Thermochemistry of 18C6 complexation with alkali,alkaline earth metal cations and ammonium ion

The object of the present study is to examine the factors governing the process of 18C6 complexation in aqueous solution by interpreting of thermodynamic parameters of the reaction in terms of observed selectivity and solvation characteristics under various temperature conditions.     

苯并咪唑羧酸及其碱土金属配合物电子光谱性质的含时密度泛函及其概念密度泛函研究

用密度泛函理论(DFT)以及B3 LYlP泛函在6-311++G**水平上,对苯并咪唑羧酸(L)及其3种碱土金属配合物ML(M=Mg,Ca,Ba)的基态(S0)结构进行优化,用含时密度泛函理论(TD-DFT)在6-311++G**水平下计算其吸收光谱.用单激发组态相互作用(CIS)法在HF/6-31+G*上优化其最低激发单重态(S1)的几何结构,用ID-DFT B3IYP/6-311++G**计算其发射光谱.结果表明,配体L与M(Ⅱ)结合成ML后,随原子序数的增大(Mg相似文献   

Theoretical study of metal ligand aromatic cation–π interactions of [Co(NH3)6]3+ with benzene

In this work, density functional theory calculations on geometries and energies of all possible conformers of the [Co(NH₃)₆]³⁺–C₆H₆ cation–π complex are described. The calculations show that stationary points are several η₂ and the η₃ structures. The most stable η₃ structure has bonding energy, after basis set superposition error correction, of 32.18 kcal/mol. The energies of η₃ structures are similar; also, the energies of η₂ structures are similar while the difference in energy between η₃ and the η₂ structures is about 2 kcal/mol. This indicates a possibility for various orientations of the benzene ring with respect to interacting ligands in the case of metal ligand aromatic cation–π (MLACπ) interactions and a possibility for the existence of these interactions in different molecular systems. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Theoretical study of aromaticity in small hydrogen and metal cation clusters X (X=H,Li, Na,K, and Cu)

Five cation clusters X (X=H, Li, Na, K, and Cu) with two possible isomers, i.e., regular trigonal structure (D_3h) and linear structure (D_∞h), have been investigated using four methods: B3LYP, B3PW91, MP2, CCSD(T) and basis set 6‐311+G(3df). The calculations show that only the regular trigonal structure (D_3h) is stable. The related neutral clusters X₃Cl (X=H, Li, Na, K, and Cu) are also investigated using two methods: B3LYP, MP2, and basis set 6‐311+G(3df). For H₃Cl species, there is no a stable structure to be found. For other four X₃Cl (X=Li, Na, K, and Cu) species, there are two stable isomers, for which the bidentate structures (C_2v‐1) [see Fig. 1 (d)] are global minima. According to the general criteria for aromaticity including resonance energy (RE) and nucleus‐independent chemical shift (NICS), the five trigonal isomers exhibit a higher degree of aromaticity. Molecular orbital analysis reveals that the five trigonal X(X=H, Li, Na, K, and Cu) isomers possess only σ‐aromaticity originating from s orbitals. For the Cu ring the d orbitals do not play a significant role in the electron delocalization effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Tuning anion‐π interaction via halogen substituent effects in cyanuric acids and its derivatives

Several anion‐π complexes of isocyanuric acid, thioderivatives and their halogen substituted derivatives with chloride anion have been studied. The geometric and energetic features, charges transfer from chloride anion to the aromatic rings and “atoms‐in‐molecules” analysis are performed and discussed for these complexes. The results show that the strength of the anion‐π interaction between cyanuric derivatives and chloride anion can be tuned by halogen‐substituting. The localized molecular orbital energy decomposition analyses shows that, in the total interaction, exchange and electrostatic energies are the dominant stabilizing forces, and the polarization energies also make a favorable contribution. Finally, solvent effect significantly weakens the anion‐π interaction between the isocyanuric derivatives and chloride anion, especially in polar solvents. © 2015 Wiley Periodicals, Inc.     

