Stoichiometric Melt Research Articles

Catalyst-free synthesis of highly functionalized triazole hexahydroquinoline carbohydrazide scaffolds via four-component cyclocondensation reaction.

A new class of multi-functional triazole hexahydroquinoline carbohydrazide named 2-amino-7,7-dimethyl-5-oxo-4-phenyl-1-(4H-1,2,4-triazol-3-yl)-1,4,5,6,7,8-hexahydroquinoline-3-carbohydrazide has been synthesized by a novel multi-component process involving the reaction of dimedone, 3-amino-1,2,4-triazole, various benzaldehyde with cyanoacetohydrazide under mild conditions in the stoichiometric melt and chloroform in sequence. The simple one-pot process, straight product isolation without applying tedious purification procedures, progression of the reaction without using any catalyst, the application of diverse aldehydes causing a high molecular diversity, the existence of several nitrogen atoms in the product structure, and the possibility of creating multiple hydrogen bonding in the final compound are attractive specifications of the present strategy.

Endohedral Ten‐Vertex Clusters [Ga@Tl10]8− in the Mixed Trielides A8GaTl10 (A=K, Rb, Cs)

AbstractThe mixed Ga/Tl trielides A8GaTl10 (A=K, Rb, Cs), which were yielded from stoichiometric melts of the elements, crystallize in the tetragonal K8ZnIn10‐type structure (SG P4/nnc, a=1018.58(3)/1047.14(6)/1077.74(10), c=1363.71(5)/1400.07(8)/1435.4(2) pm, Z=2, R1=0.0187/0.0209/0.0218 for A=K/Rb/Cs). The structures contain isolated ten‐vertex endohedral Ga‐centered clusters [Ga@Tl10]8−, in which the Tl atoms adopt a bicapped square antiprismatic shape. Although the crystallographic point group is 422 only, the cluster shape deviates only slightly from the ideal m2 (D4d) symmetry. The Ga−Tl distances of the two axial Tl(1) atoms are with 305 to 312 pm significantly longer than the eight Ga−Tl(2) bonds (approx. 290 pm). The clusters are enclosed by a shell of 24 (4 : 8 : 8 : 4) alkali cations. For K8GaTl10 and the Zn‐analog K8ZnTl10 the band structures were calculated within the framework of the APW+lo DFT method. Whereas the electron precise 10d+40 valence electron zinc compound exhibits the expected small band gap, the 41 v.e. cluster in K8GaTl10 is a radical with a half‐occupied band crossing the Fermi level. As shown from energy‐selected electron density plots, the large DOS at the Fermi level results from a half‐occupied a1 state dominated by apical Tl(1) pz contributions, which is consistent with molecular DFT studies for related ten‐vertex clusters. The bonding features in the Ga‐centered 41 v.e. clusters of the title compounds are thus intermediate between the 10d+40 Zn‐trielide [Zn@Tl10]8− and the 10d+42 v.e. systems like [Ni@Pb10]2−.

A new salt-inclusion compound, |Ag4Br|@[B7O12], with a novel type of the porous double-layered borate anion and strong anharmonicity of the “guest” sublattice

A new triclinic layered borate, |Ag4Br|@[B7O12], has been prepared by glass crystallization and slow cooling stoichiometric melts in evacuated silica ampoules. The structure is based upon a layered borate anion 7:∞2 [(4: 2Δ + 2 T) + (3: 2Δ + T)] with an architecture yet not observed among inorganic borates. The layers consist of two parts comprised of tri- and tetraborate groups; it is ∼7 Å thick and oriented parallel to (001). The interlayer space is filled by the cationic [Ag4Br]3+sublattice exhibiting disorder and anharmonicity at the silver sites. The new compound was characterized by thermal analysis, high-temperature powder X-ray diffraction, vibrational and UV–Vis–NIR spectroscopy, as well as DFT calculations. For the triclinic unit cell, the eigenvalues of the thermal expansion tensor and the orientation of the thermal expansion tensor relative to the crystallographic axes are determined. The thermal expansion of the new borate bromide is strongly anisotropic, being marginal in the plane of the B–O layers (α11 = 8.2 (1), α22 = 4.71 (3) × 10−6 °С−1) while quite large in the normal direction (α33 = 38.2 (3) × 10−6).

