No solid solution compounds in between the binaries: Syntheses and crystal structures of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2

Article abstract of DOI:10.1515/znb-2017-0188

The anion-mixed niobium tetrahalides Nb(Br_0.62(4)Cl_0.38(4))₂Cl₂ and NbI₂Cl₂ were obtained by heating NbBr₅ with NbCl₅ and NbI₅ with NbCl₅, respectively, in equimolar ratios with niobium metal in evacuated, torch-sealed silica ampoules at 720 K for 3 days. The orthorhombic title compounds form as very brittle black needles and were characterized by single-crystal X-ray diffraction [space group: Immm, Z = 4; a = 704.27(6), b = 824.13(7), c = 929.64(8) pm for Nb(Br_0.62(4)Cl_0.38(4))₂Cl₂ and a = 753.76(6), b = 829.38(7) and c = 983.41(8) pm for NbI₂Cl₂]. Surprisingly enough, these mixed-anionic halides are not isostructural with either NbCl₄, NbBr₄ or NbI₄, but crystallize isotypically with TaI₂Cl₂, thus being examples for differential site occupancy stabilized materials. Structural features of other niobium(IV) halides are compiled and compared to those of Nb(Br_0.62(4)Cl_0.38(4))₂Cl₂ and NbI₂Cl₂. Except for NbF₄, they all exhibit chains of trans-edge connected [NbX₆]^2? octahedra, which allow Peierls distortions to form Nb–Nb single bonds. The packing of these chains differ, however, depending on the actual halide or mixed-halide combination.

Full text of DOI:10.1515/znb-2017-0188

Z. Naturforsch. 2018; 73(1)b: 29–34
Olaf Reckeweg* and Thomas Schleid
No solid solution compounds in between
the binaries: syntheses and crystal structures
of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2
https://doi.org/10.1515/znb-2017-0188
crystallize isotypically, but different to orthorhombic NbI4
[7], experiments were performed to find out if a solid-
solution compound such as NbBr2−xCl2+x (xꢀ≈ꢀ0) would form
and if NbI2Cl2 could be obtained, paralleling the already
known tantalum analogue TaI2Cl2 [8]. We present here the
synthesis and single-crystal structure determination of
Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2, which surprisingly both
adopt the TaI2Cl2 structure [8]. To compare this finding
with the structures of other halides containing tetrava-
lent niobium, their structural features are compiled and
discussed here as well.
Received October 20, 2017; accepted November 17, 2017
Abstract: The anion-mixed niobium tetrahalides
Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2 were obtained by heat-
ing NbBr5 with NbCl5 and NbI5 with NbCl5, respectively, in
equimolar ratios with niobium metal in evacuated, torch-
sealed silica ampoules at 720 K for 3 days. The orthorhom-
bic title compounds form as very brittle black needles
and were characterized by single-crystal X-ray diffraction
[space group: Immm, Zꢀ=ꢀ4; aꢀ=ꢀ704.27(6), bꢀ=ꢀ824.13(7),
cꢀ=ꢀ929.64(8) pm for Nb(Br0.62(4)Cl0.38(4))2Cl2 and aꢀ=ꢀ753.76(6),
bꢀ=ꢀ829.38(7) and cꢀ=ꢀ983.41(8) pm for NbI2Cl2]. Surprisingly
enough, these mixed-anionic halides are not isostructural
with either NbCl4, NbBr4 or NbI4, but crystallize isotypi- 2 Experimental section
cally with TaI2Cl2, thus being examples for differential site
occupancy stabilized materials. Structural features of
2.1 Synthesis
other niobium(IV) halides are compiled and compared
to those of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2. Except for
Due to the air and moisture sensitivity of the reactants and
NbF4, they all exhibit chains of trans-edge connected
[NbX6]2− octahedra, which allow Peierls distortions to form
Nb–Nb single bonds. The packing of these chains differ,
however, depending on the actual halide or mixed-halide
combination.
products, all manipulations were carried out in a glove
box under permanently purified and monitored argon.
All chemicals were obtained from Strem (Kehl, Germany)
and used as received if not stated otherwise. Stoichiomet-
ric mixtures of NbCl5 (yellow powder, 99.99%) and NbBr5
Keywords: bromide; chloride; crystal structure elucida- (reddish powder, 99.9%) (overall mass: 0.3 g) were thor-
tion; iodide; tetravalent niobium.
oughly ground in an agate mortar and transferred into
silica ampoules with 0.5 g stripes of niobium foil (Nb:
1 mm thick foil, 99.8%), which was fused under dynamic
vacuum. The ampoule was heated up to 720 K within 1 day.