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution

This work is aimed at reviewing the chemical literature dealing with thermodynamic aspects of the weak complex formation (species with log K values less than about 3) between alkali and alkaline earth metal ions with low molecular weight inorganic and organic ligands in aqueous solution. The following ligands (up to hexavalent anions) were examined in detail: (i) hydroxide, chloride, sulfate, carbonate and phosphate as inorganic, and (ii) carboxylates, amines, amino acids, complexones and nucleotides as organic ligands. The paper also identifies the main reasons responsible for the dispersion of the stability data on ion pairs in the literature. When possible, the trend of stability for the different metal ions interacting with the same ligand will be considered to find predictive interaction relationships. Since the stability of weak alkali and alkaline earth metal complexes are mainly due to electrostatic interaction, simple empirical relationships were obtained between log K and the charge of the anionic ligand. The interest for alkali and alkaline earth cations rises since they are used in study of basic science as components of the supporting electrolyte and are widely diffused in natural fluids. Some examples of application of this science were presented too, to show the role of weak complex formation in the modelling process of natural systems.     

Synthesis and selectivity of sym-hydroxydibenzo-14crown-4 ionophores for protons,alkali metal cations,and alkaline earth cations in polymeric membranes

Six derivatives of sym-hydroxydibenzo-14-crown-4 have been prepared and incorporated into solvent-polymeric membranes. Responses of the membranes to protons, alkali metal cations, and alkaline earth cations have been determined. The preferred uptake of protons is attributed to proton complexation by stable crown ether alcohol and diol monohydrate species.     

Structure and stability of coinage metal fluoride and chloride clusters (MnFn and MnCln,M = Cu,Ag, or Au; n = 1–6)

Calculations in the framework of the density functional theory are performed to study the lowest‐energy isomers of coinage metal fluoride and chloride clusters (M_nF_n, M_nCl_n, M = Cu, Ag, or Au, n = 1–6). For all calculated species starting from the trimers the most stable structures are found to be cyclic arrangements. However, planar rings are favored in the case of metal fluorides whereas metal chlorides prefer nonplanar cycles. Calculated bond lengths and infrared frequencies are compared with the available experimental data. The nature of the bonding, involving both covalent and ionic contributions, is characterized. The stability and the fragmentation are also investigated. Trimers are found to be particularly stable when considering the Gibbs free energies. © 2012 Wiley Periodicals, Inc.     

Divide and Stack Up: Boron‐Based Sandwich Cluster as a Subnanoscale Propeller

Typical salts are composed of positive and negative ions that appear alternatively, whereas decorated layered materials normally have ions anchored on the polygonal sites. In this way, the ions are spatially fixed and the system is stabilized on electrostatic grounds. Here we report on a unique boron‐lithium cluster, B₇Li₄^?, which contains a disk‐like B₇ core, being sandwiched by a Li₃ ring and an isolated Li atom. All Li centers are stacked exactly on the B atoms from top or bottom, rather than being anchored on triangular B₃ sites. The cluster shows dynamic fluxionality, whose Li₃ ring rotates freely on the B₇ disk even at below room temperature (200 K), akin to a subnanoscale propeller. The rotation barrier is only 0.37 kcal mol^?1 at the single‐point CCSD(T) level. The sandwich shape facilitates intramolecular charge‐transfers, leading to a [Li₃]⁺[B₇]^3?[Li]⁺ salt complex. The [Li₃]⁺ layer has 2σ aromaticity, while [B₇]^3? core is robust with both π and σ sextets. Three‐fold π/σ aromaticity collectively stabilizes the system, as well as underlies its dynamic fluxionality. The interlayer bonding turns out to be strong, dominated by ionic interactions (of the order of 3–4 eV per Li₃/Li unit). The work demonstrates a propeller at the subnanoscale, which is dynamically fluxional despite strong covalent and ionic bonding.     

