The crystal structure of new lead monoborate hydrate, Pb5B3O8(OH)3H2O

Abstract

Abstract Pb monoborate hydrate, Pb5B3O8(OH)3H2O, was synthesized in the hydrothermal system PbCO3–Li2B4O7–H2O (T = 543 K, p = 100 bar; PbCO3/Li2B4O7 = 0.25–0.5; 10–14 days). The hexagonal structure was established from X-ray single crystal diffraction, λ(MoKα ) = 0.71073 Å; space group P63 cm; a = 9.067(3) Å, c = 24.637(9) Å, V = 1753.19 Å3; M = 7592.58; D x = 7.19 g/cm3; Z = 6; μ = 707.4 cm−1; F(000) = 3156; R = 0.067 for 624 reflections. The new phase is characterized by the alternation along [001] of simple and complex layers, formed by only Pb-polyhedra, or by Pb-polyhedra and B-triangles, respectively. The asymmetric coordination of the most Pb atoms, similar with lead oxide and Pb6B10O21, is connected with two 6s electrons, emphasizing the similarity in the nature of bonding between these compounds. The Pb(6)-atoms are disordered around 12d site with 50% occupancy. The distance between the two potential crystallographic sites is 1.24 Å. The similar split of the Pb-position was recently reported for PbBi12Mo5O34. The B(O,OH)3 groups are weakly aplanar with the apex pointing towards sheets, formed by Pb-polyhedra, due to the polarizing effects of the central cations. Similarly to other relevant examples, the B atoms in two B,O-triangles have the forth relatively near O atom neighbours, which could cause a tendency towards a tetrahedral environment of the B atoms. The pyramidal distortion of the three other borate complexes is rather to be attributed to the polarizing power of Pb atoms. Preliminary investigations of the non-linear optical behaviour of lead monoborate hydrate (powder technique) are also discussed.