The furnace was switched off after 3 days and allowed to
cool to room temperature naturally. The product mixture
consisted of brittle and black needles of NbBr4 and
Nb(Br0.62(4)Cl0.38(4))2Cl2 grown on the niobium foil.
To obtain NbI2Cl2, NbI5 had to be synthesized from
niobium powder (Nb: >99%, powder, Heraeus, Karlsruhe,
Germany) and elemental iodine (I2, crystalline, 99.5%, Alfa
Aesar, Karlsruhe, Germany) enclosed in evacuated 20 cm
long silica ampoules by putting one end with the metal
powder into a tube furnace and heating slowly to 600 K.
After 3 days, no iodine could be observed in the ampoule
anymore, but brass-colored platelets were found crystal-
lizing at the cold end of the tube and some surplus metal
powder at the hot end. NbI5 was used without further
1 Introduction
Binary niobium(IV) halides exhibit different structural
features depending on the actual anion. NbF4 [1–3] forms
a layered structure like SnF4 [4], while NbCl4 [5], NbBr4
[6] and NbI4 [7] contain metal–metal pairs with a single
bond forming chains of edge-sharing [NbX6]2− octahedra
as central structural motif. As NbCl4 [5] and NbBr4 [6]
*Corresponding author: Olaf Reckeweg, Institut für Anorganische
Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart,
Germany, Fax: +49-711-6856-4241, E-mail: olaf.reykjavik@gmx.de
Thomas Schleid: Institut für Anorganische Chemie, Universität
Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
Brought to you by | University of Minnesota Libraries
Authenticated
Download Date | 5/27/18 7:20 PM

ꢀꢀꢀꢁ
30ꢀ ꢀO. Reckeweg and Th. Schleid: Crystal structures of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2
purification. Stoichiometric mixtures of niobium powder, intensity data was performed with the software package
NbCl5 and NbI5 (with an overall mass of 0.3 g) were thor- that came with the respective diffractometer (Table 1) [9].
oughly ground in an agate mortar and transferred into The intensity data were corrected for Lorentz and polari-
a silica ampoule, which was fused under vacuum. The zation effects; the data for Nb(Br0.62(4)Cl0.38(4))2Cl2 were cor-
ampoule was heated up to 720 K within 1 day. After 3 days rected for absorption with the program Habitus [10]. The
at this temperature the furnace was switched off. The structure refinement was performed with the Shelxtl
product consisted of brittle and black needles of NbI2Cl2 program package [11, 12] in the centrosymmetric space
formed on the remaining metal powder. All niobium group Immm (no. 70) and the atomic positions (standard-
tetrahalides with the heavy halides Xꢀ=ꢀCl, Br and I are ized by the ICSD data base) of TaI2Cl2 [8] as starting values.
extremely air- and moisture-sensitive and the crystals For NbI2Cl2, the positions were taken as reported by the
split readily up into finer fibers, if pressure is applied, e.g. ICSD, only the niobium atom was placed on the tantalum
by a preparation needle.
position; for Nb(Br0.62(4)Cl0.38(4))2Cl2 the metals were also
exchanged and bromine was placed on the iodine posi-
tions, but the chlorine positions were kept. All atoms were
refined anisotropically, but the displacement coefficients
of the bromide positions in Nb(Br0.62(4)Cl0.38(4))2Cl2 were
2.2 Crystallographic studies
Single crystals of the black needle-shaped products were found to be quite large. Therefore a mixed refinement with
selected under a microscope in a glove box and sealed chloride was introduced. Selected results of the measure-
into thin-walled glass capillaries. Suitable crystals were ment and structure refinement are displayed in Tables 1–3.
mounted on a Nonius diffractometer operating with Additional crystallographic details are given in Table 1.
graphite-monochromatized MoKα radiation (λꢀ=ꢀ71.07 pm). Atomic coordinates and anisotropic and equivalent iso-
Intensity data sets were collected on specimens of suffi- tropic displacement coefficients are shown in Table 2,
cient quality at room temperature. The processing of the Table 3 displays selected bond lengths and volumes per
Table 1:ꢀSummary of single-crystal X-ray diffraction structure determination data for Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2.
