Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Mutual Effect of Functional Groups and the Radical Center on the Reactivity of Nitroxyl Radicals

This review considers the correlation between the reactivity of nitroxyl radicals (piperidine, pyrroline, pyrrolidine, imidazoline, dihydroquinoline, tetrahydroquinoline, diphenyl nitroxide, etc.) and their chemical structure in terms of the rate constants of reactions between these radicals and hydrazobenzene. 4,4′-Di(tert-butyl)diphenyl nitroxyl has the highest reactivity, and the nitroxyl radical of benzoindolopyrrolidine is the least reactive (the difference is a factor of ∼10⁴). The effects of the metal atom in stable organometallic nitroxyl radicals and of the halogen atom in halogenated nitroxyl radicals on the reactivity of the nitroxyl center are considered. Data on the effect of the nitroxyl center on the reactivity of functional groups in the piperidine nitroxyl radical are generalized. Nitroxyl radicals with an activated double bond are shown by quantum chemical calculations to form cyclic transition complexes with amines, involving both the paramagnetic center and a double bond. This explains why the activated double bond in nitroxyl radicals is more reactive in nucleophilic additions of amines than the same bond in their diamagnetic analogues. The rate constants of nitroxyl reduction with hydrazobenzene and of nitroxyl oxidation with tetranitromethane are related to the σ_ESR constant derived from isotropic hyperfine coupling constants HFC_(aN), and their correlation with Hammett constants is demonstrated. The role of solvents in the reduction and oxidation of the nitroxyl radicals is considered. The influence of hydroxyl radical-polar solvent complexes and hydroxylamine-polar solvent H complexes on the course of reactions is considered for hydrogen atom transfer in systems of a sterically hindered nitroxyl radical and hydroxylamine.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 506–528.Original Russian Text Copyright © 2005 by Malievskii, Shapiro.     

Effect of hydrogen bonding of solvent on the thermodynamic stability of cadmium ethylenediamine complexes

Changes in the stability of the cadmium(ii) ethylenediamine complexes in mixed water—DMSO solvents were studied by pH-metry and calorimetry. Complex cations [Cd(en)]²⁺, [Cd(en)₂]²⁺, and [Cd(en)₃]²⁺ are formed in aqueous solutions, and the [Cd(en)₄]²⁺ complex with a partially dentate ligand is stable in DMSO. An increase in the DMSO content in a solvent increases the stability of the complexes. The maximum increase in logK is observed for coordinatively saturated compounds. The thermodynamics of complexation is discussed from the viewpoint of solvation approach. Principal differences in the influence of aqueous-alcohol and aqueous-aprotic solvents on the stability of the metal amino complexes were revealed. Protolytic solvents exert a destabilizing effect on the multiligand complexes, because the coordination sphere is involved in H bonding.     

Solvent Effects on the 1H-NMR Chemical Shifts of Imidazolium-Based Ionic Liquids

The ¹H nuclear magnetic resonance (¹H-NMR) spectrum is a useful tool for characterizing the hydrogen bonding (H-bonding) interactions in ionic liquids (ILs). As the main hydrogen bond (H-bond) donor of imidazolium-based ILs, the chemical shift (δ_H2) of the proton in the 2-position of the imidazolium ring (H2) exhibits significant and complex solvents, concentrations and anions dependence. In the present work, based on the dielectric constants (ϵ) and Kamlet-Taft (KT) parameters of solvents, we identified that the δ_H2 are dominated by the solvents polarity and the competitive H-bonding interactions between cations and anions or solvents. Besides, the solvents effects on δ_H2 are understood by the structure of ILs in solvents: 1) In diluted solutions of inoizable solvents, ILs exist as free ions and the cations will form H-bond with solvents, resulting in δ_H2 being independent with anions but positively correlated with β_S. 2) In diluted solutions of non-ionzable solvents, ILs exist as contact ion-pairs (CIPs) and H2 will form H-bond with anions. Since non-ionizable solvents hardly influence the H-bonding interactions between H2 and anions, the δ_H2 are not related to β_S but positively correlated with β_IL.     

