Molecular motion and phase transition in perovskite-type (CH3)nNH4−nSnCl3 (n=1–4) studied by proton NMR spin–lattice relaxation

Powder X-ray diffraction, ¹¹⁹Sn NMR spectra, and ¹H NMR spin–lattice relaxation times, T₁, were measured for (CH₃)_nNH_4−nSnCl₃ (n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of ¹H T₁ was analyzed in terms of the CH₃ reorientation and other motions of the whole cation. Except for the phase transition in CH₃NH₃SnCl₃, which is from monoclinic to rhombohedral at 331 K, ¹H T₁ was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl₃]_nⁿ⁻ perovskite lattice.     

Density functional theory analysis of CaRgn complexes: (Rg=He, Ne, Ar; n=1–4)

CaRg_n⁺ (Rg=He, Ne, Ar) complexes with n=1–4, are investigated by performing using the B3LYP/6-311+G (3df) density functional theory calculations. The CaHe_n⁺ (n=1–4) complexes are found to be stable. In the case of CaNe_n⁺ and CaAr_n⁺, stable structures and stationary point were found only for n=1 and 2. For n=3 in the C_3V and the D_3h point group as well as for n=4 in the T_d (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface.     

A density functional study on hydrated clusters of orthoboric acid, B(OH)3(H2O)n (n=1–5)

We have calculated the optimized structures and stabilization energies for hydrated clusters of orthoboric acid molecule, B(OH)₃(H₂O)_n (n=1–5), with a hybrid density functional approach. Although some ion-pair structures are revealed in the case of n=4 and 5 clusters, the most stable structure is found to be a non-proton-transferred form up to n=5 hydrated clusters. The calculated IR spectra of the stable B(OH)₃(H₂O)_n of n=3–5 clusters predict small red shifts of hydrogen-bonded OH frequencies. These geometry and IR results are related to the weak acidity nature of orthoboric acid.     

Theoretical investigation on the adsorption of lithium atom on the Sin cluster (n=2–7)

Ab initio calculations are carried out to study the adsorption of Lithium atom on the Si_n cluster with n ranging from 2 to 7. At the MP2/6-31G(d) level, the structures of the neutral Si_n clusters and the Si_nLi clusters (n=2–7) are optimized. The single-point energy at QCISD/6-311+G(d,p) level for the optimized isomers are further performed. Harmonic vibrational frequency analysis at the MP2/6-31G(d) level is also undertaken to confirm that the optimize geometries are stable. Based on our results, the most favorable sites for Li adsorption on the Si_2–7 clusters are the bridge sites. In addition, the vertical ionization energies of the Si_nLi clusters and the electron affinities of the Si_n clusters are also calculated. The clear parallelism between the vertical ionization energies of Si_nLi and the electron affinities of Si_n is found. This is consistent with the fact that the framework of the Si_n in the Si_nLi cluster is similar to the structure of the corresponding negative ion .     

Ab initio study on the kinetics and mechanisms of the formation of Agn (n = 2–6) clusters

The CCSD(T)/11e-RECP//MP2/11e-RECP method was used to explore the potential energy surfaces (PESs) of the formation of Ag_n (n = 2–6) clusters. Two kinds of reaction mechanisms were revealed in the formation of Ag_n clusters, the association mechanism for the formation of Ag₂, Ag₅, and Ag₆ clusters and the association–isomerization mechanism for the formation of Ag₃ and Ag₄ clusters. Based on the canonical transition state theory, the calculated rate constants of the formation of Ag_n clusters displayed an odd–even effect: the rate constants of formation of Ag_n clusters with odd number were larger than those with even number. The rate constant of formation of Ag₄ was the lowest, whereas that of Ag₅ was the highest among Ag_n (n = 2–6) clusters. The formation of Ag₄ was the most difficult step in the aggregation process of the silver clusters. The formation of Ag₄ may be related with the critical point in the silver aggregation process.     

