Tris ligands, complexes

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). 

Partition coefficients have been measured for tris-maltolatoiron(III) and tris-ligand complexes derived from a range of A-substituted 3-hydroxy-4-pyridinones, particularly (251) with R and R variously Me, Et, pj 1325,1326 j- nge of complexes with alkyl (up to A-butyl) or... 

Tris(ligand) complexes involving ligand (41), or derivatives thereof, have been synthesized and characterized. Appending electron-releasing Ph or cyclic alkyl groups to the ligand leads to a blue... 

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. ... 

Calculations shown in Figs. 2-5 were made assuming only mono-ligand complexes with stable cations. Di- and tri-ligand complexes have been observed using spectroscopy techniques (Caminiti et al. 1984 Bilinski et al. 1986 Palmer and Drummond 1988) and have been interpreted from ex-... 

Fig. 7. Stability of aluminum complexes as a function of dissolved aluminum concentration (A) and oxalic acid concentration (B). Mono-ligand species are stable at aluminum concentrations of less than 1.3mgkg at an oxalic acid concentration of 9 mg kg" (A). Di- and tri-ligand complexes are only stable if the oxalic acid concentration exceeds about SOmgkg" and the aluminum concentration is 260mgkg" (B). (After Bilinski et al. 1986)...

In both, the cadmium(II) S-methyl-cysteine and methionine systems, mono-, bis-, and tris(ligand) complexes are formed corresponding to the six-coordinated octahedral geometry of cadmium(II). Although the corresponding zinc(ll) complexes... 

Many reports have shown that coordination compounds with chelating ligands are thermodynamically more stable than those with closely related ligands than do not chelate.lb For example, the tris(ligand) complex of nickel(II) with ethylenediamine is thermodynamically more stable than the hexa(ligand) complex formed with methylamine. Scheme 1.1. 

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