Ab Initio Calculations on Halogen Bond Between N——Br and Electron-donating Groups

Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ to gain a deeper insight into the nature of the N—Br halogen bonding. For the small complexes, H3C—Br…NH3 and H2N—Br…NH3, the primary calculation has demonstrated that the N—Br in H2N—Br…NH3 can form a much stronger halogen-bonding complex than the C—Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N>O>S; O(sp3)>O(sp2), which is adequate for the C—Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X-3 with N-bromosuccinimide are markedly lower than that of the corresponding X- with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosuccinimide. AIM analyses further confirmed the above results.     

Lantern-Type Divanadium Complexes with Bridging Ligands: Short Metal−Metal Bonds with High Multiple Bond Orders

Vanadium forms binuclear complexes with a variety of ligands often containing V≡V triple bonds. Many tetragonal divanadium paddlewheel complexes with bridging bidentate ligands have been experimentally characterized. This research exhaustively treats model tetragonal, trigonal, and digonal paddlewheel-type divanadium complexes V₂L_x (L=formamidinate, guanidinate, and carboxylate; x=2, 3, 4), each in the three lowest-energy spin states. The V−V formal bond orders are obtained from metal−metal MO diagrams for representative structures. A number of short V−V multiple bonds of order 3, 3.5, and 4 are found in these model complexes. The short V≡V triple bonds and singlet ground state predicted here for the model tetragonal complexes correspond well with the limited experimental results for the series of known tetragonal paddlewheels. Digonal divanadium lanterns with very short V−V quadruple bonds are predicted as interesting synthetic targets. The V−V bond distances are categorized into distinct ranges according to the formal bond order values from 0.5 to 4. These bond length ranges are compared with the ranges compiled for other divanadium complexes including carbonyl complexes.     

Ab Initio Molecular Orbital Calculation on Dinuclear Gold(Ⅰ)Complexes──Metal-Metal Interaction and Electronic Structure of Binuclear Gold(Ⅰ)Complexes with Bridging Bidentate Ligands

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Synthesis of 4′-Carboxy-benzo-30-crown-10 and a Thermodynamic Study of Its Complexes with Thallium and Alkali Cations in Acetonitrile Solution

A synthetic procedure has been developed for the preparation of 4-carboxy-benzo-30-crown-10. The formation of Na+, K+, Rb+, Cs+ and Tl+ complexes with the large crown ether was investigated conductometrically in acetonitrile solution at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data. It was found that the stability of the complexes vary in the order Tl+ > K+ > Rb+ > Cs+ > Na+. The data obtained in this study support the existence of a wrap around structure for the above complexes in solution. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the complexes were enthalpy stabilized but entropy destabilized. The resulting TS° vs. H°plot showed a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the large crown complexation reactions.     

Crystalline Rhodium-Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

Crystalline {Cryptand(Na⁺)}[(COD)Rh^ICl⋅Sn^II(Pc³⁻)]⁻⋅2C₆H₄Cl₂ ( 1 ) and {Cryptand(Cs⁺)}[(COD)Rh^I⋅Sn^II(Pc⁴⁻)]⁻⋅C₆H₅CH₃ ( 2 ) complexes were obtained via the interaction of [Sn^II(Pc³⁻)]⁻ and [Sn^II(Pc⁴⁻)]²⁻, respectively, with organometallic {(COD)RhCl}₂ dimer (COD is 1,5-cyclooctadiene). Dissociation of {(COD)RhCl}₂ followed by the Rh−Sn binding is observed at the formation of 1 . Elimination of the chlorine atom at the rhodium atom is observed in 2 , and rhodium is additionally coordinated to the imine nitrogen atom of Pc⁴⁻. The complexes contain mono- Pc⋅³⁻ and doubly reduced Pc⁴⁻ species, respectively, that is supported by the data of XRD analysis as well as optical and magnetic properties of 1 and 2 . There is an alternation of C-N_imine bonds in the macrocycles, which gradually increases with increasing negative charge on the macrocycle. The difference between shorter and longer bonds increases from 0.051 Å in Pc³⁻ to 0.075 Å in Pc⁴⁻. The formation of 1 is accompanied by an essential blue shift of the Q-band of starting SnPc and the appearance of a new intense band at 1031 nm. The even stronger shift of the Q-band is observed in the spectrum of 2 , but the band in the near-IR range becomes weaker. The value of effective magnetic moment of 1 is 1.76 μ_B at 300 K corresponding the contribution of the Pc³⁻ radical trianions (S=1/2). Only weak magnetic coupling with the Weise temperature of −3 K is observed in 1 due to weak π–π interaction between the macrocycles in the chains. Paramagnetic Pc³⁻ species additionally monitored by EPR spectroscopy show a strong temperature dependence of g-factor and linewidth of the EPR signal. Complex 2 is diamagnetic and EPR silent.     

