Synthesis and Structure of Two Acentric Heterometallic Inorganic–Organic Hybrid Frameworks with Both Nonlinear Optical and Ferroelectric Properties

Solvothermal reactions of Cd­(NO3)2·4H2O with aromatic polycarboxylic
acids in the presence of sodium
nitrate led to two acentric three-dimensional (3D) heterometallic
inorganic–organic hybrid frameworks, namely, [Me2NH2]­[Cd2Na3(2,4-PYDC)4]·2H2O (1) and [Me2NH2] [CdNa­(OH-m-BDC)2(H2O)2]·2H2O (2) (2,4-H2PYDC = 2,4-pyridinedicarboxylic acid, OH-m-H2BDC = 5-hydroxyisophthalic acid). The framework of 1 is constructed by a 3D inorganic Cd–Na connectivity,
which resembles a concrete reinforcement structure and features a
{CdNa}n rod-shaped chain, a {CdNa2}n helical chain, and a 20-membered
{Cd6Na14} ring. Compound 2 is built
up by one-dimensional inorganic {CdNa}n rod-shaped chains which are further connected by OH-m-BDC2– ligands, affording a 3D polymeric framework.
Compounds 1 and 2 crystallize in acentric
space groups, and both display powder second harmonic generation efficiencies
approximately 0.8 and 0.7 times, respectively, than that of the potassium
dihydrogen phosphate (KDP) powder. In addition, they also exhibit
luminescence and potential ferroelectric properties.