Synthesis, crystal structure and properties of sandwich type compounds based on {AsW9} and a hexa-nuclear unit with three supporting TM–triazole complexes

Three hexa-nuclear substituted sandwich-type arsenotungstates, Na6[{Na(H2O)}3{Ni(Htaz)}3(AsW9O33)2]·4H2O (1), Na6[{Na(H2O)}3{Co(Htaz)}3(AsW9O33)2]·8H2O (2), and Na6[{Na(H2O)0.5}3{Mn(Htaz)}3(AsW9O33)2]·11H2O (3) (taz = 1,2,4-1H-triazole), have been synthesized and structurally characterized. Basic frameworks of 1–3 are constructed from sandwich-type [{Na(H2O)n}3{M(Htaz)}3(AsW9O33)2]6− (n = 1 or 0.5) anions and sodium cations. The transition metal ions M2+ and Na+ in the central belt are coordinated by α-[AsW9O33]9− units, taz, and water molecules to form {MO4(Htaz)} and {NaO4(H2O)m} (m = 1 or 2) segments in which M2+ ions are modified with Htaz ligands. These fragments connect alternately in an edge-sharing mode forming a six-membered ring. Such a triazole coordinated six-nuclear cluster is first observed in a sandwich-type arsenotungstate system. The compounds 1–3 exhibit good electrocatalytic activity to reduce hydrogen peroxide and antiferromagnetic interactions between the trinuclear M(II) clusters. In addition, complex 1 has a potent inhibition effect on cell proliferation of HeLa cells.