A cluster with a mixed M6X12/M6X8 environment: The La6Cl11Co structure

Article abstract of DOI:10.1016/j.jssc.2009.06.002

The title compound was synthesized from La, LaCl₃ and Co under Ar atmosphere at 800 °C. It crystallizes in space group P4₂/n (no. 86) with lattice constants a=11.308(2) A and c=14.441(3) A. The structure features an isolated Co-cente

Full text of DOI:10.1016/j.jssc.2009.06.002

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A cluster with a mixed M X /M X environment: The La Cl Co structure
6
12
6 8
6
11
a,Ã
b
b
b
Chong Zheng , Hansj u¨ rgen Mattausch , Constantin Hoch , Arndt Simon
a
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
b
Max-Planck-Institut f u¨ r Festk o¨ rperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The title compound was synthesized from La, LaCl and Co under Ar atmosphere at 800 1C. It crystallizes
3
Received 28 February 2009
Received in revised form
in space group P4 /n (no. 86) with lattice constants a ¼ 11.308(2) A˚ and c ¼ 14.441(3) A˚ . The structure
2
6
features an isolated Co-centered La octahedron with all corners and edges, and 2 of its 8 triangular
2
3 May 2009
6
faces coordinated by Cl atoms. The La Co octahedron is significantly distorted, and the La coordination
Accepted 2 June 2009
Available online 6 June 2009
by Cl atoms deviates from the common close-packing arrangements found in other reduced rare earth
metal halides. Structure, bonding and physical properties of the compound have been investigated.
Keywords:
Lanthanum
Chloride
&
2009 Elsevier Inc. All rights reserved.
Cobalt
Reduced halide
1. Introduction
2 3
was prepared by the reaction of La O with concentrated HCl and
NH Cl, the product being dried under dynamic vacuum and
4
Reduced rare earth (RE) metal halides have exhibited great
chemical hospitality. They can accommodate endohedral atoms
ranging from light atoms H and B to heavy ones such as Au and Pb
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.
[
1–13]. Their structures, however, are based on simple RE
prisms or octahedra. In the latter case, the halide ligands are
coordinated to the RE octahedron at the terminal and bridging
positions. Thus these structures are derived from the M 12 prototype
in which all 12 edges of the M octahedron are bridged by the X
ligands [1,14–22]. The M coordination type where all 8 faces are
6
trigonal
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 ampoule under a vacuum of ca.
6
6
X
ꢀ
2
10 mbar. The reaction was carried out at 800 1C for 16 days. After
the reaction, the ampoule 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 approximately 80%.
EDX analyses of these single crystals, using a TESCAN scanning
electron microscope, confirmed the presence of the component
elements in the average atomic ratio of 36(3):58(3):5(3) (La:Cl:-
Co). The crystals hydrolyze in air within minutes to a white
powder.
6
6 8
X
capped by the X ligands had not been observed for discrete clusters in
the reduced RE metal halide family. Recently, we have reported the
first example of a mixed M
coordination environment is derived from the M
this contribution, we describe the synthesis, structure determination
and bonding analysis of a second example with the mixed M
environment, La Cl11Co. Its structure features isolated La
octahedra but differs from that of the previously reported compound
of similar stoichiometry Sc ) [24].
X12/M X
6 6 8
6
type, La Br10Fe, in which some
6 8
X
pattern [23]. In
6 12
X /
M X
6 8
6
6
Co
6 2
I11(C
2.2. Structure determination
2
. Experimental section
.1. Synthesis
La metal (sublimed, 99.99%; Alfa-Aesar, small pieces), LaCl
The reaction product was ground to fine powder under Ar
atmosphere and sealed in a glass capillary for phase identification
˚
2
by a modified Guinier technique [25] (CuK
a
1
:
l
¼ 1.54056 A;
˚
internal standard Si with a ¼ 5.43035 A; 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. Absorption
3
3
and Co (99.99%; Aldrich) were used as starting materials. LaCl
Ã
Corresponding author.
E-mail address: czheng@niu.edu (C. Zheng).
and polarization effect corrections were applied through a
0
022-4596/$ - see front matter & 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2009.06.002

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308
C. Zheng et al. / Journal of Solid State Chemistry 182 (2009) 2307–2311
face-indexing procedure. The structure was solved with direct
methods using the SIR97 program [26]. Full matrix least squares
refinement on F was carried out using the SHELXTL package [27].
Table 2
4
Atomic coordinates ( ꢁ 10 ) and equivalent isotropic displacement parameters
2
(A˚
2
ꢁ10
3
) for La Cl11Co.
