Series of Lead Oxide Hydroxide Nitrates Obtained by Adjusting the pH Values of the Reaction Systems

A series of lead­(II) nitrates have been synthesized by a hydrothermal method and adjusting the pH values of the reaction systems. Pb₂₀O₆­(OH)₁₆(NO₃)₁₂ and Pb₂O­(OH)­NO₃, crystallize in the centrosymmetric space group <i>P</i>1̅ and <i>Pbca</i>, respectively. The structure of Pb₂₀O₆­(OH)₁₆(NO₃)₁₂ features infinite cationic chains of [Pb₂₀O₆(OH)₁₆]_∞ running along <i>c</i> axis, and the nitrate groups as the counterions reside between adjacent chains, while the structure of Pb₂O­(OH)­NO₃ can be described as alternate stacking of cationic [Pb₂O­(OH)]_∞ layers with anionic [NO₃]⁻ layers along [001] direction by the weak Pb–O bonds, forming a 3D framework with 1D tunnels of 12-member rings (MRs). [Pb₄(OH)₄]­(NO₃)₄, crystallizing in the noncentrosymmetric space group <i>Cc</i>, has been studied as the nonlinear optical material for the first time. The second harmonic generation (SHG) measurement indicates that the SHG responses of [Pb₄(OH)₄]­(NO₃)₄ are 0.7 times that of KDP. Theoretical calculations confirmed the SHG efficiency of [Pb₄(OH)₄]­(NO₃)₄ originates from the cooperative effect of NO₃^– groups and lead oxygen polyhedras in the structure. Meanwhile, the relationship between pH value and ratio of Pb/OH^– in the molecules presents a positive correlation, which results in the diversity of these structures under different pH value