Ambient Water-Stable Dianionic Electron Donors: Intramolecular Noncovalent Conduits Assist Charge Delocalization

Electron-rich π-conjugated dianions are known to be ambient unstable and their stabilization in ambient water is yet to be realized. We report the first example of an exceptionally stable naphthalenediimide-based dianion in ambient and hot water, forming one of the most stable redox-active dianion. The half-life (t_1/2) of dianion ( 1 a²⁻ ) is more than four months in ambient water. The dianionic state was confirmed by X-ray crystallography and by various spectroscopic methods. The noncovalent electronic conduits introduced for the first time in dianions, embrace n_O→π*_C≡N interactions and aid in delocalizing the dianionic charge as validated from theoretical studies. The dianions harness strong NIR absorption and electron donor ability to organic acceptors and metal ions, which make them suitable for potential green energy applications.     

Indacyclopentadienes and Aromatic Indacyclopentadienyl Dianions: Synthesis and Characterization

A series of unprecedented metallacycles of indium, including indacyclopentadienes ( 2 ), spiro indacyclopentadienes ( 3 ), aromatic indacyclopentadienyl dianions with an In−Li bond ( 4 ), and aromatic indacyclopentadienyl dianions with an In−In bond ( 5 ), were synthesized and structurally characterized by single-crystal X-ray structural analysis for the first time. Both indacyclopentadienes 2 and 3 were synthesized by reaction of 1,4-dilithio-1,3-butadienes with InCl₃. Structural transformations between 2 and 3 were observed. Reduction of indacyclopentadienes 2 with an excess amount of lithium afforded aromatic indacyclopentadienyl dianions 4 with an In−Li bond or 5 with an In−In bond, respectively, depending on the substituents on the ring. The aromatic character of 4 and 5 was confirmed by both experimental measurements and theoretical analysis.     

Quinoid-Aromatic Resonance for Very Small Optical Energy Gaps in Small-Molecule Organic Semiconductors: A Naphthodithiophenedione-oligothiophene Triad System

Organic semiconductors with very small optical energy gaps have attracted a lot of attention for near-infrared-active optoelectronic applications. Herein, we present a series of donor-acceptor-donor (D−A−D) organic semiconductors consisting of a highly electron-deficient naphtho[1,2-b:5,6-b′]dithiophene-2,7-dione quinoidal acceptor and oligothiophene donors that show very small optical energy gaps of down to 0.72 eV in the solid state. Investigation of the physicochemical properties of the D−A−D molecules as well as theoretical calculations of their electronic structures revealed an efficient intramolecular interaction between the quinoidal acceptor and the aromatic oligothiophene donors in the D−A−D molecules; this significantly enhances the backbone resonance and thus reduces the bond length alternation along the π-conjugated backbones. Despite the very small optical energy gaps, the D−A−D molecules have low-lying frontier orbital energy levels that give rise to air-stable ambipolar carrier transport properties with hole and electron mobilities of up to 0.026 and 0.043 cm² V⁻¹ s⁻¹, respectively, in field-effect transistors.     

Adduct of NacNacAl with Benzophenone and Its Coupling Chemistry

Reaction of NacNacAl (NacNac=[DippNC(Me)CHC(Me)NDipp]⁻) with one equivalent of benzophenone affords a ketylate species NacNacAl(η²(C,O)-OCPh₂) that undergoes easy cyclization reactions with unsaturated substrates. The scope of substrates included benzophenone, aldimine (PhNC(Ph)H), quinoline, phenyl nitrile, trimethylsilyl azide, and a saturated cyclic thiourea. The latter substrate reacted by an unusual C−N cleavage that left the C=S functionality intact. The new products were characterized by NMR spectroscopy and X-ray diffraction analysis.     

Quantum chemical modeling of the stability of reduced forms of Roussin’s red esters. Effect of the nature of the ligand

The reduced forms of Roussin’s red esters [Fe₂(μ-RS)₂(NO)₄]n? (n = 1, 2; R = Ph, Pr) and their possible decomposition products were studied by quantum chemical calculations. The energy diagram of the processes that occur in a dichloromethane solution was constructed. According to this diagram, the monoanions are much more stable than the corresponding dianions. Possible dissociation paths of the dianions in solution were proposed. The anions with the propyl ligand are more stable than the anions with the phenyl ligand.     

NMR study of mono- and dilithium derivatives of alkyl and arylstannanes

Element-centered mono- and dianions of alkyl- and arylstannanes were studied by NMR spectroscopy. The ¹³C and ¹¹⁹Sn NMR chemical shifts for the dianions R₂SnLi₂ (R = Ph, Et) were measured for the first time.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2229–2231, October, 2004.     

