Investigations on the local angular distortions and the spin-Hamiltonian parameters for Ni in sulfides

The local angular distortions and the spin-Hamiltonian parameters (the g factors and the hyperfine parameters) for Ni⁺ in ABS₂ (ACu, Ag; BAl, Ga) ternary sulfides are theoretically investigated from the perturbation formulas of these parameters for 3d⁹ ions in a tetragonally distorted tetrahedron. In view of the strong covalency of such systems, the ligand orbital and spin–orbit coupling contributions are taken into account using the cluster approach. The local impurity-ligand bond angles in the Ni⁺ centers are found to be about 1.4–4.5° smaller than those of the host monovalent A sites in the pure crystals, due to size mismatching substitution. As a result, the ligand tetrahedra exhibit slight elongation in CuBS₂:Ni⁺ and slight compression in AgGaS₂:Ni⁺. The calculated spin-Hamiltonian parameters, optical transitions and the relative intensity ratios show reasonable agreement with the experimental data.     

Specific crystal structure of poly(3-hydroxybutyrate) thin films studied by infrared reflection–absorption spectroscopy

Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm⁻¹ due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH₃ group of one helix and the CO group of another helix.     

Effect of peripheral substitution on the electronic absorption and magnetic circular dichroism (MCD) spectra of metal-free azo-coupled bisphthalocyanine

A new azo-coupled bisphthalocyanine is synthesized from the corresponding quinoxaline oxime which can be obtained by the reaction of s-trans-chloroethanedial with NN conjugated metal-free phthalocyanine. The phthalocyanine is synthesized by the reaction of 4-nitro-o-phenylenediamine with 2-nitro-9,10,16,17,23,24-hexa(hexylthio)phthalocyanine. Novel compounds are characterized by elemental analysis, UV/vis, IR and ¹H NMR, and MALDI-TOF spectroscopy. The effect of the azo units on the position and intensity of the electronic absorption and magnetic circular dichroism (MCD) spectra of the bisphthalocyanine are examined for the NN conjugated metal-free phthalocyanine.     

Investigations of molecular interactions in propionic acid–N,N-dimethyl formamide binary system—FTIR study

FTIR spectra of propionic acid (PA), N,N-dimethyl formamide (DMF) and its binary mixtures with varying molefractions of the PA were recorded in the region 500–3500 cm⁻¹, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), δ(OC–N) and ν_as(CN) of DMF, ν(CO) and ν(CO) of PA have been explained in terms of the hydrogen bonding interactions between DMF and PA and dipole–dipole interaction. The intrinsic bandwidth for the vibrational modes ν_as(CN) and ν(CO) has been elucidated using Bondarev and Mardaeva model.     

Structural and vibrational studies of molecular conductors using quantum mechanical methods: 1,3-Dithiole-2-thione, 1,3-dithiole-2-one, 1,3-dioxole-2-one and 1,3-dioxole-2-thione

Computations were carried out by employing the RHF and density functional theory (DFT) methods to investigate the geometries, atomic charges, harmonic vibrational frequencies for the 1,3-dithiole-2-thione (DTT), 1,3-dithiole-2-one (DTO), 1,3-dioxole-2-thione (DOT) and 1,3-dioxole-2-one (DOO) molecules and their radical cations. The geometrical parameters and atomic charges on various atomic sites of the DTT and DOT molecules and their radical cations suggest extended conjugation in these systems. Contrary to this, for the DOO⁺ and DTO⁺ ions there is no evidence in favour of such conjugation, however, the neutral molecules exhibit some conjugation. Harmonic forced field and vibrational mode calculations provided convincing theoretical evidence for the reassignment of some fundamental vibrational modes for all the four molecules. In going from the neutral species to the charged ions for all the four cases the CC stretching frequency is found to decrease drastically. The CS stretching frequency reduces drastically for the DTT and DOT molecules as compared to their radical cations whereas the CO stretching frequency is found to increase in going from the neutral molecule to its radical cation for the DOO and DTO molecules. The ring stretching mode with a₁ symmetry and CC and CO/S stretching modes in these molecules appear to help in conversion of neutral molecule into respective radical cation and neighbouring radical cation into respective neutral molecule. Thus, there appears the feasibility of stretching vibrational mode coupling with electron transfer.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

