Simple, scalable mechanosynthesis of metal–organic frameworks using liquid-assisted resonant acoustic mixing (LA-RAM)

We present a rapid and readily scalable methodology for the mechanosynthesis of diverse metal–organic frameworks (MOFs) in the absence of milling media typically required for other types of mechanochemical syntheses. We demonstrate the use of liquid-assisted resonant acoustic mixing (LA-RAM) methodology for the synthesis of three- and two-dimensional MOFs based on Zn(ii), Co(ii) and Cu(ii), including a mixed ligand system. Importantly, the LA-RAM approach also allowed the synthesis of the ZIF-L framework that has never been previously obtained in a mechanochemical environment, as well as its Co(ii) analogue. Straightforward scale-up from milligrams to at least 25 grams is demonstrated using the metastable framework ZIF-L as the model.


Simple, scalable mechanosynthesis of metal-organic frameworks using liquid-assisted resonant acoustic mixing (LA-RAM)
Hatem M. Titi, a Jean-Louis Do, a,b Ashlee J. Howarth, b Karthik Nagapudi, c and Tomislav Friščić a *

Table of Contents
Materials and methods 2 Synthesis 3 Selected characterization data 5 Powder X-ray diffraction (PXRD) 5 Thermal analysis data 15 Fourier-transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) 20 Nuclear magnetic resonance (NMR) spectroscopy 22 Solid-state nuclear magnetic resonance (ssNMR) spectroscopy 23 N2 sorption isotherms for surface area measurements 24 References 25 Electronic Supplementary Material (ESI) for Chemical Science. This journal is © The Royal Society of Chemistry 2020

Solid-state nuclear magnetic resonance (ssNMR)
Solid-state cross-polarization magic angle spinning (CP-MAS) 13 C-and 15 N-NMR spectra were acquired on a Varian VNMRS 400 MHz NMR spectrometer operating at 100.53 MHz for 13 C, 40.51MHz for 15 N and at 399.77 MHz for 1 H using a wide-bore 4-mm T3 doubleresonance probe spinning at 13 kHz for 13 C and 8 kHz for 15 N. Cross-polarization using RAMP CP (ramped-amplitude cross-polarization) for 2 ms 13 C and 3 ms for 15 N. SPINAL-64 1 H decoupling was performed during acquisition using a 90-kHz rf field. Recycle delays are 3s for 13 C and 10s for 15 N, as number of scans for ZIF-8 is 64 scans for 13 C and 10000 scans for nitrogen, and for the mixed ligand was 1600 scans for 13 C and 5200 scans for nitrogen.

Fourier-transform infrared attenuated total reflectance spectroscopy (FTIR-ATR)
Infrared spectra were obtained using a Bruker Vertex 70 FTIR spectrometer equipped with the Platinum ATR accessory. Absorption bands are reported in wavenumbers (cm -1 ).

Thermal analysis
Thermogravimetric analysis and differential scanning calorimetry (DSC) data were measured on a TGA/DSC 1 (Mettler-Toledo, Columbus, Ohio, USA) instrument. TGA of SOD-Zn(EtIm)(MeIm) was measured on a TGA250 (TA instruments Ltd., Delaware, USA). Samples (5 to 10 mg) were placed in alumina crucibles. All measurements were done under a 25 mL min -1 stream of air, and the samples were heated from RT up to 800 °C using a constant heating ramp of 10 °C min −1 .

Scanning electron microscopy (SEM)
SEM images were recorded on a QUANTA FEG 450 electron microscope. Evacuated MOF samples were loaded on carbon tape by via dispersion in hexanes and were sputtercoated with 4 nm of platinum before measurement.

Surface area measurements (BET)
Nitrogen adsorption and desorption isotherm measurements were performed on a Micromeritics TriStar II Plus instrument at a temperature of 77 K.

Synthesis of ZIF-L and Co-ZIF-L
A mixture of Zn(NO3)26H2O (1 mmol, 298 mg) or Co(NO3)26H2O (1 mmol, 291 mg), HMeIm (8 mmol, 656 mg) and 25 µL water were added to an 8 mL plastic vial. The mixture was oscillated for 30 minutes at 30 g to yield a microcrystalline product, as confirmed by PXRD. The product was washed with 15 mL of water, followed by centrifugation at 4,500 rpm for 15 mins, three times.

Scale-up of ZIF-L synthesis to 25 grams
A mixture of Zn(NO3)26H2O (0.1 mol, 30 gram), HMeIm (0.8 mol, 66 gram) and 7.5 mL water was added to a 100 mL plastic vial. The mixture was placed in the RAM for 30 minutes at oscillation of 30 g to yield a microcrystalline product, as confirmed by PXRD.
The product was washed with 30 mL of water, followed by centrifugation at 4,500 rpm for 15 mins, three times.

Synthesis of HKUST-1
A mixture of Cu(OAc)2H2O (1.5 mmol, 300mg) and trimesic acid (1 mmol, 210 mg) was placed in an 8 mL plastic vial, along with either 75 μL, 125 μL and 150 L of a liquid additive (Table S1). The mixtures were oscillated at 95 g for 1 hour and analyzed by PXRD. Formation of clean HKUST-1 was observed with water as the liquid additive, and the product was further washed with MeOH and evacuated at 100 C for two days.