Lanthanide-based molecular alloys with hydroxyterephthalate: a versatile system

Abstract

Reactions in water between lanthanide chlorides and the disodium salt of 2-hydroxyterephthalic acid (H₂hbdc) lead to six families of lanthanide-based coordination polymers depending on the lanthanide ion and the crystal growth method. Compounds that constitute family F1 have the general chemical formula [Ln(Hhbdc)(hbdc)·9H₂O]_∞ with Ln = La–Nd and have been obtained by slow evaporation. [Ln₂(hbdc)₃(H₂O)₆·4H₂O]_∞ with Ln = Sm–Eu constitute family F2 and have been obtained by solvothermal synthesis. Family F3 includes compounds, obtained by a solvothermal method, with the general chemical formula [Ln₂(hbdc)₃(H₂O)₄·4H₂O]_∞ with Ln = Ho–Lu plus Y and compounds obtained by slow diffusion through gels with Ln = Eu–Tb. [Ln(Hhbdc)(hbdc)(H₂O)₃·H₂O]_∞ with Ln = Tb–Dy have been obtained by solvothermal methods and constitute family F4. [Gd₂(hbdc)₃(H₂O)₈·6H₂O]_∞ (F5) has been obtained by slow evaporation. The last family (F6) includes compounds with the general chemical formula [Ln₂(hbdc)₃(H₂O)₈·2H₂O]_∞ with Ln = Nd–Tb that have been obtained by slow diffusion through gel media. Gd-Based micro-crystalline powders can be obtained by direct mixing of aqueous solutions of Gd³⁺ and hbdc²⁻. Unexpectedly, the micro-crystalline powder belongs to F5 when the lanthanide solution is added to the ligand one and to F6 when the opposite occurs. This phenomenon is also observed for the Tb- and/or Eu-based heterolanthanide coordination polymers. Their optical properties have been studied in detail.