The High‐Pressure Polymorph of Ca 4 Te 5 O 14 and the Mixed‐Valent Compound Ca 13 Te VI 2/3 Te IV 3.75 O 15 (BO 3 ) 4 (OH) 3

The calcium oxidotellurates Ca2(TeIVTeVIO7), Ca2(TeIVO3)Cl2 and Ca5(TeIVO3)4Cl2 obtained from salt melts

The mixed-valent calcium oxidotellurate(IV,VI) Ca2(Te2O7) (= Ca2(TeIVTeVIO7)) and the two calcium oxidotellurate(IV) dichlorides Ca2(TeIVO3)Cl2 and Ca5(TeIVO3)4Cl2 were obtained from metal chloride salt melts. Structure determination from single crystal X-ray data revealed a unique crystal structure in each case. A common motif in the three crystal structures is the formation of a framework perforated by channels into which the stereochemically active 5s 2 electron lone pairs E of the TeIV atoms are directed. Ca2(Te2O7) belongs to category I of the Robin-Day classification of mixed-valent compounds. Its crystal structure features a double chain of condensed trigonal-pyramidal [TeIVO3] and octahedral [TeVIO6] units embedded within a framework of [CaO x ] polyhedra (x = 7–8). The Cl atoms in the crystal structures of Ca2(TeIVO3)Cl2 and Ca5(TeIVO3)4Cl2 act as spacers between isolated trigonal-pyramidal [TeO3] units and exhibit weak interactions with the 5s 2 electron lone pairs E, with Cl⋯E distances <3.6 Å.

Bi2[B2(SeO3)6]: A Metal Boroselenite with a Unique Zero-Dimensional [B2(SeO3)6]6- Anionic Group and Large Birefringence

Explorations of new types of borates are important because of their promising application in diverse fields. A new bismuth-containing boroselenite, Bi₂[B₂(SeO₃)₆], has been obtained through high-temperature solid-state reaction in a closed system. Bi₂[B₂(SeO₃)₆] possesses a zero-dimensional [B₂(SeO₃)₆]^6- anionic group that does not belong to any types of reported boroselenites. Besides, Bi₂[B₂(SeO₃)₆] is the first boroselenite with lone-pair electrons containing a metal ion as the countercation. More interestingly, on the basis of the first-principles calculations, this compound displays a large birefringence (0.090) at 1064 nm.