Uncovering the Structural Diversity of Y(III) Naphthalene-2,6-Dicarboxylate MOFs Through Coordination Modulation

Claire Wilson,Ross S. Forgan,Sarah L. Griffin

doi:10.3389/fchem.2019.00036

Abstract

Metal-organic frameworks (MOFs)—network structures built from metal ions or clusters and connecting organic ligands—are typically synthesized by solvothermal self-assembly. For transition metal based MOFs, structural predictability is facilitated by control over coordination geometries and linker connectivity under the principles of isoreticular synthesis. For rare earth (RE) MOFs, coordination behavior is dominated by steric and electronic factors, leading to unpredictable structures, and poor control over self-assembly. Herein we show that coordination modulation—the addition of competing ligands into MOF syntheses—offers programmable access to six different Y(III) MOFs all connected by the same naphthalene-2,6-dicarboxylate ligand, despite controlled synthesis of multiple phases from the same metal-ligand combination often being challenging for rare earth MOFs. Four of the materials are isolable in bulk phase purity, three are amenable to rapid microwave synthesis, and the fluorescence sensing ability of one example toward metal cations is reported. The results show that a huge variety of structurally versatile MOFs can potentially be prepared from simple systems, and that coordination modulation is a powerful tool for systematic control of phase behavior in rare earth MOFs.

Highlights

Research revolving around metal-organic frameworks (MOFs)—network structures wherein metal ions or clusters are connected by organic linkers into diverse topologies (Furukawa et al, 2013)—has rapidly increased in recent years following publication of landmark materials in the late 1990s (Chui et al, 1999; Li et al, 1999), with there being ∼70,000 MOF structures reported in the Cambridge Structural database as of 2016 (Moghadam et al, 2017)
Subjecting YCl3 and 2,6-NDC-H2 to solvothermal synthesis in DMF at 120◦C resulted in the isolation of [Y2(NDC)3(C3H7NO)2]n (1). 1 is a 3D coordination polymer, which crystallizes in the monoclinic space group P21/c
One dimensional chains of Y3+ cations running down the crystallographic c axis (Figure 2A) are connected by carboxylate units of the linkers, with three NDC2− units bridging adjacent metal ions in the (η1:η1:μ2) motif seen in the related Sc2(BDC)3 MOF (Miller et al, 2005; Perles et al, 2005)

Summary

INTRODUCTION

Research revolving around metal-organic frameworks (MOFs)—network structures wherein metal ions or clusters are connected by organic linkers into diverse topologies (Furukawa et al, 2013)—has rapidly increased in recent years following publication of landmark materials in the late 1990s (Chui et al, 1999; Li et al, 1999), with there being ∼70,000 MOF structures reported in the Cambridge Structural database as of 2016 (Moghadam et al, 2017) The reason for this interest can be attributed to the permanent porosity and vast range of structural and chemical properties that can be imparted on MOFs, leading to an array of applications from gas storage and separation (Yang and Xu, 2017) to drug delivery and biosensing (Abánades Lázaro and Forgan, 2019). The luminescent properties of one of the MOFs were examined, studying the sensing abilities of the framework in the presence of a variety of metals ions

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT