Long-lived higher excited state luminescence from new ruthenium(II)–allenylidene complexes

Resonance Raman spectra of heteroatom substituted ruthenium(II)-allenylidene complexes, obtained by irradiation into the second electronic absorption band, clearly prove the d(Ru)→π*(CCC) MLCT character of the corresponding electronic transition. The complexes are not significantly luminescent at room temperature, but in solvent glasses at 77 K, emission is observed. Only some of the complexes studied are luminescent upon irradiation into their lowest-energy absorption band. The striking finding of this study is that almost all complexes are luminescent on irradiation into their second absorption band. The emission was shown to originate from a higher lying ³MLCT state, which shows that internal conversion to the lowest excited state is very inefficient in these complexes.     

Solvent-mediated tautomerization of purine: single to quadruple proton transfer

We present calculations for the structures and the tautomerization reaction of purine and purine – (H₂O)_n (n=1–3) clusters. We find two pathways (via the carbene and the sp³-type intermediate) for the 9 ↔ 7 tautomerization of bare purine. The barrier heights for the 9 → 3 and 9 → 7 tautomerization of bare purine are calculated to be large (60–70 kcal/mol). Hydrogen bonding with the water molecule(s), however, dramatically lowers the 9 → 3 barrier by the concerted multiple proton transfer mechanism, favoring the formation of the conformer 3(H)- relative to the 7(H)-purine in the microsolvated environment, in contrast to the gas phase or the aqueous solution.     

Vibrational spectroscopic studies of metal(II) halide benzimidazole

Infrared spectra (4000–200 cm⁻¹) are reported for metal halide(II) benzimidazole complexes of the following stoichiometries: M(benz)X₂ [M=Cd, Cu; X=Cl, Br; BENZ=benzimidazole], Co(benz)₂, and Co(benz)₂X₂ [X=Cl, Br, I]. Vibrational assignments are given for all the observed bands. The analysis of the vibrational spectra indicates that there are some structure–spectra correlations. For a given series of isomorphous complexes the sum of the difference between the values of the vibrational modes of uncoordinated benzimidazole and coordinated to metal ion benzimidazole was found to increase in the order of the second ionization potentials of metals.     

Experimental infrared spectra of matrix isolated complexes of HCl with 4-substituted pyridines. Evaluation of anharmonicity and matrix effects using data from ab initio calculations

Infrared spectra have been measured for HCl complexes with 4-cyanopyridine, 4-chloropyridine, pyridine and 4-methylpyridine isolated in argon and nitrogen matrices at about 12 K. The experimental spectra are dramatically different from computed MP2/6-31+G(d,p) harmonic spectra, a consequence of the anharmonicity of the potential energy surface in the hydrogen-bonding region. Comparisons of computed and experimental data suggest that the experimental spectra correspond to complexes with HCl distances that are much longer than the computed equilibrium distances. These longer distances, R_cor(HCl), are related to the average HCl distance in the ground vibrational state of the proton-stretching mode. The value of R_cor(HCl) determines values of three effective anharmonic force constants for the HCl stretch, the NH stretch and the coupling between them for each complex. The simulated anharmonic spectra obtained when these anharmonic force constants are used in place of the corresponding harmonic constants show spectral patterns with respect to both frequencies and intensities that are very similar to those observed in the experimental spectra obtained in Ar and N₂ matrices. 1D anharmonic potential curves related to the experimental spectra are presented. They provide insight into anharmonicity of the hydrogen-bonded proton stretch for these systems, and into the sensitivity of the potential energy surface to the environment.     

FTIR studies of the CH3CN–BF3 complex in solid Ar, N2, and Xe: Matrix effects on vibrational spectra

FTIR spectra of the four isotopically substituted 1:1 complexes of acetonitrile and boron trifluoride were recorded in Ar, N₂ and Xe matrices. In Ar, previously unreported three vibrational modes of the complex were clearly observed. Several significant vibrational bands were also observed in N₂ and Xe. The observed frequency shifts on complexation, Δν, were qualitatively in good agreement with the computational results, which were calculated at the B3LYP/6-311++G(d,p) level using the optimized geometry of the C_3v eclipsed conformation. The observed magnitudes of Δν for most of the complex bands were larger than the calculated values. The BF₃ symmetric deformation mode is an exception. The observed frequency shits for this mode were smaller than the calculated values, especially in N₂. This suggests that even an inert matrix can significantly affect the vibrational spectrum of the complex.     

