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Article

Synthesis, Crystal Structure and Properties of the New Laminar Quaternary Tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu)

by
Anna V. Ruseikina
1,*,
Maxim V. Grigoriev
1,2,
Maxim S. Molokeev
3,4,5,
Alexander A. Garmonov
6,
Andrey V. Elyshev
1,
Ralf J. C. Locke
2 and
Thomas Schleid
2,*
1
Laboratory of Theory and Optimization of Chemical and Technological Processes, University of Tyumen, 625003 Tyumen, Russia
2
Institute for Inorganic Chemistry, University of Stuttgart, D-70569 Stuttgart, Germany
3
Kirensky Institute of Physics, Federal Research Center KSC SB RAS, 660036 Krasnoyarsk, Russia
4
Department of Engineering Physics and Radioelectronic, Siberian Federal University, 660041 Krasnoyarsk, Russia
5
Department of Physics, Far Eastern State Transport University, 680021 Khabarovsk, Russia
6
Institute of Physics and Technology, University of Tyumen, 625003 Tyumen, Russia
*
Authors to whom correspondence should be addressed.
Crystals 2023, 13(2), 291; https://doi.org/10.3390/cryst13020291
Submission received: 31 December 2022 / Revised: 1 February 2023 / Accepted: 6 February 2023 / Published: 9 February 2023
(This article belongs to the Special Issue Rare-Earth Metal Compounds (2nd Edition))

Abstract

:
This paper reports for the first time on the new laminar quaternary orthorhombic heterometallic quaternary tellurides SrLnCuTe3, the fabrication of which has been a challenge until this work. Data on the crystal structure of tellurides complete the series of quaternary strontium chalcogenides SrLnCuCh3 (Ch = S, Se, Te). Single crystals of the compounds were synthesized from the elements by the halogenide-flux method at 1070 K. The compounds are crystallizing in two space groups Pnma (Ln = Sm, Gd and Tb) and Cmcm (Ln = Dy–Tm and Lu). For SrSmCuTe3 (a = 11.4592(7), b = 4.3706(3), c = 14.4425(9) Å, space group: Pnma) with the largest lanthanoid cation, Sr2+ shows C.N. = 7, whereas Sm3+ reveals a diminished coordination number C.N. = 6. For SrLuCuTe3 (a = 4.3064(3), b = 14.3879(9), c = 11.1408(7) Å, space group: Cmcm) with the smallest lanthanoid cation, coordination numbers of six are realized for both high-charged cations (Sr2+ and Lu3+: C.N. = 6). The cations Sr2+, Ln3+, Cu+ each take independent positions. The structures are built by distorted [CuTe4]7– tetrahedra, forming the infinite chains { 1 [ Cu ( Te 1 ) 1 / 1 t ( Te 2 ) 1 / 1 t ( Te 3 ) 2 / 2 e ] 5 } along [010] in SrLnCuTe3 (Ln = Sm, Gd and Tb) and [100] in SrLnCuTe3 (Ln = Dy–Tm and Lu). The distortion of the polyhedra [CuTe4]7– was compared for the whole series SrLnCuTe3 by means of τ4-descriptor for the four coordinating Te2– anions, which revealed a decrease in the degree of distortion with a decreasing radius at Ln3+. The distorted octahedra [LnTe6]9– form layers { 2 [ L n ( Te 1 ) 2 / 2 ( Te 2 ) 2 / 2 ( Te 3 ) 2 / 2 ] 3 } . The distorted octahedra and tetrahedra fuse to form parallel layers { 2 [ Cu L n Te 3 ] 2 } and between them, the Sr2+ cations providing three-dimensionality of the structure are located. In the SrLnCuTe3 (Ln = Sm, Gd and Tb) structures, the Sr2+ cations center capped the trigonal prisms [SrTe6+1]12−, united in infinite chains { 1 [ Sr ( Te 1 ) 2 / 2 ( Te 2 ) 3 / 3 ( Te 3 ) 2 / 2 ] 4 } along the [100] direction. The domains of existence of the Ba2MnS3, BaLaCuS3, Eu2CuS3 and KZrCuS3 structure types are defined in the series of orthorhombic chalcogenides SrLnCuCh3 (Ch = S, Se and Te). The tellurides SrLnCuTe3 (Ln = Tb–Er) of both structure types in the temperature range from 2 up to 300 K are paramagnetic, without showing clear signs of a magnetic phase transition.

