Influence of Thermal and Mechanical Stimuli on the Behavior of Al-CAU-13 Metal-Organic Framework.

Michael T Wharmby,Steve Waitschat,Pascal G Yot,Felicitas Niekiel,Norbert Stock,Helge Reinsch,Jannik Benecke,Dominik Daisenberger

doi:10.3390/nano10091698

Abstract

The response of the metal–organic framework aluminum-1,4-cyclohexanedicarboxylate or Al-CAU-13 (CAU: Christian Albrecht University) to the application of thermal and mechanical stimuli was investigated using synchrotron powder X-ray diffraction (SPXRD). Variable temperature in situ SPXRD data, over the range 80–500 K, revealed a complex evolution of the structure of the water guest containing Al-CAU-13•H2O, the dehydration process from ca. 310 to 370 K, and also the evolution of the guest free Al-CAU-13 structure between ca. 370 and 500 K. Rietveld refinement allowed this complexity to be rationalized in the different regions of heating. The Berman thermal Equation of State was determined for the two structures (Al-CAU-13•H2O and Al-CAU-13). Diamond anvil cell studies at elevated pressure (from ambient to up to ca. 11 GPa) revealed similarities in the structural responses on application of pressure and temperature. The ability of the pressure medium to penetrate the framework was also found to be important: non-penetrating silicone oil caused pressure induced amorphization, whereas penetrating helium showed no plastic deformation of the structure. Third-order Vinet equations of state were calculated and show Al-CAU-13•H2O is a hard compound for a metal–organic framework material. The mechanical response of Al-CAU-13, with tetramethylpyrazine guests replacing water, was also investigated. Although the connectivity of the structure is the same, all the linkers have a linear e,e-conformation and the structure adopts a more open, wine-rack-like arrangement, which demonstrates negative linear compressibility (NLC) similar to Al-MIL-53 and a significantly softer mechanical response. The origin of this variation in behavior is attributed to the different linker conformation, demonstrating the influence of the S-shaped a,a-conformation on the response of the framework to external stimuli.

Highlights

Metal–Organic Frameworks (MOFs) are an important class of coordination polymers with more than 20,000 known structures
We present here the study of the behavior of Al-CAU-13H2O as function of: (i) temperature over the range 80–500 K; and (ii) mechanical pressure up to 11 GPa, using two pressure transmitting media (PTM): silicone oil and helium
LeBail fits were performed to refine the unit cell param5eotfe2r1s at each temperature point and selected diffraction patterns were fully refined by the Rietveld method, to elucidate the structural changes occurring on thermal treatment. each temperature point and selected diffraction patterns were fully refined by the Rietveld method, to elucidate the structural changes occurring on thermal treatment

Summary

Introduction

Metal–Organic Frameworks (MOFs) are an important class of coordination polymers with more than 20,000 known structures. A model example of a phase transition in MIL-53 is that between the large pore-form (space group: Imcm) and the narrow pore-form (space group: C2/c) This transition may be induced by: (i) interactions with adsorbed molecules (summarized in reference [51]); (ii) temperature [52,53]; (iii) pressure [28]; and (iv) electrical field [54,55]. Al-CAU-13 undergoes a breathing transition through conformational changes of the linker, induced by the adsorption of guest molecules [58,59]. We present here the study of the behavior of Al-CAU-13H2O as function of: (i) temperature over the range 80–500 K; and (ii) mechanical pressure up to 11 GPa, using two pressure transmitting media (PTM): silicone oil and helium (for hydrostatic conditions). HTh2eOrweaacstionbtwaiansedke(pctalactutlhaitsed: C, 3t9e.m8;pHer,a5tu.8r5e;ffooru1n2dh:, bCe,f3o7re.7b;eHin,g5c.4o5o)l.edTthoeapmhbaiseentpcuornidtyitiwonass ofuverrth1ehr.cToonrfiermmoevde ubnyrpeaocwteddetrraXn-sr-ay diffrHa2cCtiDonC,mtheeasruawrempreondtusc. tAwla-Cs AfirUst-1tr3e@atTeedt swoalvsopthrerpmaraelldy bwyitlhoaDdMinFgatnedtrtahmenetwhyitlhpyetrhaazninoel bineftoorethe strubcetuinrge odfriAedl-CovAeUrn-i1g3h,taastd1e2s0cr°iCbeidn bayir.RUeipnosnchcoeot lainl.g[5t9o].room temperature, water molecules were

In-Situ Thermodiffractometry

High Pressure In-Situ X-ray Diffraction

In Situ Synchrotron X-ray Thermodiffraction

Conclusions