Structural Extension from 0D to 3D Pillared Heterometallic 3d-4f Polyoxometalate Hybrids

Four 3d-4f heterometallic pillared polyoxometalate hybrids, namely, [Ln(2)Cu(SiW12O40)(Hina)(4)(ina)(4)(H2O)(2)]center dot(Hina)(2)center dot (I-2)(0.5) (2, 3) and [Ln(2)Cu-(SiW12O40)(Hina)(4)(ina)(4)(H2O)(3)]center dot(Hina)(2)center dot H2O (4, 5) (Ln = Tb (2), (4) Eu (3), (5), Hina = isonicotinic acid), were synthesized under hydrothermal conditions inspired by a structure of zero-dimensional (0D) Tb-based polyoxometalate [Tb-2(ina)(2)(Hina)(6)(H2O)(2)](SiW12O40) (1). Structural analysis of 1 reveals that all the N atoms of ina ligands are uncoordinated and can serve as potential coordination sites to bridge transition metals. So, the copper cation was introduced into the reaction system, and 2-5 realized the structural extension from 0D to three-dimensional pillared structures in which the two-dimensional sheets were composed of [Ln1(2)(Hina)(4)(ina)(4)(H2O)(2)] or [Ln2(2)(Hina)(4)(ina)(4)(H2O)(4)] and [SiW12O40] acted as pillars. In addition, all these compounds are characterized by X-ray diffraction, IR, thermogravimetric, UV-vis, and solid-state photoluminescence spectra.