The simplest heteronuclear metal cluster: LiBe

An electronic transition with an origin near 19203 cm⁻¹ is observed in vapour produced by YAG laser vaporization of a pressed pellet of Li and Be powders and assigned to LiBe diatomic. Vibrational analysis yields a G_1/2″=295 cm⁻¹ and G_1/2′=188 cm⁻¹. A preliminary rotational analysis gives r₀″=2.59 Å and r₀′=3.04 Å. The spectroscopy and the electronic structure are discussed and the experimental molecular constants show a very good agreement with our recent state of the art ab initio calculated values.     

Spectroscopic constants and molecular properties of CN−, SiH−, PO−, SO−, SF−, and SiS−: Density functional study

Spectroscopic constants and molecular properties of selected diatomic anions namely CN^?, SiH^?, PO^?, SO^?, SF^?, and SiS^? in their ground states have been studied in detail using the hybrid HF/DF B3LYP method. The consistency of the calculated values has been verified with four different basis sets, with improved quality. The spectroscopic constants and molecular properties calculated with the aug‐cc‐pVTZ basis set agree very well with the experimental and theoretical values wherever available. Most of the spectroscopic constants and molecular properties of the selected diatomic anions, particularly the spectroscopic constants and molecular properties of SO^? and SiS^? are reported for the first time. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

All electron ab initio investigations of the electronic states of the MoN molecule

The low lying electronic states of the molecule MoN were investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction were determined in perturbation calculations. The electronic ground state is confirmed as being ⁴∑⁻. The chemical bond of MoN has a triple bond character because of the approximately fully occupied delocalized bonding π and σ orbitals. The spectroscopic constants for the ground state and ten excited states were derived. The excited doublet states ²∑⁻, ²Γ, ²Δ, and ²∑⁺ are found to be lower lying than the ⁴Π state that was investigated experimentally. Elaborate multi-configuration configuration-interaction (MRCI) calculations were carried out for the states ⁴∑⁻ and ⁴∏ using various basis sets. The spectroscopic constants for the ⁴∑⁻ ground state were determined as r_e=1.636 Å and ω_e=1109 cm⁻¹, and for the ⁴∏ state as r_e=1.662 Å and ω_e=941 cm⁻¹. The values for the ground state are in excellent agreement with available experimental data. The MoN molecule is polar with a charge transfer from Mo to N. The dipole moment was determined as 2.11 D in the ⁴∑⁻ state and as 4.60 D in the ⁴∏ state. These values agree well with the revised experimental values determined from molecular Stark spectroscopic measurements. The dissociation energy, D_e, is determined as 5.17 eV, and D₀ as 5.10 eV.     

Spectroscopic properties of molecular anions of astrophysical and laboratory interest

Spectroscopic constants and molecular properties of the selected six diatomic anions of astrophysical and laboratory interest namely, FO⁻, CCl⁻, NS⁻, ClO⁻, ClF⁻ and AlS⁻ in their ground state have been studied in detail using hybrid HF/DF B3LYP method. The effect of basis set on spectroscopic properties has been studied with systematic improvement of basis set from aug-cc-pVDZ to aug-cc-pV5Z. The values of the spectroscopic constants and molecular properties obtained with these basis sets have been extrapolated to the complete basis set (CBS) limit. The spectroscopic properties calculated with the aug-cc-pV5Z basis set are very close to those at the CBS limit and these values agree very well with the theoretical and experimental results wherever available. Many of the spectroscopic constants and molecular properties of these anions are new and in particular those for ClF⁻ and AlS⁻ are first reported.     

