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 P1̅ and Pbca, respectively. The structure of Pb20O6­(OH)16(NO3)12 features
infinite cationic chains of
[Pb20O6(OH)16]∞ running along c 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 Cc, 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.

本研究通过水热法（hydrothermal method）并调控反应体系的pH值，合成了一系列硝酸铅(II)化合物。其中Pb₂₀O₆(OH)₁₆(NO₃)₁₂与Pb₂O(OH)NO₃分别结晶于中心对称空间群P1̅和Pbca。Pb₂₀O₆(OH)₁₆(NO₃)₁₂的晶体结构呈现沿c轴延伸的无限阳离子链[Pb₂₀O₆(OH)₁₆]∞，硝酸根基团作为抗衡离子位于相邻阳离子链之间；而Pb₂O(OH)NO₃的晶体结构可描述为：沿[001]方向借助弱Pb-O键，将阳离子[Pb₂O(OH)]∞层与阴离子[NO₃]⁻层交替堆叠，最终构筑出带有12元环（MR）一维隧道的三维骨架。[Pb₄(OH)₄](NO₃)₄结晶于非中心对称空间群Cc，本研究首次将其作为非线性光学材料开展研究。二次谐波产生（second harmonic generation，SHG）测试结果表明，[Pb₄(OH)₄](NO₃)₄的SHG响应为磷酸二氢钾（KDP）的0.7倍。理论计算证实，[Pb₄(OH)₄](NO₃)₄的SHG效率源于结构中硝酸根基团与铅氧多面体的协同效应。同时，反应体系pH值与分子中Pb/OH⁻比例呈正相关，这使得不同pH条件下产物结构呈现多样性。