Syntheses and characterization of two oxoborates, (Pb3O)2(BO3)2MO4 (M=Cr, Mo)

Two oxoborates, (Pb3O)2(BO3)2M O4 (M =Cr, Mo), have been prepared by solid-state reactions below 700 °C. Single-crystal XRD analyses showed that the Cr compound crystallizes in the orthorhombic group Pnma with a =6.4160(13) Å, b =11.635(2) Å, c =18.164(4) Å, Z =4 and the Mo analog in the group Cmcm with a =18.446(4) Å, b =6.3557(13) Å, c =11.657(2) Å, Z =4. Both compounds are characterized by one-dimensional View the MathML source∞1[Pb3O]4+ chains formed by corner-sharing OPb4 tetrahedra. BO3 and CrO4 (MoO4) groups are located around the chains to hold them together via Pb–O bonds. The IR spectra further confirmed the presence of BO3 groups in both structures and UV–vis diffuse reflectance spectra showed band gaps of about 1.8 and 2.9 eV for the Cr and Mo compounds, respectively. Band structure calculations indicated that (Pb3O)2(BO3)2MoO4 is a direct semiconductor with the calculated energy gap of about 2.4 eV.