Ab initioenergy‐adjusted pseudopotentials for the noble gases Ne through Xe: Calculation of atomic dipole and quadrupole polarizabilities

Potassium-uracil/thymine ring cleavage enhancement as studied in electron transfer experiments and theoretical calculations

We report experimental and theoretical studies on ring cleavage enhancement in collisions of potassium atoms with uracil/thymine to further increase the understanding of the complex mechanisms yielding such fragmentation pathways. In these electron transfer processes time-of-flight (TOF) negative ion mass spectra were obtained in the collision energy range 13.5-23.0 eV. We note that CNO(-) is the major ring breaking anion formed and its threshold formation is discussed within the collision energy range studied. Such a decomposition process is supported by the first theoretical calculations to clarify how DNA/RNA pyrimidine base fragmentation is enhanced in electron transfer processes yielding ion-pair formation.

Implicit and explicit solvent models for modeling a bifunctional arene ruthenium hydrogen-storage catalyst: a classical and ab initio molecular simulation study

Classical and ab initio, density functional theory- and semiempirical-based molecular simulation, including molecular dynamics, have been carried out to compare and contrast the effect of explicit and implicit solvation representation of tetrahydrofuran (THF) solvent on the structural, energetic, and dynamical properties of a novel bifunctional arene ruthenium catalyst embedded therein. Particular scrutiny was afforded to hydrogen-bonding and energetic interactions with the THF liquid. It was found that the presence of explicit THF solvent molecules is required to capture an accurate picture of the catalyst's structural properties, particularly in view of the importance of hydrogen bonding with the surrounding THF molecules. This has implications for accurate modeling of the reactivity of the catalyst.

Experimental and DFT studies on the vibrational and electronic spectra of 2-(1H-Imidazo [4,5-ƒ][1,10]phenanthrolin-2-yl)phenol

The compound 2-(1H-Imidazo [4,5-ƒ][1,10] phenanthrolin-2-yl) phenol (IPP) was synthesized, followed by structure determination by X-ray diffraction, the results of which agree well with the calculated optimized, lowest energy geometrical structure. Vibrational information was obtained by FT-IR and Raman spectroscopy which also agree well with calculations (of harmonic vibration frequencies). The calculations were carried out with density functional theory B3LYP methods using 6-311G(**) and LANL2DZ basis sets. Absorption UV-Vis experiments of IPP in CH3OH solution reveal three maximum peaks at 237.0, 274.0 and 335.0 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311G(**) in CH3OH solution, and agree to a lesser extent with gas-phase calculations.

Pyridine imines as ligands in luminescent iridium complexes

Biscyclometallated iridium complexes [Ir(ppz)₂(X^Y)][PF₆] (X^Y = pyridine imine) have been synthesised; N-alkyl complexes are emissive whilst N-aryl ones are only weakly emissive, DFT calculations shed light on the reasons for this difference.

Ultrafast photoinduced charge transport in Pt(ii) donor–acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor

The Pt(ii)-based molecular triad engages in step-wise photoinduced charge-separation; the charge recombination occurs through-space via two distinct pathways.

Some new [(thione)2Au(diamine)]Cl3 complexes: synthesis, spectroscopic characterization, computational and in vitro cytotoxic studies

Recent advances in oncology are focused on developing new complexes of gold(III) with various ligands that show augmented anti-proliferative potential and reduced toxicity as compared to cis-platin. In this study, new Au(III) complexes of the type [(thione)2Au(diamine)]Cl3 are reported, where thione=1,3-imidazolidine-2-thione (Imt), 1,3-Diazinane-2-thione (Diaz) and diamine=1,2-diaminoethane (en), 1,3-diaminopropane (pn) or 1,4-diaminobutane (bn). The solid state IR as well as (13)C and (15)N NMR data indicate that Au(III) center is bonded via sulfur of thiocarbonyl SC site of the thiones and also chelated by the diamines from the trans side of coordinated thiones. Spectroscopic data are evaluated by comparisons with calculated data from the built and optimized structure by GAUSSIAN 09 at the RB3LYP level with LanL2DZ bases set. These new Au(III) complexes based on mixed thione and diamine ligands are very similar to the square planar structure of tetracoordinate [Au(en)2]Cl3complex. In this study, cytotoxicity data for these gold(III) complexes against C6 glioma cell lines are also reported, and the results indicate some complexes have cytotoxicity comparable to cis-platin.