DFT studies on coplanar poly-cage cubanes C8+4nH8 (n=1–5)

Coplanar poly-cage cubanes C_8+4nH₈ (n=1–5) have been studied using DFT method at B3LYP/D95** level of theory, vibrational frequencies of these molecules have been calculated at B3LYP/D95** level of theory and spectrums of these molecules have been simulated else, heats of formation of these molecules also have been estimated here.     

Local analysis and comparative study of the hydrogen bonds in the linear (HCN)n and (HNC)n clusters

B3LYP/6-311+G(2d,p), the density functional theory method of 98 package, is applied to study the hydrogen bonding of a series of linear (HCN)_n and (HNC)_n molecular clusters (for n=1–10). By the localization analysis methods we developed, pair-wised σ type H-bond orders and bond energies are calculated for each pair of the two near-by molecules in both (HCN)_n and (HNC)_n clusters. The calculated results are checked well with the shortening of N–H or C–H distance, the elongation of CH or NH bond distance, and the red shift of stretching frequencies of CH or NH. All pieces of evidence show that the central pair of the two molecules forms the strongest H bond when n of (HCN)_n or (HNC)_n is even, and the two middle pairs form the two strongest H bonds when n is odd. Two terminal pairs of HCN or HNC molecules always form the two weakest H-bonds in each molecular cluster. When comparing molecular cluster energies between (HCN)_n and (HNC)_n for various values of n, the well-known (HCN)_n is found more stable than the related (HNC)_n from energy calculation. However, if outcomes of H-bond local analysis are contrasted, our analysis significantly shows that inter-molecular H-bonds inside of (HNC)_n clusters are much stronger than the corresponding H-bonds in (HCN)_n with the same n. In comparing energy differences between these related clusters per monomer, [E_(HNC)n−E_(HCN)n]/n is found decreasing monotonically as n increases. All pieces of evidence from this theoretical prediction indicate that (HNC)_n with large n is probably constructed by its relative strong H-bonds.     

First principles study of the structure, electronic state and stability of SinCm anions

Structure, electronic state and energy of Si_nC⁻ and Si_nC⁻₂ (n=1–7) anions have been investigated using the density functional theory. Structural optimization and frequency analysis are performed at the level B3LYP/6-311G(d). The charged-induced structural changes in these anions have been discussed. The strong C–C bond is also favored over C–Si bonds in the Si_nC⁻_m anions in comparison with corresponding neutral cluster. Among different Si_nC⁻ and Si_nC⁻₂ (n=1–7) anions, Si₃C⁻, Si₅C⁻ and Si₂C⁻₂ are most stable. Their stability has a decreasing tendency with the increase in the size of these clusters.     

A theoretical study of protonated OCnOH ions, n=3–8

Since ion-neutral reactions are a major component of the processes driving interstellar chemistry, most reaction network include protonated species. Besides, these ions are able to initiate chemical processes that would not occur with their neutral parents. In this contribution we report a systematic study of the protonated adducts of the OC_nO series (n=3–8) using the B3LYP level of theory. The structures of all possible O-protonated and C-protonated isomers of [OC_nOH⁺] have been determined together with their rotational constants, vibrational frequencies and intensities. Although it appears that these ions belong to two different series, odd-n and even-n, it is found that protonation occurs at the carbons second to the terminal oxygens for all n. The most stable structure is found to be the singlet ion whatever the singlet or triplet spin state of the parent species. However, due to the lack of efficient spin–orbit coupling, only the odd series [OC_nOH⁺] with n=3,5,7 should be formed on the singlet ground state surface. Analysis of the infrared intensities shows that the spectra are dominated by only one or two very strong bands (CC stretching) that carry most of the overall intensity in the 2200–2350 cm⁻¹ region.     

Complexes of cationic coinage metal clusters Mn (M=Cu, Ag, Au; n=1–4) and H2S: a theoretical study

Geometries and vibrational frequencies of complexes of cationic coinage metal clusters M_n⁺ (M=Cu, Ag, Au; n=1–4) and H₂S are computed using density functional theory. Thermochemical values for M_n⁺H₂S decomposition channels involving loss of an H atom, H₂ molecule, M atom, or M₂ molecule are also computed. Significantly different results are obtained for closed-shell (n odd) and open-shell (n even) complexes.     

