The diverse behaviour of the P–Cl bonds in the spiro–cis–ansa spermidine derivative cyclotriphosphazene towards mono-functional nucleophilic reagents

A number of new spiro–ansa spermidine derivative cyclotriphosphazenes (2–10) is synthesized in order to provide insight into the reaction mechanism for nucleophilic substitution. The structures of the compounds were determined by elemental analysis, mass (MS), ¹H, ¹⁹F (for 9) and ³¹P NMR spectroscopies. Compounds (2–8) and 9, 10 can be formed by a proton abstraction–chloride elimination and both the and reaction mechanisms, respectively.     

AM1, PM3, and PM5 calculations of the absorption maxima of basic organic dyes

The absorption maxima, λ_max, of various organic dyes such as indigo, azobenzene, phenylamine, hydrazone, anthraquinone, naphthoquinone, and malachite green were calculated using the AM1, PM3, and PM5 semiempirical molecular orbital theories with the configuration interaction singles (CIS) and random phase approximation (RPA) approaches. The calculated λ_max were then compared with the values obtained by CNDO/S, INDO/S, ab initio CIS, and time-dependent density functional theory (TD-DFT). We found that the λ_max values calculated by AM1, PM3, and PM5 were in good correlation with the observed λ_max values. When B3LYP/cc-pVDZ optimized geometries were used, the square of the correlation coefficients between the calculated and observed λ_max, , at the AM1-RPA, PM3-RPA, and PM5-RPA levels were 0.891, 0.897, and 0.927, respectively. In particular, at PM5-RPA//B3LYP/cc-pVDZ was the largest among those obtained from all the other calculations including TD/B3LYP/cc-pVDZ//B3LYP/cc-pVDZ . Accordingly, the standard deviation of the difference between observed and calculated λ_max by the linear regression function at PM5-RPA//B3LYP/cc-pVDZ was the smallest. It was therefore concluded that this method was the most promising for the prediction of λ_max of various dyes among the computational methods studied here. When AM1 optimized geometries were used, at the AM1-RPA, PM3-RPA, and PM5-RPA levels were 0.822, 0.841, and 0.901, respectively, and they were also comparable to that at TD/B3LYP/cc-pVDZ//B3LYP/cc-pVDZ. Therefore, although some calibration efforts may be needed for AM1 geometries, PM5-RPA(CIS)//AM1 may be a second candidate available for the prediction of the absorption maxima of dyes, especially in the case of emphasizing computational cost.     

First principles study of the structure, electronic state and stability of cations

Structural and electronic properties of semiconductor binary microclusters cations have been investigated using the B3LYP-DFT method in the ranges of n=1, 2 and m=1–7. Full structural optimization, adiabatic ionization potentials calculation and frequency analysis are performed with the basis of 6-311+G(d). The charged-induced structural changes in these cations have been discussed. The strong As–As bond is also favored over Al–As bonds in the cations in comparison with corresponding neutral cluster. With As_m forming the base, adding Al atom(s) in different positions would find the stable structures of cations quickly and correctly. , , and are predicted to be species with high stabilities and possible to be produced experimentally.     

Theoretical study on the structures and properties of LiCn, , and (n = 1–10) clusters

The lithium-doped carbon clusters LiC_n, , and (n = 1–10) have been investigated systemically with density functional theory (DFT) method at the B3LYP/6-311+G* level. According to the total energies of different kinds of isomers, the LiC_n, , and (n = 1–10) clusters have Li-terminated linear ground states structures, except for LiC₂, LiC₃, , and (n = 4–6). The incremental binding energies are evaluated to elucidate the stabilities of the clusters with different numbers of carbon atoms for neutral molecules, cations, and anions, respectively. Clear even–odd alternation effects are observed for the stability of the cationic clusters and anionic clusters, while for neutral LiC_n clusters the alternation effect is less pronounced. Similarly, the ionization potentials and electron affinities of LiC_n also express an obvious parity alternation. In addition, the most favorable dissociation channels are acquired according to the fragmentation energies accompanying various pathways.     

