Preparation of oxalate by precipitation method with polyethylene glycol and formation process of the precipitate

Multicomponent oxalate consisted of Fe3+ and M2- (M=Ni, Cu, CO, Zn) was pre pared by heating the polyethylene glycol (PEG) solution of metal nitrate hy drate at 358 K for 3 h. The PEG-cation complex in the solution was oxidized by the nitrate ion so that the oxalate was obtained. The structure and the composition of the cations in the obtained oxalate depended on not only th e composition of the PEG solution but also the molecular weight of PEG. The crystallinity and the particle size of the oxalate increased with an incre ase of the molecular weight of PEG. The relation between the cation composi tion in the PEG solution and that in the obtained oxalate also depended on the molecular weight of PEG. The two models that describe the formation pro cess of the PEG-cation complex and the oxalate was examined. In the first m odel, it is assumed that the coordination of Fe3+ ions and that of M2+ occu rs independently. In the second model, it is assumed that the coordination of Fe3+ and that of M2+ occurs cooperatively. The relation between the cati on composition in the PEG solution and that of the obtained oxalate was der ived from these models. According to the comparison between the experimenta l result and the consequences derived from the models, it is shown that the coordination of M2+ to PEG always occurs near the site where the coordinat ion of Fe3+ occurred. The PEG-cation complex was formed under the cooperati ve process.