Delicate Tuning of Reaction Thermodynamics via Formation of Bimetal Phenoxide: Synthesis, Structure, and Hydrogen Storage Performance

Arene-cycloalkane pairs are promising for hydrogen storage but often encounter unfavorable thermodynamic and kinetic issues in hydrogenation and dehydrogenation. A recent strategy to circumvent thermodynamic constraints involves introducing electron-donating alkali and alkaline earth metals into arene-cycloalkane pairs. However, excessive aromatic stabilization during the metalation of single-ring arene-cycloalkane leads to immoderate thermodynamic tuning in monometal organic compounds. To address this issue, we attempted to manipulate the metalation effect by introducing two metals with different electron-donating abilities to form a bimetal organic compound. Herein, the fabrication of the first bimetal organic compound with bimetal replacement of H in the −OH group of arene-cycloalkane pairs, i.e., phenol-cyclohexanol, was reported. The observed amount of H2 released from the reaction between the phenol and the metal hydride as well as the combined characterizations using X-ray diffraction and various spectroscopic techniques confirm the formation of lithium aluminum phenoxide, (LiAl)(C6H5O)4, and its phenolic complex (LiAl)(C6H5O)4·4(C6H5OH). Both compounds crystallize into tetrahedral structures but with different cation-ligand geometrical arrangements due to the presence of different ligands, i.e., C6H5O– and C6H5OH, in each structure. These bimetal organic compounds show potential for vehicular hydrogen storage, demonstrating efficient hydrogen uptake at 90 °C and partial reversibility at 140 °C.