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

Abstract

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.