Theoretical Study of Substituent Effect in Aryl Group Migration in (<Emphasis Type="Italic">para</Emphasis>-C<Subscript>6</Subscript>H<Subscript>4</Subscript>X)Mn(CO)5 Complexes

In this study, we report substituent effect on aryl group migration in (para-C₆H₄X)Mn(CO)₅ complexes using mpw1pw91 quantum chemical calculations. These calculations reveal good linear relationships between barrier energy (ΔE), activation energy (ΔH^?), activation free energy (ΔG^?) values and rate constants with Hammett constants of X-substituents. The occupancy values of Mn–CO_cis and Mn–C(O)-(para-C₆H₄X) bonds in reactant, transition state and product were calculated by Natural bond orbital (NBO) method.     

Field-induced π-polarization in barrelene derivatives: a computational study based on structural variation

Barrelene, H–C(CH=CH)₃C–H, is an unsaturated polycyclic hydrocarbon containing three isolated double bonds in a non-planar arrangement. We have studied the transmission of field effects through the barrelene framework by analyzing the small structural changes occurring in the phenyl group of many Ph–C(CH=CH)₃C–X molecules, where X is a variable substituent. Molecular geometries have been determined by quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Comparison with the results obtained for the corresponding saturated molecules, the bicyclo[2.2.2]octane derivatives Ph–C(CH₂–CH₂)₃C–X, reveals a small, but significant, field-induced π-polarization of the barrelene cage, especially when the remote substituent is a charged group. Additional evidence of π-polarization is obtained by comparing the electric dipole moments of the two sets of uncharged molecules. The structural variation of the barrelene cage caused by the variable substituent in Ph–C(CH=CH)₃C–X molecules has also been investigated. It is much larger than that of the phenyl group and depends primarily on the electronegativity of the substituent. Particularly pronounced is the concerted variation of the non-bonded distance between the bridgehead carbons of the cage, r(C···C) ₁ ^BARR , and the average of the three C–C–C angles at the cage carbon bonded to the variable substituent, α ₁ ^BARR . A scattergram of r(C···C) ₁ ^BARR versus the corresponding parameter for bicyclo[2.2.2]octane derivatives, r(C···C) ₁ ^BCO , shows that the variation of r(C···C) ₁ ^BARR becomes gradually less pronounced than that of r(C···C) ₁ ^BCO as the electronegativity of the substituent increases.     

Syntheses,Structures, and Magnetic Properties of Two Mn(II) Coordination Polymers Based on 4-Fluorocinnamic Acid and 1,10-Phenanthroline

Two Mn(II) coordination polymers, {[Mn₃ (Pfca)₆(Phen)₂] · 2DMF} _n (I) and [Mn(Pfca)₂(Phen)(H₂O)] _n (II) (HPfca = 4-fluorocinnamic acid, Phen = 1,10-phenanthroline), were synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and singlecrystal X-ray diffraction (CIF files CCDC nos. 967513 (I), 1542972 (II)). Complex I crystallizes in the triclinic crystal system, space group Pī with a = 11.0821(11), b = 12.2632(12), c = 15.0288(15) Å, α = 87.3760(10)°, β = 88.4610(10)°, γ = 81.2220(10)°, V = 2016.0(3) Å3, ρ_c = 1.369 g/cm³, M _r = 1662.25, Z = 1, F(000) = 853, μ = 0.543 mm^–1, the final R = 0.0592 and wR = 0.1681 for 15498 observed reflections with I > 2σ(I). Complex II is of monoclinic system, space group P2₁/c with a = 18.0539(19), b = 8.5806(9), c = 18.758(2) Å, β = 116.5700(10)°, V = 2599.0(5) ų, ρ_c = 1.491 g/cm³, M _r = 583.44, Z = 4, F(000) = 1196, μ = 0.567 mm^–1, the final R = 0.0337 and wR = 0.0853 for 18139 observed reflections with I > 2σ(I). Complex I features linear Mn(II)-trinuclear units, which form 1D chain structure through F···F weak interactions, and complex II is 1D polymeric Mn(II)-chains. Antiferromagnetic coupling interactions exist within Mn(II)- carboxylate trinuclear in I (J =–0.40 cm^–1) and Mn(II)-carboxylate chain in II (J =–0.45 cm^–1).     

