Magnesium monocationic complexes: a theoretical study of metal ion binding energies and gas-phase association kinetics

Bond dissociation energies (BDEs) for complexes of ground state Mg+ (2S) with several small oxygen- and nitrogen-containing ligands (H2O, CO, CO2, H2CO, CH3OH, HCOOH, H2CCO, CH3CHO, c-C2H4O, H2CCHOH, CH3CH2OH, CH3OCH3, NH3, HCN, H2CNH, CH3NH2, CH3CN, CH3CH2NH2, (CH3)2NH, H2NCN, and HCONH2) have been calculated at the CP-dG2thaw level of theory. These BDE values, as well as counterpoise-corrected MP2(thaw)/6-311+G(2df,p) calculations on the Mg+ complexes of several larger ligands, augment and complement existing experimental or theoretical determinations of gas-phase Mg+/ligand bond strengths. The reaction kinetics of complex formation are also investigated via variational transition state theory (VTST) calculations using the computed ligand and molecular ion parameters. Radiative association rate coefficients for most of these systems increase by approximately 1 order of magnitude with every 3-fold reduction in temperature from 300 to 10 K. Several of the largest molecules surveyed-notably, CH3COOH, (CH3)2CO, and CH3CH2CN-exhibit comparatively efficient radiative association with Mg+ (k(RA) > or = 1.0 x 10(-10) cm3 molecule(-1) s(-1)) at temperatures as high as 100 K, implying that these processes may have a considerable influence on the metal ion chemistry of warm molecular astrophysical environments known to contain these potential ligands. Our calculations also identify the infrared chromophoric brightness of various functional groups as a significant factor influencing the efficiency of the radiative association process.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study

The absorption spectra of styrylbenzothiazolium dye derivatives were calculated by the time-dependent density functional (TD DFT) method. The dyes of interest were (p-dimethylamino)styrylbenzothiazolium dye and its protonated form as well as aza-15(18)-crown-5(6)-containing dyes and their complexes with alkali (K⁺ and Na⁺) and alkaline-earth (Ca²⁺, Sr²⁺, and Ba²⁺) cations. Several low-lying conformers of the azacrown-containing dyes were considered. The electronic and geometric structures of the excited states responsible for the appearance of the long-wave (π-π*) absorption bands are studied. Complexation causes a hypsochromic shift of the long-wave absorption band correlating with the pyramidality of the crown ether nitrogen in the complex. The interaction of the cation with 3–4 solvent molecules or a counterion (ClO₄ ^?) considerably reduces this shift, especially in the conformers without the metal-nitrogen bond. In some cases, the long-wave absorption band is close to the absorption band of the free dye. Similar results were obtained using the polarizable continuum model of solvation. Excited-state structures of the free model dye and the free azacrown-containing dyes exhibit a tendency to bond alternation. Conversely, the cationic complexes of the crown-containing dyes and the protonated model dye exhibit a tendency to bond equalization in the excited state. The changes in the excited-state geometries of the free dyes and their complexes account for the complexation-induced fluorescence enhancement observed in the experiments.     

4,5-diazafluorene-based overcrowded alkene: a new ligand for transition metal complexes

[structure: see text] A new ligand system, where a 4,5-diazafluorene-type chelate and a methoxybenzoxanthene unit are coupled by a double bond has been synthesized and fully characterized including X-ray structure. The synthesis and UV-vis spectra of Ru(II), Os(II), and Re(I) complexes with the above-mentioned ligand are also shown.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study 2.* Effect of the metal ion— solvent interaction on the conformations of calcium complexes of arylazacrown ethers