1. Introduction

Recently, the study of four-component tellurides with various combinations of s-, d- and f-elements [1,2,3,4,5,6,7,8,9,10,11,12,13] has been of great scientific interest that is associated with their interesting structural features and potential valuable properties. The formation of various telluride coordination polyhedra centered by cations and their various combinations with each other in quaternary tellurides result in the formation of a wide range of layer or channel structures and provide the potential of changing the band gap, as well as electrical and optical characteristics [14,15,16,17,18,19,20,21]. Tellurides exerting various properties like diamagnetic [19], paramagnetic [22,23] or antiferromagnetic [10,19] are p-type semiconductors [10,22,23] or exhibit metallic properties [5,23]. Based on ab initio calculation methods, a low thermal lattice conductivity of thermodynamically stable-layered quaternary tellurides AEREMTe3 (AE = alkaline-earth element; RE = rare-earth element; M = d-element) has been recently predicted, which allows them to be used as thermoelectric materials [1,21]. The effect of lone pairs on the structural features of BaRECuTe3 tellurides has been studied, and it was determined that the character of Ba–Te interactions are ionic, and RE–Te and Cu–Te interactions are of polar-covalent character [21]. Since the compounds of a number of quaternary barium tellurides BaRECuTe3 were synthesized as early as the end of the 20th century [3,18], it allowed them to remove the problem of the existence of all possible barium chalcogenides of the type BaRECuCh3 (Ch = S, Se and Te) [24,25]; then, in the case of strontium chalcogenides, the research works were focused only on the synthesis of the sulfide and selenide compounds [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40] so far and only recently the first representative SrScCuTe3 of this telluride series was synthesized [2], the remaining representatives of the SrRECuTe3 series, as far as we know, have not been prepared. The existence of orthorhombic compounds of the entire SrRECuTe3 series, crystallizing in one space group (Pnma) only, was predicted, notably the compounds SrRECuTe3 (RE = La–Nd, Sm, Gd–Lu and Y) belong to the Eu2CuS3 structure type, and the compound SrScCuTe3 classes with the NaCuTiS3 structure type [1]. However, the scandium telluride SrScCuTe3, experimentally prepared by the ampoule method after fusing stoichiometric amounts of the elements at 1273 K for 168 h, had the space group Cmcm [2]. The crystallization of scandium compounds in this space group is consistent with studies of layered quaternary chalcogenides AEScCuCh3 (AE = Sr [26,27,33], Eu [26,41], Ba [2]; Ch = S [2,26,27], Se [2,27,33,41], Te [2]). The compounds with light rare-earth elements SrLnCuTe3 (Ln = La, Ce, Pr) are metastable according to theoretical calculations [1]. Over the past 20 years, several synthetic methods, such as the fusion of stoichiometric amounts of elements [2], the fusion of binary chalcogenides [28,30,31,32,34,38,39,40] and reductive chalcogenation of oxides [41], have been developed to prepare quaternary chalcogenides in the form of poly- and single-crystals line form; nevertheless, the halogenide-flux method turned out to be one of the most effective ones for both for a significant reduction in the time and temperature of synthesis and obtaining of homogeneous samples [4,10,18,20,22,23,33,34,35,36,37]. The experimental production of a series of quaternary strontium tellurides SrLnCuTe3 will make it possible to remove the question of the possibility of the existence of all possible quaternary strontium chalcogenides of the SrLnCuCh3 series (Ch = S, Se, Te) and will significantly complement fundamental research in the field of the chemistry of rare-earth chalcogenides.
The purpose of this research is to study a new series of quaternary tellurides with the formula SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu), namely the development of synthesis, experimental determination of the crystal structures+--- and magnetic properties.

2. Materials and Methods

2.1. Materials

The metals Sr (99.3%), Ln (La–Nd, Sm–Lu: 99.9%; Eu: 99.99%), Te (99.9%) and CsI (99.9%) were purchased from ChemPur (Karlsruhe, Germany). Cu (99.999%) was obtained from Aldrich (Milwaukee, WI, USA).

2.2. Synthesis

Single crystals of quaternary strontium tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu) were synthesized by mixing in a glove box under argon atmosphere in a stoichiometric ratio of the elements strontium, copper, tellurium and a lanthanoid (1 Sr: 1 Cu: 1 Ln (Ln = Sm, Gd–Tm and Lu): 3 Te) in the presence of an excess amount of the halogenide-flux CsI. The silica ampoules were evacuated to a pressure of 2·10–3 mbar and sealed. They were then heated in a muffle furnace from room temperature to 1120 K for 30 h and kept at this temperature for 96 h, and after that cooled to 570 K at a rate of 4 K/h, then to room temperature within 3 h. The interaction proceeded according to the reaction: Sr + Cu + Ln + 3 Te ⟶ SrLnCuTe3. The heating profiles used for the synthesis of SrLnCuTe3 representatives with Ln = Sm, Gd–Tm and Lu are presented in Figure S1a in the Supplementary Materials. The reaction product was purified from flux residues with demineralized water. Black needle-shaped crystals of SrLnCuTe3 representatives were present in the product (Figure S1b,c in Supplementary Material). While the SrLnCuTe3 samples (Ln = Tb–Er) after the removal of the flux were completely represented by single crystals of the SrLnCuTe3 compounds, in the SrLnCuTe3 (Ln = Sm, Gd, Tm and Lu) samples the yield of single crystals was only 60–80%. The resulting crystals were suitable for single-crystal X-ray diffraction analysis. Unfortunately, it was not possible to obtain high-quality powder diffraction patterns (Figure S2).
We also tried to obtain quaternary chalcogenides SrLnCuTe3 (Ln = La–Nd, Eu and Yb). Our repeated attempts were unsuccessful, however, during the synthesis, the interaction of the initial components was observed upon heating with the CsI flux, resulting in the formation of single crystals containing an alkali metal, namely CsxLn2Cu6–xTe6 (Ln = La–Nd) [19], and the samples also included single crystals of Cu0.37LnTe2, SrTe and LnTe (Ln = Eu and Yb). Disappointingly, single crystals of the SrLnCuTe3 phase were not found in the samples.

