Two lead borate-nitrates with anion-centered [OPb4] tetrahedra and two types of π-conjugated planar units showing large birefringence

Two lead borate-nitrates Pb6O4(BO3)(NO3) and Pb6O2(BO3)2(NO3)F were obtained by the high-temperature flux method. Interestingly, their crystal structure consists of anion-centered [OPb4] tetrahedra and π-conjugated BO3 and NO3 units. The first principles calculations indicate that both compounds show large birefringence.