Sequence Ion Structures and Dissociation Chemistry of Deprotonated Sucrose Anions

We investigate the tandem mass spectrometry of regiospecifically labeled, deprotonated sucrose analytes. We utilize density functional theory calculations to model the pertinent gas-phase fragmentation chemistry of the prevalent glycosidic bond cleavages (B₁-Y₁ and C₁-Z₁ reactions) and compare these predictions to infrared spectroscopy experiments on the resulting B₁ and C₁ product anions. For the C₁ anions, barriers to interconversion of the pyranose [α-glucose-H]^?, C₁ anions to entropically favorable ring-open aldehyde-terminated forms were modest (41 kJ mol^?1) consistent with the observation of a band assigned to a carbonyl stretch at ~?1680–1720 cm^?1. For the B₁ anions, our transition structure calculations predict the presence of both deprotonated 1,6-anhydroglucose and carbon 2-ketone ((4S,5S,6R)-4,5-dihydroxy-6-(hydroxymethyl)dihydro-2H-pyran-3(4H)-one) anion structures, with the latter predominating. This hypothesis is supported by our spectroscopic data which show diagnostic bands at 1600, 1674, and 1699 cm^?1 (deprotonated carbon 2-ketone structures), and at ~?1541 cm^?1 (both types of structure) and RRKM rate calculations. The deprotonated carbon 2-ketone structures are also the lowest energy product B₁ anions.

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Study of the binding sites in the biomass of <Emphasis Type="Italic">Aspergillus niger</Emphasis> wild-type strains by FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy studies were performed to confirm and to provide information on the identity and binding characteristics of the chemical groups responsible for the binding of elements using Aspergillus niger (A. niger) wild-type strains. Two absorption bands in the 3690–3615 and 2970–2895 cm^?1 regions can characterize stretching vibrations OH and CH groups in fatty acids, respectively, and intensive bands around of 1600 cm^?1 and by 1048 cm^?1 correspond to stretching vibrations of C=O groups of amides (amide I) or stretching vibrations ν(C–N). The FTIR results confirmed that no extra differences between IR spectra of A. niger in raw biomass and in solid rest after extraction with chloroform were observed. The small differences were observed in IR spectra of A. niger in chloroform after extraction.     

Analysis of the Vibrational Structure of the <Emphasis Type="Italic">n</Emphasis>–π* Transition in the High-Resolution UV Absorption Spectrum of Methacryloyl Fluoride in the Gas Phase

The UV absorption spectrum of methacryloyl fluoride molecule in the gas phase is obtained in the wavenumber range of 32300–35900 cm^?1. The resolved vibrational structure of this spectrum consists of 153 absorption bands. The assignment of all bands has been made for the first time. Values ν_00trans = 35670.0 сm^?1 and ν_00cis = 35371.1 cm^?1 are determined. The fundamental frequencies for isomers in the S₀ and S₁ states are found. Several Deslandres Tables (DTs) are constructed for the torsional vibration of the s-trans- and s-cis-isomers of the investigated molecule using the NONIUS program. The origins in these DTs correspond to bands attributed to ν₀₀, and to the fundamental frequencies of each isomer in states S₀ and S₁. These DTs are used to determine harmonic frequencies ω_e, anharmonicity coefficients х₁₁, and the frequencies of torsional vibration 0–v transitions up to high values of vibrational quantum number v for s-trans- and s-cis-isomers in both electronic states. The frequencies of torsional vibrations for the s-trans-isomer and the s-cis-isomer in the S₀ state are ν″₁ = 80.9 сm^?1 and ν″₁ = 59.8 сm^?1, respectively. The frequencies for the s-trans- isomer and the s-cis-isomer in the S₁ state are ν′₁ = 134.1 сm^?1 and ν′₁ = 103.6 cm^?1, respectively.     

A one-dimensional silver(I) coordination polymer with saccharin and pyrazine: synthesis,crystal structure,thermal analysis,FTIR spectra,and DFT studies

A silver(I) complex of saccharinate (sac) with pyrazine (pyz), [Ag(sac)(pyz)] _n , has been synthesized and characterized by elemental analysis, IR, thermal analysis, and single-crystal X-ray diffractometry. The complex crystallizes orthorhombic space group Pnma with unit cell parameters of a = 13.0073(9) Å, b = 6.4907(6) Å, c = 13.4007(9) Å, V = 1131.37(15) Å³, and Z = 4. [Ag(sac)(pyz)] _n is a one-dimensional coordination polymer, in which the sac ligand acts as a monodentate ligand through the N atom and the trigonal silver centers are linked by the bridging pyz ligands. The individual chains are connected into two-dimensional supramolemular network by aromatic π(sac)···π(pyz) stacking interactions. The FTIR spectrum of [Ag(sac)(pyz)] _n has been recorded in the region and 4,000–400 cm^?1. The optimized geometry, frequency, and intensity of the vibrational bands of [Ag(sac)(pyz)] _n were obtained by density functional theory (DFT) at the B3LYP level. The vibrational frequencies were calculated and the scaled values have been compared with the experimental FTIR data. The observed and calculated frequencies are found to be in good agreement.     

