Is Lewis Acidity in Metal Dications Triggered by Solvent Shell Fluctuations?

2018 ◽  
Author(s):  
Tony Stace
Keyword(s):  
Experimental Data ◽  
Gas Phase ◽  
Metal Ion ◽  
Time Difference ◽  
Lewis Acidity ◽  
Water Molecules ◽  
Central Metal ◽  
Residence Times ◽  
Gas Phase Clusters ◽  
Mean Residence Times

Using experimental data collected on the stabilities of gas phase clusters consisting of metal dications in association with water molecules, a model is proposed to account for Lewis acidity. It is suggested that acidity is driven be fluctuations in the numbers of water molecules surrounding a metal ion, and that these fluctuations reduce numbers in the coordination shells to below those need to stabilise a +2 charge on the metal. The timescale on which these fluctuations are calculated to occur is approximately 6 orders of magnitude longer than any of the measure mean residence times of water molecules surrounding a central metal ion. This time difference reflects both the rarity of the event require to drive acidity and the extreme nature of some of the fluctuations.

Is Lewis Acidity in Metal Dications Triggered by Solvent Shell Fluctuations?

2018 ◽  
Author(s):  
Tony Stace
Keyword(s):  
Experimental Data ◽  
Gas Phase ◽  
Metal Ion ◽  
Time Difference ◽  
Lewis Acidity ◽  
Water Molecules ◽  
Central Metal ◽  
Residence Times ◽  
Gas Phase Clusters ◽  
Mean Residence Times

Using experimental data collected on the stabilities of gas phase clusters consisting of metal dications in association with water molecules, a model is proposed to account for Lewis acidity. It is suggested that acidity is driven be fluctuations in the numbers of water molecules surrounding a metal ion, and that these fluctuations reduce numbers in the coordination shells to below those need to stabilise a +2 charge on the metal. The timescale on which these fluctuations are calculated to occur is approximately 6 orders of magnitude longer than any of the measure mean residence times of water molecules surrounding a central metal ion. This time difference reflects both the rarity of the event require to drive acidity and the extreme nature of some of the fluctuations.

Metal-Mediated Pseudo Coordination Isomerism in Complexes of Mixed Neutral Didentate and Dianionic Tridentate Pyridine-Containing Ligands

2004 ◽  
Vol 57 (6) ◽  
pp. 565 ◽  
Author(s):  
Nathaniel W. Alcock ◽  
Guy J. Clarkson ◽  
Geoffrey A. Lawrance ◽  
Peter Moore
Keyword(s):  
Hydrogen Bonding ◽  
Metal Ion ◽  
Mixed Ligand Complex ◽  
Molar Ratio ◽  
High Yield ◽  
Axial Position ◽  
Water Molecules ◽  
Central Metal ◽  
Ligand Complex ◽  
Space Group

Reaction of nickel(II) or copper(II) acetate with 2-(aminomethyl)pyridine 1 and pyridine-2,6-dicarboxylate ion 2 in aqueous methanol in a 1 : 1 : 1 molar ratio leads to the crystallization in high yield of exclusively one product in each case. For nickel(II), a neutral mixed-ligand complex [Ni · 1 · 2 · (OH2)] is obtained, whereas with copper(II) an ionic complex [Cu · 12 · (OHCH3)][Cu · 22] forms wherein each complex ion contains exclusively one type of ligand. The outcome appears to be directed by the metal ion employed, the two forms being effectively coordination isomers, albeit differing in central metal ion. The neutral complex [Ni · 1 · 2 · (OH2)] · 4¼H2O crystallizes in the triclinic space group P¯1, with two independent nickel centres and ten (some with partial occupancy) water molecules in the asymmetric unit. Each nickel lies in a distorted octahedral environment, with the three N-donor and O-donor sets occupying meridional positions. A complex system of hydrogen bonding and Π-stacking operates in the crystal, with arrays of complex units arranged in ‘dimer tapes’ surrounded by water molecules. The ionic [Cu · 12 · (OHCH3)][Cu · 22] · 2CH3OH complex crystallizes in the monoclinic P21/c space group. The cation adopts a distorted square-based pyramidal geometry with a coordinated methanol in the axial position, although another is weakly interacting in the other axial site. The anion exists in the previously described octahedral geometry with two meridionally-disposed tridentate ligands with the pyridines disposed in trans positions. Three-dimensional ordering in the structure is directed by ‘ribbons’ of hydrogen bonding.

scholarly journals The Analysis of Short-Term Dataset of Water Stable Isotopes Provides Information on Hydrological Processes Occurring in Large Catchments from the Northern Italian Apennines

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1360 ◽  
Author(s):  
Cervi ◽  
Dadomo ◽  
Martinelli
Keyword(s):  
Stable Isotopes ◽  
Isotopic Composition ◽  
Sine Wave ◽  
Hydrological Processes ◽  
Water Molecules ◽  
Residence Times ◽  
Catchment Characteristics ◽  
Mean Residence Times ◽  
Italian Apennines ◽  
Short Time

