Synthesis, structure and photochromic properties of a novel 1,6-hexanediamine trimolybdate supramolecular compound

A novel supramolecular compound 1,6-hexanediamine trimolybdate ((C6H18N2)[Mo3O10], denoted as HDAMo) has been synthesized by a hydrothermal method and its structure has been characterized by elemental analyses, Fourier transform infrared (FT-IR) spectra, single-crystal X-ray diffraction (XRD) technique. This single crystal compound consists of protonated 1,6-hexanediamine (HDA) cations and polyoxometalate [Mo3O10]2− anions. Its crystal structure belongs to monoclinic system (space group P21/n) with a=7.7508(14), b=11.467(2), c=16.167(3) Å, β=92.689(3)°, V=1435.3(5) Å3, Z=4 and Dcalc=2.619 g cm−3. The final statistics based on F2 are GOF=0.980, R1=0.0261 and wR2=0.0506 for I>2σ(I). XRD analysis revealed that in the crystal structure of HDAMo, novel infinite [Mo3O10]2− chains parallel to a axis are made up of distorted MoO6 octahedra connected by corners and edges. The protonated HDA cations occupy channels formed by [Mo3O10]2− chains and exhibit strong hydrogen bond interactions to terminal and bridging oxo groups of the chains. The [Mo3O10]2− chains linked through protonated HAD cations formed a one-dimensional network. The HDAMo compound shows novel photochromic properties, i.e., its color changes from white to reddish brown gradually under UV irradiation. XRD, FT-IR, ESR spectra and XPS are used to investigate the photochromic behavior of the compound.