Structural and stereochemical nonrigidity of 7-(heptaphenylcycloheptatrienyl) isothiocyanate

By means of DFT B3LYP/6-31G(d, p) calculations of 7-(heptaphenylcycloheptatrienyl) isothiocyanate, the dissociation–recombination mechanism for intramolecular migrations of the isothiocyanato group has been revealed, and the structure of the transition state preceding the formation of a tight ion pair has been found for the first time. According to calculations, the high activation barrier for displacements of the isothiocyanato group ΔE_ZPE^≠ = 21.3 kcal/mol is related to the stable conformation of the molecule with the equatorial–NCS group and the orthogonally located phenyl substituent in the axial position. The rearrangement of the molecule to the form favorable for migrations of the–NCS group involves the inversion of the seven-membered ring accompanied by rotation of the phenyl group.     

Vibrational analysis,conformational stability,force constants,internal rotation barriers,MP2=full and DFT calculations of 1,3-dimethyluracil tautomers

The molecular structure of 1,3-dimethyluracil (C₆H₈N₂O₂; 1,3-DMU) is studied theoretically and experimentally using Gaussian 98 calculations and different spectroscopic techniques. The vibrational spectrum for 1,3-DMU in the solid phase is recorded in the IR range 4000-400 cm^–1. Initially, in order to get the most stable structure, twelve structures were proposed for the titled compound as a result of the internal rotation of CH₃ around C–N bonds and keto-enol tautomerism. The single point energy and frequency calculations are obtained by MP2 (Full) and DFT/B3LYP methods with the 6-31G(d) basis set using the Gaussian 98 computation package. After the complete relaxation of twelve isolated isomers, the (diketo) tautomer was the only favored structure owing to its low energy relative to the other isomers and the prediction of real frequencies. This interpretation is supported by the recorded infrared spectrum that shows the presence of only the diketo tautomer. Aided by the normal coordinate analysis and potential energy distributions, a confident vibrational assignment of the fundamental frequencies is calculated. The results are discussed herein and compared with similar molecules whenever possible.     

Protonation of the Dodecahydro-<Emphasis Type="Italic">closo</Emphasis>-Dodecaborate Anion in CH<Subscript>3</Subscript>CN/CF<Subscript>3</Subscript>COOH

The behavior of the [B₁₂H₁₂]^2– anion in CH₃CN, CF₃COOH, and the CH₃CN/CF₃COOH system is studied by IR spectroscopy. Based on the IR spectroscopy data correlated with the data obtained when studying the protonation processes of boron cluster anions [B₆H₆]^2– and [B₁₀H₁₀]^2–, the possibility to prepare the protonated form of the closo-dodecaborate anion, namely monoanion [B₁₂H₁₃]^–, is concluded in CF₃COOH and the CH₃CN/CF₃COOH system. In the IR spectra of salts of the protonated forms of anions [B_nH_n]^2– (n = 6, 10, 12) in solutions and Nujol mulls, a high-frequency shift of the ν(BH) absorption bands is observed as compared with the spectra of salts of non-protonated anions Cat₂[B_nH_n] (Δν = 70–100 cm^–1).     

Electronic spectra and crystal structure of dinuclear Cu(II) ‘paddle wheel’ acetate complex containing axially coordinated 3-methyl-4-nitropyridine-<Emphasis Type="Italic">N</Emphasis>-oxide

This article presents the electronic spectral characteristics enhanced with the structural, IR and magnetic data of the copper(II) acetate complex with 3-methyl-4-nitropyridine-N-oxide. The complex of the formula, [Cu₂(OAc)₄(3-mnpn)₂], belongs to the group of the ‘paddle wheel’ type species with a very short (2.58 Å) metal–metal distance. In the electronic spectra, new bands were found at 16,000 and 24,000 cm^?1, which have been tentatively assigned to the metal–metal interactions and solid state effects, respectively. The complex show fast kinetic exchange of the apical ligand, i.e. 3-methyl-4-nitropyridine-N-oxide.     

