Treatment of gibbsite {γ-Al(OH)3} with the
lithium salts LiX {X = Cl, Br, NO3} in
water
leads to intercalation of both the cations and anions into the host
structure to give [LiAl2(OH)6]X·H2O {X = Cl, Br,
NO3}. Thermogravimetric analysis indicates that
these materials
can be readily dehydrated to give highly hydroscopic, crystalline
layered phases
[LiAl2(OH)6]X
{X = Cl, Br, NO3}. The structures of these
dehydrated phases have been determined by
synchrotron X-ray and neutron powder diffraction. The dehydrated
intercalates with {X =
Cl, Br} are isomorphous and crystallize in the
P63/mcm space group.
[LiAl2(OH)6]NO3
adopts
a similar structure but crystallizes in space group
P63/m due to disorder of the
intercalated
nitrate anions in the crystallographic ab plane. All
the intercalates consist of eclipsed Al(OH)3 layers stacked along the c-axis with the
halide or nitrate ions located at the cell edges
and midway between the Al(OH)3 layers. The
lithium ions have been located in the unfilled
octahedral sites within the Al(OH)3 layers. The
structure of the hydrated phase [LiAl2(OH)6]Cl·H2O has also been determined,
it adopts a similar structure with eclipsed
[LiAl2(OH)6]+ layers stacking along the
c-axis. However the intercalated Cl- ions
and water
molecules were found to be disordered over five sites located midway
between the Al(OH)3
layers.
The solid-state chelation of transition metal ions (Co(2+), Ni(2+), and Cu(2+)) from aqueous solutions into the lithium aluminum layered double hydroxide ([LiAl(2)(OH)(6)]Cl x 0.5H(2)O or LDH) which has been pre-intercalated with EDTA (ethylenediaminetetraacetate) ligand has been investigated. The intercalated metal cations form [M(edta)](2)(-) complexes between the LDH layers as indicated by elemental analysis, powder X-ray diffraction, and IR and UV-vis spectroscopies. If metal chloride or nitrate salts are used in the reaction with the LDH then co-intercalation of either the Cl(-) or NO(3)(-) anions is observed. In the case of metal acetate salts the cations intercalate without the accompanying anion. This can be explained by the different intercalation selectivity of the anions in relation to the LDH. In the latter case the introduction of the positive charge into LDH structure was compensated for by the release from the solid of the equivalent quantity of lithium and hydrogen cations. Time-resolved in-situ X-ray diffraction measurements have revealed that the chelation/intercalation reactions proceed very quickly. The rate of the reaction found for nickel acetate depends on concentration as approximately k[Ni(Ac)(2)](3).
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