Thermochemical properties of 2,4-dinitroanisole in N-methyl pyrrolidone and dimethyl sulfoxide

The thermochemical properties of 2,4-dinitroanisole (DNAN) in N-methy pyrrolidone (NMP) and dimethyl sulfoxide(DMSO) were studied using a RD496-2000 Calvet microcalorimeter at four different temperatures. The heat effects were measured for DNAN dissolved in NMP and DMSO and the relationships between the heat effects and the amounts of the substance were determined. The molar enthalpies and the differential molar enthalpies of dissolution processes were also obtained from the experimental data. The corresponding kinetic equations describing the two dissolution processes at different temperatures were discussed.     

Computational study of structures and properties of metallaboranes: cobalt bis(dicarbollide)

A density functional study at the BP86/AE1 level is presented for the cobalt bis(dicarbollide) ion [3-Co-(1,2-C2B9H11)2]- (1) and selected isomers and rotamers thereof. Rotation of the two dicarbollide moieties with respect to each other is facile, as judged by the small energetic separation of the three rotamers located (within 11 kJ mol(-1)) and by the low barriers for their interconversion (at most 41 kJ mol(-1)). Among the isomers differing in carbon atom positions that contain two equivalent dicarbollide ligands, the 1,7 ("carbon apart") form [2-Co-(1,7-C2B9H11)2]- is the most stable, 121 kJ mol(-1) below 1. The electronic structure of 1 is characterized in terms of molecular orbitals, population analysis, and excitation energies from time-dependent density functional theory, relevant to UV/Vis spectroscopy. Experimental 11B NMR chemical shifts of 1 are reproduced to better than 5 ppm at the GIAO-B3LYP/II' level, and the computed delta(11B) values are only little affected by rotational averaging or the presence of a polarizable continuum. Larger such effects are found for the as-yet unknown 59Co chemical shift, for which a value in the range between -1800 and -2400 ppm is predicted. Even though the accuracy achieved for the theoretical delta(11B) values is somewhat lower than that for heteroboranes at conventional ab initio levels, the level of density functional employed can afford qualitatively reliable chemical shifts, which can be useful in assignments and structural refinements of heteroboranes containing transition metal.     

Fe(II) in different macrocycles: electronic structures and properties

A theoretical comparative study of complexes of porphyrin (P), porphyrazine (Pz), phthalocyanine (Pc), porphycene (Pn), dibenzoporphycene (DBPn), and hemiporphyrazine (HPz) with iron (Fe) has been carried out using a density functional theory (DFT) method. The difference in the core size and shape of the macrocycle has a substantial effect on the electronic structure and properties of the overall system. The ground states of FeP and FePc were identified to be the 3A2g [(d(xy))2(d(z)2)2(d(pi))2] state, followed by 3E(g) [(d(xy))2(d(z)2)1(d(pi))3]. For FePz, however, the 3E(g)-3A2g energy gap of 0.02 eV may be too small to distinguish between the ground and excited states. When the symmetry of the macrocycle is reduced from D4h to D2h, the degeneracy of the d(pi) (d(xz), d(yz)) orbitals is removed, and the ground state becomes 3B2g [(d(xy))2(d(z)2)1(d(yz))2(d(xz))1] or 3B3g [...(d(yz))1(d(xz))2] for FePn, FeDBPn, and FeHPz. The calculations also show how the change of the macrocycle can influence the axial ligand coordination of pyridine (Py) and CO to the Fe(II) complexes. Finally, the electronic structures of the mono- and dipositive and -negative ions for all the unligated and ligated iron macrocycles were elucidated, which is important for understanding the redox properties of these compounds. The differences in the observed electrochemical (oxidation and reduction) properties between metal porphycenes (MPn) and metal porphyrins (MP) can be accounted for by the calculated results (orbital energy level diagrams, ionization potentials, and electron affinities).     