Ferrole-type compounds containing thiophenic or thiepinic rings in the 3,4-positions of the metallacycle

The new ferrole Fe₂(CO)₆[μ-η²,η⁴-(Fc)CC{C(H)C(R)S}CC(SiMe₃)] [R = SiMe₃ (1) and R = Fc (2)] and ruthenoles Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(H)}CC(Fc)] 3 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC(SCCFc)C(H)C(Fc)] 4, have been obtained from the reactions of M₃(CO)₁₂ (M = Fe, Ru) and FcCCSCCSiMe₃ through S-C bond activations and C-C coupling reactions. Thermolysis of Ru₂(CO)₆[μ₃-η²,η⁴,η³-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃}Ru(CO)₃}CC(Fc)] alone and in the presence of HCCFc, yielded the compounds Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)}CC(Fc)] 5 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)C(H)C(Fc)}CC(Fc)] 6, respectively. The crystal structures of the compounds 1, 3, 4 and 6 are reported.     

Silicon version of enamines: Amino-substituted disilenes by the reactions of the disilyne RSiSiR (R = SiPr[CH(SiMe3)2]2) with amines

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with secondary or primary amines produced amino-substituted disilenes R(R₂′N)SiSiHR 2a-d (R = SiⁱPr[CH(SiMe₃)₂]₂, R₂′NEt₂N (2a), (CH₂CH₂)₂N (2b), ^tBu(H)N (2c), and Ph₂N (2d)). Spectroscopic and X-ray crystallographic analyses of 2 showed that 2a-c have a nearly coplanar arrangement of the SiSi double bond and the amino group, giving π-conjugation between the SiSi double bond and the lone pair on the nitrogen atom, whereas 2d has a nearly perpendicular arrangement precluding such conjugation. Theoretical calculations indicate that π-conjugation between the π-orbital of the SiSi double bond and the lone pair on the nitrogen atom is markedly influenced by the torsional angle between the SiSi double-bond plane and the amino-group plane.     

Conformational influences of the polymorphic forms on the CO and C–H stretching modes of five saturated monoacid triglycerides studied by Raman spectroscopy at various temperatures

A study of the vibrational behavior of five saturated monoacid triacylglycerides is performed by Raman spectroscopy at various temperatures in two separate spectral ranges: 1780–1700 and 3100–2650 cm⁻¹. The samples are studied in polycrystalline phase at room temperature, in isotropic liquid phase, and in polycrystalline phase after cooling from the isotropic liquid phase. The CO stretching mode of these triglycerides changes significantly according to the temperature: we observe three components, or an unresolved doublet, or a resolved doublet. The I(2845)/I(2880) ratios (in the C–H stretching spectral region) of the different saturated monoacid triglycerides vary also according to the temperature. The study of these two indicators (the CO stretching mode and the I(2845)/I(2880) ratio) has permitted us to determine the polymorphic forms of the studied triglycerides.     

H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about CC bond

The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic ¹H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl₃ at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG^# 98.5 kJ/mol (at 298 K). The variable-temperature ¹H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d₆, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG^# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The ¹³C NMR Δδ_C(2)C(2′) values, ranging from 58 to 69 ppm in 1a–d and 49-58 ppm in 2a–d, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH₂CH₂Ph. The decrease of the Δδ_C(2)C(2′) values in 2a–d has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds.     

Heterobimetallic aluminium and zinc complex with N-arylanilido-imine ligand: Synthesis, structure and catalytic property for ring-opening polymerization of ε-caprolactone

Treatment of a N-arylanilido-imine ligand [ortho-C₆H₄(NHAr)CHN]₂CH₂CH₂ (Ar = 2,6-Me₂C₆H₃) (LH₂) with one equiv. of AlMe₃ affords a monometallic complex [C₆H₄(NHAr)–CHN)]CH₂CH₂(C₆H₄(NAr)CHNAlMe₂) (1). The monometallic complex 1 reacts with one equiv. of ZnEt₂ to give a heterobimetallic complex [C₆H₄(NAr)–CHNZnEt]CH₂CH₂[C₆H₄(NAr)–CHNAlMe₂] (2). Both complexes were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses, and the molecular structures of 1 and 2 were determined by X-ray diffraction analysis. The complexes 1 and 2 both are efficient catalysts for ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol yielding polymers with narrow polydispersity values and complex 2 initiates the polymerization in a controllable manner.     

