La6Br10Fe: A La6Fe octahedron with a mixed M6X12/M6X8 type environment

Article abstract of DOI:10.1021/ic701229q

The title compound was synthesized from La, LaBr₃, and Fe under Ar atmosphere at 800°C. It crystallizes in space group P4₁ (No. 76) with lattice constants a = 8.255(1) A and c = 30.033(6) A. The structure features an isolated Fe-centered La₆ octahedron with all corners, 9 of its 12 edges, and 3 of its 8 triangular faces coordinated, bridged, or capped by Br atoms. The La₆Fe octahedron is significantly distorted, and the La coordination by Br atoms deviates from the common close-packing arrangements found in other reduced rare earth metal halides. Band structure, bonding, and physical properties of the compound have been investigated.

Full text of DOI:10.1021/ic701229q

Inorg. Chem. 2008, 47, 2356-2361
La Br Fe: A La Fe Octahedron with a Mixed M X /M X Type
6
10
6
6 12 6 8
⊥
Environment
,
‡
§
Chong Zheng,* Hansjürgen Mattausch, Constantin Hoch, and Arndt Simon
§
§
Department of Chemistry and Biochemistry, Northern Illinois UniVersity, DeKalb, Illinois 60115,
and Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1,
D-70569 Stuttgart, Germany
Received June 22, 2007
The title compound was synthesized from La, LaBr
space group P4 (No. 76) with lattice constants a ) 8.255(1) Å and c ) 30.033(6) Å. The structure features an
isolated Fe-centered La octahedron with all corners, 9 of its 12 edges, and 3 of its 8 triangular faces coordinated,
bridged, or capped by Br atoms. The La Fe octahedron is significantly distorted, and the La coordination by Br
3
, and Fe under Ar atmosphere at 800 °C. It crystallizes in
1
6
6
atoms deviates from the common close-packing arrangements found in other reduced rare earth metal halides.
Band structure, bonding, and physical properties of the compound have been investigated.
Introduction
metal halides thus feature RE
number of main group or transition metal atoms.
this remarkably large family of compounds, several members
with Fe as interstitial have been reported. These include
6
octahedra centered by a great
9–22
Among
Metal atom cluster chemistry has made tremendous
progress in the past four decades. For the octahedral clusters,
there are mainly two structure types, M
6 6 8
X12 and M X , where
Pr
Fe
7
I
12Fe, Gd
7
I
12Fe, Y
7
I
12Fe, La12
I
17Fe
2
, Pr12
I
2
17Fe , and Gd
2
M stands for a metal atom and X a ligand, usually a
1
7,23–26
1
2
I.
The first five contain isolated RE Fe octahedral
6
chalcogen or halogen atom. In the M
of the M octahedron are bridged by the X atoms. In the
cluster, all faces are capped by X atoms. These clusters
can be linked or condensed to chains, sheets or three-
6
X12 cluster, all edges
clusters. The latter features a condensed trigonal prism
structure. In this contribution, we present a structure, bonding,
6
6 8
M X
2–8
(10) Mattausch, Hj.; Simon, A. Angew. Chem., Int. Ed. 1998, 37, 499.
Angew. Chem. 1998, 110, 498.
dimensional frameworks. In reduced rare earth (RE) metal
halide compounds, a third interstitial atom can occupy the
center of the cluster, making their electronic structures even
more interesting. The structures of many reduced rare earth
(11) Mattausch, Hj.; Oeckler, O.; Simon, A. Inorg. Chim. Acta 1999, 289,
1
74.
(
(
12) Warkentin, E.; Simon, A. ReV. Chim. Miner. 1983, 20, 488.
13) Nagaki, D.; Simon, A.; Borrmann, H. J. Less-Common Metals 1989,
1
56, 193.
⊥
Dedicated to Prof. Roald Hoffmann on the occasion of his 70th
(14) Dorhout, P. K.; Payne, M. W.; Corbett, J. D. Inorg. Chem. 1991, 30,
birthday.
4960.
*
Corresponding author. E-mail: zheng@cz.chem.niu.edu.
Northern Illinois University.
Max-Planck-Institut für Festkörperforschung.
(15) Llusar, R.; Corbett, J. D. Inorg. Chem. 1994, 33, 849.
(16) Hughbanks, T.; Rosenthal, G.; Corbett, J. D. J. Am. Chem. Soc. 1986,
108, 8289.
