Alkali Halide Cubic Cluster Anions ([Cs8X27]19-, X = Cl, Br) Isolated from Water

Article abstract of DOI:10.1021/acs.inorgchem.6b01741

Herein we report the syntheses and the X-ray structure of [Cs₈X₂₇]^19- (X = Cl, Br) clusters, the first binary cluster anions isolated in bulk crystal structures. They were obtained by electrostatic capture and face-directed recognition of the prenucleation [Cs_mCl_n]^(n-m)- clusters from water solutions, using [M₄(OH)₈(OH₂)₁₆]⁸⁺ (M = Zr^IV or Hf^IV) as the counter cations. These compounds have been thoroughly characterized with a variety of techniques including vibrational spectroscopy and superionic conductivity analysis. This work not only provides structural models for a better understanding of the nucleation of binary materials but also shows that magic number binary clusters adopting a cubic lattice structure do form, in agreement with the time-honored theoretical and spectroscopic predictions.

Full text of DOI:10.1021/acs.inorgchem.6b01741

Article
pubs.acs.org/IC
19−
Alkali Halide Cubic Cluster Anions ([Cs X ] , X = Cl, Br) Isolated
8
27
from Water
Qing Sun, Guanyun Zhang, Chen-Ho Tung, and Yifeng Wang*
Key Lab for Colloid and Interface Science of Ministry of Education, School of Chemistry and Chemical Engineering, Shandong
University, Ji’Nan 250100, People’s Republic of China
*
S Supporting Information
ABSTRACT: Herein we report the syntheses and the X-ray structure of
19‑
[
Cs X ] (X = Cl, Br) clusters, the first binary cluster anions isolated in
8 27
bulk crystal structures. They were obtained by electrostatic capture and
(
n−m)−
face-directed recognition of the prenucleation [Cs Cl ]
clusters from
m
n
8
+
IV
IV
water solutions, using [M (OH) (OH ) ] (M = Zr or Hf ) as the
4
8
2 16
counter cations. These compounds have been thoroughly characterized
with a variety of techniques including vibrational spectroscopy and
superionic conductivity analysis. This work not only provides structural
models for a better understanding of the nucleation of binary materials but
also shows that magic number binary clusters adopting a cubic lattice
structure do form, in agreement with the time-honored theoretical and
spectroscopic predictions.
1
. INTRODUCTION
having the (face-centered) cubic structures are the most
1,10,19,24,27,29
energetically favorable.
However, direct wet-chem-
Nucleation clusters are fundamental objects connecting the
molecular and the solid-state worlds and are important not only
in nature such as aerosol and mineral formation but also in
material synthesis and understanding the origin/structures/
ical synthesis of an alkali halide cluster ion and characterization
of it with X-ray crystallography have never been carried out.
In this Article, we have successfully crystallized two cubic
1
9−
1
cesium halide cluster anions from water, namely, [Cs
X ]
8 27
properties of macroscopic materials. As such, the behavior of
(
X = Cl, Br), which exhibit the CsCl-type (space group: pm3m)
̅
atoms and molecules on nanoscales is intriguing, and whether
nuclei adopt the same crystalline structure as in the extended
solid is one problem that has long piqued the interest of many
scientists. While studies have shown that the simple metallic
bonded clusters such as Au(0)
face-centered-cubic (fcc) atom-packing structures than other
structures such as icosahedral, no report based on crystallog-
raphy shows that binary compound nuclei can adopt their bulk
structures.
