C. R. Acad. Sci. Paris, t. 2, SCrie II c, p. 579-582,
1999
Oxygen in a box: an oxygen atom
surrounded
by a cube of 8 lithium
F. Albert COTTON*,
Lee M. DANIEL.& Carlos A. MURILLO,
atoms
Hong-G
ZHOU
Laboratory for Molecular Structure and Bonding, Department of Chemistry, P.O. Box 30012, Texas A&M
College Station, TX 77842-3012, USA
E-mail: cotton@tamu.edu; murillo@tamu.edu
University,
Abstract
-Although
molecular structures in which there is an oxygen atom surrounded by a tetrahedral or an
octahedral array of cations are familiar (though not common), no molecule has previously been reported in
which an oxygen atom is surrounded
by a cubic array of metal atoms. We describe here such a molecule,
(C,,H,,N,)GLi,O,
where CllHr3N3
is a bidentate, uninegative l&and. 0 1999 Academic des sciences /
Editions scientifiques et medicales Elsevier SAS.
crystal
structure
I lithium
compound
I oxide
ion
I cubic
coordination
Version
francake
abr6gCe
- Un oxygene encage : un atome d’oxyg&ne
entouk
par un cube de
8 atomes de lithium. Nous donnons ici un be1 exemple simple dun groupement L&d, qui consiste en un ion
02- sit& au centre d’un cube legerement distordu d’ions Li’. Un ligande anionique L-, de type u4q2, occupe
chacune des 6 faces de ce quasi cube. La structure moleculaire complete est donnee sur 1aJigure 1 ; une representation schematique (fg ure 2) souligne ses proprietes de symetrie. Si le ligande etait symetrique, avec des
atomes d’azote lies equivalents, la symetrie id&ale serait T,. Cependant, la nature non symetrique du ligande
abaisse celle-ci a S,. Ainsi, Li(1) et Li(8) sont equivalents et definissent un axe de symetrie d’ordre S, ; Li(2) et
Li(7) sont equivalents. Chacun des atomes Li(1) et Li(8) est lie a trois atomes d’azote N, alors que Li(2) et Li(7)
sont chacun lies B un atome N et deux atomes N’. Chaque lithium est ainsi lie B l’oxygene et a 3 azotes, formant
un environnement
approximativement
tetraedrique. Deux formes cristallines de Li,LGO ont et& caracteristes sur
le plan structural par diffraction des rayons X sur monocristal. Le spectre RMN de ‘H presente des signaux a
6,92 ppm (doublet, / = 6,0 Hz, Horrho a N’), 5,943 ppm (doublet,/=
6,6 Hz, H en para), 5,644 ppm (triplet,
/= 6,4 Hz, H en mtta), 4,274 ppm (singulet, H amine), et 1,255-1,811
ppm (multiplets, H cyclohexil, br).
L’integration correspond au rapport attendu de 1: 1: 1: 1: 10 ; la RMN de ‘Li presente deux singulets a -0,40 ppm
et -1,Gl ppm (une solution 2 M de LiCl dans D,O a et& utilisee comme standard), avec des intensites inttgrees
dans le rapport attendu de 1:s. 11 est interessant de comparer le cube L&O trouve dans ce compost avec celui
present dans l’oxyde Li,O de structure antifluorite.
Dans le nouveau compose existent des distances Li.. .Li de
2,312(6) et 2,373(5) A, a1ors q ue celles de l’oxyde Li,O sont de 2,3 10 A. L es d eux types de distances Li-0 sont
ici de 2,003(4) et 2,103(6) A, a 1ors q u’e 11es valent 2,OO A dans Li,O. 0 1999 Academic des sciences / fiditions
scientifiques et medicales Elsevier SAS.
structure
cristalline
I d&iv&
du lithium
I ion
oxyde
Molecular
compounds
in which there is an
oxygen atom surrounded
by a polyhedron
of
metal atoms are relatively uncommon.
The best
and longest known
ones are the basic carboxylates which have what is commonly
called the
basic beryllium
acetate structure
[I]. These
have the formula M,O(O,CR),,
and consist of
a tetrahedron
of metal ions with an oxide ion at
I coordination
cubique
the center and a /+RCO,-ion
on each edge. A
large number of these are formed by zinc [2],
which also gave analogous structures with carbamate ions [ 11, diphenyltriazenate
ions [3,4],
and 7-azaindolate
ions [5]. Reports from this
laboratory
[6] described
the first Cr2+, Mn2+
and Co2+ compounds
with this type of structure as well as another Zn2+ compound,
in all of
* Correspondence and reprints.
1387-1609/99/00020579
0 1999
AcadCmie
des sciences
I &itions
scientifiques
et mCdicales
Elsevier
SAS. Tous
droits
r&r&
579
F.A.