2.3. X-ray Diffraction Analysis

The intensities from single crystals of the SrLnCuTe3 series with Ln = Sm, Gd–Tm and Lu of 0.05 × 0.05 × 0.45 mm3 dimensions were collected at 293(2) K using SMART APEX II single-crystal diffractometer (Bruker AXS, Billerica, MA, USA) equipped with a CCD-detector, graphite monochromator and Mo-Kα radiation source. The orientation matrix and cell parameters were determined and refined for a set of 11,880 reflections. The unit-cell parameters correspond to orthorhombic symmetry. The space groups (Pnma and Cmcm) were determined from the statistical analysis of the intensities of all reflections. Absorption corrections were applied using the SADABS program. The structure was solved by the direct methods using packaged SHELXS and refined in the anisotropic approach using the SHELXL program [42]. The structural tests for the presence of missing symmetry elements and possible voids were produced using the PLATON program [43]. The crystallographic data are deposited in Cambridge Crystallographic Data Centre (CSD-2232062–2232066, 2232068–2232070). The data can be downloaded from the site www.ccdc.cam.ac.uk/data_request/cif (accessed on 25 January 2023)

2.4. Powder X-ray Diffraction

The powder X-ray diffraction investigation was conducted using a STADI-P diffractometer (Stoe & Cie, Darmstadt, Germany) with Ge(111)-monochromatized molybdenum Kα-radiation (λ = 71.07 pm) and copper Kα-radiation (λ = 154.06 pm). Since copper compounds are strong absorbers of copper and strontium compounds for molybdenum radiation, we were not able to record high-quality powder X-ray diffractograms (PXRD, see Figure S2).

2.5. Electron-Beam Microprobe Analysis

The SEM image of SrDyCuTe3 was acquired using an electron-beam X-ray microprobe (SX-100, Cameca, Gennevilliers, France). The EDX spectra for several examples roughly confirmed the 1:1:1 stoichiometry of all investigated SrLnCuTe3 compounds.

2.6. Magnetic Measurements

The temperature dependencies of the magnetizations of the SrLnCuTe3 representatives with Ln = Tb, Dy, Ho and Er were measured by means of the magnetic-property measuring system with helium cooling (Quantum Design MPMS3, San Diego, CA, USA) in the temperature range from 2 to 300 K in zero-field cooling (ZFC) and heating in external magnetic field (FW) modes. The field strength was 500 kOe (0.4 MA·m–1). The dependencies of the magnetizations on the magnitude of the external magnetic field were measured at room temperature (300 K) and at a temperature of 2 K, using a vibrating magnetometer as part of the same Quantum Design MPMS3 system. The magnetic properties of the SrLnCuTe3 compounds with Ln = Sm, Gd, Tm and Lu have not been studied because of the low yield of single crystals.

