A Ni-added polyoxometalate: synthesis, structure and catalytic performance

Abstract

A Ni₆-added polyoxometalate, (NH₄)_0.5Cs_1.5K₄Na₃[Ni(H₂O)₆][{BO(OH)₂}₂Ni₆(OH)(H₂O)₆(SiW₁₀O₃₇)₂]·8H₂O (1), was made with the guidance of the “lacunary-directing synthesis” strategy using a hydrothermal method and characterized by single crystal/powder X-ray diffraction, solid-state UV-vis spectroscopy, FT-IR spectroscopy, and thermogravimetric analysis. The polyoxoanion of 1 could be conceptually constructed by the synergistic directing effect of two dilacunary B-α-SiW₁₀O₃₇ fragments linked by a central [{BO(OH)₂}₂Ni₆(OH)(H₂O)₆]⁹⁺ ({B₂Ni₆}) via Ni–O–W and Ni–O–Si linkages. The {B₂Ni₆} cluster was composed of a V-shaped {Ni₆} core with an angle of 54.6° and further decorated with two BO(OH)₂ groups. Furthermore, 1 could be applied in the Knoevenagel condensation reaction as a Lewis catalyst and exhibited excellent catalytic activity under mild reaction conditions.