Solid-state syntheses of coordination polymers by thermal conversion of molecular building blocks and polymeric precursors

Article abstract of DOI:10.1021/ic300235s

The syntheses and crystal structures of a mononuclear cadmium complex and five novel coordination polymers based on 1,2,4-triazolyl benzoates are presented. The compounds ∞₃[Cd(H-Me-trz-pba)₂] (2), ∞₃[Cd(Me-3py-trz-pba)₂] (4), and ∞₃[Zn(H-Me-trz-pba)₂] (6) can be obtained by solvothermal synthesis or simple heating of the starting materials in appropriate solvents, and are also accessible by thermal conversion of the complex [Cd(H-Me-trz-pba)₂(H₂O)₄] (1), the one-dimensional (1D) coordination polymer ∞₁[Cd(Me-3py-trz-pba) ₂(H₂O)]H₂O (3), and the porous three-dimensional (3D) framework ∞₃[Zn(H-Me-trz-pba) ₂]4H₂O (5), respectively. The driving force for these conversions is the formation of thermally stable, nonporous, crystalline 3D coordination polymers. The structural transformations are accompanied by the loss of water and reveal significant changes of the coordination spheres of the metal ions caused by a rearrangement of the triazolyl benzoate ligands. Compounds 2, 4, 5, and 6 exhibit 4- and 5-fold interpenetration of diamondoid networks (dia) and are thermally stable up to 380 °C.

Full text of DOI:10.1021/ic300235s

Article
pubs.acs.org/IC
Solid-State Syntheses of Coordination Polymers by Thermal
Conversion of Molecular Building Blocks and Polymeric Precursors
Daniel Lassig, Jorg Lincke, Renata Gerhardt, and Harald Krautscheid*
̈
̈
Universitat Leipzig, Fakultat fur Chemie und Mineralogie, Johannisallee 29, D-04103 Leipzig, Germany
̈
̈
̈
S
* Supporting Information
ABSTRACT: The syntheses and crystal structures of a
mononuclear cadmium complex and five novel coordination
polymers based on 1,2,4-triazolyl benzoates are presented. The
compounds ∞3 [Cd(H-Me-trz-pba)2] (2), ∞3 [Cd(Me-3py-trz-
pba)2] (4), and 3∞[Zn(H-Me-trz-pba)2] (6) can be obtained
by solvothermal synthesis or simple heating of the starting
materials in appropriate solvents, and are also accessible by
thermal conversion of the complex [Cd(H-Me-trz-
pba)2(H2O)4] (1), the one-dimensional (1D) coordination polymer 1∞[Cd(Me-3py-trz-pba)2(H2O)2]·H2O (3), and the porous
three-dimensional (3D) framework 3∞[Zn(H-Me-trz-pba)2]·4H2O (5), respectively. The driving force for these conversions is the
formation of thermally stable, nonporous, crystalline 3D coordination polymers. The structural transformations are accompanied by
the loss of water and reveal significant changes of the coordination spheres of the metal ions caused by a rearrangement of the triazolyl
benzoate ligands. Compounds 2, 4, 5, and 6 exhibit 4- and 5-fold interpenetration of diamondoid networks (dia) and are thermally
stable up to 380 °C.