6
The product compound crystallizes in the tetragonal space
˚
Atom
Wyckoff position
x
y
z
U(eq)
group P4
2
/n (no. 86) with lattice constants a ¼ 11.308(2) A and
˚
c ¼ 14.441(3) A. The structure has been checked for possible
existence of higher symmetry by the program ADDSYM in the
PLATON package [28]. No additional symmetry element was
La(1)
La(2)
La(3)
Co
8g
8g
8g
4c
8g
8g
8g
4e
4f
2365(1)
132(1)
83(1)
4825(1)
8142(1)
8542(1)
5000
91(1)
15(1)
12(1)
11(1)
7(1)
1489(1)
ꢀ1264(1)
0
5000
found. However, the structure could only be refined to R
1
¼ 0.28,
Cl(1)
Cl(2)
Cl(3)
Cl(4)
Cl(5)
Cl(6)
Cl(7)
32(2)
6465(2)
6112(3)
5029(3)
7500
ꢀ64(2)
ꢀ1545(2)
2029(2)
835(3)
1064(3)
1242(3)
2834(2)
15(1)
23(1)
21(1)
23(1)
18(1)
28(1)
24(1)
2
and the mean |E ꢀ1| of 0.740 was low for a centrosymmetric
space group. A careful examination of the reciprocal lattice and
testing for different kinds of twinning laws revealed that by
2362(3)
2993(2)
2500
2500
2500
applying a twin matrix of (010; 10 0; 0 0 ꢀ1) the R
1
-factor
4f
ꢀ2500
ꢀ685(3)
7500
converged to 0.0443. The two twin components have nearly 1:1
ratio (48% vs. 52%). The crystallographic information including the
fractional coordinates and selected bond lengths of the compound
using the above twin model is listed in Tables 1–3.
8g
9830(3)
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
Table 3
2.3. Computational study
˚
˚
Selected bond lengths (A) up to 3.7 A and types of Cl atoms for La
6
Cl11Co.
a
Bonds
Distances
Type
The density of states (DOS) and band structure were computed
using both the tight-binding extended H u¨ ckel method (EH)
29,30] and the self-consistent linear muffin-tin orbital local
Cl(1)–La(2), –La(3); –La(1),
2.919(3), 2.939(3); 3.078(3),
3.232(3)
e, i–a; a–i
[
–La(1)
density approximation method (LDA) as implemented in the
Stuttgart-TB-LMTO-ASA program [31]. Sixty-four k-points in the
irreducible wedge of the Brillouin zone were used in the EH
computations, and 6 k-points were used during the self-consistent
convergence part in the LDA calculations. The EH parameters used
in the computation are listed in Table 4. Both EH and LDA methods
were used for a comparison of the electronic structures calculated
by the two very different programs.
Cl(2)–La(1), –La(3); –La(2)
Cl(3)–La(1), –La(2), –La(3);
2.775(3), 2.944(3); 3.101(3)
2.897(3), 3.064(3), 3.104(3);
3.015(3)
e, i–a; a–i
f, i–a; a–i
–La(3)
Cl(4)–La(1), –La(2)
3.214(2), 2.931(2)
e, i–i
Cl(5)–La(1), –La(3)
2.986(2), 3.1629(8)
3.262(3), 3.0836(9)
2.876(3), 2.998(3); 2.965(3)
e, i–i
Cl(6)–La(1), –La(2)
e, i–i
Cl(7)–La(2), –La(3); –La(2)
e, i–a; a–i
La(1)–Co
La(2)–Co
La(3)–Co
2.9895(7)
3.0100(7)
2.4616(6)
La(1)–La(2)
La(1)–La(2)
La(1)–La(3)
La(1)–La(3)
La(2)–La(3)
La(2)–La(3)
4.169(1)
4.315(1)
3.798(1)
3.9456(9)
3.772(1)
4.002(1)
2
.4. Physical property measurements
For measurement of electrical conductivity, the polycrystalline
samples were pressed into pellets of 5 mm in diameter and ca.
mm in thickness. The conventional four-contact method [32]
2
All bonds have multiplicity of 2.
was used. Susceptibility measurements were carried out on a
Quantum Design PPMS 6000 magnetometer, using sample
quantities of ca. 50 mg.
a
The notation follows Sch a¨ fer and Schnering [19]. e and f denote edge bridging
and face capping atoms of bridging atom type i, and a stands for coordination of
corners of adjacent clusters. For example, Cl(4) bridges the La(1)–La(2) edge in one
cluster, and the La(1)–La(2) edge in an adjacent one. Thus it is type e, and in both
clusters it acts as a bridging ligand, thus i–i. Cl(3) caps the La(1)–La(2)–La(3) face,
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 type a–i. Therefore a
semicolon is used to separate these two types. See Fig. 1.
