Pb-4(BO3)(2)(SO4) and Pb-2[(BO2)(OH)](SO4): New lead(II) borate-sulfate mixed-anion compounds with two types of 3D network structures

摘要

Two new lead(II) borate-sulfate mixed-anion compounds, namely, Pb-4(BO3)(2)(SO4) and Pb-2[(BO2)(OH)](SO4), have been prepared by using high-temperature melt method or hydrothermal reaction. These compounds exhibit two different types of 3D structures composed of the same anionic units of BO3 triangles and SO4 tetrahedra which are interconnected by lead(II) cations. In Pb-4(BO3)(2)(SO4), the lead(II) ions are bridged by borate anions into 3D [Pb-4(BO3)(2)](2+) architectures with 1D tunnels of 8-member rings along the a-axis, which are filled by the sulfate anions. In Pb-4(BO3)(2)(SO4), the lead(II) ions are interconnected by borate and sulfate anions into 2D Pb-B-O and Pb-S-O layers parallel to the ab plane, respectively, and these layers are further condensed into the 3D lead(II) borate-sulfate framework. TGA and DSC studies indicate that Pb-4(BO3)(2)(SO4) is congruently melting with a melting point of 689 degrees C whereas Pb-4(BO3)(2)(SO4) decomposes at approximately 335 degrees C. UV/Vis/NIR optical diffuse reflectance spectrum measurements reveal the optical band gaps of 4.03 and 4.08 eV for Pb-4(BO3)(2)(SO4) and Pb-2[(BO2)(OH)](SO4), respectively. Furthermore, the electronic structures of Pb-4(BO3)(2)(SO4) have also been calculated.