Room-temperature single-crystal X-ray studies carried out on trivalent rare
earth sulfate hydrates,
Ln2(SO4)3.xH2O,
crystallized at local ambience suggest the following arrays to be prevalent.
For Ln = La, the nonahydrate is found, hexagonal
P 63/m,
with conventional R on
|F| 0·023 for
No 1159 ‘observed’
(I >3σ(I)) diffractometer
reflections (redetermination). Although for Ln = Ce a similar structure
has been previously recorded, we have obtained that adduct as the monoclinic
C 2/c, Z
= 4, octahydrate, a phase also found for Ln = Lu and diverse
representative intermediate lanthanoids: a ≈
13·6, b ≈ 6·6, c
≈ 18·2 Å, β ≈ 102°; for Ln = Ce
(redetermination), Dy, Yb (redetermination), Lu, R was
0·022, 0·035, 0·031, 0·024 for
No 3279, 2127, 3008, 3325
respectively. The structures of two lower hydrates adventitiously obtained are
also recorded: the pentahydrate for Ln = Ce, monoclinic
C 2/c, a
15·741(3), b 9·632(3),
c 10·358(3) Å, β 119·72(2)°,
Z = 4, R 0·030 for
No 3372 (a redetermination), and
the trihydrate for Ln = Lu, orthorhombic
Cmc21, a
13·527(5), b 18·415(5),
c 9·242(7) Å, Z
= 8, R 0·040 for
No 1743. All structures are
infinite polymeric arrays, the lanthanoid atoms being bridged by sulfate ions.
Studies are also recorded for the ammonium/trivalent rare earth double
sulfate tetrahydrate salts,
(NH4)Ln(SO4)2.4H2O,
for the (hitherto) extremal members Ln = La, Tb, which are isomorphous
with the previously studied Ln = Sm monoclinic P
21/c, Z = 4 array,
a ≈ 6·6, b ≈ 19,
c ≈ 8·8 Å, β 97°;
R 0·035, 0·037 for
No 3631, 3337. The array is a
two-dimensional polymer, parallel to the ac plane.