Binding energies and electronic structures of Cu(OH2)n and Cu(NH3)n (n=1–4): anomaly of the two ligand Cu complexes

Ab initio calculations up to MP4(SDTQ) level and density functional theory have been used to estimate binding energies and electronic structures of Cu⁺(L)_n (L=OH₂, NH₃, n=1–4) complexes using TZP basis set types. The computed binding energies agree well with experimental values. General trends in structures and energetics are recorded for both Cu⁺(OH₂)_n and Cu⁺(NH₃)_n systems. The first two ligands are more strongly bound to Cu⁺ than the third and fourth molecules. The 4s–3dσ hybridization and electrostatic interactions are the main factors behind the higher binding energies for the first two ligands. Analysis of HOMO mixed orbitals in the copper ion as well as in complexes indicates shrinking of the orbital lobes directed to the ligand with shrinking more effective in the two ligand system. The lower binding energies for the third and fourth ligands were attributed to the attenuation of sdσ hybridization and decreasing of Cu–L attraction at long separation which is necessary to relieve Cu–L and L–L exchange repulsions. NBO analysis and charge-model calculations support the presence of sdσ hybridization and electron transfer to the copper ion in case of the first two ligands.     

Binding energies of germanium clusters, Gen (n = 2−5)

Gaussian-2 (G2) theory for third-row non-transition elements is used to calculate energies of germanium clusters, Ge_n (n = 2−5). The G2 energies are used to derive accurate binding energies for the clusters. The results for Ge₂ and Ge₃ are in agreement with experiment while there is some disagreement for Ge₄ and Ge₅. The binding energies are also calculated using the B3LYP density functional method with the 6–311 + G(3df,2p) basis set and compared with the G2 results and experiment.     

Crystalline calcium phenylphosphonate—thermodynamic data on n-alkylmonoamine intercalations

Lamellar crystalline calcium phenylphosphonate, as anhydrous Ca(HO₃PC₆H₅)₂ and hydrated Ca(HO₃PC₆H₅)₂·2H₂O compounds, were used as hosts for intercalation of polar n-alkylmonoamine molecules of the general formula CH₃(CH₂)_nNH₂ (n=0–4, 7) in water or 1,2-dichloroethane. An increase in the interlayer distance was observed. The exothermic enthalpic values for intercalation increased with the number of carbon atoms and with increasing concentration of the amines. The intercalation followed by a titration procedure in the solid/liquid interface with Ca(HO₃PC₆H₅)₂·2H₂O and Ca(HO₃PC₆H₅)₂ gave the enthalpy/number of carbons correlations: Δ_intH=−(1.74±0.43)–(1.30±0.13)n_c and Δ_intH=−(4.15±0.15)–(1.07±0.03)n_c, for water and 1,2-dichloroethane, respectively. A similar correlation Δ_intH=−(4.27±0.80)–(1.85±0.21)n_c was obtained in water by using the ampoule breaking procedure for Ca(HO₃PC₆H₅)₂·2H₂O. The increase in exothermic enthalpic values with the increase in n-aliphatic carbon atoms is more pronounced for the anhydrous compound and also when using the ampoule breaking procedure. The Gibbs free energies are negative. Positive entropic values favor intercalation in these systems.     

Sandwich-type transition metal complexes [(CBO)n]2M with carbon boronyl ligands (CBO)n (n=4–6)

A density functional theory investigation on a series of sandwich-type transition metal complexes [(CBO)_n]₂M (n=4–6; M=transition metals) with carbon boronyls (CBO)_n as effective aromatic ligands has been presented in this work at B3LYP level. The ground-states of these complexes possess staggered D_nd symmetries, while the corresponding eclipsed D_nh structures exist as transition states with slightly higher energies (within 5.8 kJ/mol). Carbon boronyl complexes [(CBO)_n]₂M are confirmed to be much more stable than their boron carbonyl isomers [(BCO)_n]₂M, which, on the other hand, take eclipsed ground-states with D_nh symmetries. The carbon boronyl complexes [(BCO)_n]₂M proposed in this work parallelize the well-known sandwich-type hydrocarbon complexes [C_nH_n]₂M in coordination chemistry with boronyl groups –BO isolobal to –H atoms in corresponding ligands.     