The Role of Hydrogen‐Bonding Interactions in the Ultrafast Relaxation Dynamics of the Excited States of 3‐ and 4‐Aminofluoren‐9‐ones

The dynamics of the excited states of 3‐ and 4‐aminofluoren‐9‐ones (3AF and 4AF, respectively) are investigated in different kinds of solvents by using a subpicosecond time‐resolved absorption spectroscopic technique. They undergo hydrogen‐bonding interaction with protic solvents in both the ground and excited states. However, this interaction is more significant in the lowest excited singlet (S₁) state because of its substantial intramolecular charge‐transfer character. Significant differences in the spectroscopic characteristics and temporal dynamics of the S₁ states of 3AF and 4AF in aprotic and protic solvents reveal that the intermolecular hydrogen‐bonding interaction between the S₁ state and protic solvents plays an important role in its relaxation process. Perfect linear correlation between the relaxation times of the S₁ state and the longitudinal relaxation times (τ_L) of alcoholic solvents confirms the prediction regarding the solvation process via hydrogen‐bond reorganization. In the case of weakly interacting systems, the relaxation process can be well described by a dipolar solvation‐like process involving rotation of the OH groups of the alcoholic solvents, whereas in solvents having a strong hydrogen‐bond‐donating ability, for example, methanol and trifluoroethanol, it involves the conversion of the non‐hydrogen‐bonded form to the hydrogen‐bonded complex of the S₁ state. Efficient radiationless deactivation of the S₁ state of the aminofluorenones by protic solvents is successfully explained by the energy‐gap law, by using the energy of the fully solvated S₁ state determined from the time‐resolved spectroscopic data.     

Terminal end-on coordination of dinitrogen versus isoelectronic CO: A comparison using the charge displacement analysis

The metal dinitrogen bonding in a wide series of terminal end-on dinitrogen complexes is investigated with the charge displacement analysis based on natural orbitals of chemical valence (CD-NOCV). The effect of the σ donation and π backdonation on the N N bond are discussed and compared with the observations for a series of carbonyl complexes, published in 2016 by Tarantelli et al. The σ donation is relative invariant over the series of dinitrogen complexes and has no significant effect on the N N bond strength, whereas the π backdonation causes a considerable elongation of the N N bond. Some uncommon examples of weakly bound dinitrogen with blue-shifted stretching frequency compared to free N₂ (ν = 2330 cm⁻¹) are known. The dinitrogen bonding in these complexes is simulated with a point charge. Apparently, electrostatics account for the shortened N─N bond in these systems.     

On the origin of ionic liquid‐induced variations in hydroxypropyl methacrylate propagation rate coefficients

Pulsed laser polymerizations were used to study the propagation kinetics of hydroxypropyl methacrylate (HPMA) in ionic liquids (ILs) and common organic solvents. The functional monomer was chosen to investigate the complex interplay of all interactions between monomer molecules and between monomer and solvent molecules and to obtain a deeper understanding of the impact of these interactions. The solvent effect on the HPMA propagation rate coefficient (k_p) was examined using a linear solvation energy relationship (LSER) based on Kamlet‐Taft solvatochromic parameters π*, α, and β. The results suggest that dipolarity/polarizability, associated with π*, and hydrogen bond–donating ability of the solvents, accounted for by α, majorly contribute to variations in k_p. Hydrogen bond–accepting (electron pair donating) ability of the solvents (β parameter) is of much lesser importance. In addition, LSER enables the prediction of HPMA k_p based on solvatochromic parameters of the solvents. The results suggest that interactions between the hydroxyl group of the monomer and the anion are dominant compared with classical hydrogen bonding between carbonyl and hydroxyl groups of the monomer units. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3188–3199, 2010     

Effect of the complex forming ion on the physicochemical characteristics of solvation of tetraphenylporphine complexes

The enthalpies of dissolution, transfer, and axial coordination for the Cd(II), Co(II), Mn(III), Fe(III), and Cr(III) complexes of tetraphenylporphine, H₂(TPP), in nonpolar (C₆H₆, CCl₄) and electron-donating solvents (DMF, DMSO, Py,c-C₅H₁₀NH) have been determined calorimetrically at 298.15 K. On the basis of thermogravimetrical data for the corresponding crystallosolvates the composition, thermal stability, and energy of intermolecular interaction of the metal-porphine complexes with pyridine have been calculated. Complexing in noncoordinating solvents brings about no radical change in the physicochemical characteristics of axial coordination which depend critically on the electron structure of the complex-forming metal.Translated fromfzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–850, May, 1993.     

