-shared Mn octahedra with OH− bridging groups are formed in I and II. Also the unusual structural relationship between I and II is the result of variations in the vanadate linking groups. The distinct, but comparable, roles played by [V2O7] versus pairs of [VO4] highlight the flexibility of the vanadates in directing structure. When only chloride is employed as mineralizer, a very unusual trimer forms containing three [MnO4(OH,Cl)] square pyramids that share the apical hydroxide/chloride site to form planar Mn3-μ3 groups. All of this unique chemistry reinforces the idea that halide brines are complementary mineralizers to the more traditional hydroxides and that a substantial number of new phases await discovery using these synthetic concepts.

and the group is formed by only one unique vanadium site that is repeated by twofold rotational symmetry through the shared O1 atom. The [V2O7] groups in both I and II, in contrast, are constructed of two unique vanadium sites. The infrared spectra of compounds I−III also display the expected bands in the vanadate region between 700 and 1000 cm−1 (Supporting Information, Figures S15−S17). The infrared spectra in the region of hydroxide stretching modes are shown in Figure 8 for all three compounds. They

Figure 8. Infrared spectra of O−H stretching vibrations in Ba2Mn(V2O7)(OH)Cl (I) (black), Ba4Mn2(V2O7)(VO4)2O(OH)Cl (II) (blue), and Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III) (green).

first confirm the presence of OH− in all three structures. Additionally, correlations between the O−H stretching frequencies and the overall O−H···A hydrogen bond length have been previously shown in vanadate minerals, with weaker, longer O−H···A distances corresponding to O−H stretching at higher wavenumbers.55 Interestingly, the infrared spectrum of II exhibits two distinct hydroxide bands at 3490 and 3396 cm−1, whereas the spectra of I and III exhibit only a single distinct hydroxide band at 3486 and 3488 cm−1, respectively. This can account for the two structurally unique hydroxide groups in II. We surmise that the bands around 3490 cm−1 present in all three compounds are contributed by the O−H stretching modes in the O−H···Cl hydrogen bonding common to all three structures. These are weaker hydrogen bonds, with O−H···A hydrogen bond lengths of 3.186 Å for I, 3.128 Å for II, and 3.841 Å for III. The additional band in the infrared spectrum of II occurring at 3396 cm−1 probably corresponds to the stronger O7−H7···O12 hydrogen bond with O−H···A of 2.767 Å that occurs in the [VO4] regions of Ba4Mn2(V2O7)(VO4)2O(OH)Cl.

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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.7b00229. Crystal structure data (CIF) Tables of crystallographic data for Ba2M(V2O7)(OH)Cl (M = Co, Ni), powder XRD patterns for composite reaction products, elemental analysis by EDX, supplementary structural figures, supplementary vibrational spectra (PDF)

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4. CONCLUSIONS Three new manganese vanadate structures have been identified from reactions in hydrothermal fluids performed near 600 °C and 1.5 kbar in the presence of concentrated brines. The initial goal was to examine the role of chloride mineralizers, either alone or in conjunction with hydroxide comineralizers. In this case we concentrated exclusively on Ba2+ as the counterion for both the chloride and the hydroxide sources. It turns out that the choice of this counterion has a considerable effect on the identity of the final products. The work has a number of interesting features. It demonstrates the suitability of the hightemperature hydrothermal method in synthesizing complex and

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Colin D. McMillen: 0000-0002-7773-8797 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the National Science Foundation Grant No. DMR-1410727 for financial support. I