Protonation of manganese phosphonioallenyl complexes

The addition of phosphines to the manganese allenylidene complexes Cp(CO)₂MnCCC(Ph)R (R = H, Ph) proceeds selectively at the C_α atom to result in the α-phosphonioallenyl complexes Cp(CO)₂Mn⁻-C(⁺PR₃¹)CC(Ph)R. The protonation of the latter affords the η²-(1,2)-phosphonioallenes Cp(CO)₂Mn{η²-(1,2)-HC(⁺PR₃¹)CC(Ph)R}, rather than the phosphoniovinylcarbenes Cp(CO)₂MnC(⁺PR₃¹)-HCC(Ph)R. All complexes obtained are stereochemically rigid and do not isomerize into the η²-(2,3)-phosphonioallene isomers.     

Matrix-isolation FT-IR and theoretical investigation of the competitive intramolecular hydrogen bonding in 5-methyl-3-nitro-2-hydroxyacetophenone

The paper presents the conformational, vibrational and hydrogen bond characteristics of 5-methyl-3-nitro-2-hydroxyacetophenone studied with the combined matrix-isolation FT-IR spectroscopic and theoretical (DFT/B3LYP/6-31++G^**) technique. Theoretical calculations predict three stable conformations of the studied compound. Only two of these conformations could be identified experimentally using the matrix-isolation FT-IR technique. The conformation with the intramolecular hydrogen bond OH^…ON has been found to be more stable than the conformation with the OH^…OC type of hydrogen bond by 7.28 kJ/mol. The complete assignment of the experimental spectra could be performed based on the theoretical calculations including the normal coordinate analysis and isotopic substitution.     

Tertiary phosphine abstraction from a platinum(II) coordination complex with SeCN: Crystal and molecular structures of SePTA and [SePTA-Me]I · CH3OH

Reacting [PtCl(PTA)₃]Cl(PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1^3,7]decane) with KSeCN in aqueous or MeOH medium results in the abstraction of the PTA ligands to yield SePTA. The reaction also proceeds quantitatively by direct reaction of PTA and KSeCN in water or methanol. The methylated PTA ligand, [PTA-Me]I (1-methyl-1-azonia-3,5-diaza-7-phosphatricyclo[3.3.1.1^3,7]decane iodide), reacts accordingly with KSeCN, albeit significantly slower. The crystal structure of SePTA, 1, and [SePTA-Me]I · CH₃OH, 2, revealed PSe bond distances of 2.0991(19) and 2.100(2) Å, respectively. The first order phosphorous selenium coupling constants, ¹J_P-Se (D₂O), of 722 and 788 Hz for SePTA and [SePTA-Me]I, respectively, indicates the latter is significantly less electron rich.     

Density Functional Theory studies on interactions of phosphoryl ligands with the Ca cation: Affinity and associated parameters

DFT (B3LYP/6-31G(d)) and semi-empirical (PM6) calculations of Ca²⁺ affinities on a set of substituted phosphoryl ligands were performed with complete geometry optimization. Two types of ligands were calculated: a set of trivalent [OP(R)] and a set of pentavalent [OP(R)₃] ones (R = H, F, Cl, Br, OH, OCH₃, CH₃, CN, NH₂ and NO₂), with R either directly bound to the phosphorus atom or to the para position of a phenyl ring. The affinity of the Ca²⁺ cation for the ligands was quantified in terms of interaction energy. Additionally, geometric and electronic parameters were correlated with the intensity of that interaction. Our results show that the electronic nature of the substituent mainly affects the interaction energy. Donor groups are associated with more negative interaction energies, while acceptor groups are associated with less negative interaction energies.     

