Core electrons high-spin complexes

Costas et al. have reported spectroscopic evidence for an Fe Fe complex that can be considered a structural model for the putative Fe Fe (/x-0)2 core of methane monooxygenase intermediate The synthetic complex was prepared at —80 °C in CH2CI2 by decay of a mononuclear low-spin Fe peroxo precursor. The Mossbauer spectra showed that all iron in the sample is intermediate spin (5 = 1) Fe, but the data were compatible with either a mononuclear site or a weakly coupled ( J <5cm ) symmetric dimer. Combination of the Mossbauer technique with resonance Raman and EXAFS spectroscopies provided evidence for a bis-/x-oxo bridged diiron(IV) complex. The complex of Costas et al however, is not an electronic model for intermediate Q, as the latter contains high-spin Fe sites. 

The most obvious criterion would be the use of suitable MO calculations and, in reality, in response to the accumulation of new experimental information, the theoretical investigation of f-element complexes has become a very active area. Highly sophisticated theoretical calculations certainly do not represent a routine exercise. Ab initio calculations [9] require a tremendous computational effort and, therefore approximation to introduce effective relativistic core potentials and spin-orbit interactions [10] would be highly desirable. Sophisticated calculations which treat uniformly all electrons are limited to the Xa model [11] applications of quasi-relativistic corrections [12] have been reported and errors associated with non-relativistic procedures analyzed [13]. Nevertheless, applications are still limited, although with a few exceptions, to highly symmetrical molecules. 

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