A facile strategy to adjust the density of planar triangle units in lead borate–nitrates

Abstract

Three novel lead(II) borate–nitrates were obtained through a facile hydrothermal reaction by adjusting the concentrations of the starting materials, namely, [Pb₆(μ₄-O)₄(BO₃)](NO₃) (1), H[Pb₆(μ₃-O)₂(BO₃)₂](NO₃)₃ (2) and H[Pb₈(μ₄-O)₃(μ₃-O)(BO₃)₂](NO₃)₃ (3). All three compounds feature lead(II) oxo borate layers that are separated by nitrate anions. The 2D [Pb₆(μ₄-O)₄(BO₃)]⁺ layer parallel to the ab plane in 1 is built from 1D [Pb₆(μ₄-O)₄]⁴⁺ chains along the a axis and bridging borate anions. The 2D H[Pb₆(μ₃-O)₂(BO₃)₂]³⁺ layer in 2 which is perpendicular to the b axis is composed of “isolated” Pb²⁺ and tetranuclear [Pb₄(μ₃-O)₂]⁴⁺ clusters interconnected by bridging BO₃ groups. The [Pb₈(μ₄-O)₃(μ₃-O)(BO₃)₂]²⁺ (011) layer in 3 is composed of two types of lead(II) oxo chains, namely, 1D chains of [Pb₄(μ₄-O)₂]⁴⁺ and 1D chains of [Pb₄(μ₄-O)(μ₃-O)]⁴⁺, both elongated along the a axis, which are further interconnected by bridging borate anions. This study also demonstrates that a small change in the concentration of the starting materials could result in a product with a different density of the π-conjugated planar units.