Retention model for the separation of anionic metal-EDTA complexes in ion chromatography

A retention model is derived for complex anions eluted from an anion-exchange column with multiple ionic eluents containing hydrogencarbonate, carbonate, and hydroxyl species and the sample solution, containing transition metals, anions and complexing ligand. The theory is based on the generalized ion-exchange equilibrium, protonation and complex-formation equilibria. The unknown parameters of chromatographic ion-exchange equilibrium constants for sample and eluent species are determined from the experimental retention data by iterative minimization, using a non-linear regression algorithm. The model was utilized to predict the retention behaviour of CdEDTA²⁻, CoEDTA²⁻, MnEDTA²⁻ and NiEDTA²⁻ ions. The capacity factors of complex ions were determined for wide ranges of pH values and eluent concentrations. Good agreement was obtained between the observed and predicted retentions.     

Energy levels of iodine-129 near the B state dissociation limit from two-photon spectroscopy

Two-photon sequential absorption spectroscopy has been used to selectively excite rotational structure in the B---X absorption transition of the ¹²⁹I₂ molecule up to within 2 cm⁻¹ of the dissociation limit. Vibrational and rotational constants have been obtained for the B state levels with υ = 71–79. Le Roy's equations for long-range behaviour are expressed in mass-reduced form, and it is shown that these equations can be successfully used to combine the spectroscopic constants for ¹²⁷I₂ and ¹²⁹I₂ to give improved values of the long range constants for the B state. The improved values are only slightly different from those previously obtained by the same technique for ¹²⁷I₂ alone.     

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of photolytically generated hot CF radicals

In this paper, we investigate the rotationally resolved spectra of hot CF radicals generated after IR multiphoton dissociation (IRMPD) of CFCl₃ or CF₂Cl₂ and subsequent UV photodissociation. It is shown that these conditions are advantageous for the spectroscopy of transitions involving high rotational quantum numbers and hot bands. Thus molecular constants of CF for the first vibrationally excited state of the electronic ground state (A_v=77.1 cm⁻¹, B_v=1.389 cm⁻¹, D_v=6.570×10⁻⁶ cm⁻¹) are determined for the first time or are calculated more accurately. The spectroscopic method used was resonance-enhanced multiphoton ionization (REMPI) spectroscopy.     

Thermal studies on purine complexes. VII. 8-theophylline derivatives and their silver(I) complexes

Four theophylline derivatives: 8-ethyltheophylline (ETH), 8-isopropyltheophylline (IPH), 8-propyltheophylline (PRH), and 8-phenyltheophylline (FTH) have been synthesized and characterized by spectroscopic techniques and thermal analysis. The melting points of these theophylline derivatives increase with the molecular weight, from 263.8°C (ETH) to 384.7°C (FTH). The values of the fusion enthalpy increase in the same order, from 28.4 kJ mol⁻¹ (ETH) to 36.5 kJ mol⁻¹ (FTH).

The interaction of these theophylline derivatives with Ag(I) has been studied by means of spectroscopic techniques, TG, DTG and DSC. In all cases, the pyrolysis of these compounds gave metallic silver.     

The efficacy of nitrosonaphthol functionalized XAD-16 resin for the preconcentration/sorption of Ni(II) and Cu(II) ions

Amberlite XAD-16 resin has been functionalized using nitrosonaphthol as a ligand and characterized employing elemental, thermogravimetric analysis and FT-IR spectroscopy. The sorption of Ni(II) and Cu(II) ions onto this functionalized resin is investigated and optimized with respect to the sorptive medium (pH), shaking speed and equilibration time between liquid and solid phases. The monitoring of the influence of diverse ions on the sorption of metal ions has revealed that phosphate, bicarbonate and citrate reduce the sorption up to 10–14%. The sorption data followed Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The Freundlich parameters computed are 1/n = 0.56 ± 0.03 and 0.49 ± 0.05, A = 9.54 ± 1.5 and 6.0 ± 0.5 mmol g⁻¹ for Ni(II) and Cu(II) ions, respectively. D–R isotherm yields the values of X_m = 0.87 ± 0.07 and 0.35 ± 0.05 mmol g⁻¹ and of E = 9.5 ± 0.23 and 12.3 ± 0.6 kJ mol⁻¹ for Ni(II) and Cu(II) ions, respectively. Langmuir characteristic constants estimated are Q = 0.082 ± 0.005 and 0.063 ± 0.003 mmol g⁻¹, b = (4.7 ± 0.2) × 10⁴ and (7.31 ± 0.11) × 10⁴ l mol⁻¹ for Ni(II) and Cu(II) ions, respectively. The variation of sorption with temperature gives thermodynamic quantities of ΔH = −58.9 ± 0.12 and −40.38 ± 0.11 kJ mol⁻¹, ΔS = −183 ± 10 and −130 ± 8 J mol⁻¹ K⁻¹ and ΔG = −4.4 ± 0.09 and −2.06 ± 0.08 kJ mol⁻¹ at 298 K for Ni(II) and Cu(II) ions, respectively. Using kinetic equations, values of intraparticle transport and of first order rate constant have been computed for both the metal ions. The sorption procedure is utilized to preconcentrate these ions prior to their determination in tea, vegetable oil, hydrogenated oil (ghee) and palm oil by atomic absorption spectrometry using direct and standard addition methods.     