One-Dimensional Intercalation Compound 2 HgS⋅SnBr2: Ab Initio Electronic Structure Calculations and Molecular Dynamics Simulations

The one-dimensional intercalation compound 2 HgS⋅SnBr₂ (figure; white: Hg, light gray: S, dark grey: Sn, and black: Br) is an example of the ability of weak host–guest interactions to induce structural modifications in the HgS host. The stability and dynamic behavior of the intercalation compound and its precursors HgS and SnBr₂ have been analyzed by means of DFT/plane wave calculations. The molecular dynamics simulations facilitate the understanding of the structural rearrangements during the intercalation process.     

Stereoelectronic Effects on the Nucleophilic Addition of Phosphite to the Carbonyl Double Bond: Ab Initio Molecular Orbital Calculations on Reaction Surfaces and the α-Effect

Ah initio molecular orbital calculations have been carried out on adducts of trihydroxy phosphine, P(OH)₃, and formaldehyde, H₂C=0. Stationary points were located and a reaction surface calculated. One stationary point exists as a stable pentacovalent phosphorane, and the other as a 1,3-dipolar transition state. Calculations differing in the conformation about the P-OH bonds of the phosphite reveal that an antiperiplanar (app) lone pair on oxygen to the phosphorus lone pair (acyclic analogue) raises the energy of the molecule by 1.7 kcal/mol relative to a phosphite conformation with no app lone pairs to the phosphorus lone pair (bicyclic analogue). In the transition state, the relative energy between the two conformations reverses with the acyclic analogue transition state 5 kcal/mol lower energy than the bicyclic analogue transition states. The lower energy for the acyclic analogue in the transition state is attributed to the mixing of the app lone pairs on the oxygens of the phosphite mixing with the σ orbital of the newly formed bond between phosphorus and carbon. This kinetic Stereoelectronic effect can explain why acyclic phosphites react much faster in nucleophilic reactions than bicyclic phosphites. This phenomenon suggests that the origin of the α-effect, the enhanced nucleophilicity of a base possessing a heteroatom with an adjacent unshared electron pair arises from the stereoelectronic effect.     

Synthesis and Characterization of Chiral Organogallium and Indium Complexes with Salen Ligands

Several new chiral organogallium and indium complexes with chiral Salen(1 and 2) as anxciliary ligands have been synthesized and characterized by elemental analysis,IR,^1H NMR and Mass spectroscopy.For the gallium,Mono and bimetallic complexes were obtained,whereas ring closure complexes of indium were obtained.     

Stereospecificity of Diels–Alder Reactions Validated Using Ab Initio Calculations: Synthesis of Novel Coumarin and Phenanthridine Derivatives

A new series of coumarin derivatives (2–5) was synthesized by reaction of phenylsulfonylacetonitrile (1) with 2-hydroxy-1-naphthaldehyde and/or salicyaldehyde. Compounds 3 and 5 were converted to the corresponding phenanthridine analogs 6 and 7, respectively. Compound 9a was treated with different dienophiles to furnish the endo adducts of compounds (11a–d) rather than the exo adducts. Ab initio calculations at the Hartree-Fock (HF) level using the basis set 6-31 G (d,p) was used to study and validate the stereospecificity of compounds 11a–d and showed clearly that the endo adducts were thermodynamically favorable. PM3 parameters also showed that the endo adducts are thermodynamically and kinetically favorable. Tetrahydrobenzochromenone (11) was synthesized and allowed to react with different aromatic diazonium salts to give the corresponding 4-arylazo derivatives (13), which were converted to the corresponding diazaindenophenanthrene derivatives (14) by reaction with o-diamines.     

