Methyl Cyanide Solutions Research Articles

Theoretical insight into the spectral characteristics of Fe(II)-based complexes for dye-sensitized solar cells: Functionalized bipyridyl chromophores

Fine tuning of electronic properties by virtue of the proper choice of functionalized chromophores would improve performance of absorption spectrum for dye-sensitized solar cells (DSSCs). We report herein a theoretical investigation on a series of bipyridyl Fe(II)-based complexes with general formula [FeLL′(NCS)2] (L, L′ = 4,4′-substituted-2,2′-bipyridine) by density functional theory (DFT) and time-dependent DFT (TD-DFT). Molecular geometries, electronic structures, and optical absorption spectra are predicted in methyl cyanide (MeCN) solution. [FeLL′(NCS)2] derivatives display Fe → bipyridine metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) in the range of 350–700 nm. Structural modifications by enhancing π-conjugation and introducing heteroaromatic groups on ancillary ligands lead to the upshift of most of molecular orbital energies, and remarkable increase in absorption intensity. Compared with Ru(II)-based sensitizers, bipyridyl Fe(II)-based complexes exhibit similar absorption spectral characteristics but better improving trend along with structural optimizations.

Can Polypyridyl Cu(I)-based Complexes Provide Promising Sensitizers for Dye-Sensitized Solar Cells? A Theoretical Insight into Cu(I) versus Ru(II) Sensitizers

Design of light-absorbent dyes with cheaper, safer, and more sustainable materials is one of the key issues for the future development of dye-sensitized solar cells (DSSCs). We report herein a theoretical investigation on a series of polypyridyl Cu(I)-based complexes with general formula [CuLL′]+ (L and L′ represent bipyridyl ligands) by density functional theory (DFT) and time-dependent DFT. Molecular geometries, electronic structures, and optical absorption spectra are predicted in both the gas phase and methyl cyanide solution. Our results show that all the [CuLL′]+ derivatives display Cu → bipyridine metal-to-ligand charge transfer absorption spectra in the range of 350−700 nm. Structural optimizations by enhancing π-conjugation and introducing heteroaromatic groups on ancillary ligands lead to upshift of molecular orbital energies, increase in oscillator strength, and red shift of absorption spectra. Compared with Ru(II) sensitizers, polypridyl Cu(I)-based complexes show similar optical properties an...

Theoretical Insight into the Spectral Characteristics of Fe(II)-Based Complexes for Dye-Sensitized Solar Cells—Part I: Polypyridyl Ancillary Ligands

The design of light-absorbent dyes with cheaper, safer, and more sustainable materials is one of the key issues for the future development of dye-sensitized solar cells (DSSCs). We report herein a theoretical investigation on a series of polypyridyl Fe(II)-based complexes of FeL2(SCN)2, [FeL3]2+, [FeL′(SCN)3]-, [FeL′2]2+, and FeL′′(SCN)2(L = 2,2′-bipyridyl-4,4′-dicarboxylic acid, L′ = 2,2′,2″-terpyridyl-4,4′,4″-tricarboxylic acid, L″= 4,4‴-dimethyl-2,2′ : 6′,2″ :6″,2‴-quaterpyridyl-4′,4″-biscarboxylic acid) by density functional theory (DFT) and time-dependent DFT (TD-DFT). Molecular geometries, electronic structures, and optical absorption spectra are predicted in both the gas phase and methyl cyanide (MeCN) solution. Our results show that polypyridyl Fe(II)-based complexes display multitransition characters of Fe → polypyridine metal-to-ligand charge transfer and ligand-to-ligand charge transfer in the range of 350–800 nm. Structural optimizations by choosing different polypyridyl ancillary ligands lead to alterations of the molecular orbital energies, oscillator strength, and spectral response range. Compared with Ru(II) sensitizers, Fe(II)-based complexes show similar characteristics and improving trend of optical absorption spectra along with the introduction of different polypyridyl ancillary ligands.