Table 1
6
Crystal data and structure refinement for La Cl11Co.
Formula weight
Temperature
Wavelength
1282.34
293(2) K
0
.56086 A
Tetragonal
P4 /n (no. 86)
˚
Crystal system
Space group
Table 4
2
Extended H u¨ ckel parameters.
Unit cell dimensions
˚
a ¼ 11.308(2) A
a
1
a
1
c ¼ 14.441(3) A˚
Orbital
Hii (eV)
z
z
c
c
2
2
Volume
846.6(5) A
˚
3
1
La
6s
6p
Z
4
3
ꢀ7.67
ꢀ5.01
ꢀ8.21
2.14
2.08
3.78
Density (calculated)
4.613 Mg/m
ꢀ
1
Absorption coefficient
8.396 mm
5d
1.381
0.7765
0.4586
y
Range for data collection
2.64–25.001
Index ranges
ꢀ17rhr17, ꢀ17rkr17, ꢀ21rlr21
Cl
Reflections collected
49 315
3
s
ꢀ30.0
ꢀ15.0
2.033
2.033
Completeness to
y
¼ 25.001
99.9%
3p
Absorption correction
Semi-empirical from equivalents
3312/0/86
Co
4s
Data/restraints/parameters
2
ꢀ9.21
ꢀ5.29
2.00
2.00
5.55
Goodness-of-fit on F
1.327
4p
Final R indices (I42sigma(I))
R indices (all data)
R1 ¼ 0.0443, wR2 ¼ 0.1128
3d
ꢀ13.18
2.100
0.5680
0.6060
R1 ¼ 0.0466, wR2 ¼ 0.1137
Largest diff. peak and hole
.944 and –1.673 e A
˚
ꢀ3
5
a
Exponents and coefficients in a double
z expansion of the d orbital.

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2309
3
. Results and discussion
3.1. Crystal structure
Co-centered La
Cl11Co (Fig. 1). The La
along the La3–Co–La3 axis. The apical La3–Co bond length is
6
octahedra are the main structural feature of
La
6
6
Co octahedron is significantly compressed
˚
2
.4616(6)A, whereas the basal La1–Co and La2–Co bond lengths
˚
are 2.9895(7) and 3.0100(7)A, respectively. This is to be compared
with the Pr–Co distance of 2.77 of an undistorted octahedron in
6
(Ca0.65Pr0.35)Pr I12Co [9]. This distortion is similar to that of
La
to 2.547 A and the basal ones from 2.894 to 3.007 A. The La–La
6
Br10Fe where the apical La–Fe bond lengths range from 2.414
˚
˚
˚
˚
distances vary from 3.77 to 4.31 A, compared to 3.63–4.26A in
6 6
Fig. 1. La Co octahedron coordinated by Cl atoms in the La Cl11Co structure. Atoms
are numbered as in Tables 2 and 3.
6
Fig. 3. EH DOS and COOP curves of representative bonds in La Cl11Co. In the DOS
plot, the solid curves represent the total DOS, the shaded areas and dashed curves
correspond to Co contribution and its integrated value, respectively. The vertical
dashed line indicates the Fermi level. In the COOP plot, the +region is the bonding
and the ꢀregion the antibonding area. The bond type, distance and integrated
overlap population up to the Fermi level are indicated in each panel.
6
Fig. 2. Arrangement of clusters in the structure of La Cl11Co seen in approximate
[
010] direction.

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C. Zheng et al. / Journal of Solid State Chemistry 182 (2009) 2307–2311
˚
La
normal range as in many other reduced rare earth chlorides. They
6
Br10Fe [23]. The La–Cl distances of 2.77–3.26A are within the
3.2. Electronic structure
3+
˚
are also comparable to the sum of the ionic radii of La (1.17 A for
La Cl Co is isoelectronic to La Br10Fe which has 16 cluster
6
11
6
ꢀ
˚
˚
six-coordination and 1.30 A for eight-coordination) and Cl (1.67 A).
Four corners of the octahedron (La1 2 ꢁ and La2 2 ꢁ ) are capped by
two and two corners (La3 2 ꢁ ) by one Cl atom. All 12 edges are
bridged by Cl atoms. In addition, two faces (La1–La2–La3 2 ꢁ ) are
electrons [23]. In the case of an undistorted La Cl11Co octahedral
cluster with the Cl atoms above the octahedron edges, 10 of these
electrons reside in the Co 3d core, and six in the a1g and t1u
orbitals that are of La–La bonding character [1,8,9,23,36]. As in the
6
capped by Cl atoms, whereas in La
6
Br10Fe three faces are capped.