‡
§
(
(
1) Schäfer, H.; Schnering, H. G. Angew. Chem. 1964, 76, 833.
(17) Hughbanks, T.; Corbett, J. D. Inorg. Chem. 1988, 27, 2022.
(18) Hughbanks, T.; Corbett, J. D. Inorg. Chem. 1989, 28, 631.
(19) Meyer, G.; Wickleder, M. S. Simple and Complex Halides. In
Handbook on the Physics and Chemistry of Rare Earths; Elsevier
Science Publishers: Amsterdam-London-New York-Tokyo, 2000;
Vol. 28, Chapter 177, pp 53.
2) Simon, A. Angew. Chem., Int. Ed. Engl. 1981, 20, 1. Angew. Chem.
1
981, 93, 23.
(
3) Chevrel, R.; Gougeon, P.; Potel, M.; Sergent, M. J. Solid State Chem.
1
985, 57, 25.
(
(
(
4) Hughbanks, T.; Hoffmann, R. J. Am. Chem. Soc. 1983, 105, 3528.
5) Hughbanks, T.; Hoffmann, R. J. Am. Chem. Soc. 1983, 105, 1150.
6) Simon, A. Angew. Chem., Int. Ed. Engl. 1988, 27, 159. Angew. Chem.
(20) Corbett, J. D. J. Chem. Soc., Dalton Trans. 1996, 575.
(21) Meyer, G. Z. Anorg. Allg. Chem. 2007, 633, 2537.
(22) Simon, A.; Mattausch, Hj.; Ryazanov, M.; Kremer, R. K. Z. Anorg.
Allg. Chem. 2006, 632, 919.
1
988, 100, 163.
(
7) Köhler, J.; Svensson, G.; Simon, A. Angew. Chem., Int. Ed. Engl.
1
992, 31, 1437. Angew. Chem. 1992, 104, 1463.
(23) Sweet, L. E.; Roy, L. E.; Meng, F.; Hughbanks, T. J. Am. Chem. Soc.
2006, 128, 10193.
(
(
8) Vajenine, G. V.; Simon, A. Inorg. Chem. 1999, 38, 3463.
9) Simon, A.; Mattausch, Hj.; Miller, G. J.; Bauhofer, W.; Kremer, R. K.
Metal-Rich Halides. In Handbook on the Physics and Chemistry of
Rare Earths; Elsevier Science Publishers: Amsterdam-London-New
York-Tokyo, 1991; Vol. 15, pp 191.
(24) Ruck, M.; Simon, A. Z. Anorg. Allg. Chem. 1993, 619, 327.
(25) Lulei, M.; Martin, J. D.; Corbett, J. D. J. Solid State Chem. 1996,
125, 249.
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2356 Inorganic Chemistry, Vol. 47, No. 7, 2008
10.1021/ic701229q CCC: $40.75  2008 American Chemical Society
Published on Web 03/05/2008

6 6
La Br10Fe: A La Fe Octahedron
a
and physical property study of still another phase, La
which is also characterized by discrete La Fe octahedral
clusters. The cluster is neither a M type. Its
structure represents a new type which differs from other
known compounds with the same stoichiometry RE
Pr Br10Z (Z ) Co, Ru, Os), Y 10Ru, and La ), in the
6
Br10Fe,
Table 1. Crystal Data and Structure Refinement for La6Br10Fe
formula weight
temperature
1688.41
293(2) K
6
6 6 8
X12 nor a M X
wavelength
0.56086 Å
crystal system
space group
unit cell dimensions
tetragonal
6
X10Z,
P41 (No. 76)
a ) 8.255(1) Å
c ) 30.033(6) Å
6
6
I
6 2
I10(C
1
5,18,27
coordination environment of cluster and its stacking.
