Conformational and Substitution Effects on the Donor and Reducing Strength of Tin(II) Porphyrinogens.

Meso-octaalkylcalix[4]pyrrolates are a class of redox-active porphyrinogen ligands. They have been well established in d- and f-block chemistry for over three decades but have only recently been introduced as ligands for p-block elements. Here, we present a study on the influence of meso-substituents on the redox chemistry of calix[4]pyrrolato stannate(II) dianions [2R]2- (R=Me, Et). Expansion of the normal-mode structural decomposition (NSD) method, well known for porphyrin chemistry, provides insights into the ligand conformation of a calix[4]pyrrolato p-block complex. Combined with the results of spectroscopic donor scaling, electrochemical studies, and quantum mechanical bond analysis tools, subtle but significant substitution and conformational effects on the electronic structure are revealed. Exploiting this knowledge rationalizes the role of this class of tin(II) dianions to act as potent reducing agents, but can also be expanded for other central elements. Photoexcitation boosts this reactivity further, allowing for the reduction of even challenging chlorobenzene.

Band-like transport in solution-processed perylene diimide dianion films with high Hall mobility.

It is crucial to prepare high-mobility organic polycrystalline film through solution processing. However, the delocalized carrier transport of polycrystalline films in organic semiconductors has rarely been investigated through Hall-effect measurement. This study presents a strategy for building strong intermolecular interactions to fabricate solution-crystallized p-type perylene diimide (PDI) dianion films with a closer intermolecular π-π stacking distance of 3.25 Å. The highly delocalized carriers enable a competitive Hall mobility of 3 cm2 V-1 s-1, comparable to that of the reported high-mobility organic single crystals. The PDI dianion films exhibit a high electrical conductivity of 17 S cm-1 and typical band-like transport, as evidenced by the negative temperature linear coefficient of mobility proportional to T-3/2. This work demonstrates that, as the intermolecular π-π interactions become strong enough, they will display high mobility and conductivity, providing a new approach to developing high-mobility organic semiconductor materials.

One Ligand to Bind them All: S~C~S2- Carbon- and Sulfur-Based Gem-Dianion as Structuring Ligand for Iron Polymetallic Assemblies.

Numerous synthetic models of the FeMo-co cluster of nitrogenases have been proposed to find the simplest structure with relevant reactivity. Indeed, such structures are able to perform multi-electrons reduction processes, such as the conversion of N2 to ammonia, and of CO2 into methane and alkenes. The most challenging parameter to imitate is indeed the central carbide ligand, which is believed to maintain the integrity of iron sulfide assembly during the course of catalytic cycles. The study proposes the use of bis(diphenylthiophosphinoyl)methanediide (SCS)2- as an ideal platform for the synthesis of bi- and tetra-metallic iron complexes, in which the iron-carbon interaction is maintained upon structural diversification and redox state changes.

Magnetoelectricity-Mediated Tunable Absorption and Release of Peroxide Dianions.

Peroxide dianion (O22-) has strong oxidizing activity and ease of proton abstraction and is extremely unstable. Direct and controllable adsorption and release of O22- has large application implication and is a large challenge so far. Here, we use a unique metal (Ni)-organic (diphenylalanine, DPA) framework (MOF), Ni(DPA)2, as adsorbents for absorption and release of O22-. This MOF structure has room-temperature magnetoelectricity via distortion of the Ni-centered octahedron {NiN2O4} and thus possesses a tunable ferroelectric polarization under applied electric/magnetic fields. Controllable adsorption and release of O22- are realized in such a MOF system via electrochemical redox measurements. Structural/spectroscopic characterization and calculations reveal that a number of NH active sites in the nanopores of MOF can effectively adsorb O22- by hydrogen bonds and then tunable ferroelectric polarization induces controllable release of O22- under applied magnetic fields. This work presents a constructive way for controllable adsorption and release of reactive oxygen species.

Synthesis of Homo-Metallic Heavier Analogues of Cyclobutene and the Cyclobutadiene Dianion.

The reduction of the boryl-substituted SnII bromide {(HCDippN)2 B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K2 [Sn4 {B(NDippCH)2 }4 ], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0)=-0.28, NICS(1)=-3.17), with the primary contributing resonance structures shown by Natural Resonance Theory (NRT) to involve a Sn=Sn double bond and 1,2-localized negative charges. Abstraction of the K+ cations or oxidation leads to contraction or cleavage of the Sn4 unit, respectively, while protonation generates the neutral dihydride 1,2-Sn4 {B(NDippCH)2 }4 H2 (a heavier homologue of cyclobutene) in a manner consistent with the predicted charge distribution in the [Sn4 {B(NDippCH)2 }4 ]2- dianion.

