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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]

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]