| Abstract
| - The speciation of cobalt ethanediamine (en) complexes [Co(en)x(H2O)6-2x]2+ (x = 1, 2, and 3) in aqueoussolution changes when a silica support is introduced into the solution ((en/Co = 1), (en/Co = 2), and (en/Co= 3) preparations). The pH-buffering effect of the silica support causes speciation shifts, especially for theprecursor complex [Co(en)2(H2O)2]2+ in solution, which transform into [Co(en)1(H2O)4]2+, as the main species.Once adsorbed on silica and after drying (25 and 100 °C), UV−visible and XAS characterization show that,for the (en/Co = 1) and (en/Co = 2) preparations, the Co(en)1 complexes form dimers bonded to silicathrough one silanol group per Co ([(SiO)(en)(H2O)2CoII]2(μ-O)). For the (en/Co = 3) preparation, the adsorbedCo(II) complexes are monomeric and contain two ethanediamine ligands. Upon drying at 100 °C, residualwater molecules in the coordination sphere of adsorbed Co(II) complexes may be lost reversibly, causing theestablishment of an octahedral/tetrahedral coordination equilibrium. Upon calcination at 450 °C, theethanediamine ligands are eliminated. The monomeric complex in (en/Co = 3) probably becomes graftedonto silica through two bonds ((SiO)2CoII(OH2)4), while the dimer initially formed in (en/Co = 1) and (en/Co= 2) mostly gives rise to species reminiscent of Co silicate germs.
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