The extraction equilibria of the ion associate of periodate with 1-(3,5-diamino-6-chloropyrazinecarboxyl) guanidine

The extraction equilibrium of the ion-associate of periodate with 1-(3,5-diamino-6-chloropyrazinecarboxyl) guanidine hydrochloride (DPG⁺Cl⁻) was investigated spectrophotometrically. The optimum conditions for the extraction of the ion associate DPG⁺·IO₄⁻ with cyclohexanone have been established. The ion association constants, β, K_D and K_ex and the molar absorpativity of the formed ion associate were determined. These values enable a convenient application of the investigated system for the extraction spectrophotometric determination of periodate ions in the aqueous media. The molar ratio of the ion associate was found to be 1:1 of periodate to the reagent DPG⁺Cl⁻ at pH 4–5.     

Simultaneous determination of bromide and nitrate in contaminated waters by ion chromatography using amperometry and absorbance detectors

This study describes a new ion chromatography method using a low-capacity anion exchange column with amperometric and absorbance detection for rapid and simultaneous determination of Br⁻ and NO₃⁻ in contaminated waters where one of these ions is present in excess compared to other. The use of two detectors overcomes the problem of baseline separation for Br⁻ and NO₃⁻ for accurate quantification, which was commonly encountered when using a low-capacity anion exchange column and suppressed conductivity detection mode. The method achieved accurate quantification of these two ions without requirement of baseline separation. The accuracy of 2.8% for NO₃⁻ was determined using a quality control sample obtained from UN GEMS/Water PE Study No. 6. The detection limits for Br⁻ and NO₃⁻ were 20 and 6 μg l⁻¹ (25 μl sample), respectively. Linearity of these two ions was over three orders of magnitude with a correlation coefficient >0.998. The influence of potential interfering ions was also studied followed by the determination of Br⁻ and NO₃⁻ in seawater, unsaturated zone water, soil extract and groundwater.     

Polarized absorption spectra and polarized Raman spectra of single crystals of trans(Cl2)-[CoCl2(NH3)n(H2O)4−n]Cl complexes (n = 2, 3, 4)

The title cobalt(III) complexes have been investigated by polarized absorption and Raman spectroscopies of the single crystals. The symmetry properties of the d-electron orbitals and of the vibrational modes attributable to the Raman bands of trans(Cl₂)-[CoCl₂(NH₃)_n(H₂O)_4−n]Cl complexes (n = 2, 3, or 4) were examined to elucidated the peculiar observation that ligand substitution causes no splitting of the 15 200-cm⁻¹ absorption band and the 250-cm⁻¹ Raman band. Effects of replacing the NH₃ ligand with H₂O on the electronic structure, atom–atom force constants and vibrational modes of these complex ions are briefly described.     