Ground- and excited-state electronic structure of an emissive pyrazine-bridged ruthenium(II) dinuclear complex

The synthesis, characterization, and electrochemical, photophysical, and photochemical properties of the binuclear compounds [(Ru(H8-bpy)2)2((Metr)2Pz)](PF6)2 (1) and [(Ru(D8-bpy)2)2((Metr)2Pz)](PF6)2 (2), where bpy is 2,2'-bipyridine and H2(Metr)2Pz is the planar ligand 2,5-bis(5'-methyl-4'H-[1,2,4]triaz-3'-yl)pyrazine, are reported. Electrochemical and spectro-electrochemical investigations indicate that the ground-state interaction between each metal center is predominantly electrostatic and in the mixed-valence form only a low level of ground-state delocalization is present. Resonance Raman, transient, and time-resolved spectroscopies enable a detailed assignment to be made of the excited-state photophysical properties of the complexes. Deuteriation is employed to both facilitate spectroscopic characterization and investigate the nature of the lowest excited states.     

Surface-enhanced Raman scattering spectroscopy of explosive 2,4-dinitroanisole using modified silver nanoparticles

2,4-Dinitroanisole (DNAN) is being used as a replacement for 2,4,6-trinitrotoluene (TNT) as a less-sensitive melt-cast medium explosive than TNT. In this paper, we studied the surface-enhanced Raman spectroscopy (SERS) analysis of DNAN using Ag nanoparticles (AgNPs) modified by L-cysteine methyl ester hydrochloride. Due to the formation of a Meisenheimer complex between DNAN and the modifier, the modified AgNPs can detect 20 μg/L (0.2 ng) and 0.1 mg/L (1 ng) DNAN in deionized water and aged tap water, respectively. Three other chemicals (L-cysteine, N-acetyl-L-cysteine, and L-cysteine ethyl ester hydrochloride) were used as AgNPs modifiers to study the mechanism of the SERS of DNAN. It was confirmed that the amino group of L-cysteine methyl ester hydrochloride was the active group and that the methyl ester group significantly contributed to the high SERS sensitivity of DNAN. In order to further test the mechanism of Meisenheimer complex formation, the effect of anions and cations present in natural water on the SERS of DNAN was studied. It was found that CO(3)(2-), Cl(-), and K(+) at 100 mg/L did not negatively affect the SERS of 10 mg/L DNAN, while SO(4)(2-), Na(+), Mg(2+), and Ca(2+) at 100 mg/L significantly quenched the SERS of 10 mg/L DNAN. The negative effect of the bivalent cations could be offset by SO(4)(2-).     

Syntheses, crystal structures and magnetic properties of Ni(II)–2,4-pyridine-dicarboxylates

Two new complexes [Ni(pydc)(H₂O)₂]_n (1) and [Ni₂(pydc)₂(H₂O)₅]_n (2) (H₂pydc = 2,4-pyridinedicarboxylic acid) have been obtained by hydrothermal synthetic method and characterized by single crystal X-ray analysis. In 1 six-coordinate Ni(II) ions are coordinated by pydc ligands to form 2-D layer structures; while in 2 six-coordinate Ni(II) ions are only connected into 1-D zigzag chains constructed by dinuclear nickel units. Although the coordination geometries around Ni(II) centers in both complexes are similar, their structure topologies are greatly tuned by coordination modes of pydc. Variable temperature magnetic susceptibility studies have shown that both compounds 1 and 2 may display antiferromagnetic coupling between paramagnetic metal centers mediated by bridging carboxylate groups.     

A theoretical prediction of the molecular and electronic structures,thermodynamic properties,and stability of 1,3-diazido-2-methyl-2-nitropropane (DAMNP)

1,3-Diazido-2-methyl-2-nitropropane (DAMNP) is a newly synthesized azido compound and may be a potential candidate of the plasticizer of propellants. For better understanding its properties, the molecular conformations, electronic structure, IR spectrum, thermodynamic properties, pyrolysis mechanism, and specific impulse (I _S) were studied using the B3LYP/6-31++G** method of density functional theory (DFT). The electronic structure of DAMNP was analyzed by the natural atomic charges, bond orders, donor–acceptor interactions, and molecular electrostatic potential (MEP). Results show that the main contributions to the highest occupied molecular orbital and the lowest unoccupied molecular orbital are from –N₃ and –NO₂, respectively. The most negative area on the MEP locates at the O atoms of –NO₂, which agrees with the atomic charges distributions. The pyrolysis mechanism was investigated by considering three possible bond dissociations (C–N₃, C–NO₂, and N–N₂). Results show that the pyrolysis of DAMNP starts from the rupture of N–N₂ finished cooperatively via the H-transfer process to eliminate N₂. The lowest energy needed for pyrolysis is 165.13 kJ mol^?1. To verify the reliability of the method, the organic azido compound CH₃N₃ was also considered. DAMNP has a slightly higher thermal stability than CH₃N₃. However, using DAMNP to replace the plasticizer nitroglycerin of the nitramine modified double-base propellant leads to a decrease in I _S. Therefore, whether DAMNP can be really used as a plasticizer or not is worth further considerations.     

