Spin-pairing energy, effect

Using experimental values for these quantities, /H = 313.6 kcal/mol, while Ah = 17.4 kcal/mol the difference is 296 kcal/mol. As we let the two H fragments approach each other, the HL-structure will be stabilized by the spin-pairing energy, while the ionic structures will go down by virtue of electrostatic interactions. We may assume that the two effects roughly cancel out, so that at the equilibrium distance the gap is still significant, 200 kcal/ mol or more. 

Electron Configurations, Spin-pairing Energy and Nephelauxetic Effect. .. 150... 

As reviewed by Fidelis and Mioduski57) the formation constant K of a complex with a given" ligand (or the distribution coefficient for extraction in another solvent, or an ion-exchange resin) shows a ratio (in the case of two consecutive lanthanides) which provides perceptible variations (from a constant) not only at the half-filled shell (q = 7) Gd(III) but also at the plateaux q = 3 and 4, as well as 10 and 11. These quarter-shell effects can be rationalized 217,218) by the refined spin-pairing energy theory. If D of Eq. (3) is decreased 1 % (65 cm 1) by the nephelauxetic effect in a... 

Poli R. Molybdenum open-shell organometallics. Spin state changes and pairing energy effects. Ace Chem Res 1997 30(12) 494-501. 

It is probably useful to view the stability constants and the associated thermodynamic parameters in terms of spin-pairing energy or the double-double effect. In the case of... 

Cr(C6Hii)4 is tetrahedral and a triplet however, square-planar discriminating factor. Another factor at work in these molecules is the spin pairing energies. As indicated previously, 3d valence orbitals are considerably more contracted that 4d and 5d thus the Coulomb repulsion integrals are much larger for first-row transition metal complexes and high-spin states are more favored than is the case for second and third row complexes. 

In Eq. (2), the wave-number runcorr of the first intense Laporte-allowed) electron transfer band is directly inserted, whereas fcorr in Eq. (1) has been corrected for spin-pairing energy (and in the case of f-group complexes, also for other effects of interelectronic repulsion and for the first-order relativistic effect usually called spin-orbit coupling ). These relatively minor corrections (usually below 8 kK) are not of great importance for the present review because they vanish for central atoms having no d-electrons in the groundstate, and hence, Xopt(M) and i< uncorr(M) coincide. 

Ligand substitution brings primary dispositions for spin crossover behaviour. The dominant effect is the balance of the spin pairing energy and the crystal field splitting energy A. For instance, the spin properties of some [Fe(phen)2X2]-type complexes are presented in Table 9.8. 

Fig. 3. The ionization energy of the 4f shell in oxides (empty cirdes), fluorides (squares) and other compounds (filled circles) of lanthanides, hafnium and tantalum. The effects of spin-pairing energy are compared with values of I derived from the calculated uncorrected optical electronegativities (116) for M(IV) and given as full curves appropriate for the ionization of M III). The dashed lines connect the iso-electronic 4f and 4f systems with differing oxidation state.

In Eq. (35), A cannot be directly determined by experiment, but D is the effective spin-pairing energy (for a shell with / = 2, it is... 

Molybden Open-Shell Organometallics Spin State Changes and Pairing Energy Effects, Acc. Chem. Res. 30,494, 1997 /. Organomet. Chem. 689,4291, 2004 ... 

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