The new sodium tellurido manganates(II) Na2Mn2Te3, Na2Mn3Te4, Na2AMnTe3 (A=K, Rb), and NaCsMnTe2

Z. Naturforsch. 2019; 74(9)b: 623–640

Michael Langenmaier and Caroline Röhr*

The new sodium tellurido manganates(II)

Na₂Mn₂Te₃, Na₂Mn₃Te₄, Na₂AMnTe₃(Aꢀ=ꢀK, Rb),

and NaCsMnTe₂

https://doi.org/10.1515/znb-2019-0104

ligand. The cesium salt NaCsMnTe₂(orthorhombic, space

group Cccm, aꢀ=ꢀ694.21(2), bꢀ=ꢀ1536.57(4), cꢀ=ꢀ664.47(2) pm,

Zꢀ=ꢀ4, R1ꢀ=ꢀ0.0131) likewise forms a new structure type,

which is an ordered superstructure of ThCr₂Si₂. Linear

chains ¹_∞[MnTe_4/2] of edge-sharing tetrahedra are con-

Received July 1, 2019; accepted August 4, 2019

Abstract: A series of new sodium and mixed Na/A (Aꢀ=ꢀK,

Rb, Cs) tellurido manganates have been synthesized

from melts of the pure elements (or MnTe) at maximum

temperatures of 600–1000°C. The monoclinic crystal

structures of the two pure sodium salts Na₂Mn₂Te₃(space

group C2/c, aꢀ=ꢀ1653.68(2), bꢀ=ꢀ1482.57(2), cꢀ=ꢀ773.620(10)

1

nected with similar chains [NaTe_4/2] to form [NaMnTe₂]

∞

+

layers. The larger alkali cations Cs between the layers

exhibit a cubic (CNꢀ=ꢀ8) coordination.

pm, βꢀ=ꢀ117.52°, Zꢀ=ꢀ8, R1ꢀ=ꢀ0.0225) and Na₂Mn₃Te₄(space Keywords: manganese; sodium; tellurido manganates;

group C2/m, aꢀ=ꢀ1701.99(3), bꢀ=ꢀ438.741(8), cꢀ=ꢀ691.226(12) tellurium.

pm, βꢀ=ꢀ90.3171(8)°, Zꢀ=ꢀ2, R1ꢀ=ꢀ0.0270) are both based on

a hexagonal close packed Te²⁻arrangement. Na₂Mn₂Te₃is

isotypic with Na₂Mn₂S₃and Na₂Mn₂Se₃and contains layers

of [MnTe₄] tetrahedra, which are connected via common

1 Introduction

edges to form tetramers [Mn₄Te₆]. These tetramers are fur-

Mixed-valent alkali sulfido/selenido/tellurido ferrates(II/

ther connected via μ₃-Te atoms. Na₂Mn₃Te₄crystallizes in a

III) A₁₋₂FeQ₂are a multifaceted long-known [1–3], but still

new structure type, recently also reported for the selenido

growing [4–7] compound class, which exhibits a diverse

salt Na₂Mn₃Se₄. Mn(2) forms ribbons of vertex-sharing

crystal chemistry and therewith several interesting physi-

dinuclear units ¹_∞[Te_2/2MnTe₂MnTe_2/2] running along the

cal, in particular magnetic, properties. Depending on the

short b axis of the monoclinic cell. The Te atoms of these

ratio Fe^II:Fe^IIIand the size of the counter cations, their

ribbons are also the ligands of edge-sharing [Mn(1)Te₆]

structures either contain (differently undulated) chains

+

chains of octahedra. Similar to Na₂Mn₂Te₃, the Na cations

¹_∞[FeQ_4/2] of edge-sharing tetrahedra (cf. e.g. [3, 4, 8–10])

are octahedrally coordinated and the cations occupy tetra-

or the prominent cubane-type clusters [Fe₄Q₈] [5, 6, 11]. In

hedral (Mn²⁺) and octahedral (Na , Mn²⁺) voids in the close

+

contrast, most of the analogous cobaltates ([12] and ref-

Te²⁻packing. The isotypic K/Rb salts Na₂AMnTe₃crystal-

erences therein) and manganates (see below) comprise

lize in a new structure type (orthorhombic, space group

divalent metal ions only. Attempts to oxidize these metal

Pmc2₁, aꢀ=ꢀ1069.70(4)/1064.34(2), bꢀ=ꢀ1350.24(5)/1350.47(3),

cations e.g. with an excess of sulfur, yielded complex

cꢀ=ꢀ1238.82(4)/1236.94(3) pm, Zꢀ=ꢀ4, R1ꢀ=ꢀ0.0445/0.0210). In

phases like e.g. Na₃CoS₃[12], which is not a cobaltate(III)

contrast to the simple formula indicating a Mn(III) com-

but contains di-sulfido ligands coordinated to Co(II).

pound, the complex structure contains one layer con-

Similar to the ferrates(II/III), the structural chemis-

sisting of undulated chains of edge-sharing tetrahedra

try of the manganates(II/III) is characterized by [MnQ₄]

¹_∞[Mn^IITe_4/2] separated by free ditelluride dumbbells [Te₂]²⁻

tetrahedra connected predominately via common edges.

and a second layer containing a complex chain of edge-

The connectivity of these polyhedra reaches from isolated

and vertex-sharing [Mn^IITe₄] tetrahedra, in which Mn(II) is

¹[MnQ_4/2

[MnQ₄] tetrahedra to chains

and finally differ-

]

coordinated to μ₁- and μ₂-Te²⁻ligands and an η¹-ditellurido

ent types of ‘defect’ layers. I^∞n this latter case, the basic

+

layer type differs for the smaller Li and Na compared to

+

the larger K , Rb and Cs cations. [MnQ₆] octahedra are

very rare among the S/Se/Te manganates, but occur in the

binary border phases MnQ (NaCl and/or NiAs type).

The compositions of known chalcogenido

manganates(II) are restricted mainly to the four composi-

tions (for A:Mn:Q) 6:1:4 (Aꢀ=ꢀNa–Cs), 2:1:2 (K–Cs only), 2:2:3

*Corresponding author: Caroline Röhr, Institut für Anorganische und

Analytische Chemie, Universität Freiburg, Albertstrasse 21, D-79104

Freiburg, Germany, e-mail: caroline@ruby.chemie.uni-freiburg.de

Michael Langenmaier: Institut für Anorganische und Analytische

Chemie, Universität Freiburg, Albertstrasse 21, D-79104 Freiburg,

Germany

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624ꢁ ꢁM. Langenmaier and C. Röhr: Sodium tellurido manganates(II)

+

(Na only) and 2:3:4. For the lighter alkali elements sodium resemble the HgI₂-type structure and thus contain – in

and potassium, all ortho manganates A₆MnQ₄have long contrast to the others – vertex-sharing tetrahedra. For the

been known [13, 14]. Only recently, the structural chemis- named tellurido phases, the oxidation state of manganese

try was extended by the successful preparation and char- has been proven by magnetic measurements [24]. More

acterization of the whole series of the respective rubidium recently, these chalcogenido salts containing d⁴-Mn^III

and cesium salts, which are isotypic to the Na/K com- gained some attraction due to their half-metallic ferro-

pounds (Na₆ZnO₄-type, [15]). The heavier alkali cations K, magnetic properties, which are potentially applicable for

Rb and Cs form the whole series of sulfido, selenido and spintronic devices [26, 27].

tellurido manganates(II) A₂MnQ₂[8], which crystallize

In the course of our systematic studies on the crystal

without exception in the orthorhombic K₂ZnO₂-type struc- chemistry of mixed-valent chalcogenido metallates(II/III)

ture containing linear chains of tetrahedra [MnQ_4/2]. The of iron, cobalt and manganese, the new sodium tellurido

layered manganates(II) with the smaller Li and Na counter manganates(II) Na₂Mn₂Te₃and Na₂Mn₃Te₄(cf. also [28]) as

cations can be derived from the layers of tetrahedra of the well as the mixed Na–A (Aꢀ=ꢀK, Rb) salts Na₂AMnTe₃and

CaAl₂Si₂-type structure, where tetrahedral voids between NaCsMnTe₂were obtained from melts of the elements with

every second hexagonal close packed layers of anions are Mn or MnTe as manganese source. Whereas the two pure

occupied by Mn. Na₂Mn₂S₃[16] and Na₂Mn₂Se₃[17] are iso- sodium manganates are built up of close packed layers

typic and crystallize in a singular monoclinic structure, of chalcogenide ions Q²⁻and NaCsMnTe₂is also structur-

in which Mn²⁺cations occupy ⅔ of the tetrahedral voids ally related to the already known compounds, the mixed

between two close packed sulfide/selenide layers. The A₃MnTe₃-type phases with Na/K and Na/Rb exhibit very

yet missing isotypic tellurido manganate Na₂Mn₂Te₃is complex new structures with motifs resembling those of

added herewith. Na₂Mn₃Se₄[18] and the tellurium analog the cobaltate(II) Na₃CoS₃[12].

Na₂Mn₃Te₄, which is also presented in this work, differ in

containing also [MnQ₆] octahedra as building blocks. The

only potassium salt with this composition is the sulfido

2 Experimental

salt K₂Mn₃S₄. It forms a singular monoclinic structure [19,

20], which is certainly related to the common Cs₂Mn₃S₄-

type structure of the Rb and Cs compounds A₂M₃Q₄(Qꢀ=ꢀS, 2.1 Preparation and phase analysis

Se, Te; [21]). The named manganates(II) contain Mn^IIions

in a HS-d⁵configuration. Their magnetic structures, if The new sodium tellurido manganates(II) were synthesized

known, are dominated by an anti-ferromagnetic (AFM) in corundum crucibles sealed in steel autoclaves under

ordering, with magnetic moments close to the spin-only an argon atmosphere. Starting materials were the pure

value [13–15, 18, 22].

alkali metals (Na, K: Merck, >99%; Rb, Cs: 99.99%) MnTe

The layered structures of the Li and Na compounds (powder, ABCR GmbH, Karlsruhe, 99.9%) or elemental Mn

offer the opportunity for electrochemical modifications: as source of manganese and a corresponding amount of

for example, mixed alkali compounds were obtained by the elemental tellurium (shots, ABCR GmbH, Karlsruhe).