3
volume
2046.4(6) Å
Z
4
3
Experimental Section
density (calculated)
absorption coefficient
θ range for data collection
index ranges
5.480 Mg/m
-
1
17.248 mm
1.95-24.20°
-12 e h e 12, -12e k e 12,
43 e l e 43
27112
6585 [R(int) ) 0.0576]
99.1%
Synthesis. La metal (sublimed, 99.99%; Alfa-Aesar, small
pieces), LaBr , and Fe (99.99%; Aldrich) were used as starting
materials. LaBr was prepared by the reaction of La with
concentrated HBr and NH Br, the product being dried under
3
-
3
2 3
O
reflections collected
4
independent reflections
completeness to θ ) 24.20°
absorption correction
max. and min. transmission
refinement method
data/restraints/parameters
goodness-of-fit on F
R indices (all data)
dynamic vacuum and purified twice by sublimation in a Ta container
before use. Due to air and moisture sensitivity of the reactants and
product, all handling was carried out under Ar atmosphere either
in a glovebox or through the standard Schlenk technique.
2
9
numerical
0.91064 and 0.50453
Full-matrix least-squares on F
6585/1/156
2
The stoichiometric mixture (ca. 1.0 g) of the starting materials
was arc-sealed in a Ta tube under Ar atmosphere. The Ta tube
was then sealed inside a silica glass ampule under a vacuum of ca.
2
1.100
b
R1 ) 0.0339, wR2 ) 0.0860
1.758 and -1.474 e Å-3
largest diff. peak and hole
a
-
2
1
0
mbar. The reaction was carried out at 800 °C for 21 days.
The refinement is for a twin model with the twin matrix of (0 1 0; 1
b
2
2 2
2 2 1/
After the reaction, the ampule was quenched in water and then
opened under Ar atmosphere. Many black polyhedral single crystals
were observed in the product. The yield, estimated from a Guinier
powder X-ray measurement, was nearly 100%. EDX analyses of
these single crystals, using a JEOL JSM-6510LV scanning electron
microscope, confirmed the presence of the component elements in
the average atomic ratio of 6:10:1 (La:Br:Fe). The crystals oxidize
in air within minutes to a white powder.
0 0; 0 0 -1). R1 ) Σ|Fo| - |Fc|/ΣFo|; wR2 ) [Σ[w(Fo - Fc ) ]/Σ[w(Fo ) ]]
2.
4
Table 2. Atomic Coordinates (×10 ) and Equivalent Isotropic
2
3
a
Displacement Parameters (Å × 10 ) for La Br Fe
6
10
b
Atom
x
y
z
U(eq)
La(1)
La(2)
La(3)
La(4)
La(5)
La(6)
Br(1)
Br(2)
Br(3)
Br(4)
Br(5)
Br(6)
Br(7)
Br(8)
Br(9)
2931(1)
7116(1)
8013(1)
2644(1)
6288(1)
1150(1)
4782(2)
6445(2)
1532(2)
1222(2)
8827(2)
3518(2)
5436(2)
2536(2)
281(2)
1853(1)
2372(1)
3938(1)
2089(1)
-1541(1)
6961(1)
5023(2)
1738(2)
3170(2)
3592(2)
611(2)
8387(2)
4080(2)
2319(2)
4953(2)
23(2)
3079(1)
3791(1)
1983(1)
6117(1)
3197(1)
1872(1)
3298(1)
2722(1)
5159(1)
3846(1)
4553(1)
6358(1)
4534(1)
7148(1)
2750(1)
3297(1)
6282(1)
14(1)
15(1)
13(1)
14(1)
13(1)
14(1)
19(1)
23(1)
19(1)
18(1)
28(1)
19(1)
25(1)
22(1)
26(1)
21(1)
11(1)
Structure Determination. The reaction product was ground to
fine powder under Ar atmosphere and sealed in a glass capillary
for phase identification by a modified Guinier technique (Cu KR :
1
λ ) 1.54056 Å; internal standard Si with a ) 5.43035 Å; Fujifilm
BAS-5000 image plate system). Single crystals were transferred
to glass capillaries under Na-dried paraffin oil and sealed under Ar
atmosphere. They were first examined by the precession technique
before being characterized on a STOE IPDS diffractometer with
28
monochromatized Ag K
corrections were applied through the program XRED, XSHAPE.
The structure was solved with direct methods using the SIR97
R
radiation (λ ) 0.56086 Å). Absorption
29
Br(10)
Fe
a
9715(2)
75(2)
3
0
2
4603(2)
program. Full matrix least-squares refinement on F was carried
3
1
U(eq) is defined as one-third of the trace of the orthogonalized U
out using the SHELXTL package.
The product compound crystallizes in the tetragonal space group
P4 (No. 76) with lattice constants a ) 8.255(1) Å and c )
0.033(6) Å. The structure has been checked for possible existence
of higher symmetry by the program ADDSYM in the PLATON
ij
b
tensor. Wyckoff positions for all atoms are 4a.
