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.