The electronic spectra of iron(II) complexes with α-picolinic acid and quinaldic acid

Král, M.

doi:10.1135/cccc19720046

Cited by 7 publications

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“…Kral reported three bands in the electronic spectrum of trans -[Fe(qn) 2 (H 2 O) 2 ] in aqueous acetate buffer at 440 nm (500 M −1 cm −1 , π→ e g ), 513 nm (500 M −1 cm −1 , t 2g →π *), and 800 nm (19 M −1 cm −1 , 5 T 2g → 5 E g ) 8,30. Guided by Kral's assignments, we would expect a ligand field band at 670 nm which we do not observe.…”

Section: Resultsmentioning

confidence: 99%

“…Many of the early studies on the determination of binding constants were carried out in water,6-8 and provide the foundation for the use of quinaldic acid in quantitative determinations of metal content via gravimetric analysis 9,10. Reaction of an iron(II) salt with either quinaldic acid or sodium quinaldate initially yields a red complex, [Fe(qn) 2 ], which precipitates out of aqueous solution and slowly converts to the dark blue-violet [Fe(qn) 2 (OH 2 ) 2 ] 11,12.…”

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Synthesis and Characterization of Iron(II) Quinaldate Complexes

et al. 2009

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Treatment of iron(II) chloride or iron(II) bromide with two equivalents of sodium quinaldate (qn = quinaldate or C 10 H 6 NO 2 − ) yields the coordinatively unsaturated mononuclear iron(II) quinaldate complexes Na [Fe II (qn) 2 Cl]·DMF and Na [Fe II (qn) 2 Br]·DMF, respectively. When a similar synthesis is carried out using iron(II) triflate, a solvent derived linear tri-iron(II) complex, [Fe II 3 (qn) 6 (DMF) 2 ], with two five-coordinate iron(II) centers and a single six-coordinate iron(II) center is obtained. Each of these species has been characterized using X-ray diffraction. The vibrational features of these complexes are consistent with the observed solid state structures. Each of these compounds exhibits an iron(II)-to-quinaldate(π*) charge-transfer band between 520-550 nm. These metal-to-ligand charge-transfer bands are sensitive to substitution of the quinaldates as well as alteration of the first coordination sphere ligands. However, the 1 H NMR spectra of these paramagnetic high-spin iron(II) complexes are not consistent with retention of the solid state structures in DMF solution. The chemical shifts, longitudinal relaxation times (T 1 ), relative integrations, and substitution of the quinaldate ligands provide a means to fully assign the 1 H NMR spectra of the paramagnetic materials. These spectra are consistent with coordination equilibria between five-and six-coordinate species in DMF solution. Electrochemical studies are reported to place these oxygen-sensitive compounds in a broader context with other iron(II) compounds. Iron complexes of bidentate quinoline-2-carboxylate derived ligands are germane to metabolic pathways, environmental remediation, as well as to catalytic applications.In the central nervous system, the majority of tryptophan catabolism occurs via the kynurenine pathway.1 Several of the quinoline and pyridine carboxylic acid metabolites formed are important signaling agents in neuronal pathways which are vital to the onset of certain diseases. For instance, kynurenic acid (4-hydroxyquinoline-2-carboxylic acid) plays a role in glutamate signaling in the brain and is found at elevated levels in people with schizophrenia.2 Increases in iron concentrations and picolinic acid have been observed in Alzheimer's disease.3 , 4 The number of quinoline-2-carboxylic acids found in this pathway and their involvement in brain tumor nueropathology led us to examine the iron(II) coordination chemistry of these metabolites.Since the initial recognition that quinaldic acid (quinoline-2-carboxylic acid, Hqn) can form complexes with iron(II), 5 the coordination chemistry of quinaldate with iron(II) has received a great deal of attention. Many of the early studies on the determination of binding constants were carried out in water,6 -8 and provide the foundation for the use of quinaldic acid in quantitative determinations of metal content via gravimetric analysis.9 , 10 Reaction of an iron (II) salt with either quinaldic acid or sodium quinaldate initially yields a red complex, [Fe (qn...

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%