Halogen Bonding Propensity in Solution: Direct Observation and Computational Prediction

Halogen‐bonded complexes are often designed by consideration of electrostatic potential (ESP) predictions. ESP predictions do not capture the myriad variables associated with halogen bond (XB) donors and acceptors; thus, binding interaction cannot be quantitatively predicted. Here, a discrepancy between predictions based on ESP energy difference (ΔVs) and computed gas phase binding energy (ΔEbind) motivated the experimental determination of the relative strength of halogen bonding interactions in solution by Raman spectroscopic observation of complexes formed from interacting five iodobenzene‐derived XB donors and four pyridine XB acceptors. Evaluation of ΔEbind coupled with absolutely‐localized molecular orbital energy decomposition analysis (ALMO‐EDA) deconvolutes halogen bonding energy contributions and reveals a prominent role for charge transfer (CT) interactions. Raman spectra reveal ΔEbind accurately predicts stronger interactions within iodopentafluorobenzene (IPFB) complexes than with 1‐iodo‐3,5‐dinitrobenzene (IDNB) complexes even though IPFB has similar electrostatics to IDNB and contains a smaller σ‐hole.Strongly activated halogen bond donors give rise to observable bound and unbound states in Raman spectroscopy when paired with good halogen bond acceptors. The two strongest halogen bond donors examined have almost identical electrostatic potentials, but differ vastly in theoretical binding affinity and experimental halogen bonding strength. The energy terms giving rise to this behavior are elucidated by energy decomposition analysis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/171007/1/chem202102522.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/171007/2/chem202102522_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/171007/3/chem202102522-sup-0001-misc_information.pd

Two‐Dimensional Crystals from Reduced Symmetry Analogues of Trimesic Acid

The two‐dimensional assembly of multicarboxylated arenes is explored at the liquid–graphite interface using scanning tunneling microscopy. Symmetry variations were introduced via phenylene spacer addition and the influence of these perturbations on the formation of hydrogen‐bonded motifs from an alkanoic acid solvent is observed. This work demonstrates the importance of symmetry in 2D crystal formation and draws possible links of this behavior to prediction of coordination modes in three‐dimensional coordination polymers.Crystal clear: 2D assemblies of a series of five reduced symmetry multicarboxylated molecules (such as depicted) related to trimesic acid, a prototypical high symmetry adsorbate, through the addition of phenylene spacers, are explored at the liquid–graphite interface using scanning tunneling microscopy. The 2D assembly behaviors of these multicarboxylate molecules mirror their coordination modes in 3D coordination polymers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110860/1/chem_201406332_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/110860/2/5954_ftp.pd

Functional Group Effects on the Enthalpy of Adsorption for Self-Assembly at the Solution/Graphite Interface

The thermodynamics of self-assembly have long been explored by either experimental or theoretical investigations which are often unable to account for all the factors influencing the assembly process. This work interrogates the thermodynamics of self-assembly at a liquid/solid interface by measuring the enthalpy of adsorption encompassing analyte–analyte, analyte–solvent, analyte–substrate, and solvent–substrate interactions. Comparison of the experimental data with computed lattice energies for the relevant monolayers across a series of aliphatic analytes reveals similar ordering within the series, with the exceptions of the fatty acid and bromoalkane adsorbates. Such a discrepancy could arise when the lattice energies do not account for important interactions, such as analyte–analyte interactions in solution. Flow microcalorimetry provides a uniquely inclusive view of the thermodynamic events relevant to self-assembly at the liquid/solid interface

MOFâ 5â Polystyrene: Direct Production from Monomer, Improved Hydrolytic Stability, and Unique Guest Adsorption

An unprecedented mode of reactivity of Zn4Oâ based metalâ organic frameworks (MOFs) offers a straightforward and powerful approach to polymerâ hybridized porous solids. The concept is illustrated with the production of MOFâ 5â polystyrene wherein polystyrene is grafted and uniformly distributed throughout MOFâ 5 crystals after heating in pure styrene for 4â 24â h. The surface area and polystyrene content of the material can be fineâ tuned by controlling the duration of heating styrene in the presence of MOFâ 5. Polystyrene grafting significantly alters the physical and chemical properties of pristine MOFâ 5, which is evident from the unique guest adsorption properties (solvatochromic dye uptake and improved CO2 capacity) as well as the dramatically improved hydrolytic stability of composite. Based on the fact that MOFâ 5 is the best studied member of the structure class, and has been produced at scale by industry, these findings can be directly leveraged for a range of current applications.MOFs packed with polystyrene: An unprecedented mode of reactivity of one of the best studied metalâ organic frameworks, MOFâ 5, offers a powerful approach to polymerâ hybridized porous solids. A MOFâ 5â polystyrene (MOFâ 5â PS) composite was directly produced from the monomer styrene. In the MOFâ 5â PS composites, polystyrene is grafted and uniformly distributed throughout, which leads to enhanced hydrolytic stability and unique guest adsorption.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134282/1/anie201606926_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134282/2/anie201606926-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134282/3/anie201606926.pd

