Amino-modified silicate xerogels complexed with Cu(II) as catalyst precursors. Coordination state and thermal decomposition

The sol-gel process is a useful method for preparing two series of organica lly and co-ordinately modified xerogels of the types [CuNn].N-5-n . 5xSiO(4 /2) (n < 4) and [Cu(N-N)(n)]. (N-N)(2-n). 2x SiO4/2(n less than or equal to 2), where N = NH2(CH2)(3) SiO3/2, N-N = NH2(CH2)(2)NH . (CH2)(3)SiO3/2 and x = [SiO4/2]/[N] or [SiO4/2]/[N-N]. The amino groups in the materials are coordinately active and participate partly in the coordination sphere of Cu (II) ions. The composition of the coordination sphere can be varied with th e SiO4/2 content and also as a result of the thermal decomposition of the o rganic residues at higher temperatures. Because the xerogel materials are considered to be catalyst precursors, thi s study is focused on their coordination and thermal properties. The prepar ed xerogels, such as silica, aminated silicates with N and N-N, as well as those entities complexed with Cu(II), were characterised by FT-IR spectrosc opy. During gelation and thermal decomposition the materials were analysed by electron paramagnetic resonance (EPR) spectroscopy. The xerogels were ad ditionally studied by UV-Vis absorption spectroscopy. The gaseous products of the thermal decomposition of these materials in an Ar atmosphere were in vestigated by the use of FT-IR spectroscopy coupled with TG and DTG thermal analysis. These data were complemented by temperature-programmed decomposi tion (TPDec) in a 2% O-2 + 98% Ar stream coupled with quadrupole mass spect roscopy.