Photoinduced charge separation in a PtII acetylide donor–acceptor triad based on 2-(1-pyrazole)-pyridine modified with naphthalene mono-imide electron acceptor

A class of molecular electron transfer cascades—those based on PtII complexes of 2-(1-pyrazole)-pyridine (pzpy) ligands—are reported. The synthesis of a new electron-acceptor imide-modified pzpy ligands is reported, and their application to transition-metal chemistry demonstrated by the synthesis of the PtII chloride and acetylide complexes. These donor–acceptor assemblies are promising models for investigation of photoinduced charge separation. Accordingly, picosecond time-resolved infrared (TRIR) and femtosecond transient absorption (TA) studies have been undertaken to elucidate the nature and dynamics of the lowest excited states in Pt(NAP-pyr-pyrazole)(–CC–Ph–C7H15)2. It has been established that the initial population of an MLL'CT excited state in the chromophoric [Pt(pyridine-pyrazole)(acetylide)] core is followed by an electron transfer to the naphthalimide (NAP) acceptor, forming a charge-separated state. This state is characterized by a large shift in ν(CO) vibrations of the NAP acceptor, as well as by a very intense and broad [×10 times in comparison to ν(CO)] asymmetric acetylide stretch which incorporates –CC–Pt–CC– framework and occurs at approximately 300 cm–1 lower in energy than its ground-state counterpart. In CH2Cl2 at room temperature, the charge-separated state with the lifetime of 150 ps collapses into an almost isoenergetic NAP-localized triplet state; the rate of this transformation changes upon decreasing the temperature to 263 K. This final excited state, 3NAP-(pyr-pyrazole)Pt(–CC–Ph–C7H15)2, has an unusually long, for PtII complexes, excited-state lifetime of tens of microseconds. The work demonstrates the possibility of tuning excited-state properties in this new class of PtII chromophores designed for electron-transfer cascades.

Theoretical prediction of new noble-gas molecules FNgBNR (Ng = Ar, Kr, and Xe; R = H, CH3, CCH, CHCH2, F, and OH)

We have computationally predicted a new class of stable noble-gas molecules FNgBNR (Ng = Ar, Kr, Xe; R = H, CH3, CCH, CHCH2, F, and OH). The FNgBNR were found to have compact structures with F-Ng bond lengths of 1.9-2.2 Å and Ng-B bond lengths of ~1.8 Å. The endoergic three-body dissociation energies of FNgBNH to F + Ng + BNH were calculated to be 12.8, 31.7, and 63.9 kcal mol(-1), for Ng = Ar, Kr, and Xe, respectively at the CCSD(T)/CBS level. The energy barriers of the exoergic two-body dissociation to Ng + FBNH were calculated to be 16.1, 24.0, and 33.2 kcal mol(-1) for Ng = Ar, Kr, and Xe, respectively. Our results showed that the dissociation energetics is relatively insensitive to the identities of the terminal R groups. The current study suggested that a wide variety of noble-gas containing molecules with different types of R groups can be thermally stable at low temperature, and the number of potentially stable noble-gas containing molecules would thus increase very significantly. It is expected some of the FNgBNR molecules could be identified in future experiments under cryogenic conditions in noble-gas matrices or in the gas phase.