Computational studies on structural and excited-state properties of modified chlorophyll f with various axial ligands

Time-dependent density functional theory (TDDFT) calculations have been used to understand the excited-state properties of modified chlorophyll f (Chlide f), Chlide a, Chlide b, and axial ligated (with imidazole, H(2)O, CH(3)OH, CH(3)COOH, C(6)H(5)OH) Chlide f molecules. The computed differences among the Q(x), Q(y), B(x), and B(y) band absorbance wavelengths of Chlide a, b, and f molecules are found to be comparable with the experimentally observed shifts for these bands in chlorophyll a (chl a), chl b, and chl f molecules. Our computations provide evidence that the red shift in the Q(y) band of chl f is due to the extended delocalization of macrocycle chlorin ring because of the presence of the -CHO group. The local contribution from the -CHO substituent to the macrocycle chlorin ring stabilizes the corresponding molecular orbitals (lowest unoccupied molecular orbital (LUMO) of the Chlide f and LUMO-1 of the Chlide b). All the absorption bands of Chlide f shift to higher wavelengths on the addition of axial ligands. Computed redox potentials show that, among the axial ligated Chlide f molecules, Chlide f-imidazole acts as a good electron donor and Chlide f-CH(3)COOH acts as a good electron acceptor.     

Ground-state and excited-state structures of tungsten-benzylidyne complexes

The molecular structure of the tungsten-benzylidyne complex trans-W(≡CPh)(dppe)(2)Cl (1; dppe = 1,2-bis(diphenylphosphino)ethane) in the singlet (d(xy))(2) ground state and luminescent triplet (d(xy))(1)(π*(WCPh))(1) excited state (1*) has been studied using X-ray transient absorption spectroscopy, X-ray crystallography, and density functional theory (DFT) calculations. Molecular-orbital considerations suggest that the W-C and W-P bond lengths should increase in the excited state because of the reduction of the formal W-C bond order and decrease in W→P π-backbonding, respectively, between 1 and 1*. This latter conclusion is supported by comparisons among the W-P bond lengths obtained from the X-ray crystal structures of 1, (d(xy))(1)-configured 1(+), and (d(xy))(2) [W(CPh)(dppe)(2)(NCMe)](+) (2(+)). X-ray transient absorption spectroscopic measurements of the excited-state structure of 1* reveal that the W-C bond length is the same (within experimental error) as that determined by X-ray crystallography for the ground state 1, while the average W-P/W-Cl distance increases by 0.04 ? in the excited state. The small excited-state elongation of the W-C bond relative to the M-E distortions found for M(≡E)L(n) (E = O, N) compounds with analogous (d(xy))(1)(π*(ME))(1) excited states is due to the π conjugation within the WCPh unit, which lessens the local W-C π-antibonding character of the π*(WCPh) lowest unoccupied molecular orbital (LUMO). These conclusions are supported by DFT calculations on 1 and 1*. The similar core bond distances of 1, 1(+), and 1* indicates that the inner-sphere reorganization energy associated with ground- and excited-state electron-transfer reactions is small.     

Theoretical study of electronic structures and conduction properties of copolymers based on poly(cyclopentadienylene)

Various quasi-one-dimensional superlattices (copolymers) (AmBn)x of two novel donor-acceptor polymers PPDCF ([A]x) and PPDCN ([B]x) based on poly(cyclopentadienylene) (PPD) and belonging to the class of type II staggered superlattices were investigated using a negative factor counting method in the tight-binding approximation. Both PPDCF and PPDCN consist of a bicyclopentadienylene unit bridged by an electron-accepting group >C=CF2 in PPDCF and >C=C(CN)2 in PPDCN. The trends in the electronic structures and conduction properties of the copolymers (AmBn)x as a function of the block sizes m and n, arrangement of the units (periodic or random) in the copolymer chain, and length of the copolymer chain are discussed.     