Co
type. The four Cl
atoms (Cl2 2 ꢁ and Cl7 2 ꢁ ) above the basal octahedron apices
also bridge the edges of adjacent La octahedra, and four other
6
La Br10Fe case, these 16 cluster electrons do not exceed the 18
The capping of the two triangular faces of the La
octahedron is a feature of a mixed M
6
electron limit imposed by these orbitals. However, since four
6
X12/M
6
X
8
electrons occupy the degenerate t1u orbitals in the undistorted
cluster, it should be subject to a Jahn–Teller distortion. A
compression along the local z-axis destabilizes one of the three
6
basal corner Cl atoms (Cl1 4 ꢁ ) are shared among three octahedra.
They bridge an edge of a second octahedron and are coordinated
to a corner of a third one. The two Cl atoms (Cl3 2 ꢁ ) connected to
the apical atoms cap the triangular faces of adjacent octahedra. All
other bridging Cl atoms (Cl4 2 ꢁ , Cl5 2 ꢁ and Cl6 2 ꢁ ) also
t1u orbitals that have large Co dz character and stabilizes the
2
remaining two. As we have shown for La Br10Fe, the capping of
6
the two faces will not change significantly the orbital ordering
sequence.
Fig. 3 shows the EH DOS and COOP curves for representative
coordinate to the same edges of adjacent La
In contrast to La
are shared among three La
ligands are shared between three La
Neglecting the Cl atoms above the corners, the discrete cluster
6
Co octahedra (Fig. 2).
Br10Fe where eight Br atoms above the corners
Fe octahedra, in La Cl11Co only six Cl
Co octahedra.
contacts in the La Cl11Co structure. As can be seen in the DOS plot,
6
6
below the Fermi level, all states contribute to La–Cl, La–La and
6
6
La–Co bonding. The Cl 3p band shows up as a wide peak centered
at ꢀ15 eV. The Cl 3s band lies low in energy (ꢀ30 eV) and is not
plotted. The Co 3d band is localized at ꢀ13.2 eV. The next higher
6
e
1
f
2
has the composition La
6
Cl Cl Co where e and f denote positions
level in energy is the a derived state which is of La–Co bonding
2
1g
above the edges and faces of the octahedron, respectively. As the
six e-type atoms (Cl4 2 ꢁ , Cl5 2 ꢁ and Cl6 2 ꢁ ) are shared
between adjacent clusters in the same functionality, the formula
character from the in-phase combination of the La local dz orbital
2
(local z-axis points to Co) and Co 4s. Just below the Fermi level
is a t1u derived state. It is lower in energy than that of the other
two t1u derived orbitals as a consequence of the compression
e
e
f
La
6
Cl Cl Cl Co ¼ La
6
Cl11Co follows. In the notation of Sch a¨ fer
6
6=2
2
and Schnering [19] the inter-cluster connection can be described
as La
along the z-axis of the La Co octahedron. Because of the removal
6
a2i;i2a
ðCl
f
i2i
i2a;a2i i2a;a2I;a2i
e
6
4=2
Þ ðCl Cl
6=2 8=2
Cl
6=3
Þ Co which also reduces to
of the degeneracy of the t1u level, a small band gap of ca. 0.2 eV
results.
6
La Cl11Co.
The closest La–La contact with adjacent octahedra occurs at a
˚
Fig. 4 illustrates the calculated band structure of the La Cl11Co
structure using the LDA method where the Fermi level is set to be
6
distance of 4.942 A between La1 and La2. Thus there is no La–La
bonding between different octahedra. The stacking of these
octahedra is different from the known phase of the same
the zero point of energy. Around ꢀ2.3 eV there are four a1g bands
as there are four clusters per unit cell. The relative energy order is
slightly different from that of the extended H u¨ ckel method. The
a1g bands are below the Co 3d bands. Around the Fermi level, the
t1u bands split into two groups, eight bands are below and four
6 2
stoichiometry Sc I11(C ) which is derived from the cubic close-
packing sequence and crystallizes in the space group P1 [24]. It
should also be noted there are close Cl–Cl anion contacts between
˚
clusters. For example, the Cl(3)–Cl(4) distance is 3.33 A and
above due to the compression of the La Co octahedron. The band
6
˚
Cl(3)–Cl(5) 3.23 A. However, these distances are common in
gap calculated with the LDA method is approximately 0.8 eV,
transition metal or rare earth halides. In WCl
6
, the shortest Cl–Cl
larger than that estimated by the extended H u¨ ckel method.
However, both methods give the same qualitative electronic
structure of the compound.