Синтез германата висмута с кристаллической структурой эвлитина методом литья

The conditions for the preparation of a compound with an eulithine crystal structure (ESS) during the crystallization of a stoichiometric melt in the Bi2O3 – GeO2 system by casting have been investigated. The initial components (Bi2O3 and GeO2) were placed in a platinum crucible and heated to a temperature in zone C at a rate of ~ 20 °C/min, with holding under isothermal conditions for 1 h. Then, the melt was poured from the crucible onto a heated platinum plate. The macrostructure of the surface of the crystallized samples was observed using a Stemi 2000 stereoscope (Carl Zeiss), the microstructure was observed using a Carl Zeiss Axio Observer A1m optical microscope on microsections. X-ray phase analysis (XRD) of the powder was performed on a Shimadzu XRD 6000 diffractometer (Cu Kα radiation). Atomic absorption spectrometry was carried out on a SOLAAR M device. For the first time, the possibility of obtaining Bi4Ge3O12 with the eulithine crystal structure (ESS) by fusing a stoichiometric mixture of initial oxides and subsequent cooling of the melt by casting was experimentally shown. It is shown that when using this method, it is possible not only to achieve record rates of synthesis, but also to reduce the content of platinum (which is a harmful impurity) in the resulting material by 2 times.

Electron Paramagnetic Resonance and Optical Studies of Thermoluminescence Processes in Mn-Doped YAlO3 Single Crystals

A detailed electron paramagnetic resonance (EPR), optical absorption, luminescence, and thermoluminescence (TL) study of Mn-doped YAlO3 (YAP) single crystals was performed. The crystals were grown by the Czochralski method from stoichiometric (Y/Al = 1) and yttrium-rich (Y/Al = 1.04) melts and codoped with either Si or Hf ions. The EPR measurements revealed the presence of only one type of Mn2+ center, that is, isolated Mn ions occupying Y sites (MnY2+). It was found that only in yttrium-rich crystals, the MnY2+ ions undergo recharging to MnY3+ under ionizing irradiation, indicating that this process requires the availability of sufficiently deep electron traps. The initial charge state is fully restored only after subsequent warming above 600 K. The presented results demonstrate, moreover, that MnY3+ + e → MnY2+ recombination is not the most efficient excitation channel of the green 4T1 → 6A1 emission of MnY2+, possibly because of the huge energy difference between the recombination (>5.39 eV) and excitation (3 eV) energies. In contrast, energy transfer to MnY2+ proves to be dominant. A general model of trapping and recombination mechanisms responsible for TL of YAP:Mn crystals above room temperature is proposed. Besides MnY2+ ions and the defect-related electron and hole traps intrinsic to the YAP lattice, the model includes also unintentional dopants such as FeAl2+ acting as deep hole traps, as well as MnAl4+ and CrAl3+ ions acting both as deep hole and electron traps.

Investigations on the Synthesis, Crystal Structure, Linear- and Nonlinear-Optical Properties of the Zinc Germanate Rb2ZnGe2O6.

A quaternary nonlinear-optical (NLO) zinc germanate, Rb2ZnGe2O6 (RZGO), was prepared from its stoichiometric melts, which belongs to the noncentrosymmetric space group C2221 (No. 20) and features a 3D framework formed by GeO4 tetrahedra, ZnO4 tetrahedra, and Rb+ cations filling into the void space. RZGO displays a good phase-matchable second-harmonic-generation (SHG) intensity similar to that of KH2PO4. The UV cutoff edge for RZGO was found to be approximately 0.37 μm with a broad optical band gap of 3.22 eV, indicating a large laser-induced damage threshold. Further characterizations suggested that this compound displays an excellent thermal stability (1014 °C) and melts congruently. Besides, theoretical analysis was also implemented to investigate the electronic structures and effective NLO coefficients as well as the origin of the observed SHG response for RZGO. The present study can enrich the diversity of acentric germanate structures and pave the way for the synthesis of new NLO compounds.

Single-Crystal Bismuth Thiophosphate, BiPS4, as a Nontoxic and Mechanically Robust X-ray Detector.