This study discusses a dataset of water stable isotopes from precipitation (4 rain gauges) and surficial water (9 rivers) from the northern Italian Apennines, an area in which clay-rich bedrocks widely outcrop and the runoff response to precipitation events is very rapid. The dataset has been compiled starting from existing data that had previously been published in the literature and consists of monthly values of stable isotopes oxygen-18 (18O) and deuterium (2H) lasting over the period from January 2003 to December 2006 (precipitation) and from January 2006 to December 2007 (surficial water). For this period, mean residence times estimated by means of a sine-wave fitting technique make evident the significant differences over time spent by water molecules within the 9 catchments. Moreover, isotopic compositions of rivers deviated from those of precipitations revealing the influence of some catchment characteristics in differentiating the isotopic composition in rivers. Further correlations between mean residence times of river water and selected catchment characteristics reveal the role of orography and bedrocks in delaying the water molecules during their flow-paths. In addition, time series and cross–correlation analyses indicate a certain control by the main watershed divide on the isotopic composition of river waters, which is reflected in a progressive isotopic variation with longitude. The study shows that, despite using a short-time dataset (2-years for surficial water) of sparse stable isotopes can provide remarkable indications for depicting hydrological processes in large catchments made up of clay-rich bedrocks.

Probing the Stability and Structure of Metalloporphyrin Complexes with Basic Peptides by Mass Spectrometry

2005 ◽  
Vol 11 (1) ◽  
pp. 65-72 ◽  
Author(s):  
Emily E. Jellen ◽  
Victor Ryzhov
Keyword(s):  
Gas Phase ◽  
Metal Ion ◽  
Basic Amino Acid ◽  
Quadrupole Ion Trap ◽  
Model Systems ◽  
Central Metal ◽  
Salt Bridges ◽  
Charge Solvation ◽  
The Stability ◽  
Basic Peptides

The stability and structure of non-covalent complexes of various peptides contatining basic amino acid residues (Arg, Lys) with metalloporphyrins were studied in a quadrupole ion trap mass spectrometer. The complexes of heme and three other metalloporphyrins with a variety of basic peptides and model systems were formed via electrospray ionization (ESI) and their stability was probed by energy-variable collision-induced dissociation (CID). A linear dependence for basic peptides and model compounds/metalloporphyrin complexes was observed in the plots of stability versus degrees of freedom and was used to evaluate relative bond strength. These results were then compared with previous data obtained for complexes of metalloporphyrins with His-containing peptides and peptides containing no basic amino acids. The binding strengths of Lys-containing peptide complexes in the gas phase was found to be almost as strong as that of Arg-containing complexes. Both systems showed stronger binding than His-containing peptides studied previously. To probe the structure of Arg and Lys non-covalent complexes (charge solvation versus salt bridges), two techniques, CID and ion–molecule reactions, were used. CID experiments indicate that the gas-phase complexes are most likely formed by charge solvation of the central metal ion in the metalloporphyrin by basic side chains of Arg or Lys. Results from the ion–molecule reaction studies are consistent with the charge solvation structure as well.

scholarly journals MOLECULAR STRUCTURE AND VIBRATION SPECTRA OF PIVALIC ACID

2018 ◽  
Vol 59 (7) ◽  
pp. 17
Author(s):  
Alexander E. Pogonin ◽  
Oleg A. Pimenov ◽  
Yuriy A. Zhabanov
Keyword(s):  
Molecular Structure ◽  
Ir Spectra ◽  
Gas Phase ◽  
Metal Ion ◽  
Density Functional ◽  
Pivalic Acid ◽  
Basis Sets ◽  
Potential Energy Distribution ◽  
Central Metal ◽  
Vibrational Modes

The metal carboxylates such as metal pivalates (salts of the pivalic acid (CH3)3CCOOH) attract a great interest as most promising precursors for chemical vapor deposition (CVD) technology. The possibility to use these substances in the CVD technology is specified by their good thermal stability and high volatility. For modeling of chemical reactions with metal pivalates in the gas-phase and the data on molecular structure will be very useful, in particularly information about effect of central metal ion to geometry of pivalic ligands. In the frame of this task the structures of metal pivalate molecules and pivalic acid (H(piv)) in a gas phase should be finding. The aim of present work is theoretical investigation of the geometry and IR-spectrum of H(piv) using density functional theory (DFT) methods. All calculations were performed using the Gaussian 03 program. The optimization of geometry and quadratic force field calculations were carried out using DFT functionals B3LYP, PBE, PBE0 and BP86 with correlation-consistent triple-ζ valence cc-pVTZ basis sets for O, C, and H. Appropriate assignment of vibrational modes was carried out by the potential energy distribution (PED) analysis among internal coordinates using the SHRINK program. According to DFT computations, the H(piv) molecule has an equilibrium structure of Cs symmetry with Гvib=26A'+19A''. The theoretical and experimental IR-spectra are satisfactorily agreed. The comparison of the ten intensities of highest bands in spectra allowed determining linear correlation between peaks position in experimental and modeling IR-spectra. It should be note the complicated composition of vibrational modes.

