Iron complexes hexadentate ligands

Fe(6-Mepy)3tren](PF6)2- Within the series of iron(II) complexes of the type [Fe(6-Mepy)3 (py) tren](PFg)2 containing the hexadentate ligand tris[4-(6-R)-2-pyridyl]-3-aza-3-butenyl]amine, R = H or CH3, the compounds with X = 1, 2 show a similar HS <- LS transition in solution as well as in the solid state [170]. In solution, spin-state conversion rates have been obtained as shown in Table 3. The complex with x = 0 is pure HS in solution, whereas in the solid state a gradual transition is observed extending over the range... 

Stability Constants for Iron(III) Complexes (Logio K-i for Hexadentate Ligands, Logio... 

A-Hydroxypyrimidinones, e.g., (249), and A-hydroxypyrazinones, e.g., (250), form stable tris-ligand iron(III) complexes, but these are of much lower stability than iron(III) complexes of hydroxypyridinones. Stability can, as one would expect, be increased greatly by going to analogous hexadentate ligands containing three A-hydroxypyrimidinone or A-hydroxypyrazinone units. 

A multiple-path mechanism has been elaborated for dissociation of the mono- and binuclear tris(hydroxamato)-iron(III) complexes with dihydroxamate ligands in aqueous solution. " Iron removal by edta from mono-, bi-, and trinuclear complexes with model desferrioxamine-related siderophores containing one, two, or three tris-hydroxamate units generally follows first-order kinetics though biphasic kinetics were reported for iron removal from one of the binuclear complexes. The kinetic results were interpreted in terms of discrete intrastrand ferrioxamine-type structures for the di-iron and tri-iron complexes of (288). " Reactivities for dissociation, by dissociative activation mechanisms, of a selection of bidentate and hexadentate hydroxamates have been compared with those of oxinates and salicylates. ... 

The stability of metal complex is also given by the number of chelate rings formed in the resultant ligand-metal complex. For example, desfer-rioxamine, the most widely used iron chelator, minimizes OH production by acting as a hexadentate ligand [Liu and Hider, 2002]. Unfortunately, there is not enough information on the denticity of polyphenols as metal chelators to assess the relevance of the stability of the flavonoid-metal complex formed. 

Wilson et al.37) have first reported on the sT2(Oh) 1 A Oj,) spin transition taking place in six-coordinate iron(II) complexes with the hexadentate ligand tris-[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine, where R is either H or CH3 (see Sect. 8.4). Three of these systems, viz. II, III, and IV of Sect. 8.4, show spin crossover in the solid state, and two of them, viz. II and III, also in solution, whereas IV remains fully high-spin and I fully low-spin. The pronounced differences in the magnetic behaviour between the four members of the [Fe(6-Mepy)n(py)m tren](PF6)2 series (see Sect. 

The high sensitivity of the g-values of low-spin iron(III) to structural variations and their large anisotropy imply that the prediction of the EPR spectra must be based on highly accurate structures12071. The MM-AOM method for low-spin iron(III) complexes was tested on a number of examples involving bi-, tri- and hexadentate ligands with amine and pyridyl donor sets (Table 10.8). 

Unlike the exclusively 6-coordinate iron(iii) siderophore complexes, higher coordination numbers are possible with plutonium the complex of Pu" with desferrioxamine E (DEE a hexadentate iron-binding siderophore ligand) has shown it to contain 9-coordinate [Pu(dfe)(H20)3]+ ions with a tricapped trigonal prismatic geometry (Figure 11.13). 

Table 9 Stability constants and redox potentials for iron(III) and iron(ll) complexes of hexadentate ligands...

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