Structure and two-dimensional correlation infrared spectroscopy study of two isomeric forms of the octamolybdate cluster

Two isomeric forms of the octamolybdate cluster, (NH4)2(Hbpy)2[Mo8O26](bpy)3 1 (bpy=bipydine), and [Cu2(imi)4]2[Mo8O26] 2 (imi=imidazole), were synthesized by hydrothermal method and characterized by X-ray single analysis, one-dimensional (1D) infrared spectroscopy and two-dimensional (2D) correlation infrared spectroscopy under thermal perturbation. In compound 1, the [Mo8O26] units are β-structure, and octamolybdate anion is ζ-structure in compound 2. The 2D IR correlation spectroscopy study indicates that the intensity changes of Modouble bond; length as m-dashO band are more sensitive to the temperature variation than that of the Mo–O bond. The μ-Mo–O bond and framework vibrations in compound 1 are more sensitive to the temperature variation than that for compound 2. As the vibrations of μ-Mo–O bond accompanied by the transfer of an oxygen atom, the catalysis ability of compound 1 may be higher than that of compound 2.