Lanthanide Metalloligand Strategy toward d–f Heterometallic Metal–Organic Frameworks: Magnetism and Symmetric-Dependent Luminescent Properties

On
the basis of lanthanide metalloligands, [Ln­(ODA)3]3– (H2ODA = oxydiacetic acid), three series
of d–f heterometallic metal–organic frameworks, {[Co­(H2O)6]·[Ln2(ODA)6Co2]·6H2O}n [1; Ln = Gd (1a), Dy (1b), and Er
(1c)], {[Ln2(ODA)6Cd3(H2O)6]·mH2O}n [2; Ln = Pr (2a), Nd (2b), Sm (2c), Eu (2d), and Dy (2e), m = 9, 6, or 3], and
{[Cd­(H2O)6]·[Ln2(ODA)6Cd2]·mH2O}n [3; Ln = Dy (3a), Ho (3b), Er (3c), Tm (3d), and Lu (3e), m = 6 or 12], were designed and synthesized
by a solvent volatilization and hydrothermal method. Magnetic investigation
of 1 reveals the ferromagnetic interactions between the
metal ions. In 2, LnIII ions occupied the
inversion centers, which are confirmed by the fact that the emission
intensity ratio of 5D0 → 7F1 to 5D0 → 7F2 of the EuIII ion is much more than 3 in 2d. It is worth noting that, in 2d, the intensity
ratio I(5D0→7F1)/I(5D0→7F2) could decrease significantly upon the introduction
of different hydrophilic guest molecules, which implies that the luminescent
properties of 2d have a strong dependence on the geometry
of the first coordination sphere of the EuIII ion.