Synergistic Effect between Different Coordination Geometries of Lanthanides and Various Coordination Modes of 2-Picolinic Acid Ligands Tuning Three Types of Rare 3d–4f Heterometallic Tungstoantimonates

Abstract

Three types of N-heterocyclic aromatic acid decorated 3d-4f heterometallic Keggin-type tungstoantimonates: Na4[Ln(H2O)5]2[Fe4(H2O)2(pic)4(B-β-SbW9O33)2]·26H2O [Ln3+ = La3+ (1), Pr3+ (2), Nd3+ (3), Sm3+ (4), Eu3+ (5)], Na6H4[Fe2W4O9(H2O)2(Hpic)4 (B-β-SbW9O33)2][Ln(H2O)8]2[Fe4W2O7(H2O)4(pic)2(Hpic)2(B-β-SbW9O33)2]·38H2O [Ln3+ = Gd3+ (6), Dy3+ (7)], and Na2H2{[Ln(H2O)6]2[Fe4(H2O)2(Hpic)2(pic)2(B-β-SbW9O33)2]}2·44H2O [Ln3+ = Ho3+ (8), Er3+ (9), Hpic = 2-picolinic acid] have been prepared. 1-5 comprise a quadripic-inserted Krebs-type [Fe4(H2O)2(pic)4(B-β-SbW9O33)2]10- moiety supported by two [Ln(H2O)5]3+ groups on both sides where it can be considered that four pic ligands replace eight aqua ligands located on the original Krebs-type [Fe4(H2O)10(B-β-SbW9O33)2]10- fragment to form the [Fe4(H2O)2(pic)4(B-β-SbW9O33)2]10- moiety. Remarkably, the quadripic-inserted subunits are further concatenated through the coordination role of the pic ligands to create a 3-D heterometallic framework. In contrast, the molecular units of 6-7 contain two kinds of non-Krebs-type quadripic-inserted [Fe2W4O9(H2O)2(Hpic)4(B-β-SbW9O33)2]6- and {[Ln(H2O)8]2[Fe4W2O7(H2O)4(pic)2(Hpic)2(B-β-SbW9O33)2]}4- moieties. The molecular units of 8-9 contain two identical quadripic-inserted Krebs-type {[Ln(H2O)6]2[Fe4(H2O)2(Hpic)2(pic)2(B-β-SbW9O33)2]}2- moieties, and both display a 1-D heterometallic double chain. For all we know, 1-9 stand for the first 3d-4f heterometallic tungstoantimonate hybrids functionalized by pic ligands. Particularly, the solid-state NIR photoluminescence (PL) spectrum in the range of 800-1450 nm of 3 and the solid-state visible PL spectra in the range of 500-750 nm of 4, 5, 7, and 8 at room temperature display the featured fluorescence emission bands stemming from Ln3+ cations. In the PL emission procedures of 5 and 7, energy transfer from [B-β-SbW9O33]9- fragments and pic ligands to Ln3+ ions has been observed. Additionally, the correlated color temperatures of 4, 5, 7, and 8 are indexed to 2731, 2020, 4557, and 1685 K, respectively.