Synthesis, crystal structure and luminescent properties of new lanthanide-containing coordination polymers involving 4,4′-oxy-bis-benzoate as ligand

Abstract

Reactions in water between the disodium salt of 4,4′-oxy-bis-benzoic acid (H₂oba) and lanthanide chlorides lead to three families of coordination polymers with respective general chemical formulae [Ln₂(oba)₃(H₂O)₅·H₂O]_∞ with Ln = La–Nd (Family 1), [Ln₂(oba)₃(H₂O)₆·3H₂O]_∞ with Ln = Sm–Ho or Y (Family 2) and [Ln₂(oba)₃(H₂O)_5.5·0.5H₂O]_∞ with Ln = Sm–Dy (Family 3). Compounds that belong to Family 1 are isostructural. The crystal structure has been solved on the basis of the La-containing compound. This compound crystallizes in the monoclinic system, space group P2/n (no. 13) with a = 23.622(4) Å, b = 6.066(1) Å, c = 29.414(6) Å, β = 102.034(7)°, V = 4129.0(13) ų and Z = 4. Compounds that belong to Family 2 are isostructural. The crystal structure has been solved on the Gd-containing compound. This compound crystallizes in the monoclinic system, space group P2/a (no. 14) with a = 9.9474(1) Å, b = 15.6416(2) Å, c = 28.7511(4) Å, β = 95.117(1)°, V = 4455.65(10) ų and Z = 4. Compounds that belong to Family 3 are isostructural. The crystal structure has been solved on the Gd-containing compound. This compound crystallizes in the monoclinic system, space group C2/c (no. 15) with a = 59.6523(11) Å, b = 8.2064(1) Å, c = 16.9558(2) Å, β = 95.447(1)°, V = 8262.9(2) ų and Z = 4. The three crystal structures are three-dimensional and rather compact. Their potential porosities are rather low. They have been estimated as 95 m² g⁻¹, 113 m² g⁻¹, and 36 m² g⁻¹ respectively. The luminescent properties under UV irradiation of these compounds have been explored. In particular, quantum yields, lifetimes and colorimetric coordinates of the Tb- and the Eu-containing coordination polymers have been determined. A heteronuclear coordination polymer with chemical formula [EuTb(oba)₃(H₂O)_5.5·0.5H₂O]_∞ has been synthesized and characterized. It belongs to the structural family 3. Its luminescent properties have been explored in detail in order to better understand the energy transfer mechanisms and to evaluate the tunability of these families of compounds.