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π-Conjugated-group systems are fascinating and have been pursued for nonlinear materials owing to their superior optical and electronic properties, but are so far quite limited. Here, we report a new ultraviolet (UV) nonlinear-optical (NLO) beryllium borate crystal PbBe2B2O6 that manifests an unprecedented π–π interacting BeBO5 group, constructed by interconnected π-conjugated BeO3 and BO3 units. The PbBe2B2O6 crystal has a short UV cutoff wavelength of 249 nm, phase-matching behavior in the whole transmission region from UV to IR light region (249–3166 nm), and remarkably the largest NLO effect (18.5 × KDP) among the π-conjugated UV NLO crystal materials. Theoretical calculation unravels that the highly NLO-active BeBO5 group has strong π–π interactions. This work offers an innovative source of BeO3-participating NLO materials and expands the frontier of NLO research. [ABSTRACT FROM AUTHOR]

Isostructural mixed alkali/alkaline-earth metal tellurite halides BaLiTe2O5X (X = Cl, Br) have been successfully synthesized by a mild hydrothermal method, which possess the [Te2O5]∞ chains formed by the corner-sharing connections of the TeO3 and TeO4 polyhedra. The [Te2O5]∞ chains are bridged via the LiO3 polyhedra to form the [LiTe2O5]∞ layers with 4- and 6-membered rings. The adjacent [LiTe2O5]∞ layers are linked via the BaO9 polyhedra to form the [BaLiTe2O5]∞ double layers, which are further connected via weak Ba–X–Li interactions to generate a 3D framework. Analysis of different lithium tellurites shows that the different arrangements of the Te–O and Li–O units in the lithium tellurites can be attributed to the cation–cation repulsion and lone-pair effect. Both compounds display good thermal stability, wide optical bandgaps (4.25 and 4.13 eV), and large birefringence. First-principles calculations indicate that the TeOn groups and X− determine the optical properties of BaLiTe2O5X (X = Cl, Br). [ABSTRACT FROM AUTHOR]

Two new alkali–metal bismuth iodates KBi(IO3)3(OH) (1) and NaBi(IO3)4 (2) have been synthesized by a hydrothermal method via tuning of alkali–metal ions. Compound 1 crystallizes in the space group P1̅ and features a [Bi(IO3)3(OH)]n chain with eight-membered Bi–O–I–O–Bi–O–I–O rings. The [Bi(IO3)3(OH)]n chain consists of paddlewheel-like dimeric Bi2(OH)2(IO3)4 units linked by IO3 pairs. Compound 2 in the polar space group Cc features a [Bi(IO3)4]− double layer with Bi4I4 eight-membered rings (8-MRs). NaBi(IO3)4 exhibits a strong second harmonic generation (SHG) response of ∼5.0 × KDP (KH2PO4) and a wide transmittance window (0.4–12 μm), and structure analyses and theoretical calculations reveal that polarization results mainly from the proper alignment of the IO3 groups. The calculated electronic structure based on the DFT method indicates that the BiOn and IO3 groups dominate their optical properties. [ABSTRACT FROM AUTHOR]