bulk crystal structure and are possibly the native species in
aqueous solutions of CsCl and CsBr. They were isolated in the
intercluster salts based on the cluster anion [Cs
1
9−
2
,3
8
X
27
]
in the
4
−6
7
presence of another pair of cluster cations based on Zr or Hf,
and Ag(0) less favor the
8+
IV
IV
[
M (OH) (OH ) ] (M = Zr or Hf ; the structures are
4 8 2 16
6
shown below). Structural studies suggest that electrostatic
interaction and face-directed recognition dominate the
crystallization of the cluster compounds from water. They
have also been characterized by FT-IR, Raman, powder X-ray
diffraction, thermogravity analysis, and superionic conductivity
measurements. This work provides binary cluster structures
containing magic numbers of atoms, which are helpful for a
better understanding of the nucleation of binary materials. In
3
,8
Alkali halide crystals are the typical and the simplest binary
9
ionic systems. Due to the ease of formation and the simplicity
for theoretical treatments,
studied for understanding the fundamental processes relevant
to nucleation,
salts in solutions and in aerosols. As a common material and a
simple model system, in order to understand the nucleation
processes and the structural behaviors at the nanoscale,
numerous studies have been focusing on producing and
characterizing alkali-metal halide cluster ions in the gas phase,
15
1
,10
they have been extensively
9
,11
9
12
ion attachment, hydration, and growth of
+
addition, the solution chemistry of Cs together with heavy-
1
IV
transition-metal Zr demonstrated herein may also help better
explain the chemistry in handling aqueous nuclear fuel wastes
+
IV
containing both Cs and tetravalent heavy-metal ions (e.g., Zr ,
Th , and Pu ).
IV
IV 30−34
1
,13,14
including cleaving and melting by impact,
laser ablation, ion−molecule reactions in a flowing after-
glow, and electron-spray ionization (ESI) and the recent
use of liquid helium nanodroplets. Meanwhile the studies of
over four decades using theoretical simulation,
spectroscopy (MS),
sputtering,
2
. RESULTS AND DISCUSSIONS
1
6
1
7
11
General Considerations. Although a great number of
studies have reported the capture of clusters in the size regime
1
8
1
,10,19−24
mass
11,18,25−27
18,28
and spectroscopic methods
Received: July 20, 2016
have suggested that clusters with magic numbers of atoms and
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.6b01741
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3
6,37
of “nuclei” (i.e., 0.5−2 nm), due to the use of ligands for
stabilizing the quantum-sized clusters of extremely high surface-
to-volume ratio, the distortion of the clusters from the bulk
structures is inevitable. By contrast, the nuclei’s native
structures may be preserved by using noncovalent interactions
in the synthesis. Supramolecular intercluster compounds
[Zr (OH) (OH ) ]Cl ·12H O
) may form along if evap-
4
8
2 16
8
2
oration is too fast (e.g., under reduced pressure for a few
minutes), but are ultimately converted to 1 upon aging,
indicating that 1 is thermodynamically more stable (less
soluble) than ZrOCl ·8H O. No other crystalline products
were noticed by varying reaction conditions such as temper-
ature, precursor ratio, and solution acidity. If excess amounts of
crystalline ZrOCl ·8H O and CsCl are added together to the
mother liquor of 1, although they may not be soluble, they
could be slowly converted into fine crystals of 1 in a few days,
also.
2
2
(
SICC) are “bottom-up” assemblies of different and well-
defined inorganic building blocks, a new class of ionic
2
2
3
5
materials. The interaction between the building blocks of
an SICC is noncovalent and relatively weak such as Coulombic
interaction and hydrogen bonding. Their formation depends
purely on the solubility product (K ) of the counter cluster
Compound 1 is composed of two basic building blocks, i.e.,
sp
19−
8+
ions. In this report, we have used the intercluster strategy, with
[Cs Cl ] (1a) and [Zr (OH) (OH ) ] (1b). 1a (Figure
8 27 4 8 2 16
8
+
IV
IV
the [M (OH) (OH ) ] (M = Zr or Hf ; see Scheme 1 for
1) resembles the textbook illustrations of the CsCl-type cubic
4
8
2 16
(
n−m)−
Scheme 1. Illustration for the Formation of [Cs X ]
(X
m
n
=
Cl, Br) Prenucleation Clusters in Water and the Capture of
19−
the [Cs X ] Cubic Cluster Anion (for the Case of m = 8
8
27
and n = 27 in the Illustration) by Addition of
8
+
IV
IV
a
[
M (OH) (OH ) ] (M = Zr , Hf )
4 8 2 16
a
8+
19−
Figure 1. Ball-and-stick structure of the [Cs Cl ]
(1a). Color
The [M (OH) (OH ) ] cation is shown in the ball-and-stick
8
27
4
8
2 16
1
9−
scheme: Cs, gray; Cl, green. The overall dimension of 1a, specified by
the length along a cube edge, is 10.3 Å; its diameter is 16.5 Å along the
body diagonal. Inset on the right: illustration of the CsCl-type cubic
lattice (3 × 3 × 3 Cl atoms with one Cs at each center of the eight
cubes) and the corresponding low-index planes indicated by vectors
and Miller indices.
