Metal-Cation-Independent Dynamics of Phenylene Ring in Microporous MOFs: A ²H Solid-State NMR Study

Abstract

Mobility of the organic linkers in metal–organic frameworks (MOFs) is an established phenomenon. Knowledge of the details of linker motion in MOFs could provide a great deal of information about the linker structure and the way the guest molecules interact with the organic framework. However, the mobility of the organic linkers is poorly characterized. The extent of the influence of the metal cation or guest molecules on linker motion is still unknown for MOFs with identical topologies. In this work, we have analyzed the rotational dynamics of the phenylene ring fragments of terephthalate (1,4-benzenedicarboxylate, bdc) linkers in the series of MOFs [M2(bdc)2(dabco)]·G (M = Co2+, Ni2+, Cu2+, Zn2+; dabco =1,4-diazabicyclo[2.2.2]­octane; G = none or dimethylformamide, DMF). We have established that the reorientational motion of the phenylene rings is performed by π-flipping of the plane of the ring about its C 2 axis. The dynamics of the phenylene rings is insensitive to the variation of the metal cation, whereas the loading of the guest DMF molecules provides both a significant decrease of the rate of π-flips and an increase of the activation energy for the motion of the phenylene rings.

Guests Like Gear Levers: Donor Binding to Coordinatively Unsaturated Metal Sites in MIL‐101 Controls the Linker′s Rotation

“…To derive information on the dynamics of the phenylene rings, experimental 2 H NMR spectra were fitted at each temperature according to a dynamical model and the local geometry of the linker. The line‐shape simulation protocol for investigation of structural mobility in MOFs with paramagnetic centers was previously developed in our group and reported in references and . In the particular case of the MIL‐101(Cr), it was sufficient to use 12 closest to the linker metal ion Cr 3+ centers for line‐shape modelling.…”

“…Solid-state 2 HNMR experiments were performed at 61.4 MHz on aB ruker Advance-400 spectrometer, by using ah igh-power probe with 5mmh orizontal solenoid coil and the sealed in glass tubes MIL-101 samples within the temperature range of 200-400 K. Because of the paramagnetic nature of the Cr 3 + sites (S = 3/2) in MIL-101 the correcta cquisition of the 2 HNMR line shapes requires the use of an exorcycled quadrupole-echo sequence (90 X -t 1 -90 f -t 2 -acq-t), [5c, 14] where t 1 = 20 ms, t 2 = 22 ms, and t is ar epetitiont ime fort he sequence during accumulationoft he NMR signal. The duration of the 908 pulses was 1.8 ms. To derive information on the dynamics of thep henylener ings, experimental 2 HNMR spectra were fitted at each temperature according to ad ynamical model and the local geometry of the linker.T he line-shape simulation protocolf or investigation of structural mobility in MOFs with paramagnetic centersw as previously developed in our group and reported in references [5c] and [15].I nt he particularc ase of the MIL-101(Cr), it was sufficientt ou se 12 closest to the linker metal ionC r 3 + centers for line-shape modelling. The corresponding geometrical parameters of Cr 3 + and the linker dispositionsw ere derived from the availablec rystallographic data.…”

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid‐State NMR

“…NMR relaxation measurements and lineshape analysis of 2 H NMR are among the most powerful methods for elucidating the reorientation frequencies and the trajectories of the mobile elements. A lot of research has been carried out in this respect . For example, the groups of Schurko and Loeb designed a macrocyclic rotaxane “molecular rotor” that rotates on the linkers of a MOF designated as UWDM‐1 .…”

The Influence of Chemical Modification on Linker Rotational Dynamics in Metal–Organic Frameworks

“…Many dynamic studies have employed solid-state NMR spectroscopy (ssNMR) through 2 H-lineshape analysis to characterize the rotational motion of simple p -phenylene rings within the MOF framework. [15,19–24] Separated-local-field (SLF) solid-state NMR is an alternative, attractive means of dynamic characterization as it utilizes the heteronuclear dipolar coupling as a proxy for molecular dynamics, does not require isotopic labeling, and can be used to characterize motions over a broad dynamic range with atomic resolution. [25] …”