Low-temperature photolysis of azidostyrylquinolines

Low-temperature photolysis of 2-and 4-(4′-azidostyryl)quinolines and azidohemicyanine dye, 1-methyl-4-(4′-azidostyryl)quinolinium iodide, was studied in an ether-ethanol matrix at 77 K and a methyltetrahydrofuran matrix at 5 K by means of electronic absorption spectroscopy and ESR technique. The formation of corresponding triplet nitrenes with absorption bands at 380–440 nm and zero-field splitting parameters of |D/h _cl = 0.781–0.790 cm^?1 and E = 0 was detected. It was found that the introduction of the positive charge into the azidostyrylquinoline molecule resulted in a bathochromic shift of the nitrene absorption band by ～40 nm and a decrease in the D by 0.005 cm^?1 due to charge transfer from the nitrene center to the quinoline moiety.     

Distinctive and regular features of the IR spectra of transition metal tris(acetylacetonates)

The frequencies for the IR spectra of M(Acac)₃ (M = Sc, Ti, V, Cr, Fe, Mn, and Co) were qualitatively calculated by the Hartree-Fock-Roothaan method with the MIDI basis set including p and d polarization functions. It was demonstrated that the coordination entity of the manganese complex is deformed more strongly than that of the vanadium complex. A correlation diagram for the IR bands in the 200–1600 cm^?1 range is presented for the complexes in the condensed state. A correlation was found between the experimental frequency of the M-O vibrations and the corresponding force constants.     

Structure of cyano-bridged Eu(III)—Co(III) bimetallic assembly and its application to photophysical verification of photomagnetic phenomenon

New crystal structure of Eu(DMF)₄(H₂O)₃Co(CN)₆·H₂O (DMF = N,N′-dimethylformamide) (Eu-Co) has been determined to be monoclinic, P2(1)/n, a = 19.796(12) Å, b = 8.862(11) Å, c = 17.525(10) Å, β = 96.26(5)°, V = 3056(5) ų, Z = 4. The Eu(III) ion adopts an antiprismatic eight-coordination and forms a cyano bridge with r(Eu-N) = 2.496(7) Å and Θ(Eu-N-C) = 165.7(7)° to the Co(III) ion. The complex exhibits some common features with the Eu-Fe complex. Diffuse reflectance electronic spectra and magnetic susceptibility of Eu-Cr, Eu-Mn, Eu-Fe, and Eu-Co complexes were compared. By substituting the metal ions, both electronic and structural features affected the charge transfer bands and superexchange interactions concerning cyanide ligands. In addition, only Eu-Co exhibited ⁵ D ₀ → ⁷ F ₂ and ⁵ D ₀ → ⁷ F ₁ luminescence bands at 16300 cm^?1 and 16900 cm^?1, respectively at 298 K (λ_ex = 360 nm (27000 cm^?1)), because quenching by cyano-bridged ions did not prevent Eu(III) ion from exhibiting emission. Thus, only Eu-Co may be suitable for verification of an assumption of mechanism concerning drastic photoinduced magnetic changes for Nd-Fe. Merely small decrease of magnetization was observed for Eu-Co after UV light irradiation at 2.0 K. This result was attributed to slight structural changes around cyano bridges without transitions of spin states.     

Synthesis and crystal structure of dimethylgold(III) carboxylates

Three novel carboxylate complexes were synthesized: dimethylgold(III) trifluoroacetate [Me₂Au(Tfa)]₂ (I), trimethylacetate (pivalate) [Me₂Au(Piv)]₂ (II), and benzoate [Me₂Au(OBz)]₂ (III). The starting reagent was [Me₂AuI]₂. The procedure of its synthesis provides 60% product yield. Dimethylgold(III) carboxylates were identified from the IR and ¹H NMR data. The title compounds were studied by X-ray diffraction. The unit cell parameters for I, C₈H₁₂Au₂F₆O₄: a = 15.5522(13), b = 12.9398(11), c = 15.6555(14) Å, β = 104.308(2)°, Z = 8, ρ(calcd.) = 2.959 g/cm³, space group C2/c, R = 0.0779; for II, C₁₄H₃₀Au₂O₄: a = 10.3025(3), b = 15.5952(4), c = 12.6819(3) Å, β = 105.8270(10)°, Z = 4, ρ(calcd.) = 2.224 g/cm³, space group P2₁/c, R = 0.0229; for III, C₁₈H₂₂Au₂O₄: a = 12.8050(2), b = 19.7886(3), c = 7.60300(10) Å, Z = 4, ρ(calcd.) = 2.401 g/cm³, space group Pnma, R = 0.0144. Compounds I–III have the molecular structures; the structural units are the [(CH₃)₂Au(OOCR)]₂ dimers (Au…Au 2.984–3.080 Å), R = CF₃, tert-Bu, Ph. The gold atoms have the square coordination with two carbon atoms and two oxygen atoms (Au-O 2.120–2.173 Å). The molecules in compounds I–III are united into infinite unidimensional chains connected by van der Waals interactions.     