scholarly journals Bis{2,6-bis[(E)-(4-fluorobenzylimino)methyl]pyridine}nickel(II) dinitrate dihydrate

IUCrData ◽  
2019 ◽  
Vol 4 (12) ◽  
Author(s):  
Corey R. Johnson ◽  
Ismet Basaran ◽  
Md Mhahabubur Rhaman ◽  
Douglas R. Powell ◽  
Md. Alamgir Hossain
Keyword(s):  
Metal Ion ◽  
Chelating Agent ◽  
Water Molecules ◽  
Central Metal ◽  
Central Ring ◽  
Crystal Water ◽  
Pyridine Ligands ◽  
Hydrated Salt ◽  
Nitrate Anions ◽  
Methyl Pyridine

In the title hydrated salt, [Ni(C21H17F2N3)2](NO3)2·2H2O, the central NiII ion is coordinated by six N atoms from two tridentate chelating 2,6-bis[(E)-(4-fluorobenzylimino)methyl]pyridine ligands. While the central NiII ion is six-coordinate, its environment is distorted from an octahedral structure because of the unequal Ni—N distances. The Ni—N bond lengths vary from 1.8642 (14) to 2.2131 (15) Å, while the N—Ni—N angles range from 79.98 (6) to 104.44 (6)°. Three coordinating sites of each chelating agent are almost coplanar with respect to the pyridine ring, and two pyridine moieties are perpendicular to each other. Two non-coordinating nitrate anions within the asymmetric unit balance the charges of the central metal ion, and are linked with two crystal water molecules, forming a water–nitrate cyclic tetrameric unit [O...O = 2.813 (2) to 3.062 (2) Å]. In an isolated molecule, the fluorophenyl rings of one ligand are stacked with the central ring of the other ligand via π–π interactions, with the closest centroid-to-plane distances being 3.359 (6), 3.408 (5), 3.757 (6) and 3.659 (5) Å.

Theoretical analysis of counter-current absorption of a poorly soluble gas based on the PDE-AD model

1986 ◽  
Vol 51 (6) ◽  
pp. 1222-1239 ◽  
Author(s):  
Pavel Moravec ◽  
Vladimír Staněk
Keyword(s):  
Experimental Data ◽  
Liquid Phase ◽  
Gas Phase ◽  
Transfer Functions ◽  
Packed Bed ◽  
Packed Bed Column ◽  
Interfacial Transport ◽  
Gaseous Component ◽  
Poorly Soluble ◽  
Counter Current

Expression have been derived in the paper for all four possible transfer functions between the inlet and the outlet gas and liquid steams under the counter-current absorption of a poorly soluble gas in a packed bed column. The transfer functions have been derived for the axially dispersed model with stagnant zone in the liquid phase and the axially dispersed model for the gas phase with interfacial transport of a gaseous component (PDE - AD). calculations with practical values of parameters suggest that only two of these transfer functions are applicable for experimental data evaluation.

Diffusion model for deposition of epitaxial GaAs layers prepared by the MOCVD method

1991 ◽  
Vol 56 (10) ◽  
pp. 2020-2029
Author(s):  
Jindřich Leitner ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma ◽  
Rudolf Hladina
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Kinetic Model ◽  
Gas Phase ◽  
Substrate Surface ◽  
Deposition Process ◽  
Hydrogen Atmosphere ◽  
Epitaxial Gaas ◽  
Kinetics Of ◽  
Good Agreement

The authors proposed and treated quantitatively a kinetic model for deposition of epitaxial GaAs layers prepared by reaction of trimethylgallium with arsine in hydrogen atmosphere. The transport of gallium to the surface of the substrate is considered as the controlling process. The influence of the rate of chemical reactions in the gas phase and on the substrate surface on the kinetics of the deposition process is neglected. The calculated dependence of the growth rate of the layers on the conditions of the deposition is in a good agreement with experimental data in the temperature range from 600 to 800°C.

An homogeneous growth model of gallium arsenide epitaxial layers from the gas phase

1989 ◽  
Vol 54 (11) ◽  
pp. 2933-2950
Author(s):  
Emerich Erdös ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma
Keyword(s):  
Experimental Data ◽  
Gallium Arsenide ◽  
Kinetic Study ◽  
Gas Phase ◽  
Growth Model ◽  
Epitaxial Layers ◽  
Inhomogeneous Model ◽  
Homogeneous Models ◽  
Active Centres

This paper represents a continuation and ending of the kinetic study of the gallium arsenide formation, where a so-called inhomogeneous model is proposed and quantitatively formulated in five variants, in which two kinds of active centres appear. This model is compared both with the experimental data and with the previous sequence of homogeneous models.

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