Silver(Ⅰ) Complexes with Mixed Diphosphine Ligands:Syntheses,Characterization and Spectroscopic Properties

Two novel silver(I) complexes [Ag(DPEphos)(dppe)]Cl O4(1) and [Ag(DPEphos)-(dppe)]SCN(2)(DPEphos = bis[2-(diphenylphosphino)phenyl]ether, dppe = bis(diphenylphosphino)ethane) are synthesized and characterized by IR, 1H/31 P NMR spectroscopy and fluorescence spectra. Complex 1 crystallizes in monoclinic, space group P21/c with a = 14.8821(12), b = 12.6620(11), c = 36.025(3) ?, β = 112.633(2)°, V = 6265.7(9) ?3, C62H52 Cl O5P4Ag, Mr = 1144.24, Z = 4, Dc = 1.213 g/cm3, F(000) = 2352, μ = 0.510 mm-1, the final R = 0.0616 and w R = 0.1192 for 4003 observed reflections(I 2σ(I)). Complex 2 crystallizes in monoclinic, space group P21/c with a = 14.9021(13), b = 12.6100(11), c = 35.920(3) ?, β = 112.852(2)°, V = 6220.2(9) ?3, C63H52NOP4 SAg, Mr = 1102.87, Z = 4, Dc = 1.178 g/cm3, F(000) = 2272, μ = 0.498 mm-1, the final R = 0.0912 and w R = 0.1706 for 3287 observed reflections(I 2σ(I)). In mono-nuclear complexes 1 and 2, the Ag(I) atom is chelated by DPEphos and dppe ligand. In the 31 P NMR spectra, there are splitting signals(doublets or triplets) which can be attributed to the coupling of the 107,109Ag–31P(from DPEphos or dppe ligand). All the emission peaks of these complexes are attributed to ligand-centered(π-π*) transitions.     

Metal Complexes with Novel Ambidentate Ligands: β-Enaminovinylketones with Annelated 1,2-Benzothiazine-1,1-Dioxide Fragment and Antipyrine Substituent

The data on competitive binding of ligands in metal complexes with ambidentate ligands (Schiff bases and -aminovinylketones) were summarized. Special attention is given to chemical and electrochemical syntheses and structural study of novel chelates of heterocyclic enaminoketones with antipyrine substituent that form tetrahedral (Cu²⁺, Zn²⁺) or octahedral (Co²⁺, Ni²⁺) structures.     

Organotrihalide Complexes: α-Nucleophiles and Effective Oxidizing Agents in Decomposition Reactions of Organophosphorus Compounds in Water and Surfactant Micelles

We have studied the nucleophilic and oxidative reactivity of the system HOBr/BrO^–, in water and in the presence of different types of surfactants, relative to 4-nitrophenyldiethylphosphate, 4-nitrophenyl- 4´-toluenesulfonate (nucleophilic substitution), and 4-nitrophenol (oxidation). As the source of "active" bromine, we used organotrihalide complexes. The micellar effects of the surfactants in nucleophilic substitution reactions are adequately described within both a pseudophase distribution model and an ion-exchange model. Just transferring the reaction from water to micelles of a cationic surfactant leads to an increase in the observed rates of reaction of the BrO^– ion with esters by up to a factor of 20-30 and an increase in the rate for reaction of HOBr with nitrophenol by up to a factor of 5, while the HOBr/BrO^– system is one of the most effective systems in decomposition of organophosphorus compounds.     

Ab Initio Calculations of the Conformational Preferences of 1,3-Oxathiane S-Oxide and its Analogs Containing S and SE Atoms—Evidence for Stereoelectronic Interactions Associated with the Anomeric Effects

Abstract

Stereoelectronic interactions associated with the AE and also the conformational and structural properties of 1,3-oxathiane S-oxide (1), 1,3-dithiane S-oxide (2), 1,3-thiaselenane S-oxide (3), 1,3-oxaselenane Se-oxide (4), 1,3-thiaselenane Se-oxide (5), and 1,3-diselenane Se-oxide (6) were investigated using quantum mechanical methods. These compounds were fully optimized at the B3LYP/6 – 311 + G** and HF/6 – 311 + G** levels of theory. The Gibbs Free Energy, Enthalpy, and Entropy differences (i.e., ΔG, ΔH, and ΔS) between the axial and equatorial conformations were calculated at the B3LYP/6 – 311 + G** and HF/6 – 311 + G** levels of theory. The decrease of the AE is corresponding to the decreases of calculated Δ(G _ax – G _eq) value of the above mentioned compounds. The calculated AE values are more significant for the justification of the conformational dominances of the compounds than steric effects. In this work, the relations between the Anomeric Effects, donor and acceptor orbital energies, occupancies, structural parameters, dipole–dipole interactions, and conformational behavior of the compounds have been studied.     