Article

Inorganic Chemistry

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(21) 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. (22) Kesler, S. E. Ore Forming Fluids. Elements 2005, 1, 13−18. (23) Eugster, H. P. Minerals in Hot Water. Am. Mineral. 1986, 71, 655−673. (24) Huang, Q.; Ulutagay, M.; Michener, P. A.; Hwu, S.-J. Salt Templated Open Frameworks (CU-2): Novel Phosphates and Aresnates Containing M3(X2O7)22‑ (M = Mn,Cu, X = P, As) Micropores 5.3Å and 12.7Å in Diameter. J. Am. Chem. Soc. 1999, 121, 10323−10326. (25) Queen, W. L.; West, J. P.; Hwu, S.-J.; VanDerVeer, D. G.; Zarzyczny, M. C.; Pavlick, R. A. The Versatile Chemistry and Noncentrosymmetric Crystal Structures of Salt-Inclusion Vanadate Hybrids. Angew. Chem., Int. Ed. 2008, 47, 3791−3794. (26) Queen, W. L.; Hwu, S.-J.; Reighard, S. Salt-Templated Mesoporous Solids Comprised of Interlinked Polyoxovanadate Clusters. Inorg. Chem. 2010, 49, 1316−1318. (27) Queen, W. L.; West, J. P.; Hudson, J.; Hwu, S.-J. Extended Utility of Molten-Salt Chemistry: Unprecedented Synthesis of a Water Soluble Salt-Inclusion Solid Comprised of High Nuclearity Vanadium Oxide Clusters. Inorg. Chem. 2011, 50, 11064−11068. (28) Hwu, S.-J.; Ulutagay-Kartin, M.; Clayhold, J. A.; MacKay, R.; Wardojo, T. A.; O’Connor, C. J.; Krawiec. A New Class of Hybrid Materials via Salt Inclusion: Novel Copper Arsenates Na5ACu4(AsO4)4Cl2 (A = Rb, Cs) Composed of Alternating Covalent and Ionic Lattices. J. Am. Chem. Soc. 2002, 124, 12404−12405. (29) Ranmohotti, K.G. S.; Queen, W. L.; West, J. P.; VanDerveer, D.; Hwu, S.-J. Synthesis and Structure of Ba5(V2O7)2Cl2. J. Chem. Crystallogr. 2009, 39, 303−307. (30) Martin, F. D.; Mueller-Buschbaum, H. Zur Kenntnis von KBa2V2O7Cl. Zeitschrift für Naturforschung 1994, B49, 1141. (31) Sheldrick, G. M. Crystal Structure Refinement with SHELXTL. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112−122. (32) CrystalClear; Molecular Structure Corporation of Rigaku: The Woodlands, TX, 2006. (33) Sun, K.; Litvinchuk, A. P.; Tapp, J.; Möller, A. Synthesis, crystal structures, magnetic properties, and lattice dynamics of Ba2XCu(OH)[V2O7] with X=Cl, Br. J. Solid State Chem. 2016, 236, 69−77. (34) Smith Pellizzeri, T. M.; McMillen, C. D.; Kolis, J. W. J. Solid State Chem., submitted. (35) Sanjeewa, L. D.; McGuire, M. A.; McMillen, C. D.; Garlea, V. O.; Kolis, J. W. Polar Materials with Isolated V4+ S = 1/2 Triangles: NaSr2V3O3(Ge4O13)Cl and KSr2V3O3(Ge4O13)Cl. Chem. Mater. 2017, 29, 1404−1412. (36) Wang, N.; He, Z.; Cui, M.; Guo, W.; Zhang, S.; Yang, M. Synthesis and Characterization of a Family of Vanadate Compounds Ba3M(V2O7)2 (Co,Mn, Mg or Zn) with and Edge Shared [M2O10] Dimer Structure. Cryst. Growth Des. 2015, 15, 1619−1624. (37) Zubkov, V. G.; Tyutyunnik, A. P.; Tarakina, N. V.; Berger, I. F.; Surat, L. L.; Slobodin, B. V.; Svensson, G.; Forslund, B.; Shulgin, B. V.; Pustovarov, V. A.; Ishchenko, A. V.; Cherepanov, A. N. Synthesis, crystal structure and luminescent properties of pyrovanadates A2CaV2O7 (A = Rb, Cs). Solid State Sci. 2009, 11, 726−732. (38) Day, P.; Hush, N. H.; Clark, R. J. H. Mixed valence: origins and developments. Philos. Trans. R. Soc., A 2008, 366, 5−14. (39) Allen, G. C.; Hush, N. S. Intervalence-transfer absorption I. Qualitative evidence for intervalence-transfer absorption in inorganic systems in solution and in the solid state. Prog. Inorg. Chem. 1967, 8, 357−390. (40) Domide, D.; Huebner, O.; Behrens, S.; Walter, O.; Wadepohl, H.; Kaifer, E.; Himmel, H.-J. Synthesis and Reactivity of a New Oxidation-Labile Heterobimetallic Mn6Zn2 Carbamate Cluster and Precursor to Nanosized Magnetic Oxide Particles. Eur. J. Inorg. Chem. 2011, 2011, 1387−1394. (41) Yao, H.-C.; Li, Y.-Z.; Song, Y.; Ma, Y.-S.; Zheng, L.-M.; Xin, X.Q. Inorg. Chem. 2006, 45, 59−65.

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