Synthesis, structure, and bonding in polyiodide and metal iodide-iodine systems

Confinement of Iodine Molecules into Triple-Helical Chains within Robust Metal-Organic Frameworks

During nuclear waste disposal process, radioactive iodine as a fission product can be released. The widespread implementation of sustainable nuclear energy thus requires the development of efficient iodine stores that have simultaneously high capacity, stability and more importantly, storage density (and hence minimized system volume). Here, we report high I2 adsorption in a series of robust porous metal-organic materials, MFM-300(M) (M = Al, Sc, Fe, In). MFM-300(Sc) exhibits fully reversible I2 uptake of 1.54 g g-1, and its structure remains completely unperturbed upon inclusion/removal of I2. Direct observation and quantification of the adsorption, binding domains and dynamics of guest I2 molecules within these hosts have been achieved using XPS, TGA-MS, high resolution synchrotron X-ray diffraction, pair distribution function analysis, Raman, terahertz and neutron spectroscopy, coupled with density functional theory modeling. These complementary techniques reveal a comprehensive understanding of the host-I2 and I2-I2 binding interactions at a molecular level. The initial binding site of I2 in MFM-300(Sc), I2I, is located near the bridging hydroxyl group of the [ScO4(OH)2] moiety [I2I···H-O = 2.263(9) Å] with an occupancy of 0.268. I2II is located interstitially between two phenyl rings of neighboring ligand molecules [I2II···phenyl ring = 3.378(9) and 4.228(5) Å]. I2II is 4.565(2) Å from the hydroxyl group with an occupancy of 0.208. Significantly, at high I2 loading an unprecedented self-aggregation of I2 molecules into triple-helical chains within the confined nanovoids has been observed at crystallographic resolution, leading to a highly efficient packing of I2 molecules with an exceptional I2 storage density of 3.08 g cm-3 in MFM-300(Sc).

On the Mechanism of the Iodide-Triiodide Exchange Reaction in a Solid-State Ionic Liquid

Efficient charge transport has been observed in iodide-based room-temperature ionic liquids when doped with iodine. To investigate preferred pathways for the iodide (I^-)-to-triiodide (I₃^-) exchange reaction and to clarify the origin of this high ionic conductivity, we have conducted electronic structure calculations in the crystal state of 1-butyl-3-methylimidazolium iodide ([BMIM][I]). Energy barriers for the different stages of the iodine-swapping process, including the reorientation of the I^-···I₃^- moiety, were determined from minimum energy paths as a function of a reaction coordinate. Hirshfeld charges and structural parameters, such as bond lengths and angles, were monitored during the reaction. Several bond-exchange events were observed with energy barriers ranging from 0.17 to 0.48 eV and coinciding with the formation of a twisted I^-···I₃^- complex. Striking similarities were observed in the mechanics and energetics of this charge-transfer process in relation to solid-state superionic conductors.

Structural Distortions and Charge Density Waves in Iodine Chains Encapsulated inside Carbon Nanotubes

Atomic chains are perfect systems for getting fundamental insights into the electron dynamics and coupling between the electronic and ionic degrees of freedom in one-dimensional metals. Depending on the band filling, they can exhibit Peierls instabilities (or charge density waves), where equally spaced chain of atoms with partially filled band is inherently unstable, exhibiting spontaneous distortion of the lattice that further leads to metal-insulator transition in the system. Here, using high-resolution scanning transmission electron microscopy, we directly image the atomic structures of a chain of iodine atoms confined inside carbon nanotubes. In addition to long equidistant chains, the ones consisting of iodine dimers and trimers were also observed, as well as transitions between them. First-principles calculations reproduce the experimentally observed bond lengths and lattice constants, showing that the ionic movement is largely unconstrained in the longitudinal direction, while naturally confined by the nanotube in the lateral directions. Moreover, the trimerized chain bears the hallmarks of a charge density wave. The transition is driven by changes in the charge transfer between the chain and the nanotube and is enabled by the charge compensation and additional screening provided by the nanotube.

Light Excitation of a Bismuth Iodide Complex Initiates I-I Bond Formation Reactions of Relevance to Solar Energy Conversion

