The vibrational properties of monoclinic dirutile-type $\mathrm{CoTe}{\mathrm{O}}_4$ (space group $P{2}_1/c$) were investigated by means of Raman and infrared (IR) spectroscopy on stoichiometric single crystals and theoretical density-functional theory (DFT) calculations. Experimental in situ investigations under pressure and temperature variations up to 10.1 GPa and 750 K confirmed the singular phase stability of the monoclinic lattice and the absence of any structural transition. The IR spectra exhibit modes that are not observed in the Raman spectra, thus offering a comprehensive understanding of the vibrational behavior of the title compound. The symmetry and degeneracy of modes and their contributions to the overall vibrational spectrum of $\mathrm{CoTe}{\mathrm{O}}_4$ were analyzed using group theory. DFT calculations were performed both on a cluster level and based on the crystal structure of monoclinic $\mathrm{CoTe}{\mathrm{O}}_4$ in order to gain further insights into the vibrational properties. The calculated vibrational frequencies and modes were compared with the experimental data, allowing for a detailed investigation of the lattice dynamics and the nature of the vibrational modes in $\mathrm{CoTe}{\mathrm{O}}_4$, and are corroborated with the analytical Wilson's F-G matrix method. These findings provide fundamental insights into the crystal symmetry and lattice dynamics of $\mathrm{CoTe}{\mathrm{O}}_4$. The results are discussed and compared to those of isoformular systems.

During a systematic study on formation conditions of new compounds with zemannite-type structures, crystals of ten new oxidotellurate(IV) phases were grown under hydrothermal conditions, partially by employing a drastic reduction of the water content. The crystal structures of the obtained phases were determined by single-crystal X-ray diffraction. Na₂[Ni₂(TeO₃)₃]·2.5H₂O, K₂[Ni₂(TeO₃)₃]·H₂O, K₂[Zn₂(TeO₃)₃]·2H₂O, Rb_1.25[Co₂(TeO₃)₃]·1.5H₂O and Rb_1.24[Mn₂(TeO₃)₃]·2H₂O exhibit a unit-cell with hexagonal symmetry (Z = 2, a ≈ 9.3 Å, c ≈ 7.7 Å), in which most of the other compounds with a zemannite-type structure are known to crystallize. Relative to this unit-cell, K₂[Cu₂(TeO₃)₃]·2H₂O exhibits a twofold superstructure, K₂[Co₂(TeO₃)₃]·2.5H₂O a twofold superstructure with an additional incommensurate modulation, Na₂[Cu₂(TeO₃)₃]·1.5H₂O a threefold superstructure, and Rb_1.5[Mn₂(TeO₃)₃]·1.25H₂O and Cs[Mn₂(TeO₃)₃]·H₂O a fourfold superstructure. Disorder of the alkali metal cations and crystal water molecules in the channels as well as variable water contents complicate modelling and structure refinement.

Single crystals of the two alkali metal zinc oxidotellurates(IV), Rb₂Zn(TeO₃)(CO₃)·H₂O and Na₂Zn₂Te₄O₁₁, were obtained by reactions of mixtures of ZnO, TeO₂, Rb₂CO₃ (molar ratios 2:3:6) and ZnO, TeO₂, Na₂CO₃ (molar ratios 2:3:10), respectively, with small amounts of water as a mineralizer. Both compounds crystallize as order-disorder (OD) structures of layers and feature a high stacking fault probability. The crystal structure of Rb₂Zn(TeO₃)(CO₃)·H₂O is composed of layers extending parallel to (100). The structure is composed of two kinds of non-polar OD layers consisting of trigonal-pyramidal [TeO₃]²⁻, tetrahedral [ZnO₄]⁶⁻, Rb1⁺, and CO₃ ²⁻, H₂O, Rb2⁺, respectively. Different centrings of the layer groups lead to an ambiguity in the stacking arrangement. The crystal structure of Na₂Zn₂Te₄O₁₁ is built from layers extending parallel to (001). Trigonal-pyramidal [TeO₃]²⁻ and bisphenoidal [TeO₄]⁴⁻ polyhedra form [Te₄O₁₁]⁶⁻ groups, which are connected by longer Te–O-contacts to form ¹ _∞[Te₈O₂₂]¹²⁻ double chains oriented along either [100] or [010]. These chains form non-polar layers, which appear alternatingly in two orientations related by a fourfold rotoinversion. The Zn²⁺ and Na⁺ cations are located at the layer interface. The stacking ambiguity is due to different lattices of adjacent layers.

