Double molybdates of silver and monovalent metals Текст научной статьи по специальности «Химические науки»

Condensed Matter and Interphases. 2021;23(3): 421-431

ISSN 1606-867Х (Print) ISSN 2687-0711 (Online)

Condensed Matter and Interphases

Kondensirovannye Sredy i Mezhfaznye Granitsy https://journals.vsu.ru/kcmf/

Original articles

Research article

https://doi.org/10.17308/kcmf.2021.23/3527

Double molybdates of silver and monovalent metals

T. S. Spiridonova1H, S. F. Solodovnikov2, Yu. M. Kadyrova13, Z. A. Solodovnikova2, A. A. Savina14, E. G. Khaikina13

1Baikal Institute of Nature Management, Siberian Branch of the Russian Academy of Sciences, 6 ulitsa Sakhyanovoy, Ulan-Ude, Republic of Buryatia 670047, Russian Federation 2Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Akademika Lavrentieva prospekt, Novosibirsk 630090, Russian Federation 3Banzarov Buryat State University,

24a ulitsa Smolina, Ulan-Ude, Republic of Buryatia 670000, Russian Federation

4Skolkovo Institute of Science and Technology,

30, bld. 1 Bolshoy Boulevard, Moscow 121205, Russian Federation

Abstract

The Ag2MoO4-Cs2MoO4 system was studied by powder X-ray diffraction, the formation of a new double molybdate CsAg3(MoO4)2 was established, its single crystals were obtained, and its structure was determined. CsAg3(MoO4)2 (sp. gr. P3, Z = 1, a = 5.9718(5), c = 7.6451(3) A, R = 0.0149) was found to have the structure type of Ag2BaMn(Vo4)2. The? structure is based on glaserite-like layers of alternating MoO4 tetrahedra and Ag1O6 octahedra linked by oxygen vertices, which are connected into a whole 3D framework by Ag2O4 tetrahedra. An unusual feature of the Ag2 atom environment is its location almost in the centre of an oxygen face of the Ag2O4 tetrahedron. Caesium atoms are in cuboctahedral coordination (CN = 12). We determined the structures of the double molybdate of rubidium and silver obtained by us previously and a crystal from the solid solution based on the hexagonal modification of Tl2MoO4, which both are isostructural to glaserite K3Na(SO4)2 (sp. gr. P 3m1). According to X-ray structural analysis data, both crystals have nonstoichiometric compositions Rb281Ag119(MoO 4)2 (a = 6.1541(2), c = 7.9267(5) A, R = 0.0263) and Tl3.14Ag086(MoO 4)2 (a = 6.0977(3), c = 7.8600(7) A, R = 0.0174). In the case of the rubidium compound, the splitting of the Rb/Ag position was revealed for the first time among molybdates. Both structures are based on layers of alternating MoO4 tetrahedra and AgO6 or (Ag, Tl)O6 octahedra linked by oxygen vertices. The coordination numbers of rubidium and thallium are 12 and 10.

Keywords: Double molybdates, Silver, Monovalent metals, Binary systems, X-ray diffraction study, Structure, Glaserite Acknowledgements: the authors are grateful to PhD Irina A. Prodan (Gudkova) and Ms Oksana A. Gulyaeva for recording and processing the X-ray diffraction data of the crystals on a Bruker X8 Apex CCD automated diffractometer. This research was supported by the Ministry of Science and Higher Education of the Russian Federation, projects No. 0273-2021-0008 (Baikal Institute of Nature Management, SB RAS), and No. 121031700313-8 (Nikolaev Institute of Inorganic Chemistry, SB RAS).