Theoretical investigation on icosahedral C60(FeCp)12: A hybrid of C60 and ferrocene

A perfect hybrid complex C₆₀(FeCp)₁₂ is predicted using density functional theory method_. This fullerene derivative could be view as a C₆₀ cage of which each C₅ ring coordinates a (FeCp) ligand. Theoretical calculation reveals that it has a large lowest unoccupied molecular orbital–highest unoccupied molecular orbital gap (2.53 eV) and keeps the I_h symmetry of C₆₀. But the C? C bond length of its inner C₆₀ cage trends to be uniform, which is quite different from the bonding character of C₆₀ fullerene. Further investigation reveals that the chemical bonding, TDOS and the aromaticity of the (C₅FeCp) unit in C₆₀(FeCp)₁₂ are similar as those of ferrocene molecule, which indicates the similarity of their electronic properties. So, this compound could be viewed as the combination of ferrocene molecules. Thus, its unconventional formation process from 12 Fe(Cp)₂ is proposed and the reaction energy is calculated. As the C₆₀(FeCp)₁₂ compound has the geometry framework as C₆₀ and the electronic characters as ferrocene, it would inherit the outstanding properties from both two molecules and have wild potential applications in nanochemistry. We hope our study could give some references for the further investigation and experimental synthesis research of the C₆₀(FeCp)₁₂ compound. © 2015 Wiley Periodicals, Inc.     

Typical aromatic noncovalent interactions in proteins: A theoretical study using phenylalanine

A systematic study of CH ··· π, OH ··· π, NH ··· π, and cation ··· π interactions has been done using complexes of phenylalanine in its cationic, anionic, neutral, and zwitterionic forms with CH₄, H₂O, NH₃, and NH at B3LYP, MP2, MPWB1K, and M06‐2X levels of theory. All noncovalent interactions are identified by the presence of bond critical points (bcps) of electron density (ρ( r )) and the values of ρ( r ) showed linear relationship to the binding energies (E_total). The estimated E_total from supermolecule, fragmentation, and ρ( r ) approaches suggest that cation ··· π interactions are in the range of 36 to 46 kcal/mol, whereas OH ··· π, and NH ··· π interactions have comparable strengths of 6 to 27 kcal/mol and CH ··· π interactions are the weakest (0.62–2.55 kcal/mol). Among different forms of phenylalanine, cationic form generally showed the highest noncovalent interactions at all levels of theory. Cooperativity of multiple interactions is analyzed on the basis of ρ( r ) at bcps which suggests that OH ··· π and NH ··· π interactions show positive, whereas CH ··· π and cation ··· π interactions exhibit negative cooperativity with respect to the side chain hydrogen bond interactions. In general, side chain interactions are strengthened as a result of aromatic interaction. Solvation has no significant effect on the overall geometry of the complex though slight weakening of noncovalent interactions by 1–2 kcal/mol is observed. An assessment of the four levels of theory studied herein suggests that both MPWB1K and M06‐2X give better performance for noncovalent interactions. The results also support the fact that B3LYP is inadequate for the study of weak interactions. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Formation of o‐Phenylenediamine Oligomers and their Self‐Assembly into One‐Dimensional Structures in Aqueous Medium

Summary: Uniform one‐dimensional (1D) structures of o‐phenylenediamine (oPD) oligomers are obtained by direct mix of AgNO₃ and oPD aqueous solutions at room temperature. The formation of the 1D structures involves two stages: (1) oxidation of oPD by AgNO₃, yielding individual oPD oligomers; and (2) self‐assembly of the oligomers, forming the 1D structures. Upon decreasing medium pH, the 1D structures can break‐apart to form individual oligomers, or vice versa. It is also found that both the concentration and molar ratio of reactants can influence the morphology of the structures thus formed.

Schematic illustration of the formation mechanism of 1D structures from oPD and AgNO₃, and energy‐dispersed spectrum of the precipitate.     

