Jian-Han Zhang

Cs2GeB4O9: a New Second-Order Nonlinear-Optical Crystal

A new alkali-metal borogermanate with noncentrosymmetric structure, namely, Cs2GeB4O9, has been discovered, and a large crystal with dimensions of 20 × 16 × 8 mm(3) has been grown by a high-temperature top-seeded solution method using Cs2O-B2O3 as a flux. The compound crystallizes in the tetragonal space group I4 with a = b = 6.8063(2) Å, c = 9.9523(7) Å, V = 461.05(4) Å(3), and Z = 2. It features a three-dimensional anionic open framework based on GeO4 tetrahedra and B4O9 clusters that are interconnected via corner-sharing, forming one-dimensional channels of nine-/ten-membered rings along the a and b axes, which are occupied by Cs(+) cations. Cs2GeB4O9 exhibits a very high thermal stability with a melting point of 849 °C, and it possesses a short-wavelength absorption edge onset at 198 nm determined by UV-vis transmission spectroscopy measurements on a slab of polished crystal. Powder second-harmonic generation (SHG) measurement on sieved crystals reveals that Cs2GeB4O9 is a type I phase-matchable material with a strong SHG response of about 2.8 × KH2PO4. The preliminary investigation indicates that Cs2GeB4O9 is a new promising second-order nonlinear-optical crystalline material.

Ba3[Ge2B7O16(OH)2](OH)(H2O) and Ba3Ge2B6O16: novel alkaline-earth borogermanates based on two types of polymeric borate units and GeO4 tetrahedra.

Two new barium borogermanates with two types of novel structures, namely, Ba(3)[Ge(2)B(7)O(16)(OH)(2)](OH)(H(2)O) and Ba(3)Ge(2)B(6)O(16), have been synthesized by hydrothermal or high-temperature solid-state reactions. They represent the first examples of alkaline-earth borogermanates. Ba(3)[Ge(2)B(7)O(16)(OH)(2)](OH)(H(2)O) crystallized in a polar space group Cc. Its structure features a novel three-dimensional anionic framework composed of [B(7)O(16)(OH)(2)](13-) polyanions that are bridged by Ge atoms with one-dimensional (1D) 10-membered-ring (MR) tunnels along the b axis. The Ba(II) cations, hydroxide ions, and water molecules are located at the above tunnels. Ba(3)Ge(2)B(6)O(16) crystallizes in centrosymmetric space group P1. Its structure exhibits a thick layer composed of circular B(6)O(16) units connected by GeO(4) tetrahedra via corner sharing, forming 1D 4- and 6-MR tunnels along the c axis. Ba1 ions reside in the tunnels of the 6-MRs, whereas Ba2 ions are located at the interlayer space. Both compounds feature new types of topological structures. Second-harmonic-generation (SHG) measurements indicate that Ba(3)[Ge(2)B(7)O(16)(OH)(2)](OH)(H(2)O) displays a weak SHG response of about 0.3 times that of KH(2)PO(4). Optical, thermal stability, and ferroelectric properties as well as theoretical calculations have also been performed.

New Second-Order NLO Materials Based on Polymeric Borate Clusters and GeO(4) Tetrahedra: A Combined Experimental and Theoretical Study

Three novel rubidium borogermanates with three types of noncentrosymmetric structures, namely, RbGeB(3)O(7), Rb(2)GeB(4)O(9), and Rb(4)Ge(3)B(6)O(17), have been synthesized by high-temperature solid-state reactions in platinum crucibles. The structure of RbGeB(3)O(7) features a three-dimensional (3D) anionic framework composed of cyclic B(3)O(7) groups corner-sharing GeO(4) tetrahedra. The structure of Rb(2)GeB(4)O(9) shows a 3D anionic framework based on B(4)O(9) clusters connected by GeO(4) tetrahedra via corner sharing. The structure of Rb(4)Ge(3)B(6)O(17) is a novel 3D anionic framework composed of cyclic B(3)O(8) groups, Ge(2)O(7) dimers, and GeO(4) tetrahedra that are interconnected via corner sharing. Second harmonic generation (SHG) measurements indicate that RbGeB(3)O(7), Rb(2)GeB(4)O(9), and Rb(4)Ge(3)B(6)O(17) display moderate SHG responses that are approximately 1.3, 2.0, and 1.3 × KH(2)PO(4) (KDP), respectively, which are slightly smaller than those from theoretical calculations (about 3.7, 2.8, and 2.4 × KDP, respectively).

Syntheses, crystal structures of a series of novel alkali metal or alkaline earth metal phosphites

A series of new alkali metal and alkali-earth metal phosphites, namely, NaIn3(HPO3)5(H2O)4, AIn(HPO3)2 (A = Rb, Cs) and Ba3M2(HPO3)6 (M = Al, Ga, In), have been synthesized by hydrothermal reactions. Their structures have been determined by single-crystal X-ray diffraction. The structure of NaIn3(HPO3)5(H2O)4 shows a complicated 3D anionic framework based on InO6 octahedra connected by HPO3 tetrahedra via corner-sharing, and the 3D anionic network of NaIn3(HPO3)5(H2O)4 can also be described as a new 3,5-net with a Schlafli symbol of {4.82}{42.6.87}{42.6}3{42.88}{43.62.85}{83}. Both AIn(HPO3)2 (A = Rb, Cs) feature a 2D layer composed by InO6 octahedral and HPO3 tetrahedral units with alkali metal cations filling the interlayer spaces. Ba3M2(HPO3)6 (M = Al, Ga, In) are isomorphous, and their structures feature a 3D anionic framework composed of MO6 (M = Al, Ga, In) octahedra and HPO3 tetrahedra interconnected via corner-sharing. IR and UV-vis spectra and TGA curves of these materials were also measured.

KSbB2O6 and BaSb2B4O12: Novel Boroantimonates with 3D Anionic Architectures Composed of 1D Chains of SbO6 Octahedra and B2O5 Groups

Two new boroantimonates, namely, KSbB2O6 and BaSb2B4O12, have been successfully synthesized through high-temperature solid state reactions. Their structures feature two types of novel anionic 3D frameworks composed of 1D chains of corner-sharing SbO6 octahedra that are interconnected by B2O5 groups. The 1D chains of corner-sharing SbO6 octahedra in polar KSbB2O6 (space group Cc) are extended along the c-axis, whereas those in the centrosymmetric BaSb2B4O12 (space group C2/c) are propagated along the [101] direction. The K(+) ions are located at the 1D tunnels of the anionic frameworks along both b- and c-axis, whereas Ba(2+) ions are located at the 1D tunnels of the anionic frameworks along both the a- and c-axis. KSbB2O6 is a polar material that displays weak SHG response, whereas BaSb2B4O12 is centrosymmetric and not SHG active. Studies on their optical properties, thermal stability, and band structure calculations based on DFT methods have been also performed.

A series of boroselenite-based open frameworks mediated by the cationic sizes of the alkali metals

The first four metal boroselenites, namely, K2Se3B2O10, ASeB3O7 (A = Na, K), and Li2SeB8O15, have been synthesized by high temperature solid state reactions. Interestingly, the different cationic sizes and their coordination geometries led to three different types of anionic boroselenite frameworks ranging from a one-dimensional (1D) chain, to two-dimensional (2D) layers to a three-dimensional (3D) network. K2Se2B2O10 features a novel 1D [Se3B2O10]2− chain based on isolated B2O7 and SeO3 groups. ASeB3O7 (A = Na, K) feature a layered [SeB3O7]− architecture built of 1D corner-sharing B3O7 clusters that are further bridged by Se atoms. Li2SeB8O15 features an interesting 3D [SeB8O15]2− anionic framework composed of B3O7 groups and SeO3 units. Such 3D frameworks are further interpenetrated with each other into a 2-fold interpenetrating structure.