Intermolecular hydrogen bonding of alcohols with dinitrobenzene radical anion and dianion: A combined electrochemical and DFT study.

Hydrogen bonding is one of the most important inter-molecular interactions in the field of biochemistry and medicinal chemistry. Such non-covalent interactions play a vital role in self-assembly phenomena, chemical structures, material properties and enzymatic catalysis. Herein, we present hydrogen bonding phenomenon in alcohols-dinitrobenzene (DNB) radical anion/dianion systems using electrochemical and computational approaches. First, 1,3-DNB radical anion and dianion were generated through electrochemical method and then hydrogen bonding interactions with aliphatic alcohols in DMSO are studied through cyclic voltammetry (CV). CV results show that the cathodic peak potential of 1,3-Dinitrobenzene in Dimethyl sulfoxide is shifted catholically upon addition of alcohols which represent hydrogen bonding phenomenon. Theoretical investigations are performed to gain deep insight on hydrogen bonding interaction strength in DNB-alcohol systems. H-bonding interaction of all isomers of DNB (1,2-, 1,3-, 1,4-), its corresponding radical anion, and dianion with aliphatic alcohols is studied using density functional calculations. The strength of H-bonding is evaluated both qualitatively and quantitatively using interaction energies, vibrational and electronic spectroscopic analysis. Understanding of these interactions will be helpful in gaining insight into biological systems where these interactions play significant role.

Enhanced Aromaticity and Open-Shell Diradical Character in the Dianions of 9-Fluorenylidene-Substituted Expanded Radialenes.

Radialenes and expanded radialenes are cross-conjugated macrocycles displaying poor aromatic character. In this work, three 9-fluorenylidene substituted expanded [n]radialenes (ER-n, n=3-5) with a diacetylene spacer were synthesized and their structures were confirmed by X-ray crystallographic analysis and NMR spectroscopy. They all can be easily reduced into relatively stable dianions. Detailed experimental measurements and theoretical calculations suggest that their dianions (ER-n2- , n=3-5) are stabilized by both the aromatic fluorenyl anion substituents and the central aromatic rings with formally [4n+2] delocalized π electrons. In addition, the dianions of the extended radialenes (ER-42 - and ER-52 - ) show unique open-shell diradical character with a small singlet-triplet energy gap. For comparison, their linear counterparts (L-3 and L-4) were also synthesized; their dianions exhibit very different redox and optical properties from their respective macrocycles.

Crystal structure and Hirshfeld surface analysis of the hydrated 2:1 adduct of piperazine-1,4-diium 3,5-di-nitro-2-oxidobenzoate and piperazine.

The crystal structure of the adduct piperazine-1,4-diium 3,5-di-nitro-2-oxidobenzoate-piperazine-water (2/1/2) shows the existence of a 3,5-di-nitro-salicylate dianion (DNSA2-) and a protonated piperazine-1,4-diium cation (PIP2+) along with a piperazine mol-ecule. The formula of the title adduct in the asymmetric unit is 2C4H12N2 2+·2C7H2N2O7 2-·C4H10N2·2H2O with Z = 1. The piperazine ring in the piperazine-1,4-diium cation and in the neutral piperazine mol-ecule adopt chair conformations. All O atoms in the DNSA2- moiety and the water mol-ecule act as hydrogen-bonding acceptors for various inter-molecular O-H⋯O, N-H⋯O and C-H⋯O inter-actions, which stabilize the crystal structure. Various supra-molecular architectures formed by the different inter-molecular inter-actions are discussed. The relative contribution of various inter-molecular contacts is analysed with the aid of two-dimensional (full and decomposed) fingerprint plots, indicating that H⋯O/O⋯H (50.2%) and H⋯H (36.2%) contacts are the major contributors to the stabilization of the crystal structure.

Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene-within-an-Annulene Models.

The dianion and dication of tetramesityl-substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five- and six-membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene-within-an-annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X-ray crystallographic analyses and the electronic configurations were supported by MCD spectra. Based on the 13 C NMR chemical shifts, negative and positive charges are shown to be located mainly at the outer periphery, indicating that the dianion and dication have delocalized 22-π and 18-π electron outer perimeters, respectively, and 8-π electron structure at the inner ring. Notably, the dianion has an open-shell character, whereas the dication has a closed-shell ground state.

