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S.M. Thomas, J.A. Bertrand, M.L. Occelli, F. Huggins, S.A.C. Gould. 1999. Microporous montmorillonites expanded with alumina clusters and M[mu-OH)Cu(mu-OCH2CH2NEt2)] (6)(ClO4)(3), (M = Al, Ga, and Fe), or Cr[(mu-OCH3)(mu-OCH2CH2NEt2)CUCl](3) complexes. Inorganic Chemistry 38(9): 2098-2105. Full Article

Expanded clays bipillared with [Al13O4(OH)24(H2O)12]7+ ions and with hexameric Cu complexes such as M[(-OH)Cu(-OCH2CH2NEt2)]6(ClO4)3, or with M[(-OH)Cu(-OCH2CH2NEt2)]6(PF6)3 where M = Fe, Al, Ga, form microporous materials whose stability and microporosity depend mainly on the identity of the hexamer central metal atom. In fact, a general decrease in thermal stability, interlamellar heights, surface areas, and pore volumes was noted when, in the (Cu,M) hexamer, M changed from gallium to aluminum to iron. Mossbauer results have indicated that only Fe3+ in octahedral coordination is present in the iron-containing bi-PILC samples (bi-PILC = bipillared interlayered clays). It is believed that metals such as Fe3+ and Cu2+ can interact with the interlamellar Keggin ions thereby decreasing the stability of the alumina pillars. In contrast, the intermediate Al13-PILC structure is least affected when the more stable Cr complex is used. Bi-PILC materials containing 2.7-3.4% Cr stable to 500 C have been obtained. The low polarity of the chosen solvent (acetonitrile) appears to inhibit the back-exchange of the intermediate PILC's Keggin ions with the hexameric Cu complexes. Elemental analysis together with XRD results suggests that the primary intercalation pathway was diffusion or ion exchange when Cr[(-OCH3)(-OCH2CH2NEt2)CuCl]3 or M[(-OH)Cu(-OCH2CH2NEt2)]6(ClO4)3, respectively, was used. In all preparations, bi-PILC were produced containing complexes that suffered ligand losses during the synthesis reaction. Molecular scale AFM images have shown that these complexes can be found also outside the clay interlamellar space.

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