The effect of the local interaction of a metal ion with the solvent on the conformations of calcium complexes of arylazacrown ethers and an azacrown-containing dye was studied using the density functional method with the PBE and B3LYP functionals. The structures were studied and the interaction energies were determined for the calcium complexes with n = 1–12 water or acetonitrile molecules. It was found that the inner coordination sphere of the free Ca²⁺ cation contains six H₂O or seven MeCN molecules. The cation—acetonitrile interaction energy is higher than the cation—water interaction energy up to the moment the second solvation shell of the cation is almost complete (n = 11). The inner coordination sphere of Ca²⁺ in the macrocycle cavity contains at most three water molecules, while the fourth one is displaced to the second coordination sphere. Taking into account the local interaction with the solvent (H₂O or MeCN), the conformers of the calcium complexes of arylazacrown ethers and the azacrown-containing dye were studied. It was shown that the presence of two to four water molecules in the coordination sphere of the cation reduces the relative energies of the conformers with broken metal—nitrogen bond, thus favoring ground-state metal recoordination. For Part 1, see Ref. 1. Dedicated to Academician A.L. Buchachenko on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1981–1992, September, 2005.     

Pressure-dependent OH yields in alkene + HO2 reactions: a theoretical study

The major bimolecular product of alkyl + O(2) reactions is alkene + hydroperoxyl radical (HO(2)), but in the reverse direction, the reactants are reformed to a very limited extent only. The most important products of the alkene + HO(2) reactions are alkylperoxy radical (ROO(?)), hydroxyl radical (OH) + cyclic ether, and the corresponding hydroperoxyalkyl ((?)QOOH) species. Moreover, abstraction of allylic hydrogens can compete with the addition, further complicating the possible outcome of this reaction type and its effect on low-temperature combustion chemistry. In this paper, six alkene + HO(2) reactions and the reaction between an unsaturated oxygenate and HO(2) are studied based on previously established potential energy surfaces. The studied unsaturated compounds are ethene, propene, 1-butene, trans-2-butene, isobutene, cyclohexene, and vinyl alcohol. Using multiwell master equations, temperature- (300-1200 K) and pressure-dependent rate coefficients and branching fractions are calculated for these reactions. The importance of this reaction type for the combustion of unsaturated compounds is also assessed, and we show that, to get reliable results, it is important to include the pressure-dependence of the rate coefficients in the calculations.     

On the nature of the transition metal-main group metal bond: synthesis and theoretical calculations on iridium gallyl complexes

The iridum-gallyl complex MeIr(PCy(3))(2)(GaMe(2))(Cl*GaMe(3)) exhibits a short Ir-Ga bond length of 2.381(1)-2.389(2) ?. Theoretical calculations (ZORA BP86/TZ2P) support the presence of a Ir-Ga single bond but highlight a π orbital contribution.     

A theoretical study of the solvent extraction of multipolymeric metal complexes

A mathematical treatment is demonstrated which explores the simultaneous extraction of multipolymeric complexes. The theory will predict that there may be only a finite number of species which can exist.     

The nature of unsupported uranium-ruthenium bonds: a combined experimental and theoretical study

Four new uranium-ruthenium complexes, [(Tren(TMS))URu(η(5)-C(5)H(5))(CO)(2)] (9), [(Tren(DMSB))URu(η(5)-C(5)H(5))(CO)(2)] (10), [(Ts(Tolyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (11), and [(Ts(Xylyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (12) [Tren(TMS)=N(CH(2)CH(2)NSiMe(3))(3); Tren(DMSB)=N(CH(2)CH(2)NSiMe(2)tBu)(3)]; Ts(Tolyl)=HC(SiMe(2)NC(6)H(4)-4-Me)(3); Ts(Xylyl)=HC(SiMe(2)NC(6)H(3)-3,5-Me(2))(3)], were prepared by a salt-elimination strategy. Structural, spectroscopic, and computational analyses of 9-12 shows: i) the formation of unsupported uranium-ruthenium bonds with no isocarbonyl linkages in the solid state; ii) ruthenium-carbonyl backbonding in the [Ru(η(5)-C(5)H(5))(CO)(2)](-) ions that is tempered by polarization of charge within the ruthenium fragments towards uranium; iii) closed-shell uranium-ruthenium interactions that can be classified as predominantly ionic with little covalent character. Comparison of the calculated U-Ru bond interaction energies (BIEs) of 9-12 with the BIE of [(η(5)-C(5)H(5))(3)URu(η(5)-C(5)H(5))(CO)(2)], for which an experimentally determined U-Ru bond disruption enthalpy (BDE) has been reported, suggests BDEs of approximately 150 kJ mol(-1) for 9-12.     

