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.