Synthesis, structure, and theoretical studies of a calcium complex of a unique dianion derived from 1-methyl-pyrrolidin-2-one.

The title compound, catena-poly[[tetra-kis-(1-methyl-pyrrolidin-2-one-κO)calcium(II)]-µ-(E)-1,1'-dimethyl-2,2'-dioxo-1,1',2,2'-tetra-hydro-[3,3'-bipyrrolyl-idene]-5,5'-bis-(thiol-ato)-κ2 O:O'], [Ca(C10H8N2O2S2)(C5H9NO)4] n , 1, crystallizes in the triclinic space group P . The crystal studied was twinned by non-merohedry via two different twofold operations, about the normals to (001) and (10), giving four twin domains with refined occupancies of 0.412 (4), 0.366 (4), 0.055 (1), 0.167 (4). The Ca atoms are located on centers of inversion. Each Ca is surrounded by four 1-methyl-pyrrolidin-2-one (NMP) ligands and coordinated through one of the two O atoms to two (E)-1,1'-dimethyl-2,2'-dioxo-1,1',2,2'-tetra-hydro-[3,3'-bipyrrolyl-idene]-5,5'-bis-(thiol-ate), [C10H8N2O2S2]2-, dianions (abbreviation: DMTBT). This dianion thus facilitates the formation of a 1-D polymer, which propagates in the [011] direction. These ribbons are linked by inter-molecular C-H⋯S inter-actions. Each Ca atom is in an octa-hedral CaO6 six-coordinate environment with Ca-O bond lengths ranging from 2.308 (6) to 2.341 (6) Å, cis bond angles ranging from 88.2 (2) to 91.8 (2)° and the trans angles all 180° due to the Ca atoms being located on centers of inversion. Theoretical calculations were carried out using density functional theory (DFT) and the results showed that although the central DMTBT dianion is planar there is likely some resonance across the central bond between both aza-pentyl rings, but this is not sufficient to establish a ring current. The calculated UV-vis spectrum shows a peak at 625 nm, which accounts for the deep blue-purple color of solutions of the complex.

Aromatic Metamorphosis of Thiophenes by Means of Desulfurative Dilithiation.

A new mode of aromatic metamorphosis has been developed, which allows thiophenes and their benzo-fused derivatives to be converted to a variety of exotic heteroles. This transformation involves 1) the efficient generation of key 1,4-dianions by means of desulfurative dilithiation with lithium powder and 2) the subsequent trapping of the dianions with heteroatom electrophiles in a one-pot manner. Via the desulfurative dilithiation, the sulfur atoms of thiophenes are replaced also with a carbon-carbon double bond or a 1,2-phenylene for the construction of benzene rings.

Butadienyl Diiron Complexes: Nonplanar Metalla-Aromatics Involving σ-Type Orbital Overlap.

A new class of nonplanar metalla-aromatics, diiron complexes bridged by a 1,3-butadienyl dianionic ligand, were synthesized in high yields from dilithio reagents and two equivalents of FeBr2 . The complexes consist of two antiferromagnetically coupled high-spin FeII centers, as revealed by magnetometry, Mössbauer spectroscopy, and DFT calculations. Furthermore, experimental (X-ray structural analysis) and theoretical analyses (NICS, ICSS, AICD, MOs) suggest that the complexes are aromatic. Remarkably, this nonplanar metalla-aromaticity is achieved by an uncommon σ-type overlap between the ligand p and metal d orbitals, in sharp contrast to the intensively studied planar aromatic systems featuring delocalized π-type bonding. Specifically, the σ-type interaction between the two Fe 3dxz orbitals and the butadienyl π orbital results in the formation of a six-electron conjugated system and hence enables the aromatic character.

Metastable Dianions and Dications.

A theoretical study of metastable dianions and dications has been carried out at the CCSD(T)//MP2 level. MX32- and LX42- (M=Li and Na, L=Be and Mg, X=F and Cl) have been considered as dianions, M3 X2+ (M=Li and Na, X=F and Cl), YH32+ and ZH42+ (Y=F and Cl and Z=O, S) as dications. Minima structures are found in all cases, but they are less stable than the corresponding dissociated pair of mono-ions. The dissociation profile of the molecules in two mono-ions has been explored showing in all cases a maximum that prevent their spontaneous dissociation. The strength and nature of the chemical bond in the dianions and dications have been analyzed with the QTAIM, NBO and LMOEDA method and compared to the corresponding monoanions and monocations.