Dissociation of polyether-transition metal ion dimer complexes in a quadrupole ion trap

The formation and dissociation of dimer complexes consisting of a transition metal ion and two polyether ligands is examined in a quadrupole ion trap mass spectrometer. Reactions of three transition metals (Ni, Cu, Co) with three crown ethers and four acyclic ethers (glymes) are studied. Singly charged species are created from ion-molecule reactions between laser-desorbed monopositive metal ions and the neutral polyethers. Doubly charged complexes are generated from electrospray ionization of solutions containing metal salts and polyethers. For the singly charged complexes, the capability for dimer formation by the ethers is dependent on the number of available coordination sites on the ligand and its ability to fully coordinate the metal ion. For example, 18-crown-6 never forms dimer complexes, but 12-crown-4 readily forms dimers. For the more flexible acyclic ethers, the ligands that have four or more oxygen atoms do not form dimer complexes because the acyclic ligands have sufficient flexibility to wrap around the metal ion and prevent attachment of a second ligand. For the doubly charged complexes, dimers are observed for all of the crown ethers and glymes, thus showing no dependence on the flexibility or number of coordination sites of the polyether. The nonselectivity of dimer formation is attributed to the higher charge density of the doubly charged metal center, resulting in stronger coordination abilities. Collisionally activated dissociation is used to evaluate the structures of the metal-polyether dimer complexes. Radical fragmentation processes are observed for some of the singly charged dimer complexes because these pathways allow the monopositive metal ion to attain a more favorable 2 + oxidation state. These radical losses are observed for the dimer complexes but not for the monomer complexes because the dimer structures have two independent ligands, a feature that enhances the coordination geometry of the complex and allows more flexibility for the rearrangements necessary for loss of radical species. Dissociation of the doubly charged complexes generated by electrospray ionization does not result in losses of radical neutrals because the metal ions already exist in favorable 2+ oxidation states.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study. 1. Conformers of arylazacrown ethers and their complexes with Ca2+ cation

Photoinduced recoordination of Ca²⁺ complexes of the photochromic azacrown ethers is studied by the density functional method. The study included model arylazacrown ethers containing various acceptor groups in the aromatic ring in the para position to the azacrown ether moiety and a real azacrown-containing styryl dye. It is found that both free azacrown ethers and their complexes can adopt two types of conformations: (1) axial conformations, in which the aromatic ring axis passing through the crown ether nitrogen N_cr and the opposite atom of the aromatic ring is perpendicular to the root-mean-square (RMS) plane of the crown ether (least-squares fitted plane for all the crown ether atoms), and (2) equatorial conformations, in which the aromatic ring axis only slightly deflects from the RMS plane of the crown ether. In the equatorial conformers, the metal cation is coordinated only to the O atoms of the azacrown ether cycle, the metal—nitrogen bond is broken, and N_cr is conjugated with the aromatic ring. In the axial conformers, the metal cation is additionally coordinated to N_cr. It is found that the presence of an acceptor group bearing a formal positive charge decreases the relative energy of the equatorial conformer and favors metal—nitrogen bond dissociation, which results in the recoordination of the metal cation. However, a long distance between the charged group and N_cr has the reverse effect. The photoinduced recoordination observed in the alkaline-earth metal complexes of the photochromic azacrown ethers is explained by the transitions between the axial and equatorial conformers facilitated by the charge transfer in the excited state of the complex.     

