Verbeekite, a monoclinic polymorph of PdSe, was reported for the first time in 2002 by Roberts et al. The mineral has been discovered in the Musonoi Cu-Co-Mn-U mine, Democratic Republic of Congo, and was named after Dr. Théodore Verbeek, the first geoscientist who studied the palladium mineralization there (1955-1967). Until today, the crystal structure of this very rare mineral has been unknown. By syntheses via multianvil high-pressure/high-temperature methods at 11.5 GPa and 1300 °C, synthetic verbeekite could be obtained in a high degree of purity and comparatively good crystal quality, which made it possible to determine the full crystal structure for PdSe verbeekite from single-crystal X-ray diffractometer data: I2/a, a = 671.0(2) pm, b = 415.42(8) pm, c = 891.4(2) pm, β = 92.42(3)°, V = 248.24(4) Å, R1 = 0.0368, wR2 = 0.0907 (all data). In contrast to layered PdS-type PdSe, verbeekite exhibits a novel crystal structure type of dichalcogenides of the platinum-group metals with (Se) dimer anions connecting the layers. The possibility of different arrangements of the characteristic (Se) dumbbells is the reason for the various polymorphs of the dichalcogenides, with now five known PdSe representatives.

A tellurate compound with Co/Co mixed valence states and lithium ions within orthogonally oriented channels was realized in LiCoTeO. The single-crystal structure determination revealed two independent and interpenetrating Li/O and (Co,Te)/O substructures with octahedral oxygen coordination of the metal atoms. In contrast to other mixed oxides, a honeycomb-like ordering of CoO and TeO octahedra was not observed. LiCoTeO crystallizes orthorhombically with the following unit cell parameters and refinement results: Fddd, a = 588.6(2), b = 856.7(2), c = 1781.5(4) pm, R = 0.0174, wR = 0.0462, 608 F values, and 33 variables. Additional electron density in tetrahedral voids in combination with neighboring face-linked and under-occupied octahedral lithium sites offers an excellent possible diffusion pathway for lithium ions. According to the symmetry of the crystal structure the diffusion pathways in LiCoTeO were found in two orthogonal orientations. The Co/Co mixed valence was investigated via X-ray photoelectron spectroscopy (XPS), revealing a composition comparable to that derived from single-crystal X-ray diffractometry. Magnetic susceptibility measurements underlined the coexistence of Co and Co, the title compound, however, showed no magnetic ordering down to low temperatures. The ionic conductivity of LiCoTeO was determined via alternating current (AC) electrochemical impedance spectroscopy and was found to be in the range of 1.6 × 10 S cm at 573 K.

Mg 3 TeO 6 can be synthesized at ambient pressure conditions and temperatures of 920-1070 K in a centrosymmetric, rhombohedral structure-type (R3). By means of high-pressure/high-temperature synthesis at 12.5 GPa and 1570 K a new, colorless, non-centrosymmetric high-pressure (HP) phase of Mg 3 TeO 6 is formed, crystallizing in the Ni 3 TeO 6 -type structure with the following unit cell parameters and refinement results: R3, a = 513.82(7) pm, c = 1380.7(2) pm, V = 31.57(1) nm 3 , R1 = 0.0283, wR2 = 0.0732, and GooF = 1.096. High-temperature PXRD measurements on HP-Mg 3 TeO 6 revealed exceptionally [a]