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, M₃X²⁺ (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.     

Coordination-Induced N−H Bond Splitting of Ammonia and Primary Amine of CuI−MOFs

We report a porous three-dimensional anionic tetrazolium based Cu^I−MOF 1 , which is capable of cleaving the N−H bond of ammonia and primary amine, as well as the O−H bond of H₂O along with spontaneous H₂ evolution. In the gas-solid phase reaction of 1 with ammonia and water vapor, Cu^I−MOF 1 was gradually oxidized to NH₂−Cu^II−MOF and OH−Cu^II−MOF, through single-crystal-to-single-crystal (SCSC) structural transformations, which was confirmed by XPS, PXRD and X-ray single-crystal diffraction. Density functional theory (DFT) demonstrated that Cu^I−MOF could lower N−H bond dissociation free energy of ammonia through coordination-induced bond weakening and promote H₂ evolution by the reduction potential of 1 . To our knowledge, this is the first example of MOFs that activate ammonia and amine in gas-solid manner.     

Bis-Phosphaketenes LM(PCO)2 (M=Ga,In): A New Class of Reactive Group 13 Metal-Phosphorus Compounds

Phosphaketenes are versatile reagents in organophosphorus chemistry. We herein report on the synthesis of novel bis-phosphaketenes, LM(PCO)₂ (M=Ga 2 a , In 2 b ; L=HC[C(Me)N(Ar)]₂; Ar=2,6-i-Pr₂C₆H₃) by salt metathesis reactions and their reactions with LGa to metallaphosphenes LGa(OCP)PML (M=Ga 3 a , In 3 b ). 3 b represents the first compound with significant In−P π-bonding contribution as was confirmed by DFT calculations. Compounds 3 a and 3 b selectively activate the N−H and O−H bonds of aniline and phenol at the Ga−P bond and both reactions proceed with a rearrangement of the phosphaethynolate group from Ga−OCP to M−PCO bonding. Compounds 2–5 are fully characterized by heteronuclear (¹H, ¹³C{¹H}, ³¹P{¹H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).     

Competing hydrogen‐bond acceptors in ethyl­enediammonium oxotrithio­tungstate(VI)

The structure of the title compound, (C₂H₁₀N₂)[WOS₃], consists of ethyl­ene­diammonium dications and tetra­hedral [WOS₃]²⁻ dianions, which are linked with the aid of four varieties of hydrogen bond, namely N—H⋯O, N—H⋯S, C—H⋯O and C—H⋯S. The strength and number of these hydrogen bonds affect the W—O and W—S bond distances.     

Planar Hypercoordinate Carbons in Alkali Metal Decorated CE32− and CE22− Dianions

After exploring the potential energy surfaces of M_mCE₂^p (E=S−Te, M=Li−Cs, m=2, 3 and p=m-2) and M_nCE₃^q (E=S−Te, M=Li−Cs, n=1, 2, q=n-2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V-shaped CE₂²⁻ and Y-shaped CE₃²⁻ dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals.     

Bis(μ‐5‐carboxybenzene‐1,3‐dicarboxylato‐κ2O1:O3)bis[(2,2′‐bi‐1H‐imidazole‐κ2N3,N3′)zinc]

The title compound, [Zn₂(C₉H₄O₆)₂(C₆H₆N₄)₂], consists of two Zn^II ions, two 5‐carboxybenzene‐1,3‐dicarboxylate (Hbtc²⁻) dianions and two 2,2′‐bi‐1H‐imidazole (bimz) molecules. The Zn^II centre is coordinated by two carboxylate O atoms from two Hbtc²⁻ ligands and by two imidazole N atoms of a bimz ligand, in a distorted tetrahedral coordination geometry. Two neighbouring Zn^II ions are bridged by a pair of Hbtc²⁻ ligands, forming a discrete binuclear [Zn₂(Hbtc)₂(bimz)₂] structure lying across an inversion centre. Hydrogen bonds between carboxyl H atoms and carboxylate O atoms and between imidazole H atoms and carboxylate O atoms link the binuclear units. These binuclear units are further extended into a three‐dimensional supramolecular structure through extensive O—H...O and N—H...O hydrogen bonds. Moreover, the three‐dimensional nature of the crystal packing is reinforced by the π–π stacking. The title compound exhibits photoluminescence in the solid state, with an emission maximum at 415 nm.     

