Garribba, Eugenio and Micera, Giovanni and Sanna, Daniele and Strinna Erre, Liliana (2000) The Cu(II)-2,2'-bipyridine system revisited. Inorganica Chimica Acta, Vol. 299 (2), p. 253-261. ISSN 0020-1693. Article.
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The system formed by Cu(II) and 2,2'-bipyridine (bpy) has been revisited by use of EPR and electronic absorption spectroscopies. The mono-chelated [Cu(bpy)]2+, bis-chelated trans-[Cu(bpy)2]2+ with pseudo-tetrahedral geometry due to the steric hindrance of the 3,3' hydrogen atoms and tris-chelated [Cu(bpy)3]2+ species exist in aqueous solution. In basic media hydrolysis yields [Cu(bpy)OH]+ and [Cu(bpy)(OH)2]. The dimer [Cu(bpy)(OH)]2 2+ is favoured by increasing metal ion concentration in the pH range 8-10. The EPR spectrum of the dimeric species shows well-resolved ΔM=1 and 2 features, and is different from that observed in the solid state. The zero-field splitting is consistent with a distance of ~3.4 Å between metallic centres. The behaviour of the complex system is in agreement with potentiometric data reported in the literature. In the EtOH-H2O mixture the bis-chelated complex adopts a five-coordinate cis structure exhibiting a rhombic EPR spectrum and, in basic solution, the [Cu(bpy)2(OH)]+ species is formed. The attribution of the solution species has been confirmed by the analysis of solid compounds, [Cu(bpy)SO4]•2H2O, [Cu(bpy)(H2O)2](NO3)2, [Cu(bpy)2OSO3•4H2O and [Cu(bpy)2ONO2]NO3•H2O, after dissolution.
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