Crystallographic and conformational analysis of (<Emphasis Type="Italic">E</Emphasis>)-2-isopropyl-4-(<Emphasis Type="Italic">p</Emphasis>-tolyldiazenyl)phenol

The molecular and crystal structures of the title compound, C₁₆H₁₈N₂O, were characterized and determined by single crystal X-ray diffraction method in addition to spectroscopic means such as IR, UV–VIS and ¹H NMR. The compound crystallizes in orthorhombic space group P bca, with a = 9.3350(5) Å, b = 23.4878(13) Å, c = 26.5871(12) Å, Z = 16, D _calc. = 1.1591(1) g/cm³, μ (MoK_α) = 0.073 mm^?1. Monomers of the compound in the crystal structure are linked into C(7) and C(8) chains generated by translation along the [1 0 0] direction with the aid of O–H···N type H-bonds which serve to the stabilization of periodic organization of the molecules beside major and minor component in the disordered azo fragment. In order to describe conformational flexibility and the crystal packing effects on the molecular conformation, potential barriers regarding the rotation along both Ar–N bonds were calculated by varying the related torsional degrees of freedom in every 10° ranging from ?180° to +180° via quantum chemical calculations at DFT/B3LYP level.     

Binuclear copper(II) complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid

Copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid in which the coordination polyhedra are connected by polymethylene chains of different length (1 to 5 units) were synthesized and studied by chemical and thermogravimetric analysis, IR spectroscopy, and EPR. The structure of binuclear copper(II) complex with succinic acid acyldihydrazone [Cu₂L · 4Py] · 2Py was determined by X-ray diffraction. The crystals are monoclinic: a = 14.3795(6), b = 8.8736(4), c = 15.9147(7) Å, β = 101.062(3)°, space group P2₁/c, Z = 2. The number of independent reflections with I > 2σ(I) = 2804, R = 0.042, R _w = 0.087. The copper atoms are spaced by a chain of seven σ bonds at 8.922 Å. The coordination polyhedron can be described as a tetragonal pyramid highly distorted toward a trigonal bipyramid. The EPR spectra of solutions of complexes based on malonic, succinic, glutaric, and adipinic acids exhibit a poorly resolved signal of seven HFS lines with a constant of (26.3–27.0) × 10^?4 cm^?1, which attests to the presence of weak exchange interactions between paramagnetic centers. An increase in the length of the polymethylene spaur suppresses exchange interactions, and the EPR spectrum of the complex based on pimelic acid acyldihydrazone shows a signal of four HFS lines with a constant of 43.8 × 10^?4 cm^?1 typical of monomeric copper(II) complexes.     

Crystal structure and fluorescence of a 2D cadmium(II) coordination polymer based on flexible bis(2-methylbenzimidazole) and benzenedicarboxylate co-ligands

A new coordination polymer, {[Cd(bbmb)(bdc)]} _n (bbmb = 1,1′-(1,4-butanediyl)bis-(2-methylbenzimidazole), H₂bdc = 1,3-benzenedicarboxylic acid) was synthesized under hydrothermal conditions. The complex was structurally characterized by single crystal X-ray diffraction analyses, infrared spectroscopy (IR), elemental analyses. The compound crystallizes in the monoclinic system, space group P2₁/c with a = 10.860(6) Å, b = 13.115(7) Å, c = 21.009(9) Å, β = 120.94(2)°, V = 2567(2) ų, Z = 4, C₂₈H₂₆CdN₄O₄, M _r = 594.93, D _c = 1.540 g/cm³, μ = 0.893 mm^–1. Each cadmium center is six coordinated with four O atoms from two bdc^2– anions, and two N atoms of two bbmb ligands. The complex features a 4-connected 2D (4, 4) sheet with a point symbol {4².6^2}. Fluorescence properties of the title complex were investigated.