↑

an oxidative deintercalation (i.e. partial oxidation of Mn^II) Due to the violent reactions, cautious heating rates T like

ꢀ

followed by a reductive intercalation [23].

e.g. 5 K h⁻¹(between 80 and 110°C) were applied. Subse-

Compounds containing manganese(III) are com- quently after reaching the maximum temperatures (T_max

)

paratively rare and are obtained for Se and Te only. The of 600–1000°C, the samples were slowly cooled down to

structure of the mixed-valent tellurido phase NaMn_1.56Te₂r.t. After the preparations, representative parts of the reguli

exhibits a statistic occupation of the tetrahedral voids were ground and sealed in capillaries with a diameter of

in an h.c.p. arrangement of tellurium ions [24]. The pure 0.3 mm. X-ray powder diagrams were collected on trans-

Li and Na manganates(III) AMnSe₂[17] and AMnTe₂[25] mission powder diffractometer systems (Stoe STADI-P

as well as the mixed-valent phase Na₃Mn₄Te₆(25% Mn^III, with linear PSD or Dectris Mythen 1K strip detector, MoK

[24]) likewise contain h.c.p. chalcogen arrangements with radiation, graphite monochromator). For the phase analy^α-

layer-wise Mn-filled tetrahedral voids. Whereas these Li/ sis, the measured powder diagrams were compared to the

Na compounds were directly obtained from melts of the calculated (program Lazy-Pulverix [29]) reflections of the

elements, the synthesis of the K, Rb and Cs salts AMn(Se/ target compounds and other known phases in the respec-

Te)₂(TlAgTe₂-type [17, 24]) requires starting from pre-syn- tive systems Na–(K/Rb/Cs)–Mn–Te.

thesized LiMnQ₂and the respective alkali chloride [17].

In the ternary system Na–Mn–Te several samples

Their likewise layered chalcogenido metallate anions were prepared primarily with the focus to obtain new

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M. Langenmaier and C. Röhr: Sodium tellurido manganates(II)ꢂ

ꢂ625

mixed-valent Mn(II/III) compounds. Several samples of (9.783 mmol) Na, 418.7 mg (4.899 mmol) Rb, 894.2 mg

the overall composition Na₃Mn₄Te₆, which is one of the (4.899 mmol) MnTe and 1243.7 mg (9.747 mmol) Te] at a

very rare mixed-valent tellurido manganates reported maximum temperature of 800°C, when applying a slow

in the literature [24], were heated to different maximum cooling rate of 5 K h⁻¹between 650 and 100°C. Attempts to

temperatures. In a first attempt to reproduce this com- synthesize the cesium derivative of this type [sample Na₂C-

pound directly starting from the pure elements [46.3 mg sMnTe₃: 40.9 mg (1.78 mmol) Na, 120.4 mg (0.906 mmol)

(2.01 mmol) Na, 145.3 mg (2.645 mmol) Mn and 510.6 Cs, 167.4 mg (0.917 mmol) MnTe and 234.4 mg (1.837 mmol)

(4.002) Te] a maximum temperature of 900°C has been Te, T_maxꢀ=ꢀ800°C] yielded (together with Na₆MnTe₄) the new

applied, which was reached after several heating steps compound NaCsMnTe₂, which could be finally obtained

20

4

100

20

250

↑

ꢀ

[→90 →110 →420 →480 →900 (T

in in pure phase from a stoichiometric sample NaCsMnTe₂

K h⁻¹and T in °C)]. Subsequent cooling with rates of 250 [27.1 mg (1.18 mmol) Na, 151.7 mg (1.141 mmol) Cs, 208.0 mg

(down to 700°C) and 20 K h⁻¹down to r.t. yielded the new (1.140 mmol) MnTe and 146.0 mg (1.144 mmol) Te] at the

↓

−1

ꢀ

compound Na₂Mn₃Te₄instead of Na₃Mn₄Te₆, together with same maximum temperature (cooling rate T = 10 K from

small amounts of MnTe₂. Whereas an analogous sample 650°C to r.t.). Similar to the pure sodium phases, the mixed

with a maximum temperature of 700°C also gave this new Na-(K/Rb/Cs) tellurido manganates also form dark-red

phase, a further reduced T_maxof 600°C led to the forma- crystals, which are very sensitive against moisture.

tion of the known mixed-valent compound Na₃Mn₄Te₆

(according to the phase analysis by powder X-ray diffrac-

tion together with NaTe₃, MnTe and MnTe₂). This criti- 2.2 Crystal structure determinations

cal maximum temperature agrees with the synthesis of

Na₃Mn₄Te₆as reported by Kim et al. [24], who obtained this For the single crystal structure analyses of the title com-

phase keeping stoichiometric amounts of the elements in pounds, the dark-red crystals were selected and fixed in

niobium ampules at 600°C for 1 week. The second pure loop sample holders (100 K measurements) or in glass

sodium tellurido manganate, Na₂Mn₂Te₃, was obtained capillaries (ꢀ< 0.1 mm) under dried paraffin oil. Data sets

from a Te-rich sample of the composition Na₃MnTe₆, for were collected on a diffractometer equipped with a micro-

which 38.1 mg (1.66 mmol) sodium, 104.5 mg (0.573 mmol) source and a CCD detector (Bruker APEX II Quazar, Mo

MnTe and 361.2 mg (2.831 mmol) tellurium were heated radiation, 100 K) or on a sealed tube image plate detector

up with a similar temperature program as detailed above system (Stoe IPDS-2, Ag radiation, r.t.).

to a maximum temperature of 1000°C. The cooling rates

Na₂Mn₂Te₃: The reflections on the diffraction images

were 250 K h⁻¹to 800°C and finally again 20 K h⁻¹to r.t. The collected at 100 K could be indexed with a monoclinic

powder diagram of this sample shows the additional for- C-centered lattice with lattice parameters resembling

mation of Na₃Mn₄Te₆and, due to the high tellurium excess those of the sulfido and selenido compounds Na₂Mn₂Q₃.

not surprising, NaTe₃. Both new sodium compounds form The additional reflection condition 0kl: kꢀ+ꢀlꢀ=ꢀ2n is also

dark-red platelike crystals.

compatible with the space group C2/c of these structures.

In attempts to obtain new chain/cluster compounds The refinement of the positional and ADP parameters

with compositions close to A₂MnQ₂mixtures of alkali of the Na₂Mn₂S₃structure model [16] using the program

cations A of different size were used. The respective Shelxl-2013 [30] smoothly converged to a residual value

sample NaKMnTe₂consisting of 43.2 mg (1.88 mmol) Na, R1 of 0.0225. The results of this refinement are collected in

73.8 mg (1.89 mmol) K, 344.9 mg (1.890 mmol) MnTe and the Tables 1 (first row) and 2 [35].

239.6 mg (1.878 mmol) Te, was heated with 20 K h⁻¹to 80°C

Na₂Mn₃Te₄: The lattice parameters and the general

and subsequently with 200 K h⁻¹to a T_maxof 760°C. Cooling reflection conditions of the single crystal data of Na₂Mn₃Te₄

with a rate of 10 K h⁻¹to r.t. yielded the first specimen of allowed the assignment of the possible monoclinic space

the new compounds Na₂AMnTe₃. In accordance with the groups C2/m, Cm and C2. The structure solution by Direct

excess of potassium, the known K-rich phase K₂MnTe₂Methods (program Shelxs-2013 [30]) was successful in

[8] was identified as a by-product in the X-ray powder the centrosymmetric space group C2/m and yielded one

diagram of this sample. The analogous sample containing sodium, two Mn and two Te positions. The standard-

the heavier alkali element rubidium, NaRbMnTe₂, yielded ized (Structure Tidy [36]) parameters were refined as

only a mixture of already known ternary compounds described for Na₂Mn₂Te₃above and led again to a sat-

(Rb₂MnTe₂[8], Na₆MnTe₄[13] and RbMnTe₂[24]). The iso- isfactorily low R1 value of 0.0270. However, the refined

typic Rb analog Na₂RbMnTe₂could finally be obtained ADP parameters of the octahedrally coordinated manga-

in pure phase from a stoichiometric sample [224.9 mg nese atom Mn(1) at the origin of the unit cell describe an

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626ꢁ ꢁM. Langenmaier and C. Röhr: Sodium tellurido manganates(II)

Table 1:ꢀCrystallographic data and details of the data collection and structure determination for the five new tellurido manganates(II).

Compound

ꢂ

Na₂Mn₂Te₃

ꢂ

Na₂Mn₃Te₄

ꢂ

Na₂KMnTe₃

ꢂ

Na₂RbMnTe₃ꢂ

New

NaCsMnTe₂

Structure type

ꢃ

Na₂Mn₂S₃[16]ꢃ

Na₂Mn₃Te₄[28]ꢃ

New

ꢃ

New

Crystal system

Monoclinic

ꢃ

Orthorhombic

Space group

C2/c, no. 15

C2/m, no. 12

Pmc2₁, no. 26

ꢃ

Cccm, no. 66

Temperature, K

100

r.t.