Mechanism of alkene isomerization by bifunctional ruthenium catalyst: A theoretical study

The molecular mechanism of the isomerization of 1-pentene to form (E)-2-pentene catalyzed by the bifunctional ruthenium catalyst has been investigated using density functional theory calculations. The reaction is likely to proceed through the following steps: 1) the β-H elimination to generate the ruthenium hydride intermediate; 2) the reductive elimination of the hydride intermediate to generate the nitrogen-protonated allyl intermediate; 3) the transportation of the hydrogen by the dihedral rotation with Ru–P bond acting as axis; 4) the oxidative addition to afford another hydride complex; 5) the reductive elimination of the hydride intermediate to form the C₂-C₃ π-coordinated agostic intermediate; 6) the coordination of the nitrogen to the ruthenium center to give the final product. The rate-determining step is the oxidative addition step (the process of the hydrogen moves to ruthenium center from the nitrogen atom) with the free energy of 31.2 kcal/mol in the acetone solvent. And the N-heterocyclic ligand in the catalyst mainly functions in the two aspects: affords an important internal-basic center (nitrogen atom) and works as a transporter of hydrogen. Our results would be helpful for experimentalists to design more effective bifunctional catalysts for isomerization of a variety of heterofunctionalized alkene derivatives.     

The activation of tertiary carboxamides in metal complexes: an experimental and theoretical study on the methanolysis of acylated bispicolylamine copper(II) complexes

It is a well-established concept that the C-N bond cleavage of carboxamide functions is facilitated by the coordination of a metal ion to the carbonyl oxygen atom. In contrast, the alternative C-N bond activation by coordination of a neutral tertiary carboxamide nitrogen atom has not been studied. We present the first results on the effect of nitrogen pyramidalization in N-coordinated metal complexes on the methanolysis of tertiary carboxamide groups. An analysis of the reactions products obtained from the methanol cleavage of [(N-Acyl-bpa)Cu]2+ (bpa = N,N-bispicolylamine) complexes is presented together with experimental and high-level theoretically calculated structures. The strong effect of different anions on the amide pyramidalization and subsequent C-N-bond cleavage is evaluated. We show that dichloro complexes [(N-Acyl-bpa)CuCl2] have much less activated amide groups than the corresponding triflate species. They should therefore be less reactive. However, [(N-Acyl-bpa)CuCl2] complexes dissociate in solution to give cationic monochloro complexes [(N-Acyl-bpa)Cu(S)Cl]+ (S = solvent molecule). Theoretical calculations show that the amide pyramidalization in the monochloro complexes is equal to that in the corresponding CF3SO3- salts. Consequently, chloro and triflato complexes are cleaved with similar rates and efficiencies. Parallels to and differences in the reactivity of purely organic distorted amides are discussed.     

A study of a newly synthesized ligand and its metal complexes in bulk and nano size and metal uptake efficiency

A newly synthesized ligand derived from 2-amino thiophenol and benzoic anhydride and its Co(II), Cd(II), La(III) (in bulk and nano size), and Gd(III) complexes was investigated and characterized. The maximum elimination capacity of the newly synthesized ligand was investigated towards the removal of Co(II), Cd(II), La(III), and Gd(III) ions from aqueous solutions. It was found that the ligand has the best removal ability for Cd(II) metal of 98.66% at a concentration of 0.03 mg/L.     

A theoretical study on the alkene insertion step in Rh-Yanphos catalyzed hydroformylation

This paper studied the mechanism of the alkene insertion elementary step in the asymmetric hydroformylation （AHF） catalyzed by RhH（CO）2[（R,S）-Yanphos] using four alkene substrates （CH2=CH- Ph, CH2=CH-Ph-（p）-Me, CH2=CH-C（==O）OCH3 and CH2=CH-OC（=O）-Ph, abbreviated as A1-A4）. Interestingly, the equatorial vertical coordination mode （A mode） with respect to the Rh center was found for AI and A2 but not for A3 and A4, although the equatorial in-plane coordination mode （E mode） was found for A1 -A4. The relative energy of the E mode of the -q2-intermediates is lower than that of the A mode. In the alkene insertion step, Path 1 is more favorable than Path 2 for this system. As for AI and A2, there could be a transformation between 2eq and 2ax.     

