Two {B ₆ }-Based Borates: From 1D Chain to 3D Framework

Two mixed alkali- and alkaline-earth metal borates, Na₂Ca₂[B₆O₉(OH)₄]·SO₄ (1) and KNa₂[B₆O₁₀]·HCOO (2), have been synthesized under solvothermal conditions. 1 features an anionic chain constructed from novel [B₆O₁₁(OH)₄]⁸⁻ clusters, which are linked by the hydrogen bond to form a supramolecular framework. 2 exhibits a 3D open-framework built from bowl-shaped [B₆O₁₃]⁸⁻ clusters and contain interwoven 9-membered ring channels extending along three directions within K⁺, Na⁺, and HCOO⁻ ions selectively accommodated, respectively. UV-vis diffuse reflectance spectra reveal that both compounds have ultraviolet absorption cutoff edges. Notably, 2 exhibits a moderate second-harmonic-generation response, with an intensity approximately 1.4 times that of KH₂PO₄ (KDP).