Polynuclear Silver(Ⅰ) Complexes with Phosphorus Ligands and 4,4'-Bipyridine:Synthesis,Structural Characterization and Spectroscopic Properties

Two novel silver(I) complexes {[Ag(OTf)(PPh3)(4,4'-bipy)]}∞(1) and {[Ag2-(OTf)2(dppb)3](CH3CN)4}∞(2)(OTf = trifluoromethanesulfonate, PPh3 = triphenylphophine, 4,4'-bipy = 4,4'-bipyridine, dppb = bis(diphenylphosphino)butane) have been synthesized and characterized by IR, single-crystal X-ray diffraction, fluorescence spectrum and 1H NMR spectroscopy. Complex 1 crystallizes in orthorhombic, space group Pna21 with a = 19.259(2), b = 9.85070(12), c = 16.3827(17) ?, V = 3108.0(5) ?3, C29H23F3N2O3 PSAg, Mr = 675.39, Z = 4, Dc = 1.443 g/cm3, F(000) = 1360, μ = 0.816 mm-1, the final R = 0.0675 and w R = 0.1722 for 3662 observed reflections(I 2σ(I)). Complex 2 crystallizes in triclinic, space group P1 with a = 12.9370(11), b = 13.5261(13), c = 16.4539(15) ?, α = 106.7120(10), β = 97.3830(10), γ = 113.027(2)?, V = 2441.2(4)?3, C94H96F6N4O6P6S2Ag2, Mr = 1957.43, Z = 1, Dc = 1.331 g/cm3, F(000) = 1006, μ = 0.605 mm-1, the final R = 0.0717 and w R = 0.1795 for 5128 observed reflections(I 2σ(I)). Complex 1 is of zigzag chain structure, in which each Ag atom is coordinated by one OTf- anion, two N atoms from two 4,4'-bipy molecules and one P atom from PPh3 ligand. In 2, the central Ag atom is coordinated with one OTf- anion and three P atoms from three dppb ligands, which leads to the formation of a zigzag ring-bridge-ring chain with each ring consisting of two Ag atoms and two dppb ligands.     

The Synthesis of New Triazole Ligands and Determination of Complex Stability Constants with Transition Metal Cations in Aqueous Media

Six new triazole compounds were synthesized. These compounds containing the substituted benzylidenamino group were obtained by reaction of 3-(pyridine-4-yl)-5-p-tolyl-4-amino-4H-l,2,4-triazole 1 with the corresponding aldehyde. The reduced forms were prepared with NaBH₄ in methanol. The structures of the compounds were determined by IR, ¹H NMR, and ¹³C NMR spectral data, and their interaction with cations such as Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ba²⁺, Sr²⁺, Ca²⁺, Cu²⁺, Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Ag⁺ were investigated by using UV-visible spectrophotometry. Of the tested metal cations, Cu²⁺, Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Ag⁺ complexed with the ligands. The complex stability constants (log ₁₀ K) were measured in slightly acidic aqueous media at 25.0±0.1 °C. These stability constants were determined by measuring the increase in solubility of the nearly insoluble ligand molecule due to complex formation with a soluble cation, and this method is discussed. It was found that the position of chlorine atoms on the benzene ring strongly affects the complexation of Cu²⁺ ion with these ligands.     

Coordinatively Unsaturated Amidotitanocene Cations with Inverted σ and π Bond Strengths: Controlled Release of Aminyl Radicals and Hydrogenation/Dehydrogenation Catalysis