Excess thermodynamic properties, and for the binary systems {1,2-dichloropropane + 2-alkoxyethanols} at T = 298.15 K

This article presents the experimental data of and , obtained at T = 298.15 K and atmospheric pressure, for four binary systems composed of 1,2-dichloropropane (1,2-DCP) and four 2-alkoxyethanols. The 2-alkoxyethanols are 2-methoxyethanol (2-ME), 2-ethoxyethanol (2-EE), 2-propoxyethanol (2-PE) and 2-butoxyethanol (2-BE). The of the mixture has been shown positive for 2-ME, ‘s-shaped’ for all remaining systems, being negative at low and positive at high mole fraction of 1,2-DCP. The values for all binary mixtures are also shown both positive at low and negative at high mole fraction of 1,2-DCP. The experimental results of and were fitted to Redlich–Kister equation to correlate the composition dependence of both excess properties. In this work, data were also used to test the suitability of thermodynamic models (Wilson, NRTL, and UNIQUAC equations) based on local-composition theory. The results have been qualitatively discussed in terms of the polarity, self-association, and hydrogen bond among molecules.     

Nucleophilic and electrophilic radical attack on maleic and fumaric acids in aqueous solution

Rate coefficients (k) of CH₂OH, , and radical addition to maleic and fumaric acids were investigated between pH 1 and 8. Strong pH dependences observed were attributed to changes in protonation states of acids: H₂X, HX⁻ and X²⁻. k of CH₂OH, , addition to fumaric acid decreased in the order k_H2F>k_HF^->k_F^2- in agreement with the nucleophilic character of reaction. The electrophilic radical showed opposite tendency. With maleic acid the monoanion had the highest reactivity towards nucleophilic and the lowest one towards electrophilic radicals. This is attributed to a prevalence of steric over polar effects for HM⁻.     

Structures and properties of the tin-doped carbon clusters

A systemic density functional theory study of the tin-doped carbon clusters has been carried out using B3LYP method with TZP+ basis set. For each species, the electronic states, relative energies and geometries of various isomers are reported. Except for smaller SnC₂ and the largest , the Sn-terminated linear or quasi-linear isomer is the most stable structure for clusters. The electronic ground state is alternate between ³Σ (for n-odd member) and ¹Σ (for the n-even member) for linear SnC_n and invariably ²Π for linear and , except for SnC/SnC⁺/SnC⁻,, and . The incremental binding energy diagrams show that strong even–odd alternations in the cluster stability exist for both neutral SnC_n and anionic , with their n-even members being much more stable than the corresponding odd n − 1 and n + 1 ones, while for cationic , the alternation effect is less pronounced. These parity effects also reflect in the ionization potential and electron affinity curves. By comparing with the fragmentation energies accompanying various channels, the most favorable dissociation channel for each kind of the clusters are given. All these results are very similar to those obtained previously for the clusters.     

Self-assembly, crystal structure and photoluminescent properties of a novel organic–inorganic hybrid coordination polymer: [CdCl3(CH3)3NH]

A novel organic–inorganic coordination polymer [CdCl₃(CH₃)₃NH] 1 was synthesized by the reaction of CdCl₂ with trimethylamine (TMA) at 170 °C for 5 days in ethanol and structurally characterized by means of X-ray single diffraction. The title compound affords a one-dimensional chain structure. It crystallizes in hexagonal system space group P6(3)/m with , , , γ=120.00°, , Z=2, , F(000)=266, Mr=277.86, , the final R=0.0420 and ωR=0.1020 for 355 observed reflections with I>2σ(I). The title compound consists of cation [(CH₃)₃NH]⁺ and anion chain , and they are combined by static attracting forces in the crystal. TG–DTA, XRD and IR data for the title compound are reported and discussed. The photoluminescent properties of the compound 1 were also investigated.     

Photoelectron spectroscopic study of iron–benzene cluster anions

Iron–benzene cluster anions, (n = 1–7, m = 1–4), were generated via laser vaporization and studied using mass spectrometry, anion photoelectron spectroscopy and in one case by density functional theory. Based on these studies, we propose that and Fe₁Bz₁ as well as and Fe₂Bz₁ exhibit half-sandwich structures, that and Fe₁Bz₂, and Fe₂Bz₂, as well as Fe₃Bz₂ and Fe₄Bz₂ are sandwich structures, and that and Fe₂Bz₃ and larger species form ‘rice-ball’ structures which in each case consist of benzene molecules surrounding an iron cluster core.     

Ab initio electronic and rovibrational structure of

The electronic structure of the ground state of has been investigated using relativistically-corrected CCSD(T) in conjunction with ANO-RCC (Mg) and aug-cc-pVQZ (H) basis sets. The molecular potential energy surface possessed minima corresponding to both ¹A₁ and equilibrium structures (with a ¹Σ⁺ transition state). The ¹A₁ structure possessed R_e and θ_e values of 2.0297 Å and of 22.09°, respectively. The higher-energy structure exhibited an R_e value of 2.1658 Å. Property surfaces were constructed to calculate rovibrational energies and spectral line intensities for the ground states of , (¹A′) MgHD²⁺ and . For the vibration ground state of , the vibration-averaged R_e and θ_e values were calculated to be 2.0209 Å and 22.53°, respectively. The A, B and C rotational constants were calculated to be 58.0, 2.21 and 2.11 cm⁻¹, respectively.     

