Electrochemical and Spectroscopic Behaviour of Bis(2-mercaptopyridine-N-oxide)oxovanadium(IV)

Abstract

The complex [VO(MPO) 2 ] (MPO ϭ deprotonated 2-mercaptopyridine N-oxide) was synthesized and characterized by IR spectroscopy. Its electrochemical behaviour was investigated by cyclic voltammetry in different organic solvents. The V IV /V V and V IV / V III couples could be identified. The nature of the electroactive species is strongly dependent on the solvent. The results are discussed in terms of a reaction mechanism describing the character- Elektrochemisches und spektroskopisches Verhalten von Bis(2-mercaptopyridin-N-oxid)oxovanadium(IV)Inhaltsübersicht. Der Komplex [VO(MPO) 2 ] (MPO ϭ deprotoniertes 2-mercapto-pyridin N-oxid) wurde dargestellt und IR-spektroskopisch charakterisiert. Sein elektrochemisches Verhalten wurde durch cyclische Voltammetrie in verschiedenen organischen Lö-sungsmitteln untersucht. Die Redoxpaare V IV /V V und V IV /V III wurden identifiziert. Die Natur der elektroaktiven Spezies erwies eine starke Abhängigkeit von den Lösungsmitteln. Die Ergebnisse

A journey into the electrochemistry of vanadium compounds

“…An example of oxido-vanadium(IV) complex with S-O bidentate ligand was reported [31]. The anion from-2-sulfanylpyridine-Noxide (mpo) gave the complex VO(mpo) 2 , that was investigated in different solvents.…”

“…A very simple tridentate O-N-O ligand was pyridine-2,6-dicarboxylate (dipic), that, together with phenanthroline and bipyridine, was used to prepare oxido-V(IV) homo-and heterochelates complexes [51]. Electrochemical data are reported in Table 1 (entries [30][31][32] and indicate that the differences between the V(IV) → V(III) and V(IV) → V(V) potentials of the three compounds are quite small. Such small differences, in line with the spectral and magnetic moment data, were attributed to the presence of the same principal ligand, dipic, in the same disposition of its donor points in all the three complexes, with a consequent structural similarity.…”

“…Tridentate bisphenol ligands containing S, Se or P yielded non-oxido V(IV) complexes [115], with electrochemical results that suggest metal-centered oxidations to V(V) ( Table 3, entries [29][30][31][32]. Other tridentate ligand were sulfur based phosphanes [116].…”

Ligand influence on the electrochemical behavior of some copper(II) thiosemicarbazone complexes

“…The irreversibility of this couple was also confirmed from the linear dependence of the ½Cu II ðHSPTÞðOAcÞðH 2 OÞ 2 Ð ½Cu III (SPT)(OAc)ðH 2 OÞ 2 þ H þ e À ½Cu II (HSPT)(OAc)ðH 2 OÞ 2 þ H þ e À Ð ½Cu I ðH 2 SPT)(OAc)ðH 2 OÞ 2 cathodic peak potential, E p,c with log v [15] ( Figure 4B). The number of electrons involved in the reduction process (n) and the corresponding charge transfer coefficient (a) can be determined from the slope of this line and by employing the equation [16]: E p,c ) E p,c /2 ¼ 1.857 (RT/anF) where E p,c /2 is the cathodic peak potential at half height, R is the gas constant, T is the absolute temperature (Kelvin) and F is the Faraday. Assuming n ¼ 1, an a value (0.62) is obtained which is in the expected range for a single one-electron transfer step [14].…”

“…Similar features were observed for the same couples of Cu(II) complexes with HAET and HApCIPT. Moreover, the i p,a /v 1/2 ratio remains approximately constant along the whole range of the sweep rate indicating that a coupled chemical reaction takes place after the charge transfer process and characteristics for the ECE (electrochemical reaction coupled between two charge processes) mechanism [16].…”