structure, while the [Cs X ] cubic cluster is shown using the space-
filling representation. Color scheme: blue, Zr or Hf ; red, O; white
and gray, H; green, Cl or Br; gray, Cs. In the structure of
8
27
IV
IV
8
+
IV
IV
[
M (OH) (OH ) ] (M = Zr or Hf ), each M (blue) is
4 8 2 16
coordinated to eight oxygen atoms (red) from four aqua ligands and
four μ -OH.
36,37
.
2
3
6,37
the structure) hydroxo cluster
as the counter cation, to
̅
crystal lattice structure (space group pm3m; right inset of
3
capture and to stabilize the cesium halide prenucleation
clusters, and successfully isolated two cesium halide cluster
anions, which resemble four unit cells of the bulk structure of
Figure 1). It consists of 3 = 27 Cl ions in total, placing three Cl
−
ions along each edge and a Cl ion at the single interior site and
each of the six face sites of the cubic lattice. The tetragonal
pm3
̅
m CsCl type.
packing of Cl anions on the facets of 1a resembles the (001)
plane of a cubic lattice. Each Cs ion occupies the interior site
of a cube comprising eight vertex Cl ions.
+
Synthesis and Structure. Notably, many prenucleation
clusters (e.g., [Cs Cl ]
(
n−m)−
, Scheme 1) are naturally occurring
m
n
in alkali halide aqueous solutions, especially of relatively high
Since the successful synthesis of 1, we have devoted many
efforts to the syntheses of analogous compounds based on
other alkali halides and Zr /Hf clusters. However, only
3
8
concentrations. This is probed herein using ESI-MS in the
analysis of a CsCl (3.0 M) solution. The ESI-MS results reveal
IV
IV
+
negligible abundance of individual Cs and a series of more
[Cs Br ]·3[Zr (OH) (H O) ]·5Br·42H O (2), [Cs Cl ]·3-
8
27
4
8
2
16
2
8
27
+
−
abundant clusters [Csm+1Cl ] and [Cs Cl ] with m in the
[Hf (OH) (H O) ]·5Cl·42H O (3), and [Cs Br ]·3-
m
m
m+1
4 8 2 16 2 8 27
(
m−n)
range 1−11 (Figure S1). No multicharged [Cs Cl ]
species were observed, likely due to the limitation of the ESI-
MS technique. The abundance is the largest for [Cs Cl] in the
[Hf (OH) (H O) ]·5Br·42H O (4), all containing
4 8 2 16 2
1
m
n
9−
19−
[Cs Cl ] (3a) or [Cs Br ] (2a and 4a) building blocks,
8 27 8 27
+
were successfully obtained afterward (Figures S2−S5).
Compounds 1−3 crystallize in the F43c space group, while 4
crystallizes in the space group Pm3m, all belonging to the cubic
2
−
positive mode ESI and [CsCl ] in the negative mode ESI and
̅
2
decreases dramatically with nuclearity.
̅
8
+
Addition of [Zr (OH) (H O) ] (in the form of 1.0 M
ZrCl4
crystal system. The unit cells of 1−3 have similar volume (ca.