Spectres infrarouges et structure des anions 2-methylallyle, CH3-C(CH2)2- et triméthylèneméthane, C(CH2)3

The infrared spectra of solid samples of C₄H₇K and C₄D₇K have been investigated in the 4000 to 30 cm⁻¹ range. A complete assignment of intramolecular fundamentals of C₄H₇⁻ and C₄D₇⁻ ions and of potassium-allyl vibrations is proposed and the intramolecular force constants are calculated. The C(CH₂)₃²⁻ anion has been identified spectroscopically. Structures of C₃H₅⁻, C₄H₇⁻ and C(CH₃)₃²⁻ are discussed and compared with those optimised by the MINDO/3 method.     

Matrix-isolation spectroscopy of Pb2

Fluorescence and Raman scattering were observed from Pb₂ isolated in neon and argon matrices. Two new excited states were observed by two-photon stepwise excitations, which involve low-lying electronic states of Pb₂. Most spectroscopic constants of the states observed could be given and complement previous results. Two resonance Raman progressions with ω_c = 112.5 and 123.1 cm⁻¹ and a single Raman signal at 80 cm⁻¹ were observed in argon matrices. The ω_c = 123.1 cm⁻¹ Raman signal which had recently been assigned to a larger Pb cluster was shown to arise from Raman scattering within the electronically excited A state of Pb₂ at 5500 cm⁻¹.     

Determination of absorptivity and formation constant of a chalcone association complex

A UV spectrometric method was developed to determine the molar absorptivity (_C) and formation constant (K_c) of the association complex of unsubstituted chalcone in cyclohexane, in the concentration range from 4.00·10⁻⁴ to 2.00·10⁻² mol dm⁻³. The thermodynamic and spectroscopic magnitudes such as K_c and _C contribute to the understanding of the physicochemical behavior of several ,β-unsaturated carbonylic compounds, of low solubility in water, as it is the case of numerous flavonoids of chemical and biological importance. The studied association complex, formed by two chalcone molecules, is characterized by the constants _C (300.8 nm)=4.98·10⁴ dm³ mol⁻¹ cm⁻¹ and K_c=5.58·10³. The method proposed is convenient for the study of solute–solute molecular associations particularly those due to dipole–dipole interactions.     

Protonation of polyamines in NaCl aqueous solution and binding of Cl by polyammonium cations

Equilibrium constants relative to the binding of Cl⁻ by nine open chain polyammonium cations (di, tri and tetra) were determined by potentiometric measurements (H⁺-glass electrode), at T=25°C. To this end the protonation constants of these amines were measured in NaCl aqueous solutions, in the ionic strength range 0.1<I≤1 mol dm⁻³. The different amines (some of which are N-alkyl substituted) were chosen in order to consider several factors affecting the values of protonation constants, the chloride complex formation constants and the dependence on ionic strength of apparent protonation constants. As concerns these last two points, it was found that fully N-alkyl substituted amines behave in a very similar way, with respect to partially or non-substituted ones. Simple linear relationships are reported involving chloride formation constants, parameters for the dependence on ionic strength of protonation constants and charges in polyammonium cations. The complexes formed by two linear polyamines with NO₃⁻ have also been studied for comparison. Literature data are examined.     

Stability,spectroscopic constants,and dissociation of CO2+: A theoretical study

Stability, spectroscopic constants, and dissociation of CO²⁺ have been studied in detail using ab initio MP2, CCSD and CCSD(T) methods, and density functional B3LYP method. The stability and the ambiguity between the ground and metastable state of the molecular dication have been discussed. The spectroscopic constants of the molecular dication have been compared with the experimental and theoretical values wherever available. Various charge symmetric and charge asymmetric dissociation pathways of CO²⁺ have been investigated. After dissociation, the fragmented atoms and ions are considered to be either in their ground or in their metastable state. Interesting results have been obtained for the charge symmetric and charge asymmetric dissociation of the diatomic dication. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Fundamental equilibrium analysis on the ion-pair extraction of dibenzo-18-crown-6 complex of alkali metal ions with picrate ion into 1,2-dichloroethane