An interplay between infrared multiphoton dissociation Fourier-transform ion cyclotron resonance mass spectrometry and density functional theory computations in the characterization of a tripodal quinolin-8-olate Gd(III) complex

A new hexadentate, tripodal 8-hydroxyquinoline based ligand (QH3) and its gadolinium(III) tris-chelated (GdQ) complex with hemicage structure was investigated by using high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FTICRMS). The protonated adduct of the free ligand and its hemicage tripodal Gd(III) complex, [GdQ + H](+), were first observed in experiments of electrospray ionization (ESI) with a linear ion trap (LTQ) mass spectrometer and further investigated by using high resolution FTICRMS. Gas-phase dissociation of the protonated Gd(III) complex, by infrared multiphoton dissociation (IRMPD) FTICR MS, demonstrated a fragmentation pattern with six main product cluster ions labeled as [Fn](+) (n = 1 up to 6). These product ions suggest the elimination of 7-amino-alkyl or 7-alkyl chains of the hemicage moiety. High resolution MS conditions allowed the elucidation of the fragmentation pattern and product ion structures along with the determination, among the isotopic pattern of Gd, of the chemical compositions of closely related species, which differ in terms of hydrogen content. Among the Gd six naturally stable isotopes, (158)Gd is the most abundant, and its peak within each cluster was used as a reference for distinguishing each product ions. Computational DFT investigations were applied to give support to some hypothesis of fragmentation pathways, which could not have been easily justified on the basis of the experimental work. Furthermore, computational studies suggested the coordination geometry of the protonated parent complex and the five- and four-coordinated complexes, which derive from its fragmentation. Furthermore, experimental and computational evidences were collected about the octet spin state of the parent compound.

Synthesis, CP-MAS NMR Characterization, and Antibacterial Activities of Glycine and Histidine Complexes of Cd(SeCN) 2 and Hg(SeCN) 2

The synthesis and characterization of cadmium and mercury complexes of selenocyanate of the type [(L)M(SeCN)₂] are described, where L is L-Histidine (His) or L-Glycine (Gly) and M is Cd²⁺ or Hg²⁺. These complexes are obtained by the reaction of 1 equivalent of respective amino acids with metal diselenocyanate precursor in a mixture of solvents (methanol : water = 1 : 1). These synthesized compounds are characterized by analytical and various spectroscopic techniques such as elemental analysis (EA), IR, H,1 and C13 NMR in solution and in the solid state for C13 and N15. The in vitro antibacterial activities of these complexes have been investigated with standard type cultures of Escherichia coli (MTCC 443), Klebsiella pneumoniae (MTCC 109), Pseudomonas aeruginosa (MTCC 1688), Salmonella typhi (MTCC 733), and Staphylococcus aureus (MTCC 737).

Infrared spectra of NgBeS (Ng = Ne, Ar, Kr, Xe) and BeS2 in noble-gas matrices

Laser-ablated beryllium atom has been codeposited at 4 K with hydrogen sulfide in excess noble gas matrices. Four noble-gas compounds NgBeS (Ng = Ne, Ar, Kr, Xe) and the BeS(2) molecule are identified on the basis of the S-34 isotopic substitution, DFT and CCSD(T) theoretical predictions, and a comparison of noble-gas substitution. The agreement between the experimental and calculated vibrational frequencies supports the identification of these molecules. The dissociation energies are calculated at 1.6, 12.6, 10.7, and 13.4 kcal/mol for NeBeS, ArBeS, KrBeS, and XeBeS, respectively, at the CCSD(T) level. The BeS Lewis acid molecule favors strong chemical binding between the Be and Ng atoms.