1
1
Without applying the twinning law, the R value could only be
3
refined to 0.192. The two twin components have nearly 1:1 ratio.
The crystallographic information including the fractional coordinates
and selected bond lengths of the compound is listed in Tables 1-3.
Computational Study. The density of states (DOS) and band
structure were computed using both the tight-binding extended
3
2
package. No additional symmetry element was found. The mean
E2 - 1| is low at 0.567, and the F
2
< F
2
value of 11.5 is very
/F (max) < 0.04.
|
o
c
high for the weak reflections with 0 < F
Examination of the reciprocal space revealed that the crystal
possesses a twinning by merohedry. By applying the twinning
1
matrix of (0 1 0; 1 0 0; 0 0 -1) the R -factor converged to 0.0339.
c
c
3
3,34
Hückel method (EH)
orbital local density approximation method (LDA) as implemented
and the self-consistent linear muffin-tin
3
5
in the Stuttgart-TB-LMTO-ASA program. Here, 64 k-points in
the irreducible wedge of the Brillouin zone were used in the EH
computations, and approximately, 50 k-points were used during the
self-consistent convergence part in the LDA calculations. Scalar
relativistic equation using the Barth-Hedin local exchange potential
was used. Default basis set and Wigner-Seitz radii were used, and
empty spheres added in the interstitials according to the standard
(
27) Mattausch, Hj.; Hoch, C.; Simon, A. Z. Anorg. Allg. Chem. 2005,
6
31, 1423.
(
(
28) Simon, A. J. Appl. Crystallogr. 1970, 3, 11.
29) XRED32 1.26, X-SHAPE 2.05, Crystal Optimisation for Numerical
Absorption Correction; Stoe & Cie. GmbH: Darmstadt, 2004.
30) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(
(
(
31) Sheldrick, G. M. SHELXTL, version 6.10; Bruker Analytical Instru-
ments Inc.: Madison, Wisconsin, 2000.
32) Spek, A. L. Acta Crystallogr., Sec. A: Found. Crystallogr. 1990, 46,
C34.
(33) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397.
(34) Whangbo, M. H.; Hoffmann, R.; Woodward, R. B. Proc. R. Soc.
London 1979, A366, 23.
(35) Andersen, O. K.; Jepsen, O. Phys. ReV. Lett. 1984, 53, 2571.
Inorganic Chemistry, Vol. 47, No. 7, 2008 2357

Zheng et al.
Table 3. Selected Interatomic Distances [Å] and Types in La6Br10Fe
a
atom contacts
distances
type
e, i-i
Br(1)-La(1), -La(2), -La(4), -La(5)
Br(2)-La(1), -La(2), -La(5); -La(3)
Br(3)-La(1), -La(4), -La(5); -La(6)
Br(4)-La(1), -La(6); -La(2), -La(4)
Br(5)-La(2), -La(3); -La(1), -La(6)
Br(6)-La(3), -La(5); -La(2), -La(4)
Br(7)-La(2), -La(6); -La(3)
Br(8)-La(3), -La(4), -La(6); -La(5)
Br(9)-La(3), -La(6); -La(1), -La(4)
Br(10)-La(1), -La(4), -La(2), -La(5)
La(1)-Fe
3.101(2), 3.270(2), 3.094(2), 3.112(2)
3.094(2), 3.302(2), 3.063(2); 3.146(2)
3.072(2), 3.148(2), 3.040(2); 3.148(2)
3.059(2), 2.968(2); 3.539(2), 3.263(2)
3.057(2), 3.139(2); 3.670(3), 3.547(2)
2.966(2), 3.100(2); 3.557(2), 3.223(2)
2.980(2), 3.163(2); 3.291(2)
3.162(2), 3.105(2), 3.209(2); 3.358(2)
f, i-a; a-i
f, i-a; a-i
e, i-a; a-i
e, i-a; a-i
e, i-a; a-i
e, i-a; a-i
f, i-a; a-i
e, i-a; a-i
e, i-i
3.085(2), 3.197(2); 3.509(2), 3.596(2)
3.123(2), 3.099(2), 3.251(2), 3.124(2)
2.982(2)
2.896(2)
2.894(3)
3.007(2)
2.547(3)
2.414(3)
4.086(1)
4.107(1)
3.956(1)
3.927(1)
4.244(1)
3.754(1)
3.922(1)
4.221(1)
3.884(1)
3.612(1)
3.799(1)
3.945(1)
La(2)-Fe
La(3)-Fe
La(4)-Fe
La(5)-Fe
La(6)-Fe
La(1)-La(2)
La(1)-La(4)
La(1)-La(5)
La(1)-La(6)
La(2)-La(3)
La(2)-La(5)
La(2)-La(6)
La(3)-La(4)
La(3)-La(5)
La(3)-La(6)
La(4)-La(5)
La(4)-La(6)
a
1
The notation follows the work of Schäfer and Schnering. The letters e and f denote edge bridging and face capping atoms of atom type i, and a stands
