Pb4(BO3)2(SO4) and Pb2[(BO2)(OH)](SO4): New lead(II) borate-sulfate mixed-anion compounds with two types of 3D network structures
Two new lead(II) borate-sulfate mixed-anion compounds, namely, Pb 4 (BO 3 ) 2 (SO 4 ) and Pb 2 [(BO 2 )(OH)](SO 4 ), 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 BO 3 triangles and SO 4 tetrahedra which are interconnected by lead(II) cations. In Pb 4 (BO 3 ) 2 (SO 4 ), the lead(II) ions are bridged by borate anions into 3D [Pb 4 (BO 3 ) 2 ] 2+ architectures with 1D tunnels of 8-member rings along the a -axis, which are filled by the sulfate anions. In Pb 2 [(BO 2 )(OH)](SO 4 ), 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 (BO 3 ) 2 (SO 4 ) is congruently melting with a melting point of 689 °C whereas Pb 2 [(BO 2 )(OH)](SO 4 ) decomposes at approximately 335 °C. UV/Vis/NIR optical diffuse reflectance spectrum measurements reveal the optical band gaps of 4.03 and 4.08 eV for Pb 4 (BO 3 ) 2 (SO 4 ) and Pb 2 [(BO 2 )(OH)](SO 4 ), respectively. Furthermore, the electronic structures of Pb 4 (BO 3 ) 2 (SO 4 ) have also been calculated.
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