Homo- and heterometallic luminescent 2-D stilbene metal–organic frameworks

Abstract

Metal-organic frameworks (MOFs) can provide a matrix for the assembly of organic chromophores into well-defined geometries, allowing for tuning of the material properties and study of structure-property relationships. Here, we report on the effect of the coordinated metal ion on the luminescence properties of eight isostructural MOFs having the formula M(1)2M(2)L3(DMF)2 (M(1) = M(2) = Zn (1), Cd (2), Mn (3), Co (4); M(1) = Zn, M(2) = Cd (5), Mn (6), Co (7); M(1) = Co, M(2) = Mn (8); L = trans-4,4'-stilbene dicarboxylate), synthesized by reaction of the appropriate metal nitrate or mixtures of metal nitrates with LH2 in DMF. The crystal structures of 2, 3 and 5-8 were determined by X-ray diffraction to be composed of trinuclear metal clusters linked by stilbene dicarboxylate linkers in a paddlewheel geometry, extending to form a 2-D layered structure. In the mixed-metal cases, the larger metal ion was found to occupy the octahedral site in the cluster while the smaller ion occupies the tetrahedral positions, suggesting a selective, ligand-directed assembly process for the mixed-metal species. Variable temperature magnetic measurements for paramagnetic MOFs 3 and 6-8 were consistent with the site occupancies determined crystallographically, and indicated weak intra-cluster antiferromagnetic coupling for 3 and 8. Comparison between the crystal structures of 2, 3 and 5-8 and those reported for 1 and 4 in the literature reveal close resemblances between linker environments, with important intermolecular stilbene-stilbene geometries that are comparable in all cases. Interestingly, pale-colored 1-3 and 5-7 display very similar emission profiles upon excitation at λ(ex) = 350 nm, whereas dark-colored 4 and 8 do not exhibit detectable emission spectra. The bright, well-resolved luminescence of 1, 2 and 5 is ascribed to rigidification of the linker upon coordination to the d(10) metal ions, whereas the weaker emission observed for 3, 6 and 7 is presumably a result of quenching due to close proximity of the linker to one or more paramagnetic ions. Time-resolved measurements for 1, 2, 5 and 6 reveal biexponential emission decays, where the lifetime of the longer-lived state corresponds to observed variations in the nearest-neighbor cofacial stilbene-stilbene distances in their crystal structures. For 3, a monoexponential decay with shorter lifetime was determined, indicating significant paramagnetic quenching of its emissive state.

Solvent‐Triggered Reversible Phase Changes in Two Manganese‐Based Metal–Organic Frameworks and Associated Sensing Events

“…These chains further stack together to form a staggered ABC pattern geometry along the c axis (Figure b and Figure S1 c in the Supporting Information). The reaction conditions for Mn‐sdc‐1 used herein are different from those previous reported, but the powder X‐ray diffraction (XRD) patterns are identical.…”

A Heterometallic Three-Dimensional Metal−Organic Framework Bearing an Unprecedented One-Dimensional Branched-Chain Secondary Building Unit

“…This benefited from the large discrepancy of the atomic mass between Cd 2+ (112.441) and Ca 2+ (40.078), as any incorrect assignment of the atomic sites will lead to strikingly unrealistic thermal ellipsoids and other related issues during the structure refinement. Such MOF assemblies from a mixture of Cd 2+ and Ca 2+ sources thus have an advantage for structure determination by X-ray crystallography, in stark contrast to those heterometallic MOFs bearing mixed metals with similar atomic mass, such as Zn/Co and Mn/Co [23,66]. MOF 1 crystallizes in the tetragonal crystal system space group I41/a (Table 1), and its asymmetrical unit contains three Cd 2+ , three Ca 2+ , three BTB and one HCOO bridging ligands, together with one coordinated DEF (to Cd3) and six coordinated H2O solvates (two to Cd1, one to Cd2, one to Ca1, and two to Ca2).…”

“…This benefited from the large discrepancy of the atomic mass between Cd 2+ (112.441) and Ca 2+ (40.078), as any incorrect assignment of the atomic sites will lead to strikingly unrealistic thermal ellipsoids and other related issues during the structure refinement. Such MOF assemblies from a mixture of Cd 2+ and Ca 2+ sources thus have an advantage for structure determination by X-ray crystallography, in stark contrast to those heterometallic MOFs bearing mixed metals with similar atomic mass, such as Zn/Co and Mn/Co [23,66].…”

“…Heterometallic metal−organic frameworks (MOFs) merge the traits of two or more different metal ions in one ordered array with synergistic advantages that can be applied to catalysis [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ], gas adsorption [ 9 , 10 , 11 , 12 , 13 ], bioimaging [ 14 , 15 , 16 ], and other applications [ 17 , 18 , 19 , 20 , 21 ]. The heterometal can be introduced by the direct one-pot assembly of mixed metal sources and ligands [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], or from preformed secondary building units (SBUs) [ 17 , 18 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Post-synthetic metal coordination to the functionalized ligands [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ] and transmetalation/incorporation of ions into the SBUs have also been reported [ 3 ,…”

Magnetism and Luminescence of a MOF with Linear Mn3 Nodes Derived from an Emissive Terthiophene-Based Imidazole Linker

“…There appear to be fewer reports of emissive dicarboxylic organic linkers used in the design of emissive MOFs. Examples include 4,4′,4″-nitrilotrisbenzoic acid (H 3 NTB), [ 9 ] trans -4,4′-stilbene dicarboxylic acids [ 10 , 11 ], and 4,4′-ethyne-1,2-diyldibenzoate [ 12 ] as intrinsic emissive linkers; tetrakis (4-carboxyphenyl) ethylene [ 13 ] has been employed as an aggregation-induced emissive linker. Our studies have focused on expanding the family of emissive MOFs through the design of a new emissive dicarboxylic linker with the aim of enabling emission in the most well-studied MOF topologies based on linear (1,4-benzene) dicarboxylate linkers (e.g., MOF-5 [ 14 , 15 ] and UiO-66 [ 16 ]).…”