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Our exploration in vanadate selenites by using boric acid flux method has successfully lead into a new phase, namely, γ-V 2 Se 2 O 9. Single crystal X-ray diffraction indicates its a new structure which crystallizes in monoclinic space group P 2 1 /c with a lattice parameter of a ​= ​7.4857 (12) Å, b ​= ​7.4388 (8) Å, c ​= ​13.042 (2) Å, β ​= ​106.619 (9)°. Its crystal structure features novel 2D electroneutral [V 2 Se 2 O 9 ] layers composed of 1D [V 2 SeO 9 ]4- chains that are further bridged by Se (1)O 3 triangular pyramids. [V 2 SeO 9 ]4- chain consist corner-sharing of VO 6 and tridentate Se (2)O 3. Unlike previously reported α - and β -V 2 Se 2 O 9 with isolated [V 4 O 18 ]16− tetramers, corner-sharing of VO 6 octahedra lead into a 1D [V 2 O 9 ]8- chain in γ-V 2 Se 2 O 9. X-ray powder diffraction and thermal behavior analysis were performed to study its phase purity and thermal stability. Optical diffuse reflectance spectra associated with Tauc's fitting indicates a direct bandgap semiconductor with an energy value of 2.34 ​eV, which consistent with the theoretical prediction. As a compare, the electronic bandgaps of three polymorphs were studied and shows a sequence of α -V 2 Se 2 O 9 < β -V 2 Se 2 O 9 <γ-V 2 Se 2 O 9. Density of states were also calculated to reveal the origin of the bandgaps and bond interactions. [Display omitted] γ-V 2 Se 2 O 9 was obtained by boric acid flux method in vanadate selenite system. Its crystal structure features novel 2D electroneutral [V 2 Se 2 O 9 ] layers composed of 1D [V 2 SeO 9 ]4- chains that are further bridged by Se (1)O 3 triangular pyramids. [V 2 SeO 9 ]4- chain consist corner-sharing of VO 6 and tridentate Se (2)O 3. UV–Vis diffuse reflectance spectroscopy coupled with Tauc's analysis indicates a direct semiconductor with a bandgap value of 2.34 ​eV, and its energy transition type was further supported by first-principles electronic structure calculation. • γ-V 2 Se 2 O 9 was obtained by boric acid flux method for the first time. • Unlike α - and β -V 2 Se 2 O 9 with isolated [V 4 O 18 ]16− tetramers, corner-sharing of VO 6 forms 1D [V 2 O 9 ]8- chains in γ-V 2 Se 2 O 9. • UV–Vis diffuse reflectance spectroscopy coupled with Tauc's fitting indicates γ-V 2 Se 2 O 9 as a direct bandgap of 2.34 ​eV. [ABSTRACT FROM AUTHOR]

A mixed amines thiogermanate (NH 4) 2 [NH 2 (CH 3) 2 2 Ge 2 S 6 was reported. Its structure features isolated [Ge 2 S 6 4− anions which are separated by NH 4 + and [NH 2 (CH 3) 2 +. UV–Vis diffuse reflectance spectroscopy coupled with Tauc's analysis indicates an indirect optical transition semiconductor with an energy gap value of 3.50 eV. Furthermore the energy transition type was supported by first-principles electronic structure calculation. A mixed amines thiogermanate, namely (NH 4) 2 [NH 2 (CH 3) 2 2 Ge 2 S 6 has been successfully synthesized by solvothermal reaction. Single crystal X-ray diffraction indicates the compound crystallizes in monoclinic space group P 2 1 / c with the lattice parameters: a = 6.9647(14) Å, b = 15.719(3) Å, c = 7.2042(14) Å, β = 92.76(3)°. The structure features a zero-dimensional [Ge 2 S 6 4− anions which are separated by NH 4 + and [NH 2 (CH 3) 2 +. Hydrogen bond interactions play a crucial role in its structure formation. X-ray powder diffraction and TG-DSC measurements were performed to study its phase purity and thermal stability. UV–Vis diffuse reflectance spectroscopy coupled with Urbach fitting indicates an indirect optical transition semiconductor with a bandgap value of 3.50 eV. The result of first-principles electronic structure calculation supported the experimental indirect optical transition but the value was under estimated as 3.061 eV. Density of states and population analysis were also calculated to reveal the origin of the bandgap and bond interaction for its structure formation. [ABSTRACT FROM AUTHOR]

Two new heterometallic uranyl-organic frameworks (UOFs), [Cd(phen)2(H2O)2][(UO2)2(BDC)3]·2H2O (1) and [Ni(phen)3][(UO2)2(BDC)3]·2H2O (2), were obtained under hydrothermal conditions. Both crystal structures were characterized by single-crystal X-ray diffraction analyses and the results indicate that both complexes feature a similar 2D honeycomb framework that is connected by rigid benzenedicarboxylate (BDC) ligands and uranyl units. BDC works as a linker to bridge neighboring UO22+ units, where UO22+ is tris-chelated. Different guest molecules guided the stacking of 2D layers and lead into their 3D supramolecular crystal structures with different space groups. As a result, 1 crystallized in a polar space group Cc, whereas 2 belongs to a chiral space group P6122. Thermogravimetric measurements were performed to study their thermal stability. UV-visible diffuse reflectance spectroscopy measurements indicate an experimental optical bandgap of 3.87 eV and 3.63 eV, respectively, for 1 and 2. Luminescent studies of both samples show strong green light emissions. [ABSTRACT FROM AUTHOR]