Controlled Synthesis of Large Single Crystals of Metal‐Organic Framework CPO‐27‐Ni Prepared by a Modulation Approach: In situ Single‐Crystal X‐ray Diffraction Studies

Abstract

The size of single crystals of the metal‐organic framework CPO‐27‐Ni was incrementally increased through a series of modulated syntheses. A novel linker modulated synthesis using 2,5‐dihydroxyterephthalic acid and the isomeric ligand 4,6‐dihydroxyisophthalic acid yielded large single crystals of CPO‐27‐Ni (∼70 μm). All materials were shown to have high crystallinity and phase purity through powder X‐ray diffraction, electron microscopy methods, thermogravimetry, and compositional analysis. For the first time single‐crystal structure analyses were carried out on CPO‐27‐Ni. High BET surface areas and nitric oxide (NO) release efficiencies were recorded for all materials. Large single crystals of CPO‐27‐Ni showed a prolonged NO release and proved suitable for in situ single‐crystal diffraction experiments to follow the NO adsorption. An efficient activation protocol was developed, leading to a dehydrated structure after just 4 h, which subsequently was NO‐loaded, leading to a first NO loaded single‐crystal structural model of CPO‐27‐Ni.

In Situ single-crystal synchrotron X-ray Diffraction Studies of Biologically Active Gases in Metal-Organic Frameworks

“…However, complete activation, i.e., a residual occupancy of O w ~0% could not be achieved even after treatment under high vacuum and temperature; a similar behaviour was also observed in a previous study. 30 There are several possible reasons for this. Some residual water may be trapped in blocked one-dimensional channels on surface contact of the crystal with the glue used to hold it in place.…”

“…1, where the framework shows the expected space group number 148 and characteristic hexagonal channels seen in Ni-CPO-27. 30 O w shows an occupancy of 5.9(19)%, the framework is therefore considered dehydrated.…”

“…A similar effect was seen with NO in NiCPO27. 30 This is not unexcepted nor undesirable as the competition between water and NO is what allows controlled release. 17 A reduction in CO bond length on cooling was expected, as Long and co-workers found spectroscopically that CO in Ni-CPO-27 was adsorbed non-classically and was blue shifted on binding.…”

“…35 Co-4,6-dhip crystallizes in long needles, whereas Ni-CPO-27 forms broader hexagonal rods (Figures S4). 30 If the hexagonal channels run down the length of the Co-4,6dhip needle then the available surface area from which to lose water will be signi cantly reduced, therefore making dehydration harder.…”

“…We have previously published data on NO binding in Ni-CPO-27. 30 In this study we investigate the binding mechanism of CO and NO in Ni-CPO-27 and for the rst time of its structural conformer MOF Co-4,6-dhip. An e cient activation protocol is determined and the MOF gas adsorption properties towards CO and NO are probed as previous work showed a reduced release of NO in the Co/Ni-4,6-dhip framework, while other works have disclosed a higher a nity of this framework toward H 2, 10,31 when compared to CPO-27.…”