Lead(II) and cadmium(II) compounds with 2,4-dichlorophenoxyacetic acid (2,4D) and 2-(2,4-dichlorophenoxy)-propionic acid (2,4DP): Synthesis and properties

The paper presents the conditions under which compounds of the commercial herbicides, 2,4-dichlorophenoxyacetic acid (2,4D; C₈H₆O₃Cl₂) and 2-(2,4-dichlorophenoxy)-propionic acid (2,4DP; C₉H₈O₃Cl₂), with lead(II) and cadmium(II) are formed and the results of the examination of their properties.On the basis of the elemental analysis and Pb and Cd determination, the following molecular formulae for the obtained compounds were proposed: Pb(C₈H₅O₃Cl₂)₂.H₂O, Cd(C₈H₅O₃Cl₂)₂.₂H₂O, Pb(C₉H₇O₃Cl₂)2·H₂O and Cd(C₉H₇O₃Cl₂)₂·H₂O. Water solubility of the synthesized complexes at room temperature was examined. X-ray powder analysis was carried out. The discussion of IR spectra and conductivity data is presented. Thermal decomposition of these compounds in air was studied by TG/MS methods.This revised version was published online in November 2005 with corrections to the Cover Date.     

Template synthesiS: Geometrical and electronic structures of the Fe nitrosyl complex formed by bis(S-methylisothiosemicarbazone)-2,4-pentandione

Sodium acetylacetonate reacts with S-metliylisothiosemicarbazidium nitrate and Fe(NO₃)₃ · 9H₂O in ethanol to make [Fe(HL)NO]NO₃, in which H₃L is bis(S-methyl-isothiosemicarbazone)-2,4-puntandione. The [Fe(HL)NO]⁺ cation has a square pyramidal structure with the HL^2- arranged around the central ion in the basal plane and the nitrogen atom of the NO group in the apical position, with the iron atom diverging from the plane of the base of the pyramid by 0.477 Å. The FeN0 moiety has a linear structure (FeNO = l72.7°). XRD, IR, and Mössbauer spectroscopy have been combined with calculations on the electronic structure to demonstrate that the Fe-NO bond is covalent.Chemical Institute, Academy of Sciences of Moldavian SSR. Applied Physics Institute, Academy of Sciences of the Moldavian SSR. Kishinev. Institute of Crystallography, Academy of Sciences of the USSR. Kurnakov Institute for General and Inorganic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No, 3, pp. 376–381, May–June, 1991. Original article submitted February 18, 1991.     

Bonding properties and electronic structures of glycylglycinato copper(II) complexes. Molecular structure of acetylhistaminegly-cylglycinatocopper(II) dihydrate

Summary Mixed ligand diglycinatocopper(II) complexes of the Cu(glygly)L·nH₂O type, where glygly stands for [NH₂-CH₂ CONCH₂CO₂]^2– and L for imidazole (n = 1.5), N-methylimidazole (n = 1), 2-methylimidazole (n = 2), 4-methylimidazole (n = 2), 4-phenylimidazole (n = 2), N-acetylhistamine (n = 2) and NH₃ (n = 2), were prepared and characterized by elemental analyses, i.r., vis. and e.p.r. spectroscopic measurements. The molecular structure of [Cu(glygly)(achmH)]·2H₂O (achmH = acetylhistamine) was determined using three dimensional XRD data. The structure consists of distorted square planar [Cu(glygly)-(achmH)] units interconnected via the peptide oxygen at the apex to complete a square pyramidal structure, Cu—O-(peptide) 2.477(2) Å. The H₂O molecules, not binding directly to the copper ion, involve in intermolecular hydrogen bonding with the copper units. The dianionic glygly ligand and the imidazole ring bind strongly to the central copper ion with Cu—N(amino) 2.045(6) Å, Cu—N-(peptide) 1.891(5) Å, Cu—O(carboxylate) 2.001(4) Å and Cu—N(imidazole) 1.956(5) Å. The dihedral angle between the imidazole nucleus and the CuN₃O xy plane is 6.0°. Similar structures with a CuN₃O coordination plane are proposed for the imidazole complexes, based on spectroscopic data. The bonding properties of the glygly ligand and the unidentate imidazole ligands are elucidated and discussed with reference to the electronic structures of the complexes deduced from Gaussian analyses.     