Solvent effects on the polymerization of multi-armed vinyl biphenyl derivatives containing pendant oligo(oxyethylene)cyclotriphosphazenes

Polymerization of vinyl biphenyl derivatives containing a pendant oligo(oxyethylene)cyclotriphosphazene (VBMEP, ? (OCH₂CH₂)nOCH₃, n = 1; VBDEP, n = 2; VBTEP, n = 3) was carried out in various solvents. The conversions of these monomers increased with increasing β values, solvent hydrogen bond acceptor abilities, indicating that the hydrogen bond formation is the most important factor in the polymerization. ¹³CNMR study showed that the reactivity of the monomer is influenced by the hydrogen bond interaction. In ethanol, the kinetic orders of monomer and initiator concentrations for the polymerization of VBDEP were different from those in 1,2-dichloroethane (DCE), which suggest the predominant occurrence of primary radical termination. The intrinsic viscosity of poly(VBDEP) with M?_n = 22 000 in DCE was two times higher than that in ethanol, and plots of intrinsic viscosity versus conversion of VBDEP gave a straight line. The results suggest that the polymer chains in ethanol are in a coiled conformation, whereas in DCE they are in a relatively extended structure, and that the propagation is affected by the conformational change. These behaviors originated from the hydrogen bond formation between polymers and solvents are discussed. The copolymerization of styrene with multiarmed monomers and the properties of polycascade polymers obtained are also described. © 1993 John Wiley & Sons, Inc.     

EPR studies on some copper(II) complexes of 1,4,7,10-tetra-azadecane and its hexamethyl derivative

EPR studies have been carried out on solutions of the complexes [Cu(trien)NCS](NO₃), [Cu(trien)I]I, [Cu(Me₆trien)NCS]B?₄ and [Cu(Me₆trien)](ClO₄)₂, (trien = 1,4,7,10-tetraazadecane; Me₆trien = hexamethyl trien) in different solvents to investigate the solute-solvent interactions. From calculations of the 4s contribution in the ground state and bond parameters it is found that the axial bond in [Cu(trien)NCS](NO₃) dissolved in pyridine is weaker than that in the other complexes dissolved in different solvents. For the two methylated complexes, in spite of the +I effect of the methyl group, the in-plane copper-nitrogen bonds are found to be weak, which is probably due to the changes in structure caused by methylation.     

CH3SH和CH3SLi分子间的锂键和氢键共存型相互作用

在CH₃SLi＋CH₃SH势能面上求得锂键和氢键共存型复合物的两种稳定构型. 频率分析表明, 与单体相比复合物中S(5)—Li(6)键伸缩振动频率发生红移, 而C(8)—H(10)键伸缩振动频率发生蓝移. 经B3LYP/6-311＋＋G**, MP2/6-311＋＋G**及MP2/AUG-CC-PVDZ水平计算的含基组重叠误差(BSSE)校正的复合物?中相互作用能分别为－58.99, －57.87和－62.89 kJ•mol^－1. 采用自然键轨道(NBO)理论, 分析了复合物中单体轨道间的电荷转移, 电子密度重排及其与相关键键长变化的本质等. 采用分子中的原子(AIM)理论分析了复合物中氢键和锂键的电子密度拓扑性质．在极化连续模型(PCM)下, 考察了溶剂化效应. 结果表明, 所考察的水、二甲亚砜、乙醇和乙醚等四种溶剂均使单体间的相互作用能增大, 且溶剂对复合物中的锂键结构及其振动频率具有显著的影响, 而对复合物中的氢键的振动频率影响不大.     