For citation: Spiridonova T. S., Solodovnikov S. F., Kadyrova Yu. M., Solodovnikova Z. A., Savina A. A., Khaikina E. G. Double molybdates of silver and monovalent metals. Kondensirovannye sredy i mezhfaznye granitsy=Condensed Matter and Interphases. 2021;23(3): 421-431. https://doi.org/10.17308/kcmf.2021.23/3527

Для цитирования: Спиридонова Т. С., Солодовников С. Ф., Кадырова Ю. М., Солодовникова З. А., Савина А. А., Хайкина Е. Г. Двойные молибдаты серебра и одновалентных металлов. Конденсированные среды и межфазные границы. 2021;23(3): 421-431. https://doi.org/10.17308/kcmf.2021.23/3527

И Tatyana S. Spiridonova, e-mail: spiridonova-25@mail.ru

© Spiridonova T.S., Solodovnikov S.F., Kadyrova Yu. M., Solodovnikova Z. A., Savina A.A., Khaikina E. G., 2021

The content is available under Creative Commons Attribution 4.0 License.

1. Introduction

Double molybdates of alkaline elements with divalent and trivalent metals are well known as promising phosphors [1-6], ferroelectrics and ferroelastics [7-9], solid electrolytes [1013], electrode [14-19], laser [20-24], and other materials. A prominent place in the series of double molybdates is also occupied by phases formed in the M2MoO4-M2MoO4 systems (M, M - alkaline elements). The largest number of publications is devoted to M2MoO4-Li2MoO4 (M = K, Rb, Cs) systems and the double molybdates MLiMoO4 formed in them. The compounds melt congruently and have developed polymorphism, and ferroelectric and ferroelastic properties [25-32]. Based on the results of studying the Na2MoO4-Li2MoO4 system by visual polythermic method, differential thermal analysis and X-ray powder diffraction, it was concluded in [25, 33, 34] that there are the phases with compositions 3:1 and 6:1 in the system; however, both compounds were not isolated and characterised. In the systems M2MoO4-Na2MoO4 (M = K, Rb, Cs), double molybdates M2-xNa.MoO4 (M = K, Rb, Cs) were found [33, 35-39], which crystallize in the structure type of glaserite K3Na(SO4)2 [40]. Unlike stoichiometric Cs3Na(MoO4)2 [39], in the systems M2MoO4-Na2MoO4 (M = K, Rb) the glaserite-type phases have upper temperature limits of stability and noticeable homogeneity ranges: K2-xNaxMoO4 (0.40 < x < 1.0) [36] and Rb2-xNaxMoO4 (0.50 x < 0.67) [37]. Another compound RbNa3(MoO4)2 revealed in the Rb2MoO4-Na2MoO4 system is unstable at room temperature [37].

Until now, data on double molybdates of silver and monovalent metals were absent, although studies of the corresponding binary systems were undertaken. Thus, according to [41, 42], in the Ag2MoO4-Li2MoO4 system intermediate phases are not formed, while the authors of [43] on the base of the results of a visual polythermic analysis of the Ag2MoO4-Na2MoO4 system made a conclusion about formation of a continuous series of solid solutions with a minimum. The formation of continuous solid solutions of the spinel type was also confirmed by X-ray diffraction studies of the latter system [44]. One of the compositions of this solid solution (NaAgMoO4) was studied in [45, 46]. The formation of boundary solid solutions was reported for the Ag2MoO4-Tl2MoO4 system [47, 48].

The first double molybdate of silver and an alkali metal was obtained by us when studying the Ag2MoO4-Rb2MoO4 system. The compound Rb3Ag(MoOj2 melts at 435 °C and has a glaserite structure type [49]. Later, in the similar potassium containing system, we obtained a hexagonal double molybdate, K7-xAg1+x(MoO4)4 (0 < x < 0.4) [50], which crystallizes in its own structure type and at 334 °C undergoes a reversible first-order phase transition from the acentric form (sp. gr. P63mc) into centrosymmetric one.

In this study, we investigated the Ag2MoO4-Cs2MoO4 system and determined the crystal structure of the compound formed in it. In addition, the structure of double rubidium-silver molybdate was refined and an X-ray diffraction analysis of one of the members of the solid solution formed in the Ag2MoO4-Tl2MoO4 system on the base of the high-temperature modification of thallium molybdate [51] was performed.

