A Barrel‐Shaped Metal‐Organic Blue‐Box Analog with Photo‐/Redox‐Switchable Behavior

International audienceDonor acceptor interactions are ubiquitous in the design and understanding of host-guest complexes. Despite their non-covalent nature, they can readily dictate the self-assembly of complex architectures. Here, we present a photo-/redox-switchable metal-organic nanocapsule, assembled using lanthanide ions and viologen building blocks, that relies on such donor-acceptor interactions. We highlight the potential of this unique barrel-shaped structure for the encapsulation of suitable electron donors, akin to the well-investigated "blue-box" macrocycles. The light-triggered reduction of the viologen units has been investigated by single-crystal-to-single-crystal X-ray diffraction experiments, complemented by magnetic, optical and solid-state electrochemical characterizations. Density functional theory (DFT) calculations were employed to suggest the most likely electron donor in the light-triggered reduction of the viologen-based ligand

Synthesis and Electronic Structure Determination of Uranium(VI) Ligand Radical Complexes

   Pentagonal bipyramidal uranyl complexes of salen ligands, N,N’-bis(3-tert-butyl-(5R)-salicylidene)-1,2-phenylenediamine, in which R = tBu (1a), OMe (1b), and NMe2 (1c), were prepared and the electronic structure of the one-electron oxidized species [1a-c]+ were investigated in solution. The solid-state structures of 1a and 1b were solved by X-ray crystallography, and in the case of 1b an asymmetric UO22+ unit was found due to an intermolecular hydrogen bonding interaction. Electrochemical investigation of 1a-c by cyclic voltammetry showed that each complex exhibited at least one quasi-reversible redox process assigned to the oxidation of the phenolate moieties to phenoxyl radicals. The trend in redox potentials matches the electron-donating ability of the para-phenolate substituents. The electron paramagnetic resonance spectra of cations [1a-c]+ exhibited gav values of 1.997, 1.999, and 1.995, respectively, reflecting the ligand radical character of the oxidized forms, and in addition, spin-orbit coupling to the uranium centre. Chemical oxidation as monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy afforded the one-electron oxidized species. Weak low energy intra-ligand charge transfer (CT) transitions were observed for [1a-c]+ indicating localization of the ligand radical to form a phenolate / phenoxyl radical species. Further analysis using density functional theory (DFT) calculations predicted a localized phenoxyl radical for [1a-c]+ with a small but significant contribution of the phenylenediamine unit to the spin density. Time-dependent DFT (TD-DFT) calculations provided further insight into the nature of the low energy transitions, predicting both phenolate to phenoxyl intervalence charge transfer (IVCT) and phenylenediamine to phenoxyl CT character. Overall, [1a-c]+ are determined to be relatively localized ligand radical complexes, in which localization is enhanced as the electron donating ability of the para-phenolate substituents is increased (NMe2 > OMe > tBu)

Thermal Expansion Behavior of M^I[AuX₂(CN)₂]‑Based Coordination Polymers (M = Ag, Cu; X = CN, Cl, Br)

Two sets of <i>trans-</i>[AuX₂(CN)₂]⁻-based coordination polymer materialsM­[AuX₂(CN)₂] (M = Ag; X = Cl, Br or M = Cu; X = Br) and M­[Au­(CN)₄] (M = Ag, Cu)were synthesized and structurally characterized and their dielectric constants and thermal expansion behavior explored. The M­[AuX₂(CN)₂] series crystallized in a tightly packed, mineral-like structure featuring 1-D <i>trans-</i>[AuX₂(CN)₂]⁻-bridged chains interconnected via a series of intermolecular Au···X and M···X (M = Ag, Cu) interactions. The M­[Au­(CN)₄] series adopted a 2-fold interpenetrated 3-D cyano-bound framework lacking any weak intermolecular interactions. Despite the tight packing and the presence of intermolecular interactions, these materials exhibited decreased thermal stability over unbound <i>trans-</i>[AuX₂(CN)₂]⁻ in [^<i>n</i>Bu₄N]­[AuX₂(CN)₂]. A significant dielectric constant of up to ε_r = 36 for Ag­[AuCl₂(CN)₂] (1 kHz) and a lower ε_r = 9.6 (1 kHz) for Ag­[Au­(CN)₄] were measured and interpreted in terms of their structures and composition. A systematic analysis of the thermal expansion properties of the M­[AuX₂(CN)₂] series revealed a negative thermal expansion (NTE) component along the cyano-bridged chains with a thermal expansion coefficient (α_CN) of −13.7(11), −14.3(5), and −11.36(18) ppm·K^–1 for Ag­[AuCl₂(CN)₂], Ag­[AuBr₂(CN)₂], and Cu­[AuBr₂(CN)₂], respectively. The Au···X and Ag···X interactions affect the thermal expansion similarly to metallophilic Au···Au interactions in M­[Au­(CN)₂] and AuCN; replacing X = Cl with the larger Br atoms has a less significant effect. A similar analysis for the M­[Au­(CN)₄] series (where the volume thermal expansion coefficient, α_V, is 41(3) and 68.7(19) ppm·K^–1 for M = Ag, Cu, respectively) underscored the significance of the effect of the atomic radius on the flexibility of the framework and, thus, the thermal expansion properties

