Synthesis, crystal structure and quantum study of organoammonium polyoxomolybdate with one-dimension chain containing face-shared molybdenum–oxygen octahedra

Organoammoinium polyoxomolybdate [(enH)2(H2Mo6O20)]∞ was formed in autogeneous pressure at 160 °C for 120 h. The colorless crystals of polyoxomolybdate were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The crystals are in monoclinic system with a space group P21/n and a = 8.0844(16), b = 14.413(3), c = 8.9153(18) Å, β = 98.12(3)°, V = 1013.8(4) Å3, Z = 4. The final R = 0.0375, wR = 0.0706 for 2370 reflections [I > σ(I0)].The crystals are constructed by one-dimension infinite inorganic chains with Mo6O20 unit as building block and protonated ethylenediamine cations located in between the inorganic chains. There are many hydrogen bonds between the chains and between the chains and the cations. IR spectrum of the title compound exhibited the vibration absorption of Modouble bond; length as m-dashO, Mo–O–Mo bonds and protonated ethylenediamine cations, and suggests the presence of N–H–O and O–H–O hydrogen bonds. Quantum calculation gives the distribution of charges and the composition of frontier molecular orbits. From the calculation results, it can be inferred that protonation must have occurred on the terminal oxygen atom (O3) due to its smallest charge value and the terminal oxygen atom (O3) forms hydrogen bonds with the O12 atoms of the adjacent chain (2.936 Å); and that Mo1 atom will first receive the reduced electron. The electron transition taking place between HOMO and LUMO belongs basically to O → Mo charge transfer transition.