Undergraduate Research Symposium 2020 Metal-Ligand Bond Dynamics in Metal-Organic Frameworks Confirmed by Variable Temperature Vibrational Spectroscopy BroBrzoezekk group Stacey Andreeva and Carl Brozek Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR Background Results Discussion Dynamic chemical bonds reversibly break and reform with 42 b f 1563-1560cm-1 40 1414-1407 cm -1 A wide variety of common MOFs were examined to minimal heat, light, or pressure. This type of bonding is -100oC establish quantitative relationship between MOF 38 responsible for the basic mechanism of crystallization for 36 metal-linker bond dynamicity and material composition. 8 many material systems because erroneous bond formation 34 other systems with varying metal ions and linkers (MUV-10 can be corrected through facile 200o32 C (Ca), MUV-10 (Mn), Mg-MOF-74, MOF-5, MIL-125, reversal until the material s y 30 152 3 -1515 cm-1 1348-1347 cm-1 MIL-125-NH2, UiO-66, and sodium benzoate) were settles into the most favorable 28 additionally analyzed and all have shown to possess the crystalline phase.1 A particularly b f iAntiferromagnetic carboxylates with redshifting character with greater important class of crystalline s yFerromagnetic temperatures. Most shifts are reversible and dependent on materials that emerge from this 1800 1700 1600 1500 1400 1300 1200 the identity of metal and ligand. dynamic process are metal-organic -1 -1 -1 -1 -1 Metal cluster Wavenumber (cm-1) v8 (cm ) v3 (cm ) v8 shift (cm ) v3 shift (cm ) Δ v (cm ) frameworks (MOFs). MOF of MIL-125 CuBTC 1590 1363 5.785 5.785 227 Variable temperature vibrational spectroscopy shows a lowering MUV-10 (Ca) 1640 1340 7.714 5.303 300 architecture is dependent on two building blocks: the MUV-10 (Mn) 1620 1330 2.1 7.1 290 in energy of the stretches associated with dynamic bonds Mg-MOF-74 1580 1370 3.514 1.929 210 metal ions or metal clusters and the organic ligands that at increased temperatures, indicative of bond weakening. MOF-5 1590 1435 3.857 1.6 155 bridge the metals. MOFs nd applications in elds ranging MIL-125 1590 1398 4.339 7.231 192 MIL-125-NH2 1590 1382 1.935 - 208 from industry to medicine2,3 and determining their 1380 1370 1360 1350 UiO-66 1585 1400 3.857 5.785 185 1.0 Sodium 1552 1419 4.821 6.749 133 mechanistic behavior (such as phase transitions, growth 1368 benzoate 0.8 mechanism) would be essential to answering basic science The dynamic building principle behind metal-organic questions relating to structure-property relationships.4 0.6 1366 heating frameworks presents a fascinating platform to explore and 0.4 1364 establish interesting structure-property relations.5 By Hypothesis and Model 0.2 cooling understanding this relationship, more general insights can 1362 For the past two decades, MOFs have been viewed as rigid 0.0 1595 be made regarding important material behavior such as structures, but we propose that even after formation, 0.8 crystallization and self-healing responsiveness. Insight into 1593 MOFs contain metal-ligand bonds that remain dynamic 0.6 their labile nature would provide a predictive model of such that the crystalline structure contains mixtures of 0.4 their growth mechanism and inspire important applica-1591 partially bound and unbound arrangements. tions such as the use of MOFs for self-healing conductive 0.2 1589 membranes or as smart materials as well as how dynamic 0.0 O 1610 1600 1590 1580 -100 -50 0 50 100 150 200 bonding impacts the behavior of robust materials overall. O Wavenumber (cm-1) Temperature (ºC) M M R O R O low temperature high temperature strong bonding weak bonding Methods References To understand this metal-ligand interaction, our research 1. Howarth, A. J., Peters, A., Vermeulen, N., Wang, T., Hupp, J., and Farha, O. Best Practices for the Syn- 0C-O focuses on monitoring the changes in the vibrational frequencies thesis, Activation, and Characterization of Metal-Organic Frameworks. Chem. Mater., 2016, 29, 26-39. 2. Li, P., Li J., Feng, X., Li, J., Hao, Y., Zhang, J., Wang, H., Yin, A., Zhou, J., Ma, X., and Wang, B. Metal-or- -1 as a function of temperature. We hypothesize that metal-carboxylate ganic frameworks with photocatalytic bactericidal activity for integrated air cleaning. Nat. Com., -2 2019, 10 (1), 2177. bonds — which constitute the majority 0 3. Gong, X., Noh, H., Gianneschi, N. C., and Omar K. Farha. Interrogating Kinetic versus Thermody- of MOFs — are especially dynamic, -3 cooling namic Topologies of Metal–Organic Frameworks via Combined Transmission Electron Microscopy -1 with large fraction of these bonds and X-ray Diraction Analysis. J. Am. Chem. Soc., 2019, 141, 15, 6146-6151.-4 1610 1600 1590 1580 existing in unbound states. eat ing heat 4. Redfern, L. R., Farha, O. K. Mechanical properties of metal-organic frameworks. Chem. Sci., 2019, -2 W avenum ber (cm −1) h ing 10, 10666. -3 5. Gaillac, R., Pullumbi, P., and Coudert, F.-X. Melting of Zeolitic Imidazolate Frameworks with Dier- 0 ent Topologies: Insight from First-Principles Molecular Dynamics. J. Phys. Chem. C, 2018, 122, 6730− -4 6736. -1 1610 1600 1590 1580 Wavenumber (cm−1) The dynamicity of metal-carboxylate The wavenumber of the vibrational -2 stretches that connect the building mode changes with respect to tempera- blocks of the frameworks can be ob- ture. Opaque markers are the values -3 served by temperature-dependent Dif- fitted to a Gaussian function and trans- Higher T, more B, fuse Reflectance IR spectroscopy. parent markers are the experimental -4 smaller wavenumber 1610 1600 1590 1580 Shown above is the symmetric vibra- values. Wavenumber (cm−1) tional mode of C-O in MIL-125. Subtracted Reflectance (%) Normalized Reflectance Normalized Reflectance % Reflectance % Reflectance Wavenumber (cm-1)