The role of ligand-gated conformational changes in enzyme catalysis.

Structural and biochemical studies on diverse enzymes have highlighted the importance of ligand-gated conformational changes in enzyme catalysis, where the intrinsic binding energy of the common phosphoryl group of their substrates is used to drive energetically unfavorable conformational changes in catalytic loops, from inactive open to catalytically competent closed conformations. However, computational studies have historically been unable to capture the activating role of these conformational changes. Here, we discuss recent experimental and computational studies, which can remarkably pinpoint the role of ligand-gated conformational changes in enzyme catalysis, even when not modeling the loop dynamics explicitly. Finally, through our joint analyses of these data, we demonstrate how the synergy between theory and experiment is crucial for furthering our understanding of enzyme catalysis.

Synthesis of 1,1'-Bis(1-Methyl/Chloro-2,3,4,5-Tetraphenyl-1-Silacyclopentadienyl) [Ph4C4Si(Me/Cl)-(Me/Cl)SiC4Ph4] from Silole Anion [MeSiC4Ph4]-•[Li+ or Na+] and Silole Dianion [SiC4Ph4]2-•2[Li+]; Oxidative Coupling of Silole Anion [MeSiC4Ph4]-•[Li+ or Na+] by Ferrous Chloride (FeCl2) and Oxidative Coupling and Chlorination of Silole Dianion [SiC4Ph4]2-•2[Li+] by Cupric Chloride (CuCl2).

A reaction of silole anion {[MeSiC4Ph4]-•[Li+ or Na+] (1) with anhydrous ferrous chloride (FeCl2) in THF (tetrahydrofuran) gives 1,1'-bis(1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl) [Ph4C4Si(Me)-(Me)SiC4Ph4] (2) with precipitation of iron metal in high yield. Silole dianion {[SiC4Ph4]2-•2[Li+] (3) is added to anhydrous cupric chloride (CuCl2) in THF at -78 °C, then the dark red solution changes into a greenish solution. From the solution, a green solid is isolated, and stirring it in toluene at room temperature provides quantitatively 1,1'-bis(1-chloro-2,3,4,5-tetraphenyl-1-silacyclopentadienyl) [Ph4C4Si(Cl)-(Cl)SiC4Ph4] (4) with precipitation of copper metal in toluene. The green solid is suggested to be 1,1'-bissilolyl bisradical [Ph4C4Si-SiC4Ph4]2• (8), and lithium cuprous chloride salts {[Li2CuICl2]+•[CuICl2]-}. Both reactions are initiated by single-electron transfer (SET) from the electron-rich anionic silole substrates (1 and 3) to iron(II) and copper(II).

Mono- and Dianion of a Bis(benzobuta)tetraazapentacene Derivative.

A bis(benzobuta)tetraazapentacene derivative was reduced to its radical anion and its dianion, using potassium [18]crown-6 anthracenide in THF. Both reduced species were characterized by UV/Vis spectroscopy of the isolated species and by spectroelectrochemistry. Two distinct single-crystal structures of the dianion and an EPR spectrum of the radical anion were obtained. Contrary to other azaacenes, the lowest energy absorption in the UV/Vis spectrum of the dianion is redshifted in comparison to that of the neutral compound.

Optical pH measurement system using a single fluorescent dye for assessing susceptibility to dental caries.

Sugar-rich diets and poor dental hygiene promote the formation of a biofilm (plaque) that strongly adheres to the dental enamel surface and fosters the evolution of aciduric bacteria. The acid contributes to demineralization of the exterior tooth enamel, which accelerates after the pH drops below a critical value (∼5.5) for extended time periods resulting in the need for restorative procedures. Preventative techniques to alert the dentist and caries-susceptible patients regarding vulnerability to dental decay require a clinical measure of plaque activity. Therefore, there is a need to evaluate the acid production capability of plaque deposits in the pits and fissures of occlusal and interproximal regions. A ratiometric fluorescence pH-sensing device has been developed using an FDA-approved dye and LED excitation. Fluorescein spectral profiles were collected using a spectrometer and analyzed with a spectral unmixing algorithm for calibration over the pH range of 4.5 to 7. An in vivo pilot study on human subjects was performed using a sucrose rinse to accelerate bacterial metabolism and to measure the time-dependent drop in pH. The optical system is relatively immune to confounding factors such as photobleaching, dye concentration, and variation in excitation intensity associated with earlier dye-based pH measurement techniques.

