Structure and spectroscopic characterization of the quaternary system: Copper(II), pyridine-2,6-dicarboxylate, 2,2′-bipyridyl and pyridine

Conclusion The x-ray structural results confirm what has been ascertained by thermodynamic and spectroscopic data in aqueous solution(7). It is evident that the addition of pyridine to the solution containing the mixed species Cu(bipy)(pydca)(H₂O)] leads to the substitution of a water molecule directly bound to copper(II) ion by a pyridine molecule. This experiment also demonstrated the presence of a water molecule in the equatorial plane of the complex.The subsequent diffractometric study on single crystals derived from the copper(II)/bipy/pydca system revealed the existence in the solid state of Cu₂(bipy)₂(pydca)₂] · 4H₂O. Thus the pydca dianion, instead of forming the statistically favoured mixed complex Cu(bipy)(pydca)], gives rise to crystals containing two different copper(II) environments: Cu(pydca)₂]^2– and Cu(bipy)₂]²⁺, linked by O-carboxylate bridges. The facility with which Cu(bipy)(pydca)(py)] can be obtained shows that the addition of pyridine prevents the formation of polynuclear species.