Time‐Resolved In Situ X‐ray Diffraction Reveals Metal‐Dependent Metal–Organic Framework Formation

Abstract

Versatility in metal substitution is one of the key aspects of metal-organic framework (MOF) chemistry, allowing properties to be tuned in a rational way. As a result, it important to understand why MOF syntheses involving different metals arrive at or fail to produce the same topological outcome. Frequently, conditions are tuned by trial-and-error to make MOFs with different metal species. We ask: is it possible to adjust synthetic conditions in a systematic way in order to design routes to desired phases? We have used in situ X-ray powder diffraction to study the solvothermal formation of isostructural M (bdc) dabco (M=Zn, Co, Ni) pillared-paddlewheel MOFs in real time. The metal ion strongly influences both kinetics and intermediates observed, leading in some cases to multiphase reaction profiles of unprecedented complexity. The standard models used for MOF crystallization break down in these cases; we show that a simple kinetic model describes the data and provides important chemical insights on phase selection.

Investigation of the Kinetic Stabilization of a Ce4+‐based MOF by in‐situ Powder X‐ray Diffraction

“…For example, the MIL‐88 framework with composition [ M III 3 (μ 3 ‐O)(OH)(H 2 O) 2 (BDC‐NH 2 ) 3 ] is formed as intermediate product during the synthesis of the Al‐MOFs [Al(OH)BDC‐NH 2 )] or Al‐MIL‐53‐NH 2 and [Al 3 (μ 3 ‐O)(OH)(H 2 O) 2 (BDC‐NH 2 ) 3 ] or Al‐MIL‐101‐NH 2 as well as during the synthesis of the iron MOF [Fe(OH)BDC)] or Fe‐MIL‐53 . Similarly, in the system M 2+ /DABCO/H 2 BDC ( M 2+ = Co 2+ , Ni 2+ , Cu 2+ or Zn 2+ ; DABCO = diazabicyclo‐[2.2.2]octane and H 2 BDC = terephthalic acid) it was reported that in most cases, initially a kagome framework can be observed, which converts further to a denser square grid lattice with identical composition of [ M II 2 (BDC) 2 (DABCO)] . However, these examples involve exclusively porous solids, retaining the valence of the metal ion.…”

“…Using synchrotron X‐ray radiation, it is possible to measure PXRD patterns with high temporal resolution in‐situ during the synthesis and thus gain important information, especially about the occurring crystalline products. This allows, for example, the identification of crystalline intermediates, which are only short‐lived during the reaction . In addition, the crystallization kinetics can be assessed and compared at different temperatures or using different heating methods .…”

Synthesis and Luminescence Properties of New Metal-Organic Frameworks Based on Zinc(II) Ions and 2,5-Thiophendicarboxylate Ligands

“…The apparently greater stability of the phase 6 could result from an increased density and dimensionality of the metal-organic framework due to "polycondensation" of the isolated trinuclear building units {Zn 3 (RCOO) 6 }, found in 5, into infinite chains, featured in 6. Such an important interplay between the thermodynamics and kinetics of the formation of the crystals of MOFs is rarely reported in such chemistry [24,25].…”

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

“…This model has the advantage of parameterising nucleation and crystal growth as two separate events and was developed for the hydrothermal formation of zeolites and subsequently used by a number of groups for study of the solvothermal crystallisation of MOFs. 17,19,40 Although we studied the crystallisation of (2) at four different temperatures (90, 100, 110 and 120°C), owing to the limited amount of beamtime available, only at the higher two temperatures did the reactions reach completion. However, we can measure the induction time for the onset of crystallisation for all temperatures by inspection of the crystallisation data and this shows a significant retardation of crystallisation as the reaction temperature is lowered, as shown in Table 1.…”