Treanor pumping of CO initiated by CO laser excitation

An experiment is discussed in which CO can be excited up to energies of several electronvolts by the absorption of infrared radiation from a relatively low-power CO laser. Furthermore, experimental results are examined through kinetic modelling. In the experiment, the beam of an intracavity-chopped CO laser operating on all lines at 500 mW and containing a few milliwatts of the fundamental ν= 1→0 band component, is focused into an absorption cell containing a mixture of CO and Ar. The absorption of this infrared radiation is monitored by the optoacoustic effect. A second CO laser operating cw and capable of providing 8 W on all lines but not lasing on the ν= 1→0 band component, is then focused into the same volume in the absorption cell. With both lasers simultaneously focused into the absorption cell, strong fluorescence from the irradiated region is detected by a photomultiplier tube. Modulation of the signal intensity with time is observed, and indicates chemical destruction of the CO in the cell. An analysis and kinetic modelling calculation of this experiment shows that it is possible to excite CO up to high vibrational quantum numbers (ν40) at gas temperatures up to 800 K. by means of CO laser irradiation at the fundamental ν= 1→0 band component. One source responsible for the fluorescence signal observed in the experiment is identified as the 4th positive A ¹Π→X ¹Σ⁺ spontaneous emission. Although the present kinetic model does not incorporate the chemical processes that may lead to the production of additional fluorescing species such as C₂, good agreement is obtained with the observed fluorescence signal characteristics.     

The ν(OH/OD) band shape of strong hydrogen bonded dimers of phosphinic acids. Phenomenology and formation models

The infrared spectra of phosphinic acid R₂POOH dimers (R=CH₃, CH₂Cl, C₆H₅) have been studied in CCl₄ and CH₂Cl₂ solutions (T=300 K). The infrared spectra of deuterated R₂POOD dimers (R=CH₃, CH₂Cl) were also studied in the gas phase (T=400–550 K) and solid state (T=100–300 K). They are compared with previously studied spectra of the light (non-deuterated) dimers in the gas phase, in the solid state and in low-temperature argon matrices (T=12–30 K) in the 4000–400 cm⁻¹ spectral region. It is found that the strong and broad ν(OH) dimer bands have similar shapes, nearly equal values of bandwidth and low-frequency shift, and possess the Hadzi ABC structure irrespective of the type of acid, significant differences of dimerization enthalpies, influence of solvent, the type of H-bonded complexes (cyclic dimers in the gas phase, in solutions, and in inert matrices, and infinite chains in the solid state), and temperature in the range 12–600 K. Isotopic ratio of the first moments of light and deuterated acid bands has been measured. Analysis of the ν(OH/OD) band of hydrogen bonded dimers of phosphinic acids shows that the interaction between the two intermolecular bonds O–HOP in a cyclic complex plays virtually no role in the mechanism of the ν(OH/OD) band formation; the shape of ν(OH/OD) band is controlled mainly by the POOH(D)O fragment; and the band shape of strong hydrogen bonded complexes is formed by a number of vibrational transitions from the ground state to different combination levels in the region 3500–1500 cm⁻¹.     

Studies on some salicylaldehyde Schiff base derivatives and their complexes with Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II)

The formation constants of some transition metal ions Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II) binary complexes containing Schiff bases resulting from condensation of salicylaldehyde with aniline (I), 2-aminopyridine (II), 4-aminopyridine (III) and 2-aminopyrimidine (IV) were determined pH-metrically in ethanolic medium (80%, v/v). The formation constants were determined for all binary complexes. The important infrared (IR) spectral bands corresponding to the active groups in the four ligands and the solid complexes under investigation were studied. The solid complexes have been synthesized and studied by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats-Redfern equation. It was found that the thermal decomposition of the complexes follow second order kinetics. The thermodynamic parameters of the decomposition are also reported. The electronic absorption spectra of the investigated ligands were carried out to determine the pK(a) values spectrophotometrically.     

Semiempirical SCF/CI interpretation of the origin of the catalytic activity of transition metal-macrocycle complexes

Semiempirical self-consistent field (SCF) and configuration interaction (CI) calculations of the intermediate neglect of differential overlap (INDO) type are applied to the analysis of the electronic transitions of the hexaazacyclophane base and its Ni and Cu complexes. The ground states (¹A_g for the ligand and Ni complex, ²B_1g for the Cu complex) are planar structures of D₂h symmetry. The low-energy region of the UV-visible spectra, whose analysis may help to recognize the catalytic active sites of the complexes is associated with d → d transitions in the Ni complex, and M → L charge transfer in the Cu complex.     

Polarized infrared and Raman spectra of CsHSeO4 and CsDSeO4 single crystals

The polarized absorption infrared spectra of CsHSeO₄ and CsDSeO₄ single crystals and polarized Raman spectra of the CsHSeO₄ single crystal were measured at room temperature. The polarization features of the internal vibrations of the HSeO⁻₄ ions are predicted on the basis of the X-ray structure assuming strong couping between the vibrations of the two shortest Se---O bonds and an intermediate Se---O bond. The bending methods γOH and δOH of a hydrogen bond appear at 805 cm⁻ and 1258 cm⁻¹, respectively. The νOH absorption has the ABC structure due to Fermi resonance of νOH with the overtones of the δOH and γOH vibrations. A similar shape of the νOH band is observed in the Raman spectra. The νOD absorption has a different shape from that of νOH. Intra-chain coupling was observed for the νOH and νOD vibrations.     