First-principle calculations on the structures and electronic properties of the CO-adsorbed (SnO2)2 clusters

To clear the adsorption site of CO on the surface of the nanosized SnO₂ film, the structures, stability, and electronic characteristics of the CO-adsorbed (SnO₂)₂ clusters have been investigated by using PW91 functional. The more stable configurations of these CO(SnO₂)₂ clusters derive from CO are adsorbed on the lower energy excited-state (SnO₂)₂ clusters rather than on the ground-state (SnO₂)₂ clusters. The calculated adsorption energies for CO on the lower energy excite-state (SnO₂)₂ clusters are up to 1.363–1.454 eV which is transferred from physical adsorption to chemical adsorptions. CO adsorption increases the kinetic stability and decreases the conductivity of the lower energy excited-states (SnO₂)₂ clusters.

     

Theoretical study on the spectroscopic properties and electronic structures of heteroleptic phosphorescent Ir(III) complexes

The geometries, spectroscopic and electronic structures properties of a series of heteroleptic phosphorescent Ir(III) complexes including N981, N982, N983, N984 have been characterized by density functional theory calculations. The excited‐state properties of the Ir(III) complexes have been characterized by CIS method. The ground‐ and excited‐state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. By using the time‐dependent density functional theory method, the absorption and phosphorescence spectra were calculated based on the optimized ground‐ and excited‐state geometries, respectively. The results show that the absorption and emission data agree well with the corresponding experimental results. The calculated results also revealed that the nature of the substituent at the 4‐position of the pyridyl moiety can influence the distributions of HOMO and LUMO and their energies. In addition, the charge transport quality has been estimated approximately by the calculated reorganization energy (λ). Our result also indicates that the positions of the substitute groups not only change the transition characters but also affect the charge transfer rate and balance, and complex N982 is a very good charge transfer material for green OLEDs. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

镍和钯两种金属配合物电子结构和光谱性质的理论研究

采用密度泛函理论(DFT),在PBE0/6-31+G(d)-LANL2DZ水平下优化了Ni和Pd两种金属配合物A和B的基态几何构型,并在相同水平下进行了频率分析以确认都是实频.利用含时密度泛函理论(TD-DFT)和极化连续介质模型(PCM),在TD-PBE0/6-31+G(d)-LANL2DZ水平下,计算了配合物A和B在二氯甲烷溶剂中的电子结构和吸收光谱.计算结果表明,与中心配位原子Pd相比,Ni较强的配位作用使配合物A具有较小的HOMO-LUMO能级差,从而导致配合物A的最大吸收波长发生红移.     

New layered rubidium rare-earth selenides: syntheses,structures, physical properties,and electronic structures for RbLnSe(2)

The compounds RbLnSe(2) (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Ho, Er, Lu) have been synthesized by means of the reactive flux method at 1173 K. These isostructural compounds, which have the alpha-NaFeO(2) structure type, crystallize with three formula units in space group D(3d)(5)-R(-)3m of the trigonal system in cells at T = 153 K of dimensions (a, c in A) La, 4.4313(4), 23.710(3); Ce, 4.3873(3), 23.656(3); Pr, 4.3524(11), 23.655(7); Nd, 4.3231(5), 23.670(4); Sm, 4.2799(4), 23.647(3); Gd, 4.2473(7), 23.689(5); Tb, 4.2197(4), 23.631(3); Ho, 4.1869(6), 23.652(5); Er, 4.1541(8), 23.576(7); Lu, 4.1294(6), 23.614(5). The structure consists of close-packed Se layers in a pseudocubic structure distorted along [111]. The Rb and Ln atoms occupy distorted octahedral sites in alternating layers. The Rb-centered octahedra share edges with the Ln-centered octahedra between layers. Within a given layer, both the Rb-centered and Ln-centered octahedra share edges with themselves. RbTbSe(2) and RbErSe(2) exhibit Curie-Weiss paramagnetism between 5 and 300 K, and RbCeSe(2) exhibits Curie-Weiss paramagnetism between 100 and 300 K. The optical transitions for RbCeSe(2), RbTbSe(2), and RbErSe(2) are in the 2.0-2.2 eV region of the spectrum, both from diffuse reflectance spectra and from first-principles calculations. These calculations also provide insight into the electronic structures and chemical bonding in RbLnSe(2). A quadratic fit for the lanthanide contraction of the Ln-Se distance is superior to the linear one only if the closed-shell atoms La and Lu are included.