The titration of iodide into acetonitrile solutions of BiI₃ resulted in the formation of [BiI₆]^3-. Ligand-to-metal charge transfer (LMCT) excitation of [BiI₆]^3- yielded a transient species assigned as the diiodide anion I₂^•- directly ligated to Bi, [Bi(I₂^•-)I_x]ⁿ. With 20 ns time resolution, transient absorption measurements revealed the appearance of two species assigned on the analysis of the iodine molecular orbitals as an η² ligated I₂^•-, [(η²-I₂)BiI₄]^3- (λ_max = 640 nm), and an η¹ species [(η¹-I₂)BiI₄]^3- (λ_max = 750 nm). The rapid appearance of this intermediate was attributed to intramolecular I-I bond formation. The [(η²-I₂)BiI₄]^3- subsequently reacted with 1 equiv of iodide to yield [(η¹-I₂)BiI₅]^4-. Interestingly, [(η¹-I₂)BiI₅]^4- decayed to ground state products with a first-order rate constant of k = 2 × 10³ s^-1. Under the same experimental conditions, I₂^•- in CH₃CN rapidly disproportionates with a tremendous loss of free energy, ΔG^o = -2.6 eV. The finding that metal ligation inhibits this energy wasting reaction is of direct relevance to solar energy conversion. The photochemistry itself provides a rare example of one electron oxidized halide species coordinated to a metal ion of possible relevance to reductive elimination/oxidation addition reaction chemistry of transition metal catalysts.

Formation and distortion of iodidoantimonates(III): the first isolated [SbI6]3- octahedron

The ability to intentionally construct, through different types of interactions, inorganic-organic hybrid materials with desired properties is the main goal of inorganic crystal engineering. The primary deformation, related to intrinsic interactions within inorganic substructure, and the secondary deformation, mainly caused by the hydrogen bond interactions, are both responsible for polyhedral distortions of halogenidoantimonates(III) with organic cations. The evolution of structural parameters, in particular the Sb-I secondary- and O/N/C-H...I hydrogen bonds, as a function of temperature assists in understanding the contribution of those two distortion factors to the irregularity of [SbI₆]^3- polyhedra. In tris(piperazine-1,4-diium) bis[hexaiodidoantimonate(III)] pentahydrate, (C₄H₁₂N₂)₃[SbI₆]₂·5H₂O (TPBHP), where the isolated [SbI₆]^3- units were found, distortion is governed only by O/N/C-H...I hydrogen bonds, whereas in piperazine-1,4-diium bis[tetraiodidoantimonate(III)] tetrahydrate, (C₄H₁₂N₂)[SbI₄]₂·4H₂O (PBTT), both primary and O-H...I secondary factors cause the deformation of one-dimensional [{SbI₄}_n]^n- chains. The larger in spatial dimensions piperazine-1,4-diium cations, in contrast to the smaller water of crystallization molecules, do not significantly contribute to the octahedral distortion, especially in PBTT. The formation of isolated [SbI₆]^3- ions in TPBHP is the result of specific second coordination sphere hydrogen bond interactions that stabilize the hybrid structure and simultaneously effectively separate and prevent [SbI₆]^3- units from mutual interactions. The temperature-induced changes, further supported by the analysis of data retrieved from the Cambridge Structural Database, illustrate the significance of both primary and secondary distortion factors on the deformation of octahedra. Also, a comparison of packing features in the studied hybrids with those in the non-metal containing piperazine-1,4-diium diiodide diiodine (C₄H₁₂N₂)I₂·I₂ (PDD) confirms the importance and hierarchy of different types of interactions.

Fourier transform infrared and Raman spectroscopy in the study of phase transitions in dipyrazolium iodide triiodide: Experimental and theoretical analysis

The paper presents the Infrared and Raman spectra of the powdered [C₃N₂H₅⁺]₂[I^-∙I₃^-] crystal at the temperature intervals of 11-270K, covering two low-temperature phase transitions: discontinuous at 182/188K (cooling/heating) and continuous at 254K. The research shows that the vibrational states of the pyrazolium cations change significantly during discontinuous phase transition (III→II), while the continuous nature of successive structural transformation is more subtle and displays an insignificant change in the temperature coefficient of numerous vibrations during the II→I PT at 254K. The spectacular changes at Raman spectra above 188K confirm a huge rebuilding of inorganic network from [I^-∙I₃^-] to [I₄^2-]. Additionally, a complete geometry optimization was carried out in the solid state in order to obtain minimum structures and bonding properties. The theoretical results correspond well with the experimental data. Moreover, the infrared spectrum in harmonic approximation was calculated, and a comparative vibrational analysis was performed. CRYSTAL09 vibrational results appear to be in a good agreement with the experimental ones.

Structure and interstitial iodide migration in hybrid perovskite methylammonium lead iodide

Hybrid perovskites form an emerging family of exceptional light harvesting compounds. However, the mechanism underpinning their photovoltaic effect is still far from understood, which is impeded by a lack of clarity on their structures. Here we show that iodide ions in the methylammonium lead iodide migrate via interstitial sites at temperatures above 280 K. This coincides with temperature dependent static distortions resulting in pseudocubic local symmetry. Based on bond distance analysis, the migrating and distorted iodines are at lengths consistent with the formation of I₂ molecules, suggesting a 2I⁻→I₂+2e⁻ redox couple. The actual formula of this compound is thus (CH₃NH₃)PbI_3−2x(I₂)_x where x∼0.007 at room temperature. A crucial feature of the tetragonal structure is that the methylammonium ions do not sit centrally in the A-site cavity, but disordered around two off-centre orientations that facilitate the interstitial ion migration via a gate opening mechanism.

