hide
Free keywords:
Lanthanides; Hydrothermal synthesis; Hybrid frameworks; Coordination polymers
Abstract:
Two novel hydrated holmium(III) succinates with formula [Ho2(C4H4O4)3(H2O)4]·6H2O (1) and [Ho2(C4H4O4)3(H2O)2]·H2O (2) have been synthesized from aqueous solution under ambient and hydrothermal conditions, respectively. Single‐crystal X‐ray diffraction shows that HoIII is nine‐coordinate in both compounds even though their structures are markedly different, the main distinctive features being the [H2O]/[C4H4O42–] ratio in the coordination sphere, the conformation and coordination ability of the succinate ions, and the resulting framework dimensionality. Compound 1 is a 2D hybrid polymer and its crystal structure is unprecedented for rare‐earth succinates. It consists of centrosymmetric dimers of edge‐sharing HoO7(H2O)2 polyhedra linked by succinate ions in the [100] and [101] directions. Hydrogen‐bonded hydration water molecules connect layers to give three‐dimensional stability. Compound 2 is built up from infinite chains of HoO8(H2O) polyhedra linked by succinates that result in a 3D architecture. This structure shows that hydrothermal conditions favor an increase in the overall dimensionality of these hybrids, in agreement with theoretical considerations. The compounds were characterized by FTIR and Raman spectroscopy, thermal analysis, and variable‐temperature magnetic susceptibility measurements and the results are discussed in connection with the structural findings. The effect of the dimensionality on the thermal stability of both structures after removal of the hydration water molecules is also analyzed.