2. Experimental

Commercially available AgNO3, TlNO3 (analytical reagent grade), Mo03 (chemically pure grade), Cs2CO3 (extra-pure grade) reagents were used as starting materials. M2MoO4 (M = Ag, Tl) was obtained by calcining stoichiometric amounts of MNO3 and MoO3 with gradually increasing temperatures from 300-350 to 450 °C (in the case of silver) and up to 500 °C (in the case of thallium) for 50 h. Caesium molybdate was synthesised by the reaction Cs2CO3 + MoO3 = Cs2MoO4 + CO2 with annealing at 450-550 °C for 80 h. The thermal and crystallographic characteristics of the obtained compounds agreed with the literature data.

Powder X-ray diffraction (PXRD) analysis was carried out using a Bruker D8 ADVANCE automated powder diffractometer (l CuKa, secondary monochromator, scanning step 20 = 0.02076°).

X-ray single crystal diffraction data for crystal structure determinations were taken at room temperature using Bruker-Nonius X8 Apex automated diffractometer with a two-dimensional CCD detector (MoKa-radiation, graphite monochromator, j-scanning with a scanning interval of 0.5°) in the hemisphere of reciprocal space. Calculations for solving and refinement of the structures were performed using the SHELX-97 software package [52].

3. Results and discussion

3.1. Cs2M°O4-Ag2M°O4 system and crystal structure of CsAg3(MoOJ2

The Cs2MoO4-Ag2MoO4 system was studied by PXRD in the subsolidus region in the entire concentration range with a step of 5-10 mol% (2.5 mol% in some cases). The formation of an intermediate compound CsAg3(MoO4)2 was established (the composition was found by single crystal structure determination). According to PXRD data, the formation of this compound begins at 300 °C; however, a singlephase CsAg3(MoO4)2 sample was not obtained. An increase of the duration of reaction mixtures calcination (up to 500 h), an expansion of the temperature range (up to the limits of subsolidus temperatures), as well as the use of stoichiometric AgNO3, Cs2MoO4, MoO3 or Ag2MoO4, Cs2CO3, MoO3 mixtures as starting components instead of simple silver and caesium molybdates, did not lead to a positive result.

Single crystals of CsAg3(MoO4)2 suitable for X-ray structural analysis were obtained by spontaneous crystallization of the melt of a sintered sample of the compound, which was heated to 470 °C, kept at this temperature for 30 min and cooled at a rate of 4°/h down to 200 °C (then in a switched-off and cooling further). Crystal data and the structure

refinement results are given in Table 1, the atomic coordinates and interatomic distances are listed in Tables 2 and 3.

The structure of CsAg3(MoO4)2 was solved in the trigonal sp. gr. P3 and it was found to be isostructural to Ag2BaMn(VO4)2 [53]. The Mo atoms and 2/3 silver atoms (the Ag2 position) were tetrahedrally coordinated with the Mo-O distances 1.743(4)-1.776(2) A, Ag2-O 2.314(2)-2.499(4) A. An unusual feature of the Ag2 environment is its location almost in the centre of the oxygen face of Ag2O4 tetrahedron (Fig. 1), which was also found in the K6 68Ag132(MoO4)4 structure [50]. The remaining third of silver atoms (Ag1) are located in octahedra with equal Ag1-O bond lengths of 2.446 (2) A. The structure is based on glaserite-like layers of alternating MoO4-tetrahedra and Ag1O6-octahedra, which are linked by oxygen vertices and interconnected in a whole three-dimensional framework by Ag2O4 tetrahedra (Fig. 1). The negative charge of the framework is compensated by caesium cations in cuboctahedral coordination (CN = 12); the Cs-O distances are 3.182(7)-3.451(1) A.