ꢃ

100

Lattice parameters, pm, deg

ꢂa

ꢃ

1653.68(2)

1482.57(2)

773.620(10) ꢃ

117.52

1682.09(4)

4

ꢃ

1701.99(3)

438.741(8)

691.226(12)

90.3171(8)

516.15(2)

2

ꢃ

1069.70(4) ꢃ

1350.24(5) ꢃ

1238.82(4) ꢃ

ꢃ

1064.34(2) ꢃ

1350.47(3) ꢃ

1236.94(3) ꢃ

ꢃ

694.21(2)

1536.57(4)

664.47(2)

ꢂb

ꢂc

ꢂβ

ꢃ

Volume of the unit cell, 10⁶pm³

1789.29(11) ꢃ

1777.93(7) ꢃ

708.79(3)

4

4.37

Z

8

3.88

ꢃ

8

4.25

ꢃ

Density (X-ray), g cm⁻³

Diffractometer

Radiation

4.25

4.64

Bruker AXS Quazar

MoK

Stoe IPDS2 ꢃ

Bruker AXS Quazar

MoK

AgK

ꢃ

^α14.7

4.8–40.9

7495

1575

6.1 ^α

16.6

ꢃ

^α14.9

2.7–35.3

5954

739

0.0130

−1

μ

,

mm

Absorption coefficient

13.2

ꢃ

Mo/AgK_α

θ range, deg

2.0–36.6

16 892

3808

1.5–25.6

31 227

7177

1.5–36.5

48 797

7975

No. of reflections collected

No. of independent reflections

R_int

0.0178

0.0125

0.0585

0.0246

Corrections

Lorentz, polarisation, absorption

Multi-Scan [31]

ꢃ

Xshape [32] ꢃ

Direct methods (Shelxs-97 [33])

Shelxl-97 [34]

Multi-Scan [31]

Structure solution

Structure refinement

No. of free parameters

Goodness-of-fit on F²

Flack x

ꢃ

165

1.091

–

ꢃ

29

1.120

–

ꢃ

148

1.054

0.01(8)

ꢃ

148

ꢃ

17

1.191

–

1.068

−0.001(3)

R values [for refl. with Iꢁ>ꢁ2σ(I)]

ꢂR1

ꢂwR2

ꢃ

0.0225

0.0499

ꢃ

0.0270

0.0638

ꢃ

0.0445

0.0795

ꢃ

0.0210

0.0434

ꢃ

0.0131

0.0254

R values (all data)

ꢂR1

ꢃ

0.0250

ꢃ

0.0282

ꢃ

0.0557

ꢃ

0.0227

0.0437

ꢃ

0.0135

ꢂwR2

0.0507

0.0644

0.0826

0.0255

Residual elect. density, e⁻ꢁ×ꢁ10⁻⁶pm⁻³

+3.1/ꢁ−ꢁ1.8

+2.7/ꢁ−ꢁ5.9

+1.4/ꢁ−ꢁ1.4

+3.5/ꢁ−ꢁ1.3 ꢃ

+1.2/ꢁ−ꢁ1.3

Table 2:ꢀAtomic coordinates and equivalent isotropic displacement

calculated and visualized with the programs Jana2006

[37] and DrawXTL [38] (cf. Fig. 1a and b) indicated a small

displacement of this Mn atom from its special position.

Thus, equivalent alternatives for the structure refinement

are (i) the application of a structure model in the acen-

tric subgroup Cm together with a 1:1 inversion twin, (ii)

the refinement of a Mn(1) split position in the centrosym-

metric space group C2/m or (iii) an anharmonic treatment

of the Mn(1) site applying a higher ADP tensor for this

atom. Due to the only small deviation of Mn(1) from the

special position 2a and the only marginal improvements

of the R values and residual densities in the F_o–F_cmap,

the final structure refinement included herein (Tables 1

and 4, [35]) is the simple harmonic anisotropic refinement

parameters/pm²for the crystal structure of Na₂Mn₂Te₃.

Atomsꢂ Wyckoff ꢂ

position

xꢂ

yꢂ

zꢂ

U_eq

Na(1) ꢃ 4e

Na(2) ꢃ 4e

Na(3) ꢃ 8f

Mn(1) ꢃ 8f

Mn(2) ꢃ 8f

Te(1) ꢃ 8f

Te(2) ꢃ 8f

Te(3) ꢃ 8f

ꢃ

0ꢃ 0.27885(11)ꢃ

0ꢃ 0.56632(11)ꢃ

1/4ꢃ 136(3)

ꢃ 0.11176(10)ꢃ 0.08308(8)ꢃ 0.1565(2)ꢃ 217(3)

ꢃ

0.31142(3)ꢃ 0.23876(3)ꢃ 0.23331(6)ꢃ 91.8(7)

0.21214(3)ꢃ 0.42020(2)ꢃ 0.29194(6)ꢃ 90.7(7)

0.35221(2)ꢃ 0.07610(2)ꢃ 0.43314(2)ꢃ 79.3(4)

0.12821(2)ꢃ 0.27893(2)ꢃ 0.04236(2)ꢃ 94.4(4)

0.10690(2)ꢃ 0.11465(2)ꢃ 0.54977(3)ꢃ 127.3(4)

ellipsoid elongated towards the Te(2) ligands [max./min. in the centrosymmetric space group C2/m. The electron

r.m.s. values: 913(15) and 127(5) pm²]. A detailed analysis density minimum in the F_o–F_cmap of −5.9 e⁻ꢀ×ꢀ10⁻⁶pm⁻³,

of the electron density distribution at this special posi- which lies in the direct vicinity of Mn(1), is a consequence

tion with the help of difference electron density maps of this choice. A similar small disorder of the octahedrally

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ꢂ627

c

0

b

Na(3)

Na(1)

a

c

0

a

Na(1)

b

Te(1)

g

Mn(1)

Mn(2)

Te(2)

f

h

Te(1)

Mn(2)

Te(2)

Mn(1)

c

Mn(1)

a

d

Te(1)

Mn(2)

Te(1)

Te(3)

c

Fig. 1:ꢀCrystal structure of Na₂Mn₂Te₃(Na₂Mn₂S₃-type). (a) Perspective view of the unit cell with a single tellurido manganate sheet extended

to the left and the Te nets to the right; (b) projection of the subfigure a along (100); (c) details of the layers of [MnTe₄] tetrahedra (cf. Table 3

for the interatomic distances; gray polyhedra: [MnTe₄] tetrahedra; yellow polyhedra: [NaTe_5,6] coordination polyhedra; red/yellow/green

spheres: Mn/Na/Te; program DrawXTL [38]).

coordinated Mn(1) cations was very recently described for group Pmc2₁. The structure solution, using the methods

the isotypic selenido compound Na₂Mn₂Se₃[17].

and programs described above, yielded all 10 tellurium

Na₂AMnTe₃: The diffraction images of crystals of the positions, the four manganese and the two heavier alkali

two compounds Na₂KMnTe₃and Na₂RbMnTe₃exhibit sites. The positions of the overall five crystallographi-

mmm Laue symmetry. The only additional reflection cally different sodium cations were extracted from dif-

condition h0l: lꢀ=ꢀ2n leads uniquely to the acentric space ference electron density maps. The conclusive Flack

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Table 3:ꢀSelected interatomic distances (pm) and coordination numbers in the crystal structure of Na₂Mn₂Te₃.

Atoms Distanceꢂ Labelꢂ Mult.ꢂ CNꢂ Atoms Distanceꢂ Labelꢂ Mult.ꢂ CNꢂ Atoms

ꢂ

Distanceꢂ Labelꢂ

CN

Na(1) ꢃ – Te(2) ꢃ 319.7(1)ꢃ

ꢃ – Te(3) ꢃ 326.2(1)ꢃ

ꢃ – Te(1) ꢃ 332.7(1)ꢃ

ꢃ

2ꢁ×ꢁꢃ

ꢃ Na(2) ꢃ – Te(2) ꢃ 323.2(1)ꢃ

ꢃ

2ꢁ×ꢁꢃ

ꢃ Na(3)ꢃ – Te(3) ꢃ 303.7(1)ꢃ

ꢃ

2ꢁ×ꢁꢃ

ꢃ

ꢃ – Te(1) ꢃ 330.2(1)ꢃ

ꢃ – Te(1) ꢃ 334.7(1)ꢃ

2ꢁ×ꢁꢃ

ꢃ

ꢃ – Te(2) ꢃ 308.3(1)ꢃ

ꢃ – Te(3) ꢃ 311.5(2)ꢃ

ꢃ – Te(3) ꢃ 324.2(1)ꢃ

ꢃ – Te(1) ꢃ 354.1(1)ꢃ

2ꢁ×ꢁꢃ

6ꢃ

ꢃ

2ꢁ×ꢁꢃ

6ꢃ

ꢃ

5

Mn(1)ꢃ – Te(3) ꢃ 269.6(1)ꢃ a

ꢃ – Te(2) ꢃ 275.3(1)ꢃ b

ꢃ – Te(2) ꢃ 275.3(1)ꢃ c

ꢃ – Te(1) ꢃ 277.4(1)ꢃ d

ꢃ – Mn(1)ꢃ 323.9(1)ꢃ

ꢃ Mn(2)ꢃ – Te(3) ꢃ 270.8(1)ꢃ e

ꢃ

ꢃ – Te(2) ꢃ 275.0(1)ꢃ f

ꢃ – Te(1) ꢃ 278.4(1)ꢃ g

ꢃ – Te(1) ꢃ 279.2(1)ꢃ h

ꢃ

4ꢃ

ꢃ

4ꢃ

ꢃ

Te(1) ꢃ – Mn(1)ꢃ 277.4(1)ꢃ d

ꢃ – Mn(2)ꢃ 278.4(1)ꢃ g

ꢃ – Mn(2)ꢃ 279.2(1)ꢃ h

ꢃ – Na(2) ꢃ 330.2(1)ꢃ

ꢃ Te(2) ꢃ – Mn(2)ꢃ 275.0(1)ꢃ f

ꢃ Te(3) ꢃ – Mn(1)ꢃ 269.6(1)ꢃ a

ꢃ

ꢃ – Mn(1)ꢃ 275.3(1)ꢃ b

ꢃ – Mn(1)ꢃ 275.3(1)ꢃ c

ꢃ – Na(3) ꢃ 308.3(1)ꢃ

ꢃ – Na(1) ꢃ 319.7(1)ꢃ

ꢃ – Na(2) ꢃ 323.2(1)ꢃ

ꢃ

ꢃ – Mn(2)ꢃ 270.8(1)ꢃ e

ꢃ – Na(3) ꢃ 303.7(1)ꢃ

ꢃ – Na(3) ꢃ 311.5(2)ꢃ

ꢃ – Na(3) ꢃ 324.2(1)ꢃ

ꢃ – Na(1) ꢃ 326.2(1)ꢃ

ꢃ

ꢃ – Na(1) ꢃ 332.7(1)ꢃ

ꢃ

ꢃ – Na(2) ꢃ 334.7(2)ꢃ

ꢃ

3ꢁ+ꢁ3ꢃ

2ꢁ+ꢁ4

ꢃ – Na(3) ꢃ 354.1(1)ꢃ

3ꢁ+ꢁ4ꢃ

ꢃ

Table 4:ꢀAtomic coordinates and equivalent isotropic displacement

for the structure of NaCsMnTe₂, which represents a new

structure type, are listed in the last column of Table 1 and

in Table 8 [35].

parameters/pm²for the crystal structure of Na₂Mn₃Te₄.