Bismuth thiophosphate, BiPS4, is a promising nontoxic, high-density ternary chalcogenide semiconductor. Polycrystalline BiPS4 was synthesized from the stoichiometric melt of Bi, P, and S. Phosphorus was purified via an in-situ sublimation method. Single crystals of BiPS4 were grown using a modified vertical Bridgman method with a thermal gradient of 18 °C/cm. The material exhibits an electrical resistivity of 2 × 109 Ω·cm. The Knoop hardness of the single crystals is 128 ± 0.8 kg mm-2. A blocking contact behavior was observed with asymmetric contacts of Ga/BiPS4/Ag. A clear photocurrent response was observed from a BiPS4 crystal under an electric field as low as 1.14 V mm-1. Using a tungsten X-ray source, an X-ray sensitivity of 52 μ Gy-1 cm-2 was measured under an electric field of 80 V mm-1. When a single-crystal BiPS4 radiation detector device was used in a pulse-height radiation detection system, a clear charge collection response was observed under a 241Am α-particle radiation source.

Overlooked Binary Compounds Uncovered in the Reinspection of the La-Au System: Synthesis, Crystal Structures, and Electronic Properties of La7Au3, La3Au2, and La3Au4.

Although compound formation between two elements is well studied, thorough investigations make it possible to uncover new binary compounds. A re-examination of the La–Au system revealed three new phases, which were characterized with respect to their structural and electronic properties as well as thermal stability: La7Au3 (Th7Fe3 type, space group P63mc, Pearson code hP20) appears to be metastable. It can be obtained by slow crystallization from a stoichiometric melt. La3Au2 (U3Si2 type, space group P4/mbm, Pearson code tP10) is stable up to 1013 K, where it decomposes peritectically. La3Au4 (Pu3Pd4 type, space group R3̅, Pearson code hR14) is thermally stable up to at least 1273 K. In addition, the crystal structures of La2Au (anti-PbCl2 type, space group Pnma, Pearson code oP12) and α-LaAu (FeB type, space group Pnma, Pearson code oP8) could be determined by single-crystal X-ray diffraction. The electronic structures and chemical bonding have been evaluated from first principles calculations. They show that all compounds can be viewed as electron-rich, polar intermetallics.

Elucidation of LiCl encapsulated Bridgman growth of AlSb crystal

Aluminum antimonide (AlSb) possessing an indirect bandgap of 1.6 eV at room temperature offers a good option as a room-temperature dual-carrier radiation detector. However, the growth of AlSb crystal suffers from high reactivity of Al, causing sticking problems and polycrystallinity. Our work demonstrates experimentally that LiCl fully encapsulated Bridgman growth of AlSb is possible from near-stoichiometric AlSb melt. This leads to avoiding the interaction between the pyrolysis Boron Nitride (pBN) crucible and the melt, drastically decreasing nucleation on the peripheral crucible. Additionally, optimizing the melt composition and growth parameters provided a full understanding of LiCl encapsulated Bridgman growth of AlSb. Adding a slight amount of extra Sb into the stoichiometric AlSb melt can reduce the surface tension of the melt and enhance the stability of LiCl encapsulation efficiency. Conversely, it can also raise the risk of constitutional supercooling and promotes macroscopic defect formation. Accordingly, an optimized process was employed to obtain inclusion-free AlSb crystals with large grains (over 5 × 5 mm2) and homogeneous stoichiometric composition.

Flux-growth of Ce:LiY6O5(BO3)3 single crystals during the Czochralski pulling from nearly congruent Ce:Li6Y(BO3)3 and their optical properties

Ce:Li6Y(BO3)3 (LYBO) is a promising thermal neutron scintillator that can be grown into bulk single crystals by the Czochralski method although it melts incongruently. This study achieves 1-inch Ce:LYBO, and demonstrates the collateral flux-growth of LiY6O5(BO3)3 (LYOB) single crystals at the bottom of the crucible during the pulling of LYBO from a stoichiometric melt. Both LYBO and LYOB belong to monoclinic crystal system with the same space group. Thermal analysis shows that LYOB itself is more incongruent than LYBO, decomposing mainly into Y16.86B8O38 phase when heated up to 1500 ​°C. In contrast to the typical bluish emission of Ce-doped scintillators, like the case of Ce:LYBO, Ce:LYOB crystals exhibit a broad emission peaking in the orange wavelength region, as a result from an extraordinarily large Stokes shift. The ultrafast photoluminescence (PL) decay of Ce:LYOB is due to dominant non-radiative processes that also cause obvious luminescence quenching. This study reports for the first time high-quality Ce:LYOB single crystals, which are characterized in terms of single crystal diffraction, thermal analysis, optical transmittance, excitation and PL at room temperature, PL decay and Raman spectroscopy.