3. Results

3.1. Crystal Structures of the SrLnCuTe3 Series

According to the data of X-ray diffraction analysis of single crystals, the compounds SrLnCuTe3 (Ln = Sm, Gd and Tb) crystallize in the orthorhombic space group Pnma with the structure type (ST) Eu2CuS3, and the other SrLnCuTe3 members (Ln = Dy–Tm and Lu) adopt the orthorhombic space group Cmcm with the structure type of KZrCuS3. The crystallographic data, details of the data collections, atomic coordinates, thermal displacement parameters, bond lengths and bond angles are given in Table 1, Table 2 and Table 3 as well as S1 and S2 in the section Supplementary Material. Similar structural types were observed in the quaternary chalcogenides of the alkaline-earth elements AELnCuCh3 (AE = Sr, Ba; Ch = S, Se and Te) [2,3,18,20,26,27,29,30,31,32,33,34,35,37,38,39].
The crystal structures of the SrLnCuTe3 series of strontium tellurides of different structural types have both similarities and differences (Figure 1). The similarity lies in the fact that in all the SrLnCuTe3 crystal structures of both structure types, the Sr2+ and Ln3+ cations take independent crystallographic positions. Aside from the structures of the entire SrLnCuTe3 series being built by distorted [CuTe4]7– tetrahedra, they are connected by two common vertices into infinite linear chains { 1 [ Cu ( Te 1 ) 1 / 1 t ( Te 2 ) 1 / 1 t ( Te 3 ) 2 / 2 e ] 5 } and distorted octahedra [LnTe6]9– and connected by common edges and vertices into layers { 2 [ L n ( Te 1 ) 2 / 2 ( Te 2 ) 2 / 2 ( Te 3 ) 2 / 2 ] 3 } along the [010] direction in SrLnCuTe3 (Ln = Sm, Gd and Tb) adopting the structure type of Eu2CuS3 and along the [100] direction in SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu), having the structure KZrCuS3 type. The distorted octahedra and tetrahedra also form parallel two-dimensional layers { 2 [ Cu L n Te 3 ] 2 } and between them, there are Sr2+ cations providing the three-dimensionality of the structure. While the Cu+ and Ln3+ cations form the same coordination polyhedra in different structural types, the Sr2+ cations have different coordination environments. Strontium cations in the compounds SrLnCuTe3 (Ln = Sm, Gd and Tb) are coordinated by seven Te2– anions to form the coordination polyhedron of a capped trigonal prism [ SrTe 6 + 1 ] 12 with the symmetry mm2. These monocapped trigonal prisms are articulated by facets and edges to form layers { 2 [ Sr ( Te 1 ) 2 / 2 ( Te 2 ) 3 / 3 ( Te 3 ) 2 / 2 ] 4 } located parallel to the (001) plane. However, in the compounds SrLnCuTe3 (Ln = Dy–Tm and Lu) the strontium cations are found in a trigonal-prismatic coordination environment [ SrTe 6 ] 10 . The polyhedra have a local symmetry of 6 ¯ m2 (high symmetry coordination) and are connected by facets and form one-dimensional chains { 1 [ Sr ( Te 1 ) 2 / 2 ( Te 2 ) 3 / 3 ( Te 3 ) 2 / 2 ] 4 } along the [100] direction.
Thus, the three-dimensional crystal structure of SrLnCuTe3 (Ln = Sm, Gd and Tb) and SrLnCuTe3 (Ln = Dy–Tm and Lu) is resulting from two-dimensional layers formed by octahedra and tetrahedra in the ac and bc planes, accordingly, these layers are separated by naked dimer ribbons or by alternating polymeric chains formed in turn by monocapped trigonal prisms and naked trigonal prisms, respectively (Figure 1).
As the radius of ri(Ln3+) decreases, the parameters of the unit cell also decrease (notably, the values of the unit-cell parameters b, c and a in space group Pnma correspond to a, b and c in space group Cmcm), the volumes of the unit cells decrease from 723.33(5) Å3 for SrSmCuTe3 to 690.28(6) Å3 for SrLuCuTe3 (Table 1 and Table 2), as well as the distance d(Ln—Te) in the interval 3.1161(9)–3.0075(5) Å (Figure 2 and Table S1 in the Supplementary Material), that result in a decrease in coordination saturation for Ln3+. Since the distorted octahedra [LnTe6]9– in all compounds are connected with tetrahedra [CuTe4]7– to form two-dimensional layers { 2 [ Cu L n Te 3 ] 2 } , a decrease in the cation radius ri(Ln3+) results in crystal-chemical compression of the layers. The change in the strontium coordination polyhedron from a monocapped trigonal prism [ SrTe 6 + 1 ] 12 to the trigonal prism [SrTe6]9– manifests in changing the structure type from Eu2CuS3 to KZrCuS3 and space group from Pnma to Cmcm (Figure 1). Similar transformations were observed for AELnCuCh3 (AE = Ba, Sr, Eu; Ch = S, Se) already [20,30,31,33,35,39,41,44,45].
In the SrLnCuTe3 (Ln = Sm, Gd and Tb) structures of the structure type Eu2CuS3, the coordination polyhedron   [ SrTe 6 + 1 ] 12 six distances of d(Sr—Te) are shorter than 3.39 Å, and the seventh distance d(Sr—Te) gradually increases: 3.650(2) Å (SrSmCuTe3) → 3.667(2) Å (SrGdCuTe3) → 3.692 Å (SrTbCuTe3) (Table S1, Figure 2). A similar trend was observed for the isostructural compounds EuLnCuS3 [46] and SrLnCuS3 [30,40]. In the structures for SrLnCuTe3 (Ln = Dy–Tm and Lu) of the structure type KZrCuS3, the cations Sr2+ have six distances d(Sr—Te), being shorter than 3.38 Å and two additional anions Te2− (2 × 3.905(2) Å (SrDyCuTe3), 2 × 3.8843(9) Å (SrHoCuTe3), 2 × 3.866(2) Å (SrErCuTe3), 2 × 3.8550(8) Å (SrTmCuTe3), 2 × 3.830(2) Å (SrLuCuTe3). The seventh and the eighth telluride anion are not included in the coordination of Sr2+ due to the very weak interactions.
All currently known compounds of formula SrLnCuCh3 with Ch = S [30,33,39], Se [33,35] and Te [this work] are shown in Figure 3. There, the ionic radii of the divalent anions (Ch2–) are plotted against the ionic radii of the cations of the trivalent lanthanoid cations (Ln3+). The lines represent virtual boundaries between each type of structure and have been arbitrarily added to the diagram to provide a visual breakline between modifications. The chalcogenides SrLnCuCh3 are isostructural. When transiting from sulfur to tellurium, the anion sublattice expands (r(S2–) = 1.84 Å, r(Se2–) = 1.98 Å, r(Te2–) = 2.21 Å [47]). The change of the structure type from Eu2CuS3 to KZrCuS3 in sulfides occurs at the Y/Er boundary [39,45]; in selenides, it is found at the Dy/Ho boundary [33,41]; and in tellurides, it meets the Tb/Dy boundary (Figure 3). Thus, the larger the chalcogenide radius, the earlier the change of the structure type and the space group from Pnma to Cmcm in the SrLnCuCh3 series of quaternary chalcogenides takes place.
The barium compounds BaLnCuTe3 were previously discovered as quaternary tellurides [2,3,20,21]. In these tellurides, the change of space group occurs on the lightest rare-earth elements BaLaCuTe3 (Pnma)/BaPrCuTe3 (Cmcm) [3,20]. The ionic radius of barium ri(Ba2+) = 1.38 Å is larger than that one of strontium ri(Sr2+) = 1.21 Å [47]. The smaller the radius of the alkaline-earth cation, the smaller the number of compounds crystallizing in the space group Cmcm, and the cations AE2+ later become six-fold coordinated.
It can be assumed that in the quaternary strontium tellurides, the replacement of monovalent copper (ri(Cu+) = 0.60 Å [47]) with silver (ri(Ag+) = 1.00 Å [47]) will result in the change of the space group in compounds containing rare-earth elements of the very beginning of the lanthanoid series or as in the case of the barium tellurides BaLnAgTe3 [3,20,21], all the series will crystallize in Cmcm.
We also compared the distortion degree to the [CuTe4]7– coordination polyhedra in the crystalline SrLnCuTe3 structure series. Deviations from the symmetry of tetrahedra [CuTe4]7– can be affected by distances d(Cu—Te), d(Te···Te), angles ∠(Te—Cu—Te). To estimate the degree of distortion for the polyhedra [CuTe4]7–, the distortion coefficients were calculated using the methods proposed in [48,49],
D I ( T e C u T e ) = ( i = 1 6 | T e C u T e i T e C u T e m | ) ( 6 · T e C u T e m ) ,
where DI is a distortion index, TeCuTei is the i-tetrahedral angle (Table S2), TeCuTem is an angle of a regular tetrahedron that equals 109.47°.
D ( C u T e ) = ( i = 1 4 | C u T e i C u T e m | ) ( 4 · C u T e m ) ,
D ( T e T e ) = ( i = 1 6 | T e T e i T e T e m | ) ( 6 · T e T e m ) ,
where CuTei and TeTei refer to the individual values (Table S1), CuTem and TeTem are the theoretic bond lengths for a coordination number of 4, equal to 2.81 Å and 4.42 Å, respectively, calculated from the values of the ionic radii ri(Cu+) and ri(Te2 –) [47].
In the series of the SrLnCuTe3 compounds, a decrease in the deviation of bond angles ∠(Te—Cu—Te) from the symmetric coordination and the formation of the most symmetric structure [CuTe4]7– in transition to the compounds SrLnCuTe3, containing Ln3+ with a small ionic radius are observed (Table 4). However, there is an increase in the degree of weakening of the bonds d(Cu—Te). Distortions are more distinct in distances d(Cu—Te) than in d(Te···Te) and ∠(Te—Cu—Te). Probably, the local character of distortions in the d(Cu—Te) bonds does not affect the general character of the symmetry within the structure.
The tetracoordinated environment can also be characterized using the τ4-descriptor [50]. The values of τ4 are the following: for ideal tetrahedral structures it is 1.00, for trigonal-pyramidal structures 0.85, for seesaw structures 0.64–0.07 and for perfect square planar structures 0.00. The τ4 values of the tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu) of both structure types range from 0.955 to 0.984 (Table 4 and Figure 4), indicating that the coordination geometry around Cu+ is distorted by 10–30% from an ideal tetrahedron to a trigonal pyramidal structure. A greater distortion of tetrahedra is observed in compounds crystallizing in space group Pnma4 varies from 0.955 to 0.961) than in Cmcm4 varies from 0.979 to 0.996) (Figure 4). A jump in the τ4-descriptor occurs at the boundary of the change of structure types. As ri(Ln3+) decreases, a decrease in the distortion of the tetrahedron is observed.