The mechanism underpinning the photovoltaic effect in hybrid perovskite solar cells has remained unclear. Here, Green and co-workers suggest that iodide ions in methylammonium lead iodide perovskite migrate via interstitial sites and undergo a redox reaction to form molecular iodine and free electrons.

Testing the tools for revealing and characterizing the iodine-iodine halogen bond in crystals

To understand what tools are really suitable to identify and classify the iodine-iodine non-covalent interactions in solid organic polyiodides, we have examined the anisotropy of the electron density within the iodine atomic basin along and across the iodine-iodine halogen bond using the Laplacian of electron density, one-electron potential and electron localization function produced by Kohn-Sham calculations with periodic boundary conditions. The Laplacian of electron density exhibits the smallest anisotropy and yields a vague picture of the outermost electronic shells. The one-electron potential does not show such a deficiency and reveals that the valence electron shell for the halogen-bond acceptor iodine is always wider than that for the halogen-bond donor iodine along its σ-hole direction. We have concluded that the one-electron potential is the most suitable for classification of the iodine-iodine bonds and interactions in complicated cases, while the electron localization function allows to distinguish the diiodine molecule bonded with the monoiodide anion from the typical triiodide anion.

Self-Assembly of Iodine in Superfluid Helium Droplets: Halogen Bonds and Nanocrystals

We present evidence of halogen bond in iodine clusters formed in superfluid helium droplets based on results from electron diffraction. Iodine crystals are known to form layered structures with intralayer halogen bonds, with interatomic distances shorter than the sum of the van der Waals radii of the two neighboring atoms. The diffraction profile of dimer dominated clusters embedded in helium droplets reveals an interatomic distance of 3.65 Å, much closer to the value of 3.5 Å in iodine crystals than to the van der Waals distance of 4.3 Å. The profile from larger iodine clusters deviates from a single layer structure; instead, a bi-layer structure qualitatively fits the experimental data. This work highlights the possibility of small halogen bonded iodine clusters, albeit in a perhaps limited environment of superfluid helium droplets. The role of superfluid helium in guiding the trapped molecules into local potential minima awaits further investigation.

Two iodine-rich (dimethylphosphoryl)methanaminium iodides

The reaction of

Stability of dye-sensitized solar cells under extended thermal stress

The graphical abstract shows 5 equivalent DSCs in masterplate configuration and their performance stability under thermal stress @85 °C during 4700 h. Ru505/L12 cells resulted the most stable dye/electrolite pair by retain more than 95% of initial efficiency.

N-(4-Hydroxyphenyl)acetamide against diiodine towards polyiodide dianion

N-(4-Hydroxyphenyl)acetamide decreases the total amount of diiodine which is available for the iodination of tyrosil residues of thyroglobulin, while it inhibits the activity of thyroid peroxidase.

An unusual photoconductive property of polyiodide and enhancement by catenating with 3-thiophenemethylamine salt

We serendipitously discovered an unusual photoconductive property of polyiodide, which can be further enhanced through interaction with 3-thiophenemethylamine iodine salt.

Bimetallic copper and zinc-catalyzed oxidative cycloaddition of 3-aminopyridazines and nitriles: a direct synthesis of 1,2,4-triazolo[1,5-b]pyridazines via C–N and N–N bond-forming process

One-pot formation of 1,2,4-triazolo[1,5-b]pyridazine derivatives is presented in this manuscript, in which the targets are offered via cooperative Cu(i)/Zn(ii)-catalyzed tandem C–N addition and I₂/KI-mediated intramolecular N–N bond formation.

Enantiopure and racemic radical-cation salts of bis(2′-hydroxylpropylthio)(ethylenedithio)TTF with polyiodide anions

The chiral TTF-based donor molecule BHPT-EDT-TTF has produced enantiopureR,RandS,Sradical-cation salts with polyiodide anions I₃⁻and I₈²⁻.

Controlled Synthesis of Polyions of Heavy Main-Group Elements in Ionic Liquids

Ionic liquids (ILs) have been proven to be valuable reaction media for the synthesis of inorganic materials among an abundance of other applications in different fields of chemistry. Up to now, the syntheses have remained mostly “black boxes”; and researchers have to resort to trial-and-error in order to establish a new synthetic route to a specific compound. This review comprises decisive reaction parameters and techniques for the directed synthesis of polyions of heavy main-group elements (fourth period and beyond) in ILs. Several families of compounds are presented ranging from polyhalides over carbonyl complexes and selenidostannates to homo and heteropolycations.