Spectrophotometric and spectroscopic studies of complexation of 8-hydroxyquinoline with π acceptor metadinitrobenzene in different polar solvents

The complexation of electron donor–acceptor complexes of 8-hydroxyquinoline (8HQ) and metadinitrobenzene (MNB) have been studied spectrophotometrically and thermodynamically in different polar solvent at room temperature. A new absorption band due to charge transfer (CT) transition is observed in the visible region. A new theoretical model has been developed which take into account the interaction between electronic subsystem of 8HQ and MNB. The results indicate the extent of charge transfer complexes (CTCs) formation to be more in less polar solvents. Stoichiometry of the complex was found to be 1:1 by straight line method and ¹H NMR between donor and acceptor at the maximum absorption bands. Ionization potential (I_D) and resonance energy (R_N) were determined from the CT transition energy in different solvents. The formation constants of the complexes were determined in different polar solvents from which ΔG° formation of the complexes was estimated and also extinction coefficient of the charge transfer complex (CTC) was calculated. Oscillator strength, transition dipole strengths and maximum wavelength of the CTC (λ_CT) in various solvents and IR spectra of the CTC have also been discussed. It has been observed that all parameters described above changed with change in polarity and concentration of donor.     

Kinetics and mechanism of urethane formation catalyzed by organotin compounds. II. The reaction of phenyl isocyanate with methanol in DMF and cyclohexane under the action of dibutyltin diacetate

The kinetics of the dibutyltin diacetate (DBTDA)-catalyzed reaction of phenyl isocyanate with methanol in DMF and cyclohexane have been studied by monitoring the rate of change of the absorbance of the reaction mixture at 281.6 and 280.9 nm, respectively. Our results indicate that the mechanism of the reaction is independent of the nature of the (inert) solvent. The subsequent reaction steps are (i) complexation of methanol to DBTDA, (ii) dissociation of the complex into a proton and an anion of composition [(n-C₄H₉)₂Sn(OCOCH₃)₂(OCH₃)]^?, (iii) insertion of the isocyanate into the tin—alkoxy bond (the rate-determining step), and (iv) methanolysis of the thus-formed urethane precursor with simultaneous regeneration of the anion. The rate of the catalyzed reaction increases on goin from coordinating to noncoordinating solvents. The following sequence in order of increasing rate constant was observed: DMF < dibutyl ether < cyclohexane. This is because in coordinating solvents, DBTDA and methanol, apart from forming a complex with each other, also form complexes with the solvent.     

Ultrafast Relaxation Dynamics of the Excited States of 1‐Amino‐ and 1‐(N,N‐Dimethylamino)‐fluoren‐9‐ones

The dynamics of the excited states of 1‐aminofluoren‐9‐one (1AF) and 1‐(N,N‐dimethylamino)‐fluoren‐9‐one (1DMAF) are investigated by using steady‐state absorption and fluorescence as well as subpicosecond time‐resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen‐bonded form in aprotic solvents, the excited‐state intramolecular proton‐transfer reaction is the only relaxation process observed in the excited singlet (S₁) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen‐bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S₁(LE), or S₁(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge‐transfer, S₁(TICT), state. A crossing between the excited‐state and ground‐state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S₁(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen‐bond‐donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen‐bonded complex formed between the S₁(TICT) state and the solvent is possibly avoided and the hydrogen‐bonded complex is weakly emissive.     

Synthesis of new boron complexes: application to transfer hydrogenation of acetophenone derivatives

Two new boron complexes were synthesized from N‐[3‐(methylmercapto)aniline]‐3,5‐di‐tert‐butylsalicylaldimine ( LH ) with boron reagent BPh₃ or BF₃.Et₂O. These boron complexes are stable and easily soluble in protic solvents such as ethanol (C₂H₅OH) but hardly soluble in nonprotic solvents such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂) and tetrahydrofuran (THF). All new boron complexes have been fully characterized by both analytical and spectroscopic methods. The catalytic activities of complexes [LBPh₂], 2 , and [LBF₂], 3 , in the transfer hydrogenation of acetophenone derivatives were tested. Stable boron complexes were found to be efficient catalysts in the transfer hydrogenation of aromatic ketones in good conversions up to 99% in the presence of iso‐PrOH/KOH. Copyright © 2011 John Wiley & Sons, Ltd.     