for coordination of corners of adjacent clusters. For example, Br(1) bridges the La(1)-La(2) edge in one cluster, and the La(4)-La(5) edge in an adjacent
one. Thus, it is type e, and in both clusters, it acts as a bridging ligand, thus i-i. Br(2) caps the La(1)-La(2)-La(5) face and, thus, is type f. It is a terminal
ligand to La(3) in an adjacent cluster, thus the notation i-a. Consider La(3) in the current cluster, it is also type a-i. Therefore a semicolon is used to separate
these two types. See Figure 1.
Table 4. Extended Hückel Parameters
octahedral La
Fe unit, however, only nine Br atoms lie above
Fe
6
a
a
orbital
Hii (eV)
ꢀ1
ꢀ2
c1
c2
edges and three above faces of the octahedron. The La
6
octahedron is very distorted as shown in Figure 1. The
La-La distances vary from 3.61 (La3-La6) to 4.24 Å
La
6s
-7.67
-5.01
-8.21
-22.07
-13.1
-9.10
-5.32
-12.6
2.14
2.08
3.78
2.588
2.131
1.90
1.90
5.35
6
5
p
d
1.381
0.7765
0.4586
(La2-La3). The La-Br distances of 2.97–3.67 Å are within
Br
Fe
4s
the normal range as in many other reduced rare earth
bromides. The main distortion is the contraction along the
La5-La6 direction. Four corners of the octahedron (La1,
La2, La3, and La6) are coordinated by two, one corner (La5)
by one, and one (La4) by three Br atoms. The 9 bridged
edges are La2-La5, La3-La5, La4-La5, La1-La6,
La2-La6, La3-La6, La1-La2, La1-La4, and La2-La3.
Out of the 12 Br atoms above the octahedron apexes, 4 also
4
p
4s
4
3
p
d
2.000
0.5505
0.6260
a
Exponents and coefficients in a double ꢀ expansion of the d orbital.
procedure. The average Wigner-Seitz radius was 2.55 Bohr in the
LDA computations. The EH parameters used in the computation
are listed in Table 4.
Physical Property Measurements. For conductivity measure-
ment, the polycrystalline samples were pressed into pellets of 5
mm in diameter and ca. 2 mm in thickness. The conventional four-
contact method was used. Susceptibility measurements were
carried out on a Quantum Design PPMS 6000 magnetometer, using
sample quantities of ca. 50 mg.
6
bridge the edge or cap the face of an adjacent La octahedron
and 8 are shared with another two La octahedra, linking
6
3
6
one corner and bridging one edge or capping one face of
these two octahedral as shown in Figure 2.
Neglecting the Br atoms above the apex atoms, the discrete
e
Brf
cluster has the composition La
6
Br
9
3
Fe where e and f
Results and Discussion
denote positions above the edges and faces of the octahedron,
respectively. As the e-type atoms Br1 and Br10 are shared
between adjacent clusters in the same functionality, the
Crystal Structure. So far, all known reduced rare earth
halides based on the octahedral RE
the RE 12Z cluster with a cuboctahedral X atom arrange-
ment above the edges of the octahedron. The packing of these
clusters leads to vacancy variants of the rocksalt type
structure. Some relevant structures are listed in Table 5. The
structure of La
variation from the known structures. It contains the familiar
6
Z unit are derived from
e
Br 4/2Brf
e
formula La
6
Br
5
3
6
Fe ) La Br10Fe results. In the
6
X
1
notation of Schäfer and Schnering the complicated intercon-
nection can be described as La
a-i,i-a
f
i-i
i-a,a-i
6
(Br
6/2) (Br 4/2Br
2/2
i-a,a-i,a-i
e
Br
12/3) Fe which also reduces to La Br10Fe. The
6
superscript i stands for the bridging and face capping Br
6
Br10Fe is a first example of a significant
ligands, while the notation a for the corner coordinating
a-i,i-a
ligands. Br
, therefore, is a ligand that is coordinated to
(
36) van der Pauw, L. J. Philips Res. Rep. 1958, 13, 1.