The Features of Electronic Conduction in InAs

The electrical properties of n-type crystals of InAs compound, grown from stoichiometric melt by the horizontal zone melting method, have been investigated in the temperature range of 4.2 K-300 K before and after fast neutron irradiation up to high integral fluences of 2×1018n?cm-2. At a fixed temperature electrons concentration (n) increases almost by one order during irradiation, and practically does not change with increasing of temperature. n increases only slightly by increasing of temperature near 300 K, both before and after irradiation. When ? 4×1018cm-3 the change of during irradiation is negligible. Comparison of experimental data of mobility with theory shows that the privileged scattering mechanism of electrons at 300 K is scattering on optical phonons in InAs with 1016-1017 cm-3 and scattering on ions of impurity in InAs with n~1018-1019 cm-3. The analysis shows that during irradiation point type scattering centers of donor-type structural defects with shallow levels in the forbidden zone appear. Consequently, the mobility decreases during irradiation. At 300 K in sample with electrons concentration of 3×1016 cm-3 the mobility decreases by 5 times after irradiation, which is equivalent to the formation of 1.5×1019cm-3 charged point scattering centers.

The Features of Electronic Conduction in InAs

The electrical properties of n-type crystals of InAs compound, grown from stoichiometric melt by the horizontal zone melting method, have been investigated in the temperature range of 4.2 K-300 K before and after fast neutron irradiation up to high integral fluences of 2×1018n∙cm-2. At a fixed temperature electrons concentration (n) increases almost by one order during irradiation, and practically does not change with increasing of temperature. n increases only slightly by increasing of temperature near 300 K, both before and after irradiation. When ≥ 4×1018cm-3 the change of during irradiation is negligible. Comparison of experimental data of mobility with theory shows that the privileged scattering mechanism of electrons at 300 K is scattering on optical phonons in InAs with 1016-1017 cm-3 and scattering on ions of impurity in InAs with n~1018-1019 cm-3. The analysis shows that during irradiation point type scattering centers of donor-type structural defects with shallow levels in the forbidden zone appear. Consequently, the mobility decreases during irradiation. At 300 K in sample with electrons concentration of 3×1016 cm-3 the mobility decreases by 5 times after irradiation, which is equivalent to the formation of 1.5×1019cm-3 charged point scattering centers.

Phase diagram of the Ag2SnS3–ZnS pseudobinary system for Ag2ZnSnS4 crystal growth

The phase equilibrium of the Ag2SnS3–ZnS pseudobinary system for the growth of Ag2ZnSnS4 (AZTS) crystals was investigated using the equilibration-quenching technique. The growth mechanism of AZTS follows the peritectic reaction liquid phase + ZnS phase ↔ AZTS phase, which occurs at a composition of ~20 mol% ZnS and a temperature of approximately 700 °C. The AZTS polycrystalline sample was obtained from the stoichiometric melt growth. The kesterite structure of the AZTS sample without secondary phases was identified by a combination of X-ray diffraction and Raman spectroscopy measurements. The electron carrier concentration and conductivity, determined by the Hall effect measurement, were (3.0–6.3) × 1015 cm−3 and (5.6–9.2) × 10−4 S/cm, respectively. The slightly Zn-rich and S-poor composition led to n-type conduction in the AZTS because of the dominant Zn antisites on Ag (ZnAg) and S vacancy (VS) defects. Therefore, this study can make a significant contribution to the research and application of AZTS materials.

A Nonlinear Optical Switchable Sulfate of Ultrawide Bandgap

Nonlinear optical (NLO) switchable materials have attracted intense attention because of their promising applications in optoelectronic devices. However, previous studies are mainly limited to mole...

New mixed-valent alkali chain sulfido ferrates A 1+x [FeS2] (A = K, Rb, Cs; x = 0.333–0.787)