Cotton
et al.
which
the edge-bridging
ligands
are N,N’diphenylformamidinate
anions. An Fe2+ compound
in which the central tetrahedral
Fe40
core is surrounded
by the formamidinate
ligands in a different
arrangement
was also
described
[ba]. Most
recently
we reported
structural
variations
in the ligands around the
oxo-centered
building
block using a tridentate
ligand and Mn2+ and Fe2+ metal ions [Gc].
Two relevant reports appeared
in 1996: a
structurally
complex compound
in which there
is an octahedral
L&O core [7], and a cage consisting of a face-centered
array of I4 Li atoms
[8]. In the latter case, the oxygen atom is also
octahedrally
surrounded
by a set of 6 near
neighbors;
another set of 8 lithium
atoms are
slightly further.
We describe here a simple example of a L&O
unit which is a slightly distorted
cube of Li’
ions with an 02- ion at the center. On each of
the six faces of the quasicube
there is a ,u~, q2
anionic ligand, L-. The entire molecular
structure is shown in jgure I; a schematic drawing,
(y”;o
Nf N
L’
jgure 2, makes its symmetry
the ligand were symmetrical,
properties
clear. If
with equivalent
Figure
1. Molecular
structure
of Li,L,O.
Lithium,
oxygen and nitrogen atoms are shown at the 40 % probability
level; hydrogen
atoms are omitted
and carbon atoms are
drawn at an arbitrary
radius for clarity. Some important
interatomic
distances
(A) are Li(l)...Li(2):
2.373(5),
Li(l)...Li(lD):
2.312(6),
Li(l)-O(1):
2.003(4),
Li(2)O(1): 2.103(G).
580
Figure
2. Schematic
representation
the symmetry
properties.
of L&,0
showing
ligated nitrogen
atoms, the idealized symmetry
would
be Th. However,
the unsymmetrical
nature of the ligand lowers the symmetry to S,.
Thus Li( 1) and Li(8) are equivalent and define
the S, axis of symmetry and Li(2) to Li(7) are
equivalent.
The atoms Li( 1) and Li(8) are each
bonded to three N atoms while Li(2)-Li(7)
are
each bonded to one N and two N’ atoms. Each
Li atom is thus bonded to 0 and 3 N atoms in
an approximately
tetrahedral
array.
Two crystalline
forms of L&L,0
have been
structurally
characterized
by single-crystal X-ray
crystallography
‘. The ‘H NMR shows signals
at 6.92 ppm (doublet,
/ = 6.0 Hz, ortbo H
to N’), 5.943 pp m (doublet, J = 6.6 Hz,
para H), 5.644 ppm (triplet, / = 6.4 Hz, meta
H), 4.274
ppm
(singlet,
amine
H), and
1.255-1.8
11 ppm (multiplets,
br, cyclohexyl
H’s). The integration
is in the expected ratio of
1: 1: I : 1:lO; ‘Li NMR
shows two singlets at
-0.40 ppm and -1.61 ppm (2 M LiCl in D,O
’ Rhombohedral
form: data collection
was performed
at
213(2)K
on a Nonius
FAST area detector.
Formula
C,,H,,N,,Li80.6Et,0,
space group Rj , (E = 22.X03(4)
A,
c = 16.407(l)
A, V= 7389(2) A’, 2 = 3, independent
reflections 2 162 [R(int) 0.06251, goodness-of-fit
on F’ 1.074,
final R indices [I > 2 cr (I)] Rl = 0.060, wR2 = 0.149, final R
indices for all data Rl = 0.071, wR2 = 0.161. Monoclinic
form: data collection was performed
at 173(2) K on a Nonius CAD4
serial diffractometer
using omega-rhera
scans.
Formula
C,,H,,N,,I.i,0,2THE
space group P2,/c, n =
14.100(4),
b = 12.046 (3) and c = 21.336(5)
A, b =
95.77(l)“,
V = 3606(2) A3, Z = 2, independent
reflections
4862 [R(int) = O.OGOl], goodness-of-fit
on F’ 1.007, final
R indices [I > 2 (T (J)] Rl = 0.049, wR2 = 0.094, final R
indices for all data Rl = 0. I8 I, wR2 = 0.125.
An oxygen
atom
surrounded
by 8 lithium
atoms
Efforts to reproduce
this reaction by introduction of liquid H,O to solutions of Li’L- were
unsuccessful,
presumably
because Li,LGO
is
itself sensitive to water:
L&L60
Li’L-
8
6
4
2
Cl
-2
-4
-6
Figure 3. ‘Li NMR
of L&L,0
showing two singlets with
integrated
intensities
in the expected
ratio of 1:3. Top:
actual spectrum.
