New lipophilic 3-hydroxy-4-pyridinonate iron(iii) complexes: synthesis and EXAFS structural characterisation

Abstract

New tris-iron(III) chelates of 3-hydroxy-4-pyridinone ligands derived from maltol (3-hydroxy-2-methyl-4-pyrone) or ethylmaltol (2-ethyl-3-hydroxy-4-pyrone), including a variety of N-aryl (phenyl, 4'-tolyl, 4'-(n-butyl)phenyl, 4'-(n-hexyl)phenyl) and N-benzyl (4'-methylbenzyl, 4'-fluorobenzyl and 4'-(trifluoromethyl)benzylamine) substituents on the nitrogen atom of the pyridinone ring, have been prepared. Characterization by C,H,N elemental analysis and thermogravimetric measurements indicates that most of the complexes are obtained as hydrates of general formula ML3.xH2O. Structural characterization of these difficult to crystallize lipophilic complexes has been achieved by EXAFS spectroscopy. Solutions of iron(III) complexes of maltol, ethylmaltol, 1,2-dimethyl-3-hydroxy-4-pyridinone and 1-phenyl-2-methyl-3-hydroxy-4-pyridinone in methanol-water mixtures were also examined by EXAFS. Distances from the central atom to ligand atoms, within 6 A of the metal, have been determined in the solid and solution samples and the results show that the structure observed in the powder is maintained in solution. The local structure around the metal centre, bond distances and bond angles, does not change significantly with variable lipophilicity, thus indicating that ligands may be tailored according to specific needs without altering their chelation properties. EXAFS data analysis for this set of tris-iron(III) compounds illustrates the important contribution of both intra-ligand and inter-ligand multiple scattering pathways through the metal centre to a peak observed in the FT spectrum at twice the metal ligand distance (approximately 4 A). The present results demonstrate that EXAFS features at twice the metal-ligand distance are valuable in the assignment of molecular geometry and that location of hydration water molecules, by EXAFS analysis, is limited by the geometry of the complexes, in particular for those in which ligands containing phenyl rings are present.

Novel 3-hydroxy-4-pyridinonato oxidovanadium(IV) complexes to investigate structure/activity relationships

“…The vanadium-oxygen bond lengths do not vary significantly between the various pyridinone complexes, thus showing that the local structure around the metal centre is not appreciably modified by changing the substituents on the ring nitrogen atom. An identical conclusion was obtained from an EXAFS study of a group of iron(III) complexes of similar 3-hydroxy-4-pyridinones [20] and both analyses corroborate the fact that the hidrophilic/lipophilic balance of the 3-hydroxy-4-pyridinone complexes can be tuned without significantly altering the local structure around the metal centre.…”

Ruthenium complexes of 3-hydroxy-4-pyranones and of 3-hydroxy-4-pyridinones

“…The EXAFS results for Ru III (etmalt) 3 are consistent with its being anhydrous, as indicated by thermogravimetric and CH analyses. The contrast between hydrated Ru III (dmpp) 3 and anhydrous Ru III (etmalt) 3 conforms to the generally observed pattern of most metal(III) complexes of 3-hydroxy-4-pyranonates being anhydrous but those of 3-hydroxy-4-pyridinonate ligands having waters of crystallisation [29]. Our results again demonstrate the usefulness of EXAFS methods in the establishment of local structure in compounds for which single crystal X-ray diffraction studies cannot be performed, though they are not sufficiently detailed and precise to distinguish between fac and mer geometry nor to define secondary hydration.…”

“…Ruthenium-oxygen distances to the nearer donor oxygen of these bidentate ligands are, unsurprisingly, a little shorter to ruthenium(III) than to ruthenium(II), but distances to the further of the donor oxygens of each ligand are essentially the same for the two oxidation states. The ruthenium hydroxypyranone and hydroxypyridinone complexes have, as expected, similar structures to the equivalent iron complexes [28,29]. Ruthenium-oxygen distances are compared with their iron-oxygen equivalents in Table 4; the former are only marginally greater.…”

“…Data analysis was performed using the EXAFS suite of programs [27]. The methodology developed and used for the multiple scattering analysis of iron, ruthenium, gallium, gadolinium and dysprosium complexes of this family of ligands, as anhydrous materials, as hydrates, and in aqueous solution is fully described elsewhere [28,29]. Tris(pentane-2,4-dionato)-ruthenium(III), Ru(pd) 3 …”

3-Hidroksipiridin-4-oni (I. dio): Priprava i kelirajući učinak

“…Zanimljivo istraživanje u tom kontekstu objavili su Schlindwein i sur. 35 Pripravljeni su, izolirani i okarakterizirani kompleksi Fe(III) : 3,4-HP = 1 : 3 u čvrstom stanju i u otopini za nekoliko različitih N-aril supstituiranih 3,4-HP derivata. Trodimenzijske strukture kompleksa određene su proširenom finostrukturnom spektroskopijom rendgenske apsorpcije (krat.…”