Syntheses, structures and electrochemical properties of a class of 1-D double chain polyoxotungstate hybrids [H₂dap][Cu(dap) ₂]_0.5[Cu(dap)₂(H₂O)][Ln(H ₂O)₃(α-GeW₁₁O₃₉)] ·3H₂O

A series of novel organic-inorganic hybrid 1-D double chain germanotungstates [H₂dap][Cu(dap)₂]_0.5[Cu(dap) ₂(H₂O)][Ln(H₂O)₃(α-GeW ₁₁O₃₉)]·3H₂O [Ln = La^III (1), Pr^III (2), Nd^III (3), Sm^III (4), Eu ^III (5), Tb^III (6), Er^III (7)] (dap = 1,2-diaminopropane) have been hydrothermally prepared and structurally characterized by elemental analyses, powder X-ray diffraction (PXRD), IR spectra, thermogravimetric (TG) analyses, X-ray photoelectron spectroscopy (XPS) and single-crystal X-ray diffraction. The most prominent structural feature of 1-7 is that the [Ln(H₂O)₃(α-GeW₁₁O ₃₉)]^5- moieties are firstly connected with each other via the W-O-Ln-O-W bridges creating a 1-D {[Cu(dap)₂(H ₂O)][Ln(H₂O)₃(α-GeW₁₁O ₃₉)]}_n^3n- polymeric chain and then two adjacent antiparallel 1-D polymeric chains are linked together through [Cu(dap) ₂]²⁺ linkages giving rise to the rare organic-inorganic hybrid 1-D Cu^II-Ln^III heterometallic double-chain architectures. To the best of our knowledge, 1-7 represent the first 1-D double-chain Cu^II-Ln^III heterometallic germanotungstates. The variable-temperature magnetic susceptibilities of 2, 4 and 7 have been investigated. Furthermore, the solid-state electrochemical and electro-catalytic properties of 3 and 4 have been measured in 0.5 mol L^-1 Na ₂SO₄ + H₂SO₄ aqueous solution by entrapping them in a carbon paste electrode. 3 and 4 display apparent electro-catalytic activities for nitrite, bromate and hydrogen peroxide reduction.