3.2. Crystal structure of Rb281Ag119(MoOJ2

As we showed in [49], Rb3Ag(Mo04)2 is the only intermediate compound of the Rb2MoO4-Ag2MoO4 system. A single-phase sample of the double rubidium-silver molybdate was synthesised by

Table 1. X-ray structure analysis data for CsAg3(MoO4)2

Formula CsAg,(MoO„)2

Formula weight (g/mol) 776.40

Crystal system Trigonal

Space group P3

Unit cell dimensions a = 5.9718(5) Â, с = 7.6451(3) Â

y (Â3) / Z 236.115(12) / 1

Calculated density (g cm-3) 5.460

Crystal size (mm) 0.15 x 0.06 x 0.06

m(MoKa), mm-1 12.502

0 range (o) 5.328-61.126

Miller index ranges -8 ^ h ^ 8, -7 ^ к ^ 8, -10 ^ 1 ^ 10

Reflections collected/unique 3234 / 490 [Rnt= 0.0265]

Number of variables/constraints 24 / 0

Goodness-of-fit on F (GOF) 1.158

Extinction coefficient 0.0087(6)

Final R indices [I > 2s(I)] R(F) = 0.0149, wR(F2) = 0.0349

R indices (all data) R(F) = 0.0158, wR(F2) = 0.0353

Largest difference peak / hole (e Â-3) 0.81/-1.15

Таблица 2. Координаты и эквивалентные изотропные тепловые параметры атомов в структуре CsAg3(MoO4)2

Atom x/a y/b z/c Ueq(ÂT

Mo 0.6667 0.3333 0.25304(5) 0.01327(11)

Ag1 0 0 0 0.02048(11)

Ag2 0.3333 0.6667 0.19216 0.02805(13)

Cs 0 0 0.5 0.02047(12)

O1 0.6667 0.3333 0.4810(5) 0.0306(9)

O2 0.7014(4) 0.631(4) 0.1792(3) 0.0242(4)

* Ueq = 4(U11 + + 0.75U33-U12) / 9.

Table 3. Selected interatomic distances (Â) in CsAg_(MoO4)2

Mo-tetrahedron Ag1-octahedron

Mo1-O1 1.743(4) Ag1- O2 2.446(2) x 6

-O2 1.776(2) x 3

<Mo1-O> 1.768

Cs-polyhedron Ag2-tetrahedron

Cs-O2' 3.181(2) x 6 Ag2- O2 2.314(2) x 3

-O1 3.4509(2) x 6 O1 2.499(4)

<Cs-O> 3.316 <Ag2 -O> 2.360

Fig. 1. Crystal structure of CsAg3(MoO4)2

annealing a stoichiometric mixture of Ag2Mo04 and Rb2Mo04 at 380 °C for 100 h. Crystals suitable for X-ray structural analysis were obtained by spontaneous crystallisation from the melt. The preliminary results of X-ray structural analysis were previously published by us in [49]. In this study, the composition of the Rb2 81Ag119(MoO4)2 crystal and its structure were corrected and refined (Tables 4-6).

Note that the solid-state synthesis of a singlephase sample of the composition described above was not successful. After annealing the reaction mixtures of silver and rubidium molybdates,

even at highest subsolidus temperatures, only Rb3-xAg1+x(MoO4)2 (0 < x < 0.10) samples were single-phase. Probably, the found crystal composition has an extremely high silver content and can be obtained only from melts.

In the structure of Rb2 81Ag119(MoO4)2 (sp. gr. P3m1) of the glaserite type K3Na(SO4)2 [40], molybdenum atoms have tetrahedral oxygen coordination with the distances Mo-O 1.730(6)-1.773(3) A. The Ag1 atoms are in octahedra with the equal bond lengths Ag-O 2.483(3) A. The structure is based on layers of alternating MoO4 tetrahedra and Ag1O6 octahedra linked by

Table 4. X-ray structure analysis data for Rb281Ag119(MoO4)2 and Tl314Ag086(MoO4)2

