Inelastic neutron scattering and vibrational spectra of 2-(N-methyl-α-iminoethyl)-phenol and 2-(N-methyliminoethyl)-phenol: Experimental and theoretical approach

The infrared, Raman, and inelastic neutron scattering (INS) spectra of two ortho-hydroxy aryl Schiff’s bases, 2-(N-methyliminoethyl)-phenol and 2-(N-methyl-α-iminoethyl)-phenol, were recorded. Ab initio molecular orbital calculations employing the DFT (B3LYP) method with the 6-31G** basis set for both compounds were done. Assignments of vibrational modes within the 3500–50 cm⁻¹ spectral region were carried out. On the basis of the DFT calculations, four rotomers of 2-(N-methyl-α-iminoethyl)-phenol were analysed.     

DFT studies on nonlinear optical properties of neutral nest-shaped heterothiometallic [MOS3Py5Cu3X] (M = Mo, W; X = F, Cl, Br, I) clusters

Theoretical calculations were carried out on some neutral nest-shaped heterothiometallic cluster compounds [MOS₃Py₅Cu₃X] (M = Mo, W; X = F, Cl, Br, I) with the high first static hyperpolarizabilities β values. The geometries of these cluster compounds were optimized by the restricted DFT method at B3LYP level with LanL2DZ base set without any constrains. In order to understand the relationship between the first static hyperpolarizabilities and the compositions of these clusters, the frontier orbital compositions and energy gaps between the HOMO and LUMO orbitals were calculated and analysed. In these clusters the HOMO orbitals are mainly composed of halogen atoms and the first static hyperpolarizability increases from F to I atom. The LUMO orbitals of clusters [MoOS₃Py₅Cu₃X] are comprised of Mo, O and S atoms while the LUMO orbitals of clusters [WOS₃Py₅Cu₃X] composed of W atom and pyridine ring. The energy gaps between the HOMO and LUMO orbitals of the clusters [MoOS₃Py₅Cu₃X] are smaller than those of the clusters [WOS₃Py₅Cu₃X]. As a result the first static hyperpolarizability values of the clusters [MoOS₃Py₅Cu₃X] are higher than those of the clusters [WOS₃Py₅Cu₃X].     

Effects of the substituting groups and proton abstraction on the nonlinear optical properties of heteroleptic bis-tridentate Ru(II) complexes

The second-order nonlinear optical (NLO) properties have been carried out on a series of Ru(II) complexes with different 4′-substituted terpyridine derivatives and the tridentate ligand 2,6-bis(benzimidazole-2-yl)pyridine by using density functional theory (DFT). The introduction of different substituents enhances the static first hyperpolarizabilities in various degrees. Time-dependent density functional theory (TD-DFT) calculations indicate that the additional metal-to-ligand charge transfer (MLCT) transition, which is vectorially opposite to the intraligand charge transfer (ILCT) transition, could contribute to the smaller β_vec in species with electron-withdrawing groups compared to ones with electron-donating groups. The stepwise deprotonation brings about a change in electron density of the benzimidazole moiety and finally makes the moiety turn to be as donor, which subsequently leads to an efficient second-order NLO switching. For the species 3 with electron-donating group, the β_vec value of the mono-deprotonated system is 49.9 and 11.1 times as small as that of its diprotonated and fully deprotonated ones.     

Thermochemical Study of the Cyanophenol Isomers

The standard (p° = 0.1MPa) molar enthalpies of formation for 2-, 3- and 4-cyanophenol in the gaseous phase were derived from the standard molar enthalpies of combustion in oxygen at T = 298.15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpies of sublimation at 298.15 K, measured by Calvet microcalorimetry: 2-cyanophenol, (32.8 ± 2.1) kJ-mol^–1; 3-cyanophenol, (37.8 ± 2.2) kJ-mol^–1; 4-cyanophenol, (35.1 ± 2.5)-kJ-mol^–1. Ab initio geometry optimizations of the three cyanophenols and respective phenoxyl radicals and phenoxide anions were performed using the 6-31G* basis sets. Single-point MP2 and DFT energy calculations allowed the estimation of the enthalpies of formation in the gaseous phase, the O—H bond dissociation energies, and the gas-phase acidities of the three cyanophenols. The theoretical results are generally in good agreement with the experimental findings.     

