The Cu(II)-2,2′-bipyridine system revisited

• Published in: Inorganica Chimica Acta 2000-03, Vol.299 (2), p.253-261
• Main Authors: Garribba, Eugenio, Micera, Giovanni, Sanna, Daniele, Strinna-Erre, Liliana
• Format: Article
• Language: English
• Subjects: Bipyridine complexes; Copper complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(99)00508-3

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 Δ M=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–H 2O 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)SO 4]·2H 2O, [Cu(bpy)(H 2O) 2](NO 3) 2, [Cu(bpy) 2OSO 3]·4H 2O and [Cu(bpy) 2ONO 2]NO 3·H 2O, after dissolution.