Furfuraldenevalinate system: Solution chemistry of denticity reduction, gas and solid phase complexing behavior

Denticity reduction of Schiff base of 2 furfural (fural) and l-valine(val) in the presence of Co(II), Ni(II), Cu(II) and Zn(II) ions is investigated. The bidentate fural or val present in the metal coordination sphere interacts with the incoming ligand and forms a tridentate Schiff base furfuraldenevalinate of denticity three. This reduction in the denticity is due to entropy effect and that leads to the fusion of two independent rings, a strong interligand interaction. The Schiff base species identified are MAB, M(AB)B and M(AB)2 [AB-Schiff base; A-fural; B-val; M-Co(II), Ni(II) and Zn(II)]. Cu(II) forms only MAB. The Schiff base species are formed around the neutral pH. The gas phase studies are carried out through ab initio HF/6-31G⁎ and MP2/6-31G⁎ methods. The Schiff base ligand AB is tridentate and it binds through furan and carboxylato oxygens and imino nitrogen. The binding relationship is carboxylato oxygens > imino nitrogen > furan oxygen. The order of binding in solution phase is Co(II) < Ni(II) < Cu(II) > Zn(II). The solid state study also confirms the above results.