triazoles and pyridines were found to exhibit promising
coordination chemistry for the synthesis of MOFs.5,22,23
INTRODUCTION
■
Metal−organic frameworks (MOFs) have gained increasing interest,
because of their high diversity of possible structures. Because of their
distinct properties as porous materials, this novel class of hybrid
materials exhibits a high potential for such applications as gas
separation and storage,1−6 sensors,7,8 and heterogeneous catalysis.9
Topological analyses are commonly used to classify this wide
field of possible framework structures.10−12 Despite the fact that
coordination polymers often form complex structures, a large
percentage of published networks can be simplified to the
topologies of basic inorganic compounds.10,12,13 The most
common, especially for interpenetrated frameworks (29.9%), is
the diamondoid topology (dia) with the point symbol {66}.14
In many cases of porous diamondoid networks, interpenetra-
tion leads to a significant reduction of porosity, but is also
accompanied by an enhanced thermal stability, because of
additional stabilizing interactions (hydrogen bonding, π···π
interactions) between the interwoven nets.12,13
For numerous molecular compounds, the phenomenon of
polymorphism is observed. In these cases, different crystal
structures can be found, because of varying packing interactions
between the respective molecules.15 An extended interpretation
of this concept introduces the term of supramolecular isomerism,
which is used for networks with the same composition but with
different topologies.15,16
Based on two substituted 1,2,4-triazolyl benzoates24 (Chart 1),
we herein present the syntheses and crystal structures of a
Chart 1. The Ligands (H-Me-trz-pba)− and (Me-3py-trz-
pba)−
cadmium complex as well as five zinc and cadmium coordina-
tion polymers. Furthermore, we report on the conversion of
complexes, coordination polymers of lower dimensionality and
porous networks into crystalline, interpenetrated 3D coordina-
tion polymers with a high thermal stability up to 380 °C. To our
best knowledge, a systematic investigation of such thermal conver-
sions of suitable precursors to 3D coordination polymers based on
full rearrangements of the coordination spheres of the metal ions
and the loss of solvent molecules has not been reported so far.
RESULTS AND DISCUSSION
■
The potential of MOFs forming highly ordered porous
structures has been impressively shown by the isoreticular series
of Yaghi and co-workers,17 the well-known HKUST-1 (Cu3(btc)2,
where btc = 1,3,5-benzene tricarboxylate)2,18 and the MIL series
From [Cd(H-Me-trz-pba)2(H2O)4] (1) to 3∞[Cd(H-Me-trz-
pba)2] (2). The complex [Cd(H-Me-trz-pba)2(H2O)4] (1) was
of Fer
́
ey et al.19−21 Apart from pure carboxylates, ligands with a
Received: February 1, 2012
combination of nitrogen-containing heterocycles such as 1,2,4-
© XXXX American Chemical Society
A
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a
Table 1. Selected Bond Lengths and Angles of 1
a
Symmetry codes for 1: a: 0.5 − x, y, 1 − z.
a
Table 2. Selected Bond Lengths and Angles of 2
a
Symmetry codes for 2: a: 1 − x, 1 − y, z; b: 1.25 − x, −0.25 + y, −1.25 + z; c: −0.25 + x, 1.25 − y, −1.25 + z.
obtained from Cd(OAc)2·2H2O and H(H-Me-trz-pba) in H2O/
MeCN (1:1, v/v) by diffusion at room temperature after
21 days. Compound 1 crystallizes in the monoclinic space
group I2/a (No. 15) with four formula units per unit cell.
(Bond lengths and bond angles for 1 are given in Table 1.)
The Cd2+ ion is distorted octahedrally coordinated by two
monodentate triazole units of (H-Me-trz-pba)¯ in trans
orientation and four water molecules.
Table 2.) In addition, phase-pure microcrystalline material
of 2 can be synthesized in multigram scale by reflux of
Cd(OAc)2·2H2O and H(H-Me-trz-pba) in H2O/MeCN
(1:1, v/v) for 48 h (see Figure SI-13 in the Supporting
Information). 2 crystallizes in the noncentrosymmetric
orthorhombic space group Fdd2 (No. 43) with eight for-
mula units per unit cell. The Cd2+ ion resides on the 2-fold
axis and is highly distorted octahedrally coordinated by two
monodentate 1,2,4-triazole units and by two chelating
carboxylate groups.
Whereas 1 is only accessible via diffusion, single crystals
3
of ∞[Cd(H-Me-trz-pba)2] (2) were obtained from Cd-
(OAc)2·2H2O and the protonated ligand under solvothermal
conditions. (Bond lengths and bond angles for 2 are given in
For the neutral network of 2, the common dia topology
(point symbol {66}) is built up by the linkage of the Cd2+ ions
B
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Figure 1. Single-net (50% ellipsoids, left) and space-filling projection of five interpenetrated nets of 2 (right).
