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Free keywords:
rare earth metals; aluminides; iodide; intermetallic compounds; cluster compounds
Abstract:
Reacting pieces of La, LaI3 and Al filings (molar ratio 22 : 8 : 15) at
800 degrees C-825 degrees C results in La24Al12I21 (70% yield) together
with La10Al5I8 (10% yield), besides known La3Al2I2 and La2Al2I. Both
new compounds form golden coloured needles. La10Al5I8 is brittle,
whereas La24Al12I21 is shaped as hair-like easily deformable bundles.
Both are monoclinic, space group C2/m, La24Al12I21 with a = 35.753(7)
angstrom, b = 4.327(1) angstrom, c = 27.442(6) angstrom, beta =
116.62(3)degrees and La10Al5I8 with a = 19.649(1) angstrom, b =
4.296(1) angstrom, c = 18.0290(1) angstrom and beta = 96.67(3)degrees.
The La atoms form trigonal prisms condensed into double chains along
[010]. The La prisms are centered by Al atoms which form Al-6 rings
connected into chains. The La-Al strands are surrounded by I atoms in
La24Al12I21, whereas in La10Al5I8 they are connected to form corrugated
sheets separated by close packed layers of I atoms together with Al
atoms. The octahedral voids around the Al atoms are occupied by La
atoms, and such La6Al clusters are connected via opposite edges to
octahedra chains along [010].
