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, [Ni20(C5H6O4)20(H2O)8] x 40 H2O (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(C5H6O4)20(OH)4(H2O)10] x 38 H2O (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 metal-organic hybrid materials in a matter of minutes is an important step towards developing commercially viable routes for producing this valuable class of materials.