Steam-assisted assemblies of {Ni6PW9}-based inorganic–organic hybrid chains: synthesis, crystal structures and properties

Abstract

Three hexa-Ni-substituted Keggin phosphotungstate chains, namely, [Ni(en)₂]{[Ni₆(μ₃-OH)₃(H₂O)₂(en)₃(B-α-PW₉O₃₄)](H₂N-bdc)}·8H₂O (1), H₂{[Ni₆(μ₃-OH)₃(H₂O)₂(en)₃(B-α-PW₉O₃₄)](tda)}·7H₂O (2), and NaH₂[Ni(en)₂(H₂O)₂]{[Ni₆(μ₃-OH)₃(H₂O)(en)₃(B-α-PW₉O₃₄)(PW₁₂O₄₀)](1,4-bdc)}·7H₂O (3) (H₂N-bdc = 5-aminoisophthalic acid; tda = 2,5-thiophenedicarboxylic acid; 1,4-bdc = dicarboxybenzene; en = ethylenediamine), have been obtained in a steam-assisted conversion manner for the first time. They were fully characterized by elemental analysis, thermogravimetric analysis, IR spectroscopy, diffuse reflectance spectroscopy, and powder X-ray diffraction. Single-crystal X-ray structure analyses indicate that {Ni₆PW₉} secondary building units bridged by different dicarboxylic ligands through the Ni-carboxylate interaction give rise to the formations of chains 1–3, where the H₂N-bdc bridged ligand as well as the unprecedented {(Ni₆PW₉)PW₁₂} species are reported for the first time in the Ni₆-substituted polyoxometalates family. Additionally, their thermal stabilities, magnetic and electrochemical properties were also investigated in detail.