DFT/TD-DFT Investigation of Electronic Structures and Spectra Properties of Cu-Based Dye Sensitizers

Molecular geometries, electronic structures, and optical absorption spectra were investigated using density functional theory (DFT) at the B3LYP/6-31G(d) and B3LYP/DZVP levels for [CuL(2)](+) and [CuL(2)][PF(6)] (L = 6,6'-dimethyl-2,2'-bipyridine-4,4'-dimethylformate), both in the gas phase and in methyl cyanide (MeCN) solution. The vertical excitation energies were calculated within the framework of the time-dependent DFT (TD-DFT) approach, whereas the solvent effects were taken into account using the polarizable continuum model (C-PCM). Our results show that the five highest occupied molecular orbitals (HOMOs) are composed of a set of distorted degenerate Cu 3d orbitals, whereas the four lowest unoccupied molecular orbitals (LUMOs) are the bipyridine ligand pi*(C horizontal lineN) orbitals. The spectra in the range of 400-600 nm were found to originate from metal-to-ligand charge-transfer (MLCT) transitions, whereas the spectra in the range of 350-400 nm are excitations mainly from the metal Cu 3d orbitals to the carboxyl pi* orbitals. The solvent effects lead to changes in both the geometries and the absorption spectra. The results of this work suggest that copper-based complexes might be effective sensitizers for next-generation dye-sensitized solar cells.

Monomeric, dimeric and polymeric structure of the uranium trichloride hydrates

Three different uranium trichloride hydrates of the formulas UCl 3 · 2H 2O · 2CH 3CN, UCl 3 · 6H 2O and UCl 3 · 7H 2O have been isolated from methylcyanide solutions of UCl 4, with a 1–5% water content, by reduction with liquid zinc amalgam. The crystal and molecular structures of the hydrates have been determined by X-ray single crystal analysis. UCl 3 · 2H 2O · 2CH 3CN crystallizes in the triclinic system (space group P 1 ¯ ) forming infinite zigzag chains in the [0 1 0] direction. The coordination polyhedron of the uranium atom is a bicapped trigonal prism, formed by two oxygen atoms of the water molecules, four bridging chlorine atoms, one terminal chlorine atom and one nitrogen atom of the methylcyanide molecule. UCl 3 · 6H 2O crystallizes in the monoclinic system (space group P2/ n), with a monomeric structure. The uranium ion is eight-coordinated by two chlorine atoms and six oxygen atoms of the water molecules, which form a distorted square antiprism. UCl 3 · 7H 2O crystallizes in the triclinic system in the space group P 1 ¯ . The characteristic feature of this structure are [(H 2O) 7UCl 2U(H 2O) 7] 4+ dimers. The coordination polyhedra, in the form of a tricapped trigonal prism, are linked through the complex network of the hydrogen bonds. UCl 3 · 6H 2O and UCl 3 · 7H 2O are isostructural with their lanthanide analogues.

Synthesis and characterisation of chiral lanthanide complexes: Tetraethylammonium tetrakis [(-)cyclic O,O′-1(R),2(R)-dimethylethylene dithiophosphato] lanthanide(III), {(C 2H 5) 4N}{Ln[(-)S 2PO 2C 4H 8] 4}, (Ln = Nd, Eu)

The chiral cyclic (-)O,O′-1R,2R dimethylethylene dithiophosphate ligand ion, [(-)bdtp] −, the achiral ion, and the corresponding tetrakis lanthanide(III) complexes, {NEt 4}{Ln[(-)bdtp] 4}, (Ln = Nd, Eu) have been prepared. The characterisation, structure and spectral properties of the compounds are discussed. The electronic, MCD and CD spectra have been examined for methylcyanide solutions in the spectral range 14000–50000 cm −1. The energies, oscillator, dipole and rotational strengths of the bands have been measured and the assignments to the electronic transitions of intraligand, 4f–4f and charge-transfer type performed. With the neodymium complex a broad Cotton effect at 38450 cm −1 has been assigned to a charge-transfer transition. With the europium complex hypersensitive 7F 0⇀ 5D 2 (21350 cm −1) and CD sensitive 7F 1, 5F 0⇀ 5D 1 (18990, 19050 cm −1) bands have been identified from the comparison between absorbance, MCD and CD spectra.

