Structure and Nonlinear Optical Properties of the Family of Lead and Barium Nonaborates with a Zeolite-Like Framework

The structures of new nonaborates, (Pb, Ba) 3(OH)[B9O16][B(OH)(3)] (space group P31c) and B(a)3Na(OH)[B9O16][B(OH)(4)] (space group P1), synthesized under hydrothermal conditions, have been investigated. These structures differ from the structure of the previously studied nonaborate Pb-3(OH)[B9O16][B(OH)(3)] (space group P31c) in the occupation of the zeolite nonaframework, which, in the case of the (Ba, Na) borate, contains a larger number of cations and OH groups. Despite this difference, all the structures have a high trigonal or pseudotrigonal symmetry, which suggests the existence of the structure type or the family of nonaborates. The structural similarity is violated by the presence B(OH)(4)(1-) of tetrahedra instead of neutral trigonal groups B(OH)(3) in channels of the (Ba, Na) borate. The latter polyhedra are characterized by a pseudomonoclinic arrangement that corresponds to the space group Cc with the true triclinic group P1. The ability of nonaborates to generate the optical second harmonic as a function of the specific features of their crystal structures is discussed.