Coumarin‐tethered (benz)imidazolium salts and their silver(I) N‐heterocyclic carbene complexes: Synthesis,characterization, crystal structure and antibacterial studies

A series of new sterically modulated chlorocoumarin‐substituted (benz)imidazolium salts and their bis‐N‐heterocyclic carbene silver(I) complexes were prepared and characterized. The complexes were prepared in good yields following the in situ deprotonation method by treating azolium salts with silver(I) oxide in the dark. All the compounds were characterized using various spectroscopic and analytical methods. Additionally, one of the benzimidazolium salts was characterized using single‐crystal X‐ray diffraction technique. In this salt, intermolecular π–π stacking interactions operate between benzimidazole as well as coumarin heterocyclic systems with adjacent molecules. In the preliminary antibacterial studies, the silver complexes were found more active than the corresponding salts against a panel of bacterial strains. Interestingly, the complexes displayed improved antibacterial efficacy against Escherichia coli strain, comparable with that of the standard drug ampicillin.     

Hydroxo Bridged Dinuclear Rare Earth Complexes: Syntheses and Crystal Structures of [Ln2(phen)4(H2O)4(OH)2](NO3)4(phen)2 with Ln = Er,Lu

Reactions of phenanthroline (phen) and Er(NO₃)₃ · 5 H₂O or Lu(NO₃)₃ · H₂O in CH₃OH/H₂O yield [Ln₂(phen)₄(H₂O)₄(OH)₂](NO₃)₄(phen)₂ with Ln = Er ( 1 ), Lu ( 2 ). Both isostructural complex compounds crystallize in the triclinic space group P 1 (no. 2) with the cell dimensions: a = 11.257(2) Å, b = 11.467(2) Å, c = 14.069(2) Å, α = 93.93(2)°, β = 98.18(1)°, γ = 108.14(1)°, V = 1696.0(6) ų, Z = 1 for ( 1 ) and a = 11.251(1) Å, b = 11.476(1) Å, c = 14.019(1) Å, α = 93.83(1)°, β = 98.27(1)°, γ = 108.27(1)°, V = 1689.0(3) ų, Z = 1 for ( 2 ). The crystal structures consist of the hydroxo bridged dinuclear [Ln₂(phen)₄(H₂O)₄(OH)₂]⁴⁺ complex cations, hydrogen bonded NO₃^– anions and π‐π stacking (phen)₂ dimers. The rare earth metal atoms are coordinated by four N atoms of two phen ligands and four O atoms of two H₂O molecules and two μ‐OH groups to complete tetragonal antiprisms. Via two common μ‐OH groups, two neighboring tetragonal antiprisms are condensed to a centrosymmetric dinuclear [Ln₂(phen)₄(H₂O)₄(OH)₂]⁴⁺ complex cation. Based on π‐π stacking interactions and hydrogen bonding, the complex cations and (phen)₂ dimers form 2 D layers parallel to (1 0 1), between which the hydrogen bonded NO₃^– anions are sandwiched. The structures can be simplified into a distorted CsCl structure when {[Ln₂(phen)₄(H₂O)₄(OH)₂](NO₃)₄} and (phen)₂ are viewed as building units.     

Interaction between ions and substituted buckybowls: A comprehensive computational study

Complexes formed by substituted buckybowls derived from corannulene and sumanene with sodium cation or chloride anion have been computationally studied by using a variety of methods. Best results have been obtained with the SCS‐MP2 method extrapolated to basis set limit, which reproduces the highest‐level values obtained with the MP2.X method. All bowls form stable complexes with chloride anion, with stabilities ranging from ?6 kcal/mol in the methylated corannulene derivative to ?45 kcal/mol in the CN‐substituted sumanene. The opposite trend is observed in sodium complexes, going from deeply attractive complexes with the methylated derivatives (?36 kcal/mol with sumanene derivative) to slightly repulsive ones in the CN‐substituted bowls (2 kcal/mol in the corannulene derivative). Anion complexes are stabilized by large electrostatic interactions combined with smaller though significant dispersion and induction contributions. Conversely, cation complexes are stabilized by large induction contributions capable of holding together the bowl and the cation even in cases where the electrostatic interaction is repulsive. The effect of substitution is mainly reflected on changes in the molecular electrostatic potential of the bowl and, thus, in the electrostatic contribution to the interaction. Therefore, the variations in the stability of the complexes on substitution could be roughly predicted just considering the changes in the electrostatic interaction. However, other contributions also register changes mainly as a consequence of displacements on the position of the ion at the minimum, so the accurate prediction of the stability of this kind of complexes requires going further than the electrostatic approach. © 2014 Wiley Periodicals, Inc.     

