A molecular orbital analysis shows that the antiferromagnetic contributions to magnetic coupling, favoring a lowspin ground state for a dimer containing two weakly interacting metal centers, can be analyzed in terms of pairwise interactions of dimeric molecular orbitals, with the square of the splitting in energy between the members of a pair being a measure of the stabilization of the low-spin state. The effect of geometrical distortions, electronegativity, and variation of substituents on the magnetic interaction in dimeric systems is examined in detail for singly bridged L,M-X-ML, ( n = 3 , 4 , 5); Cu~C16~and other doubly bridged species where the bridging ligands are halogens, OR, pyridine N-oxides, oxalate, squarate; and the acetate bridged dimers C u ~ ( R C 0 0 ) 4 . The emphasis is on d9 Cu(I1) dimers, but other transition metal systems are also analyzed. Transition metal complexes containing more than one metal atom with unpaired electrons can generally be categorized according to their magnetic behavior into three main groups depending on the strength of the metal-metal interaction. In the noninteracting type the magnetic properties of the dimer (or polymer) a re essentially unchanged from the paramagnetic monomer. In the strongly interacting type formation of relatively strong metal-metal bonds occurs, and the molecule will display simple diamagnetic behavior (for even numbers of electrons). In this paper the properties of weakly interacting metal ions will be investigated. In such compounds this weak coupling between the electrons of the two metal ions leads to low-lying excited states of different spin which can be populated a t thermal energies (SI000 cm-I). The resulting magnetic behavior will be antiferromagnetic or ferromagnetic, depending on whether the low spin (spins paired) or high spin (spins parallel) state is the ground state, respectively. These interactions-often termed superexchange because of the large distances involved (3-5 A) between the metal ions-have been observed in a wide variety of compounds. I 5 In experimental studies the magnetic interaction between spins SA and Sg for atoms A and B is usually written in a form suggested originally by Heisenberg, Dirac, and Van

Orbital interactions in metal dimer complexes

The trans-influence: its measurement and significance

XPS spectra of nine model polymers containing oxygen functional groups are studied. The measured O 1s binding energies were 532.8 eV for ether and alcohol oxgens, 532.2 eV for ketone oxygens and 532.2 and 533.7 eV for the carbonyl- and ether-type oxygens in ester groups, respectively. Comparison with previous experimental and theoretical O 1s binding energies for these groups is also presented. Absolute O Is binding energies of polymers are not in agreement with those published by other groups. However, with the exception of ketone oxygens, binding energy shifts observed for the various functional groups are comparable.

XPS O 1s binding energies for polymers containing hydroxyl, ether, ketone and ester groups

Transition metals are finding increasing use in organic synthesis on the borderline between “organic” and “inorganic” chemistry. Advantage is taken thereby of the fact that metal-induced CC bond formation often takes place with remarkable selectivity. The rapid development that has taken place in this area of chemistry is clearly demonstrated by the carbene complexes, examples of which are now known for almost all transition elements, and which have transformed from organometallic curiosities into synthetically useful reagents in less than two decades since the first studies of E. O. Fischer. They are not only suitable as carbene-transfer agents but also undergo interesting cycloadditions with other ligands in the co-ligand sphere. Their manipulation requires techniques no more complicated than those for Grignard reactions. Thus, carbene complexes can also be used in the synthesis of natural products such as vitamins or antibiotics.

Carbene Complexes in Organic Synthesis [New Synthetic Methods (47)]

Publisher Summary Tin (Sn) compounds are well-recognized both in basic research and in industrial applications. Tin NMR spectroscopy includes three magnetically active tin isotopes namely, 115Sn, 117Sn , and l19Sn. However, most tin NMR parameters refer to the 119Sn nucleus owing to its properties such as abundance, magnetic moment, and NMR frequency. This chapter describes: (1) the compilation and updation of 119Sn chemical shifts (δ 119Sn) from studies on organotin compound and inorganic tin compounds, (2) indirect nuclear spin-spin couplings, (3) relaxation mechanisms concerning the 119Sn nucleus, and (4) experimental details for 1I9Sn-NMR measurements. It is observed that with modem equipment there are, in principle, no serious experimental difficulties in observing 119Sn resonances either directly or by heteronuclear double resonance. δ 119Sn data, available for all kinds of tin compounds, significantly allows using this parameter in an empirical way in order to find models for the qualitative interpretation of δ 119Sn. This also applies to couplings involving the l19Sn nucleus, which serve as a sensitive tool in the discussion of structure and bonding. All 119Sn-NMR parameters of tin compounds largely concern measurements in the liquid state.

119Sn-NMR Parameters

/pdf/an-x-ray-photoelectron-spectroscopic-study-of-charge-1mlowgrxjw.pdf

An x-ray photoelectron spectroscopic study of charge distributions in tetracovalent compounds of nitrogen and phosphorus

Hydrogen-1 nuclear magnetic resonance study of unsymmetrical mercury compounds from bis(trimethylsilyl)mercury and diorganomercurials

Metal-silicon bonded compounds. 12. Crystal and molecular structure of hexameric trimethylsilyllithium, [LiSiMe3]6

Structure of hexameric trimethylsilyllithium, a folded chair

Oxygen 1s and carbon 1s binding energies have been measured for a wide variety of compounds containing the carbonyl group. It is concluded that most of the oxygen 1s ionizations include a rather large amount of electronic relaxation corresponding to ..pi.. electron donation from the groups bonded to the carbonyl groups. The data are analyzed in two different ways to derive ..pi..-donor relaxation energies. The two resulting sets of relaxation energies are in fair agreement, and either set may be used to estimate the relative ..pi..-donor abilities of substituents.

/pdf/pi-donor-relaxation-in-the-oxygen-1s-ionization-of-carbonyl-1nzcgypupw.pdf

Theodore F. Schaaf

Papers

An x-ray photoelectron spectroscopic study of charge distributions in tetracovalent compounds of nitrogen and phosphorus

Hydrogen-1 nuclear magnetic resonance study of unsymmetrical mercury compounds from bis(trimethylsilyl)mercury and diorganomercurials

Metal-silicon bonded compounds. 12. Crystal and molecular structure of hexameric trimethylsilyllithium, [LiSiMe3]6

Structure of hexameric trimethylsilyllithium, a folded chair

.pi.-Donor relaxation in the oxygen 1s ionization of carbonyl compounds