Monitoring Dynamics, Structure, and Magnetism of Switchable Metal–Organic Frameworks via ¹H‐Detected MAS NMR

Abstract

We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal–organic frameworks at natural abundance by 1H‐detected solid‐state NMR. Very fast MAS rates at room and cryogenic temperatures and a set of tailored radiofrequency irradiation schemes help overcome the sensitivity and resolution limits often associated with the characterisation of MOF materials. We demonstrate the approach on DUT‐8(Ni), a framework containing Ni2+ paddle‐wheel units which can exist in two markedly different architectures. Resolved 1H and 13C resonances of organic linkers are detected and assigned in few hours with only 1–2 mg of sample at natural isotopic abundance, and used to rapidly extract information on structure and local internal dynamics of the assemblies, as well as to elucidate the metal electronic properties over an extended temperature range. The experiments disclose new possibilities for describing local and global structural changes and correlating them to electronic and magnetic properties of the assemblies.

Immunoaffinity-Induced Signal Depression of Cu-MOF-74 for Label-Free Electrochemical Detection of Cardiac Troponin I

“…Metal–organic frameworks (MOFs) are a type of porous nanocrystalline materials composed of metal ions and multidentate organic ligands, which have been widely used in many fields such as catalysis, adsorption, optics, electricity, magnetism, and separation . In recent years, the research of MOFs as electrochemical biosensing materials has attracted increasing interest due to their unique advantages of structure and physicochemical properties like large surface area, controllable pore size, and excellent electroactivity or electrocatalysis. − For example, Yang et al have synthesized functionalized MOF nanosheets containing plenty of Ru­(dcbpy) 3 2+ (4,4′-dicarboxylic acid-2,2′-bipyridyl) and employed MOF as an electrochemiluminescence (ECL) probe to construct a “signal-on” ECL immunosensor.…”

“…Metal−organic frameworks (MOFs) are a type of porous nanocrystalline materials composed of metal ions and multidentate organic ligands, 1 which have been widely used in many fields such as catalysis, 2 adsorption, 3 optics, 4 electricity, 5 magnetism, 6 and separation. 7 In recent years, the research of MOFs as electrochemical biosensing materials has attracted increasing interest due to their unique advantages of structure and physicochemical properties like large surface area, controllable pore size, and excellent electroactivity or electrocatalysis.…”

Deconvolution of metal apportionment in bulk metal-organic frameworks

“…S26 to S31). As a result, the Mg/Ni arrangement in which Ni 2+ ions are FM-coupled induces broad 13 C NMR peaks, characteristic of paramagnetic solids, and the Mg/Ni arrangement in which Ni 2+ ions are AFM-coupled generates much narrower 13 C NMR peaks with similar spectral features to those found in diamagnetic Mg-MOF-74 (6,16,17).…”

“…1) (10). The chemical shift changes induced by paramagnetic ions have been shown effective in probing the local bonding configuration of atoms proximate to metal ions in oxides and hydroxides (11)(12)(13), as well as SSNMR studies of monometallic MOFs (14)(15)(16)(17)(18)(19)(20)(21). Here, we 13 C-labeled carboxylate groups of Mg 1−x Ni x -MOF-74 samples (fig.…”

Mixed-Metal Ni2+–Mn2+ Paddle Wheels in the Metal–Organic Framework DUT-8(Ni1–xMnx) as Electron Paramagnetic Resonance Probes for Monitoring the Structural Phase Transition

“… , This kind of flexibility can be altered by introducing a second transition-metal ion into the PW. ,, It was shown further that microcrystals of DUT-8­(Ni) which are smaller than 500 nm are not flexible anymore and remain in the metastable op phase even in the absence of any adsorbate . The Ni 2+ –Ni 2+ PW units in DUT-8­(Ni) cause no EPR signal at X-band frequency (ν = 9.4 GHz) up to room temperature, which might be explained by the large zero-field splitting of the two antiferromagnetically coupled Ni 2+ ions, each of them having an electron spin S Ni = 1 ground state due to their 3d 8 electron configuration (see the Supporting Information for a more detailed discussion). ,,− However, introducing a second-transition metal ion with an odd number of electrons can overcome this difficulty as we have shown in the cases of doping DUT-8­(Ni) with Cu 2+ (3d 9 ) or Co 2+ (3d 7 ). , In case of Cu 2+ doping, the formation of ferromagnetically coupled mixed-metal Ni 2+ –Cu 2+ PW units with a characteristic electron spin state S = 3/2 was observed . In case of Co 2+ doping, we observed a characteristic magnetic state of Ni 2+ –Co 2+ PWs, which we interpreted as a coupling between the S = 3/2 electron spin state of the Co 2+ ion and the S = 1 spin state of the Ni 2+ ion with significant antiferromagnetic exchange pathways .…”