Synthesis and spectroscopic behavior of some oxovanadium(IV) and oxovanadium(V) complexes of 7-iodo-8-hydroxyquinoline-5-sulfonate

Journal of the Brazilian Chemical Society

Baran, Enrique J.¹  González-Baró, Ana C.¹  Universidad Nacional de La Plata, La Plata, Argentina¹ 

关键词: oxovanadium(V);    oxovanadium(IV);    IR spectra;    electronic spectra;    pre-resonance Raman spectra.;   

DOI  :  10.1590/S0103-50532001000200014

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

As part of a series of model studies related to vanadium biochemistry1, we have recently investigated the structural, spectroscopic, magnetic, electrochemical and thermal behavior of a number of oxovanadium complexes with halogenated derivatives of 8-hydroxyquinoline (oxine) as ligands2-6, which normally produce complexes containing VN2O2 environments. Coordination spheres with nitrogen and oxygen donors are found, for example, in the active site of vanadium-depending haloperoxidases and in other natural systems1. These studies have also been extended to other related ligands7,8 and in this paper we present results on the spectroscopic behavior of a series of oxovanadium(IV) and oxovanadium(V) complexes with 7-iodo-8-hydroxyquinoline-5-sulfonate as a ligand.Among the oxine derivatives used as analytical reagents, the 5-sulfonic acids have an important hydrophilic character conferring to its metal complexes an unusually high water solubility9. On the other hand, the 7-substituted-8- hydroxyquinoline-5-sulfonic acids, developed also as analytical reagents, present a higher selectivity at the expense of their sensitivity10. One of these reagents is the 7-iodo substituted acid, usually known as ferron (Figure 1), due to its excellent and almost specific capacity of coloration of the Fe(III) ion11. It appears as an interesting ligand for our model studies, as it coordinates the vanadium via the nitrogen of the heterocycle and via the phenolic oxygen atom, keeping the sulfonate group uncoordinated. This is the general behavior of oxine (QH) and some of its derivatives, which were previously studied12-20.    Even though it is present as the potassium salt, containing the -SO3-/K+ moiety, in the vanadium complexes described in this paper, we will maintain the nomenclature ferron for simplicity. It is well known that a black, water insoluble, complex of stoichiometry [Q2VO(OH)] is generated by reaction of vanadium(V) with 8-hydroxyquinoline (QH)12-14, which according to a suggestion of Giacomelli et al. may be considered as an inorganic analog of a carboxylic acid3,15. According to this proposal, species of the types [Q2VOO]- and [Q2VO(OR)] can be considered as salts and esters, respectively. Concerning the vanadium(V)/ferron system, the acid, the potassium salt and the methoxo complex have been briefly described in the literature, but have been scarcely characterized16. These three compounds, together with a vanadium(IV) complex of stoichiometry [VO(ferron)2], were prepared and spectroscopically characterized in this study.   ExperimentalSyntheses[VO(ferron)2].5H2O (1). This complex was obtained adapting procedures described in the literature for the preparation of complexes with other derivatives of oxine as ligands2,17. 2.00g (5.7 mmol) of 7-iodo-8-hydroxy- quinoline-5-sulfonic acid (Sigma) were dissolved in 50 cm3 of distilled water containing a few KOH platelets. To the resulting orange-red solution, 1.5 cm3 of a 50% VOCl2 solution (Carlo Erba) were added dropwise, under continuous stirring. A green solid precipitates immediately. The mixture was held in digestion over a water bath during 3 h and finally the product was filtered by suction through a fritted glass funnel, washed several times with water and dried in vacuum over P4O10. The elemental analysis agrees with the proposed stoichiometry (Found: C, 23.05; H, 2.1; N, 2.97; S, 7.03; V, 5.5. Calc. for C18H18O14N2 S2I2K2V: C, 23.14; H, 1.94; N, 3.00; S, 6.87; V, 5.45%).K[VO(ferron)2O].4H2O (2). This and the other oxovanadium (V) complexes were prepared following general procedures described in the literature16.1.54 g (4.4 mmol) of the sulfonic acid and 0.20 g (1 mmol) of V2O5 (Merck) were dissolved in 5 cm3 of a KOH (2 mol dm-3) solution, keeping the system over a boiling water bath, until a brownish colored solution is obtained. After cooling to room temperature, and addition of 40 cm3 of acetone, a yellow suspension was immediately obtained. The solid was separated by centrifugation and washed twice with 10 cm3 of acetone. After rapid evaporation of the remnant acetone in vacuum, the product was dried in an oven at 105o C, turning to a brownish-yellow coloration. The composition was confirmed by the analytical results (Found: C, 21.98; H, 1.67; N, 2.85; S, 6.60; V 5.3.Calc. for C18H16O14 N2S2I2K3 V: C, 22.25; H, 1.65; N, 2.88; S, 6.61; V, 5.25 %).[VO(ferron)2OH] (3). 0.15 g (0.15 mmol) of compound 2 were mixed with 2 cm3 of glacial acetic acid to form a paste to which 10 cm3 of acetone were immediately added. The obtained black suspension was centrifuged and the separated solid washed several times with acetone. The remnant acetone was eliminated in vacuum and the final drying was performed by warming the product during 30 min over a water bath. The composition was confirmed by chemical analysis (Found: C, 24.95; H, 1.12; N, 3.22; S, 7.40; V, 6.0. Calc. for C18H9O10N2 S2I2K2V: C, 25.11; H, 1.05; N, 3.25; S, 7.45; V, 5.92 %).[VO(ferron)2OCH3] (4). 0.15 g (0.17 mmol) of 3 were dissolved at room temperature, with stirring, in 12 cm3 of methanol. The undissolved solid was separated from the reddish solution by centrifugation. The methoxo complex was precipitated by addition of 30 cm3 of benzene to the solution, and separated by centrifugation. After several washings with benzene it was dried in vacuum and characterized by chemical analysis (Found: C, 26.00; H, 1.28; N, 3.24; S, 7.30; V, 5.9. Calc for C19 H11O10N2S2 I2 K2V: C, 26.08; H, 1.26; N, 3.20; S, 7.33; V, 5.82%). The potassium salt of the ligand, prepared for comparative purposes, was obtained by mixing hot aqueous solutions of the acid and KOH in a 1:1 molar ratio. The salt precipitated after cooling22.Spectroscopic measurementsThe infrared spectra were recorded with a Perkin Elmer 580 B spectrophotometer, using the KBr pellet technique. Raman spectra were obtained with a Jarrell-Ash 25-300 instrument equipped with a ITT-FW 130 photomultiplier. For the measurements, samples were dissolved in 1:1 DMF:H2O solutions and excited with different Ar+ and Kr+ laser lines within the absorption ranges of the electronic spectra. The power ranged between 30 and 60 mW and the spectral width was 5 cm-1. Excitation profiles were constructed with the relative line intensities, obtained by comparison of peak areas.Electronic absorption spectra of the ligand and the complexes, in different solvents, were measured on a Hewlett-Packard 8452 A diode-array spectrophotometer, using 10 mm quartz cells.  Results and DiscussionSyntheses of the complexesThe oxovanadium(IV) complex, [VO(ferron)2].5H2O (1), could be obtained for the first time, using a similar procedure as that employed for the synthesis of VO2+ complexes with other oxine derivatives2,17. The oxovanadium(V) compounds K[VO(ferron)2O].4H2O (2), [VO(ferron)2OH] (3), and [VO(ferron)2OCH3] (4) were obtained adapting methods described in the literature16.It is probable that in the

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