Reactions and properties of some trimethyleneplatinum(IV) complexes: X. Reaction with iodide and thiocyanate ions

The reaction between the platinacyclobutanes [ PtX 2(CH 2CRR′C H 2)L 2] (X  Cl, Br; L  C 5H 5N, 4-CH 3C 5H 4N; R, R′  H, CH 3; R  H, R′  CH 3, C 6H 5) and iodide and thiocyanate ions in methyl cyanide solution has been studied. The C 3 moiety is eliminated as the cyclopropane and the process is first order with respect to the platinacyclobutanes and zero to half order with respect to the salt (MY). With the iodides the rate increases in the order Li < Na < K, Et 4N, and methyl substitution in the cyclobutane ring reduces the rate of reaction with Et 4NI. Added pyridine retards the reaction when L  C 5H 5N (X  Cl; R, R′  H) and added dimethylsulphoxide accelerates it. The mechanism suggested involves dissociation of an L ligand and attack of Y − ions and of M +Y − ion pairs on the five-coordinate intermediate formed.

The photodecomposition of platinacycloalkanes in solution.: I. 1,3-propanediylplatinum(IV) compounds

The gaseous products of the photolysis at 25°C of the platinacyclobutane compounds [X 2 PtCH 2CH 2C H 2(N-N)] where X = Cl, Br and N-N = 1,10-phenanthroline, 2,2′-bipyridine, (CH 2NMe 2) 2, (C 5H 5N) 2 in several solvents, in the absence and presence of various additives, have been determined. With solvents of relatively low dielectric constant (e.g. CH 2Cl 2), over 85 mol % of the hydrocarbon products was propene, the formation of which appears to involve a direct transfer of a hydrogen atom between neighbouring groups in the ring. With solvents of relatively high dielectric constant (MeCN, Me 2SO) in the presence of species, e.g. I −, SbPh 3, having a high trans effect, cyclopropane is the main volatile product. The effect of added halide ion and of the mixed solvents Me 2SO/PhMe and Me 2SO/PhSH indicates that ionisation of the platinacyclobutane and the formation of platinum substituted propyl ion-radicals precede the formation of cyclopropane (and the small amounts of ethylene produced). The photolysis of [X 2 PtCH 2CH 2C H 2(MeCN) 2] in methyl cyanide solution in the presence of Et 3RNX′ (X′ = Cl, R = H; X′ = Br, R = Et) gives appreciable amounts of ethylene in the products (up to 25 mol %). It is suggested that the halide ions add to the platinum to give negatively charged platinacyclobutane species, the photodecomposition of which may give C 2H 4.

Transient species formed by pulse radiolysis of solutions of N-methylacetamide (NMA) in methyl cyanide: Comparison of the reaction mechanisms of electrolysis and radiation chemistry

Radiolytic oxidation of N-methylacetamide (NMA) in methyl cyanide solutions containing LiClO 4 is studied using pulse radiolysis coupled with fast spectrophotometric absorption techniques. The radicals and radical-ions formed upon pulse radiolysis are compared with the transient species involved in the anodic electro-chemical oxidation mechanism of NMA in the same system. The pulse radiolysis results indicate the formation of the CH 3CONHCH 2 . radical absorbing in the UV region with a maximum at 340 nm. The participation of this species is suggested in one step of the mechanism proposed in the electrochemical process.

Preparation and crystal structure of oxotechnetium bis(thiomercaptoacetate) and its relationship to radiopharmaceuticals labeled with technetium-99m

The compound was prepared by adding an ammonium pertechnectate solution to a 10% v/v thioglycolate solution (pH and .5), waiting 10m, then adding a 30 wt % solution of Bu/sub 4/NBr. The yellow-brown precipitate was purified by recrystallization. Intensity measurements were made on a diffractometer employing a THETA to 2 THETA scan and graphite monochromatized molybdenum-potassium ..cap alpha.. radiation. The compound was assigned to the monoclinic space group C/sub m/ with a = 10.451(5)A, b = 14.855(8)A, c = 9.927(7)A, ..beta.. = 114.88(5)A, with two groups per unit cell. Bond lengths, bond angles, and a representative drawing are included. The compound has two moderately intense bands in its optical spectrum: lambda/sub max/(nm) 325,415 (epsilon(L mol/sup -1/ cm/sup -1/) 3100, 3700, respectively in methyl cyanide solution, and is weakly paramagnetic in the solid state with an effective moment lying between 1.2 to 1.5..mu../sub B/ (295/sup 0/K).