Systematic phase formation studies in the system Mn^II/Te^IV/O/‐(H) using either solid‐state reactions between stoichiometric MnO:TeO₂ mixtures or hydrothermal reactions under basic conditions led to crystal growth of two polymorphs (α‐, γ‐) of MnTeO₃, Mn₆Te₅O₁₆, Mn₁₅(TeO₃)₁₄(OH)₂ and Mn₃(TeO₃)₂(OH)₂. Although α‐MnTeO₃ and Mn₆Te₅O₁₆ have been reported previously, crystal structure refinements were missing so far. Whereas α‐MnTeO₃ crystallizes in a unique structure (space group Pbca, Z=16), Mn₆Te₅O₁₆ (Pnma, Z=4) is isotypic with its Co‐homologue. The previously unknown phases γ‐MnTeO₃ (Pbca, Z=8), Mn₁₅(TeO₃)₁₄(OH)₂ ( , Z=3) and Mn₃(TeO₃)₂(OH)₂ (P6₃mc, Z=4) all have isotypic relationships, namely with ZnTeO₃, Co₁₅(TeO₃)₁₄F₂ and M₃(TeO₃)₂(OH)₂ (M=Ni, Co), respectively. Common to all crystal structures of the five manganese(II) oxidotellurate(IV) phases is the presence of [MnO₅] or [MnO₆] polyhedra and isolated trigonal‐pyramidal [TeO₃] groups (except for one of the Te^IV atoms in Mn₆Te₅O₁₆ [TeO₄] bisphenoids) as principal building units, which share corners and edges with the [MnO_5/6] groups. The resulting three‐dimensional frameworks are dominated by the influence of the stereochemically active 5 s² electron lone pair situated at the Te^IV atom, leading to the formation of channels or interstices. Quantitative comparisons between the corresponding isotypic crystal structures are given.

Synthetic single crystals of K[(Cu^II,Mn^II,Mn^III)₂(TeO₃)₃]·2H₂O were obtained from an overconcentrated alkaline aqueous solution in the system K₂O-MnO-CuO-TeO₂ under hydrothermal conditions at T ≤ 220 °C. Subeuhedral single crystals have been investigated by means of single-crystal X-ray diffraction. The crystal structure of this new zemannite-type representative adopts a monoclinic twofold superstructure. The doubling of the unit-cell volume is accompanied by a hexagonal-to-monoclinic symmetry reduction, resulting in threefold twinning with individual crystal domains following the space group symmetry P2₁. Refinements of site-occupation factors and the evaluation of bond valences suggest a distribution of di- and trivalent cations at the octahedrally coordinated M sites with a ratio (Cu^II + Mn^II):Mn^III approximating 1:1. Based on arguments about the cation sizes and the individual bond valence sums, a distribution of Cu^II_1–xMn^III_x and Mn^II_x Mn^III_1–x at each two of the four M sites can be assumed with x between ~ 0.14 and ~ 0.50. The K⁺ cations and H₂O molecules inside the channels are located off the central channel axis. In contrast to most other known zemannite-type phases, the extra-framework atoms show full occupancies and are not disordered. The distribution of the channel contents supports the anisotropic deformation of the surrounding framework, which follows the local symmetry reduction as required for the Jahn-Teller distortion of the octahedrally coordinated M sites within the framework. The arrangement of the deformed channels can be understood as the origin of the existing superstructure.