Synthesis, Characterization, and Optical Properties of Organic–Inorganic Hybrid Layered Materials: A Solvent-Free Ligand-Controlled Dimensionality Approach Based on Metal Sulfates and Aromatic Diamines

A new family of organic–inorganic hybrid layered materials based on cadmium and zinc sulfates was synthesized using 1,2-phenylenediamine (OPD), 1,3-phenylenediamine (MPD), and 1,4-phenylenediamine (PPD) as organic templates and ligands. The diamines act as structure-directing agents to obtain one-dimensional (1D), 2D, and 3D frameworks. Six new materials were obtained utilizing a simple, solvent-free synthesis approach: 1D: (OPD)2ZnSO4 1, (OPD)2CdSO4 2; 2D: (MPD)2ZnSO4 3, (MPD)2CdSO4 4; 3D: (PPD)ZnSO4 5, (PPD)CdSO4 6. The synthesis method proved to be scalable and robust. The crystal structures were determined using data from X-ray powder diffraction measurements (XRPD). It was observed that the type of amine determines the dimensionality of the obtained materials. 1D, 2D, and 3D structures were obtained using ortho-, meta-, and para-phenylenediamine isomers, respectively. The phase purity of the samples was confirmed by elemental analysis, and the morphology of the crystallites was studied using scanning electron microscopy. The thermal stability was determined by thermogravimetry and nonambient XRPD techniques. Additional characterization was performed for the two non-centrosymmetric, polar materials 3 and 4. Second-order nonlinear optical properties were examined using both experimental measurements (second harmonic generation) and theoretical calculations.

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