Lanthanum Lead Oxide Hydroxide Nitrates with a Nonlinear Optical Effect

Two
new lanthanum lead oxide hydroxide nitrates with acentric structure,
[LaPb8O­(OH)10(H2O)]­(NO3)7 (1) and [LaPb8O­(OH)10(H2O)]­(NO3)7·2H2O (2), have been prepared under subcritical hydrothermal
conditions and crystallize in the space groups of Cc and P212121, respectively.
The crystal structure of compound 1 consists of the novel
[LaPb8O­(OH)10(H2O)]7+ clusters
regularly arranged along the ab plane with nitrate
ions as the counterions around the clusters by Pb–O bonds,
developing into a three-dimensional net framework, while the structure
of compound 2 is composed of [LaPb8O­(OH)10(H2O)]7+ clusters and [NO3]− groups as the bridging groups, forming a three-dimensional
net framework with crystallized water molecules filling in the gaps.
The experiments confirmed that compound 1 is the residue
of compound 2 after efflorenscence. Besides, the [LaPb8O­(OH)10(H2O)]7+ clusters
present mirror symmetry in structures of the two compounds. The second-harmonic-generation
(SHG) measurements for the two nitrates indicate that the SHG responses
for compounds 1 and 2 are 1.3 and 1.1 times
that of KH2PO4, respectively. Theoretical calculations
confirmed that the SHG efficiency of compounds 1 and 2 mainly arises from the NO3– groups in the structure.