Formula Rb^Ag^MoOJ, TUAg^MoOJ,

Formula weight (g/mol) 688.42 1054.37

Crystal system Trigonal Trigonal

Space group P3m1 P3m1

Unit cell dimensions a = 6.1541(2) Â a = 6.0977(3) Â

с = 7.9267(5) Â с = 7.8600(7) Â

V (Â3) / Z 259.99 (2) / 1 253.10 (3) / 1

Calculated density (g cm-3) 4.397 6.918

Crystal size (mm) 0.13 x 0.10 x 0.02 0.09 x 0.09 x 0.05

m(Mo^a), mm-1 3.645 53.840

0 range (o) 2.26-28.83 2.09-30.50

Miller index ranges -10 < h < 8, -10 < к <7, -5 < h < 8, -8 < к < 6,

-13< l <9 -11 < l < 10

Reflections collected/unique 2370 / 504 [Rint = 0.0299] 2306 / 330 [Rint = 0.0314]

Number of variables/constraints 25 / 0 22 / 0

Goodness-of-fit on F (GOF) 1.271 1.087

Extinction coefficient 0.0016 (3) 0.0035 (4)

Final R indices [I > 2s(I)] R(F) = 0.0263 R(F) = 0.0174

wR(F2) = 0.0625 wR(F) = 0.0419

R indices (all data) R(F) = 0.0272 R(F) = 0.0189

wR(F2) = 0.0627 wR(F) = 0.0425

Largest difference peak/hole (e Â-3) 1.00 / -1.21 0.87 / -0.87

Table 5. Coordinates and equivalent isotropic thermal parameters of atoms in the structure of

Rb2.81Ag1.19(MoO4)2

Atom Occ. x/a y/b z/с Ueq (ÂT

Mo 1 0.6667 0.3333 0.25304(5) 0.0149(2)

Ag1 1 0 0 0 0.0221(2)

Ag2 0.10(1) 0.3333 0.6667 0.179(5) 0.047(7)

Rb1 0.90(1) 0.3333 0.6667 0.1580(3) 0.0205(4)

Rb2 1 0 0 0.5 0.0296(3)

O1 1 0.6667 0.3333 0.4810(5) 0.055(2)

O2 1 0.7014(4) 0.631(4) 0.1792(3) 0.0321(7)

*Ueq = 4U + U22 + °-75U33-U12) / 9

Table 6. Main interatomic distances (Â) in the structure of Rb2 81Agj 19(MoO4)2

Mo-tetrahedron Rb1-polyhedron

Mo-O1 1.730(6) Rb1-O1 2.705(7)

-O2 1.773(3) x 3 -O2 3.0990(5) x 6

-O2' 3.296(4) x 3

<Mo-O> 1.762 <Rb1-O> 3.119

Ag1-octahedron Rb2-polyhedron

Ag1-O2 2.483(3) x 6 Rb2-O2 3.033(4) x 6

Ag2-polyhedron -O1 3.5531(1) x 6

Ag2-O1 2.54(4) <Rb2-O> 3.293

-O2 3.085(2) x 6

<Ag2-O> 3.007

common oxygen vertices (Fig. 2). The negative charge of the layers is compensated by two types of rubidium cations (CN = 12 and 10); the total range of Rb-O distances is 2.706(7) -3.553(1) Â. An additional position of silver (Ag2) near the Rb1 position (CN = 10) at the distance Rb1-Ag2 0.17(4) Â was found, which partially replaces rubidium in Rb1; the Ag2-O bond lengths are 2.54(4)-3.085(2) Â (CN = 7).

