Three Lanthanum MOF Polymorphs: Insights into Kinetically and Thermodynamically Controlled Phases

Abstract

RPF-4 is a family of polymeric frameworks prepared with rare-earth elements and the versatile ligand 4,4'-(hexafluoroisopropylidene)bis(benzoic acid). We have found that during the synthesis procedure up to three different polymorphs can be obtained. Their crystal structures are here presented. The three networks have unusual topologies, the three being uninodal penta-coordinated, two of them unknown up to now, and the other named hxg-d-5-Imma. They are here described and compared. DFT calculations of the relative energies for the three polymorphs show that the most often obtained structure is a metastable phase, which appears to be, next to others, thermodynamically more stable.

Dynamic Calcium Metal–Organic Framework Acts as a Selective Organic Solvent Sponge

“…[32][33][34][35] These connections exist in both compounds in an edge-crossing manner, similar to those of the LnPF-4 g-polymorph (A-type channels). [36] However, the ligand can exhibit various torsion angles; when the channels are occupied by the solvent (AEPF-1) all the channels have the same configuration (A type), whereas after extracting the solvent (AEPF-1 dry ), two kinds of alternated configurations appear (A' and A'').…”

Structural variety in ytterbium dicarboxylate frameworks and in situ study diffraction of their solvothermal crystallisation

“…This situation can be contrasted with the case of (1) where needleshaped crystals of several hundred microns were found, consistent with a short period of nucleation and extended onedimensional crystal growth found by the Gualtieri fit to the crystallisation data. 13 Inspection of the rate constants is also informative: for (2) the rate constant for crystal growth is similar for that of nucleation and much larger than for (1). This suggests a rather different crystal growth mechanism for the two materials, which is not surprising given their very different structures with the open-framework one-dimensional channels of (1) contrasting with the interpenetrated networks of (2).…”

“…Although increasingly elaborate, custom-made ligands are employed to design new frameworks, it is often the case that new materials may be simply formed from a given set of metals and ligands; this is because the MOF that crystallises from a particular reagent mixture may not be the only material that forms under those conditions, with subtle changes in temperature, time, solvent compositions having an influence over the resulting product. For example, in the case of lanthanum combined with the ligand 4,4′-(hexafluoroisopropylidene)bisIJbenzoic acid), three different MOFs polymorphs were found, with the most commonly seen computed to be a metastable phase, 13 highlighting how fine control of synthesis conditions is needed in order to isolate a desired material. Further, for lanthanide materials, the decrease in ionic radius across the lanthanide series mean that variety of structures can form depending on the lanthanide chosen (or the mixture of lanthanides in mixed-metal systems).…”

Synthesis, crystal structure, supramolecular assembly, and thermal stability of two new lanthanide coordination polymers based on α-naphthoxyacetate

“…Over the past decades, the construction of lanthanidecarboxylate frameworks has attracted considerable attention in various related fields, due to their fascinating network topologies [1][2][3][4] and promising applications in catalysis, luminescence, molecular adsorption and magnetism, etc. [5][6][7][8][9][10].…”