Zeolitic Open-Framework Borates with Noncentrosymmetric Structures and Nonlinear Optical Properties.

Area of Science:

• Inorganic Chemistry
• Materials Science
• Crystal Engineering

Background:

• Zeolitic materials are crucial for catalysis and separation.
• Borates and aluminoborates offer diverse structural possibilities.
• Structure-directing agents (SDAs) are key to controlling framework formation.

Purpose of the Study:

• To synthesize novel zeolitic pentaborates and aluminoborates.
• To investigate the role of ethylenediamine as an SDA.
• To explore the structure-property relationships, particularly nonlinear optical (NLO) behavior.

Main Methods:

• Solvothermal synthesis.
• Single-crystal and powder X-ray diffraction.
• Powder second-harmonic generation (SHG) measurements.
• Infrared and UV-Vis diffuse reflectance spectroscopy.
• Electronic structure calculations.

Main Results:

• Three zeolitic pentaborates, including two 3D aluminoborates (2 and 3), were successfully synthesized.
• Material 1 is a noncentrosymmetric (NCS) 2D layered borate.
• Materials 2 and 3 possess distinct NCS (dia topology) and centrosymmetric (CS, cag topology) 3D zeolitic frameworks, respectively, derived from the same fundamental building blocks.
• NCS materials 1 and 2 exhibit nonlinear optical activity, with material 2 showing type I phase-matchable SHG response comparable to KDP.

Conclusions:

• Ethylenediamine acts as an effective SDA for creating diverse zeolitic borate and aluminoborate structures.
• Framework topology and symmetry are dictated by the arrangement of fundamental building blocks and SDA's role.
• The synthesized NCS materials 1 and 2 demonstrate significant potential for nonlinear optical applications.