Structure and spectra of a series of eight-co-ordinate complexes of lanthanoids(III) with diethyldithiocarbamate of general formula Na[Ln(Et2NCS2)4](Ln = La to Yb, except Pm)

A series of diethyldithiocarbamates (Et2dtc) of all the lanthanoids from La to Yb. except Pm, of general formula Na[Ln(Et2dtc)4] have been prepared. The X-ray crystal and molecular structure of the lanthanum complex has been determined from diffractometer data. Crystals are monoclinic, space group P21, with a= 21.154(13). b= 21,445(15), c= 15.584(9)Å, β= 101.56(4)°, Z= 8. The structure was refined by least-squares techniques to R 0.089 for 4 412 observed reflections. The structure consists of Na+ and [La(Et2dtc)4]- ions: in the anion the lanthanum atom is co-ordinated by eight sulphur atoms forming a distorted dodecahedron. Conductance and spectral measurements show that the eight-co-ordinate structure persists in methyl cyanide solutions. The electronic spectra have been investigated for methyl cyanide solutions in the spectral range 5–39 kK, and bands attributed to electronic transitions of intraligand, charge-transfer, and f–f type. With the cerium(III) complex, intense bands at ca. 23 kK are attributed to f–d or inverted electron transitions.

Electronic spectra of eight-co-ordinate complexes of some lanthanoids-(III) with OO′-diethyl dithiophosphate

A series of OO′-diethyl dithiophosphates (ddtp) of the trivalent lanthanoids La, Ce, Pr, Nd, Sm, Eu, Tb, and Ho, general formula [NEt4][Ln(ddtp)4], have been prepared. The electronic spectra have been investigated for methyl cyanide solutions in the spectral range 7 000–45 000 cm–1 and bands attributed to electronic transitions of f—f, charge-transfer, and f—d type. With the cerium(III) complex five bands in the spectral range 27 000–37 000 cm–1 are attributed to the five 4f→5d transitions. With the samarium, europium, and ytterbium compounds, a number of electron-transfer transitions are found and the ligand molecular orbitals involved are discussed.

Combined effects of temperature and pressure upon the charge transfer to solvent spectrum of iodide in water and non-aqueous solvents. Local structural effects and ion pair formation

The energies of the first absorption band maxima for iodide in water, methanol, isopropanol, n-butanol and propylene carbonate do not shift linearly to higher energies when the pressure is increased from atmospheric to 2000 p.s.i. in contrast to previous suggestions. The shift is linear in methyl cyanide but less than that found previously at higher pressures. The temperature shift (dEmax/dT) decreases slightly with increasing pressure as expected. A normalising pressure is proposed, above which a linear relationship occurs. Spectral behaviour at sub-normalising pressures should thus facilitate understanding the nature of the solvation of ions in aqueous and non-aqueous media, and that of the bulk liquid. At high temperatures a liquid under pressure has a considerably reduced dielectric constant and a computer program was used to resolve a new band arising in methyl cyanide solutions. The presence of a solvent shared ion pair was deduced. Indirect evidence for a similar situation in isopropanol was also obtained.

On a new fluorescence emission band in Eu (III) solutions in light and heavy water and in methyl cyanide

A new fluorescence emission band in aqueous and methyl cyanide solutions of Eu(III) is reported. It is much broader than the f—f bands, and appears upon excitation at about 250–300 mμ. λ max changes from 350 to 410 mμ as water concentration is decreased. Changing from light to heavy water has little effect on the new band.

2,2′-Bipyridyl complexes of the niobium(V) and tantalum(V) halides

Methyl cyanide solutions of the pentahalides NbCl5, TaCl5, and TaBr5 react with 2,2′-bipyridyl (bipy) at ca. 0° to yield compounds of general formula MX5 bipy (MeCN). These are believed to be seven-co-ordinate and to contain a molecule of ‘lattice’ methyl cyanide. Under similar reactions conditions niobium(V) bromide and tantalum(V) iodide react to give MX5bipy2; no pure product was isolated from the related reaction involving niobium(V) iodide. At room temperature direct reaction of niobium(V) and tantalum(V) iodide with methyl cyanide leads to the formation of 1 : 1 adducts Ml5,MeCN. Compounds were characterised by their electronic and vibrational (i.r. and Raman) spectra.

