Syntheses, structures and properties of three organic-inorganic hybrid polyoxotungstates constructed from {Ni₆PW₉} building blocks: from isolated clusters to 2-D layers

Three new hexa-Ni^II-substituted organic-inorganic hybrid polyoxotungstates, H[Ni_0.5(en)(H₂O)][Ni₆(en)₃(OAc)₂(Tris)(H₂O)₂(B-α-PW₉O₃₄)]·5H₂O (1), [Ni(en)₂][Ni₆(en)₃(μ₃-OH)₃(1,3-bdc)(H₂O)₂(B-α-PW₉O₃₄)]·9H₂O (2) and [Ni(en)(H₂O)₄]₃[Ni₆(en)₃(Tris)(1,3-bdc)_1.5(B-α-PW₉O₃₄)]₂·8H₂O (3) (en = ethylenediamine, Tris = tris(hydroxymethyl)aminomethane, 1,3-bdc = 1,3-benzenedicarboxylate) were hydrothermally synthesized and characterized. Both 1 and 3 contained {Ni₆(Tris)(en)₃(B-α-PW₉O₃₄)} units, whereas 2 was constructed from [Ni₆(en)₃(μ₃-OH)₃(B-α-PW₉O₃₄)] units. 1 is a new monomer. 2 comprises a 1-D chain built by [Ni₆(en)₃(μ₃-OH)₃(B-α-PW₉O₃₄)] structural building units (SBUs) linked by 1,3-bdc ligands. 3 represents the first 2-D polyoxometalate cluster-organic frameworks (PCOFs) with a honeycomb-like lattice that consists of [Ni₆(en)₃(Tris)(B-α-PW₉O₃₄)] SBUs linked by 1,3-bdc ligands. 1 indicated ferromagnetic coupling interactions existing in the hexa-Ni^II clusters. 1-3 showed excellent adsorption capabilities for MB and 3 exhibited good electrocatalytic activities for H₂O₂ and NaNO₂ reduction.