DFT study on the intermolecular interactions between Aun (n = 2–4) and thymine

Density functional B3LYP method with 6-31++G** basis set is applied to optimize the geometries of the luteolin, water and luteolin–(H₂O)_n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin–H₂O, nine steady luteolin–(H₂O)₂ and ten steady luteolin–(H₂O)₃, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin–(H₂O)_n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.     

Quantum chemical interpretation of the effects induced by tetramethylethylenediamine and dimethoxyethane in RLi non-polar monomer systems

The energetic and electronic parameters of various mono- and bidentate complexes of CH₃Li with N- and O-containing electron donors were calculated by the MNDO method. It was shown that N,N,N′,N′-tetramethylethylenediamine (TMD) forms a more stable bidentate complex with CH₃Li than 1,2-dimethoxyethane (DME). However, DME, in contrast to TMD, may form a bis-bidentate complex with CH₃Li in which the C Li bond is weakened to a higher degree than in complexes of CH₃Li with N-containing electron donors. Much lower steric hindrance of DME, as compared to that of TMD, makes an easy formation of bis- and tris-monodentate complexes of DME with CH₃Li possible; in these bis- and tris-monodentate complexes DME was simulated by (CH₃)₂O. Parameters of the C Li bond in the tris-monodentate complexes of (CH₃)₂O and tetrahydrofuran (THF) with CH₃Li are comparable to those of the bis-bidentate complex CH₃Li · 2 DME. These results are in qualitative agreement with experimental data, according to which THF and DME, in contrast to TMD, can favor the formation of separated ion pairs as active sites in anionic polymerization.     

Halogen Bonding： An AIM Analysis of the Weak Interactions

A series of complexes formed between halogen-containing molecules and ammonia have been investigated by means of the atoms in molecules （AIM） approach to gain a deeper insight into halogen bonding. The existence of the halogen bond critical points （XBCP） and the values of the electron density （Pb） and Laplacian of electron density （V2pb） at the XBCP reveal the closed-shell interactions in these complexes. Integrated atomic properties such as charge, energy, polarization moment, volume of the halogen bond donor atoms, and the corresponding changes （△） upon complexation have been calculated. The present calculations have demonstrated that the halogen bond represents different AIM properties as compared to the well-documented hydrogen bond. Both the electron density and the Laplacian of electron density at the XBCP have been shown to correlate well with the interaction energy, which indicates that the topological parameters at the XBCP can be treated as a good measure of the halogen bond strength In addition, an excellent linear relationship between the interatomic distance d（X…N） and the logarithm of Pb has been established.     

Solvent effects on the thermodynamics of the formation of hydrogen bonded complexes ofm-cresol III

Thermodynamic parameters for the hydrogen bonded complexes of m-cresol with various bases in the solvent benzene have been determined from calorimetric and spectroscopic data. These data were analyzed by linear solvation energy relationships. When combined with data previously determined for the same complexes in CCl₄ and cyclohexane solvents, it is shown that solvent effects on the thermodynamics of hydrogen bond formation are due to solvation of the free m-cresol and base through dipolar and perhaps donor-acceptor interactions.     

Cationic Exciplexes: Role of Hydrogen Bonding in Deactivation and Electronic Coupling

Emissive properties for the cationic exciplex (A⁺*/D→A^.D^.+) of an isoquinolinium cation tethered to a substituted arene ( 1⁺ ) are strongly affected by hydrogen bonding solvents. At equal dielectric constant (ϵ), the ground-to-excited state energy gaps (ΔG) and solvent reorganization energies (λ_s) decrease from nitriles to aliphatic alcohols. The corresponding decrease from aliphatic alcohols to high hydrogen bond acidity solvents is ∼3 times larger. The exciplex decay (k_Ex), largely determined by unfolding of the exciplex to a stretched conformer, changes in a complex way depending on the strength of the hydrogen bond ability of these solvents. In contrast, the electronic couplings between the exciplex ground, excited, and charge transfer states do not show a solvent functionality dependence.