4
8
2
16
3
4,39
3
) to a CsCl aqueous solution (1.0 M) followed by
34 000 Å ) and contain eight equivalent points each, while each
evaporation of solvent under ambient conditions successfully
captured an octacesium chloride cluster, and yielded colorless
block crystals in a few days, formulated as [Cs Cl ]·
unit cell of 4 contains only one equivalent point and has a
smaller cell size of 4523 Å . More crystallographic data of 1−4
are included in Table S1. By contrast, none of the rock-salt-type
alkali halides, nor CsI, which has a larger cell parameter, forms
the same type of compounds as 1−4; instead, they tend to
crystallize independently from the aqueous solutions.
3
8
27
3
[Zr (OH) (H O) ]·5Cl·42H O (1). It is noteworthy that
4 8 2 16 2
the synthesis is simple and the yield is high, e.g., 60% for 1 (in
Zr). Needle-like colorless crystals of ZrOCl ·8H O (formally
2
2
B
DOI: 10.1021/acs.inorgchem.6b01741
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
a can be viewed as a four-unit-cell segment of the CsCl
Article
1
We speculate the protons in the channels (of the solvent
water molecules; see Figure S6) may exhibit some mobility
when bias is applied. Hence, the ionic conductivity (σ) was
measured by ac impedance according to the published method,
for which crystals were ground into powder, which was further
structure. Alternatively, 1a can also be viewed as a Cs Cl single-
8
unit cell stabilized by 26 Cl anions. Hence, 1a, together with 2a,
3
a, and 4a, has been the first example of I−VII group binary
cluster compounds that adopt the essential structural aspects of
the crystalline solid and were isolated and characterized by
crystallography.
44
pressed into pallets. For comparison, a well-known Zr-oxo
1
,2,18,27
On the other hand, the Cs Cl core
cluster, ZrOCl ·8H O (formally [Zr (OH) (OH ), was
2
2
4
8
)16]Cl
2 8
8
7
+
(Figure 2B) of 1a can be regarded as the [Cs Cl ] cluster that
also studied. Figure S7 shows the real (Z′) and imaginary (Z″)
parts of the complex-plane impedance data. Both 1 and the
ZrOCl ·8H O show well-behaved Nyquist plots of typical ionic
8
7
has been detected by ESI-MS (Figure S1).
2
2
conductors. The Cole−Cole plot was well fitted by a single
half-circle, indicating that the observed conductivity is
attributed to the material itself. The circular arc fitting indicates
that the σ values are 1.05 × 10− and 6.78 × 10 S cm ,
respectively, at 296 K and 100% relative humidity (RH). The
higher conductivity of 1 can be tentatively attributed to its
regular channels and the larger content of solvent water per
5
−6
−1
3
volume (0.010 H O per Å ; see Figure S6) than that of ZrOCl ·
2
2
3
8
H O (0.0013 H O per Å ).
2 2
Face-Directed Recognition of the Clusters. The ratio of
a and 1b in 1 is 1:3. Namely, six 1b clusters face-to-face attach
to the six surfaces of each 1a cube, while each 1b is shared by
1
Figure 2. (A) Cs Cl and (B) Cs Cl cores of 1a.
8
8
7
two 1a clusters. 1a carries the highest negative electron density
45
among all the known clusters, and 1b also carries a highly
positively charged core (note that all the positive charges are
The eight Cs atoms in 1a (Figure 1) are symmetrically
identical, while the 27 Cl atoms are classified into four types by
distributed over the Zr (OH) tetragon). Hence electrostatic
4
8
attraction between the two building blocks should play an
important role in the structural stability of 1.