3.2. Magnetic Properties of the SrLnCuTe3 Series (Ln = Tb–Er)

The temperature dependencies of the sample magnetizations have a shape characteristic of paramagnets (Figure 5). They are described with high accuracy by the Curie–Weiss law at temperature ranges from 100 to 300 K. The Curie constants C calculated from these dependencies, the effective magnetic moments μ and the Curie–Weiss temperatures ϴ are shown in Table 5. The values of C and μ are very close to the theoretical ones for the corresponding independent magnetic cations. The values of the Curie–Weiss constants ϴ in all the samples are positive, which indicates the ferromagnetic nature of the interaction of magnetic Ln3+ cations (Ln = Tb–Er) with a decrease in temperature, however, Curie temperatures are below 2 K. The dependences of magnetization on the external magnetic field are linear at a temperature of 300 K. The parameters C and μ calculated from them are also listed in Table 5.
Magnetic field dependencies at 2 K calculated with reference to one formula unit are shown in Figure 6. Their view is characteristic of a ferromagnet slightly above the Curie temperature, where saturation is not reached up to very strong fields. Theoretically, the saturated magnetization for Tb3+ and Er3+ cations is 9 μB, and for Dy3+ and Ho3+ 10 μB.
The magnetization curve of SrDyCuTe3 shows such a strong tendency to saturation that it can be assumed that there occurs ferromagnetic ordering; however, the temperature dependencies of the magnetization do not provide reasons to claim that the transition to the ferromagnetic state at 2 K really took place. The value of the magnetic moment per one formula unit is almost two times less than the moment of the free cation Dy3+ (10 μB). The cause of this behavior remains unclear.