Vibrational spectra of the hexachlorouranate and hexachlorothorate ions; UCl 62− and ThCl 62−

Raman and infra-red spectra of UCl 2− 6 and ThCl 2− 6 have been obtained from methyl cyanide solutions of their alkylammonium or alkylphosphonium salts. The fundamentals are assigned in terms of the molecular point group O h and their relation to vibrational progressions in the ultra-violet spectra is discussed. A force constant calculation indicates that UCl 2− 6 and ThCl 2− 6 have MCl bonds significantly stronger than those of PbCl 2− 6. The influence on the vibrational spectra of the incomplete ⨍-shell in UCl 2− 6 is also noted and discussed.

Thermodynamic, ultrasonic, spectroscopic and miscibility studies of water + methyl cyanide solutions

The ultrasonic absorption, excess volumes and mutual solubilities of mixtures of methyl cyanide and water are reported together with the near infra-red absorption spectra of 6 m HOD in deuterium oxide containing methyl cyanide. These properties of methyl cyanide and water mixtures are compared with those of tertiary butyl alcohol and water mixtures and discussed in terms of the effects of added methyl cyanide on the structure of water.

Oxidations of organic compounds by cobaltic salts. Part VIII. The oxidation of benzyl ethers

The oxidations of three benzyl ethers and diphenyl ether in aqueous methyl cyanide solution are essentially first-order with respect to both substrate and oxidant. The overall reactivities are in the sequence PhCH2OMe < PhCH2OCH2Ph < PhCH2OC6H11 < PhOPh. The oxidations are faster than those of similar hydrocarbons, but very much slower than that of benzyl alcohol. An outer sphere mechanism of oxidation is suggested. Quantitative analyses show that the oxidation products from the benzyl ethers are benzaldehyde, benzoic acid, and sometimes the corresponding benzoate ester. Attack occurs on the benzylic CH2 group, and there is negligible ring fission.

Oxidations of organic compounds by cobaltic salts. Part X. The oxidation of aromatic hydrocarbons

The oxidations of a series of aromatic hydrocarbons and of cyclohexane by cobaltic perchlorate in aqueous methy cyanide solution are essentially of the first order with respect to both substrate and oxidant. The general reactivity sequence is: p–NO2·C6H4Me < C6H12 < PhCH2·CH2Ph ∼ PhMe ∼ PhEt < Ph2CH2 < p–But·C6H4Me < Ph2 < naphthalene < anthracene, phenanthrene, and an outer-sphere mechanism of oxidation is suggested. The fast oxidations of biphenyl and of the condensed polycycles are postulated to involve direct abstraction of a π-electron, but the initial attack on the aralkyl hydrocarbons may be on the side-chain, in view of the oxidisability of cyclohexane.The products obtained from the oxidations of toluene, ethylbenzene, and bibenzyl vary markedly with solvent composition. In 50% methyl cyanide solution the oxidation of toluene is effected exclusively on the side-chain, but in 70% methyl cyanide other products are formed and the proportion of side-chain oxidation is decreased. Only the methyl substituent of p-t-butyltoluene is attacked, but no recognisable product could be obtained from the oxidation of biphenyl. The dependence of the rate of oxidation of toluene on methyl cyanide concentration, and on the acidity of the medium, are very similar to those found for the oxidation of benzyl ethers, and are explained similarly.

The far infrared spectra of some co-ordination compounds of the thallium(III) halides

The infrared specta (667–222 cm.–1) of the complexes Ph4AsTIX4, TIX3(1 pyridine)2, TIX3(2,2′-bipyridyl), TIX3(1,10-phenanthroline), TICl3(di-2-pyridylamine), and Tl(ethylenediamine)2X3(X = Cl or Br) have been recorded and the thallium–chlorine stretching vibrations assigned. The TlCl4– ion is considered to be tetrahedral in acetone and methyl cyanide solution. TlCl3(py)2 is shown to exist as Tl(py)4Cl2+ TlCl4– in acetone solution.