Platinum electrodeposition on unsupported carbon nano-onions

An effort to develop smaller, well-dispersed catalytic materials electrochemically on high-surface-area carbon supports is required for improved fuel cell performance. A high-surface-area carbon material of interest is carbon nano-onions (CNOs), also known as multilayer fullerenes. The most convenient synthesis method for CNOs is annealing nanodiamond particles, thus retaining the size of the precursors and providing the possibility to prepare very small nanocatalysts using electrochemical techniques. In terms of pure metal catalysts, platinum is the most common catalyst used in fuel cells. The combination of Pt nanoparticles with CNOs could lead to new catalytic nanomaterials. In this work, this was accomplished by using a rotating disk-slurry electrode (RoDSE) technique. The Pt/CNO catalysts were prepared from slurries that contained functionalized CNOs and K(2)PtCl(6) as the platinum precursor in aqueous 0.1 M H(2)SO(4) solution. X-ray photoelectron spectroscopy results showed that 37% of the Pt on the CNOs is metallic Pt whereas 63% had higher binding energies, which is evidence of higher oxidation states or the presence of Pt atoms and clusters on CNOs. However, aberration-corrected scanning transmission electron microscopy of the Pt/CNOs confirmed the presence of Pt atoms and clusters on CNOs. Thermal gravimetric analysis showed the excellent thermal stability of the Pt/CNOs and a lower onset potential for the electrochemical oxidation of methanol compared to that of commercial Pt/Vulcan catalyst material. The computational method confirmed the Pt atoms' location at CNOs surface sites. Geometric parameters for distances between Pt atoms in the 3Pt/CNOs molecular system from our theoretical calculations are in agreement with the respective parameters obtained experimentally. The combination of CNO with RoDSE presents a new highly dispersed catalyst nanomaterial.

Heterotrimetallic compounds containing Mo-M-Li [M = K, Rb and Cs] clusters: synthesis, structure, bonding, aromaticity and theoretical investigations of Li2M2 [M = K and Rb] and Cs4 rings

A new polydentate fac-trioxo molybdenum complex, [MoO(3)L](3-) {LH(3) = nitrilotriacetic acid}, has been synthesized by the reaction of lithium molybdate with iminodiacetic acid. The trinegative complex anion coordinates the alkali metal cations, K(+), Rb(+) or Cs(+). The potassium, rubidium and cesium complexes, [Li{K(H(2)O)(2)}MoO(3)L](n) (1), [Li{Rb(H(2)O)(2)}MoO(3)L](n) (2) and [Cs{Li(H(2)O)}(2)MoO(3)L](n) (3), form heterotrimetallic coordination chains, containing planar rings of Li(2)M(2) (M = K or Rb) and Cs(4). Theoretical investigations on these rings were carried out using NICS calculations and ab initio ring current maps, revealing aromaticity to be of limited significance.

Experimental and DFT studies on the vibrational and electronic spectra of 9-anthracenemethanol

Vibrational spectral measurements were made for 9-anthracenemethanol. Optimized geometrical structure and harmonic vibration frequencies were computed based on ab initio and density functional theory B3LYP methods using 6-311G(**) and LANL2DZ basis sets. The equilibrium geometries got from all of the methods and basis were compared with X-ray diffraction results. The IR and UV-vis spectra of the title compound were computed using all of the methods and choose the most appropriate way to discuss. And the absorption spectra were calculated both in gas phase and in CH(3)CH(2)OH and CH(3)CN solution. The calculated results matched well with the experimental values. On the basis, the first excited state electronic transition energy has been calculated using time-dependent density functional theory.

Toward accurate theoretical thermochemistry of first row transition metal complexes

The recently developed correlation consistent Composite Approach for transition metals (ccCA-TM) was utilized to compute the thermochemical properties for a collection of 225 inorganic molecules containing first row (3d) transition metals, ranging from the monohydrides to larger organometallics such as Sc(C(5)H(5))(3) and clusters such as (CrO(3))(3). Ostentatiously large deviations of ccCA-TM predictions stem mainly from aging and unreliable experimental data. For a subset of 70 molecules with reported experimental uncertainties less than or equal to 2.0 kcal mol(-1), regardless of the presence of moderate multireference character in some molecules, ccCA-TM achieves transition metal chemical accuracy of ±3.0 kcal mol(-1) as defined in our earlier work [J. Phys. Chem. A2007, 111, 11269-11277] by giving a mean absolute deviation of 2.90 kcal mol(-1) and a root-mean-square deviation of 3.91 kcal mol(-1). As subsets are constructed with decreasing upper limits of reported experimental uncertainties (5.0, 4.0, 3.0, 2.0, and 1.0 kcal mol(-1)), the ccCA-TM mean absolute deviations were observed to monotonically drop off from 4.35 to 2.37 kcal mol(-1). In contrast, such a trend is missing for DFT methods as exemplified by B3LYP and M06 with mean absolute deviations in the range 12.9-14.1 and 10.5-11.0 kcal mol(-1), respectively. Salient multireference character, as demonstrated by the T(1)/D(1) diagnostics and the weights (C(0)(2)) of leading electron configuration in the complete active self-consistent field wave function, was found in a significant amount of molecules, which can still be accurately described by the single reference ccCA-TM. The ccCA-TM algorithm has been demonstrated as an accurate, robust, and widely applicable model chemistry for 3d transition metal-containing species with versatile bonding features.

