Iron tris ligand complex

Structures of l-hydroxy-2-pyridinonate and 3-hydroxy-2-p5rridino-nate complexes may be compared with those of the more extensively studied 3-hydroxy-4-pyridinonates through the published crystal structures of their tris-ligand iron(III) complexes. The iron(III) tris-ligand complex of l-n-butyl-3-hydroxy-2-pyridinone has fac geometry it crystallizes as a trihydrate 135). 

Treatment of the tris(dialkyldithiocarbamato)iron(III) complexes in benzene with a controlled amount of concentrated hydrohalic acid affords the black bis(ligand) complexes [FeX(S2CNR2)2] (X = Cl, Br or I).306 For X = Cl the complexes may also be prepared by irradiation of the tris-(ligand) complex in a halogenated solvent. This free radical reaction is believed to proceed via excited-state labilization of one ligand followed by attack of solvent.307 Analogous complexes of pseudohalide ions (X = NCO, NCS- or NCSe ) have been obtained from reaction of the parent tris complex with the appropriate Ag+ salt.380 Representative complexes of this class have been shown by X-ray diffraction methods to have square pyramidal structures (71) in which the sulfur atoms of the two bidentate ligands comprise the basal plane (Fe—S 2.228 2.30 A) with the halide ion in the apical position (Fe—Cl 2.26-2.28 A).309 310 In the cases examined the metal atom sits 0.6 A out of the mean S4 plane in the direction of the apical halide ion. 

Complexes with other Bidentate 1,4-Diimines. The thermodynamic stability of the five-membered iron(II) 1,4-diimine chelate ring in low-spin complexes is illustrated by the facile autoxidation of saturated amine complexes to the corresponding colored 1,4-diimine complexes. The first example of this oxidative dehydrogenation is shown in equation (14), and the more recently studied " reaction (15) is known to involve iron(III) species and radical intermediates. Interestingly, the complex [Fe(CN)4(HN=CHCH=NH)] can be obtained by oxidizing [Fe(CN)4(en)] , whereas the tris-ligand complex of this smallest diimine ligand has yet to be prepared. 

The tris-ligand complex of iron(II) and 3-hydroxyiminopentane-2,4-dione (isonitrosoacetylacetone) (35) is low-spin, but must be near the spin-crossover region since it is formed from its components on the stopped-flow timescale. ... 

Little meaningful physical data on these complexes has appeared yet. The study of their reactivity is complicated by the effects of the substituents on the cyclobutadiene ring and the other ligands present. Until more information is available on the properties of the recently prepared unsubstituted cyclobutadieneiron tricarbonyl (XVIII) 38) and similar molecules, it is hard to be certain which properties are due to the presence of a cyclobutadiene group. Thus while cyclobutadieneiron tricarbonyl (XVIII) is easily oxidized by ferric chloride in ethanol (as are other diene-iron tri-carbonyl complexes, albeit to different types of product), tetraphenyl-cyclobutadieneiron tricarbonyl (XIII) is very resistant to this reagent, and indeed to most others, presumably mainly due to the steric hindrance of the phenyls. 

The most stable iron(IV) species seem to be those containing dithiocarbamate or related ligands such as the low-spin cationic iron tris (dithiocarbamate) complex obtained by oxidation of the neutral iron(III) parent (the high-spin air-sensitive iron(II) anion is also available by reduction) [100]. 

The mixed thiazole-pyrazole system 25 (Dq(Ni2+)=1110 cm-1) yields a tris(ligand) iron(II) complex in which one of the ligand molecules is depro-tonated. For the complex perchlorate a complete and fairly abrupt transition occurs below room temperature but no associated hysteresis was observed [27]. 

Bis(2 -methoxyphenyl)-l,10-phenanthroline, bmpphen (2), forms a high-spin bis- but not a low-spin tris-ligand iron(II) complex due to interligand repulsion. ... 

Pyrrole units form part of the coordinating entities of Schiff base ligands derived from pyrrole 2-carboxaldehyde, for example in the iron(II) complex of the ligand derived from pyrrole 2-carboxaldehyde and trien, which is low-spin despite the feeble coordinating properties of the pyrrole—CH=N— units. The synthesis, structure, and spectroscopic and electrochemical properties of tris-ligand iron(III) complexes of phenyldipyrromethenate (dipyrrin, (129)), and its... 

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. 

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