Magnetic circular dichroism assignment of the longest wavelength band of a series of tetrahedral d OXY- and Thioanions

Room temperature magnetic circular dichroism spectra have been obtained for MoS²⁻₄, MoO²⁻₄, WS²⁻₄, ReS⁻₄, VS³⁻₄, VO³⁻₄ and OsO₄ through their first and second charge-transfer bands. These measurements demonstrate that the band at longest wavelength (ν₁ band) must be assigned to a t₁ → 2e transition for all the compounds investigated.     

Structural, spectral and antimicrobial studies of copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone

Six new copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone (HL) have been synthesized and characterized by different physicochemical techniques like molar conductivity measurements, magnetic studies and electronic, infrared and EPR spectral studies. Five of the complexes have been found to possess the stoichiometry [CuLX], where X = Cl (1), Br (2), NO₃ (3), NCS (4), N₃ (5). The complex prepared from copper sulfate has the composition [Cu₂L₂SO₄] · (H₂O)₂ (6). In all the complexes the deprotonated ligand, L and the anion were found to be coordinated to the Cu(II) ion. The terdentate nature of the ligand is evident from the IR spectra. The metal ligand bonding parameters evaluated from the EPR spectra indicate strong in-plane σ and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for complexes 1, 3, 4 and 5, while the complexes 2 and 6 are assigned a square pyramidal geometry. Crystal structure of the complex [CuLCl] reveals two molecules per asymmetric unit of a monoclinic lattice, with space group symmetry P2₁/n. The complexes [ CuLBr ₂] (2) and [CuLNCS] (4) crystallized into triclinic lattices with space group . Compound 2 exists as a thiolate bridged copper(II) dimer. The antimicrobial activity of the ligand and the copper complexes were tested against five types of bacteria isolated from clinical samples. The complexes were found to be active against Bacillus sp., Vibrio cholera O1, Staphylococcus aurus and Salmonella paratyphi.     

Isomeric complexes of ruthenium(II) with neutral heterocyclic schiff base ligands. High resolution proton resonance spectra of trans-cis isomeric pairs of RuX2L2 (L = 2-arylpyridinecarboxaldimine, X = Cl, Br) and comparison of their physical properties

The reaction of 2-arylpyridinecarboxaldimine [RH₄C₆NC(H)Py, L (1)] with hydrated RuX₃ (X = Cl, Br) in boiling C₂H₅OH affords dark crystals of RuX₂L₂. Two geometrical isomers of the compound have been isolated and characterized by analytical and spectroscopic data. The trans isomer of RuCl₂L₂ shows a single sharp band for ν(Ru---Cl), whereas two bands are observed for the corresponding cis isomer. The highresolution ¹H NMR spectra of the isolated complexes are reported and completely assigned. All the complexes have multiple t₂→π^*(L) transitions in the visible region. Each of the complexes display a quasi-reversible oxidative response due to an Ru^III/Ru^II couple in the range 0.25–0.40 V vs S.C.E. at a platinum working electrode. The formal potentials of this couple obey the Hammett relationship. The ligand-based irreversible oxidations are also briefly noted.     

Vibrational spectra of σ-allylmanganese pentacarbonyl

The vibrational spectra of σ-(C₃H₅)Mn(CO)₅ are reported. Assignment of bands is made and carbonyl force constants are calculated. The results indicate that the Mn(CO)₅ moiety has C_4ν symmetry. The calculated angle between the axial and equatorial carbonyl groups is approximately 95°. The bonding in this compound is very similar to that in (CH₃)Mn(CO)₅.

In the far-infrared region, seven bands are expected in C_4ν symmetry (3A₁ + 4E), and all are observed.     

Gas and solution phase chloroiodomethane short-time photodissociation dynamics in the B-band absorption

Resonance Raman spectra were obtained within and to the red of the B-band absorption spectrum of gas phase chloroiodomethane and chloroiodomethane in cyclohexane solvent. The spectra show the fundamental and overtones of the nominal C---I stretch (nν₅) and combination bands of the CH₂ wag (ν₃), I---C---Cl bend (ν₆), and the CH₂ scissor (ν₂) fundamentals with the C---I stretch bands (nν₅). The chloroiodomethane B-band short-time photodissociation dynamics have significant substituent effects relative to the B-band of iodomethane due to the presence of the C---Cl chromophore n(X) → σ^* (C---X) transitions ≈170 nm that are close to the B-band absorption of chloroiodomethane but absent in iodomethane.     