Molecular first hyperpolarizabilities of retinal and its derivatives

The hyper-Rayleigh scattering technique (HRS) has been used to determine the molecular first hyperpolarizabilities β of retinal, retinoic acid, vitamin A acetate and a retinal Schiff base in its protonated and unprotonated form. The former is responsible for the linear and non-linear optical properties of bacteriorhodopsin. A previous examination of these compounds by HRS at 1064 nm yielded surprisingly high β-values. Here, we report HRS measurements performed at 1064, 1300 and 1500 nm. The derived hyperpolarizabilities are self-consistent with the two-state model for all three wavelengths, but they are one order of magnitude lower than those reported previously.     

Theoretical Study of the Substituent Effects on the Nonlinear Optical Properties of a Room‐Temperature‐Stable Organic Electride

Excess‐electron compounds can be considered as novel candidates for nonlinear optical (NLO) materials because of their large static first hyperpolarizabilities (β₀). A room‐temperature‐stable, excess‐electron compound, that is, the organic electride Na@(TriPip222), was successfully synthesized by the Dye group (J. Am. Chem. Soc. 2005 , 127, 12416). In this work, the β₀ of this electride was first evaluated to be 1.13×10⁶ au, which revealed its potential as a high‐performance NLO material. In particular, the substituent effects of different substituents on the structure, electride character, and NLO response of this electride were systemically studied for the first time by density functional theory calculations. The results revealed that the β₀ of Na@(TriPip222) could be further increased to 8.30×10⁶ au by introducing a fluoro substituent, whereas its NLO response completely disappeared if one nitryl group was introduced because the nitro‐group substitution deprived the material of its electride identity. Moreover, herein the dependence of the NLO properties on the number of substituents and their relative positions was also detected in multifluoro‐substituted Na@(TriPip222) compounds.     

Synthesis of 1,3-bis(acetylacetonyloxy)- and 1,3-bis(benzoylacetonyloxy)benzene and their complexation with lanthanide ions

Claisen condensation of 1,3-bis(methoxycarbonylmethoxy)benzene with acetone and acetophenone afforded new chelating ligands consisting of two β-diketonate fragments, viz., 1,3-bis(acetylacetonyloxy)benzene and 1,3-bis(benzoylacetonyloxy)benzene, which are linked to each other through the resorcinol spacer. In the crystal, 1,3-bis(acetylacetonyloxy)benzene, unlike the starting ester, adopts a planar conformation and exists in the enol form. The acidities of these compounds and their complexation with lanthanide ions in aqueous ethanolic solutions were studied by pH-potentiometry. Depending on the concentration conditions and pH, the La³⁺, Gd³⁺, and Lu³⁺ ions form 1 : 1, 1 : 2, or 1 : 3 complexes with bis(β-diketones). The stability of the complexes increases as the atomic number of the lanthanide increases (La³⁺ < Gd³⁺ ≤ Lu³⁺). The complexation constants and selectivity of complexation substantially increase with increasing degree of deprotonation of the ligands, which indicates that both chelate groups of the ligands are simultaneously involved in coordination. The Ph substituents in bis(β-diketone) have a considerable effect on the composition and stability of complexes with lanthanide ions due to additional noncovalent inner-sphere interactions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 614–622, March, 2005.     

Electron Counting in Carbaalane Clusters with Cubic Aluminum Core

Extended Hückel Theory (EHT) and Density Functional Theory (DFT) calculations on hexacapped cubic aluminum clusters of the type [(AlH)₈(μ₄-CH)_6−n (μ₄-H) _n ]^+/−q (n ≤ 6) indicate that their favored number of skeletal electron pairs (SEP), 12 SEPs for n ≥ 3, 14 SEPs for n = 2, 16 SEPs for n = 1 and 18 SEPs for n = 0, depends on the relative number of the two types of capping ligands: one-orbital ligands such as H and conical three-orbital CH units. Although only 16- and 18-SEP species have been isolated so far, DFT calculations indicate that 14-SEP clusters of the type [(AlR′)₈(μ₄-CR)₄(μ₄-X)₂]²⁺ (X = one-orbital ligand) should be synthesized. Computed 12-SEP models were not found to be energy minima, but this should not preclude the possibility for stabilizing such species, for example with bulky substituents. Changing the CR capping ligands into AlR units in the above series is expected to limit their electron counts to 12 SEPs. The incorporation of a main-group atom in the middle of the cube does not change the favored cluster electron count. However, calculations indicate that only 12-SEP species are likely to be synthesized. Dedicated to Professor Günter Schmid on the occasion of his 70th birthday     

