Spin-admixed

An interesting example of a spin-admixed nonheme iron(lll) complex with S - (3/2, 5/2) ground state is the organometallic anion [Fe CeCls) which has four pentachloro phenyl ligands in tetrahedrally distorted planar symmetry [122]. 

An intermediate spin state (a quartet 4A2) similarly is feasible for five-coordinate iron(III) though, as pointed out by Kahn [118], the situation may be more complex. If the states are close in energy then they can interact through spin-orbit coupling to give a so-called spin-admixed ground state. 

Spin-admixed Fe(IIl)-P and high spin-low spin equilibria... 

Spin admixed case, anisotropic [elongated tetragonal bipyramid of Fe(III), S = 5/2]... 

Table 27 Formulae for the spin admixed states of d5 configuration...

Fig. 67 Modeling of the spin-admixed system 6Aig - 4A2g. Left Energy levels in the zero field. Centre components of the product function for Az/hc = 500 cur1, /he = 460 cm-1, gx=gz = 2.0. Right effect of the energy gap to the effective magnetic moment...

At the edge of the intermediate-field scale the high-spin and low-spin patterns strongly interfere, and the appropriate model should take into account spin-admixed states (this is instantaneously covered by the calculation in the complete d7 basis of 120 functions). 

The six-coordinate species is spin-admixed (S = 3/2,5/2) while the predominantly five-coordinate species (1-OH) is high spin (S = 5/2). The spin states have significance, it will be shown in interpreting some of the kinetics results. Reversible binding of NO to 1-H20 leads to formation of the linearly bonded diamagnetic porphyrin nitrosyl, (TMPS)Fen(NO + )(H20), (1-NO). The product of reaction of 1-OH with NO has a noticeably different UV/visible spectrum from that of 1-NO, and this was ascribed to the species (TMPS)Fen(NO + )(OH). 

Figure 2 Possible oxidation and spin states of iron porphyrins and the d orbital configurations expected in each case. AU of these states (excluding high-spin d, which is not included in the figure) have been observed for iron porphyrins, and are discussed in this article. In addition, the spin-admixed 5 = 3/2,5/2 state of Fe " and the alternative orbital configuration for low-spin Fe , with dxy higher in energy than dxi,dyz are also discussed...

The highly saddled octaethytetraphenylporphyrinato-iron(III) chloride complex has been shown to be spin-admixed, with largely S = 5/2 but with some S = 3/2 character. in comparison, both tetraazaporphyrin ... 

A trichnic crystalline form of [TPPFe0S02CF3] has been reported to have two crystaUographically and magnetically distinct crystal lattice sites, one of which (1) is unique in that its structure is temperature dependent, whereas the second spin-admixed site (2) has a structure that is essentially independent... 

OTHER INTERACTIONS IN MONONUCLEAR SYSTEMS 8.6.1 Spin-admixed states... 

Fig. 8.33. Energy levels of a spin-admixed system 6At —4A2 in the zero field.

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