Vibrational spectra, structure and hydrogen bonding of 5-tert-butylpyrazole and its zinc complexes

New zinc complexes [L₂ZnX₂] with X=Cl (I), Br (II), I (III) and NO₃ (IV), [L₃Zn(OClO₃)]ClO₄ (V) and [L₄Zn](ClO₄)₂ (VI) with 5-tert-butylpyrazole as ligand L were synthesized and characterized by infrared-, Raman-, mass- and NMR-spectroscopy. The assignment of the vibrational frequencies for the complexes in the range of 4000–80 cm⁻¹ is proposed. Analysis of the IR spectra in the range of ν_NH frequencies shows that 5-tert-butylpyrazole forms cyclic associates in the solid using intermolecular NHN hydrogen bonds. This was proven by a crystal structure determination, which showed that L exists as tetramers in the solid state. In solution there is an equilibrium between tetramers and monomers and, probably, dimers or trimers. In the complexes, the NH-groups of L form intramolecular H-bonds with the X-group. The intramolecular H-bond in VI has interionic character and partially dissociates in solution at high dilution. Ligand vibrations that are sensitive to the coordination and the dependence of their frequencies on the anionic group X has been revealed.     

Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine

Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pK_a = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm⁻¹ and a band at 811 cm⁻¹ due to the ν_s(C₃N) mode of the perturbed amine. The strongest phenol, CNP (pK_a = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH⁺---O⁻) absorption between 3000−1800 cm⁻¹, by the ν_as(C₃N⁺) and ν_s(C₃N⁺) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pK_a = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm⁻¹ and 950–400 cm⁻¹ regions due to the ν(NH⁺O⁻) and ν(OHN) modes, respectively.     

Correlations between dynamical properties and features of potential energy surfaces for the light atom transfer reactions O+HCl→OH+Cl AND Cl+HCl→ClH+Cl

A three-dimensional quasiclassical trajectory study of the dynamics of the light atom transfer reaction O(³P) + HCl(ν=0)→ OH + Cl was carried out employing two LEPS potential energy surfaces (I and II). Attention was focused mainly on three-dynamical properties; the oscillatory behavior of partial cross sections as a function of collision energy; the rotational excitation of the products; and the influence of reagent rotation on reactivity. Distinct differences were found between surfaces I and II with respect to these properties. The examination of individual trajectories indicated that there is a significant difference in the nature of these surfaces. While surface I is governed by weak repulsive forces, surface II is governed by strong attractive forces which tend to direct the reactants toward a collinear geometry. The present results confirm conclusions reached from an earlier study of the reaction Cl+HCl→ClH+Cl concerning correlations between dynamical properties and features of potential energy surfaces. For surfaces of the type that we termed HREP, since they are of repulsive nature and they lead to highly rotationally excited products, no significant oscillations of partial cross sections are obtained and reagent rotation promotes the reaction. On the other hand, for surfaces of the type that we termed COLD (collinearly directing), since they tend to direct the reactants toward a collinear geometry and form rotationally “cold” products, significant oscillations of partial cross sections are obtained and reagent rotation causes a decline in reactivity.     

Synthesis and spectroscopic studies of novel Cu(II), Co(II), Ni(II) and Zn(II) mixed ligand complexes with saccharin and nicotinamide

Four novel mixed ligand complexes of Cu(II), Co(II), Ni(II) and Zn(II) with saccharin and nicotinamide were synthesised and characterised on the basis of elemental analysis, FT-IR spectroscopic study, UV–Vis spectrometric and magnetic susceptibility data. The structure of the Cu (II) complex is completely different from those of the Co(II), Ni(II) and Zn(II) complexes. From the frequencies of the saccharinato CO and SO₂ modes, it has been proven that the saccharinato ligands in the structure of the Cu complex are coordinated to the metal ion ([Cu(NA)₂(Sac)₂(H₂O)], where NA — nicotinamide, Sac — saccharinato ligand or ion), whilst in the Co(II), Ni(II) and Zn(II) complexes are uncoordinated and exist as ions ([M(NA)₂(H₂O)₄](Sac)₂).     

IR-induced photorotamerization of propanal and 3-chloropropanal in low-temperature matrices. Ab initio optimization of conformer geometries, and calculation of torsional barrier heights

Propanal and 3-chloropropanal have been studied in solid Ar and N₂ matrices. A fast IR-induced cis → gauche process was found for propanal, whereas the reverse process occurred in the dark upon warming the matrices. A very fast process was found for 3-chloropropanal in Ar; in N₂ it was 60 times slower. The reverse process occurred upon warming in the dark also for this compound. Ab initio calculations were carried out for both compounds at the 4–31G level, and the results were used in interpreting the experimental results. Geometries of the conformers were fully optimized and torsional potential-energy barrier heights calculated.