Raman Detected Sensing of Volatile Organic Compounds by Vapochromic Cu[AuX₂(CN)₂]₂ (X = Cl, Br) Coordination Polymer Materials

Two vapochromic coordination polymers Cu­[AuX₂(CN)₂]₂ (X = Cl, <b>1</b>; X = Br, <b>2</b>) were prepared and spectroscopically characterized. Exposure of these solid materials to the volatile organic compounds dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, 1,4-dioxane, and ethylene glycol (glycol) resulted in distinct color, and IR and Raman changes. The thermal stability of the analyte-bound materials was assessed by thermogravimetric analysis. Single-crystal structures of Cu­(analyte)₄[AuX₂(CN)₂]₂ (analyte = DMF, DMSO; X = Cl, Br) revealed an isostructural set of 1-D coordination polymer chains, where the analyte molecules were equatorially O-bound to the Cu­(II) centers while axially bound [AuX₂(CN)₂]⁻ units bridged these Cu­(II) centers, while Cu­(glycol)₄[AuBr₂(CN)₂]₂ is molecular, with monodentate glycol units. The structure of Cu₂(OH₂)₄[AuCl₂(CN)₂]₄·4dioxane is a 2-D coordination polymer network with H₂O-bridged Cu­(II) centers and dioxane units hydrogen bonded between the 2-D sheets. The intense Raman <i>v</i>_CN stretches for <b>1</b>, <b>2</b>, and their adducts form distinct, signature patterns. These “antenna” Raman <i>v</i>_CN stretches are an effective means for sensing VOCs, and their characteristic patterns can be used to identify the VOC being detected

Thermal Expansion Behavior of M^I[AuX₂(CN)₂]‑Based Coordination Polymers (M = Ag, Cu; X = CN, Cl, Br)

Two sets of <i>trans-</i>[AuX₂(CN)₂]⁻-based coordination polymer materialsM­[AuX₂(CN)₂] (M = Ag; X = Cl, Br or M = Cu; X = Br) and M­[Au­(CN)₄] (M = Ag, Cu)were synthesized and structurally characterized and their dielectric constants and thermal expansion behavior explored. The M­[AuX₂(CN)₂] series crystallized in a tightly packed, mineral-like structure featuring 1-D <i>trans-</i>[AuX₂(CN)₂]⁻-bridged chains interconnected via a series of intermolecular Au···X and M···X (M = Ag, Cu) interactions. The M­[Au­(CN)₄] series adopted a 2-fold interpenetrated 3-D cyano-bound framework lacking any weak intermolecular interactions. Despite the tight packing and the presence of intermolecular interactions, these materials exhibited decreased thermal stability over unbound <i>trans-</i>[AuX₂(CN)₂]⁻ in [^<i>n</i>Bu₄N]­[AuX₂(CN)₂]. A significant dielectric constant of up to ε_r = 36 for Ag­[AuCl₂(CN)₂] (1 kHz) and a lower ε_r = 9.6 (1 kHz) for Ag­[Au­(CN)₄] were measured and interpreted in terms of their structures and composition. A systematic analysis of the thermal expansion properties of the M­[AuX₂(CN)₂] series revealed a negative thermal expansion (NTE) component along the cyano-bridged chains with a thermal expansion coefficient (α_CN) of −13.7(11), −14.3(5), and −11.36(18) ppm·K^–1 for Ag­[AuCl₂(CN)₂], Ag­[AuBr₂(CN)₂], and Cu­[AuBr₂(CN)₂], respectively. The Au···X and Ag···X interactions affect the thermal expansion similarly to metallophilic Au···Au interactions in M­[Au­(CN)₂] and AuCN; replacing X = Cl with the larger Br atoms has a less significant effect. A similar analysis for the M­[Au­(CN)₄] series (where the volume thermal expansion coefficient, α_V, is 41(3) and 68.7(19) ppm·K^–1 for M = Ag, Cu, respectively) underscored the significance of the effect of the atomic radius on the flexibility of the framework and, thus, the thermal expansion properties

Copper(II) Dihalotetracyanoplatinate(IV) Coordination Polymers and Their Vapochromic Behavior