Pathway studies in the fragmentation of Ge(CH3)4 involving Ge(3d,3p,3s) and C(1s) inner-shell photoexcitation in the range 49.5–450 eV

The dissociative multiple photoionization of tetramethylgermane (Ge(CH₃)₄) in the valence, and in the Ge(3d,3p,3s) and C(1s) inner-shell regions has been studied by using time-of-flight mass spectrometry coupled to synchrotron radiation in the range 49.5–450 eV. Total and individual photoion yields have been recorded as a function of the incident photon energy. Several discrete resonances over a structureless giant resonance are observed below the Ge(3p), Ge(3s) and C(1s) threshold regions. The structureless giant resonance corresponding to the Ge(3d) presumably arises from the continuum enhancement caused by the 3d→εf transition. Various monocations of H⁺, H₂⁺, CH_n⁺ (n=0–4), C₂H_n⁺ (n=0–5), GeH_n⁺, GeCH_n⁺, GeC₂H_n⁺, and GeC₃H_n⁺ are detected in the whole energy range. Dissociation processes have also been investigated by photoelectron–photoion and photoion–photoion coincidence methods. The dominant dissociation channel is found to be CH_n⁺–GeCH_n⁺ in the whole energy examined. Specific energy dependence of dissociation processes is observed in the Ge(3p) and Ge(3s) regions. With the help of ab initio HF/6-311++G(2df,p) calculation, we roughly estimated the photoabsorption positions and symmetries for the discrete core hole states.     

Quantum mechanical study of tautomerism of methimazole and the stability of methimazole–I2 complexes

DFT and ab initio theoretical methods were used to calculate the relative stability of tautomers in the methimazole (MMI). The calculations show that the thione form of MMI 1 is more stable than the thiol tautomer in good agreement with the experimental results. The DFT and ab initio calculations were also used to determine the stability of MMI–I₂ complexes. All methods suggest that the methimazole in the MMI–I₂ complex exists almost exclusively as the thione tautomer. The Gibbs free energy difference between planar and perpendicular forms of thione tautomer of MMI–I₂ complex indicates that the planar form is the predominant complex. The counterpoise corrected Gibbs free energy also shows that the MMI–I₂(plan.) complex is more stable than the MMI–I₂(perp.) complex. These predictions are in good agreement with the experimental results. By using the natural bond orbital (NBO) approach, the effects of charge transfer interactions on the stability of MMI–I₂ complexes were investigated. The LP₃(S)→σ*(I–I) and LP₃(I)→σ*(N–H) charge transfer interactions may be very important in the stability of the planar form. The results show that the LP₃(S)→σ*(I–I) charge transfer interaction causes a greater increase in the σ*(I–I) antibond occupation number, and concomitantly, a greater increase in the corresponding I–I bond length in the planar complex with respect to the perpendicular complex. The LP₃(S)→σ*(I–I) charge transfer interaction is assisted by NHI intermolecular hydrogen bonding. The atom in molecule (AIM) analysis shows that the charge density and its Laplacian at the SI bond critical point of the planar complex is greater than the perpendicular complex.     

Density functional study on the structure and stability of positive iron rare-gas complexes, FeXn (X=Ar, Xe; n=1–6)

The structures and atomization energies of positively charged complexes of iron with argon and xenon, Fe⁺X_n (X=Ar, Xe; n=1–6) are investigated by density functional theory calculations. We explain the special stability of some of these complexes (“magic numbers”) – that has been observed in previous laser ablation and multi-photon ionization experiments – and predict their geometries.     