A computational study on the reactivity enhancement in the free radical polymerization of alkyl α‐hydroxymethacrylate and acrylate derivatives

The free radical polimerizability behavior of alkyl α‐hydroxymethacrylate (RHMA) derivatives ( M1–M3 ) has been modeled by considering the propagation of the dimeric units of the compounds of interest. All the transition structures in this class of monomers are stabilized by long‐range C?O…H? C interactions. The RHMA monomer bearing the ester functionality ( M2 ) polymerizes slightly faster than the one with the ether functionality ( M1 ) because of stronger electrostatic interactions between the C?O and H? C groups. 2‐(Methoxycarbonyl)allyl benzoate ( M3 ) shows higher reactivity as compared to M1 and M2 due to stronger electrostatic interactions. The same type of study has been carried out for hexyl ( M4 ), benzyl ( M5 ), and phenyl ( M6 ) acrylate derivatives whose increasing reactivity has been attributed to the presence of C?O…H? C, C?O…H‐? as well as π–π stabilizing interactions, respectively. While B3LYP/6‐31+G(d) has been used to locate the stationary points along the free radical polymerization of nonaromatic species, long‐range stabilizing interactions have only been detected with M06‐2X/6‐31+G(d). The kinetics that we obtain with this latter methodology for the free radical polymerization reactions of M1 – M6 agree well qualitatively with experiment. An implicit solvent model has reproduced the kinetics of M1–M3 in benzene the best. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Achieving Adaptive Aromaticity in Cyclo[10]carbon by Screening Cyclo[n]carbon (n=8−24)

Discovery of species with adaptive aromaticity (being aromatic in both the lowest singlet and triplet states) is particularly challenging as cyclic species are generally aromatic either in the ground state or in the excited state only, according to Hückel's and Baird's rules. Inspired by the recent realization of cyclo[18]carbon, here we demonstrate that cyclo[10]carbon possesses adaptive aromaticity by screening cyclo[n]carbon (n=8?24), which is supported by nucleus‐independent chemical shift (NICS), anisotropy of the current‐induced density (ACID), π contribution of electron localization function (ELF_π) and electron density of delocalized bonds (EDDB) analyses. Further study reveals that the lowest triplet state of cyclo[10]carbon is formed by in‐plane ππ* excitation. Thus, the major contribution to the aromaticity from out‐of‐plane π molecular orbitals does not change significantly in the lowest singlet state. Our findings highlight a crucial role of out‐of‐plane π orbitals in maintaining aromaticity for both the lowest singlet and triplet states as well as the aromaticity dependence on the number of the carbon in cyclo[n]carbon.     

Syntheses and Crystal Structures of Ln(phen)2(NO3)3 with Ln = Pr,Nd, Sm,Eu, Dy,and phen = 1,10‐phenanthroline

Five new complex compounds of the formula Ln(phen)₂(NO₃)₃ were prepared. The X‐ray structural analyses indicate that they crystallize isostructurally in the monoclinic space group C2/c (no. 15) with cell dimensions for example for Pr(phen)₂(NO₃)₃: a = 11.194(1) Å, b = 18.095(2) Å, c = 13.101(2) Å, β = 100.52(1)°, V = 2609.1(6) ų, Z = 4. The crystal structures consist of [Ln(phen)₂(NO₃)₃] complex molecules. The rare earth atoms are coordinated by four N atoms of two phen ligands and six O atoms of three nitrato groups to complete a distorted bicapped dodecahedron. The [Ln(phen)₂(NO₃)₃] complex molecules are assembled via π‐π stacking interactions between the neighboring phen ligands to form 1D columnar chains, which are then arranged in the crystal structures according to pseudo 1D close‐packed patterns.