Structural Proof for the First Dianion of a Polychloride: Investigation of [Cl8 ](2.)

The polychloride salt [CCl(NMe2 )2 ](+) 2 [Cl8 ](2-) was synthesized and crystallized in the ionic liquid [BMP]OTf. The compound was fully characterized by Raman spectroscopy as well as X-ray single-crystal structure determination, and represents the first example of a polychloride dianion to be described. Detailed gas-phase and solid-state calculations concerning the nature of the bonding situation were also performed.

1,2,4-triazole-derived carbene complexes of gold: characterization, solid-state aggregation and ligand disproportionation

Ligand redistribution reactions are well documented for silver(I) N-heterocyclic carbene (NHC) complexes of the type [AgX(NHC)] (X = halido ligand), but only two reports have been described in the literature for gold analogues of the general formula [AuX(NHC)]. In both cases, the NHCs in question were exceptionally strong donors. To probe the dependence of ligand redistribution processes on NHC donor strength, a model study was conducted using a weakly donating 1,2,4-triazolin-5-ylidene (tazy) ligand and different halido coligands. For [AuX(tazy)] (X = Cl, Br, OAc, tazy = 4-benzyl-1-methyl-1,2,4-triazolin-5-ylidene), no ligand redistribution was found, while a reversible disproportionation between [AuI(tazy)] in solution and [Au(tazy)2][AuI2] in the solid state was observed and studied by means of X-ray crystallography, NMR and UV-Vis spectroscopy, as well as DFT calculations.

Size controllable redispersion of sintered Au nanoparticles by using iodohydrocarbon and its implications

Downsizing large Au particles into small particles with controllable size remains challenging. In this study, we redispersed large sintered Au particles on activated carbon (Au/C) to highly dispersed nanoparticles with uniform distribution and controllable size after treatment with iodohydrocarbons. The Au/C catalyst was conducted for a number of deactivation/regeneration cycles with negligible deterioration in catalytic performance for acetylene hydrochlorination. The redispersion behavior reveals a reverse agglomeration process in the presence of iodohydrocarbons under mild conditions. This behavior is significantly related to the C-I bond dissociation energy (BDE) and adsorption of iodic species on Au particles. A novel protocol for controlling the size and predicting the redispersion efficiency of Au particles is established by correlating with the C-I BDEs of iodohydrocarbons. The molecular-level interpretation of redispersion provides a thorough mechanism based on experimental results. This study presents an efficient method for the easy regeneration of sintered Au-based catalysts for practical applications.

Nontypical iodine–halogen bonds in the crystal structure of (3E)-8-chloro-3-iodomethylidene-2,3-dihydro-1,4-oxazino[2,3,4-ij]quinolin-4-ium triiodide

Two kinds of iodine–iodine halogen bonds are the focus of our attention in the crystal structure of the title salt, C12H8ClINO+·I3−, described by X-ray diffraction. The first kind is a halogen bond, reinforced by charges, between the I atom of the heterocyclic cation and the triiodide anion. The second kind is the rare case of a halogen bond between the terminal atoms of neighbouring triiodide anions. The influence of relatively weakly bound iodine inside an asymmetric triiodide anion on the thermal and Raman spectroscopic properties has been demonstrated.

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Source of Cooperativity in Halogen-Bonded Haloamine Tetramers

Inspired by the isostructural motif in α-bromoacetophenone oxime crystals, we investigated halogen-halogen bonding in haloamine quartets. Our Kohn-Sham molecular orbital and energy decomposition analysis reveal a synergy that can be traced to a charge-transfer interaction in the halogen-bonded tetramers. The halogen lone-pair orbital on one monomer donates electrons into the unoccupied σ*N-X orbital on the perpendicular N-X bond of the neighboring monomer. This interaction has local σ symmetry. Interestingly, we discovered a second, somewhat weaker donor-acceptor interaction of local π symmetry, which partially counteracts the aforementioned regular σ-symmetric halogen-bonding orbital interaction. The halogen-halogen interaction in haloamines is the first known example of a halogen bond in which back donation takes place. We also find that this cooperativity in halogen bonds results from the reduction of the donor-acceptor orbital-energy gap that occurs every time a monomer is added to the aggregate.

Iodine uptake and enhanced electrical conductivity in a porous coordination polymer based on cucurbit[6]uril

Iodine uptake and enhanced electrical conductivity have been observed in a solid material built by cucurbit[6]uril units and an iodide matrix.

Bi(iii) polybromides: a new chapter in coordination chemistry of bismuth

A new family of bismuth coordination compounds – Bi(iii) polybromides – is introduced.