Synthesis and application of diphenylbis (3,5-dimethylpyrazol-1-yl)methane to form η-arene complexes of molybdenum

The neutral nitrogen-bidentate ligand, diphenylbis(3,5-dimethylpyrazol-1-yl)methane, Ph₂CPz′₂, can readily be obtained by the reaction of Ph₂CCl₂ with excess HPz′ in a mixed-solvent system of toluene and triethylamine. It reacts with [Mo(CO)₆] in 1,2-dimethoxyethane to give the η²-arene complex, [Mo(Ph₂CPz′₂)(CO)₃] (1). This η²-ligation appears to stabilize the coordination of Ph₂CPz′ ₂ in forming [Mo(Ph₂CPz′₂)(CO)₂(N₂C₆H₄NO₂-p)][BPh₄] (2) and [Mo(Ph₂CPz′₂)(CO)₂(N₂Ph)] [BF₄] (3) from the reaction of 1 with the appropriate diazonium salt but the stabilization seems not strong enough when [Mo{P(OMe)₃} ₃(CO)₃] is formed from the reaction of 1 with P(OMe)₃. The solid-state structures of 1 and 3 have been determined by X-ray crystallography: 1-CH₂Cl₂, monoclinic, P2₁/n, a = 11.814(3), b = 11.7929(12), c = 19.46 0(6) Å, β = 95.605(24)°, V = 2698.2(11) ų, Z = 4, D_calc = 1.530 g/cm³ , R = 0.044, R_w = 0.036 based on 3218 reflections with I > 2σ(I); 2 (3)-1/2 hexane-1/2 CH₃OH-1/2 H₂O-1 CH₂Cl₂, monoclinic, C2/c, a = 41.766(10), b = 20.518(4), c = 16.784(3) Å, β = 101.871(18)°, V = 14076(5) ų, Z = 8, D_calc = 1.457 g/cm³, R = 0.064, R_w = 0.059 based on 5865 reflections with I > 2σ(I). Two independent cations were found in the asymmetric unit of the crystals of 3. The average distance between the Mo and the two η²-ligated carbon atoms is 2.574 Å in 1 and 2.581 and 2.608 Å in 3. The unfavourable disposition of the η²-phenyl group with respect to the metal centre in 3 and the rigidity of the η²-arene ligation excludes the possibility of any appreciable agostic C---H → Mo interaction.     

Polarized absorption spectra and polarized Raman spectra of single crystals of trans(Cl2)-[CoCl2(NH3)n(H2O)4−n]Cl complexes (n = 2, 3, 4)

The title cobalt(III) complexes have been investigated by polarized absorption and Raman spectroscopies of the single crystals. The symmetry properties of the d-electron orbitals and of the vibrational modes attributable to the Raman bands of trans(Cl₂)-[CoCl₂(NH₃)_n(H₂O)_4−n]Cl complexes (n = 2, 3, or 4) were examined to elucidated the peculiar observation that ligand substitution causes no splitting of the 15 200-cm⁻¹ absorption band and the 250-cm⁻¹ Raman band. Effects of replacing the NH₃ ligand with H₂O on the electronic structure, atom–atom force constants and vibrational modes of these complex ions are briefly described.     

Electronic absorption and emission spectra and computational studies of some 2-aryl, 2-styryl, and 2-(4′-aryl)butadienyl quinazolin-4-ones

The relatively less popular group of quinazoline heterocyclic compounds is searched theoretically for compounds with promising classical and nonlinear optical properties, e.g. fluorescence and high (hyper)polarizabilities. Candidates for NLO materials are found among the general series of -4-(3H)-quinazolonyl-ω-aryl polyenes 1, 2, 3 and their fluorescence spectra are registered experimentally. CIS/6-31G* calculations provide no reliable predictions of observed UV/Vis and fluorescence spectra. However, semiempirical CISD PM3 calculations predict fairly well the observed bathochromic effects arising from extension of polyene chains (CHCH)_n, n=0–2, and donor substitution in the aryl fragments. The observed fluorescence is assigned to planar quinonoid S1 emissive states, while ground S0 state geometries of compounds with n=0 are nonplanar, and with n>0 are planar. We find high TDHF PM3 static polarizabilities for all studied molecules, as well as high hyperpolarizabilities β SHG and γ THG.