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1. Structural Insights into Ni(II), Cu(II), and Zn(II) Coordination Complexes of Arylazoformamide and Arylazothioformamide Ligands

   https://doi.org/10.3390/cryst15100869  

   Tiwari, Laxmi; Nelson, Jake; Waynant, Kristopher V (October 2025, Crystals)

   Understanding how redox-active ligands coordinate to metal centers of different oxidation states is essential for applications ranging from metal remediation and recycling to drug discovery. In this study, coordination complexes of nickel(II), copper(II), and zinc(II) chloride salts were synthesized by mixing the salts with either arylazoformamide (AAF) or arylazothioformamide (ATF) ligands in toluene or methanol. The AAF and ATF ligands coordinate through their 1,3-heterodienes, N=N–C=O and N=N–C=S, respectively, and, due to their known strong binding, the piperidine and pyrrolidine formamide units were selected, as was the electron-donating methoxy group on the aryl ring. A total of 12 complexes were obtained, representing potential chelation events from ligand-driven oxidation of zerovalent metals and/or coordination of oxidized metal salts. The X-ray crystallography revealed a range of coordination patterns. Notably, the Cu(II)Cl2 complexes, in the presence of ATF, produce [ATF-CuCl]2 dimers, supporting a potential reduction event at the copper, while other metals with ATF and all metals with AAF remain in the 2+ oxidation state. Hirshfeld analysis was performed on all complexes, and it was found that most interactions across the complexes were dominated by H…H, followed by Cl…H/H…Cl, with metals showing very little to no interaction with other atoms. Spectroscopic techniques such as UV–VIS absorption, NMR (when diamagnetic), and FTIR, in addition to electrochemical studies support the metal–ligand coordination. 

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2. Dendritic Pillar[6]Arenes with Fixed Planar Chirality for Stereoselective Inclusions in Water: A Case of Facile Differentiation of Cocaine Adulterants, Levamisole and Dexamisole

   https://doi.org/10.1002/anie.202514676  

   Kumar, Nitesh; Karmakar, Pratik; Politeski, Matthew D; Hansen, Alexandar R; Ward, Carson E; Mortensen, Christopher; Hadad, Christopher M; Pratumyot, Kornkanya; Badjić, Jovica D (October 2025, Angewandte Chemie International Edition)

   Abstract We describe the preparation, conformational dynamics, and stereoselective recognition characteristics of water‐soluble pillar[6]arenespS–2¹²⁻andpR–2¹²⁻. These two novel and diastereomeric cavitands comprise a 2,5‐bis(ethoxy)pillar[6]arene core with one of six phenylene ring conjugated to two hexaanionic dendrons. Each dendron includes an (S)−glutamic acid amidated with twotris‐carboxylic Behera's amines. CavitandspS–2¹²⁻andpR–2¹²⁻were obtained in six synthetic steps and resolved by column chromatography. The results of¹H NMR and circular dichroism spectroscopic measurements are in line withpS/pR–2¹²⁻having unidirectional orientation of alkoxy substituents (i.e., planar chirality) and no observable interconversion for, at least, 2 weeks. Computational studies supported with¹H DOSY NMR measurements revealed that sufficiently bulky dendrons require high activation energy to pass through the pillararene's cylindrical cavity therefore inhibiting rotation of the phenylene holding them. With the unique and chiral binding pocket,pS–2¹²⁻(pR–2¹²⁻) formed inclusion complexes with cocaine adulterants levamisole and dexamisole (K_d > mM), with their racemic mixture showing separate¹H NMR spectroscopic resonances. In this way, dendritic pillar[6]arenes can be used as chiral shift reagents for determining enantiopurity of pharmaceuticals but also for examining a variety of chiral recognition processes, sensing of chiral molecules, and stereoselective sequestrations in aqueous media. 