The Theoretical and Experimental Investigation of the Fluorinated Palladium β-Diketonate Derivatives: Structure and Physicochemical Properties

To search for new suitable Pd precursors for MOCVD/ALD processes, the extended series of fluorinated palladium complexes [Pd(CH₃CXCHCO(R))₂] with β-diketone [tfa−1,1,1-trifluoro-2,4-pentanedionato (1); pfpa−5,5,6,6,6-pentafluoro-2,4-hexanedionato (3); hfba−5,5,6,6,7,7,7-heptafluoro-2,4-heptanedionato (5)] and β-iminoketone [i-tfa−1,1,1-trifluoro-2-imino-4-pentanonato (2); i-pfpa−5,5,6,6,6-pentafluoro-2-imino-4-hexanonato (4); i-hfba-5,5,6,6,7,7,7-heptafluoro-2-imino-4-heptanonato (6)] ligands were synthesized with 70–80% yields and characterized by a set of experimental (SXRD, XRD, IR, NMR spectroscopy, TG) and theoretical (DFT, Hirshfeld surface analysis) methods. Solutions of Pd β-diketonates contained both cis and trans isomers, while only trans isomers were detected in the solutions of Pd β-iminoketonates. The molecules 2–6 and new polymorphs of complexes 3 and 5 were arranged preferentially in stacks, and the distance between molecules in the stack generally increased with elongation of the fluorine chain in ligands. The H…F contacts were the main ones involved in the formation of packages of molecules 1–2, and C…F, F…F, NH…F contacts appeared in the structures of complexes 4–6. The stability of complexes and their polymorphs in the crystal phases were estimated from DFT calculations. The TG data showed that the volatility differences between Pd β-iminoketonates and Pd β-diketonates were minimized with the elongation of the fluorine chain in the ligands.     

Hyperpolarizability of 6-vertex carboranes quantum chemical study

Structure and molecular first hyperpolarizability (β) of nitro-amino-substituted 6-vertex 1,6-carboranes are investigated by means of DFT calculations. The results obtained have revealed that the relative orientation of substituents with respect to the carborane cage influences bond lengths distribution in the cage, which leads to significant changes in the values of hyperpolarizabilities. Calculations with different basis sets have demonstrated that the value of β is not significantly affected by the choice of basis set. The calculated data shows that hyperpolarizability of carborane molecules substituted for carbon atoms is lower than when substituted for boron atoms. For latter molecule, the value of β is of the same order as that of para-nitroaniline molecule.     

Photoswitching of the third-order nonlinear optical properties of azobenzene-containing phthalocyanines based on reversible host–guest interactions

Two water soluble azobenzene and phthalocyanine dyads with D–π–A alignment were synthesized. It was found that both compounds showed very large molecular cubic hyperpolarizabilities which are at the order of 10⁻³⁰ esu as the result of their unique chemical structure. The azobenzene moieties of these compounds, upon alternating illumination of UV and visible light, could reversibly associate with α-CD to form inclusion complexes through host–guest interaction in aqueous media, resulting in apparent influences to the 3rd NLO properties of these compounds. This influence is especially significant for the phthalocyanine whose central metal atom is copper (II). The molecular cubic hyperpolarizability γ of the inclusion complex for the copper phthalocyanine is 2.1 × 10⁻³⁰ esu. When the inclusion complex dissociated under the illumination of 365 nm light, γ value increased to 4.2 × 10⁻³⁰ esu, which is a 100% enhancement. Taking account of the large molecular cubic hyperpolarizabilities of these compounds, the present materials are potential as ideal 3rd NLO photoswitching systems.     