their coordination numbers, namely, one μ -Cl at the center, six
8
μ -Cl at the face sites, 12 μ -Cl at the edges, and eight μ -Cl at
4
2
1
However, examination of the syntheses and structures
the vertices. The ionic bond lengths in 1a are Cs−(μ -Cl) =
8
1
9−
indicates that recognition of the [Cs X ] (X = Cl or Br)
3
.64 Å, Cs−(μ -Cl) = 3.63 Å, Cs−(μ -Cl) = 3.51 Å, and Cs−
8 27
4
2
8+
clusters by the [M (OH) (OH ) ] (M = Zr or Hf) clusters
(
μ -Cl) ≈ 3.74 Å. For comparison, in the pm3
̅
4
8
2 16
1
40
plays a more important role in the formation and the
thermodynamic stabilities of compounds 1−4. Despite that
rock salt-type alkali halides could also form highly negatively
charged species (e.g., an fcc unit cell of bulk NaCl with Cl on
the Cs−Cl distance is uniformly 3.56 Å. Hence the Cs−(μ -
4
Cl) and Cs−(μ -Cl) in 1a are longer than the bulk Cs−Cl
8
distance by ca. 0.08 Å, while that of Cs−(μ -Cl) is shorter than
2
the bulk by 0.05 Å. Analogous results are obtained for
structures of 2a, 3a, and 4a with respect to those of pm3
or CsBr structures (Table S2).
̅
the surface has a formula of Na14Cl43), reaction of ZrCl with a
4
mixture of alkali halide solutions containing LiCl, NaCl, KCl,
RbCl, and CsCl gave purely 1 as the sole product before
Previously, numerous theoretical and experimental studies
have shown that magic number alkali halide clusters are
saturation of the other salts, while reaction of ZrCl
4
1
2,18,41,42
energetically favorable structures.
For example, Martin
independently with any of the alkali chlorides except CsCl
(FrCl was not checked) did not yield analogous structures to 1.
Besides, CsI, which has a larger cell parameter (than both CsCl
and CsBr), does not form interclusters with
43
used total energy calculations to show that the 3 × 3 × 3
+
structure has the lowest energy for [Na Cl ] ions (n = 1−
n
n−1
1
8), and recently this was confirmed using mass spectroscopy
8+
by the observation of the abundance peak of the 3 × 3 × 3
[M
4
(OH)
8
(OH
2
)
]
16
(M = Zr or Hf) as well. Therefore,
+
18
(
NaF) Na ion. Herein the present Cs X cores of the
only when the CsCl-type cubic crystal’s cell length matches the
dimension of 1b (or 2b, 3b, 4b) can the intercluster compound
13
8 7
1
9−
[
Cs X ]
(X = Cl, Br) are also magic number clusters
Figure 2B). On the other hand, previous structural studies
8
27
(
form (Figure 3). For 1, the edge length of a Cs Cl27 unit in bulk
8
based on energy minimization in vacuo showed that the
neighbor counterion distance is smaller than the bulk and
increases with the size of the clusters, while the surfaces of a
CsCl is 8.22 Å (Table 1), while formation of 1 causes this edge
length to slightly elongate to 8.51 Å. The O−O distances of the
adjacent interfacial oxygen atoms (i.e., d and d as indicated in
1 2
1
magic cluster are buckled. In these respects, the theoretically
Figure 3) of 1a are 4.39 and 5.04 Å and are near half of the
edge length of 1a and 3a (ca. 8.50 Å). As the cell length
becomes slightly larger than that of CsBr, the edge length of a
bulk Cs Br unit can still match the d and d of 2b and 4b,
optimized structures are, however, different from the present
unit-cell clusters synthesized by the wet chemical approach, in
which interactions with counterions and water molecules tend
to constrain the ionic bonds.
8
27
1
2
respectively; hence 2 and 4 can form. However, the edge length
Superionic Conductivity. The cavities beyond 1a and 1b
in 1 are filled with disordered Cl anions and water molecules,
which are interconnected into channels throughout the crystal
structure (Figure S6A). Thermogravity analyses (TGA)
indicate that the crystal water and the aqua ligands of 1b
begin to release above room temperature and are completely
lost at ca. 200 °C, and afterward HCl is released until ca. 500
of a bulk Cs8I27 unit of CsI (9.14 Å) is already too large to
8
+
match the values of d and d of [M (OH) (OH ) ] (M = Zr
1
2
4
8
2 16
or Hf), and hence no analogous intercluster can from.