Compound
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
Nb(Br0.62(4)Cl0.38(4))2Cl2
289.17
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
NbI2Cl2
Mr
417.61
Crystal color
Crystal shape
Crystal size, mm3
Crystal system
Space group (no.)
Z
Black
Black
Needle
Needle
0.12ꢁ×ꢁ0.08ꢁ×ꢁ0.02
Orthorhombic
Immm (71)
4
0.25ꢁ×ꢁ0.1ꢁ×ꢁ0.1
Orthorhombic
Immm (71)
4
Lattice parameters: a/b/c, pm
704.27(6)/824.13(7)/929.64(8) ꢂ
753.76(6)/829.38(7)/983.41(8)
V, Å3
539.57(8)
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
614.78(9)
4.51
724
12.7
D
calcd, g cm−3
3.56
F(000), e
524
μ, mm−1
Diffractometer
12.5
Nonius κ CCD (Bruker AXS)
MoK /71.07/graphite
293(α2)
Enraf-Nonius CAD4
MoK /71.07/graphite
293(α2)
Radiation/λ, pm/monochromator ꢂ
T, K
ꢂ
ꢂ
ꢂ
ꢂ
Ranges, 2θmax, deg
hkl range
60.1
53.9
9, 11, 13
3116/469
422
9, 10, 12
1681/414
335
Reflections: measured/unique
Unique reflections with Foꢁ>ꢁ4 σ(Fo)ꢂ
Rint/Rσ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
0.061/0.029
22
0.066/0.147/1.176
<0.00005
+1.7/−1.5
432938
0.062/0.035
19
0.044/0.099/1.095
<0.00005
+2.4/−1.1
407489
Refined parameters
R1a/wR2b/GoFc (all refl.)
Max. shift esd−1 (last ref. cycle)
Δρfin (max/min), e− Å−3
CSD number
2
2
2
2
aR1ꢁ=ꢁΣꢁ|ꢁ|ꢁFoꢁ|ꢁ–ꢁ|ꢁFcꢁ|ꢁ|ꢁ/Σꢁ|ꢁFoꢁ|; bwR2ꢁ=ꢁ[Σw(Fo ꢁ–ꢁFc2)2/Σw(Fo )2]1/2, wꢁ=ꢁ[σ2(Fo )ꢁ+ꢁ(xP)2ꢁ+ꢁyP]−1, where Pꢁ=ꢁ(Max(Fo , 0)ꢁ+ꢁ2Fc2)/3 and x and y are constants
adjusted by the program; cGoFꢁ=ꢁSꢁ=ꢁ[Σw(Fo ꢁ–ꢁFc2)2/(nobsꢁ–ꢁnparam)]1/2, where nobs is the number of data and nparam the number of refined parameters.
2
Brought to you by | University of Minnesota Libraries
Authenticated
Download Date | 5/27/18 7:20 PM

ꢁꢀꢀꢀ
O. Reckeweg and Th. Schleid: Crystal structures of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2ꢃ
ꢃ31
Table 2:ꢀAtomic coordinates, anisotropic and equivalent isotropic displacement parametersa (U in pm2) of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2.
Atom
Wyckoff site
Site occupation
x/a
y/b
z/c
Ueq
Nb
4e
4j
1
0.151(4):0.099(4)
0.157(4):0.093(4)
1
0.2797(2)
0
0
0
0
0.1912(2)
0.2170(2)
0
224(5)
320(9)
310(8)
256(7)
Br1/Cl1
Br2/Cl2
Cl3
0
½
4j
8n
0.2576(3)
0.2838(3)
Nb
I1
4e
4j
1
1
1
1
0.2871(2)
0
0
0
0
0.19413(11)
0.22705(11)
0
192(4)
265(4)
259(4)
196(6)
I2
4j
½
Cl
8n
0.2668(3)
0.2882(3)
aUeq is defined as a third of the orthogonalized Uij tensors.
Table 3:ꢀSelected atomic distances (d in pm) in niobium tetrahalides.