High stable sandwich-type polyoxometallates based on . Synthesis, chemical properties and characterization of [(A-β-SiW9O34)2(MOH2)3CO3] (M = Y and Yb)

Highly hydrolytic and thermally stable sandwich-type polyoxometallates of [(A-β-SiW₉O₃₄)₂(MOH₂)₃CO₃]¹³⁻ (M = Y³⁺ and Yb³⁺) have been synthesized at room temperature by stoichiometric reactions of the trilacunary ligand with M³⁺ in 0.1 M carbonate solution. The new complexes were isolated as sodium and mixed sodium/potassium salts and were characterized by elemental analysis, IR, ¹³C and ²⁹Si NMR, UV–Vis spectroscopy, TGA, DSC and single crystal structure analysis. The crystal structure of the complexes consist of two lacunary Keggin moieties which are linked by a (H₂OMO)₃C belt into an assembly of virtual C₂ symmetry. Each M³⁺ ion adopts a mono-capped trigonal-prismatic coordination. The C₂ axis of the complexes and the local 3-fold axis of the MO₆ group lies in the (H₂OMO)₃C belt plane. The trigonal prismatic geometry is achieved by the two terminal oxygen atoms of an edge shared pair of WO₆ octahedra from each moiety and two oxygen from the belt, and the cap by one external water ligand. The hydrolytic and thermal stabilities of the complexes and the reasons that prove the retention of the isomeric form of the trilacunary ligand upon complexation are discussed.     

Unique charge ordering of manganese in a new mixed valent phosphate

A new mixed-valent manganese phosphate, , has been synthesized using hydrothermal method. Its monoclinic C2/c structure (a=12.5506(16) Å, b=10.4816(18) Å, c=13.6723(10) Å, β=103.758(11)°) forms a 3D framework of MnO₆ octahedra, MnO₅ trigonal bipyramids, PO₄ and PO₃OH tetrahedra. The main structural feature of this phosphate deals with its [Mn₄O₁₆]_∞ chains running along , which are interconnected through PO₄ and PO₃OH tetrahedra, forming intersecting tunnels running along [110], and [001]. The geometry of the [Mn₄O₁₆]_∞ chains and the charge ordering of manganese in the latter are unique: they consist of trimeric units of divalent manganese “” alternating with single trivalent Mn^IIIO₆ octahedra along . In each “” unit one central Mn^IIO₆ octahedron shares two opposite edges with two Mn^IIO₅ trigonal bipyramids. Along , one Mn(II) octahedron alternates with one Mn(III) octahedron by sharing one corner. The relationships between the structure of this unique charge ordered phosphate and other manganese phosphates are discussed.     

The elliptical Penning trap: Experimental investigations and simulations

The application of an additional azimuthal quadrupolar electrostatic field to a Penning trap leads to a field configuration referred to as an elliptical Penning trap. The resulting changes of the radial ion motions have been investigated experimentally and by use of simulations. The eigenfrequencies, i.e., the magnetron frequency and the reduced cyclotron frequency , are found to be shifted with respect to those of the standard Penning trap ω₋, ω₊, respectively. As the shift of the magnetron frequency is larger than that of the reduced cyclotron frequency their sum is also a function of the ellipticity and no longer equal to the cyclotron frequency in the absence of an electric trapping field ω_c=qB/m. The frequency shifts were investigated for argon and fullerene ions. The experimental studies were performed by time-of-flight (ToF) analysis of the ion cyclotron resonance and by Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS). The experimental and simulated values are in agreement with theoretical predictions [M. Kretzschmar, this issue] when the influence of higher multipole terms is taken into account.     

Specific fragmentation of [(CH3)2CO]Arn heteroclusters induced by the Ar L23- and O K-shell excitation

Ionic fragmentation following the inner-shell photoexcitation of [(CH₃)₂CO]Ar_n heteroclusters was investigated in the Ar L₂₃- and O K-edge regions. A partial ion yield (PIY) measurement revealed that and various acetone fragments (, , , , and CH_mCO⁺) were produced following the Ar L₂₃-shell excitation. In the O K-edge region, the PIY of O⁺ exhibited a sharp resonance peak at the O 1s → π^*(CO) resonance excitation. The selective O⁺ formation was interpreted as the suppression of statistical fragmentation, which was dominant in isolated acetone, owing to the dissipation of excess energy into Ar clusters.     