NMR Crystallography Reveals Carbonate Induced Al-Ordering in ZnAl Layered Double Hydroxide

Layered double hydroxides (LDHs) serve a score of applications in catalysis, drug delivery, and environmental remediation. Smarter crystallography, combining X-ray diffraction and NMR spectroscopy revealed how interplay between carbonate and pH determines the LDH structure and Al ordering in ZnAl LDH. Carbonate intercalated ZnAl LDHs were synthesized at different pH (pH 8.5, pH 10.0, pH 12.5) with a Zn/Al ratio of 2, without subsequent hydrothermal treatment to avoid extensive recrystallisation. In ideal configuration, all Al cations should be part of the LDH and be coordinated with 6 Zn atoms, but NMR revealed two different Al local environments were present in all samples in a ratio dependent on synthesis pH. NMR-crystallography, integrating NMR spectroscopy and X-ray diffraction, succeeded to identify them as Al residing in the highly ordered crystalline phase, next to Al in disordered material. With increasing synthesis pH, crystallinity increased, and the side phase fraction decreased. Using ¹H−¹³C, ¹³C−²⁷Al HETCOR NMR in combination with ²⁷Al MQMAS, ²⁷Al-DQ-SQ measurements and Rietveld refinement on high-resolution PXRD data, the extreme anion exchange selectivity of these LDHs for CO₃²⁻ over HCO₃⁻ was linked to strict Al and CO₃²⁻ordering in the crystalline LDH. Even upon equilibration of the LDH in pure NaHCO₃ solutions, only CO₃²⁻ was adsorbed by the LDH. This reveals the structure directing role of bivalent cations such as CO₃²⁻ during crystallization of [M²⁺₄M³⁺₂(OH)₂]²⁺[A²⁻]₁⋅yH₂O LDH phases.     

CO2 Capture with Silylated Ethanolamines and Piperazines

Amine treatment is commonly used to capture CO₂ from exhaust gases and from ambient air. The Si−N bond in aminosilanes is capable of reacting with CO₂ more readily than amines. In the current study we have synthesized trimethylsilylated ethanolamines, diethanolamines and piperazines and investigated their reaction toward CO₂. All products were characterized by ¹H, ¹³C, and ²⁹Si NMR, RAMAN spectroscopy as well as mass spectrometry. The product of a twofold CO₂-insertion into bis-trimethylsilylated piperazine was analysed by single-crystal X-ray diffraction. Furthermore, quantum chemical calculations (DFT) were used to supplement the experimental results. Geometry optimizations and NBO calculations for each starting material were carried out at the B3LYP level with different basis sets. DFT calculations at the B3LYP, WB97XD and M062x level were conducted for geometry optimization and frequency calculations to examine the thermochemical data. The calculations were carried out both for the gas phase and in solvent environment. The calculated reaction enthalpies varied between −37 and −107 kJ mol⁻¹, while experimental values around −100 kJ mol⁻¹ were determined.     

Study of Ground State Interactions of Enantiopure Chiral Quaternary Ammonium Salts and Amides,Nitroalkanes, Nitroalkenes,Esters, Heterocycles,Ketones and Fluoroamides

Chiral phase-transfer catalysis provides high level of enantiocontrol, however no experimental data showed the interaction of catalysts and substrates. ¹H NMR titration was carried out on Cinchona and Maruoka ammonium bromides vs. nitro, carbonyl, heterocycles, and N−F containing compounds. It was found that neutral organic species and quaternary ammonium salts interacted via an ensemble of catalyst ⁺N−C−H and (sp²)C−H, specific for each substrate studied. The correspondent BArF salts interacted with carbonyls via a diverse set of ⁺N−C−H and (sp²)C−H compared to bromides. This data suggests that BArF ammonium salts may display a different enantioselectivity profile. Although not providing quantitative data for the affinity constants, the data reported proofs that chiral ammonium salts coordinate with substrates, prior to transition state, through specific C−H positions in their structures, providing a new rational to rationalize the origin of enantioselectivity in their catalyses.     

Crystalline Diradical Dianions of Pyrene-Fused Azaacenes

Although diradicals and azaacenes have been greatly attractive in fundamental chemistry and functional materials, the isolable diradical dianions of azaacenes are still unknown. Herein, we describe the first isolation of pyrene-fused azaacene diradical dianion salts [(18-c-6)K(THF)₂]⁺[(18-c-6)K]⁺⋅ 1 ^2−.. and [(18-c-6)K(THF)]²⁺⋅ 2 ^2−.. by reduction of the neutral pyrene-fused azaacene derivatives 1 and 2 with excess potassium graphite in THF in the presence of 18-crown-6. Their electronic structures were investigated by various experiments, in conjunction with theoretical calculations. It was found that both dianions are open-shell singlets in the ground state and their triplet states are thermally readily accessible owing to the small singlet–triplet energy gap. This work provides the first examples of crystalline diradical dianions of azaacenes with considerable diradical character.     

