Heteroatom-Modulated Assembly of Hexalanthanoid-Containing Polyoxometalate-Based Coordination Networks

Two series of lanthanoid (Ln)-containing polyoxometalates (POMs) {[Ln6(ampH)4(H2O)24-n(ampH2)n(PW11O39)2]·21H2O (Ln = Tb, n = 0 (1), Ln = Er, n = 1 (2)) and K2[Ln6(ampH)4(H2O)22(SiW11O39)2]·23H2O (Ln = Tb (3), Er (4)) (ampH2 = (aminomethyl) phosphonic acid)} have been synthesized with tri-lacunary Keggin-type POMs containing different types of heteroatoms. Compounds 1 and 2 display neutral organic-inorganic hybrid POM molecules containing {Ln6(ampH)4} ({Ln6}) cores sandwiched by two {PW11O39} units. By changing the heteroatoms from PV to SiIV, the extended 2D networks of 3 and 4 were successfully isolated where the adjacent {Ln6} clusters were connected by {SiW11O39} moieties. Luminescence performances and magnetic properties of 1-4 have been systematically surveyed. The solid-state fluorescence spectra of 1-4 display characteristic emissions of Ln components resulting from the 4f-4f transitions, and energy transfer from the POM segments to Ln3+ centers in 1 and 3 has been observed based on the lifetime decay behaviors. Furthermore, all compounds can be utilized as electrocatalysts toward reduction of nitrite with high stability.