Thermochemical properties of the rare earth complexes with pyromellitic acid

Fourteen rare earth complexes with pyromellitic acid were synthesized and characterized by means of chemical and elemental analysis, and TG–DTG. The constant-volume combustion energies of complexes, Δ_cU, were measured by a precise rotating-bomb calorimeter (RBC-type II). Their standard molar enthalpies of combustion, , and standard molar enthalpies of formation, , were calculated at T = 298.15 K. The relationship of and with the atomic numbers of the elements in the lanthanide series was examined. The results show that a certain amount of covalence is present in the chemical bond between rare earth cations and the ligand.     

Low-temperature heat capacities and standard molar enthalpy of formation of the solid-state coordination compound trans-Cu(Ala)2(s) (Ala = l-α-alanine)

Low-temperature heat capacities of the solid coordination compound trans-Cu(Ala)₂(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C_p,m) with the reduced temperatures (X), [X = f (T)], by a least square method. The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)₂(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)₂·H₂O(s) + 2Ala (s)} and 2:1 HAc (aq) in 100 ml of 2 mol dm⁻³ HCl, respectively, and trans-Cu(Ala)₂(s) in the solvent [2:1 HAc (aq) + 2 mol dm⁻³ HCl] at T = 298.15 K were determined to be , , and by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess thermochemical cycle.     

A TEM investigation of the (Bi1−xSrx)FeO3−x/2, 0.2≤x≤0.67, solid solution and a suggested superspace structural description thereof

A careful transmission electron microscopy (TEM) investigation of an incommensurately modulated member of the (Bi_1−xSr_x)Fe³⁺O_3−x/2□_x/2, 0.2≤x≤0.67, solid solution has been carried out. High resolution (HR) TEM imaging is used to show the presence of at least 6-fold twinning on a rather fine (5 nm) scale. The (3+1)-d superspace group symmetry is suggested to be or one of the non-centrosymmetric sub-groups thereof, namely , , and . A superspace construction is then used to propose the nature of the local compositional ordering and, hence, of the oxygen-deficient slab that intergrows with the perovskite slab to produce the observed solid solution phase. The proposed compositional superspace atomic surfaces can be used to produce model structures at any composition within the solid solution range.     

Steady and dynamic rheological behaviors of sodium carboxymethyl cellulose entangled semi-dilute solution with opposite charged surfactant dodecyl-trimethylammonium bromide

The steady and dynamic rheological behaviors of sodium carboxymethyl cellulose (NaCMC) entangled semi-dilute solution filled with different concentrations of dodecyl-trimethylammonium bromide (C₁₂TAB) were investigated. The results reveal that the zero shear rate viscosity (η₀) and dynamic modules (G′and G″) increase with C₁₂TAB concentration (C_s), and there exist three scaling regions divided by two critical C₁₂TAB concentrations (C₁, C₂ and , respectively, from steady and dynamic tests). The increase of viscosity and modules with C_s is ascribed to formation of network due to C₁₂TAB micelles bridging NaCMC chains. The two critical C₁₂TAB concentrations implies that the structure evolution of NaCMC–C₁₂TAB complex is exposed to three states with increasing C_s, i.e., no network formation, network extent progressive formation and perfect network formation, respectively. Moreover, are a little lower than C₁, C₂, indicating that the dynamic test is more sensitive to detect the structure change of the complex as compared with steady test. Furthermore, it is found that as NaCMC concentration increases, , and increase.     

Modeling of vibration–electronic–chemistry coupling in the atomic–molecular oxygen system

The comprehensive analysis of the kinetic processes in the atomic–molecular oxygen system is conducted on the base of the novel state-to-state model involving both electronically and vibrationally excited O₂ molecules: and O(³P), O(¹D) atoms as well as vibrationally excited O₃(¹A₁) molecules. The model describes properly experimental data on the total removal rate of vibrationally excited molecules, the temporal evolution of the population of , and on the variation of vibrational temperature of behind strong shock wave. It is demonstrated that to describe with reasonable accuracy the variation of macroscopic flow parameters (pressure, temperature, density, and velocity) in the post shock region it is sufficient to use the widely applied model of mode approximation but in order to predict properly the species concentrations and populations of vibronic states of molecules just downstream the shock front it is needed to use state-to-state consideration.