Cationic amidotitanocene complexes [Cp₂Ti(NPhAr)][B(C₆F₅)₄] (Cp=η⁵-C₅H₅; Ar=phenyl ( 1 a ), p-tolyl ( 1 b ), p-anisyl ( 1 c )) were isolated. The bonding situation was studied by DFT (Density Functional Theory) using EDA-NOCV (Energy Decomposition Analysis with Natural Orbitals for Chemical Valence). The polar Ti−N bond in 1 a–c features an unusual inversion of σ and π bond strengths responsible for the balance between stability and reactivity in these coordinatively unsaturated species. In solution, 1 a–c undergo photolytic Ti−N cleavage to release Ti(III) species and aminyl radicals ⋅ NPhAr. Reaction of 1 b with H₃BNHMe₂ results in fast homolytic Ti−N cleavage to give [Cp₂Ti(H₃BNHMe₂)][B(C₆F₅)₄] ( 3 ). 1 a–c are highly active precatalysts in olefin hydrogenation and silanes/amines cross-dehydrogenative coupling, whilst 3 efficiently catalyzes amine-borane dehydrogenation. The mechanism of olefin hydrogenation was studied by DFT and the cooperative H₂ activation key step was disclosed using the Activation Strain Model (ASM).     

Ab Initio Calculations on Nitramide and Its Methyl Derivatives( Ⅱ )——The Harmonic Force Fields and Vibrational Spectra of Nitramide and Its Isotopic Derivatives

The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXAS at the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harmonic force field was scaled by using empirical scale factors which are transferred from other molecules and provided an a priori prediction of fundamental frequencies and intensities. The average deviations between predicted vibrational frequencies of nitramide and experimental IR spectrum in an argon matrix are 63 cm-1 for symmetric vibrations and 41 cm-1 for antisymmetric modes. A new set of scale factors was optimized in this paper. These scale factors reduced the average deviations to 2. 3 cm-1 for symmetric modes and 0. 8 cm-1 for antisymmetric ones. The vibrational spectra of three isotopic derivatives of nitramide were predicted by using the force field resulted from the optimized set of scale factors, which are in good agreement with their experimental data in an argon matrix.     

Boron-Centered Lewis Superacid through Redox-Active Ligands: Application in C−F and S−F Bond Activation

A series of redox-responsive ferrocenyl-substituted boranes and boronic esters were synthesized. Oxidation of the ferrocenyl ligand to the ferrocenium resulted in a drastic increase in the Lewis acidity beyond the strength of SbF₅, which was investigated experimentally and computationally. The resulting highly Lewis acidic boron compounds were used for catalytic C−F and S−F bond activation.     

Onset of Amorphous Structure in CaCO3: Geometric and Electronic Structures of (CaCO3) n (n?=?2–7) Clusters by Ab Initio Calculations

Electronic structures, vibrational analyses, stabilization energies and amorphicity were analyzed for the most stable configurations of the neutral gas phase clusters of calcium carbonate (CaCO₃) _n (n?=?2?C7). Minimum-energy structures were generated through simulated annealing using a mix of molecular dynamics/semiempirical optimization and then full optimization at the ab initio level (RHF/6-31G*). HF-level results are calibrated versus MP2/6-31G* results. Though many clusters are symmetric, the structural arrangements are not crystalline and resemble neither calcite nor aragonite. In general, greater symmetry means a lower stabilization energy. The BSSE- and zero point energy-corrected stabilization energies appear to plateau at about ?113?kcal/mol when n?=?7. Amorphous clusters start appearing when n?=?4 and the lowest-energy minima for n????5 are of C₁ symmetry. No solvent effect is necessary to induce amorphism.     

State-Selected Unimolecular Decomposition of δ-Valerolactam(+) and δ-Valerolactam(2)(+) Cations: Theory and Experiment

The near threshold photofragmentation pattern of δ-valerolactam(+) and δ-valerolactam(2)(+) has been recorded combining electron/ion coincidence techniques and vacuum ultraviolet synchrotron radiation. The experimental method yields the fragment intensity as a function of the internal energy deposited into the parent cation, up to 3.1 eV above the first ionization threshold. In parallel, ab initio studies on the δ-valerolactam(+) and δ-valerolactam(2)(+) cations and their ionic and neutral fragmentation products have been performed with the aim of determining the isomers of the ionic products observed experimentally as well as of their neutral counterparts. These computations were performed using the PBE0 exchange-correlation functional and the aug-cc-pVDZ basis set. We found good agreement between the calculated reaction enthalpies and experimental appearance energies of the ions. More generally, our experimental and theoretical results reveal that the fragmentation of the ionic species of interest leads to a multitude of neutral and ionic fragments, which may be formed after intramolecular isomerization and complex decomposition processes. Multistep reaction pathways are expected.