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1. Nickel( ii ) complexes based on dithiolate–polyamine binary ligand systems: crystal structures, hirshfeld surface analysis, theoretical study, and catalytic activity study on photocatalytic hydrogen generation

   https://doi.org/10.1039/d1dt00352f  

   Adhikari, Suman ; Bhattacharjee, Tirtha ; Bhattacharjee, Sharmila ; Daniliuc, Constantin Gabriel ; Frontera, Antonio ; Lopato, Eric M. ; Bernhard, Stefan ( April 2021 , Dalton Transactions)

   null (Ed.)

   To ascertain the influence of binary ligand systems [1,1-dicyanoethylene-2,2-dithiolate (i-mnt −2 ) and polyamine {tetraen = tris(2-aminoethyl)amine, tren = diethylene triamine and opda = o -phenylenediamine}] on the coordination modes of the Ni( ii ) metal center and resulting supramolecular architectures, a series of nickel( ii ) thiolate complexes [Ni(tetraen)(i-mnt)](DMSO) ( 1 ), [Ni 2 (tren) 2 (i-mnt) 2 ] ( 2 ), and [Ni 2 (i-mnt) 2 (opda) 2 ] n ( 3 ) have been synthesized in high yield in one step in water and structurally characterized by single crystal X-ray crystallography and spectroscopic techniques. X-ray diffraction studies disclose the diverse i-mnt −2 coordination to the Ni +2 center in the presence of active polyamine ligands, forming a slightly distorted octahedral geometry (NiN 4 S 2 ) in 1 , square planar (NiS 4 ) and distorted octahedral geometries (NiN 6 ) in the bimetallic co-crystallized aggregate of cationic [Ni(tren) 2 ] +2 and anionic [Ni(i-mnt) 2 ] −2 in 2 , and a one dimensional (1D) polymeric chain along the [100] axis in 3 , having consecutive square planar (NiS 4 ) and octahedral (NiN 6 ) coordination kernels. The N–H⋯O, N–H⋯S, N–H⋯N, N–H⋯S, N–H⋯N, and N–H⋯O type hydrogen bonds stabilize the supramolecular assemblies in 1 , 2 , and 3 respectively imparting interesting graph-set-motifs. The molecular Hirshfeld surface analyses (HS) and 2D fingerprint plots were utilized for decoding all types of non-covalent contacts in the crystal networks. Atomic HS analysis of the Ni +2 centers reveals significant Ni–N metal–ligand interactions compared to Ni–S interactions. We have also studied the unorthodox interactions observed in the solid state structures of 1–3 by QTAIM and NBO analyses. Moreover, all the complexes proved to be highly active water reduction co-catalysts (WRC) in a photo-catalytic hydrogen evolution process involving iridium photosensitizers, wherein 2 and 3 having a square planar arrangement around the nickel center(s) – were found to be the most active ones, achieving 1000 and 1119 turnover numbers (TON), respectively. 

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2. Synthesis and supramolecular organization of the iodide and triiodides of a polycyclic adamantane-based diammonium cation: the effects of hydrogen bonds and weak I⋯I interactions

   https://doi.org/10.1039/D0CE01730B  

   Mezentsev-Cherkes, Ivan A. ; Shestimerova, Tatiana A. ; Medved'ko, Aleksei V. ; Kalinin, Mikhail A. ; Kuznetsov, Alexey N. ; Wei, Zheng ; Dikarev, Evgeny V. ; Vatsadze, Sergey Z. ; Shevelkov, Andrei V. ( March 2021 , CrystEngComm)

   A careful selection of organic and inorganic components enables the production of unusual structure types with promising practical properties by facile syntheses. In this paper, we describe novel supramolecular architectures comprising organic adamantane-like divalent building blocks and iodide or polyiodide anions. Highly acidic conditions facilitated the formation of a doubly protonated organic ligand out of 5,7-dimethyl-1,3-diazaadamantane that generates three different crystal structures with inorganic counterions. In these structures, cationic substructures are constructed by transforming neutral organic ligands into [(C 10 N 2 H 20 )I] + or [(C 10 N 2 H 20 )(H 2 O)] 2+ cations, which crystallize with charge-compensating iodine-based anions of different complexities. All three crystal structures are characterized by various noncovalent forces, ranging from strong (N)H⋯I, (O)H⋯I, and (N)H⋯O hydrogen bonds to secondary and weak I⋯I interactions. Raman and diffuse reflectance spectroscopy as well as DFT calculations were employed to describe the electronic structures and optical properties of new supramolecular architectures, with particular attention to the role of non-covalent interactions. 

