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

Three types of N-heterocyclic aromatic acid decorated 3d-4f heterometallic Keggin-type tungstoantimonates: Na-4[Ln(H2O)(5)](2)[Fe-4(H2O)(2)(pic)4(B-beta-SbW9O33)(2)]center dot 26H(2)O [Ln(3+) = La3+ (1), Pr3+ (2), Nd3+ (3), Sm3+ (4), Eu3+ (5)], Na6H4[Fe2W4O9(H2O)(2)(Hpic)(4) (B-beta-SbW9O33)(2)][Ln-(H2O)(8)](2)[Fe4W2O7(H2O)(4)(pic)(2)(Hpic)(2)(B-beta-SbW9O33)(2)]center dot 38H(2)O [Ln(3+) = Gd3+ (6), Dy3+ (7)], and Na2H2{[Ln-(H2O)(6)](2)[Fe-4(H2O)(2)(Hpic)(2)(pic)(2)(B-beta-SbW9O33)(2)]}(2)center dot 44H(2)O [Ln(3+) = Ho3+ (8), Er3+ (9), Hpic = 2-picolinic acid] have been prepared. 1-5 comprise a quadripic-inserted Krebs-type [Fe-4(H2O)(2)(pic)(4)(B-beta-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 [Fe-4(H2O)(10)(B-beta-SbW9O33)(2)](10-) fragment to form the [Fe-4(H2O)(2)(pic)(4)(B-beta-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-beta-SbW9O33)(2)](6-) and {[Ln-(H2O)(8)](2)[Fe4W2O7(H2O)(4)(pic)(2)(Hpic)(2)(B-beta-SbW9O33)(2)]}(4-) moieties. The molecular units of 8-9 contain two identical quadripic-inserted Krebs-type {[Ln(H2O)(6)](2)[Fe-4(H2O)(2)(Hpic)(2)(pic)(2)(B-beta-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 Ln(3+) cations. In the PL emission procedures of 5 and 7, energy transfer from [B-beta-SbW9O33](9-) fragments and pic ligands to Ln(3+) 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.