Room-temperature single-crystal X-ray structure determinations are known for a
number of ‘maximally hydrated" nitrates of, in particular, the
lighter lanthanoid elements; in all cases, all nitrates coordinate as
O,O′-bidentate ligands so
that the series may be represented at the outset as
Ln(O2NO)3.x
H2O. Two distinct triclinic P 1
hexahydrate phases of similar cell dimensions are recognized, the most
distinctive distinguishing feature being that in the La, Ce phase the
11-coordinate Ln is surrounded by three
O,O′-bidentate nitrate and
five O-unidentate water molecule ligands; the domain of
the other, with four coordinated water molecules, extends from Ln = Pr
to Ln = Dy (inclusive of Y). At local ambience, we have crystallized
heavier members of the series as pentahydrates, isomorphous with the
previously characterized Ln = Eu example, also containing a molecule of
the form
[Ln(O2NO)3(OH2)4]
(with a molecule of water of crystallization), but a different stereoisomer to
that found in the Ln = Pr(-)Dy array. Structure determinations are
recorded for Ln = Dy, Er, Yb, conventional R on
|F| 0·042, 0·034,
0·029 for No = 3858,
3980, 3935 independent ‘observed’ (I >
3σ(I)) diffractometer reflections. For Ln =
Lu a new tetrahydrate phase is described, monoclinic
P21/n, a
7·379(7), b 10·364(5),
c 14·26(1) Å, β 96·09(7)°,
Z = 4, R 0·048 for
No 2324, together with a new
triclinic P 1 trihydrate, a
12·591(4), b 12·144(3),
c 7·355(2) Å, α 80·22(2),
β 77·68(3), γ 62·30(2)°, Z
= 4, R 0·051 for
No 4552. In both of the latter, Lu
is nine-coordinate, with three bidentate nitrate groups and three coordinated
water molecules; remarkably, the two independent molecules of the asymmetric
unit in the triclinic phase are distinct isomers, one having the water
molecules fac, derivative of the 10-coordinate array of
the Pr(-)Yb series with quasi-3 symmetry, while the
other, like that in the monoclinic phase, is mer.
Location of the energy levels of the rare-earth ions in BaF2 and CdF2