Synthesis and crystal structure of new carbonate NaPb2(CO3)2(OH)

Crystals of a new lead carbonate, NaPb2(CO3)2(OH), sp. gr. P31c, were prepared by hydrothermal synthesis. The crystal structure was established by the heavy-atom method without knowing the exact chemical formula of the compound. The polar structure of the carbonate and the distortion of the pseudosymmetry described by the supergroup P 3 1c are caused by the acentric arrangement of the oxygen atoms providing the satisfactory coordination of Pb and Na atoms. The bonds between a hydroxyl group and two crystallographically independent Pb atoms are directed along the c-axis and have different lengths. The study of the carbonate by the second harmonic generation method in a temperature range of 20–250°C revealed the nonlinear optical properties comparable with the similar properties of quartz. The comparison of the structure of the new carbonate with a number of carbonates demonstrated that the new compound is structurally similar to ewaldite BaCa(CO3)2, diorthosilicate NaBa3[Si2O7](OH), and Ba[AlSiO4]2 containing a double silicon—oxygen layer.