1
9−
FT-IR Data. The size match between the [Cs X ] (X =
8
27
8+
Cl or Br) and [M (OH) (OH ) ] (M = Zr or Hf) not only
4
8
2 16
minimizes the distance between the charge centers (noteworthy
1
9−
that this demands the interfacial X anions of [Cs X ] (X =
8
27
IV
IV
°
C, leaving ZrO and CsCl (Figure S5).
Cl or Br) to be located as close to Zr /Hf as possible) but
2
C
DOI: 10.1021/acs.inorgchem.6b01741
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
−
1
4
(
50−1050 cm , which are assigned to Zr−(OH)−Zr and Zr−
OH ) bonds, are all shifted in 1 or 2. The hydrogen bonding
2
should also contribute to the stability of the interclusters 1−4.
Solution NMR Data. The interaction between the
8+
(m−n)
[
Zr (OH) (OH ) ] clusters and the [Cs Cl ]
species
4
8
2 16
m
n
in solution was also analyzed using Cl-35 NMR (Figure S8).
Data show that strong interaction causes broadening of the Cl-
3
5 signals, implying various chemical environments of Cl, likely
(
m−n)
due to hydrogen bonding of the [Cs Cl ]
species to
m
n
8+
[
Zr (OH) (OH ) ] in water solutions. However, ESI-MS
4 8 2 16
8
+
results show that [Zr (OH) (OH ) ] did not induce a
4
8
2 16
(
m−n)
change to the [Cs Cl ]
speciation (Figure S9). Due to the
m
n
face-directed molecular recognition and likely the low solubility
of the intercluster compounds, only the octa-Cs cluster can be
8
+
p r e c i p i t a t e d b y [ Z r ( O H ) ( O H ) ]
o r
Hf (OH) (OH ) ] , and with the progression of solvent
4
8
2
1 6
8+
[
4
8
2 16
(
m−n)
evaporation all the [Cs Cl ]
species of various nuclearities
m
n
Figure 3. Structures of 1a and 1b in 1 from the top and (insets on the
right) from the side. L is the center-to-center distance of Cl at
neighbor vertices. d and d are the distances between two adjacent O
are converted to 1a ultimately.
Comparing to other studies in which the prenucleation
clusters were also captured from water by adding nanosized
molecules, e.g., isolation of the uranyl cluster compounds by
adding macrocyclic curbit[n]urils (n = 5, 6, 7, 8), it is
therefore realized herein that weak interactions such as
hydrogen bonding and Couloumbic interactions may be
generally useful in isolation of the native species from water.
1
2
atoms near the interface of 1a and 1b.
4
9
Table 1. Selected Crystallographic Parameters of the
a
Building Blocks
edge length of bulk
Cs8X27 unit, Å
salt
L, Å
d(O···O), Å
4+
It is also interesting that we have observed that Zr ions can
4
0
CsCl
8.22
8.51 in 1;
d = 4.39, d = 5.04 in 1;
selectively form intercluster compounds with Cs+ in the
presence of a common halide anion. As aqueous nuclear fuel
1
2
8
.49 in 3
8.72 in 2;
.69 in 4
d = 4.38, d = 5.01 in 3
1 2
4
6
40
33,34
CsBr
CsI
8.46; 8.54
d = 4.47, d = 5.02 in 2;
1 2
wastes contain irradiative isotopes of both Cs and Zr,
the
8
d = d = 4.72 in 4
1 2
compounds and the solution chemistry reported herein may
help better explain the aqueous nuclear fuel processing
operations.
4
7,48
9.14
a
Under ambient conditions, CsCl, CsBr, and CsI form the
interpenetrating primitive cubic lattice structure (the so-called
CsCl-type” structure), while other alkali halides form the fcc rock-
“
3
. CONCLUDING REMARKS
salt structure.
