Nickel(II) and cerium(IV) ethyleneurea, ethylenethiourea and propyleneurea adducts

Abstract

The NiCl2 · 6eu, NiCl2 · 6etu, Ce(SO4)2 · 6pu and Ce(SO4)2 · 6etu adducts (eu = ethyleneurea, etu = ethylenethiourea and pu = propyleneurea) were prepared by a solid state procedure, and characterized by C, H and N elemental analysis, i.r. spectroscopy, thermogravimetry (t.g.) and differential scanning calorimetry (d.s.c.). The i.r. results show that eu and pu coordinate through oxygen, whereas etu coordinates through nitrogen. The NiCl2 · 6eu adduct is green, whereas the NiCl2 · 6etu adduct is yellow. This fact suggests that the Δo separation is larger for the latter adduct. On the other hand, both cerium adducts are white, suggesting that, for pu and etu cerium sulfate adducts, a ligand-to-metal charge-transfer promotes the reduction of CeIV to CeIII. The t.g. thermal stability sequences are: etu > pu > eu and Ni > Ce. Cerium adducts release the six ligand molecules in a single mass loss step, suggesting that all ligand molecules are in equivalent coordinative positions (same bond length and strength). On the other hand, nickel adducts exhibit three mass loss steps in the thermal degradation (release of ligand molecules) process. This suggests that, for these compounds, there are three distinct coordinative positions, with distinct bond lengths and strengths, probably due to the Jahn–Teller effect. All four adducts melt before the onset of thermal degradation, with etu adducts exhibiting the higher melting temperatures and melting enthalpies, as a consequence of stronger intermolecular forces.