Microwave synthesis of hybrid inorganic - Organic porous materials: phase-selective and rapid crystallization

Microwave synthesis of two porous nickel glutarates was compared with conventional hydrothermal synthesis. The cubic nickel glutarate, [Ni ₂₀(C₅H₆O₄)₂₀(H ₂₀)8]̇40H₂₀ (1), was synthesized by conventional electrical heating in several hours or days, depending on synthesis temperature. Crystallization was greatly accelerated by microwave irradiation, in which more stable, tetragonal nickel glutarate, [Ni₂₂(C₅H ₆O₄)₂₀(OH)₄(H₂O) ₁₀]38H₂O (2), was formed within a few minutes, suggesting the efficiency of the microwave technique in the synthesis of porous hybrid materials. The cubic phase 1 is formed preferentially at low pH, low temperature, and especially under conventional electrical heating. In contrast, the tetragonal phase 2 is obtained favorably at high pH, high temperature, and especially with microwave irradiation. This work demonstrates that the microwave method provides not only the very fast synthesis of a hybrid material, but also the possibility to discover a new porous hybrid material not yet identified by conventional hydrothermal synthesis. The hydrothermal formation of metalorganic hybrid materials in a matter of minutes is an important step towards developing commercially viable routes for producing this valuable class of materials.