Splitting of the Rb/Ag position in molybdates was revealed for the first time. As for tungstates, it was found earlier in the structure Ag3+xRb9-xSc2(WO4)9, (x ~ 0.11) [54], and a similar splitting of the K/Ag position was found by us in the structure of Ag132K668(MoO4)4 [50]. Such disordering and splitting of positions of large alkali cations is still rare. Examples are rubidium-containing defect pyrochlores RbNb2O5F [55], RbAla33WL67O6

[56], ferroelectric solid electrolytes RbTiOAsO4

[57] and RbSbOGeO4 [58] of the KTiOPO4 type. As a rule, this is considered as the ability of the structure to have potential ionic conductivity and/or ferroelectricity [59]. Indeed, some rubidium-containing defect pyrochlores and many members of the KTiOPO4 family are bright examples of phases with these properties [58, 60]. This tendency is confirmed by the fact that the Ag3+Rb9-Sc2(WO4)9 (x - 0.11) studied by us probably has rubidium ion conductivity [54], and nonstoichiometric phases of the glaserite type can also be solid electrolytes [61].

Fig. 2. General view of the Rb2 81Agj 19(MoO4)2 structure

3.3. Crystal structure of Tl314Ag086(MoOJ2

According to [47, 48], in the Tl2MoO4-Ag2MoO4 system, boundary solid solutions are formed, including those based on the high-temperature hexagonal form a-Tl2MoO4 of the K3Na(SO4)2 glaserite type [51]. Using spontaneous crystallisation of a molten sample of Tl3Ag(MoO4)2 synthesized by solid-state reactions from a stoichiometric mixture of simple molybdates, we obtained crystals suitable for X-ray structural analysis from the region of the specified solid solution and refined their crystal structure.

The composition of the studied crystal of the glaserite type, Tl314Ag0 86(MoO4)2 (sp. gr. P3m 1), was determined by refinement of the site occupancies of the thallium and silver cations, which showed that the occupancy of thallium sites is 100 % within the experimental error limits, while the silver site contains an admixture of thallium. The correctness of this model is confirmed by a decrease in ^-factor from 0.0235 to 0.0174, and the determined crystal composition fell into the range of the solid solution based on a-Tl2MoO4. The results of the structural refinement are given in Table 4, and the atomic coordinates and interatomic distances are shown in Tables 7 and 8.

In general, the structure of Tl314Ag0 86(MoO4)2 repeats the above-described structure of isostructural Rb281Ag119(MoO4)2 (Fig. 2). Molybdenum atoms are tetrahedrally coordinated with the distances Mo-O 1.760 (6)-1.765(3) A, and the (Ag, Tl) atom has octahedral coordination with equal bond lengths (Ag, Tl)-O 2.535(4) A, which is longer than the distance Ag1-O 2.483(3) A in Rb2 81Ag119(MoO4)2 (see above) and is significantly shorter than the corresponding distance Tl1-O 2.769(10) A in the structure of a-Tl2MoO4 [51]. Thallium atoms of two sorts with CN = 12 and 10 have the common distance range Tl-O 2.495(7)-3.5243(4) A, which is close to the lengths of the corresponding bonds Tl-O 2.467(16)-3.682(16) A in a-Tl2MoO4 [51].

4. Conclusions

The subsolidus region of the system Ag2MoO4-Cs2MoO4 was studied by PXRD, the compound with the composition CsAg3(MoO4)2 crystallising in the structure type of Ag2BaMn(VO4)2 (sp. gr. P3, Z = 1) was revealed and its structure was determined.

Table 7. Coordinates and equivalent isotropic thermal parameters of atoms in the structure of

Tl,HAg0,6(MO°4)2

Atom Occ. x/a y/b z/c Uq (A2)*

Mo 1 0.6667 0.3333 0.29677(10) 0.0195(2)

(Ag, Tl) 0.877(5)Ag+0.123Tl 0 0 0 0.0282(3)

Tl1 1 0.3333 0.6667 0.16186(4) 0.0328(2)

Tl2 1 0 0 0.5 0.0316(2)

O1 1 0.6667 0.3333 0.5207(10) 0.062(3)

O2 1 0.8232(4) 0.6464(7) 0.2181(6) 0.0399(10)

*Ueq = 4(U11 + + 0-75U33-U12) / 9

Table 8. Main interatomic distances (A) in the structure of Tl Ag (MoO4)2

Mo-tetrahedron Tl1-polyhedron

Mo-O1 1.760(8) Tl1-O1 2.495(7)

