Geometries, stability and aromaticity of , [M(Al2P2)] (M = Li, Na, K, Cu) and N(Al2P2) (N = Be, Mg, Ca, Zn) clusters

Geometrical structure, aromaticity and other properties of , [M(Al₂P₂)]⁻ (M = Li, Na, K, Cu) and N(Al₂P₂) (N = Be, Mg, Ca, Zn) species are theoretically investigated with density functional theory (DFT) methods. Calculation results show that for species, the planar structure, with D_2h symmetry at the ¹A_g state, is the global minimum at the B3LYP/6-311+G_* level. Natural bond orbital (NBO) analysis indicates the existence of delocalization in the most stable species and its pyramidal complexes. Nucleus-independent chemical shift (NICS) and molecular orbital (MO) analysis further reveal that that pyramidal [M(Al₂P₂)]⁻ and N(Al₂P₂) species preserve the aromatic nature of the most stable unit.     

Structures, electron affinities, and vibrational frequencies of the mono-, di-substituted SF6 radicals

Optimized molecular structures, electron affinities, and IR-active vibrational frequencies have been predicted using five different hybrid Hartree–Fock/density functional theory (DFT) methods for a series of mono-, di-substituted SF₆ compounds. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated [J.C. Rienstra-Kiracofe, G.S. Tschumper, H.F. Schaefer, S. Nandi, G.B. Ellison, Chem. Rev. 102 (2002) 231]. The equilibrium configurations of the anions and are found to be a zigzag geometry with ²A electronic state. Three different types of the neutral-anion energy separation reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities of the mono-, di-substituted SF₆ compounds obtained at the KMLYP function are 1.48 eV (SF₆), 3.20 eV (SF₅Cl), 3.49 eV (SF₅Br), 1.59 eV (SF₅CF₃), 3.21 eV (CF₃SF₄Cl), 3.59 eV (CF₃SF₄Br), 1.36 eV (CF₃SF₄CH₃), 2.32 eV (CF₃SF₄CF₃), respectively.     

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.     

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.     

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.     

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.     

Theoretical determination of absolute free energy of reduction of plastoquinone-9 in photosystem II and of plastoquinone-n in DMF

We employed static continuum electrostatics and multi-conformation continuum electrostatics (MCCE) methods to determine the reduction potential () of PQ-9 in a section of Photosystem II (PSII). Both methods relied on the finite difference Poisson–Boltzmann (FDPB) solution. The static method brings out a value (0.01 V) that is close to the experimental one (0.05 V), thereby demonstrating that the surrounding environment critically decides the net free energy change. The value obtained from MCCE (0.04 V) is even closer to the observed value, thereby indicating the importance of protein side-chain and proton motions in the electron transfer process. Furthermore, density functional theory-dielectric polarisable continuum model (DFT-DPCM) was employed to calculate the absolute free energy of reduction of plastoquinone-n (PQ-n, where n is the number of isoprenoid units) in N,N dimethyl formamide (DMF) solvent. The DFT-DPCM method produced reduction potential values of −0.59 and −0.65 V for PQ-1 and PQ-9, respectively. These are more or less in agreement with the experimentally reported values of −0.64 and −0.62 V, respectively.     

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.     

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.     

Carbon- and nitrogen-centered radicals produced from l-lysine by radiation-induced oxidation: A pulse radiolysis study

Radical species generated from the reactions of a basic amino acid, l-lysine (Lys), with hydroxyl radicals (OH) and sulfate radical anion () have been detected by the method of pulse radiolysis. On the basis of electron transfer reactivities toward tetranitromethane (TNM), it was demonstrated that reducing carbon-centered radicals are generated as a result of hydrogen abstraction from CH₂ of Lys with a G-value of 1.9 × 10⁻⁷ mol J⁻¹. On the other hand, direct oxidation of l-Lys by formed a transient species with different spectroscopic properties, most likely, the ε-N-centered Lys radical.     