Scandium complexes with the tetraphenylethylene and anthracene dianions.

The structural study of Sc complexes containing dianions of anthracene and tetraphenylethylene should shed some light on the nature of rare-earth metal-carbon bonding. The crystal structures of (18-crown-6)bis(tetrahydrofuran-κO)sodium bis(η6-1,1,2,2-tetraphenylethenediyl)scandium(III) tetrahydrofuran disolvate, [Na(C4H8O)2(C12H24O6)][Sc(C26H20)2]·2C4H8O or [Na(18-crown-6)(THF)2][Sc(η6-C2Ph4)2]·2(THF), (1b), (η5-1,3-diphenylcyclopentadienyl)(tetrahydrofuran-κO)(η6-1,1,2,2-tetraphenylethenediyl)scandium(III) toluene hemisolvate, [Sc(C17H13)(C26H20)(C4H8O)]·0.5C7H8 or [(η5-1,3-Ph2C5H3)Sc(η6-C2Ph4)(THF)]·0.5(toluene), (5b), poly[[(µ2-η3:η3-anthracenediyl)bis(η6-anthracenediyl)bis(η5-1,3-diphenylcyclopentadienyl)tetrakis(tetrahydrofuran)dipotassiumdiscandium(III)] tetrahydrofuran monosolvate], {[K2Sc2(C14H10)3(C17H13)2(C4H8O)4]·C4H8O}n or [K(THF)2]2[(1,3-Ph2C5H3)2Sc2(C14H10)3]·THF, (6), and 1,4-diphenylcyclopenta-1,3-diene, C17H14, (3a), have been established. The [Sc(η6-C2Ph4)2]- complex anion in (1b) contains the tetraphenylethylene dianion in a symmetrical bis-η3-allyl coordination mode. The complex homoleptic [Sc(η6-C2Ph4)2]- anion retains its structure in THF solution, displaying hindered rotation of the coordinated phenyl rings. The 1D 1H and 13C{1H}, and 2D COSY 1H-1H and 13C-1H NMR data are presented for M[Sc(Ph4C2)2]·xTHF [M = Na and x = 4 for (1a); M = K and x = 3.5 for (2a)] in THF-d8 media. Complex (5b) exhibits an unsymmetrical bis-η3-allyl coordination mode of the dianion, but this changes to a η4 coordination mode for (1,3-Ph2C5H3)Sc(Ph4C2)(THF)2, (5a), in THF-d8 solution. A 45Sc NMR study of (2a) and UV-Vis studies of (1a), (2a) and (5a) indicate a significant covalent contribution to the Sc-Ph4C2 bond character. The unique Sc ate complex, (6), contains three anthracenide dianions demonstrating both a η6-coordination mode for two bent ligands and a µ2-η3:η3-bridging mode of a flat ligand. Each [(1,3-Ph2C5H3)2Sc2(C14H10)3]2- dianionic unit is connected to four neighbouring units via short contacts with [K(THF)2]+ cations, forming a two-dimensional coordination polymer framework parallel to (001).

A Dimeric η1 ,η5 -Germole Dianion Bridged Titanium(III) Complex with a Multicenter Ti-Ge-Ge-Ti Bond.

Dimeric germole dianion bridged TiIII and ZrIV complexes have been synthesized. In these complexes, the germole dianion adopts a formal η1 ,η5 coordination to the two metal centers. The bonding situation in these bridged dimers is dominated by a covalent Ge-Ge interaction that results, for example, in a strong antiferromagnetic coupling of the d1 Ti centers.

Acetonyltri-phenyl-phospho-nium 2,3,5-tri-phenyl-tetra-zolium tetra-chlorido-cuprate(II).

The title compound, (C21H20OP)(C19H15N4)[CuCl4], was obtained by reacting CuCl2·2H2O with a mixture of one equivalent of acetonyltri-phenyl-phospho-nium chloride and one equivalent of 2,3,5-tri-phenyl-tetra-zolium chloride in aceto-nitrile. In the structure, the Cu centre in the dianion is bonded to four chloride ligands and adopts a distorted tetra-hedral geometry. The phospho-nium cation likewise adopts the expected tetra-hedral geometry. The tetra-zolium ring forms dihedral angles of 77.68 (10), 26.85 (11) and 66.48 (10)° with the planes of the benzene rings of the substituent groups. In the crystal, weak C-H⋯Cl hydrogen-bonding inter-actions involving both cations and the anion give rise to a three-dimensional supra-molecular structure.