the corner of the current La octahedron but also bridges an
6
2358 Inorganic Chemistry, Vol. 47, No. 7, 2008

6 6
La Br10Fe: A La Fe Octahedron
Table 5. Lattice Constants (Length in angstroms and Angles in degrees) and Space Groups of Some Fe-Containing and 6–10 Type Reduced Rare Earth
Metal Halides
compound
a
b
c
R
ꢁ
γ
space group
cluster type
ref
La6Br10Fe
Pr7I12Fe
Gd7I12Fe
Y7I12Fe
Pr12I17Fe2
Gd2Fe2I
Pr6Br10Co
Pr6Br10Ru
Pr6Br10Os
Y6I10Ru
8.255(1)
15.833(1)
15.492
30.033(6)
10.734(1)
10.624(2)
10.661(1)
9.830(2)
17.180(2)
7.538(3)
7.606(4)
7.614(2)
7.629(1)
7.955(1)
7.875(1)
P41
R3j
mixed M6X12/M6X8
M6X12
M6X12
M6X12
M6X12
condensed trigonal prisms
M6X12
M6X12
M6X12
M6X12
M6X12
M6X12
this work
17
17
17
26
24
15
15
15
R
3
j
15.351(1)
11.798(4)
4.0143(5)
9.359(4)
9.206(4)
9.272(2)
9.456(2)
9.687(1)
9.588(1)
R3
j
11.791(2)
114.87(2)
104.82(4)
93.19(2)
P1j
P63/mmc
P1j
9.243(5)
9.505(3)
9.486(3)
9.643(2)
9.728(1)
9.648(1)
97.37(4)
97.08(4)
97.09(2)
97.20(2)
97.34(1)
97.24(2)
107.3 l(4)
107.47(4)
107.48(2)
105.04(2)
105.56(1)
105.32(2)
110.17(3)
109.69(4)
109.83(2)
107.79 (2)
107.81(1)
107.69(2)
P
P
P
1
j
1
j
1
j
18
27
27
La6I10(C2)
Ce6I10(C2)
P1j
P
1
j
edge or caps a face of an adjacent octahedron. It bridges an
edge or caps a face of the current octahedron but is
coordinated to the corner of an adjacent octahedron. An
example is Br(3) (see Figure 1), it bonds to the current La(6)
corner and caps an adjacent La(1)-La(4)-La(5) face. It can
also be considered as capping the current La(1)-La(4)-La(5)
hand and the irregular arrangement of Br and Fe atoms in
La Br10Fe is obvious from Figure 3. The question arises what
might be the driving force behind the distortion.
6
Electronic Structure. The distortion could be of electronic
3+
-
2-
-
origin. A formal electron partition of (La ) (Br )10Fe ·6e
6
6
shows that there are 16 cluster electrons in the La Fe
i-a,a-i,a-i
2-
face and bonding to an adjacent La(6) corner. The Br
octahedron including those of (formal) Fe and 6 electrons
type ligands are shared by three La
6
octahedrons in the same
forming metal-metal bonds in the La
for the RE 12Fe cluster with the X atoms arranged above
the RE edges have shown that 10 of these electrons reside
in the Fe 3d orbitals, and 6 in the a1g and t1u orbitals that are
6
cage. Previous studies
sense. An example is Br(5) (see Figure 2), which appears
three times in Figure 1. Table 3 classifies all the ligands in
detail according to this system of notations.
6
X
6
9
,16,17,23
The pronounced asymmetry of the Br coordination poly-
of La-La bonding character.