MOFâ 5â Polystyrene: Direct Production from Monomer, Improved Hydrolytic Stability, and Unique Guest Adsorption

An unprecedented mode of reactivity of Zn4Oâ based metalâ organic frameworks (MOFs) offers a straightforward and powerful approach to polymerâ hybridized porous solids. The concept is illustrated with the production of MOFâ 5â polystyrene wherein polystyrene is grafted and uniformly distributed throughout MOFâ 5 crystals after heating in pure styrene for 4â 24â h. The surface area and polystyrene content of the material can be fineâ tuned by controlling the duration of heating styrene in the presence of MOFâ 5. Polystyrene grafting significantly alters the physical and chemical properties of pristine MOFâ 5, which is evident from the unique guest adsorption properties (solvatochromic dye uptake and improved CO2 capacity) as well as the dramatically improved hydrolytic stability of composite. Based on the fact that MOFâ 5 is the best studied member of the structure class, and has been produced at scale by industry, these findings can be directly leveraged for a range of current applications.Mit Polystyrol gepackte MOFs: Eine bisher unbekannte Reaktivität eines der am besten untersuchten Metallâ organischen Gerüstmaterialien, MOFâ 5, bietet Zugang zu polymerhybridisierten porösen Festkörpern. Ein MOFâ 5â Polystyrol(MOFâ 5â PS)â Komposit wurde direkt aus dem Monomer Styrol hergestellt. Das Polystyrol ist im MOFâ 5â PSâ Gerüst einheitlich verteilt und bewirkt eine erhöhte Hydrolysestabilität.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134159/1/ange201606926.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134159/2/ange201606926-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134159/3/ange201606926_am.pd

Effects of molecular geometry on the STM image contrast of methyl- and bromo-substituted alkanes and alkanols on graphite

Scanning tunneling microscopy (STM) images have been collected for a series of substituted alkanes and alkanols that form ordered overlayers at room temperature on highly ordered pyrolytic graphite surfaces. Molecules that have been imaged possess an internal bromide, with or without terminal alcohol groups (HO(CH2)(9)CHBr(CH2)(10)OH and H3C(CH2)(16)CHBr(CH2)(16)CH3), an internal -OH group (H3C(CH2)(16)CHOH(CH2)(16)CH3), and an internal methyl group (H3C(CH2)(16)CHCH3(CH2)(16)CH3). These data allow comparison to the STM image contrast reported previously for molecules in which -OH, -Br, and -CH3 groups were located in terminal positions of alkane chains adsorbed onto graphite surfaces. When the functional groups were in gauche positions relative to the alkyl chain, and thus produced molecular features that protruded toward the tip, the functional groups were observed to produce bright regions in a constant current STM image, regardless of the STM contrast behavior observed for these same functional groups when they were in terminal positions of adsorbed alkyl chains. These observations are in excellent agreement with theoretical predictions of the STM behavior of such systems. Additionally, several interesting packing structures have been observed that have yielded insight into the intermolecular forces that control the packing displayed by these overlayers

Dual Modification of MOFs Improves Dispersion and Ionic Conductivity of Mixed Matrix Membranes

Nonaqueous redox flow batteries (NARFBs) are a promising class of energy storage devices, but the lack of a chemically stable, conductive membrane that exhibits size-selectivity over redox-active species prevents their broader implementation. Recently, metal–organic frameworks (MOFs) have been implemented into mixed-matrix membranes (MMMs) for NARFBs, but the effects of the MOF linker functionality on membrane properties are not well-understood. In this work, we develop a series of MOF-based MMMs by blending postsynthetically modified variants of UiO-66-NH2 with poly(ethylene-co-vinyl acetate). The modification of UiO-66-NH2 with sulfate groups initially resulted in poor dispersion throughout the MMMs, but when dual-modified with poly(N-isopropylacrylamide), MOF dispersion throughout the MMM was improved, and ionic conductivity was significantly higher than the UiO-66-NH2 MMMs. Furthermore, the dual-modified MMMs demonstrated excellent size-selectivity by blocking redox active species transport. This work demonstrates a synergy between the MOF functional groups to improve MMM properties critical for the development of practical NARFBs

Metal Effects on the Sensitivity of Isostructural Metal–Organic Frameworks Based on 5‑Amino-3-nitro‑1<i>H</i>‑1,2,4-triazole

Two energetic metal–organic frameworks (MOFs), Co-ANTA and Zn-ANTA, are synthesized from 5-amino-3-nitro-1<i>H</i>-1,2,4-triazole (ANTA) and exhibit superior oxygen balance, density, and thermal stability compared to ANTA. The superior oxygen balance is achieved through a combination of hydroxide ligands and deprotonated linkers. Although the materials are isostructural and have similar density, oxygen balance, and sensitivity to heat, their impact sensitivities are significantly different. Similar to ANTA, Zn-ANTA is fairly insensitive to impact. By contrast, the impact sensitivity of ANTA is increased significantly after coordination polymerization with cobalt. The disparate impact sensitivities of the compounds might be attributed to the different electronic configurations of the metal ions constituting the frameworks