A CYCLIC VOLTAMMETRIC STUDY OF MANGANO(II) UNDECATUNGSTOSILICATE - ANILLUSTRATIVE EXAMPLE OF THE REDUCTION, PROTONATION AND DISPROPORTIONATION PATHWAYS OF TRANSITION-METAL SUBSTITUTED HETEROPOLYTUNGSTATES IN AQUEOUS-SOLUTION
A. Muller et al., A CYCLIC VOLTAMMETRIC STUDY OF MANGANO(II) UNDECATUNGSTOSILICATE - ANILLUSTRATIVE EXAMPLE OF THE REDUCTION, PROTONATION AND DISPROPORTIONATION PATHWAYS OF TRANSITION-METAL SUBSTITUTED HETEROPOLYTUNGSTATES IN AQUEOUS-SOLUTION, Inorganica Chimica Acta, 257(2), 1997, pp. 231-239
Mangano(II) undecatungstosilicate [(H2O)MnSiW11O39](6-) was studied by
cyclic voltammetry in aqueous solution at various pH values. The pi-I
-dependent wave patterns are influenced by additional processes and we
re further investigated by variation of scan rates, substance concentr
ation and buffer concentration, focussing on the first 2-electron redu
ction. Polarographic data and results obtained from [(H2O)CoSiW11O39](
6-) and [(H2O)(2)Mn-4(PW9O34)](10-) were included for comparison. A su
itable pH range of 2.5-9 was determined from monitoring the decay of [
(H2O)MnSiW11O39](6-) by electronic spectroscopy over a period of sever
al weeks. Around pH 5, the cyclic voltammetric wave patterns appear mo
re distorted than at higher and lower pH values. Conditions were speci
fied under which the reoxidation scans exhibit two species with differ
ent degrees of protonation. The results were interpreted in terms of p
rotonation and successive disproportionation of reduced species and su
ggest that a complex network of reversible reaction pathways takes pla
ce during the initial reduction processes of [(H2O)MnSiW11O39](6-) and
related compounds in aqueous solution.