Atomsꢂ Wyckoff ꢂ

position

xꢂ

yꢂ

zꢂ

U_eq

Na

ꢃ

4i

ꢃ

0.20004(12)ꢃ 0ꢃ

0ꢃ 0ꢃ

0.2459(4)ꢃ

0ꢃ

246(5)

518(6)

Mn(1) ꢃ 2a

Mn(2) ꢃ 4i

3 Results and discussion

0.41676(4)ꢃ 0ꢃ 0.37553(9)ꢃ 115.8(10)

Te(1)

Te(2)

ꢃ

4i

0.56540(2)ꢃ 0ꢃ 0.23192(4)ꢃ

0.16249(2)ꢃ 0ꢃ 0.75333(4)ꢃ

118.7(6)

128.2(6)

3.1 The pure sodium tellurido manganates

Na₂Mn₂Te₃and Na₂Mn₃Te₄

parameters support the non-centrosymmetric structure The two new pure sodium tellurido manganates(II)

and the absence of twins. A noticeable Na–(K/Rb) (sta- Na₂Mn₂Te₃and Na₂Mn₃Te₄were obtained in the form of

tistical) exchange at the overall seven cation positions is dark-red platelike crystals from melts of the three ele-

not observed. For the final refinement, the atomic coordi- ments Na, Mn and Te or alternatively from Na, MnTe and

nates were standardized and a consistent labeling of the Te. Na₂Mn₃Te₄is formed only at maximum temperatures

manganese and tellurium atoms was applied (cf. Struc- above 700°C. Samples of the target or closely related

ture description). The final crystal data are collected in compositions heated to 600°C yielded the known mixed-

two intermediate columns of Table 1 and in Table 6 (see valent phase Na₃Mn₄Te₆[25] instead. Further details of the

also [35]).

synthesis of the two sodium compounds are collected in

NaCsMnTe₂: The dark-red crystals of the Cs com- the Experimental section.

pound NaCsMnTe₂also exhibit an orthorhombic, in this

Na₂Mn₂Te₃crystallizes in the monoclinic space group

case small and C-centered, unit cell. The two further C2/c and is isotypic to the analogous sulfido manganate

reflection conditions (0kl: lꢀ=ꢀ2n and h0l: lꢀ=ꢀ2n) allowed Na₂Mn₂S₃obtained (from sodium carbonate, sulfur and

for two different space groups, the centrosymmetric manganese), characterized and described by Klepp et al.

Cccm and the acentric Ccc2 group. The structure was as early as 1983 [16]. The isotypic selenido manganate

solved and completed (Na position) as described above Na₂Mn₂Se₃[17] was obtained from Na, MnSe and Se at a

in the space group Cccm. Similar to the K and Rb com- maximum temperature of 850°C by Kim and Hughbanks

pounds Na₂AMnTe₃, the distribution of the two different also already 20 years ago [17]. Further compounds forming

alkali cations is distinct, hints to a statistic distribution this structure type are not known. Different views of

of the cation positions are missing. The final parameters the crystal structure of Na₂Mn₂Te₃are shown in Fig. 1.

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The layered tellurido manganate anion contains two crys- and are thus also not convertible by e.g. an electrochemi-

+

cal redox-induced Na exchange.

tallographically different manganese and three tellurium

atoms, all at general Wyckoff positions 8f (Table 2). The

Te atoms form undulated hexagonal close packed layers

(3⁶nets after Schläfli) which are running perpendicular

to (100) (green nets at the right hand side of the struc-

ture drawing in Fig. 1a and b). The sheets are stacked

in a hexagonal close packed (h.c.p.; ꢀ|:AB:ꢀ|) sequence.

Between each second layer, ⅔ of the tetrahedral voids

are occupied by Mn²⁺cations resulting in layers [Mn₂Te₃]

of edge and vertex-sharing [MnTe₄] tetrahedra. The occu-

pation of the tetrahedral interstices results in ribbons of

equally oriented pairs of tetrahedra (cf. gray bars with

arrows in Fig. 1c). The chalcogenido manganate layers

finally consist of units of four edge-sharing tetrahedra

(blue dotted ellipse in Fig. 1c), which are further con-

nected via the μ₃-Te(1) ligands. The common edges within

the tetramers [Mn₄Te(2,3)₄Te(1)_6/3] are formed by Te(2)

and Te(3). The shortest Mn–Mn contacts are lying within

this tetramer and are 329.0 [Mn(1)–Mn(2)] and 323.9 pm

[Mn(1)–Mn(1)] long. The Mn–Te distances (labeled a–h)

in the tellurido manganate sheets are with 269.6–279.2 pm

in the expected range (Table 3). They are shorter than the

sum of Shannons radii (287 pm, [39]), but similar to the

values found in other tellurido manganates(II), like e.g. in

the ortho salts A₆MnTe₄(275–282 pm, [13, 15]). The sodium

cations occupy two special positions 4e [site symmetry 2;

The monoclinic crystal structure of the second pure

sodium title compound Na₂Mn₃Te₄[28], which is iso-

typic to the very recently reported selenido analog [18],

contains one Na, two Mn and two Te positions (Table 4).

Similar to Na₂Mn₂Te₃, the structure exhibits tellurido

manganate sheets, but in this case Mn(II) is both tetrahe-

drally and octahedrally coordinated, though it should be

pointed out that the latter bonding situation is very rare in

alkali sulfido/selenido/tellurido manganates. The Mn(1)

atoms at the unit cell origin (2a, point group symmetry

2/m) are these octahedrally coordinated Mn²⁺cations

([Mn(1)Te(1)_4/4Te(2)_2/3], blue polyhedra in Fig. 2). The

[Mn(1)Te₆] octahedra are connected via opposite edges to

form chains running along the b axis of the monoclinic

cell. As expected, the Mn–Te bond lengths are with 293.3

(a) and 325.7 pm (b, Table 4) significantly larger than

inside the [Mn^IITe₄] tetrahedra. However, as illustrated

by the 99% ellipsoids of the refinement in the centrosym-

metric space group C2/m [Mn(1) at 0,0,0, cf. Experimental

section for details of the refinements] and the differ-

ence electron density map (Fig. 2a and b) Mn(1) is evi-

dently slightly disordered around the 2a site (Δ≈25 pm),

leading to a distortion of the octahedra towards a square

pyramid and to two different distances b to the Te(2) octa-

hedra tips of ≈300 and 350 pm. The very same situation

has been described for the isotypic selenido compound

Na₂Mn₃Se₄[18]. The second type of Mn(II) cations in the

structure of Na₂Mn₃Te₄[Mn(2), Wyckoff site 4i, m sym-

metry] are tetrahedrally coordinated by four Te²⁻anions

([MnTe(1)_2/4Te(2)_2/3], gray polyhedra in Fig. 2), whereby

two tetrahedra form dinuclear units sharing a common

edge. These dimers are again connected via four common

corners to form strands, which are again running along

b. The Mn(2)–Te bond lengths are again in the range

common for tetrahedral building blocks (270.8–279.2

pm, Table 5). The ribbons of octahedra and tetrahedra

are fused and form puckered layers [Mn₃Te₄]²⁻in the b–c

plane, which are ꢀ|:AB:ꢀ|ꢀ stacked along [100]. Between the

+

Na(1) and Na(2)] and one general position [Na(3)]. The Na

cations at C₂symmetric positions occupy (overall ⅔) of

the octahedral voids in the interstitial layers between the

tellurido manganate sheets. Similar to the Mn centered

tetrahedra, [Na(1,2)Te₆] pairs of octahedra form ribbons,

which are arranged – under the exclusion of face-shar-

ing – between the ribbons of [MnTe₄] tetrahedra of the

adjacent layers. The Na–Te distances within these octahe-

dra are 320–335 pm (Table 3). A separated Na(1) octahedral

coordination polyhedron is shown at the right hand side

of in Fig. 1a and b. The Na(3) cations are located within

the (expanded) Te₃-rings of the tellurium sheets and thus

exhibit a five-fold coordination by Te²⁻, with Na–Te dis-

tances of 304–354 pm (cf. the second isolated polyhedron

in Fig. 1a and b).

Even though the structure of the long-known com-

pound Na₃Mn₄Te₆shows some similarities with the new

phase described above (monoclinic C lattice, h.c.p. sub-

structure of Te, sheets of vertex- and edge-sharing [MnTe₄]

tetrahedra), the connection of the [MnTe₄] tetrahedra

within the sheets is fundamentally different. The two sim-

ilar-looking compounds Na₂Mn₂Te₃and Na₃Mn₄Te₆show

+

layers, Na cations (Wyckoff position 4i) are interspersed,

which exhibit an octahedral coordination with very

similar distances like in Na₂Mn₂Te₃(d_Na−Teꢀ=ꢀ317.3–356.9

pm, yellow polyhedra). In contrast to the simple Te²⁻

layers found in Na₂Mn₂Te₃[3⁶nets, (defect) CaAl₂Si₂-type]

and the tellurido compounds with the larger A cations [4⁴

nets, ThCr₂Si₂-type, see below], the Te atoms in Na₂Mn₃Te₄

form 3³ꢀ·ꢀ4²nets: the planar nets running in the a–c plane

at yꢀ=ꢀ¼ and ¾ are marked by red arrows in Fig. 2c; the

second set of slightly puckered similar nets along the

no crystallographic relation (cf. the discussion below) diagonal are marked by blue arrows. The four-membered

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0.2

y=0

z

0.1

a

0

Te(1)

Mn(1)

Te(2)

b

−0.1

b

−0.2

a

−0.04

0

0.04

x

a

Mn(2)

Te(1)

c

a

d

Mn(1)

Te(2)

Na

Mn(2)

Te(2)

b

Mn(1)

b

Mn(2)

Te(2)

Te(1)

c

0

b

c

d

Fig. 2:ꢀCrystal structure of Na₂Mn₃Te₄. a/b: details of the surrounding of Mn(1), with the difference electron density around Mn(1) plotted

at a level of 3 (solid) and 15 (red net) e⁻ꢁ×ꢁ10⁻⁶pm⁻³(a) and difference electron density map with isolines of 1 e⁻ꢁ×ꢁ10⁻⁶pm⁻³(b). (c) Projection

of the structure along c; (d) perspective view of the tellurido manganate sheet, with Mn ellipsoids at a level of 99% (cf. Fig. 1 for a detailed

legend and Table 5 for interatomic distances).

