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1. Selective crystallization of four bis(phthalocyaninato)lanthanoid( iii ) polymorphs

   https://doi.org/10.1039/d1ce00936b  

   Dailey, Maegan ; Besson, Claire ( October 2021 , CrystEngComm)

   Bis(phthalocyaninato)lanthanoid( iii ) (LnPc 2 ) complexes have attracted significant attention for their exceptional optical, electronic and magnetic properties. Crystallization of these compounds usually requires cumbersome methods such as sublimation and electrocrystallization, which is a significant limitation to both structural determinations and the preparation of high purity materials at scale. We report here the selective crystallization of four polymorphs of LnPc 2 obtained exclusively by the slow evaporation of saturated solutions. The obtained phase depends on the initial oxidation state of the LnPc 2 molecule and the choice of solvent. Single-crystal X-ray diffraction studies were used to determine 14 new structures including Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, Er and Yb, as well as correct previous mis-identifications from the literature. We provide a detailed comparison of molecular structure and crystal packing in all LnPc 2 polymorphs. The primary feature in all phases is columnar stacking based on parallel π–π interactions, with a variety of slip angles within those stacks as well as secondary interactions between them. Chemical redox and acid–base titrations, performed on re-dissolved crystals demonstrate that LnPc 2 + and LnPc 2 − are easily obtained through weak oxidizing and reducing agents, respectively. Additionally, we show that the protonated form of the NdPc 2 − complex has a nearly identical UV-vis spectrum to that of neutral NdPc 2 , explaining some of the confusion over chemical composition in previously published literature. 

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2. 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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3. Synthesis of SCO FeII complexes with novel π-extended 2,2'-biimidazole ligands

   Yergeshbayeva, S. ; Shatruk, M. ( April 2021 , National Meeting of the American Chemical Society)

   null (Ed.)

   Spin crossover (SCO) is a phenomenon observed for certain transition metal complexes with electronic configuration 3d4-3d7. The conversion between the low-spin (LS) and high-spin (HS) states is usually driven by a variety of external perturbations, such as temperature, pressure, or light. The switching between the enthalpically preferred LS state and entropically favorable HS state is accompanied by dramatic changes in the metal-ligand bond lengths, unit cell volume, optical absorption spectrum, and magnetic susceptibility.1 These changes make SCO materials suitable for applications in sensors, memory, and display devices. One of the central challenges in the SCO research is to initiate strongly cooperative interactions known to lead to abrupt spin transitions and thermal hysteresis that can be harvested as a memory effect. One of the strategies to enhance the cooperativity is to design SCO complexes with supramolecular interactions such as π-stacking of aromatic fragments or hydrogen bonding.2 In this work, we report syntheses and characterization of heteroleptic complexes of [Fe(tpma)(L)](ClO4)2 (tpma = tris(pyridin-2-ylmethyl)amine) with novel π-extended biimidazole-type ligands (L) bearing 2,3-dimethyl-naphthalene-, 6,7-dimethyl-2,3-diphenyl-quinoxaline, and 2,3-dimethyl-anthracene pendant fragments. Solvent-free naphthalene-functionalized complex [Fe(tpma)(xnap-bim)](ClO4)2 exhibits abrupt spin transition at T1/2 = 127K with a narrow 1 K hysteresis loop. In contrast, polymorph of this complex that contains one interstitial molecules of pyridine exhibits gradual SCO. Anthracene-functionalized complex [Fe(tpma)(anthra-bim)](ClO4)2 also crystallizes as two polymorphs. Structural studies at 100, 230, and 300 K revealed dramatic changes in the N-Fe-N biting angles and Fe-N distances, indicating the occurrence of temperature-induced SCO. Complex [Fe(tpma)(quin-bim)](ClO4)2 (quin-bim = 6,7-dimethyl-2,3-diphenyl-quinoxaline-2,2’-biimidazole) showed only HS state at 100 and 230 K. In the crystal packing the mononuclear cations form stacks along b axis. We discuss how the observed magnetic behavior correlates with changes in the crystal packing and interactions between the pendant aromatic substituents on the aforementioned complexes. 

