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1. Isoreticular Tolerance and Phase Selection in the Synthesis of Multi‐Module Metal–Organic Frameworks for Gas Separation and Electrocatalytic OER

   https://doi.org/10.1002/anie.202422635  

   Xiao, Yuchen; Bu, Xianhui; Feng, Pingyun (January 2025, Angewandte Chemie International Edition)

   Abstract Although metal–organic frameworks are coordination‐driven assemblies, the structural prediction and design using metal‐ligand interactions can be unreliable due to other competing interactions. Leveraging non‐coordination interactions to develop porous assemblies could enable new materials and applications. Here, we use a multi‐module MOF system to explore important and pervasive impact of ligand‐ligand interactions on metal‐ligand as well as ligand‐ligand co‐assembly process. It is found that ligand‐ligand interactions play critical roles on the scope or breakdown of isoreticular chemistry. With cooperative di‐ and tri‐topic ligands, a family of Ni‐MOFs has been synthesized in various structure types including partitioned MIL‐88‐acs (pacs), interruptedpacs(i‐pacs), and UMCM‐1‐muo. A new type of isoreticular chemistry on the muo platform is established between two drastically different chemical systems. The gas sorption and electrocatalytic studies were performed that reveal excellent performance such as high C₂H₂/CO₂selectivity of 21.8 and high C₂H₂uptake capacity of 114.5 cm³/g at 298 K and 1 bar. 

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2. Chiral and Achiral Crystal Structures of Au ₂₅ (PET) ₁₈ ⁰ Reveal Effects of Ligand Rotational Isomerization on Optoelectronic Properties

   https://doi.org/10.1002/chem.202202760  

   Kuda‐Singappulige, Gowri_Udayangani; Window, Phillip_S; Hosier, Christopher_A; Anderson, Ian_D; Aikens, Christine_M; Ackerson, Christopher_J (November 2023, Chemistry – A European Journal)

   Abstract The crystal structures of 4 ligand‐rotational isomers of Au₂₅(PET)₁₈are presented. Two new ligand‐rotational isomers are revealed, and two higher‐quality structures (allowing complete solution of the ligand shell) of previously solved Au₂₅(PET)₁₈clusters are also presented. One of the structures lacks an inversion center, making it the first chiral Au₂₅(SR)₁₈structure solved. These structures combined with previously published Au₂₅(SR)₁₈structures enable an analysis of the empirical ligand conformation landscape for Au₂₅(SR)₁₈clusters. This analysis shows that the dihedral angles within the PET ligand are restricted to certain observable values, and also that the dihedral angle values are interdependent, in a manner reminiscent of biomolecule dihedral angles such as those in proteins and DNA. The influence of ligand conformational isomerism on optical and electronic properties was calculated, revealing that the ligand conformations affect the nanocluster absorption spectrum, which potentially provides a way to distinguish between isomers at low temperature. 

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3. Metal-ligand interactions in a redox active ligand system. Electrochemistry and spectroscopy of [M(dipyvd)2]n+ (M=Zn, Ni, n=0, 1, 2)

   https://doi.org/10.3389/fchem.2023.1295289  

   Fleming, Connor; Vu, Son; Brook, David_J R; Agrestini, Stefano; Pellegrin, Eric; DaRos, Jeffrey (November 2023, Frontiers in Chemistry)

   Reaction of nickel and zinc triflates with the tridentate leucoverdazyl 1-isopropyl-3,5-di (2′-pyridyl)-6-oxo-2H-tetrazine (dipyvdH) and triethylamine resulted in the neutral coordination compounds M(dipyvd)₂(M = Ni,Zn). In acetonitrile, both compounds undergo two one electron oxidation processes, Zn (dipyvd)₂ at −0.28 V and −0.12 V and Ni(dipyvd)₂ at −0.32 V and −0.15 V vs ferrocene/ferricenium. Oxidations are ligand based resulting in an intermediate mixed valence species and a cationic bis(verdazyl) compound respectively. Oxidation of the ligand changes a localized, antiaromatic, non-planar 8π electron anion to a planar, delocalized 7π electron radical. The change in ligand structure results in an increase in the octahedral ligand field splitting from 10,500 cm^–1to ∼13,000 cm^–1, suggesting an increase in the pi acceptor character of the ligand. In the mixed valence species, spectroscopic data suggests minimal interaction between ligands mediated by the metal center; i.e., these are class I-II systems in the Robin-Day classification. 

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4. Metal- versus ligand-centered reactivity of a cobalt-phenylenediamide complex with electrophiles

   https://doi.org/10.1039/d4dt01655f  

   Zou, Minzhu; Kuruppu, Sewwandi; Emge, Thomas J; Waldie, Kate M (August 2024, Dalton Transactions)

   A cobalt complex with a phenylenediamide redox-active ligand reacts with an electrophilic trifluoromethyl source to generate a robust Co–CF₃bond, while in contrast, treatment with alkyl electrophiles occurs at the ligand scaffold. 

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5. Structural determinants driving homoserine lactone ligand selection in the Pseudomonas aeruginosa LasR quorum-sensing receptor

   https://doi.org/10.1073/pnas.1817239116  

   McCready, Amelia R.; Paczkowski, Jon E.; Henke, Brad R.; Bassler, Bonnie L. (December 2018, Proceedings of the National Academy of Sciences)

   Quorum sensing is a cell–cell communication process that bacteria use to orchestrate group behaviors. Quorum sensing is mediated by signal molecules called autoinducers. Autoinducers are often structurally similar, raising questions concerning how bacteria distinguish among them. Here, we use thePseudomonas aeruginosaLasR quorum-sensing receptor to explore signal discrimination. The cognate autoinducer, 3OC₁₂homoserine lactone (3OC₁₂HSL), is a more potent activator of LasR than other homoserine lactones. However, other homoserine lactones can elicit LasR-dependent quorum-sensing responses, showing that LasR displays ligand promiscuity. We identify mutants that alter which homoserine lactones LasR detects. Substitution at residue S129 decreases the LasR response to 3OC₁₂HSL, while enhancing discrimination against noncognate autoinducers. Conversely, the LasR L130F mutation increases the potency of 3OC₁₂HSL and other homoserine lactones. We solve crystal structures of LasR ligand-binding domains complexed with noncognate autoinducers. Comparison with existing structures reveals that ligand selectivity/sensitivity is mediated by a flexible loop near the ligand-binding site. We show that LasR variants with modified ligand preferences exhibit altered quorum-sensing responses to autoinducers in vivo. We suggest that possessing some ligand promiscuity endows LasR with the ability to optimally regulate quorum-sensing traits. 

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