Compound
ꢂ
d(Nb–Nb) (bonding)ꢂ d(Nbꢁ·ꢁ·ꢁ·ꢁNb)ꢂ d(Nb–X) (above Nb–Nb)ꢂ d(Nb–X) (above Nbꢁ·ꢁ·ꢁ·ꢁNb)ꢂ d(Nb–X) (single bonded)
NbF4 [1]
NbF4 [2]
NbF4 [3]
NbCl4 [5]
NbBr4 [6]
NbI4 [7]
NbI2Cl2
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
408.1ꢂ
408.3ꢂ
499.8ꢂ
499.9ꢂ
–ꢂ
–ꢂ
204.0ꢂ
204.2ꢂ
204.0
204.0
408.8ꢂ
499.4ꢂ
–ꢂ
204.4ꢂ
185.8
302.9ꢂ
379.4ꢂ
242.5ꢂ
273.8ꢂ
290/289ꢂ
288.57(14)ꢂ
265.32(18)ꢂ
241.1ꢂ
257.5ꢂ
275/273ꢂ
274.98(14)ꢂ
254.54(19)ꢂ
229.1
245.4
270/265
239.5(3)
234.4(3)
311.3ꢂ
406.8ꢂ
331ꢂ
436ꢂ
321.0(3)ꢂ
310.4(3)ꢂ
433.0(4)ꢂ
394.2(5)ꢂ
Nb(Br0.62(4)Cl0.38(4))2Cl2ꢂ
formula unit of Nb(Br0.62(4)Cl0.38(4))2Cl2, NbI2Cl2 and binary zꢀ=ꢀ0.2282(2) [3]) resulting in a significantly smaller Nb–F
niobium(IV) halides.
bond length (Table 3). This seems to make sense, as the
Further details of the crystal structure investigations fluorine atom on this position is only connected to a single
may be obtained from FIZ Karlsruhe, 76344 Eggenstein- metal atom (Fig. 1).
Leopoldshafen, Germany (fax: +49-7247-808-666; e-mail:
crysdata@fiz-karlsruhe.de) on quoting the deposition
numbers CSD-432938 for Nb(Br0.62(4)Cl0.38(4))2Cl2 and CSD- 3.2 The crystal structures of NbX4
407489 for NbI2Cl2.
(Xꢁ=ꢁCl and Br), Nb(Br0.62(4)Cl0.38(4))2Cl2
and NbI2Cl2
All compounds can be basically traced back on the CdI2
3 Results and discussion
structure. Thus the halide anions are forming a hexagonal
closest packing and the metal cations occupy a quarter of
3.1 The crystal structure of NbF4
the octahedral interstices in an ordered way. Due to the
available electron (4d1) at the Nb4+ core, the formation of a
NbF4 crystallizes in the SnF4-type structure [4]. The metal weak metal–metal bond is observed and the niobium(IV)
cation is coordinated in an octahedral fashion by six fluo- cations move from the centers of their coordination octa-
ride anions. Layers are formed by corner-sharing of these hedra to form metal pairs with a short Nb–Nb distance
[NbF6]2− octahedra expressed with the Niggli connectivity that are just about 10% longer than those (286 pm, 8ꢀ×)
pattern ∞2[NbFv Ft ] (v: vertex-connecting; t: terminal). found in W-type niobium metal [13]. An alternative
4/2 2/1
The crystal structure data reported so far [1–3] are very description for this crystal structure is that of a column
similar, but the most recent measurement performed on formed by trans-edge-sharing [NbX6]2− octahedra with
single crystals shows a smaller c axis and the only freely two significantly different alternating Nb–Nb distances
refined crystallographic coordinate for the only fluorine (Table 3, Fig. 2). This can be attributed to the stabilizing
position 4c (0, 0, z) not fixed by symmetry considerably effect due to a Peierls distortion [8]. Each chain of octa-
deviates from the older reports (zꢀ=ꢀ0.25 [1, 2] compared to hedra ∞1[NbX4e/2 X2t/1 ] (e: edge-connecting; t: terminal) is
Brought to you by | University of Minnesota Libraries
Authenticated
Download Date | 5/27/18 7:20 PM

ꢀꢀꢀꢁ
32ꢀ
ꢀO. Reckeweg and Th. Schleid: Crystal structures of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2
b
Nb
Cl
BrCl
a
c
Fig. 2:ꢀView on the ∞1[Nb(Br,Cl)4e/2Clt2/1 ] chain of octahedra in
Nb(Br0.62(4)Cl0.38(4))2Cl2. Thick black lines indicate covalent bonding,
broken lines indicate the metal–metal single bond. NbI2Cl2 is not
displayed as both crystal structures are isotypic.