Table 5:ꢀSelected interatomic distances (pm) and coordination numbers in the crystal structure of Na₂Mn₃Te₄.

Atoms

ꢂ Distanceꢂ Labelꢂ Mult.ꢂ CNꢂ Atoms

ꢂ Distanceꢂ Labelꢂ Mult.ꢂ CN

Na ꢃ – Te(1) ꢃ 317.3(2)ꢃ

ꢃ – Te(2) ꢃ 320.7(2)ꢃ

ꢃ

2ꢁ×ꢁꢃ

ꢃ Mn(1)ꢃ – Te(1) ꢃ 293.3(1)ꢃ a

ꢃ

4ꢁ×ꢁꢃ

ꢃ Mn(2) ꢃ – Te(2) ꢃ 272.3(1)ꢃ c

ꢃ

2ꢁ×ꢃꢁ

2ꢁ×ꢁꢃ

ꢃ

ꢃ – Te(2) ꢃ 325.7(1)ꢃ b

2ꢁ×ꢁꢃ

6ꢃ

ꢃ – Te(1) ꢃ 272.3(1)ꢃ d

ꢃ – Te(1) ꢃ 272.9(1)ꢃ e

ꢃ – Mn(2)ꢃ 330.7(1)ꢃ u

ꢃ

ꢃ – Te(2) ꢃ 346.1(3)ꢃ

ꢃ

4

ꢃ – Te(2) ꢃ 356.9(3)ꢃ

ꢃ

6ꢃ

1ꢁ×ꢃꢁ

Te(1)ꢃ – Mn(2)ꢃ 272.3(1)ꢃ c

ꢃ – Mn(2)ꢃ 272.9(1)ꢃ e

ꢃ – Mn(1)ꢃ 293.3(1)ꢃ a

ꢃ – Na ꢃ 317.3(2)ꢃ

ꢃ

ꢃ Te(2) ꢃ – Mn(2) ꢃ 272.3(1)ꢃ c

2ꢁ×ꢁꢃ

ꢃ

ꢃ – Na

ꢃ 320.7(2)ꢃ

2ꢁ×ꢁꢃ

ꢃ – Mn(1) ꢃ 325.7(1)ꢃ b

ꢃ

2ꢁ×ꢁꢃ 4ꢁ+ꢁ2ꢃ

ꢃ – Na

ꢃ 346.1(3)ꢃ

ꢃ 356.9(3)ꢃ

ꢃ

ꢃ 3ꢁ+ꢁ4ꢃ

rings of these tellurium nets coincide with the ‘bases’ of while Na₂Mn₃Se₄and Na₂Mn₃Te₄exhibit einer double

the [Mn(1)Te₆] (blue layers) and the [NaTe₆] octahedra chains of [Mn₂Q₆] dinuclear units.

(red layers).

Even though the structure type of the two compounds

Na₂Mn₃Se₄and Na₂Mn₃Te₄[18] is singular, it is however 3.2 Mixed tellurido manganates Na₂AMnTe₃

closely related to the isopointal sodium sulfido metallate

Na₂Cu₂ZrS₄[40]: in the latter compound, the chalcogen

(Aꢀ=ꢀK, Rb)

packing as well as the arrangements of the [ZrS₆] and the DespiteitsverysimpleoverallcompositionA₃MnTe₃, which

[NaS₆] octahedra are similar. The only difference is the suggests the presence of Mn(III), the mixed tellurido man-

connection of the [Cu^IIS₄] tetrahedra, which form zweier ganates Na₂AMnTe₃(Aꢀ=ꢀK, Rb) exhibit an unexpectedly

single zig-zag chains along b sharing two adjacent edges, complex crystal structure. However, the bonding situation

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is closely related to that in the cobaltate Na₃CoS₃[12], The sodium cations Na(1), which exhibit a trigonal bipy-

where Q–Q bonds are present and the metal cation is kept ramidal coordination, are located at the same mirror

at an oxidation state of +II. For Na₃CoS₃, the polyanions plane.

formed are already complex, but the two manganates

The second mirror plane (at xꢀ=ꢀ0, layers B, Fig. 3b)

Na₂AMnTe₃show an even more diverse structural chem- again contains angulated chains of [MnTe₄] tetrahedra

istry. The new chiral orthorhombic structure type (space also running along the c axis. In this case, the tetrahedra

group Pmc2₁) consists of five crystallographically differ- are connected via edges exclusively; their overall formula

1

ent sodium and two K/Rb cations (Table 6). The anionic is thus [MnTe_4/2]²⁻. These chains around yꢀ≈ꢀ0 are stag-

∞

building blocks contain four manganese and 10 tellurium gered against the chains of the adjacent layers A. The

sites, which are labelled according to their bonding fea- mirror planes B are additionally occupied by [Te(31,32)₂]²⁻

tures. The polyanions are best divided into two different dumbbells, which are not connected to manganese atoms,

layers coinciding with the mirror planes at xꢀ=ꢀ½ (layers A) but fill the space between the [MnTe_4/2]²⁻chains. Due to the

and xꢀ=ꢀ0 (B). The layers consist of chains formed by two ratio of these [Te₂]²⁻dumbbells and the [MnTe_4/2]²⁻tetrahe-

crystallographically different Mn(II) cations each.

dra of 1:2 the total composition and charge of this layer

The layers A are formed by chains of [Mn(1,2)Te₄] B [Mn₂Te₄]⁴⁻[Te₂]²⁻ꢀ=ꢀ[Mn₂Te₆]⁶⁻is again similar to that of

tetrahedra, alternately connected via common edges the overall formula. The cations Na(2) are also located at

and corners (Fig. 3a). The chains of layer A are running this mirror plane and are stuffed between the ditelluride

along [001] around yꢀ≈ꢀ½. Whereas Mn(1) is coordinated dumbbells and the Te(¾) atoms of the chains. They show

by monatomic tellurido ligands Te²⁻only, the η₁tellurido a pentagonal-bipyramidal 7-fold coordination by Te atoms

ligand bonded to Mn(2) is a ditelluride dumbbell (transparent yellow polyhedron in Fig. 3d).

[Te(21,22)₂]²⁻. The chains are composed of vertex-sharing

The remaining alkali cations (the three sodium Na(3),

dinuclearunits[Te(2)_1/2Te(1)Mn(1)Te(12)₂Mn(2)(Te₂)Te(2)_1/2], Na(4), Na(5) and the two Rb/Cs cations) are located close

which themselves consist of the edge-sharing tetrahedra to xꢀ=ꢀ¼ (and ¾) and thus form only very slightly puckered

[Mn(1)Te(1)Te_3/2] and [Mn(2)(Te)₂Te_3/2]. The overall formula nets with the Schläfli symbol 3.5.3.5. (Na nodes)ꢀ+ꢀ3².5.3.5.

1

of the chains within the layer A is thus [Mn₂Te₆]⁶⁻and (Rb nodes) (3:2). The five-membered rings of this net

∞

therewith meets the composition of the whole compound. of cations are centered by the Te(12) and Te(34) atoms

Table 6:ꢀAtomic coordinates and equivalent isotropic displacement parameters/pm²for the crystal structures of Na₂AMnTe₃(Aꢁ=ꢁK, Rb).

Atomsꢂ Wyckoff ꢂ

position ꢂ

xꢂ

yꢂ

zꢂ

U_eq

ꢂ

Aꢀ=ꢀKꢂ

Aꢀ=ꢀRb

Aꢀ=ꢀKꢂ

Aꢀ=ꢀRb

Aꢀ=ꢀKꢂ

Aꢀ=ꢀRb

Aꢀ=ꢀKꢂ

Aꢀ=ꢀRb

Na(1) ꢃ 2b

Na(2) ꢃ 2a

Na(3) ꢃ 4c

Na(4) ꢃ 4c

Na(5) ꢃ 4c

ꢃ

1/2ꢃ

0ꢃ

1/2ꢃ

0ꢃ

0.0790(5)ꢃ

0.4296(5)ꢃ

0.0061(5)ꢃ 0.00606(15)ꢃ

0.5078(4)ꢃ 0.50723(16)ꢃ

0.2545(4)ꢃ 0.25215(14)ꢃ

0.30032(3)ꢃ

0.1070(3)ꢃ

0.4320(2)ꢃ

0.3282(7)ꢃ

0.3230(3)ꢃ

337(14)ꢃ

307(13)ꢃ

375(10)ꢃ

340(9)ꢃ

254(7)

207(6)

146(4)

137(3)

163(4)

−0.0007(6)ꢃ

−0.0037(3)ꢃ

0.2685(4)ꢃ 0.26977(17)ꢃ

0.2802(5)ꢃ 0.27845(17)ꢃ

0.2155(6)ꢃ 0.21766(19)ꢃ

0.2220(3)ꢃ

0.2586(3)ꢃ

0.5817(5)ꢃ 0.58479(17)ꢃ

0.2507(4)ꢃ 0.24983(16)ꢃ

0.1721(5)ꢃ 0.17129(19)ꢃ

0.4955(3)ꢃ

0.8367(3)ꢃ

0.0784(2)ꢃ

0.4820(2)ꢃ

455(13)ꢃ

A(1)