Therefore, the 16
hedron around the La
6
Fe octahedron has two important
electrons do not exceed the 18 electron limit imposed by
these orbitals. As four electrons occupy the degenerate t1u
orbitals in the regular cluster, it could be susceptible to a
Jahn–Teller distortion. A contraction along the local z-axis
consequences. First, the La octahedron is heavily distorted,
in first approximation squeezed along a 4-fold axis as
described earlier. As seen in Table 3, the four La-Fe
distances in the waist (La1-La2-La3-La4) of the octahe-
dron are between 2.89 and 3.01 Å, whereas the La-Fe bonds
to the “apical” atoms (La5-Fe and La6-Fe) are much
shorter, 2.55 and 2.41 Å, respectively. This differentiation
of the La-Fe distances is quite unusual and even exceeds
that in La12
I
17Fe
2
where the distances 2.87 vs 2.71 Å have
been found. Second, the rocksalt-type arrangement, i.e.,
the common close-packing of Br atoms and the La Fe unit
is lost. The rather dramatic difference of the common close-
packing arrangements of I and Ru atoms in Y 10Ru on one
2
5
6
6
I
Figure 1. La6Fe octahedron coordinated by Br atoms in the La6Br10Fe
structure. Atoms are numbered as in Tables 2 and 3.
Figure 2. Arrangement of La6Fe in the structure of La6Br10Fe along the
[0 1 0] (top) and along [1, 1, 0] (bottom) directions.
Inorganic Chemistry, Vol. 47, No. 7, 2008 2359

Zheng et al.
e
f
of (too) close contacts between Br and Br (2.58 Å). These
states are therefore omitted in the figure. They are absent
for the experimentally observed arrangement of atoms
(Figure 4d and h) as they should be.
The occupation of the cluster centered by an Fe atom adds
the e
e), the number of cage orbitals with La-La bonding
character is the same as in the empty cluster. However, the
2g* set is of La-Fe antibonding and a2u La-Br antibonding.
The 18 electron limit is reached with the occupation of the
g 6
, t2g blocks. In the case of the La Br12Fe cluster (Figure
4
t
1
6
t
1u orbitals. It has been pointed out that the 18 electron
38,39
limit is not strictly obeyed.
6 8
In the hypothetical La Br Fe
cluster, too, the number of cage orbitals is preserved, and
according to the above reasoning the t1u orbital is the HOMO.
Due to the deviation from O
La Br9+3Fe cluster (Figure 4g) and, even more in the distorted
one, the degeneracy of the HOMO is removed.
Figure 5 is the calculated band structure of La Br10Fe using
h
symmetry in the idealized
6
6
the LDA method where the Fermi level is set to be the zero
point of energy. The relative energies of the bands deviate
quite significantly from the EH-MO’s, in particular con-
cerning the a1g; however, the general feature regarding the
electron count is preserved. In the -2.3 to -1.9 eV region,
there are four bands corresponding to the four a1g orbitals
6
of the four La Fe octahedra in the unit cell. In the -1.7 to
-
1.0 eV region, there are 20 Fe d bands. Because of the
Figure 3. Comparison of the arrangements of I and Ru atoms in Y6I10Ru
distortion, these split into four groups with the indicated
energy order. Just below the Fermi level, there are 8 of the
18
(
top) with those of Br and Fe atoms in La6Br10Fe (bottom). The structures
are projected approximately along the [-1, -2, 3] and [1, 0, 1] directions,
respectively. Dark spheres are Ru, Fe, and unit cells outlined.
1
2 t1u derived bands, the other 4 are above the Fermi level
as a result of the distortion. The LDA estimate of the band
gap is approximately 0.7 eV corresponding to a semiconduc-
tor. This method, however, is well-known for underestimat-
ing the sizes of band gaps.
will destabilize one of the three t1u orbitals that have mainly
Fe dxz, dyz, and p
z
character and stabilize the remaining two.