The photophysics of 7H-adenine: A quantum chemical investigation including spin–orbit effects

Vertical and adiabatic electronic spectra have been investigated by means of combined density functional and multi-reference configuration interaction methods. Spin–orbit coupling has been determined employing a non-empirical spin–orbit mean-field operator. In the vertical absorption spectrum of isolated 7H-adenine, the transitions to the lowest ¹ state, the optically bright ¹ state, and a so far unknown ¹(π_H → (Ryd, σ^*)) state are predicted to lie very close to each other. The strong ¹ transition at 4.8 eV is the lowest excitation of ¹(π → π^*) type in 7H-adenine. It is red shifted by about 0.3 eV with respect to the corresponding excitation in the 9H-tautomer. We find the global minimum on the S₁ potential energy hypersurface at about 4.2 eV for a ¹ electronic structure. A potential well with a minimum at 4.3 eV exhibits mixed ¹ character. A planar ¹ structure with a potential energy of 4.6 eV constitutes a stationary point on the S₁ surface. At the present stage it is unclear whether it corresponds to a minimum or a saddle-point. The lowest-lying ¹(π → (Ryd, σ^*)) state is metastable with respect to N₇–H₁₄ bond dissociation. Its inner (Rydberg) potential well with an adiabatic excitation energy of 4.6 eV represents another minimum on the S₁ PEH. From the theoretical results presented in this work, we conclude that isolated 7H-adenine will be able to emit photons for excitation energies below 4.7 eV(264 nm). Above this threshold singlet excited 7H-adenine can undergo ultrafast non-radiative relaxation to the electronic ground state, either by hydrogen detachment via the ¹(π → (Ryd, σ^*)) channel or via a conical intersection of the ¹ state along a ring puckering mode. The ³ T₁ state can be efficiently populated via intersystem crossing from one of the S₁ potential energy wells. Large-amplitude motions in the T₁ state along an out-of-plane distortional coordinate lead to significant configuration interaction of the ¹ and ¹ structures which lend intensity to the phosphorescence.     

Franck–Condon simulation of photoelectron spectroscopy of HOO: Including Duschinsky effects

Geometry optimization and harmonic vibrational frequency calculations were performed on the and states of HOO and state of HOO⁻. The electron affinity and the term energy () of HOO were calculated at various theory levels. Franck–Condon analyses and spectral simulations were carried out on the and photodetachment processes. The spectral simulations of vibrational structures based on the computed Franck–Condon factors are in excellent agreement with the observed spectra. In addition, the equilibrium geometrical parameters of the state of HOO⁻ and state of HOO were obtained in the spectral simulations.     

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.     

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.     

Effects of substituent and solvent on the structure and spectral properties of maleimide derivatives

The maximum absorption wavelength , emission wavelength (λ_em) and the related oscillator strength (f) of the maleimides in the ground and first excited states were calculated by using the DFT, CIS and the time-dependent density functional theory (TD-DFT) methods, where the molecular structures were optimized by DFT/B3LYP/6-31G^* calculation. Solvent effects on the maleimides were examined using the PCM simulation at DFT/B3LYP level with the 6-31G^* basis set. For N-substituted maleimide, the substituent gives only a slight influence on the maleimide chromophore, while planar conformation of PhMLH leads to the improvement in π-delocalization from substituent to maleimide unit. For 3,4-substituted maleimide, the steric repulsion between substituent and maleimide chromophore influences the extent of π-delocalization and the molecular conformation. The calculated and λ_em of maleimides are in good agreement with the experimental data. In the gas phase, both absorption and emission peaks are red-shift as compared to the non-substituted maleimide. Under solvent environment, the more planar conformation of PhMLH shows a blue-shift in the calculated and λ_em as compared with other N-substituted maleimides. For 3,4-substituted maleimides, the effect of substitution produces the most significant spectral red-shift as compared to other maleimides.     