Center: full fit. Bottom:
individual
component plots.
was used as an external standard)
with integrated intensities in the expected ratio of 1:3, as
shown in figure 3.
It is interesting
to compare
the L&O cube
found in this compound
with that in the ordinary oxide, L&O, which has the antifluorite
structure.
In the new compound
there are
Li...Li
distances of 2.312(6) A and 2.373(5) A
while those in L&O are 2.3 10 A. The two types
of Li-0
distances here are 2.003(4)
A and
2.103(6)
A, while those in Li,O are 2.000 A.
The preparation
of the compound
was first
accomplished
by accident during a reaction of
Li’L- with a transition
metal cation in THF
solution
‘. It became clear that the operative
reaction, which occurred because of the slow
ingress of adventitious
water is:
8 Li’L-
s The transition
where.
+ H,O
-+ Li,LGO
metal complexes
else-
References
[l]
+ H,O
+
+
2 LiOH
LiOH
+ 6 Li’L-
+ HL
The direct synthesis of L&L60
was achieved
according
to the following
procedure:
A Li’L(1.56 g, 8.0 mmol) solution
in THF was carefully layered with hexanes in a Schlenk tube,
and the system was connected
through
a
U-shaped fine frit to a small flask charged with
a blue CuSO,.5
H,O (0.05 g, 0.2 mmol) microcrystalline solid containing
an equivalent amount
of H,O. The flask was gently heated once a
week with a heat gun during 2 months of water
vapor diffusion
until a white solid of CuSO*
was left. Pale green crystals of Li,LG0.2
THF
were obtained
in almost quantitative
yield;
Li,L60.6
Et,0
can be prepared
in a way
similar to the above procedure.
The L&L,0
has a very pale green color,
which is puzzling.
We tentatively attribute
it to
an impurity
from the starting material which
might contain a large conjugated
system.
The structure of L&L,0
suggests to us that it
might
be possible
to prepare
analogues
in
which L is replaced by other anions that could
also serve as pLq, q2 ligands, as for example 2pyridyl
NRor the anion
of 7-azaindole;
perhaps the use of a symmetrical
anionic ligand
such as PhNC(H)NPhwould lead to a compound
with full T, symmetry.
Furthermore,
anions such as Cl- and S2- might also be placed
into the lithium
cube. These questions remain
to be explored
Acknowledgments
+ 2 HL
of L- will be described
+ H,O
(a) Bragg W., Morgan
G.T., Proc. Roy. Sot. Lond. A
104 (1923) 437-451;
(b) Tulinsky A., Worthington
C. R., Pignataro El., Acta
Crystallogr.
12 (1959) 623626;
(c) Tulinsky A., Acta Crystallogr.
12 (1959) 626634;
(d) Tulinsky A., Worthington
C. R., Acta Crystallogr.
12 (1959) 634-637.
We thank the Robert A. Welch Foundation
and Texas A&M
University for supporting
this
work, and Mrs. Lana Frenkel for assistance with
‘Li NMR.
[2] (a) Koyoma
H., Saito Y., Bull. Chem. Sot. Jpn. 27
(1954). 112-l 14;
(b) Hiltunen
L., Leskela M., Mikela M., Niinisto, Acta
Chem. Stand., Ser. A 41 (1987) 548-555;
(c) Clegg W., Harbron D. R., Homan C. D., Hunt I? A.,
Little I. R., Straughan
B. I?, Inorg. Chim. Acta 186
(1991) 51-60.
[3] Belforte A., Calderazzo
F., Englert
Chem. 30 (1991) 3778-3781.
U., Strahle J., Inorg.
581
F.A.
Cotton
et al.
[4] Corbett M., Hoskins
(I 970) 261-264.
B.F., Inorg.
Nucl.
Chem.
Lett. 6
[5] Lee C.-F., Chin K.-E, Peng S.-M., Che C.-M., J, Chem.
SOL, Dalton Trans. (1993) 467-470.
[6] (a) Cotton EA., Daniels L.M., Falvello L.R., Matonic
J.H., Murillo
C.A., Wang X., Zhou
H.-C.,
Inorg.
Chim. Acta 266 (1997) 91-102;
(b) Cotton EA., Murillo
C.A., Pascual I., Inorg. Chem.
(1999) 2746-2749;
582
(c) Cotton EA., Dan&
C.A., Pascual I., Inorg.
L.M., Jordan IV. G.T., Murillo
Chim. Acta (1999) (accepted).
[7] Driess M., Pritzkow
H., Martin S., Rell S., Fenske D.,
Baum G., Angew. Chem. Int. Ed. Engl., 35, 986-988.
[8] Clegg W., Horsburgh
L., Dennison
P.R., Mackenzie
Chem.
Commun.
(1996)
F.M.,
Mulvey
R.E.,
1065-1066.