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4. Crystal structures of two copper(I)–6,6′-dimethyl-2,2′-bipyridyl (dmbpy) compounds, [Cu(dmbpy) 2 ] 2 [ M F 6 ]· x H 2 O ( M = Zr, Hf; x = 1.134, 0.671)

   https://doi.org/10.1107/S2056989021007295  

   Wang, Yiran ; Nisbet, Matthew L. ; Poeppelmeier, Kenneth R. ( August 2021 , Acta Crystallographica Section E Crystallographic Communications)

   The syntheses and crystal structures of two bimetallic molecular compounds, namely, bis[bis(6,6′-dimethyl-2,2′-bipyridine)copper(I)] hexafluoridozirconate(IV) 1.134-hydrate, [Cu(dmbpy) 2 ] 2 [ZrF 6 ]·1.134H 2 O (dmbpy = 6,6′-dimethyl-2,2′-bipyridyl, C 12 H 12 N 2 ), (I), and bis[bis(6,6′-dimethyl-2,2′-bipyridine)copper(I)] hexafluoridohafnate(IV) 0.671-hydrate, [Cu(dmbpy) 2 ] 2 [HfF 6 ]·0.671H 2 O, (II), are reported. Apart from a slight site occupany difference for the water molecule of crystallization, compounds (I) and (II) are isostructural, featuring isolated tetrahedral cations of copper(I) ions coordinated by two dmbpy ligands and centrosymmetric, octahedral anions of fluorinated early transition metals. The tetrahedral environments of the copper complexes are distorted owing to the steric effects of the dmbpy ligands. The extended structures are built up through Coulombic interactions between cations and anions and π–π stacking interactions between heterochiral Δ- and Λ-[Cu(dmbpy) 2 ] + complexes. A comparison between the title compounds and other [Cu(dmbpy) 2 ] + compounds with monovalent and bivalent anions reveals a significant influence of the cation-to-anion ratio on the resulting crystal packing architectures, providing insights for future crystal design of distorted tetrahedral copper compounds. 

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5. Examining polymer‐protein biophysical interactions with small‐angle x‐ray scattering and quartz crystal microbalance with dissipation

   https://doi.org/10.1002/jbm.a.37479  

   Upadhya, Rahul ; Di Mare, Elena ; Tamasi, Matthew J. ; Kosuri, Shashank ; Murthy, N. Sanjeeva ; Gormley, Adam J. ( December 2022 , Journal of Biomedical Materials Research Part A)

   Polymer‐protein hybrids can be deployed to improve protein solubility and stability in denaturing environments. While previous work used robotics and active machine learning to inform new designs, further biophysical information is required to ascertain structure–function behavior. Here, we show the value of tandem small‐angle x‐ray scattering (SAXS) and quartz crystal microbalance with dissipation (QCMD) experiments to reveal detailed polymer‐protein interactions with horseradish peroxidase (HRP) as a test case. Of particular interest was the process of polymer‐protein complex formation under thermal stress whereby SAXS monitors formation in solution while QCMD follows these dynamics at an interface. The radius of gyration (R_g) of the protein as measured by SAXS does not change significantly in the presence of polymer under denaturing conditions, but thickness and dissipation changes were observed in QCMD data. SAXS data with and without thermal stress were utilized to create bead models of the potential complexes and denatured enzyme, and each model fit provided insight into the degree of interactions. Additionally, QCMD data demonstrated that HRP deforms by spreading upon surface adsorption at low concentration as shown by longer adsorption times and smaller frequency shifts. In contrast, thermally stressed and highly inactive HRP had faster adsorption kinetics. The combination of SAXS and QCMD serves as a framework for biophysical characterization of interactions between proteins and polymers which could be useful in designing polymer‐protein hybrids.

    

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