A(2)

ꢃ

4c

0.21975(4)ꢃ 0.29934(19)ꢃ

0.26218(4)ꢃ 0.19882(19)ꢃ

0.49539(4)ꢃ

0.83540(4)ꢃ

0.07895(8)ꢃ

0.48216(8)ꢃ

0.45517(8)ꢃ

0.21011(8)ꢃ

0.05131(3)ꢃ

0.30426(3)ꢃ

382(5)ꢃ 101.7(7)

399(5)ꢃ 114.4(7)

243(4)ꢃ

247(4)ꢃ

248(4)ꢃ

239(4)ꢃ

0.19831(3)ꢃ

0.32787(7)ꢃ

0.46297(6)ꢃ

0.03708(7)ꢃ 0.45439(19)ꢃ

0.04325(7)ꢃ 0.20812(19)ꢃ

0.13242(3)ꢃ 0.03820(10)ꢃ

0.34731(3)ꢃ

0.42324(2)ꢃ

0.65474(3)ꢃ

0.14828(3)ꢃ

0.14545(3)ꢃ

0.15407(3)ꢃ

0.39761(3)ꢃ

0.59711(3)ꢃ

0.07380(2)ꢃ

Mn(1) ꢃ 2b

Mn(2) ꢃ 2b

Mn(3) ꢃ 2a

Mn(4) ꢃ 2a

1/2ꢃ

0ꢃ

1/2ꢃ

1/2ꢃ 0.32499(17)ꢃ

1/2ꢃ 0.45944(15)ꢃ

0ꢃ 0.03978(18)ꢃ

0ꢃ 0.04119(17)ꢃ

1/2ꢃ

90(2)

91(2)

97(2)

92(2)

Te(1)

Te(2)

ꢃ

2b

0.12935(7)ꢃ

0.34101(8)ꢃ

0.42356(4)ꢃ

0.65730(8)ꢃ

0.14231(8)ꢃ

0.15089(8)ꢃ

0.15388(7)ꢃ

0.39414(8)ꢃ

0.59469(8)ꢃ

0.07459(5)ꢃ

289(2)ꢃ 108.8(8)

274(2)ꢃ

0.30507(8)ꢃ

0.00159(6)ꢃ

0.17100(9)ꢃ

0.61941(9)ꢃ

0.63706(8)ꢃ

0.02502(8)ꢃ

0.28947(9)ꢃ

0.22087(9)ꢃ

0.33184(6)ꢃ

96.6(8)

81.8(5)

88.5(7)

Te(12) ꢃ 4c

Te(21) ꢃ 2b

Te(22) ꢃ 2b

0.29425(6)ꢃ

0.29096(2)ꢃ

0.00155(2)ꢃ 242.4(13)ꢃ

1/2ꢃ

0ꢃ

1/2ꢃ

0ꢃ

0.16930(3)ꢃ

0.61086(3)ꢃ

0.63849(3)ꢃ

0.02785(3)ꢃ

0.28281(3)ꢃ

0.22001(3)ꢃ

276(2)ꢃ

299(2)ꢃ 108.0(8)

269(2)ꢃ

258(2)ꢃ

285(2)ꢃ 104.8(8)

287(2)ꢃ 101.3(8)

Te(3)

Te(4)

ꢃ

2a

88.3(7)

89.7(7)

Te(31) ꢃ 2a

Te(32) ꢃ 2a

Te(34) ꢃ 4c

0.20575(6)ꢃ

0.21003(2)ꢃ

0.33329(2)ꢃ 267.1(13)ꢃ

93.3(5)

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ꢁM. Langenmaier and C. Röhr: Sodium tellurido manganates(II)

b

Te(1)

Te(22)

g

Rb(2)

Te(2)

Te(21)

Te(31)

d

f

Mn(2)

e

Na(2)

Rb(1)

n

Na(4)

Na(2)

Te(4)

b

Te(12)

Mn(1)

Te(32)

c

a

Na(5)

Te(34)

Te(1)

Mn(4)

c

Na(1)

c

j

h

l

0

k

Na(3)

a

m

i

Mn(3)

b

Te(3)

b

Rb(2)

Na(5)

Te(32)

Te(31)

Mn(2)

Te(12)

Na(4)

Na(2)

Mn(1)

Rb(1)

Te(34)

c

0

Na(3)

Mn(4)

Mn(3)

Na(3)

a

Na(1)

c

d

Fig. 3:ꢀCrystal structure of Na₂AMnTe₃. (a) Chains [Mn(1,2)₂Te₆]⁶⁻(layer A) around xꢁ≈ꢁ½. (b) Chains [Mn(3,4)₂Te₄]⁴⁻and [Te₂]²⁻dumbbells (layer

B) around xꢀ≈ꢁ0 and 1. (c) Cation nets [Rb and Na(3) to Na(5)] at xꢁ≈ꢁ¼ and ¾. (d) Perspective view of the unit cell together with all cation

coordination spheres (Rb, brown sticks) and polyhedra (Na, yellowish polyhedra; cf. Table 7 for interatomic distances and their labels).

forming those common edges of the [MnTe₄] tetrahedra, 280/284 pm for the ‘free’ ditelluride anions. These slightly

which are oriented perpendicular to the mirror planes. decreased bond lengths of bonded dichalcogenid anions

The three sodium cations exhibit distorted octahedral are similarly observed for other dichalcogenido metallates

coordination spheres (yellow polyhedra in Fig. 3d) with (like e.g. Na₃CoS₃[12]) and are sufficiently discussed in the

Na–Te distances in the range 312–386 pm (Table 7). As literature [43, 44].

expected from the increased ionic radii, the heavier alkali

+

cations K and Rb are coordinated by eight [A(2): 7ꢀ+ꢀ1] tel-

lurium atoms with larger distances of minimum 356 pm. 3.3 NaCsMnTe₂

The respective coordination spheres are shown by thin

brown ‘bonds’ in Fig. 3d.

NaCsMnTe₂crystallizes in a new, very simple, but never-

The Mn–Te bond lengths within the [MnTe₄] tetra- theless new, orthorhombic structure type (space group

hedra are again in the usual range between 269 and 282 Cccm). The crystal parameters are collected in the last

pm. Compared to the pure Na compounds above, these column of Table 1 and in Table 8, interatomic distances

Te-richer compounds exhibit μ₁- and μ₂-Te²⁻ligands only can be found in Table 9.

and the tetrahedra are less connected with each other. In

The compound exhibits the largest differences in the

+

addition to the one or two Mn²⁺cations, five to seven A

size of the two alkali cations, Na and Cs . Consequently,

cations round out the tellurium coordination spheres. The the cations are again fully ordered at two crystallographi-

Te(22) and Te(32) atoms, which are not connected to man- cally different positions with very diverse coordination

+

ganese, show a 1 Teꢀ+ꢀ8 A coordination sphere (Table 7), numbers of four (tetrahedra, for Na , transparent yellow

+

which is likewise observed in binary alkali (poly)tellurides polyhedra in Fig. 4) and eight (cubes, for Cs ). The tellu-

(cf. discussions in [41, 42]). The Te–Te bonds within the rido manganate(II) polyanions are linear chains of edge-

dumbbells amount to 276/278 pm for the [Te₂] ligands and sharing tetrahedra [MnTe_4/2], which are running along the

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M. Langenmaier and C. Röhr: Sodium tellurido manganates(II)ꢂ

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Table 8:ꢀAtomic coordinates and equivalent isotropic displacement

[8]). The bond angles Te–Mn–Te within the tetrahedra

are 106.4–114.5° and the polyhedra are therewith slightly

stretched along the chain direction. The [NaTe_4/2] tet-

rahedra are connected among each other in a similar

manner, the Na–Te distance of 305.2 pm is also somewhat

decreased with respect to the sum of the Shannon radii of

320 pm. Similar short values can be found e.g. for Na(3)

with CNꢀ=ꢀ5 in Na₂Mn₂Te₃(303.7 pm, Table 2), whereas the

Na–Te distances within octahedra are commonly some-

what larger (e.g. Na₂Mn₂Te₃: d_Na−Teꢀ=ꢀ320–334 pm). Both

chains of tetrahedra share the tellurium atoms and are

thus connected to PbO-like layers [NaMnTe₂], which are

also the building blocks in the prominent ThCr₂Si₂-type

iron arsenido and chalcogenido superconductors and

generally in many alkali-poorer chalcogenido-metallates

parameters/pm²for the crystal structure of NaCsMnTe₂.

Atoms Wyckoff position

x

y

z

U_eq

Na

Cs

Mn

Te

4a

4e

4b

8l

0

1/4

0

1/4

110(2)

1/4

0

133.4(5)

1/2 1/4 77.1(9)

0.21609(2) 0.60639(2)

0

76.8(4)

Table 9:ꢀSelected interatomic distances (pm) in the crystal structure

of NaCsMnTe₂.

Atoms

ꢂ

Distanceꢂ

Labelꢂ

Freq.ꢂ

CN

Na ꢃ

– Te ꢃ

– Mnꢃ

– Na ꢃ

– Cs ꢃ

305.229(13)ꢃ

391.65(2)ꢃ

399.533(12)ꢃ

431.36(2)ꢃ

277.173(12)ꢃ

277.174(12)ꢃ

305.232(13)ꢃ

391.65(2)ꢃ

399.531(12)ꢃ

431.36(2)ꢃ

ꢃ

4ꢁ×ꢁꢃ

2ꢁ×ꢁꢃ

4ꢁ×ꢁꢃ

2ꢁ×ꢁꢃ

4ꢁ×ꢁꢃ

2ꢁ×ꢁꢃ

ꢃ

4

Cs ꢃ

+

ꢃ

with larger counter-cations K to Cs . Analogously, the

+

8

4

larger cation Cs in NaCsMnTe₂occupies the alkali (Th in

Mnꢃ

Te ꢃ

a

the aristotype) position between the layers. The pseudo-

tetragonal orthorhombic unit cell, in which the a and the

c axis are of comparable lengths, is a consequence of this

structure relation. Not surprisingly, the new structure

type can be crystallographically derived by a group sub-

group relation [45–48] from the BaAl₄/ThCr₂Si₂-type by

firstly applying a t2 symmetry reduction from the space

group I4/mmm of the aristotype to Fmmm (basis change:

a′ꢀ=ꢀaꢀ–ꢀb, b′ꢀ=ꢀaꢀ+ꢀb). Secondly, a k2 symmetry reduction

leads directly to the space group Cccm of NaCsMnTe₂(cf.

