Synthetic approaches for accessing rare-earth analogues of UiO-66

Abstract

Rare-earth (RE) analogues of UiO-66 with non-functionalised 1,4-benzenedicarboxylate linkers are synthesised for the first time, and a series of synthetic approaches is provided to troubleshoot the synthesis. RE-UiO-66 analogues are...

Unravelling the synthesis of a rare-earth cluster-based metal–organic framework with spn topology

“…This is in contrast to what is observed in RE-UiO-66, which contains a 12-connected hexanuclear cluster node, and the material remains stable to 200 °C. 20 This suggests that the 6connected hexanuclear RE(III)-cluster node may be less stable at high temperatures than the 12-connected hexanuclear RE(III)-cluster node, somewhat consistent with previous reports on the lack of stability of under-connected RE-clusters. 13 In addition, corroborating the results obtained by PXRD and SCXRD, scanning electron microscopy (SEM) images (Fig.…”

“…This is most likely due to the difficulty in translating synthetic procedures from Zr-MOFs to RE-MOFs, which often requires changing several reaction parameters, including the type of modulator, reactant ratios, temperature, and time. 19,20 Another possible reason for the shortage of under-connected RE-cluster nodes in the literature is the reported lack of thermodynamic stability of the hexanuclear RE-cluster with open metal sites, which has been suggested to undergo a rearrangement to yield RE-oxo chains. 13 In our pursuit to obtain a RE analogue of MOF-808, henceforth denominated as Y-CU-45 (Fig.…”

Fluoro-Bridged Clusters in Rare-Earth Metal–Organic Frameworks

“…The 2-fba modulator worked well, producing a Ho-MOF isostructural to UiO-66, this in accordance with a recent report of UiO-66 RE-MOFs. 38 Surprisingly, upon closer inspection of the crystallographic data (Table S2), there is evidence to suggest fluoro bridges in the clusters and not the reported OH bridges (Figure 2 and Figure S1).…”

“…The use of fluorinated modulators, such as 2-fba or 2,6-dfba (Figure ), has been widely and successfully implemented in the area of RE MOFs, always with reports of μ 3 -OH-bridged clusters in their structures (Table S1). − …”

“…If the presence of fluorine is indeed confirmed in these RE MOFs, some of the observed properties could be attributed to the fluoro-bridged RE clusters (Table S1). ,− For example, in a recent report, a terbium hexacluster containing μ 3 -F bridges was compared to the μ 3 -OH-bridged analogue . The fluorinated compound had higher photoluminescence, a property reported in some of these MOFs.…”