4. Conclusions

For the first time, there are eight new layered heterometallic quaternary strontium tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu). Single crystals were synthesized by the ampoule method from stoichiometric mixtures of the initial elements Sr, Ln, Cu and Te in the presence of CsI as halogenide flux. It is established that orthorhombic tellurides SrLnCuTe3 (Ln = Sm, Gd and Tb) crystallize in the space group Pnma with the structure type of Eu2CuS3, whereas SrLnCuTe3 (Ln = Dy–Tm and Lu), the space group Cmcm with the structure type KZrCuS3, is formed. It is shown that both types of crystal structures show octahedra around Ln3+ and tetrahedra around Cu+ of Te2– anions as coordination spheres, but differ in the coordination of the alkaline-earth element. In the SrLnCuTe3 compounds (Ln = Dy–Tm and Lu), Sr2+ is characterized by highly symmetric trigonal-prismatic coordination, while in the compounds SrLnCuTe3 (Ln = Sm, Gd and Tb), a less symmetrical capped trigonal prism occurs. Both structures are formed from layers that are separated by either dimeric ribbons formed by the capped trigonal prisms or alternating chains formed by the naked prisms. The distortion of the polyhedron [CuTe4]7– is compared for the entire SrLnCuTe3 series using the t4-descriptor for four coordinated ions. It is established that the lowest degree of distortion of tetrahedra is characteristic of SrLuCuTe3. The tellurides SrLnCuTe3 (Ln = Tb–Er) of both structure types are paramagnetic in the temperature range from 2 to 300 K and are supposed to have ferromagnetic Curie temperatures below 2 K. The experimental magnetic characteristics are consistent with the corresponding calculated parameters.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst13020291/s1.

Author Contributions

Conceptualization, A.V.R. and M.V.G.; software, A.V.R. and M.V.G.; validation, A.V.R.; formal analysis, M.V.G., M.S.M. and R.J.C.L.; investigation, M.V.G.; resources, T.S.; data curation, A.V.R., T.S. and M.V.G.; writing—original draft preparation, A.A.G., A.V.R., T.S. and M.V.G.; writing—review and editing, A.V.R., M.S.M., A.A.G. and T.S.; visualization, M.S.M., A.A.G. and M.V.G.; project administration, A.V.R.; funding acquisition, M.V.G. and A.V.E. All authors have read and agreed to the published version of the manuscript.

Funding

The research was supported by the Tyumen region within the framework of the grant agreement in the form of a grant to non-profit organizations no. 89-don dated 7 December 2020.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data supporting the conclusions is included within the manuscript and is available on request from the corresponding authors.