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3. Synthesis, structural characterization and NMR studies of group 10 metal complexes with macrocyclic amine N-heterocyclic carbene ligands

   https://doi.org/10.1039/C7DT04666A  

   Lu, Taotao; Liu, Zhiming; Steren, Carlos A.; Fei, Fan; Cook, Tabitha M.; Chen, Xue-Tai; Xue, Zi-Ling (January 2018, Dalton Transactions)

   A series of Ni( ii ), Pd( ii ) and Pt( ii ) complexes [ML][PF 6 ] 2 [L = L 1 , M = Ni ( 1 ), Pd ( 2 ), Pt ( 3 ); L = L 2 , M = Ni ( 4 ), Pd ( 5 ), Pt ( 6 )] and [Pt(L 2 )(acac)] ( 7 ) have been prepared by the reactions of two tetradentate macrocyclic amine-NHC ligand precursors, [H 2 L 1 ][PF 6 ] 2 and [H 2 L 2 ][PF 6 ] 2 , with Ni(OAc) 2 ·4H 2 O, Pd(OAc) 2 and Pt(acac) 2 in the presence of NaOAc. Complex 7 is isolated along with 6 from the same reaction between [H 2 L 2 ][PF 6 ] 2 and Pt(acac) 2 . There are two atropisomers in 1–3 and two achiral conformers in 4–6 . The crystal structures of 1–3 and one conformer of 4–6 ( 4a–6a ) have been determined by single-crystal X-ray diffraction studies. The metal ion is found to reside in the cavity of the macrocyclic ring and adopts a square-planar configuration. Detailed NMR studies including variable-temperature NMR spectroscopy reveal a dynamic interconverting process between two atropisomers of 1–3 in the solutions via a ring twisting mechanism. Two conformers in the equilibrated solution of 4–6 , probably arising from the orientation of two amine N–H bonds with respect to the coordination plane, exchange slowly. Time-dependent 1 H NMR spectra show that one conformer ( 4a–6a ) in solution converts into the other ( 4b–6b ) via the inversion of the nitrogen atom. 

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4. Self assembled cages with mechanically interlocked cucurbiturils

   https://doi.org/10.1080/10610278.2021.1908546  

   Brady, Kimberly G.; Liu, Bingqing; Li, Xiaopeng; Isaacs, Lyle (October 2021, Supramolecular Chemistry)

   null (Ed.)

   We report preparation of (bis)aniline ligand 4 which contains a central viologen binding domain and its subcomponent self-assembly with aldehyde 5 and Fe(OTf)2 in CH3CN to yield tetrahedral assembly 6. Complexation of ligand 4 with CB[7] in the form of CB[7]•4•2PF6 allows the preparation of assembly 7 which contains an average of 1.95 (range 1-3) mechanically interlocked CB[7] units. Assemblies 6 and 7 are hydrolytically unstable in water due to their imine linkages. Redesign of our system with water stable 2,2’-bipyridine end groups was realized in the form of ligands 11 and 16 which also contain a central viologen binding domain. Self-assembly of 11 with Fe(NTf2)2 gave tetrahedral MOP 12 as evidenced by 1H NMR, DOSY, and mass spectrometric analysis. In contrast, isomeric ligand 16 underwent self-assembly with Fe(OTf)2 to give cubic assembly 17. Precomplexation of ligands 11 and 16 with CB[7] gave the acetonitrile soluble CB[7]•11•2PF6 and CB[7]•16•2PF6 complexes. Self-assembly of CB[7]•11•2PF6 with Fe(OTf)2 gave tetrahedron 13 which contains on average 1.8 mechanically interlocked CB[7] units as determined by 1H NMR, DOSY, and ESI-MS analysis. Self-assembly of CB[7]•16•2PF6 with Fe(OTf)2 gave cube 13 which contains 6.59 mechanically interlocked CB[7] units as determined by 1H NMR and DOSY measurements. 

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5. Thermodynamics of pillararene·guest complexation: blinded dataset for the SAMPL9 challenge

   https://doi.org/10.1039/D1NJ05209H  

   Deng, Chun-Lin; Cheng, Ming; Zavalij, Peter Y.; Isaacs, Lyle (January 2022, New Journal of Chemistry)

   We report an investigation of the complexation between a water soluble pillararene host (WP6) and a panel of hydrophobic cationic guests (G1–G20) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry in phosphate buffered saline. We find that WP6 forms 1 : 1 complexes with K a values in the 10 4 –10 9 M −1 range driven by favorable enthalpic contributions. This thermodynamic dataset serves as blinded data for the SAMPL9 challenge. 

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