19−
We have successfully captured the [Cs X ]
(X = Cl, Br)
four-unit-cell, prenucleation clusters from water, by using
8
27
also maximizes the hydrogen bonding between the aqua ligands
of 1b and the interfacial Cl atoms of 1a (the lower inset of
Figure 3). Herein hydrogen bond formation is also
spectroscopically evidenced by the IR spectra of the
compounds (Figure 4). Comparing the IR spectra of ZrOCl2·
8+
IV
IV
[
M (OH) (OH ) ] (M = Zr or Hf ) to form intercluster
4 8 2 16
compounds, without using covalent ligands. 1a−4a are the first
examples of I−VII group binary clusters that adopt the essential
structural aspects of the crystalline solid and were isolated and
characterized by X-ray crystallography. These clusters provide
structural models for understanding the nucleation of binary
materials and meanwhile have confirmed the previously
theoretically predicted smallest alkali halide clusters. Face-
directed recognition is demonstrated to play an essential role in
the intercluster formation. Moreover, the ability to form
interclusters, as well as the strong interaction between Cs-halide
prenuclei and Zr-oxo clusters, provides information for a better
understanding of aqueous nuclear fuel processing operations.
8
H O and 1 (curves a and b), the emergence of the additional
2
−1
fine features in the range 2800−3700 cm assigned to O−H
stretching is caused by hydrogen bonding to Cl. Meanwhile
also due to hydrogen bonding, the bending mode of OH in
−1
−1
ZrOCl ·8H O (1620 cm ) is shifted to 1630 cm in 1 and to
2
2
−1
1614 cm in 2; other bands of ZrOCl ·8H O, in the range
2 2
4
. EXPERIMENTAL SECTION
Reagents. Analytical-grade CsCl, CsBr, CsI, zirconium(IV)
butoxide (80% in n-butanol), ZrCl (98%), and xylenol orange were
4
purchased from Macklin Inc. HfCl (98+%) was obtained from Alfa-
4
Aesar. Zirconium(IV) acetylacetonate (98%) was supplied by Aladdin
Co. Acids, bases, and cetyltrimethylammonium bromide were supplied
by Sinopharm Chemical Reagent Co., Ltd. All other chemicals were
obtained from commercial sources and used as received. Deionized
water (18.25 MΩ) was used for all the experiments.
General Procedure for Syntheses. To 10 mL of a 1.0 M ZrCl
4
solution (or HfCl solution) was added CsCl. The final concentration
4
of CsCl is near 1.0 M. After being filtered through a 0.22 μm
membrane filter, the solution was allowed to stand under ambient
conditions for solvent evaporation. Colorless and high-quality block
Figure 4. FTIR spectra of (a) ZrOCl ·8H O, (b) 1, and (c) 2.
2
2
D
DOI: 10.1021/acs.inorgchem.6b01741
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Inorganic Chemistry
Article
crystals formed after 1 week. Alternatively, a faster protocol can be
used. For this, the filtrate was rotary evaporated under reduced
pressure until a precipitate formed. The supernatant was withdrawn for
further evaporation under ambient conditions to give the final product.
The product was collected by filtration and air-dried with suction for
were dissolved in neutral water to give solutions containing ca. 0.02 M
halide. A 2.00 mL amount of the sample solution and 1.00 mL of a
−1
10.0 g L K CrO solution were mixed in a beaker. The mixture was
2
4
titrated by a AgNO3 solution (ca. 0.02 M; the concentration is
precisely titrated using the K CrO4 standard solution). The color
2
10 min. Yields are based on fine crystalline samples. The formulas of
changed from yellow to red at the end point. The concentrations of
halides in the sample solutions were then determined based on the
titration end point and the predefined calibration curve (which was
determined using a series of KCl solutions). Each sample was titrated
at least three times to give an average value of halide content in the
sample.
the compounds are based on crystallography, TGA, and elemental
analysis.