Abstract Four new mixed-valent chain alkali metal (A) sulfido ferrates of the general structure family A 1 + x Fe x II Fe 1 − x III S 2 ${A}_{1+x}\left[{\text{Fe}}_{x}^{\text{II}}{\text{Fe}}_{1-x}^{\text{III}}{\text{S}}_{2}\right]$ were synthesized in the form of tiny green-metallic needles from nearly stoichiometric melts reacting elemental potassium with natural pyrite (A = K) or previously prepared Rb2S/Cs2S2 with elemental iron and sulfur (A = Rb/Cs). The crystal structures of the compounds were determined by means of single crystal X-ray diffraction: In the (3+1)D modulated structure of K7.15[FeS2]4 (space group Ccce(00σ 3)0s0, a = 1363.87(5), b = 2487.23(13), c = 583.47(3) pm, q = 0,0,0.444, R1 = 0.055/0.148, x = 0.787), a position modulation of the two crystallographically different undulated [ FeS 4 / 2 ] ∞ 1 ${}_{\infty }{}^{1}\left[{\text{FeS}}_{4/2}\right]$ tetrahedra chains and the surrounding K cations is associated with an occupation modulation of one of the three potassium sites. In the case of the new monoclinic rubidium ferrate Rb4[FeS2]3 (x = 1 3 $\frac{1}{3}$ ; space group P21/c, a = 1640.49(12), b = 1191.94(9), c = 743.33(6) pm, β = 94.759(4)°, Z = 4, R1 = 0.1184) the undulation of the tetrahedra chain is commensurate, the repetition unit consists of six tetrahedra. In the second new Rb ferrate, Rb7[FeS2]5 (x = 0.4; monoclinic, space group C2/c, K7[FeS2]5-type; a = 2833.9(2), b = 1197.36(9), c = 744.63(6) pm, β = 103.233(4)°, Z = 4, R1 = 0.1474) and its isotypic mixed Rb/Cs-analog Rb3.6Cs3.4[FeS2]5 (a = 2843.57(5), b = 1226.47(2), c = 759.890(10) pm, β = 103.7170(9)°, R1 = 0.0376) the chain buckling leads to a further increased repetition unit of 10 tetrahedra. For all mixed-valent ferrates, the Fe–S bond lengths continuously increase with the amount (x) of Fe(II). The buckling of the chains is controlled through the local coordination of the S atoms by the variable number of A cations of different sizes.

Mixed Mn/In chalcogenides [formula omitted]Q4 (A = Na, K, Rb, Cs; Q = S, Se, Te)

The series of new mixed chalcogenido metallates A3I(MnIn)Q4 containing MnII and InIII in a 1:1 ratio were systematically studied as model systems for the respective structurally diverse mixed-valent ferrate(II,III) analogs. The title compounds were synthesized from stoichiometric melts (Tmax ​= ​700–1000 ​°C) consisting of elemental chalcogen and indium, the manganese monochalcogenides MnQ, and either the alkali metals themselves or the alkali sulfides Na2S, Na2S or Cs2S2 (for the sulfides) as starting materials. The K, Rb and Cs salts of all chalcogens form the orthorhombic Na3Fe2S4-type structure uniformly (Pnma, e.g. a ​= ​725.50(2), b ​= ​1189.63(3), c ​= ​1148.76(3) pm, Z ​= ​4, R1 ​= ​0.0194 for A/Q ​= ​K/S), which contains buckled chains of edge-sharing tetrahedra. They are thus isotypic to the mixed-valent Na, K and Rb sulfido and selenido ferrates. The coordination numbers (CN) of the two crystallographically different A cations are 6 and 6 ​+ ​1. In contrast, the sodium sulfido metallate Na3(MnIn)S4, which is isostructural to Na3(MnGa)S4 and crystallizes in the tetragonal β-Ca3Ga2N4-type structure (I41/acd, a ​= ​1324.55(4), c ​= ​1906.94(7) pm, Z ​= ​4, R1 ​= ​0.0394), has no analog among the ferrates(II/III). The metallate anion consists of supertetrahedra (tetrahedra of corner-sharing tetrahedra) [Mn2In2S6S4/2]6−, which are connected via four vertices to form two interpenetrating diamond-like networks. The coordination numbers of the two Na+ cations are increased to 4 ​+ ​1 and 6. The sodium selenido salt Na3(MnIn)Se4 is isotypic with Na2Mn3Te4 (=Na2Mn[6](Mn2[4])Te4; monoclinic, C2/m, a ​= ​1605.5(2), b ​= ​415.64(4), c ​= ​671.02(7) pm, β ​= ​90.831(7)∘, Z ​= ​2, R1 ​= ​0.0316) and exhibits dimers of two edge-sharing tetrahedra [M2Se6], which are further connected via four vertices to form ribbons running along the short b axis. The Na+ CN is further reduced to 4(+2) Q. In accordance with the very similar ionic radii of Mn2+ and In3+, no superstructures based on Mn/In (which are distinguishable by X-ray diffraction methods) ordering are found. The structure chemistry of the overall eleven new compounds is compared with those of the corresponding mixed-valent ferrates A3Fe2II/IIIQ4 and the alkaline-earth trielates A3II(Al/Ga/In)2(N/P/As)4.