Fig. 5). Thereby the Ba/Th Wyckoff position 2a transforms

to 4e (Cs), the 4d site [Cr/Al(1)/M in the chalcogenido

metallates AM₂Q₂] splits into 4a (Na) and 4b (Mn), again

without any free positional parameter. The 4e position of

the aristotype (0,0,z) with a free z parameter and point

group 4mm is transformed to the 8l position of the Te

anions (∼¼, ∼¼+z, 0; cf. Table 8).

ꢃ

2ꢁ×ꢁꢃ

ꢃ

2ꢁ+(2ꢁ+ꢁ4)

c

0

Cs

Na

Te

For the closely related Li/K sulfido manganate

KLiMnS₂, Bronger et al. reported the statistic occupation

+

of Li and Mn²⁺at the Cr sites of the aristotype [49].

b

Mn

a

3.4 Classification of the title compounds

within the family of alkali chalcogenido

manganates

Fig. 4:ꢀCrystal structure of NaCsMnTe₂(cf. Table 9 for interatomic

distances; caption of Fig. 1).

The five title compounds can be classified within the

families of known alkali chalcogenido (excluding

c axis. The Mn–Te distance of 277.2 pm is again approx. oxygen) manganates(II) and (III). To that, Table 10 con-

10 pm shorter than the sum of Shannons radii (287 pm, tains the basic structure data of all compounds reported

[39]), but very similar to the bond lengths in the chains in the literature. The manganates can obviously be cate-

of the pure alkali compounds (K/Rb/Cs)₂MnTe₂forming gorized according to the connectivity of the [MnQ₄] tetra-

the K₂ZnO₂-type structure (e.g. Cs₂MnTe₂: d_Mn−Teꢀ=ꢀ277.3 pm hedra into (i) ‘ortho’ salts containing isolated tetrahedra,

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636ꢁ ꢁM. Langenmaier and C. Röhr: Sodium tellurido manganates(II)

Fig. 5:ꢀStructure relations (if possible, with a crystallographic group-subgroup relation) of Li/Na chalcogenido manganates basing on a

hexagonal close packing of Q²⁻(left, CaAl₂Si₂-aristotype) and (right) K/Rb/Cs-containing compounds related to the ThCr₂Si₂-aristotype (see text).

(ii) ‘ino’ compounds containing chains of edge-con- extended to the respective manganates(II) of rubidium

nected tetrahedra ¹[MnQ_4/2] and (iii) finally several types and cesium, which are indeed isotypic to the Na/K salts

of ‘phyllo’ manga^∞nates of different types with layered [15]. Attempts to prepare other Rb/Cs metallate(II) salts

manganate polyanions. The two new isotypic ‘phyllo’ of this type (i.e. Co, Zn, Cd compounds) are subject of

compounds Na₂Mn₃Se₄[18] and Na₂Mn₃Te₄are the only ongoing work. The Na₆ZnO₄-type structure exhibits a

examples of S/Se/Te manganates containing (besides a h.c.p. arrangement of the chalcogenid ions and is crys-

tetrahedral) an octahedrally coordinated Mn(II). Despite tallographically connected by a group-subgroup relation

this general difference, the structure can be related to the with the Mg-type (h.c.p.) structure (cf. discussion and

remaining layered Li/Na manganates, if the compounds Bärnighausen symmetry tree in [15]). In contrast to the

are categorized according to their basic Q packing (see less A-richer ‘ino’ and ‘phyllo’ manganates discussed

+

below).

below, also the larger Rb and Cs cations occupy (dis-

(i) For the lighter alkali elements sodium and potas- torted) octahedral and even tetrahedral voids in the

sium, the ortho metallate salts A₆M^IIQ₄of the 3d ele- chalcogenide close packing.

ments Mn and Co, which strongly prefer the oxidation

For some ‘ino’ and all ‘phyllo’ manganates(II) and

state +II in S, Se and Te compounds, are long-known (III), the basic chalcogenide packing is determined by the

[13, 14, 53–56]. All compounds of this composition form different coordination spheres of the A cations: the pure

the Na₆ZnO₄-type structure. While lithium salts of this Li and Na salts can be derived from a hexagonal close

+

type are missing, the structure family has recently been packing of Q²⁻(3⁶nets), in which all cations (A and Mn²⁺)

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M. Langenmaier and C. Röhr: Sodium tellurido manganates(II)ꢂ

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Table 10:ꢀSummary of known alkali chalcogenido manganates.

Type

ꢂ

OS of Mn ꢂ General

ꢂ

Individual

ꢂ

Referenceꢂ Structure ꢂ Space

ꢂ

Mn–Q distance/pmꢂ

ꢂ

Building blocks,

comments, etc.

composition compound(s)

type

group

(CN)^b

Ortho- ꢃ

2

ꢃ

A₆MnQ₄

A₂MnQ₂

ꢃ

(Na/K)₆MnS₄

(Na/K)₆MnSe₄

(Na/K)₆MnTe₄

(Rb/Cs)₆MnS₄

(Rb/Cs)₆MnSe₄

(Rb/Cs)₆MnTe₄

ꢃ

[13, 14]

[13]

ꢃ

Na₆ZnO₄

ꢃ

P6₃mc

ꢃ

242.4–246.7

254.5–259.2

275.4–278.6

248.7–250.7

260.7–263.0

280.0–282.4

ꢃ

Isolated tetrahedra

ꢃ

[MnQ₄]

[13]

[15]

Ino-

ꢃ

(K/Rb/Cs)₂MnS₂

ꢃ

[8]

ꢃ

K₂ZnO₂

New

CaAl₂Si₂

ThCr₂Si₂

ꢃ

Ibam

Cccm

ꢃ

243.5–247.4

256.2–257.6

275.2–277.3

cf. Table 9

ꢃ

Linear chains of

[MnQ_4/2] tetrahedra

(K/Rb/Cs)₂MnSe₂ꢃ [8]

(K/Rb/Cs)₂MnTe₂ꢃ [8]

a

NaCsMnTe₂

LiNaMnS₂

ꢃ

̅

[23]

P3m1

(244.3–247.8)

Li/Mn statistically

distributed

Li(K/Rb/Cs)MnS₂ꢃ [49]

I4/mmm ꢃ (243.9–252.7)

a

ꢃ

A₃MnQ₃

ꢃ

Na₂(K/Rb)MnTe₃

ꢃ

New

ꢃ

Pmc2₁

ꢃ

cf. Table 7

ꢃ

Te–Te bonds

Phyllo-ꢃ

2

ꢃ

A₂Mn₂Q₃

ꢃ

Na₂Mn₂S₃

Na₂Mn₂Se₃

Na₂Mn₂Te₃

ꢃ

[16]

ꢃ

Na₂Mn₂S₃ꢃ C2/c

ꢃ

239.3–246.5

251.9–260.2

269.6–279.2

Sheets of edge-sharing

tetrahedra

ꢃ

[17]

a

ꢃ

A₂Mn₃Q₄

ꢃ

Na₂Mn₃Se₄

ꢃ

[18]

ꢃ

Na₂Mn₃Te₄ꢃ C2/m

ꢃ

252.2–254.9(4)

272.1–296.9(6)

272.3–272.9(4)

272.1–296.9(6)

239.7–245.3

ꢃ

Sheets of [MnQ₄]

tetrahedra and [MnQ₆]

octahedra

ꢃ

Na₂Mn₃Te₄

^a, [28]

Na₂Mn₃Te₄ꢃ C2/m

ꢃ

K₂Mn₃S₄

[19, 20]

[50–52]

[18, 21]

[21]

Singular

Cs₂Mn₃S₄

ꢃ

P2/c

Ibam

ꢃ

cf. Fig. 2

Defect variants of

ThCr₂Si₂type layers

(Rb/Cs)₂Mn₃S₄

(Rb/Cs)₂Mn₃Se₄

(Rb/Cs)₂Mn₃Te₄

241.9–246.0

254.1–257.9

275.1–277.6

ꢃ

2.25

ꢃ

Na₃Mn₄Te₆

NaMn_1.56Te₂

ꢃ

[24]

ꢃ

Singular

CaAl₂Si₂

ꢃ

C2/m

ꢃ

277.0–280.6

274.9–280.8

ꢃ

Defect variants of the

CaAl₂Si₂-layers

̅

P3m1

ꢃ

3

ꢃ

AMnQ₂

ꢃ

(Li/Na)MnSe₂

(Li/Na)MnTe₂

(K/Rb/Cs)MnSe₂ꢃ [17]

(K/Rb/Cs)MnTe₂[24]

ꢃ

[17]

[25]

ꢃ

LiMnSe₂

TlAgTe₂

ꢃ

P3m1

ꢃ

255.5–259.7

276.8–278.4

256.9 (Aꢁ=ꢁRb)

277.7–278.2

ꢃ

Ordered defect variants

with CaAl₂Si₂layers

Ordered defect variants

with ThCr₂Si₂layers

̅

I4m2

̅

I4m2

ꢃ

^aThis work. ^bDistances from derived coordinates in brackets. OS, (averaged) oxidation state.

