Ions, closed-shell

For an open-shell system, try converging the closed-shell ion of the same molecule and then use that as an initial guess for the open-shell calculation. Adding electrons may give more reasonable virtual orbitals, but as a general rule, cations are easier to converge than anions. 

We shall now briefly describe the well-known temperature-independent Langevin diamagnetism of closed-shell ions, such as K+ and Cl in KCl and similar Inorganics, such as Si02, AI2O3, and the zeolites, as well as the covalent organic compounds. Since all such... 

Catalano et al. reported the synthesis and characterization of a new series of Pd°-based metallocrypates that bind Tl1 ion in the absence of attractive ligand interactions through metal-lophilic connections. The cationic species have been characterized by a variety of methods and have considerable stability. From the solid-state structural data it is apparent that interaction of the metal atoms with one another is the dominant bonding interaction within the metallocryptate cavity. The characterization of complexes supports the concept of metallophilic behavior as a fundamental component of bonding in closed-shell systems. These materials may ultimately serve as prototypical systems for detection of closed-shell ions 946... 

This difference between Fe2+ and Zn2+ is eventually related to the presence of unfilled d-orbitals in Fe2+, whereas Zn2+ is a closed-shell ion. The organization of these d-orbitals is sensitive to the environment. In bulk water, Fe2+(aq) is coordinated by six water molecules, which leads to the splitting of the d-orbitals into... 

Closed-shell ions are among the most important intermediates in solution chemistry, and no treatise on reactive intermediates (including the present one) would be complete without extensive sections on carbocations and carbanions, if not also on heteroanalogues of the above species. Nevertheless, closed-shell ions are conspicuously absent from matrix isolation studies, apart from a few cases where such species were coincidentally formed in discharges, or where charged species were deliberately isolated by mass spectrometry (cf. Section 6.4). The reason for... 

These are photoinduced electron transfer reactions between two ions. The closed-shell ions then form free radicals which can be charged or neutral, these primary photochemical products being very reactive. One example of this process is the electron transfer between a uranyl cation and a nitrate anion... 

Several classes of FAB desorbed, closed-shell Ions have been found to decompose upon colllslonal activation In an unprecedented manner. The fragmentation occurs for Ions with long alkyl chains and Involves parallel losses of the elements of CnH2n+2 Initiated from the alkyl terminus. 

Hydrolytic reactions are of crucial importance in biological systems. Since no redox chemistry is involved in such reactions, nature has selected closed-shell ions for such reactions, although in a number of cases Mn(II), and even other... 

Table II.2. Antishielding factors for some closed shell ions, a Calculated for the free ion Calculated for the crystal" ion, the ion in the solid...

Mass and Electron Parities, Closed-Shell Ions and Open-Shell Ions 6.6.1 Electron Parity... 

The fragmentation of these radical cations without any rearrangement or without any cleavage of an even number of bonds such as occurs in rings necessarily leads to an even-electron, or closed shell, ion and to a neutral radical. The parity rules were discussed in Section 6.6. 

The production of a radical cation from an even-electron, or closed shell, ion is necessarily accompanied by that of a radical corresponding to the homolytic cleavage of a bond ... 

A closed-shell ion fragments to yield another closed-shell ion, through the loss of a whole molecule, in this case ethylene. In such ions with an even number of electrons, a hydrogen atom transfer no longer requires a six-atom ring. 

The principal elements lhal form closed-shell ions with the same electron configurations as the inert gases of column 8. The charge Z associated with the ion is indicated along the bottom of the figure. 

We think of the ionic solids as made up of closed-shell ions, so that to a first approximation, the electronic structure is like that of the inert-gas solids. Two important differences arise, however, from the transfer of protons to make ions first, the electronic states on different ions are not the same and, second, the spacing is sufficiently reduced that there are important effects from the matrix elements between states on adjacent ions. It will be best to begin with the simplest description, as we have in other systems, and introduce complications as we go one reason for this is that many properties are understandable without the full complexity of the true electronic structure. 

All the extinction data fit the Langmuir curves (eqn. (1)) well or fairly well, implying adsorption on approximately equivalent, non-interacting or only weakly interacting sites. The combining constants are generally consistent with the frequency shifts, for the closed-shell ions, but for NP and Co r they are relatively very much stronger and their order is inverted. When allowance is made for a non-specific... 

In this case, however, the ISi jO component is at infinite dilution in a host of essentially pure YSi cO. Now we assume that Goldschmidt s first rule applies, i.e., we assume that if I and Y " " had exactly the same ionic radius then the standard free energy changes of reactions (1) and (4) would be the same. The actual difference between the standard free energy changes is assumed to be due to the work done in straining crystal and melt by introducing a cation which is not the same size as the site. This is a reasonable assumption for closed-shell ions such as Ca, Sr, and Mg " " and it also appears to work in those cases, such as the lanthanides, where crystal field effects are small (Blundy and Wood, 1994). For first row transition ions such as Co, and Cu, however,... 

E.I.Dashevskaya and E.E.Nikitin, Correlation of adiabatic states between perturbed rotor and Renner-Teller limits for a closed-shell ion + open shell diatom system, Z. phys. Chem. 214, 1001 (2000)... 

Kimachi, S. Ikeda, S. Miki, H. Azumi, T. Crosby, G. A. Spectroscopic and magnetic studies of complexes of d10 closed-shell ions. Coord. Chem. Rev. 1994, 132, 43-50. 

In Chap. 3 of this volume the luminescence of the octahedral uranate group is discussed. The emission is also due to a charge-transfer transition, but the spectra show a rich vibrational structure which yields additional information not available for the closed-shell ions under discussion (with the possible exception of the CrO complex). These studies can be helpful for a better understanding of the luminescence of the closed-shell transition-metal ions. 

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