-O2 1.765(4) x 3 -O2 3.0825(7) x 6

-O2' 3.413(4) x 3

<Mo-O> 1.764 <Tl1-O> 3.123

(Ag, Tl)-octahedron Tl2-polyhedron

(Ag, Tl)-O2 2.535(4) x 6 Tl2-O2 2.898(4) x 6

-O1 3.5243(4) x 6

<Tl2-O> 3.211

We determined the structure and composition of double rubidium-silver molybdate, and performed X-ray structure analysis of a member of the solid solution on the base of the high-temperature form of thallium molybdate formed in the system Ag2MoO4-Tl2MoO4. It was confirmed

that Rb2.81Ag1.19(Mo04)2 and H^go.J^0^

(crystal compositions were determined by X-ray structure analysis) are of the glaserite structure type. In the case of the rubidium containing phase, splitting of the Rb/Ag position was revealed for the first time in molybdates. This phenomenon usually indicates the ability of the structure to have potential ionic conductivity and/or ferroelectricity.

Author contributions

All authors made an equivalent contribution to the preparation of the publication.

Conflict of interests

The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.

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Information about the authors

Tatiana S. Spiridonova, PhD in Chemistry, Researcher, Laboratory of Oxide Systems, Baikal Institute of Nature Management, Siberian Branch of the Russian Academy of Sciences (BINM SB RAS), Ulan-Ude, Russian Federation; e-mail: spiridonova-25@mail.ru. ORCID iD: https://orcid. org/0000-0001-7498-5103.

SergeyF. Solodovnikov, DSc in Chemistry, Professor, Leading Researcher, Laboratory of Crystal Chemistry, Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences (NIIC SB RAS), Novosibirsk, Russian Federation; e-mail: solod@niic.nsc.ru. ORCID iD: https://orcid.org/0000-0001-8602-5388.

Yulia M. Kadyrova, PhD in Chemistry, Researcher, Laboratory of Oxide Systems, Baikal Institute of Nature Management, Siberian Branch of the Russian Academy of Sciences (BINM SB RAS) and Senior Lecturer of the Department of General and Analytical Chemistry, Faculty of Chemistry, Banzarov Buryat State University (BSU), Ulan-Ude, Russian Federation; e-mail: yliychem@yandex.ru. ORCID iD: https://orcid. org/0000-0002-0106-8096.

T. S. Spiridonova et al. Double molybdates of silver and monovalent metals

Zoya A. Solodovnikova, PhD in Chemistry, Researcher, Laboratory of Crystal Chemistry, Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences (NIIC SB RAS), Novosibirsk, Russian Federation; e-mail: zoya@niic.nsc.ru. ORCID iD: https://orcid.org/0000-0001-5335-5567.

Alexandra A. Savina, PhD in Chemistry, Senior Researcher, Laboratory of Oxide Systems, Baikal Institute of Nature Management, Siberian Branch of the Russian Academy of Sciences (BINM SB RAS), Ulan-Ude, Russian Federation and Researcher, Skolkovo Institute of Science and Technology, Moscow, Russian Federation, e-mail: a.savina@skoltech.ru. ORCID iD: https://orcid.org/0000-0002-7108-8535.

Elena G. Khaikina, DSc in Chemistry, Professor, Chief Researcher, Laboratory Oxide Systems, Baikal Institute of Nature Management, Siberian Branch of the Russian Academy of Sciences (BINM SB RAS) and Professor of the Department of Inorganic and Organic Chemistry, Faculty of Chemistry, Banzarov Buryat State University (BSU), Ulan-Ude, Russian Federation; e-mail: egkha@mail.ru. ORCID iD: https://orcid. org/0000-0003-2482-9297.

Received 20 June 2021; Approved after reviewing 28 June 2021; Accepted for publication 15 July 2021; Published online 25 September 2021. Translated by Valentina Mittova Edited and proofread by Simon Cox