Correlating cluster size and NLO response of complexes aggregated with bifurcated metal bonds: a DFT study

In the present work, the cooperativity effect on the NLO response of clusters aggregated with bifurcated metal bonds is reported by DFT calculations at the CAM-B3LYP/6-311++G(d,p) level. Linear clusters of (LiN(CHO)₂)_1-5 and (NaN(CHO)₂)_1-5 which are connected with bifurcated metal bonds have been selected as model systems. Stabilization energies, polarizability, first hyperpolarizability, energy gap of HOMO and LUMO, and charge transfer (CT) were obtained at the same level of optimization. In the studied clusters, first hyperpolarizability is increased by cluster size and its values were obtained in ranges of 606.1–1327.4 and 1239.4–2071.1 a.u. for (LiN(CHO)₂)_1-5 and (NaN(CHO)₂)_1-5 clusters, respectively. The many-body analysis was carried out to determine two-body and many-body contributions in total interaction-induced properties. TD-DFT calculations were performed to compute the crucial electronic transitions of the related clusters. UV–vis spectra exhibit red shift due to cooperativity effects.     

Synthesis and characterization of some binuclear metal complexes with a pentadentate azodye ligand: An experimental and theoretical study

A novel series of binuclear complexes with Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) ions derived from a pentadentate azo dye ligand (H₃L) was synthesized and structurally investigated by various physicochemical analyses, namely, scanning electron microscopy, transmission electron microscopy, NMR, UV–visible spectroscopy, and Electron-Spin Resonance (ESR) studies. The infrared spectral data revealed characteristic bands due to ν(N=N) and ν(C=O) at 1606 and 1631 cm⁻¹ in the free ligand. However, their positions shifted and appeared at ~1564 and ~1592 cm⁻¹ on coordination, suggesting the involvement of carbonyl oxygen and azo nitrogen in complex formation. The spectral data suggested octahedral geometry for the complexes. The kinetic parameters such as order and activation energy were determined from the thermal decomposition values. X-ray powder diffraction analysis showed the orthorhombic nature of the cadmium complex. Furthermore, Density functional theory (DFT) calculations were also recorded to describe the insight bonding. The synthesized compounds were tested for in vitro antibacterial activity against K. aerogenes, S. aureus, B. acidoterrestris, E. coli, and V. cholerae strains by the cup-plate method. In addition, the interactions that occurred in the protein–ligand complexes have been predicted by docking analysis.     

Chalcanthrene-fullerene complexes: A theoretical study

In this work we have considered a series of 10 chalcanthrenes-fullerene complexes that were studied by the BLYP density functional theory (DFT) approach. A complete series of chalcanthrenes (C₁₂H₈XY, in which X, Y = O, S, Se, Te) where computed in several combinations in order to demonstrate the effect of structural changes on the electronic properties of the complexes under consideration. The optimized geometries, dissociation energies, and vibrational spectra of the chalcanthrenes-fullerene complexes are reported.     

Photochemistry of transition metal hydrides and dihydrogen complexes: theoretical aspects

The mechanism of the photochemical reactions of transition-metal hydrides and dihydrogen complexes is discussed on the basis of recently published potential-energy curves and qualitative energy-level diagrams.     

Possible gas-phase ion pairs in amine-HCl complexes. An ab initio theoretical study

Ab initio MO calculations were performed for complexes between HCl and NH₃, CH₃NH₂, (CH₃)₂NH and (CH₃) ₃N. SCF geometry optimization for the latter three complexes gives double-minimum potential surfaces, which become single- minimum surfaces when electron correlation is considered. It is proposed that (CH₃)₃NHCl may be an ion pair in the gas phase.