Nucleophilic destruction of organophosphate toxins: A computational investigation

Computed reaction enthalpies, free energies, and activation barriers in vacuo are presented for the nucleophilic detoxification of the organophosphorus compounds (H)(HO)P(O)F, (H)(H₃CO)P(O)F and (H₃C)(CH(CH₃)₂O)P(O)F via the reaction R₁OH + (R₂)(R₃O)P(O)F → (R₂)(R₃O)P(O)(OR₁) + HF for a wide variety of R₁OH nucleophiles. Density functional theory at the B3LYP/6-311++G(d,p) computational level was employed for all the calculations. A multi-step Wright-type reaction mechanism [J. B. Wright, W.E. White, J. Mol. Struct. (THEOCHEM) 454 (1998) 259], which proceeds via a proton transfer from the nucleophile to the fluorine atom through the phosphinyl oxygen atom, was consistently found to have a lower activation barrier in the gas-phase than for the corresponding mechanism that operates via a proton transfer from the nucleophile directly to the fluorine atom. Of the nucleophilic agents investigated, peroxybenzoic acid and o-iodosobenzoic acid had the lowest classical activation barrier for the Wright-type mechanism.     

Hyperpolarizability of donor-acceptor azines subject to push-pull character and steric hindrance

The push-pull character of two series of donor-acceptor azines has been quantified by ¹³C, ¹⁵N chemical shift differences of the partial C(1)N(1) and N(2)C(2) double bonds in the central linking C(1)N(1)-N(2)C(2) unit and by the quotient of the occupations of the bonding π and anti-bonding π^∗ orbitals of these bonds. Excellent correlation of the latter push-pull parameter with the corresponding bond lengths d_CN strongly recommend both the occupation quotients π^∗/π and the corresponding bond lengths as reasonable sensors for quantifying the push, pull character along the CN-NC linking unit, for the donor-acceptor quality of the two series of azines and for the molecular hyperpolarizability ß₀ of these compounds. Within this context, reasonable conclusions concerning the interplay of steric hindrance in the chromophore, push-pull character and hyperpolarizability of the azines and their application as NLO materials will be drawn.     

Bis(amino)allenylidene complexes by displacement of the MeO group in methoxy allenylidene complexes of chromium and tungsten. Synthesis, DFT calculations and solid-state structures of new bis(amino)allenylidene complexes

Pentacarbonyl dimethylamino(methoxy)allenylidene tungsten, [(CO)₅WCCC(OMe)NMe₂] (1b), reacts with one equivalent of primary amines, H₂NR, by selectively replacing the methoxy group to give dimethylamino(amino)allenylidene complexes, [(CO)₅WCCC(NHR)NMe₂]. When the amine is used in excess both terminal groups, OMe as well as NMe₂, are replaced by the primary amino group giving [(CO)₅WCCC(NHR)₂ ]. The NHR substituent in these complexes may be modified by deprotonation with LDA followed by alkylation. The replacement of the methoxy group in 1b by a secondary amino group, NR₂, can be achieved by a stepwise process. Addition of Li[NR₂] to the C_γ atom of 1b affords an alkynyl tungstate. Subsequent OMe⁻ elimination induced by TMS-Cl/SiO₂ yields the allenylidene complexes [(CO)₅WCCC(NR₂)NMe₂]. When bidentate diamines are used instead of monoamines both substituents, OMe and NMe₂, are replaced and allenylidene complexes are formed in which C_γ constitutes part of a 5-, 6-, or 7-membered heterocycle. The reaction of [(CO)₅CrCCC(OMe)NMe₂] (1a) with diethylene triamine affords an allenylidene complex with a heterocyclic endgroup carrying a dangling CH₂CH₂NH₂ substituent. All reactions follow a strict regioselective attack of the nucleophile at C_γ and proceed with good to excellent yields. The addition of N-H to the C_αC_β bond is not observed. By applying either one of these routes nearly any substitution pattern in bis(amino)allenylidene complex can be realized.