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3. Synthesis and structural characterization of metal complexes with macrocyclic tetracarbene ligands

   https://doi.org/10.1039/C7NJ02485A  

   Fei, Fan ; Lu, Taotao ; Chen, Xue-Tai ; Xue, Zi-Ling ( January 2017 , New Journal of Chemistry)

   Fourteen Ag( i ), Au( i ), Ni( ii ), Pd( ii ), and Pt( ii ) complexes with macrocyclic tetradentate N-heterocyclic carbene (NHC) ligands were prepared via reactions between three macrocyclic tetrabenzimidazolium salts and metal precursors. All except two Au complexes were characterized using single-crystal X-ray diffraction. Three different structures, including a trinuclear one containing a NHC–Ag–(H 2 O) moiety and a hexanuclear propeller-like supramolecular assembly, are found for Ag–NHC complexes. Nine complexes of group 10 metal ions adopt square-planar geometry, in which the different ring-sizes of the macrocyclic tetracarbene ligands lead to a variation of metal–carbene bond lengths. π–π stackings are observed between the rigid aromatic benzimidazole rings in the nickel group complexes. 

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4. Single-conformation spectroscopy of cold, protonated D PG-containing peptides: switching β-turn types and formation of a sequential type II/II′ double β-turn

   https://doi.org/10.1039/D1CP04852J  

   Lawler, John T. ; Harrilal, Christopher P. ; DeBlase, Andrew F. ; Sibert, Edwin L. ; McLuckey, Scott A. ; Zwier, Timothy S. ( January 2022 , Physical Chemistry Chemical Physics)

   d -Proline ( D Pro, D P) is widely utilized to form β-hairpin loops in engineered peptides that would otherwise be unstructured, most often as part of a D PG sub-unit that forms a β-turn. To observe whether D PG facilitated this effect in short protonated peptides, conformation specific IR–UV double resonance photofragment spectra of the cold (∼10 K) protonated D P and L P diastereomers of the pentapeptide YAPGA was carried out in the hydride stretch (2800–3700 cm −1 ) and amide I/II (1400–1800 cm −1 ) regions. A model localized Hamiltonian was developed to better describe the 1600–1800 cm −1 region commonly associated with the amide I vibrations. The CO stretch fundamentals experience extensive mixing with the N–H bending fundamentals of the NH 3 + group in these protonated peptides. The model Hamiltonian accounts for experiment in quantitative detail. In the D P diastereomer, all the population is funneled into a single conformer which presented as a type II β-turn with A and D P in the i + 1 and i + 2 positions, respectively. This structure was not the anticipated type II′ β-turn across D PG that we had hypothesized based on solution-phase propensities. Analysis of the conformational energy landscape shows that both steric and charge-induced effects play a role in the preferred formation of the type II β-turn. In contrast, the L P isomer forms three conformations with very different structures, none of which were type II/II′ β-turns, confirming that L PG is not a β-turn former. Finally, single-conformation spectroscopy was also carried out on the extended peptide [YAA D PGAAA + H] + to determine whether moving the protonated N-terminus further from D PG would lead to β-hairpin formation. Despite funneling its entire population into a single peptide backbone structure, the assigned structure is not a β-hairpin, but a concatenated type II/type II′ double β-turn that displaces the peptide backbone laterally by about 7.5 Å, but leaves the backbone oriented in its original direction. 

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5. Crystal structures of three copper(II)–2,2′-bipyridine (bpy) compounds, [Cu(bpy) 2 (H 2 O)][SiF 6 ]·4H 2 O, [Cu(bpy) 2 (TaF 6 ) 2 ] and [Cu(bpy) 3 ][TaF 6 ] 2 and a related coordination polymer, [Cu(bpy)(H 2 O) 2 SnF 6 ] n

   https://doi.org/10.1107/S2056989021000633  

   Nisbet, Matthew L. ; Hiralal, Emily ; Poeppelmeier, Kenneth R. ( February 2021 , Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   We report the hydrothermal syntheses and crystal structures of aquabis(2,2′-bipyridine-κ 2 N , N ′)copper(II) hexafluoridosilicate tetrahydrate, [Cu(bpy) 2 (H 2 O)][SiF 6 ]·4H 2 O (bpy is 2,2′-bipyridine, C 10 H 8 N 2 ), (I), bis(2,2′-bipyridine-3κ 2 N , N ′)-di-μ-fluorido-1:3κ 2 F : F ;2:3κ 2 F : F -decafluorido-1κ 5 F ,2κ 5 F -ditantalum(V)copper(II), [Cu(bpy) 2 (TaF 6 ) 2 ], (II), tris(2,2′-bipyridine-κ 2 N , N ′)copper(II) bis[hexafluoridotantalate(V)], [Cu(bpy) 3 ][TaF 6 ] 2 , (III), and catena -poly[[diaqua(2,2′-bipyridine-κ 2 N , N ′)copper(II)]-μ-fluorido-tetrafluoridotin-μ-fluorido], [Cu(bpy)(H 2 O) 2 SnF 6 ] n , (IV). Compounds (I), (II) and (III) contain locally chiral copper coordination complexes with C 2 , D 2 , and D 3 symmetry, respectively. The extended structures of (I) and (IV) are consolidated by O—H...F and O—H...O hydrogen bonds. The structure of (III) was found to be a merohedral (racemic) twin. 

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