First principles study of microscopic structures and layer-anion interactions in layered double hydroxides intercalated various univalent anions

Density functional theory has been used to investigate microscopic structures and electronic properties of LDHs containing F⁻, Cl⁻, Br⁻, I⁻, OH⁻, , , . Both electrovalent bonds and covalent bonds were found in the layer. For halogen anions, the strength of interaction was accorded with electronegative intensity. And the LUMOs dispersed throughout the interlayer region. While for complicated anions, the strength was accorded with the discrepancy of electronegative intensity between center atom and bonding atoms, the LUMOs almost localized in interlayer anions. p Orbital of metal cations and s orbital of anions provided major contributions to electrovalent parts of system, while s orbital of metal cations and p orbital of anions provided major contributions to covalent parts. This has the further significance in Forcefield design for LDHs simulation. Multiple hydrogen bonds were existed in LDHs-X system. The more the number of multiple hydrogen bonds formed, the weaker the strength of single multi-hydrogen bonds was. Multiple hydrogen bonds will bring stronger interaction between interlayer guest anion and host LDHs-layer than single hydrogen bond.     

Electroreduction of anions on chemically etched and electrochemically polished Bi(1 1 1) electrode

Electroreduction kinetics of to anions at chemically etched (CHE) and electrochemically polished (EP) Bi(1 1 1) electrodes has been studied using rotating disc electrode method. The surface nanostructure of CHE Bi(1 1 1) and EP Bi(1 1 1) electrodes has been studied by in situ STM and the very different values of root mean squared roughness (Rms) have been obtained (1000 times higher for CHE Bi(1 1 1) (Rms  143 nm) than for EP Bi(1 1 1) (Rms  0.145 nm)). The influence of the nanoroughness of CHE Bi(1 1 1) on the current density, heterogeneous reaction rate constant and corrected Tafel plots (cTp) has been demonstrated. For CHE Bi(1 1 1) the more pronounced inhibition of electroreduction reaction at moderate negative surface charge density has been observed in comparison with EP Bi(1 1 1), caused by the differences in surface charge density and also in diffuse layer ψ₀ potential drop values at crystallographically different homogeneous regions (planes) exposed at the surface of the macroheterogeneous polycrystalline CHE Bi(1 1 1) surface. The very low apparent transfer coefficient α_app obtained indicates the nearly activationless charge transfer mechanism for electroreduction at the CHE Bi(1 1 1) electrode similarly to EP Bi(1 1 1). However, α_app only very weakly depends on Rms for the Bi electrodes at high negative surface charge densities where the values of ψ₀ potential are nearly equal for different planes at fixed electrode potential. At very high negative surface charge densities the cationic catalysis through the adsorbed ion pairs is possible.     

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.     

The electronic gas-phase spectrum of B3 radical revisited

The gas-phase electronic spectrum of cyclic-B₃ (D_3h) radical has been remeasured in a supersonic molecular beam using a mass-selective resonant 2-color 2-photon technique, leading to a revision of previously reported spectroscopic constants. The species was prepared by ablation of a boron nitride rod in the presence of helium. Ab intio calculations on the geometries and vertical electronic excitation energies, as well as mass identification, indicate that the detected band, centered at 21848.77(2) cm⁻¹, is the origin of the cyclic-¹¹B₃ system. A spectral fit yields the rotational constants as B″ = 1.2246(45) and C″ = 0.62131(72) cm⁻¹ in the ground state, and B′ = 1.1914(44) and C′ = 0.61173(69) cm⁻¹ in the excited 2 ²E′ state.     

Effects of ion-pairing on rate of electron transfer between immobilized gold nanoclusters and soluble redox probes

Hydrophilic gold nanoclusters were tethered onto gold electrodes modified with mixed 1-octane thiol/1,9-nonane dithiol monolayers. The heterogeneous electron transfer (ET) kinetics of soluble redox species in the supporting electrolyte were investigated at these electrodes by cyclic voltammetry (CV) in the presence and absence of the ion-pairing anions and . The redox species investigated, [Fe(CN)₆]^3−/4− and [Co(C₁₂H₈N₂)₃]^3+/2+ where oppositely charged. The results presented here reveal that the rate of ET for the negatively charged redox species decreases with decreasing ionic charging time constant of the electrolyte. The opposite trend is observed for the positively charged redox species.