The coordination polymers [Cu­(H₂O)₂(μ₂-NC)₄PtX₂] (X = Cl, Br) form networks of square grid sheets that align in a staggered manner with one another via weak X···X interactions. Upon stepwise dehydration, the layers fuse, forming a 3-D network of distorted cubes. The materials were tested for visible vapochromic, Raman, and IR response to dimethyl sulfoxide, <i>N,N</i>-dimethylformamide, and pyridine. Analyte-bound coordination polymers of the form Cu­(analyte)₂[PtX₂(CN)₄] were structurally characterized by PXRD and found to form layers of square grids that align through X···X interactions. The reaction of [Cu­(H₂O)₂(μ₂-NC)₄PtX₂] with concentrated aqueous NH₃ generated [PtBr­(CN)₄(NH₃)]⁻ and [PtCl­(CN)₄(OH)]^2– anions that were incorporated into 1-D chain structures. UV–visible reflectance data show that a combination of shifting d–d transitions and the visible Br–Pt LMCT absorption band in [Cu­(H₂O)₂(μ₂-NC)₄PtBr₂] results in a greater vapochromic effect in comparison to that in chlorine-containing analogues

Enabling a High-Throughput Characterization of Microscale Interfaces within Coated Cathode Particles

Lithium ion batteries represent an emerging field. The development of battery materials could benefit from quick techniques that enable atomic-level diagnostics. High performance cathodes, such as high-voltage spinel, often require coatings to protect against the destructive electrochemical environments at the particle-to-electrolyte interface. The preparations of these coating are still in the early phases of development, and their analytical inspection by high resolution scanning and transmission electron microscopy (HR-S/TEM) techniques presents a significant challenge due to the microscale dimensions of cathode particles. In this work, a high throughput ultramicrotome technique was assessed for the characterization of the particle to coating interface. The ultramicrotome technique enabled the rapid preparation of cross-sections with a thickness of 126 ± 66 nm as determined by electron energy loss spectroscopy (EELS) measurements. Cathode particles composed of high-voltage spinel, LiNi0.5Mn1.5O4 (LNMO), coated with lithium niobate (LiNbO3) were synthesized and cross-sections were inspected using HR-S/TEM techniques. These ultra-thin cross-sections enabled the ability to obtain nanoscale information regarding the composition and crystallinity of the particle-to-coating interface over lateral areas of &gt;1 µm. Accessible correlations between the electrochemical performance of the LiNbO3 coated LNMO particles and the HR-S/TEM results were enabled by the high-throughput method. Discharge capacity measurements were acquired over a series of 100 electrochemical cycles for both the LiNbO3 coated and the as-prepared LNMO particles. The limitations of the ultramicrotome technique are also discussed herein with respect to the coating morphology and the procedure for guidance toward technique optimization. The rapid preparation of ultra-thin cross-sections can assist the advancement of protective coatings on the surfaces of cathode particles for an efficient characterization of bulk-to-surface interfaces

Stoichiomorphic Halogen-Bonded Cocrystals. A Case Study of 1,4-Diiodotetrafluorobenzene and 3-Nitropyridine

The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the P21/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the P1- space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine-nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 3) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. 1H → 13C and 19F → 13C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Mechanism of Perfluoro-Nickelacyclopentane Formation from Tetrafluoroethylene: Effects of Ancillary Ligand Bite Angle

Metallacyclopentanes are important reaction intermediates for catalytic processes, such as selective ethylene oligomerization and diene cyclooligomerization. Reactions of fluoroalkenes with low-valent first row transition metal complexes tend to form stable fluorometallacyclopentane products. DFT studies conducted herein indicate that conversion of three-coordinate Ni­(η2-C2F4)­L2 complexes (L2 = 2 monodentate or one bidentate chelate) to perfluorometallacycle products Ni­[κ2-(CF2)4-]­L2 occurs preferentially via a four-coordinate intermediate Ni­(η2-C2F4)2L2; an alternative three-coordinate pathway via Ni­(η2-C2F4)2L occurs only when L is extremely bulky. The transition structure for cyclization requires a dramatic increase in the L–Ni–L angle, which is perpendicular to the C–C bond-forming plane and initially affords a kinetic metallacycle intermediate resembling a trigonal bipyramidal geometry with one equatorial vacant site. The donor solvent, or intramolecular O-donor association with this intermediate, provides a low-energy pathway to the formation of the more stable square-planar metallacycle product. For bidentate chelate ligands, differential bite angles affect both coordination of a second C2F4 ligand and the cyclization step. For small-bite-angle chelates, the cyclization transition state energies are higher relative to monodentate analogues. An experimental investigation of wide bite-angle bis­(phosphine) ligands such as DPEphos and Bisbi showed the formation of additional nickelacyclopentane products with the coordination of a single P center to each Ni [DPEphos = bis­(2-diphenylphosphino-phenyl) ether; Bisbi = 2,2′-bis­(diphenylphosphino-methyl)-1,1′-biphenyl]