[
Cs Cl ]·3[Zr (OH) (H O) ]·5Cl·42H O (1), and [Cs Cl ]·
8 27 4 8 2 16 2 8 27
3
[Hf (OH) (H O) ]·5Cl·42H O (3) were synthesized following
4 8 2 16 2
the above procedure. Yield: 60% of 1 based on Zr and 72% for 3
based on Hf. Anal. Calcd for 1: Zr, 20.6; Cl, 21.3. Found: Zr, 20.1; Cl,
2
2.0. Anal. Calcd for 3: Hf, 33.6; Cl, 17.8. Found: Hf, 33.4; Cl, 18.0.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b01741.
■
For the synthesis of [Cs Br ]·3[Zr (OH) (H O) ]·5Br·42H O (2),
the 1.0 M Zr(IV) bromide solution was prepared by dissolving
Zr(OBu) in excess HBr, and the following steps are the same as the
above. Anal. Calcd for 2: Zr, 16.2; Br, 37.9. Found: Zr, 16.1; Br, 38.2.
The yield was 32% based on Zr(OBu) . To synthesize [Cs Br ]·
3
solution was prepared first and the following steps were the same as
the general procedure. For preparation of a Hf(IV) bromide solution,
8
27
4
8
2
16
2
*
S
4
4
8
27
[Hf (OH) (H O) ]·5Br·42H O (4), a 1.0 M Hf(IV) bromide
4 8 2 16 2
Experimental details and more characterization data
(PDF)
X-ray crystallographic data for 1 (CIF)
X-ray crystallographic data for 2 (CIF)
X-ray crystallographic data for 3 (CIF)
X-ray crystallographic data for 4 (CIF)
the precipitate obtained by adding NaOH to HfCl (1 M) was washed
five times with deionized water and then was quantitatively dissolved
in HBr. The yield was ca. 10% based on HfCl . Anal. Calcd for 4: Hf,
4
4
27.5; Br, 32.8. Found: Hf, 27.6; Br, 32.7.
Methods. All the moisture-sensitive materials were stored and
weighed in a glovebox in which the H O concentration is lower than
2
AUTHOR INFORMATION
Corresponding Author
*E-mail (Y. Wang): yifeng@sdu.edu.cn.
Notes
■
0.1 ppm. FT-IR was recorded on a PerkinElmer Spectrum Two IR
spectrometer. Raman spectra were obtained on a NEXUS 670 FT-IR
with 532 nm excitation. Powder X-ray diffraction (PXRD) was
recorded on a Bruker D8 Advance X-ray diffraction instrument using
Cu Kα radiation (40 kV and 40 mA). Single-crystal X-ray diffraction
was performed using a Bruker SMART APEX II diffractometer with a
graphite-monochromatic Mo Kα radiation source (λ = 0.710 73 Å) at
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
1
73 K. The distance of the sample to the detector was set to 6.19 cm.
■
A charge-coupled device (CCD) array detector was used to collect the
data. The structures of the compounds were solved/refined by Olex2
v1.2 software with the SHELX package. Hydrogen atoms of
Y.W. thanks the National Natural Science Foundation of China
(21473104 and 21401117) and Natural Science Foundation of
Shandong Province (ZR2014BQ003) for financial support, and
C.T. thanks Shandong University for a startup fund
8+
[
M (OH) (OH ) ] (M = Zr or Hf) were added theoretically and
4 8 2 16
were not included in the refinement. The crystal data and refinement
(
104.205.2.5).
details are summarized in Table S1. TGA was performed on an SDT
−1
Q600 instrument from 40 to 1000 °C at a heating rate of 10 °C min ,
−1
REFERENCES
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■
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measurement frequency ranged from 0.01 Hz to 1 MHz. Cl-35
NMR (in aqueous solution) data were recorded using a Bruker
Advance III 400 MHz spectrometer at 298 K.
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DOI: 10.1021/acs.inorgchem.6b01741
Inorg. Chem. XXXX, XXX, XXX−XXX