A new sandwiched-type polyoxotungstate containing {Cd₄} transition-metal cluster: Synthesis, structure and luminescent property

A new sandwiched polyoxometalate [HK₁₁Cd₄Cl ₂(PW₉O₃₄)₂]·18H₂O (1), incorporating a unique hybrid tetranuclear cadmium cluster (abbreviated to {Cd₄}) with two trivacant polyanions [B-α-PW₉O ₃₄]^9-, has been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectroscopy, UV-vis, and single-crystal X-ray diffraction analysis. Crystal data for 1: monoclinic, space group C2/c, a = 19.2997(4), b = 13.8014(3), c = 31.9819(8) Å, β = 102.764(2)°, V = 8308.3(3) ų, Z = 4, P₂O ₈₆Cl₂K₁₁Cd₄W₁₈H ₃₇, M_r = 5735.13, D_c = 4.584 mg·mm ^-3, F(000) = 10084, μ = 26.579 mm^-1, the final R = 0.0378 and wR = 0.0989 for 6558 observed reflections (I > 2σ(I)). X-ray crystallographic study shows that the molecular structure of 1 contains four cadmium atoms. Two CdO₆ distorted octahedra and two CdO₅Cl distorted octahedra combine with each other in turn via edge-sharing, resulting in a regular rhomb-like cluster sandwiched between two {B-α-PW ₉O₃₄} units. Further, the sandwich-type polyoxoanions were connected by K⁺ ions to form a complicated 3-D open-framework through connecting with each terminal O atom of the [Cd₄Cl ₂(PW₉O₃₄)₂]₁₂- polyoxoanions. In addition, compound 1 exhibits photoluminescence property at room temperature and the band gap can be assessed at 3.25 eV.