ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

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Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

https://anthropology.ucsd.edu/_files/Faculty%20Files/schoeninger-publications/DeNiro-Schoeninger1984.pdf

Nitrogen and carbon isotopic composition of bone collagen from marine and terrestrial animals

Publisher Summary The chapter focuses on a general description of the force fields that are most commonly used at present, and it gives an indication of the directions of current research that may yield better functions in the near future. After a brief survey of current models, mostly generated during the 1990s, the focus of the chapter is on the general directions the field is taking in developing new models. The most commonly used protein force fields incorporate a relatively simple potential energy function: The emphasis is on the use of continuum methods to model the electrostatic effects of hydration and the introduction of polarizability to model the electronic response to changes in the environment. Some of the history and performance of widely used protein force fields based on an equation on simplest potential energy function or closely related equations are reviewed. The chapter outlines some promising developments that go beyond this, primarily by altering the way electrostatic interactions are treated. The use of atomic multipoles and off-center charge distributions, as well as attempts to incorporate electronic polarizability, are also discussed in the chapter.

https://dasher.wustl.edu/ponder/papers/advprotchem-66-27-03.pdf

Force fields for protein simulations

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The reactions of Sc+, Ti+, and V+ with CO are studied as a function of translational energy in a guided‐ion‐beam tandem mass spectrometer. Formation of both metal‐carbide and metal‐oxide ions are observed and rationalized by a direct atom abstraction mechanism. At high energies, the ScC+ and ScO+ cross sections exhibit additional features that are unusual but can be explained by an impulsive pairwise mechanism and formation of excited‐state product ions, respectively. Thresholds of the reaction cross sections are interpreted to give the 0 K bond energies (in eV) D0(ScC+)=3.34±0.06, D0(TiC+)=4.05±0.24, D0(VC+)=3.87±0.14, D0(ScO+)=7.11±0.08, D0(TiO+)=6.88±0.07, and D0(VO+)=5.81±0.17. Additional studies are used to help verify the bond energy for ScO+ and yield a recommended value of 7.14±0.11 eV. The nature of the bonding in MO+ and MC+ is discussed and compared for these three metal ions.

Reaction of Sc+, Ti+, and V+ with CO. MC+ and MO+ bond energies

Gas-phase metal ion ligation: collision-induced dissociation of aquairon (Fe(H2O)x+) and iron-methane (Fe(CH4)x+) (x=1-4)

Binding energies for the inner hydration shells of Ca2+: An experimental and theoretical investigation of Ca2+(H2O)x complexes (x = 5–9)

https://link.springer.com/content/pdf/10.1016%2Fj.jasms.2007.03.011.pdf

An electrospray ionization source for thermochemical investigation with the guided ion beam mass spectrometer

Bond dissociation energies of M+[O(CH3)2]x, x = 1−3; M+[(CH2OCH3)2]x, x = 1 and 2; and M+[c-(C2H4O)4], where M = Rb and Cs are reported. The bond dissociation energies (BDEs) are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon (measured using guided ion beam mass spectrometry). In all cases, the primary dissociation channel observed experimentally is endothermic loss of one ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion−molecule collisions, internal energy of the complexes, and unimolecular decay rates. The experimentally determined BDEs for the monodentate ligand complexes are in good agreement with conventional ideas of electrostatic ligation of gas-phase ions and with recent ab initio calculations by Feller et al. (average discrepancy of 5 ± 6 kJ/mol). The experimentally determined BDEs for the multidentate ligand complexes do not ag...

Cation−Ether Complexes in the Gas Phase: Bond Dissociation Energies of M+(dimethyl ether)x, x = 1−3, M+(1,2-dimethoxyethane)x, x = 1 and 2, and M+(12-crown-4) Where M = Rb and Cs

P. B. Armentrout

Papers

Reaction of Sc+, Ti+, and V+ with CO. MC+ and MO+ bond energies

Gas-phase metal ion ligation: collision-induced dissociation of aquairon (Fe(H2O)x+) and iron-methane (Fe(CH4)x+) (x=1-4)

Binding energies for the inner hydration shells of Ca2+: An experimental and theoretical investigation of Ca2+(H2O)x complexes (x = 5–9)

An electrospray ionization source for thermochemical investigation with the guided ion beam mass spectrometer

Cation−Ether Complexes in the Gas Phase: Bond Dissociation Energies of M+(dimethyl ether)x, x = 1−3, M+(1,2-dimethoxyethane)x, x = 1 and 2, and M+(12-crown-4) Where M = Rb and Cs