Band gap bowing of nanocrystalline Zn(1−x)CaxO thin films for blue and ultraviolet optoelectronic applications

Alloying materials having different band gaps is a tool to tailor the optical energy gaps of semiconducting materials. In the present study, the effect of alloying ZnO with CaO was investigated. Thin films of Zn_(1−x)Ca_xO (0 ≤ x ≤ 0.20) were deposited on glass substrates by spray pyrolysis technique. All the films possessed nanocrystalline grains and crystallinity deteriorated with increase in Ca²⁺ substitution level. Elemental composition analysis confirmed the presence of Ca in the samples. Films showed good optical transmission in the visible and near infrared region and the absorption edge blue-shifted with Ca²⁺ substitution. Optical energy gap enhanced by 9.89% upon 20% Ca²⁺ substitution. Photoluminescence analysis also confirmed band gap broadening with mesovalent cation substitution.     

Bis­(melaminium) dl‐malate tetrahydrate

The crystal structure of the title melaminium salt, bis(2,4,6‐tri­amino‐1,3,5‐triazin‐1‐ium) dl ‐malate tetrahydrate, 2C₃H₇N₆⁺·C₄H₄O₅²⁻·4H₂O, consists of singly protonated melaminium residues, dl ‐malate dianions and water mol­ecules. The melaminium residues are connected into chains by four N—H⃛N hydrogen bonds, and these chains form a stacking structure along the c axis. The dl ‐malate dianions form hydrogen‐bonded chains and, together with hydrogen‐bonded water mol­ecules, form a layer parallel to the (100) plane. The conformation of the malate ion is compared with an ab initio molecular‐orbital calculation. The oppositely charged moieties, i.e. the stacks of melaminium chains and hydrogen‐bonded dl ‐malate anions and water mol­ecules, form a three‐dimensional polymeric structure, in which N—H⃛O hydrogen bonds stabilize the stacking.     

Transmetalation Reactions of Aromatic Dilithionickelole: Synthesis of Heterobimetallic Complexes Featuring Metalloles as Diene Ligands

The aromatic metallole dianions are important metallaaromatic compounds because of their various reactivities and extensive synthetic applications. Herein we report the reactions of dilithionickelole with MgCl₂, EtAlCl₂, Cp*ScCl₂, Cp*LuCl₂ and Pt(COD)Cl₂ (COD=1,5-cyclooctadiene) affording a series of Ni/M heterobimetallic complexes of the general formula (η⁴−C₄R₄M)Ni(COD), in which the metalloles act as diene ligands, as suggested by single-crystal X-ray, NMR and theoretical analyses. In these reactions, two electrons of the nickelole dianion transferred to Ni, representing different reactivity compared with main-group metallole dianions.     

Gallium “Shears” for C=N and C=O Bonds of Isocyanates

Digallane [L¹Ga−GaL¹] ( 1 , L¹=dpp-bian=1,2-[(2,6-iPr₂C₆H₃)NC]₂C₁₂H₆) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C−N−Ga fragments to afford [L¹(O=C−NR)Ga−Ga(RN−C=O)L¹] (R=Ph, 3 ; R=Tos, 4 ). The reactions with both isocyanates result in new C−C and N−Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C−N−Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga−N bond of the same fragment to afford compound [L¹Ga−Ga(AllN− C=O)₂L¹] ( 5 ) (All=allyl). In the presence of Na metal, the related digallane [L²Ga−GaL²] ( 2 ; L²=dpp-dad=[(2,6-iPr₂C₆H₃)NC(CH₃)]₂) is converted into the gallium(I) carbene analogue [L²Ga:]⁻ ( 2 A ), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂(THF)₅]{L²Ga[EtN−C(O)]₂GaL²} ( 6 ), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂]₂[L²Ga(p-MeC₆H₄)(N−C(O))₂−N(p-MeC₆H₄)]₂ ( 7 ), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃]₂[L²Ga-(μ-O)₂-GaL²] ( 8 ), and generation of the further addition product [Na₂(THF)₅][L²Ga(CyNCO₂)]₂ ( 9 ). Complexes 3 – 9 have been characterized by NMR (¹H, ¹³C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.