Tuning the Electronic Coupling in Cyclometalated Diruthenium Complexes through Substituent Effects: A Correlation between the Experimental and Calculated Results

A common bridging ligand, 3,3′,5,5′‐tetrakis(N‐methylbenzimidazol‐2‐yl)biphenyl, and four terpyridine terminal ligands with various substituents (amine, tolyl, nitro, and ester groups) have been used to synthesize ten cyclometalated diruthenium complexes 1 ²⁺– 10 ²⁺. Among them, compounds 1 ²⁺– 6 ²⁺ are redox nonsymmetric, and others are symmetric. These complexes show two Ru^III/II processes and an intervalence charge transfer (IVCT) transition in the one‐electron oxidized state. The potential separation (ΔE) of 1 ²⁺– 10 ²⁺ has been correlated to the energy difference ΔG⁰, the energy of the IVCT band E_op, and the ground‐state delocalization coefficient α². Time‐dependent (TD)DFT calculations suggest that the absorptions in the visible region of 1 ²⁺– 6 ²⁺ are mainly associated with the metal‐to‐ligand charge‐transfer transitions from both ruthenium ions and to both terminal ligands and the bridging ligand. However, the energies of these transitions vary significantly. DFT calculations have been performed on 1 ²⁺– 6 ²⁺ and 1 ³⁺– 6 ³⁺ to give information on the electronic structures and spin populations of the mixed‐valent compounds. The TDDFT‐predicted IVCT excitations reproduce well the experimental trends in transition energies. In addition, three monoruthenium complexes have been synthesized for a comparison study.     

A computational study on the substituent effects and product stereoselectivity of the intermolecular formal aza-[3+3] cycloaddition reaction between vinylogous amides and α,β-unsaturated imine cations

The substituent effects and product stereoselectivity of the title reaction has been studied using density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level of theory. It was found that the substituents do not perturb the mechanism of intermolecular formal aza-[3+3] cycloaddition. Our calculations also show that methyl or benzyl groups on the N atom of vinylogous amide favor the addition step, but alkyl substituents on the either N atom or terminal C atom of α,β-unsaturated imine cation have opposite effects. Alkyl substituents on the N atom of α,β-unsaturated imine cation may lower the activation barriers for elimination of amide. The steric interaction between two substituents leads to the formation of major product both thermodynamically and kinetically.     

Donor/Acceptor Effects on the Linear and Nonlinear Optical Properties of Geminal Diethynylethenes (g‐DEEs)

A series of geminal diethynylethenes (g‐DEEs) with electron‐donating and/or electron‐accepting (D/A) groups were synthesized via a Pd‐catalyzed cross‐coupling sequence. The UV/VIS spectra for donor–acceptor (D–A) functionalized g‐DEEs 5, 8 , and 11 show distinctive absorption trends attributable to intramolecular charge‐transfer (ICT). The bond‐length‐alternation (BLA) index for the cross‐conjugated enediyne framework varies slightly with different terminal substituents as determined by density‐functional theory (DFT) calculations and single‐crystal X‐ray analysis. Ultrafast third‐order optical nonlinearities for the g‐DEEs were measured by the differential optical Kerr effect (DOKE) technique and show that terminal donor–acceptor substitution of g‐DEEs enhances molecular second hyperpolarizabilities (γ) in comparison to donor or acceptor g‐DEEs. A small increase in the two‐photon‐absorption cross‐section (σ⁽²⁾) is observed in the series 9 – 11 as a result of increased functionalization. The effects of donor/acceptor substitution on electron delocalization along the cross‐conjugated enediyne structure are evaluated on the basis of natural‐bond‐orbital (NBO) analysis. Solid‐state structures of the four derivatives 3b, 4b, 7 and 8 were characterized by single‐crystal X‐ray structural analysis and show an asymmetric unit cell for one derivative, D–A g‐DEE 8 .     

Experimental and DFT Studies on the DNA-binding Properties of Ruthenium(II) Complexes [Ru(phen)2L]2+(L = o-MOP, o-MP, o-CP and o-NP)

A series of ruthenium(II) complexes with electron-donor or electron-acceptor groups in intercalative ligands, [Ru(phen)₂(o-MOP)]²⁺ (1), [Ru(phen)₂(o-MP)]²⁺ (2), [Ru(phen)₂(o-CP)]²⁺ (3) and [Ru(phen)₂(o-NP)]²⁺ (4), have been synthesized and characterized by elementary analysis, ES-MS, ¹H NMR, electronic absorption and emission spectra. The binding properties of these complexes to CT-DNA have been investigated by spectroscopy and viscosity experiments. The results showed that these complexes bind to DNA in intercalation mode and their intrinsic binding constants (K_b) are 1.1, 0.35, 0.53 and 1.7 × 10⁵ M⁻¹, respectively. The subtle but detectable differences occurred in the DNA-binding properties of these complexes are mainly ascribed to the electron-withdrawing abilities of substituents (–OCH₃ < –CH₃ < –Cl < –NO₂) on the intercalative ligands as well as the intramolecular H-bond (for substituent –OCH₃) which increase the planarity area of the intercalative ligand to some extent. The density functional theory (DFT) calculations were also performed and used to further discuss the trend in the DNA-binding affinities of these complexes.     