AB INITIO POTENTIAL ENERGY SURFACE AND PREDICTED ROVIBRATIONAL SPECTRA FOR THE Kr–N2O COMPLEX

The potential energy surface for the Kr – N 2 O complex is calculated using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] with a large basis set including midpoint bond functions. The interaction energies are obtained by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The CCSD(T) potential is found to have two minima corresponding to the T-shaped and linear Kr – ONN structures. The geometry for the T-shaped configuration is very close to the experimental results. The two-dimensional discrete variable representation method is applied to calculate the rovibrational energy levels with N 2 O at its ground and ν3 excited states. The calculated transition frequencies and spectroscopic constants are in good agreement with the observed values.

Benchmark of density functional theory methods on the prediction of bond energies and bond distances of noble-gas containing molecules

We have tested three pure density functional theory (DFT) functionals, BLYP, MPWPW91, MPWB95, and ten hybrid DFT functionals, B3LYP, B3P86, B98, MPW1B95, MPW1PW91, BMK, M05-2X, M06-2X, B2GP-PLYP, and DSD-BLYP with a series of commonly used basis sets on the performance of predicting the bond energies and bond distances of 31 small neutral noble-gas containing molecules. The reference structures were obtained using the CCSD(T)∕aug-cc-pVTZ theory and the reference energies were based on the calculation at the CCSD(T)∕CBS level. While in general the hybrid functionals performed significantly better than the pure functionals, our tests showed a range of performance by these hybrid functionals. For the bond energies, the MPW1B95∕6-311+G(2df,2pd), BMK∕aug-cc-pVTZ, B2GP-PLYP∕aug-cc-pVTZ, and DSD-BLYP∕aug-cc-pVTZ methods stood out with mean unsigned errors of 2.0-2.3 kcal∕mol per molecule. For the bond distances, the MPW1B95∕6-311+G(2df,2pd), MPW1PW91∕6-311+G(2df,2pd), and B3P86∕6-311+G(2df,2pd), DSD-BLYP∕6-311+G(2df,2pd), and DSD-BLYP∕aug-cc-pVTZ methods stood out with mean unsigned errors of 0.008-0.013 Å per bond. The current study showed that a careful selection of DFT functionals is very important in the study of noble-gas chemistry, and the most recommended methods are MPW1B95∕6-311+G(2df,2pd) and DSD-BLYP∕aug-cc-pVTZ.

Molecular structure and infrared spectra of (HXeCN)n (n=2, 3 or 4)

The structure, energetics, and vibrational spectra of the (HXeCN)2 dimer were investigated at the CCSD(T), MP2 and B3LYP levels. Such properties of the (HXeCN)3 trimer and (HXeCN)4 tetramer were investigated at the B3LYP level. The dimer, trimer, and tetramer were predicted to have a C2h, C2v, and D2d structure, respectively. In all of these oligomers, the N⋯Xe intermonomeric interaction is the most important one for holding the monomers together. Included with the ZPVE and BSSE, the stabilization energy of the dimer is 12.36 kcal/mol at the CCSD(T) level, while those of the dimer, trimer, and tetramer are 10.42, 18.23, and 31.34 kcal/mol, respectively, at the B3LYP level. At the B3LYP level, with respect to those of the isolated monomer, the C-Xe and Xe-H asymmetric stretching frequencies are shifted by -11.2 and +128.0 cm(-1) for the dimer, -51.6, +220.7 and -11.5, +96.6 cm(-1) for the trimer, and -14.1 and +201.8 cm(-1) for the tetramer.