2 2 2
m m m
2
m
2
m
t2
c,a,b
I
(no. 71) →I 11 (no. 12) →I 1 1 (no. 12)
This produces only a small difference, which can
c
be identified by the small deviation of the monoclinic
angle from βꢀ≈ꢀ90° if the I-centered monoclinic setting
is used instead of the standard C-centered one (Table 4,
Figs. 3 and 4). This also explains the fact that the first unit
cell parameters were obtained from X-ray powder meas-
urements reported for all niobium tetrahalides with the
heavy halides using an orthorhombic unit cell [14]. The
bond lengths observed are as expected in between those
found for pure NbCl4 [5] and pure NbBr4 [6] (Table 3). The
halide anions bridging the niobium cations, which form
the columns, are recruited from the larger, thus more
easily polarizable congeners. The singly-bonded halide
anions, however, consist of the less polarizable ones such
as chloride.
Nb
F
b
a
Fig. 1:ꢀPerspective view on the unit cell of NbF4.
surrounded by four other chains of the same kind, which
are shifted by half of the respective unit-cell length, in the
direction in which the columns propagate. The chains are
held together just by relatively weak van-der-Waals forces,
well explaining the brittle nature of the crystals and the
relatively high wR2 of the structure refinements (Table 1),
as the crystallinity of the specimens is low as the direc-
tional forces are poor.
The difference between the NbX4-type structure (Xꢀ=ꢀCl
or Br) and the TaI2Cl2 structure [8] adopted by both of the 3.3 The crystal structure of NbI4
title compounds consists just of a slight rotation of the
columns in the pure NbX4-type structure removing the The central structural motif of NbI4 is once more a
∞1[NbIe4/2It2/1
halide anions from special positions and thus reducing
the symmetry according to
chain (e: edge-connecting; t: terminal) of
]
fused [NbI6]2− octahedra, but here the chains have a
Table 4:ꢀUnit cell parameters (pm, deg) and f. u. (formula volume in Å3) of NbX4 (Xꢁ=ꢁCl, Br and I), NbI2Cl2 and Nb(Br0.62(4)Cl0.38(4))2Cl2.
Compound
ꢂ
Unit cell parametersꢂ
f. u. (experimental)ꢂ
f. u. (from binaries)
NbCl4
NbBr4
NbI4
ꢂ
ꢂ
ꢂ
ꢂ
682.3/814.0/885.2//91.9ꢂ
718.2/861.2/936.3//92.2ꢂ
767/1323/1393//90ꢂ
753.8/829.4/983.4//90ꢂ
704.3/824.1/929.6//90ꢂ
122.8ꢂ
144.7ꢂ
176.7ꢂ
153.7ꢂ
134.9ꢂ
–
–
–
NbI2Cl2
149.8
129.4
Nb(Br0.62(4)Cl0.38(4))2Cl2 ꢂ
Brought to you by | University of Minnesota Libraries
Authenticated
Download Date | 5/27/18 7:20 PM

ꢁꢀꢀꢀ
O. Reckeweg and Th. Schleid: Crystal structures of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2ꢃ
ꢃ33
b
Nb
Cl
BrCl
b
a
Nb
I
c
a
c
Fig. 3:ꢀPerspective view of the unit cell of Nb(Br0.62(4)Cl0.38(4))2Cl2
along the crystallographic a axis. Thick black lines indicate covalent
bonding, broken lines indicate the metal–metal single bond.
Fig. 5:ꢀPerspective view of the unit cell of NbI4 along to the crystal-
lographic a axis. Thick black lines indicate covalent bonding, broken
lines indicate the metal–metal single bond.
each other in the direction of the crystallographic b axis,
but the Nb4+ cations are not directly located above or below
each other as in NbX4 (Xꢀ=ꢀCl and Br), Nb(Br0.62(4)Cl0.38(4))2Cl2
or NbI2Cl2. Moreover, the chains above and below each
other are shifted also by one period of metal cations as
indicated by the alternating short and long metal–metal
distances. Therefore, a different environment for the
chains results and thus a different symmetry, not directly
related to the NbCl4- and TaI2Cl2-type compounds.