Coordination chemistry of di-2-pyridylketone. Synthesis, spectroscopic investigations, X-ray studies and DFT calculations of Re(III) and Re(V) complexes

The paper presents a combined experimental and computational study of Re(III) and Re(V) complexes containing di-2-pyridylketone and its gem-diol form – [ReCl₃(dpk-N,O)(PPh₃)] (1), [ReCl₃(dpk-N,N′)(OPPh₃)] (2) and [ReOBr₃(dpk-OH)]·2(dpkH⁺Br⁻) (3). All the complexes have been characterized spectroscopically and structurally (by single-crystal X-ray diffraction). The complex 2 has been additionally studied by magnetic measurement. The magnetic behavior of 2 is characteristic of mononuclear octahedral Re(III) complex with d⁴ low-spin (³T_1g ground state) and arise because of the large spin–orbit coupling (ζ = 2500 cm⁻¹), which gives diamagnetic ground state. DFT and time-dependent (TD)DFT calculations have been carried out for [ReCl₃(dpk-N,N′)(OPPh₃)] and [ReOBr₃(dpk-OH), and their UV–vis spectra have been discussed on this basis.     

Ab initio CPHF calculations of first hyperpolarizabilities of nitrogen-containing polyenes with donor—acceptor substituents

Ab initio CPHF calculations of static hyperpolarizabilities (β) were carried out in order to clarify the effects of nitrogen-atom substitution in π-conjugated chains with donor—acceptor substituents. The β values decrease gradually with the number of nitrogen atoms, and change drastically with the position of nitrogen-atom substitution in the polyenes. The effects of nitrogen-atom substitution are explained by the energy levels and the shapes of the frontier orbitals.     

DFT Calculations of 1H NMR Chemical Shifts of Geometric Isomers of Conjugated Linolenic Acids,Hexadecatrienyl Pheromones,and Model Triene-Containing Compounds: Structures in Solution and Revision of NMR Assignments

A DFT study of the ¹H NMR chemical shifts, δ(¹H), of geometric isomers of 18:3 conjugated linolenic acids (CLnAs), hexadecatrienyl pheromones, and model triene-containing compounds is presented, using standard functionals (B3LYP and PBE0) as well as corrections for dispersion interactions (B3LYP-D3, APFD, M06–2X and ωB97XD). The results are compared with literature experimental δ(¹H) data in solution. The closely spaced “inside” olefinic protons are significantly more deshielded due to short-range through-space H^…H steric interactions and appear close to or even beyond δ-values of aromatic systems. Several regularities of the computational δ(¹H) of the olefinic protons of the conjugated double bonds are reproduced very accurately for the lowest-energy DFT-optimized single conformer for all functionals used and are in very good agreement with experimental δ(¹H) in solution. Examples are provided of literature studies in which experimental resonance assignments deviate significantly from DFT predictions and, thus, should be revised. We conclude that DFT calculations of ¹H chemical shifts of trienyl compounds are powerful tools (i) for the accurate prediction of δ(¹H) even with less demanding functionals and basis sets; (ii) for the unequivocal identification of geometric isomerism of conjugated trienyl systems that occur in nature; (iii) for tackling complex problems of experimental resonance assignments due to extensive signal overlap; and (iv) for structure elucidation in solution.     

Fine‐Tuning of Saponification‐Triggered Gelation by Strategic Modification of Peripheral Substituents: Gelation Regulators

A pioneering approach towards controlling the efficiency of saponification assisted gelation in ethyl ester based Zn^II‐complexes have been described. Using four new ester containing bis‐salen Zn^II complexes ( C1–C4 ) involving different para‐azo phenyl substituted ligands it has been clearly shown that gelation efficiency is greatly influenced by the electronic effects of the substituents (‐H ( C1 ), ‐CH₃ ( C2 ), ‐NO₂ ( C3 ), and ‐OCH₃ ( C4 )). Morphological, photophysical, and rheological investigations corroborated the experimental observations well and established that gelation efficiency was enhanced with electron‐withdrawing characteristics of substituents ( C4 < C2 < C1 < C3 ). This conclusion was also supported by DFT studies.