Bridging the Salt-Inclusion and Open-Framework Structures: The Case of Acentric Ag4B4O7X2 (X = Br, I) Borate Halides.

An acentric borate family, Ag4B4O7X2 (X = Br, I), has been prepared by slow cooling stoichiometric melts in evacuated silica ampules. Their crystal structure is comprised of two porous interpenetrating frameworks and demonstrates a further development of the "salt-inclusion" architecture toward a "covalent-inclusion" structure. The (Ag2X)+ sublattice shows strong anharmonic vibrations. Thermal expansion is strongly anisotropic because of the presence of condensed rigid kernite boron-oxygen chains aligned perpendicular to the c axes.

Surface ZnSe:Ca layers with hole conductivity

The authors investigate the effect of treating n-ZnSe substrates with boiling aqueous Ca(NO3)2 suspension on their electrical and luminescent properties. Base substrates were cut from bulk pure zinc selenide crystals grown from a stoichiometric melt by the Bridgman method. It was found that the Ca-doping of the substrates causes an almost complete “quenching” of the low-energy orange emission band with a maximum near ħωmax ≈ 1,95 eV and a significant increase in the efficiency of the edge blue luminescence band.

Growth and characterization of Cs2LiLaCl6:Ce single crystals

Cs2LiLaCl6:Ce (CLLC) is a promising scintillator material for dual gamma/neutron detection. The vertical Bridgman technique, with a LiCl-rich melt and high axial temperature gradient, was used to grow transparent CLLC crystals for the first time. The stoichiometric CLLC powder melted incongruently with a melting range of 343–442 °C. Additional LiCl suppressed the formation of Cs3LaCl6 second phase, which was identified in crystals grown from stoichiometric melts. CLLC was found to have a Stokes shift of about 1358 cm−1 and a photoluminescence decay time of 34.6 ns. Direct electron-hole capture by Ce3+ ions and core-valence luminescence were the main contributors to the X-ray induced luminescence spectrum. A ∅9 × 8 mm3 cylinder of the CLLC crystal with 0.5at% Ce had an energy resolution of 7.1% at 662 keV. The scintillation decay times of the CLLC crystal excited with 662 keV gammas were 79 ns and 1491 ns.

Crystal structure of the high-temperature form of the trisulfide Cs2S3 and the (3+1)D modulated structure of the telluride K37Te28

Abstract The high-temperature polymorph of the trisulfide Cs2S3, which has been synthesized from Cs2S2 and elemental sulfur, crystallizes in a new structure type (monoclinic, space group P21/c, a=999.97(4), b=1029.30(5), c=2642.07(12) pm, β=90.083(2)°, Z=16, R1=0.0324). The structure contains four crystallographically independent angled S 3 2 − ${\rm{S}}_3^{2 - }$ trisulfide ions with S–S distances of 205.7–208.3 pm. The distorted b.c.c. packing of the anions and their insertion in the five-membered rings of 3.53+3.5.3.5. (1:1) Cs nets are similarly found in the r.t. form (Cmc21, K2S3-type structure) and the two polymorphs differ mainly in the orientation of the S3 groups. The second title compound, K37Te28, was synthesized from stoichiometric melts of the elements. It forms a complex (3+1)D modulated tetragonal structure (space group I41/amd (00σ 3)s0s0, q=(0, 0, 0.5143), a=1923.22(2), c=2626.66(4) pm, Z=4, R1all=0.0837). According to K37Te28=K37[Te(1X)]8[Te(2X)2]6[Te(3X)8] the structure contains three different types of Te anions: The two crystallographically different isolated telluride anions [Te(1X)]2− are coordinated by 9/10 K+ cations. Three [Te(2X)2]2− dumbbells (d Te-Te=277.9/286.4 pm) are arranged to ‘hexamers’. The Te(31) and Te(32) atoms are located in columns of face-sharing K square antiprisms. Their z position modulation, which is accompanied by a smaller shift of the surrounding K+ cations, results in the decomposition of the [Te(3X)8]2 chain in a sequence |:Te3–Te2–Te2–Te3–Te2–Te2–Te2:| of dumbbells Te2 2− (d Te–Te=304 pm) and hypervalent linear trimers Te3 4− (d Te–Te=325 pm).