Acknowledgments

We gratefully acknowledge the help of Björn Blaschkowski for the magnetic measurements and Jean-Louis Hoslauer for the PXRD investigations, both at the Institute for Inorganic Chemistry at the University of Stuttgart.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. View at the orthorhombic crystal structures of the SrLnCuTe3 series (Ln = Dy–Tm and Lu) with the space group Cmcm (top view), and the SrLnCuTe3 series (Ln = Sm, Gd and Tb) of the space group Pmma (bottom view), along the a-axis and the b-axis, respectively, together with the telluride coordination polyhedra formed around metal cations.
Figure 1. View at the orthorhombic crystal structures of the SrLnCuTe3 series (Ln = Dy–Tm and Lu) with the space group Cmcm (top view), and the SrLnCuTe3 series (Ln = Sm, Gd and Tb) of the space group Pmma (bottom view), along the a-axis and the b-axis, respectively, together with the telluride coordination polyhedra formed around metal cations.
Crystals 13 00291 g001
Figure 2. The M–Te distances in both structures of the SrLnCuTe3 series (Ln = Sm, Gd–Tm and Lu).
Figure 2. The M–Te distances in both structures of the SrLnCuTe3 series (Ln = Sm, Gd–Tm and Lu).
Crystals 13 00291 g002
Figure 3. Structure field diagram of SrLnCuCh3 chalcogenides with Ch = S [39,45], Se [33,41] and Te [this work]. Description: color background corresponds to a defined structure type (yellow: BaLaCuS3, blue: Ba2MnS3, green: KZrCuS3, orange: Eu2CuS3).
Figure 3. Structure field diagram of SrLnCuCh3 chalcogenides with Ch = S [39,45], Se [33,41] and Te [this work]. Description: color background corresponds to a defined structure type (yellow: BaLaCuS3, blue: Ba2MnS3, green: KZrCuS3, orange: Eu2CuS3).
Crystals 13 00291 g003
Figure 4. Calculated τ4-descriptor values for the [CuTe4]7– polyhedra in the crystal structures of the SrLnCuTe3 series.
Figure 4. Calculated τ4-descriptor values for the [CuTe4]7– polyhedra in the crystal structures of the SrLnCuTe3 series.
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Figure 5. Field-dependent magnetic moment at 300 K (left), temperature-dependent specific magnetization and reciprocal magnetic susceptibility at 500 kOe (right) of SrLnCuTe3 samples with Ln = Tb–Er. The measurements of low-temperature magnetization were performed in the zero-field cooled (ZFC) and nonzero-field cooled (FC) modes.
Figure 5. Field-dependent magnetic moment at 300 K (left), temperature-dependent specific magnetization and reciprocal magnetic susceptibility at 500 kOe (right) of SrLnCuTe3 samples with Ln = Tb–Er. The measurements of low-temperature magnetization were performed in the zero-field cooled (ZFC) and nonzero-field cooled (FC) modes.
Crystals 13 00291 g005
Figure 6. Magnetization curves of SrLnCuTe3 samples with Ln = Tb–Er at 2 K.
Figure 6. Magnetization curves of SrLnCuTe3 samples with Ln = Tb–Er at 2 K.
Crystals 13 00291 g006
Table 1. Main parameters of processing and refinement of the SrLnCuTe3 (Ln = Sm, Gd and Tb) samples.
Table 1. Main parameters of processing and refinement of the SrLnCuTe3 (Ln = Sm, Gd and Tb) samples.
SrSmCuTe3SrGdCuTe3 SrTbCuTe3
Molecular weight684.31691.21692.88
Space groupPnma
Structure typeEu2CuS3
Z4
a (Å)11.4592(7)11.3886(7)11.3418(7)
b (Å)4.3706(3)4.3534(3)4.3491(3)
c (Å)14.4425(9)14.4522(9)14.4326(9)
V3) 723.33(5)716.53(5)711.91(6)
ρcal (g/cm3)6.2846.4076.465
μ (mm–1)30.00631.35132.173
Reflections measured128111188012049
Reflections independent939930929
Reflections with Fo > 4σ(Fo)779756711
2θmax (°)54.9754.9355.01
h, k, l limits–14 ≤ h ≤ 14; –5 ≤ k ≤ 5; –18 ≤ l ≤ 18
Rint0.1060.0810.092
Refinement results
Number of refinement parameters38
R1 with Fo > 4σ(Fo)0.0320.0290.034
wR20.0820.0680.078
Goof1.1081.0501.002
∆ρmax(e/Å3)1.7561.2071.692
∆ρmin(e/Å3)–1.809–1.263–1.616
Extinction coefficient, ε0.0026(2)0.0022(2)0.0036(2)
CSD-number223206822320642232069
Table 2. Main parameters of processing and refinement of the SrLnCuTe3 (RE = Dy–Tm and Lu) samples.
Table 2. Main parameters of processing and refinement of the SrLnCuTe3 (RE = Dy–Tm and Lu) samples.
SrDyCuTe3SrHoCuTe3SrErCuTe3SrTmCuTe3SrLuCuTe3
Molecular weight696.46698.89701.22702.89708.93
Space groupCmcm
Structure typeKZrCuS3
Z4
a (Å)4.3405(3)4.3314(3)4.3258(3)4.3198(3)4.3064(3)
b (Å)14.4298(9)14.4179(9)14.4123(9)14.4037(9)14.3879(9)
c (Å)11.2972(7)11.2532(7)11.2176(7)11.1902(7)11.1408(7)
V3)707.54(5)702.85(4)699.36(6)696.28(4)690.28(6)
ρcal (g/cm3)6.5386.6056.6606.7056.822
μ (mm–1)32.93633.78334.63735.48037.237