The ion-pair extraction equilibria of dibenzo-18-crown-6 (DB18C6) complexes of Na⁺, K⁺, Rb⁺ and Cs⁺ (M⁺) with picrate ion (Pic⁻) into 1,2-dichloroethane (1,2-DCE) have been studied at 25.0°C. In the case of the Rb⁺ and Cs⁺ systems, the extraction results were interpreted by taking into consideration the formation of a (DB18C6)₂ -M⁺ complex in 1,2-DCE. The thermodynamic constants of extraction, , and ion-pair formation in 1,2-DCE, , of ion pairs of the DB18C6-M⁺ complexes with Pic⁻ were determined. By using the distribution coefficient of M⁺·Pic⁻ the thermodynamic formation constants of the DB18C6-M⁺ complexes in 1,2-DCE, , were evaluated. Consequently the component equilibrium constants of the ion-pair extraction were completely determined and a contribution of these constants to the difference of value was discussed. The value in 1,2-DCE is quite high compared with that in solvating solvents and log decreases linearly with increasing Gutmann donor number of solvents.     

Vibronic and resonance Raman spectra of NO2impurity ions in the body-centered alkali halide crystals

The low-temperature resonance secondary radiation spectrum as well as the absorption and luminescence excitation spectra of NO₂⁻ impurity ions in cesium halides have been studied. The energy relaxation processes and NO₂⁻ equilibrium orientation and reorientation problems have also been discussed. It was shown that the systems under study were characterized by average Stokes' losses and strong lattice distortions, exemplified by the Generation of a number of low-frequency local and pseudolocal vibrations. The inhomogeneous broadening in CsCl-NO₂⁻ and CsI-NO₂⁻ spectra was extremely large for the simple molecular impurity systems, leading to the interesting peculiarities of energy relaxation processes. Unlike some alkali halide crystals with NaCl structure the impurity NO₂⁻ does not rotate in the lattices with CsCl structure. The NO₂⁻ equilibrium orientation in cesium halides was fixed: both the molecular axis and the axis perpendicular to the molecular plane were directed in (100) directions of the crystal.     

Heteroleptic platinum(II) complexes of macrocyclic thioethers and halides: the crystal structures of [Pt(9S3)Cl2], [Pt(9S3)Br2], and [Pt(9S3)I2]

The synthesis, spectroscopic, and crystal structures of three heteroleptic thioether/halide platinum(II) (Pt(II)) complexes of the general formula [Pt(9S3)X₂] (9S3=1,4,7-trithiacyclononane, X=Cl⁻, Br⁻, I⁻) are presented. All three 9S3/dihalo complexes form very similar structures in which the Pt(II) center is surrounded by a cis arrangement of two halides and two sulfur atoms from the 9S3 ligand. The third sulfur from the 9S3 forms a long distance interaction with the Pt center resulting in an elongated square pyramidal structure with a S₂X₂+S₁ coordination geometry. The distances between the Pt(II) center and axial sulfur shorten with larger halide ions (Cl⁻=3.260(3) Å>Br⁻=3.243(2) Å>I⁻=3.207(2) Å). These distances are consistent with the halides functioning as π donor ligands, and their Pt---S axial distances fall intermediate between Pt(II) thioether complexes involving π acceptor and σ donor ligands. The ¹⁹⁵Pt NMR chemical shift values follow a similar trend with an increased shielding of the platinum ion with larger halide ions. The 9S3 ligand is fluxional in all of these complexes, producing a single carbon resonance. Additionally, a related series of homoleptic crown thioether complexes have been studied using ¹⁹⁵Pt NMR, and there is a strong correlation between the chemical shift and complex structure. Homoleptic crown thioethers show the anticipated upfield chemical shifts with increasing number of coordinated sulfurs. Complexes containing four coordinated sulfur donors have chemical shifts that fall in the range of −4000 to −4800 ppm while a value near −5900 ppm is indicative of five coordinated sulfurs. However, for S₄ crown thioether complexes, differences in the stereochemical orientation of lone pair electrons on the sulfur donors can greatly influence the observed ¹⁹⁵Pt NMR chemical shifts, often by several hundred ppm.