So far, the cluster core La Fe with halogen atoms above all
6
edges of the octahedron has been considered. In order to
The Jahn–Teller effect would clearly favor a distortion of
take the unusual coordination by Br atoms above both edges
the cluster as observed in La
able whether this effect is the only one or even the dominant
effect. In Th Br15Fe, the octahedron is regular in spite of a
very similar bonding configuration except for one more cage
6
Br10Fe. However, it is question-
e
Brf
and faces into account as it occurs in the La
6
Br
9
3
Fe
cluster, a systematic study at the EH level (without charge
iteration) has been performed for different arrangements
6
4
0
starting from empty La
6
cores. For simplicity and for the
6
electron compared to La Br10Fe. The cause for the distor-
purpose of comparing with the classic Cotton-Haas orbital
tion of the cluster in the latter compound has rather to be
sought in the strongly varying coordinations of the La atoms
37
ordering, we ignore the apical Br atoms. As is well-known,
the effect of the addition of apical ligands is mainly the
increase of the HOMO–LUMO gap, but the orbital ordering
in the vicinity of the HOMO–LUMO energy range will
by Br atoms. The earlier mentioned compounds Pr
6
Br10Z
(Z ) Co, Ru, Os), Y 10Ru and La ) exhibit (distorted)
6
I
6 2
I10(C
octahedral coordinations of all RE atoms by five halogen
and the endohedral atoms. In contrast, the La atoms in
9
remain the same. Calculations with apical ligands (not
shown here) indeed confirmed our expectation. The cage
orbitals of bonding and nonbonding character are compared
6
La Br10Fe have coordinations by 5Br + Fe and 6Br + Fe,
respectively. It seems that the radius ratio RE/halogen is a
critical parameter, and subtle size effects are responsible for
the enhanced coordination number of the large La atom.
in Figure 4. The idealized La
symmetry, while the La Br9+3 and experimental clusters
have C symmetry.
The all familiar patterns of 8 and 12 obitals for the
regular La Br12 and La Br clusters, respectively, are shown
in Figure 4a and b. For the mixed Br arrangement in the
La Br9+3 cluster (Figure 4c and g), 13 orbitals are found in
6 6
Br12 and La Br12 clusters have
O
h
6
6
Physical Properties. The physical properties of La Br10Fe
1
3
7
are in agreement with the analysis of the chemical bonding
described above. The resistivity measured in the temperature
range from 5 to 300 K is in the order of 10 MΩ cm. Because
6
6
8
e,f
6
the energy range of the cage orbitals. Five of them are
actually of Br p character, pushed to high energy because
(38) Payne, M. W.; Corbett, J. D. Inorg. Chem. 1990, 29, 2246.
(
39) Mattausch, Hj.; Zheng, C.; Kienle, L.; Simon, A. Z. Anorg. Allg. Chem.
2
004, 630, 2367.
(
40) Böttcher, F.; Simon, A.; Kremer, R. K.; Buchkremer-Hermanns, H.;
(
37) Cotton, F. A.; Haas, T. E. Inorg. Chem. 1964, 3, 10.
Cockcroft, J. K. Z. Anorg. Allg. Chem. 1991, 598, 25.
2360 Inorganic Chemistry, Vol. 47, No. 7, 2008

6 6
La Br10Fe: A La Fe Octahedron
Figure 4. La-La bonding orbitals in the empty regular (a) La6Br12, (b) La6Br8, (c) La6Br9+3, and (d) the experimental La6Br9+3 clusters, as well as the
corresponding Fe-centered species (e-h). The symmetry labels for the idealized La6Br9+3 and experimental La6Br9+3 clusters denote the corresponding
orbitals in the octahedron clusters from which they are derived.
at 155 K saturating in a field of 7 T. The magnetic behavior
of La Br10Fe is consistent with the closed-shell electron
6
configuration as discussed.
Conclusion
6
A new reduced rare earth metal halide La Br10Fe has been
synthesized. Its structure represents a novel mixed M
type that has not been observed previously. The cluster
is characterized by a significantly distorted RE octahedron.
6 12
X /
6 8
M X
6
Because of the discreteness of the clusters in the structure,
the compound is an insulator.
Figure 5. Band structure of La6Br10Fe calculated by the LDA method.
Acknowledgment. We thank R. Bailey for assisting the
EDX measurement, E. Brücher for the magnetic susceptibility
measurements, G. Siegle for the conductivity measurements,
and C. Kamella for help with the drawings.
of the high value, the measurement had large fluctuations.
Both the results of band structure calculations and measure-
ment are in agreement with expectation as the discreteness
of the cluster due to interconnection via nonmetal atom
bridges in all surrounding corners generally results in
Supporting Information Available: Listing of X-ray crystal-
lographic details in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
6
insulators or semiconductors. The magnetic susceptibility
measurement revealed nonmagnetic behavior (ꢂ ≈ 0) after
correction for an impurity which orders ferromagnetically
IC701229Q
Inorganic Chemistry, Vol. 47, No. 7, 2008 2361