Reflections measured74036637669399316818
Reflections independent484484483482480
Reflections with Fo > 4σ(Fo)420462444446429
2θmax (°)54.87854.93454.92254.93855.016
h, k, l limits –5 ≤ h ≤5; –18 ≤ k ≤ 18; –14 ≤ l ≤ 14
Rint0.0740.0440.0620.0700.073
Refinement results
Number of refinement parameters24
R1 with Fo > 4σ(Fo)0.0260.0180.0230.0180.025
wR20.0590.0400.0540.0430.045
Goof1.0551.1091.1021.0791.088
∆ρmax (e/Å3)1.4131.2441.6040.8591.781
∆ρmin (e/Å3)–1.472–1.293–1.638–0.906–1.853
Extinction coefficient, ε0.0011(1)0.00184(9)0.0008(1)0.00125(9)0.00082(7)
CSD-number22320622232065223206322230702232066
Table 3. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters of the SrLnCuTe3 series (Ln = Sm, Gd–Tm and Lu).
Table 3. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters of the SrLnCuTe3 series (Ln = Sm, Gd–Tm and Lu).
Atomx/ay/bz/cUiso*/Ueq2)
SrSmCuTe3
Sr0.26969(11)1/40.50279(9)0.0267(3)
Sm0.01491(5)1/40.74492(4)0.0215(2)
Cu0.24071(13)1/40.22143(12)0.0312(4)
Te10.05395(7)1/40.11132(6)0.0217(2)
Te20.41676(7)1/40.10364(6)0.0226(2)
Te30.26215(7)1/40.83011(6)0.0212(2)
SrGdCuTe3
Sr0.26663(9)1/40.50313(8)0.0243(3)
Gd0.01350(4)1/40.74611(3)0.0188(2)
Cu0.24205(12)1/40.22125(11)0.0288(4)
Te10.05418(6)1/40.11125(5)0.0190(2)
Te20.42077(6)1/40.10495(5)0.0196(2)
Te30.26121(6)1/40.83009(5)0.0186(2)
SrTbCuTe3
Sr0.26394(11)1/40.50354(9)0.0247(3)
Tb0.01132(5)1/40.74680(4)0.0200(2)
Cu0.24340(14)1/40.22102(12)0.0281(4)
Te10.05508(7)1/40.11105(6)0.0190(3)
Te20.42398(7)1/40.10569(6)0.0196(3)
Te30.25953(7)1/40.82978(6)0.0183(2)
SrDyCuTe3
Sr00.75369(9)1/40.0313(4)
Dy0000.0245(2)
Cu00.47094(13)1/40.0301(4)
Te100.07951(6)1/40.0217(3)
Te200.35881(4)0.06439(5)0.0253(2)
SrHoCuTe3
Sr00.75402(7)1/40.0258(2)
Ho0000.0194(2)
Cu00.47067(9)1/40.0269(3)
Te100.07945(4)1/40.0179(2)
Te200.35906(3)0.06332(4)0.0192(2)
SrErCuTe3
Sr00.75401(9)1/40.0248(3)
Er0000.0193(2)
Cu00.47055(12)1/40.0273(4)
Te100.07917(5)1/40.0183(2)
Te200.35928(4)0.06242(5)0.0190(2)
SrTmCuTe3
Sr00.75437(7)1/40.0230(3)
Tm0000.0176(2)
Cu00.47054(9)1/40.0254(3)
Te100.07905(4)1/40.0164(2)
Te200.35962(3)0.06173(4)0.0172(2)
SrLuCuTe3
Sr00.75465(9)1/40.0234(3)
Lu0000.0173(2)
Cu00.47013(12)1/40.0261(4)
Te100.07884(6)1/40.0169(2)
Te200.36010(4)0.06020(5)0.0177(2)
Table 4. The degree of distortion DI of tetrahedra for the compounds SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu).
Table 4. The degree of distortion DI of tetrahedra for the compounds SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu).
CompoundStructure TypeDI(Te—Cu—Te)DI(Cu—Te)DI(Te···Te)τ4
SrSmCuTe3Eu2CuS30.02140.0491 0.01570.955
SrGdCuTe3Eu2CuS30.02080.04990.01550.957
SrTbCuTe3Eu2CuS30.01920.05120.01520.961
SrDyCuTe3KZrCuS30.01820.05210.01610.979
SrHoCuTe3KZrCuS30.01740.05330.01730.980
SrErCuTe3KZrCuS30.01640.05410.01810.981
SrTmCuTe3KZrCuS30.01550.05500.01910.982
SrLuCuTe3KZrCuS30.01400.05640.02050.984
Table 5. Magnetic characteristics for the SrLnCuTe3 series (Ln = Tb–Er).
Table 5. Magnetic characteristics for the SrLnCuTe3 series (Ln = Tb–Er).
SrTbCuTe3SrDyCuTe3SrHoCuTe3SrErCuTe3
Space groupPnmaCmcm
Structure typeEu2CuS3KZrCuS3
Experimental μ 300 KB)9.5710.3410.499.33
Experimental μ2–300 KB)9.8010.6310,599.64
Calculated μB)9.72110.64610.6079.581
Experimental C300 K (K·m3·kmol–1)0.1440.1680.1730.137
Experimental C2–300 K (K·m3·kmol−1)0.1510.1780.1760.146
Calculated C (K·m3·kmol−1)0.1490.1780.1770.144
θp (K)5.22.91.10.5
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Ruseikina, A.V.; Grigoriev, M.V.; Molokeev, M.S.; Garmonov, A.A.; Elyshev, A.V.; Locke, R.J.C.; Schleid, T. Synthesis, Crystal Structure and Properties of the New Laminar Quaternary Tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu). Crystals 2023, 13, 291. https://doi.org/10.3390/cryst13020291

AMA Style

Ruseikina AV, Grigoriev MV, Molokeev MS, Garmonov AA, Elyshev AV, Locke RJC, Schleid T. Synthesis, Crystal Structure and Properties of the New Laminar Quaternary Tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu). Crystals. 2023; 13(2):291. https://doi.org/10.3390/cryst13020291

Chicago/Turabian Style

Ruseikina, Anna V., Maxim V. Grigoriev, Maxim S. Molokeev, Alexander A. Garmonov, Andrey V. Elyshev, Ralf J. C. Locke, and Thomas Schleid. 2023. "Synthesis, Crystal Structure and Properties of the New Laminar Quaternary Tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu)" Crystals 13, no. 2: 291. https://doi.org/10.3390/cryst13020291

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