occupy tetrahedral and/or octahedral voids. Structures by alkali cations, the latter with a distorted octahedral

belonging to this family are collected in the symmetry tree coordination by the chalcogen atoms. Despite the similar

depicted at the left hand side of Fig. 5. The aristotype for building blocks, A/M coordinations, unit cell dimensions

the layered compounds is CaAl₂Si₂(or similarly La₂O₃). All and the same space group (Ibam), the K₂ZnO₂-type is not

salts containing K, Rb or Cs (optionally together with Li crystallographically related to the layered compounds of

or Na) contain these larger cations in a cubic eight-fold the ThCr₂Si₂-aristotype (e.g. Cs₂Mn₃S₄-type). In contrast,

coordination by Q. In these cases, the basic chalcogen the new compound CsNaMnTe₂, which contains layers

arrangement corresponds to the nine-fold close packing [NaMnTe₂] built up of two fused parallel [NaTe_4/2] and

[49] consisting of 4⁴nets and ThCr₂Si₂/BaZn₂P₂as aristo- chains of [MnTe_4/2] tetrahedra, can be very simply derived

type (right hand side of Fig. 5).

from this aristotype (cf. structure description above

(ii) Similar to the ortho salts, the sulfido, selenido and the right hand side symmetry tree in Fig. 5). For the

and tellurido chain (‘ino’) manganates A₂MnQ₂, which ternary lithium K/Rb/Cs compounds of this type, a Li/

are known for the heavier alkali elements K, Rb and Cs Mn cation ordering, which leads to the subgroup Cccm, is

only [8], are all isotypic (K₂ZnO₂-type). The orthorhom- not observed [49]. LiNaMnS₂, in which both A cations are

1

∞

bic structure contains linear chains [MnQ_4/2] separated small and which analogously belongs to the h.c.p. type

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family, also exhibits a statistical occupation of Li and Only a metric transformation, which was already dis-

Mn at the tetrahedral voids of the respective aristotype cussed in [16], can be quoted (cf. Fig. 5).

CaAl₂Si₂(Fig. 5, left). The complex new structure of the

For Na₂Mn₃Se₄[18] and the tellurium analogue

two mixed compounds Na₂(K/Rb)MnTe₃, which exhibit Na₂Mn₃Te₄, the Se/Te arrangement consists of 3⁶.4²nets

the formula of a metallate(III) containing edge-sharing (cf. Fig. 1 in Sec. 3.1). Therefore, these two special com-

dimers, contains Mn^IIbesides ditelluride ligands in addi- pounds, which contain [MnQ₆] octahedra in addition the

tion to Te²⁻and thus represents a basically new class of the common [MnQ₄] tetrahedra, can be denoted ‘inter-

chalcogenido manganates. Nevertheless, the structure – mediates’ between the h.c.p./CaAl₂Si₂(3⁶nets) and the

among other anions – contains chains similar to those of ThCr₂Si₂(4⁴nets) structure family.

the common K₂ZnO₂-type structure. The strong buckling

K-Cs: The layered manganates of the larger cations

+

+ +

of the chains in Na₂(K/Rb)MnTe₃, which exhibit a similar K , Rb and Cs are ordered defect variants of the

charge as the linear chains in A₂MnQ₂, again shows, that tetragonal ThCr₂Si₂/PbO-type layers. Comparable to

pure packing effects determine the shape of this struc- Li/Na manganates(III), the removal of ½ of the tetra-

ture motif; electronic contributions, atom pairing, charge hedra of the aristotype (t2 symmetry reduction from

̅

ordering or magnetic interactions are not the reason for I4/mmm to I4m2) leads to the TlAgTe₂-type structure

the strong differences in the shape of chalcogenido met- of the manganates(III) AMnQ₂(Aꢀ=ꢀK, Rb, Cs; Qꢀ=ꢀSe,

allate chains (cf. discussion for the mixed-valent ferrates Te; [17, 24]). A chain-like occupation of the tetrahedral

in [9]).

voids by Mn and Na leads to the tetragonal structure of

(iii) The structures of the layered (‘phyllo’) lithium CsNaMnTe₂(cf. above and Fig. 5). The group-subgroup

and sodium chalcogenido metallates are fundamentally relations associated with the ¾ occupation of the tet-

different from those of the larger alkali cations. Li/Na: rahedra in the Cs₂Mn₃S₄-type structure of the Rb and Cs

The layered manganates(II) with the smaller lithium salts A₂M₃Q₄, which have long been known for the whole

or/and sodium cations can be derived from the trigo- chalcogen series S/Se/Te, were described by Bronger

nal layers of tetrahedra in the CaAl₂Si₂-type structure: et al. in [21]. Equally, the symmetry relation of the sin-

whereas the mixed-valent manganat(II/III) NaMn_1.56Te₂gular monoclinic structure of the potassium analog

show a statistical occupation of the tetrahedral voids K₂Mn₃S₄to the Cs₂Mn₃S₄- and the ThCr₂Si₂-type was

in the aristotype, the manganates(III) (Li/Na)MnSe₂[17] already pointed out by this group [19].

and (Li/Na)MnTe₂[25] exhibit polar layers, in which

only ½ of the tetrahedra of each layer are occupied,

^{crystallographically leading to the t2 subgroup P3m1}4 Summary and outlook

(Fig. 5, left). In the mixed-valent phase Na₃Mn₄Te₆Mn²⁺

cations occupy ⅔ of the tetrahedral voids between The two tellurido manganates Na₂Mn₂Te₃and Na₂Mn₃Te₄are

each second pair of hexagonal close packed Te layers. isotypic to the respective selenides and round out the series

The monoclinic structure of space group C2/m is thus of pure sodium metallates(II) containing layered structures

again crystallographically related to the CaAl₂Si₂-aris- with a h.c.p. of chalcogenide ions. Whereas the Mn^IIions in

totype (Fig. 5, left): the general t3 symmetry reduction Na₂Mn₂Te₃occupy only tetrahedral voids, Na₂Mn₃Te₄exhib-

̅

from the trigonal (space group P3m1) to the monoclinic its the rare octahedral coordination of Mn in addition. The

C-centered crystal system (C2/m) is followed by a tri- two mixed alkali manganates Na₂AMnTe₃(Aꢀ=ꢀK, Rb) crys-

pling of the monoclinic b axis, which allows to create tallize in a new complex orthorhombic structure consisting

the ⅓ empty tetrahedral voids along [010]. The crys- of buckled chains resembling the chains in the common

tallographic a–b plane coincides with the manganate compounds A₂MnQ₂, isolated ditelluride anions Te₂²⁻and

layers. In the likewise monoclinic C centered structure chains of alternately edge- and vertex-sharing [MnTe₄] tet-

of Na₂Mn₂S₃[16], Na₂Mn₂Se₃[17] and the title compound rahedra with one η¹-ditellurido ligand. These three anions

Na₂Mn₂Te₃a different ordering of a ⅔ occupation of the are arranged in two different layers, which both reflect the

tetrahedral voids occurs. In this case, the unit cell con- compounds overall composition (B: 2ꢀ×[MnTe_4/2]²⁻ꢀ+ꢀTe₂²⁻; A:

tains two layers of tetrahedra along the stacking direc- [Mn₂Te₂Te(Te₂)Te_2/2]⁶⁻). The layers are separated by Na–(K/

tion, which needs a doubling of c in the first step of a Rb) nets. The alkali coordination numbers are adjusted to

symmetry reduction. However, the observed C centering the different sizes of the cations, leading to distinct posi-

does not coincide with the former trigonal unit cell basis tions of the two cation types and a fixed 2:1 composition

and there is consequently no direct group-subgroup rela- of Na:K/Rb. Attempts to obtain the analogous Na/Cs com-

tion between the CaAl₂Si₂and the Na₂Mn₂S₃structure. pound yielded the 1:1 phase NaCsMnTe₂instead. Its new

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M. Langenmaier and C. Röhr: Sodium tellurido manganates(II)ꢂ

ꢂ639

+

[19] W. Bronger, M. Böhmer, D. Schmitz, Z. Anorg. Allg. Chem.

2000, 626, 6.

orthorhombic structure contains Cs in a cubic eight-fold

coordination and linear chains [MnTe_4/2] fused to paral-

lel chains [NaTe_4/2]. Therewith, the structure is an ordered

derivative Cs[NaMnTe₂] of the ThCr₂Si₂-type. Similar (if pos-

sible also crystallographic group-subgroup) relations to the

basic structure types CaAl₂Si₂(h.c.p. chalcogen packing,

pure Li/Na salts) and ThCr₂Si₂(nine-fold Q packing, K/

Rb/Cs salts) are discussed for the new and all literature

reported alkali manganates(II) and (III).

Even though the attempts to synthesize new mixed-

valent manganates(II/III) were thus not yet successful, the

title compounds obtained suggest a reinvestigation of the

alkali chalcogenido-metallates of other two-valent metals

like e.g. Zn, Cd and Hg. In the respective ternary systems

A–M^II–Q many phases related to A₆MnQ₄(Aꢀ=ꢀNa–Cs), the

different layered Na chalcogenido manganates(II) and in

particular compounds with di-chalcogenido ligands are

still missing.

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Acknowledgements: We would like to thank the Deutsche

Forschungsgemeinschaft for financial support.

[32] X-Shape (version 1.03), Crystal Optimization for Numerical

Absorption Correction, Stoe & Cie GmbH, Darmstadt (Germany)

2005.

[33] G. M. Sheldrick, Shelxs-97, Program for the Solution of Crystal

Structures, University of Göttingen, Göttingen (Germany) 1997.

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[35] CCDC 1922197 (Na₂Mn₂Te₃), 1922198 (Na₂Mn₃Te₄), 1922199

(Na₂KMnTe₃), 1922200 (Na₂RbMnTe₃), and 1922201

(NaCsMnTe₂) contain the supplementary crystallographic data

for this paper. These data can be obtained free of charge from

the Cambridge Crystallographic Data Centre via www.ccdc.cam.

ac.u k /data_request/cif.

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The new sodium tellurido manganates(II) Na2Mn2Te3, Na2Mn3Te4, Na2AMnTe3 (A=K, Rb), and NaCsMnTe2

DOI: 10.1515/znb-2019-0104

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Article abstract of DOI:10.1515/znb-2019-0104

Full text of DOI:10.1515/znb-2019-0104

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