Lanthanide Anionic Metal–Organic Frameworks Containing Semirigid Tetracarboxylate Ligands: Structure, Photoluminescence, and Magnetism

A series of lanthanide anionic metal–organic frameworks,
[NH2(CH3)2]­[Ln­(MDIP)­(H2O)] (Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6),
Dy (7); H4MDIP = methylenediisophthalic acid)
and [NH2(CH3)2]­[Ln­(MDIP)­(H2O)]·0.5NH­(CH3)2 (Ln = Er (8), Tm (9), Yb (10)), have been synthesized
and characterized. In compounds 1–7, the adjacent Ln3+ ions are intraconnected to form infinite
metal-carboxylate oxygen chain-shaped building blocks along the [001]
direction. In compounds 8–10, MDIP
ligands bridge dinuclear lanthanide centers to form three-dimensional
frameworks which can be rationalized as a (4,8)-connected topological
net with the Schläfli symbol of (410.614.84)­(45.6)2. Dimethylamine cations
occupy the vacancy of all the compounds as counterions. The photophysical
properties of trivalent Pr, Nd, Sm, Eu, Tb, Dy, Er, Yb compounds at
room temperature were investigated and showed that MDIP is an efficient
sensitizer of the luminescence of both the Tb3+ ion emitting
visible light and the Yb3+ ion emitting in the near-IR.
Antiferromagnetic interactions between Gd3+ ions were observed
from magnetic susceptibility data.