4 Conclusion
The crystal structures of the niobium tetrahalides have
been compiled and compared. The title compounds
Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2 exhibit the bond lengths
expected for compounds with a mixed halide occupa-
tion (Table 3), but Nb(Br0.62(4)Cl0.38(4))2Cl2 does not form
the expected solid-solution structure between NbCl4 and
NbBr4. Instead, Nb(Br0.62(4)Cl0.38(4))2Cl2 adopts the TaI2Cl2-
type [7] structure, which is also assumed by NbI2Cl2 – as
expected. This cannot be explained by a more dense
packing, as the volume expands for both NbI2Cl2 and
Nb(Br0.62(4)Cl0.38(4))2Cl2. Even replacing as little as about
62% or more of the bridging halide anions drives the
c
Nb
b
Br
a
Fig. 4:ꢀPerspective view of the unit cell of NbX4 (Xꢁ=ꢁCl and Br) along
to the crystallographic b axis (setting: monoclinic I). Thick black
lines indicate covalent bonding, broken lines indicate the metal–
metal single bond.
different orientation relative to each other than for NbX4 new orthorhombic compounds Nb(Br0.62(4)Cl0.38(4))2Cl2 and
(Xꢀ=ꢀCl and Br), Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2. In Fig. 5 NbI2Cl2 away from the monoclinic symmetry of the cor-
it can be seen that the chains in NbI4 are positioned above responding pure binary halides such as NbCl4 and NbBr4.
Brought to you by | University of Minnesota Libraries
Authenticated
Download Date | 5/27/18 7:20 PM

ꢀꢀꢀꢁ
34ꢀ ꢀO. Reckeweg and Th. Schleid: Crystal structures of Nb(Br0.62(4)Cl0.38(4))2Cl2 and NbI2Cl2
[3] M. Strecker, Dissertation, University of Hannover, Hannover
1994; see also: ICDD 45–1208.
[4] R. Hoppe, W. Dähne, Naturwissenschaften 1962, 49, 254.
[5] D. R. Taylor, J. C. Calabrese, E. M. Larsen, Inorg. Chem. 1977,
16, 721.
[6] S. L. Benjamin, Y.-P. Chang, A. L. Hector, M. Jura, W. Levason,
G. Reid, G. Stanning, Dalton Trans. 2016, 45, 8192.
[7] L. F. Dahl, D. L. Wampler, Acta Crystallogr. 1962, 15, 903.
[8] H.-J. Meyer, Z. Naturforsch. 1991, 46b, 289.
[9] Nonius-κ-CCD Software and Enraf-Nonius CAD4 Software,
Nonius BV, Delft (The Netherlands) 1997.
[10] W. Herrendorf, H. Bärnighausen, Habitus, A Program for the
Optimization of the Crystal Shape for Numerical Absorption
Correction (implemented in X-shape), Universität Karlsruhe,
Karlsruhe (Germany) 1993, Universität Gießen, Gießen
(Germany) 1996.
A possible explanation for this can be derived from the
stabilization of structures at high temperatures by differ-
ential site occupancy [15], which is in our case a competi-
tion between the entropy given by the mixed occupation
of anionic sites and the entropy found due to the higher
symmetry and the less dense packing of the octahedral
∞1[NbX4e/2 X2t/1 ] chains.
Acknowledgments: We thank Prof. Dr. H.-Jürgen Meyer
(Institut für Anorganische Chemie, Universität Tübingen)
for the permission to use the data for NbI2Cl2 acquired in
the frame of the research work performed for the doctoral
thesis of O. R.
[11] G. M. Sheldrick, Shelxl-97, Program for the Refinement
of Crystal Structures, University of Göttingen, Göttingen
(Germany) 1997.
[12] G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112.
[13] S. E. Rasmussen, Acta Chem. Scand. 1977, A31, 79.
[14] R. E. McCarley, B. A. Torp, Inorg. Chem. 1962, 2, 540.
[15] H. F. Franzen, M. Köckerling, Prog. Solid State Chem. 1995,
23, 265.
References
[1] F. P. Gortsema, R. Didchenko, Inorg. Chem. 1965, 4, 182.
[2] H. Schäfer, H. G. von Schnering, K. J. Niehues,
H. G. Nieder-Vahrenholz, J. Less-Common Met. 1965, 9, 95.
Brought to you by | University of Minnesota Libraries
Authenticated
Download Date | 5/27/18 7:20 PM