˚
˚
contact is 3.16 A [33], in TbCl it is 3.07 A [34]. In the reduced rare
˚
6
earth halide Gd Cl N, it is 3.26 A [35].
3
3
Fig. 4. Band structure of La
6
Cl11Co calculated by the LDA method.

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C. Zheng et al. / Journal of Solid State Chemistry 182 (2009) 2307–2311
2311
3
.3. Physical properties
[2] H. Mattausch, A. Simon, Angew. Chem. Int. Ed. 37 (1998) 499–502.
[
[
[
3] H. Mattausch, O. Oeckler, A. Simon, Inorg. Chim. Acta 289 (1999) 174–190.
4] E. Warkentin, A. Simon, Rev. Chim. Miner. 20 (1983) 488–495.
5] D. Nagaki, A. Simon, H. Borrmann, J. Less-Common Met. 156 (1989) 193–205.
The resistivity measured in the temperature range from 20 to
3
00 K revealed an insulating behavior with resistivity in the order
[6] P.K. Dorhout, M.W. Payne, J.D. Corbett, Inorg. Chem. 30 (1991) 4960–4962.
[
[
7] R. Llusar, J.D. Corbett, Inorg. Chem. 33 (1994) 849–853.
8] T. Hughbanks, G. Rosenthal, J.D. Corbett, J. Am. Chem. Soc. 108 (1986)
of M cm. Both the results of band structure calculation and
O
measurement are in agreement with expectation as the discrete-
ness of the cluster due to interconnection via non-metal atom
bridges in all surrounding corners generally results in insulators or
semiconductors [21]. The magnetic susceptibility measurement of
8
289–8290.
[9] T. Hughbanks, J.D. Corbett, Inorg. Chem. 27 (1988) 2022–2026.
10] T. Hughbanks, J.D. Corbett, Inorg. Chem. 28 (1989) 631–635.
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Earths, vol. 28, Elsevier Science Publishers, Amsterdam, London, New York,
Tokyo, 2000, pp. 53–129 (Chapter 177).
[
[
6
La Cl11Co revealed essentially non-magnetic behavior, consistent
with the closed-shell electron configuration as discussed above.
The correction of the measured susceptibility for diamagnetic core
contributions leads to temperature independent (van Vleck-type)
[12] J.D. Corbett, J. Chem. Soc. Dalton Trans. (1996) 575–587.
[
13] A. Simon, H. Mattausch, M. Ryazanov, R.K. Kremer, Z. Anorg. Allg. Chem. 632
2006) 919–929.
(
[14] R. Chevrel, P. Gougeon, M. Potel, M. Sergent, J. Solid State Chem. 57 (1985)
25–33.
paramagnetism in the order of 700 ꢁ10ꢀ6 cm mol which is a
3
ꢀ1
[
[
[
[
15] F.A. Cotton, T.E. Haas, Inorg. Chem. 3 (1964) 10–17.
16] T. Hughbanks, R. Hoffmann, J. Am. Chem. Soc. 105 (1983) 3528–3537.
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18] J. K o¨ hler, G. Svensson, A. Simon, Angew. Chem. Int. Ed. Engl. 31 (1992)
1437–1456.
6
value frequently found for compounds containing discrete M units.
4
. Conclusions
[
[
[
19] H. Sch a¨ fer, H.G. Schnering, Angew. Chem. 76 (1964) 833–849.
20] A. Simon, Angew. Chem. Int. Ed. Engl. 20 (1981) 1–22.
21] A. Simon, Angew. Chem. Int. Ed. Engl. 27 (1988) 159–183.
A second example of a reduced rare-earth metal halide with
the mixed M environment, La Cl11Co, has been reported
6
X12/M
6
X
8
6
[22] G.V. Vajenine, A. Simon, Inorg. Chem. 38 (1999) 3463–3473.
[
23] C. Zheng, H. Mattausch, C. Hoch, A. Simon, Inorg. Chem. 47 (2008)
in this manuscript. The synthesis, structure and bonding of the
compound are also described. It is possible that more phases of
this type exist and deserve to be explored.
2356–2361.
[
[
[
24] D.S. Dubis, J.D. Corbett, Inorg. Chem. 26 (1987) 1933–1940.
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Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Crystallogr. 32
(1999) 115–119.
Acknowledgments
[
[
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We thank V. Duppel for assisting the EDX measurement,
E. Br u¨ cher for the magnetic susceptibility measurements, G. Siegle
for the conductivity measurements, and C. Kamella for help with
the drawings.
[29] R. Hoffmann, J. Chem. Phys. 39 (1963) 1397–1412.
[
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[
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