Two new inorganic–organic hybrid materials based on β- and γ-octamolybdate clusters: Synthesis, structure determination and solid-state photochromic properties

Two new POMs containing the β- and γ-octamolybdate isomer have been successfully isolated at room temperature. The TGA shows that the β-octamolybdate isomer is thermally more stable than the γ-octamolybdate isomer. The solid-state photochromic properties of the POMs depend on the nature of the organic cations and in the topology of the cluster. [Display omitted] •The β and γ isomers of the octamolybdate cluster can be isolated at room temperature with organoammonium cations.•The TGA analysis shows that the β-octamolybdate isomer is thermally more stable than the γ-octamolybdate isomer.•The solid-state photochromic properties of POMs would depend both on the topology of the cluster and on the stabilizing cation. Two new hybrid inorganic–organic compounds, namely (iPr2NH2)2(NH4)2[Mo8O26] (1) and (C4H7N2)4[Mo8O26(C4H6N2)2]·2H2O (2), have been synthesized from room temperature, and characterized by vibrational spectroscopies, thermal gravimetric analysis (TGA) and single-crystal X-ray diffraction. Compound (1) contains a β-octamolybdate anionic cluster (β-[Mo8O26]4−) stabilized with two ammonium [NH4]+ and two diisopropylammonium [iPr2NH2]+ cations. Compound (2) is built upon a γ-octamolybdate anionic cluster (γ-[Mo8O26]4−) functionalized by two neutral 2-methylimidazole (C4H6N2) molecules, and stabilized by four protonated 2-methylimidazolium [C4H7N2]+ cations. Single-crystal X-ray diffraction analyses reveal that the compounds have 2D and 3D supramolecular structures resulting from electrostatic and H-bonding interactions between inorganic and organic entities. Both compounds exhibit distinct solid-state photochromic properties at room temperature which vary with the nature of both the polyoxometalate clusters and the organoammonium cations.