Scheme 1. Reaction Conditions for the Syntheses of 1 and 2
Figure 2. (Left) Comparison of the powder X-ray patterns of 1 and 2 (Cu Kα1: λ = 154.060 pm). (Right) Temperature-dependent powder
diffraction pattern (Guinier−Simon diagram) of 1.
as four-connected nodal points. In addition, a 5-fold interpenetra-
tion of type Ia with a full interpenetration vector (FIV) of 709 pm
in the crystallographic c-direction was found, leading to a non-
porous network with no solvent accessible voids.13,15,25,26 (Graphic
depictions of 2 are shown in Figure 1.)
Beside the described synthesis routes, phase-pure 2 can be
obtained via the thermal conversion of 1 under the loss of
solvent molecules (Scheme 1).
As can be seen from the temperature-dependent powder
X-ray diffraction pattern (TD-PXRD), 1 is thermally stable up
to 200 °C. In the temperature region of 200−310 °C, an
amorphous phase is observed. Above 310 °C, a crystalline
phase with a new powder pattern is detected, which can be
assigned to compound 2 (see Figure 2). The newly formed
5-fold interpenetrated coordination polymer 2 eventually
remains intact up to a temperature of 380 °C.
This conversion is confirmed by DTA/TG-MS analysis (see
Figure 3). Up to 170 °C a mass loss of 12.2% was found, which
correlates perfectly with the calculated weight loss of 12.2% for
four water molecules per formula unit, indicated by the MS
signal m/z = 18. In compliance with TD-PXRD, thermogravimetry
reveals a thermal stability of 2 up to 380 °C. Above this
temperature, 2 decomposes under the release of carbon dioxide
(m/z = 44). Therefore, it can be concluded that, after the loss
of the four water molecules per formula unit of 1, a full
rearrangement of ligands and metal ions occurred, leading to the
C
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Figure 3. DTA/TG-MS analysis of 1. The black trace represents the thermogravimetry (TG) signal, while the blue trace represents the differential
thermal analysis (DTA) signal and the green traces represent the mass spectroscopy (MS) signals.
Figure 4. Part of the crystal structures of 3 (left) and 4 (right).
formation of the three-dimensional network of 2. Within this
rearrangement, all coordinative bonds are broken and reformed,
which is evidenced by the change of the coordination mode.
Whereas in 1, the ligand coordinates with the electronically favored
nitrogen atom (+I-effect of the methyl group), in 2, coordination
of the sterically less-shielded nitrogen atom is observed.
monoclinic acentric space group Pc (No. 7) with two formula
units per unit cell. In 3, the Cd2+ ion is located on the inversion
center and is distorted octahedrally coordinated by two
monodentate carboxylates, two water molecules, and two
pyridine rings in trans orientation (Figure 4). In addition,
strong intramolecular hydrogen bonds with an O···O distance
of 260.9(4) pm (see Table 3) between the noncoordinating
oxygen atoms of the carboxylates and the aquo ligands are
observed. Hence, the positions of the carboxylate groups are
fixed.
In contrast to the one-dimensional (1D) coordination
polymer 3, 4 represents a three-dimensional coordination
polymer with 4-fold interpenetration. The Cd2+ ion is distorted
octahedrally coordinated by two monodentate triazole units in
cis-orientation and chelating carboxylate groups, the pyridine
rings do not interact with the metal ions. Therefore, the ligands
act as linear linkers leading to a network with the point symbol
{66} and dia topology. Whereas a single framework possesses
a high porosity, the four interwoven nets lead to an almost
1
From ∞ [Cd(Me-3py-trz-pba)2(H2O)2]·H2O (3) to
3∞[Cd(Me-3py-trz-pba)2] (4). In the case of the ligand
(Me-3py-trz-pba)−, a similar relation between the products
1∞[Cd(Me-3py-trz-pba)2(H2O)2]·H2O (3) and 3∞[Cd(Me-3py-
trz-pba)2] (4) can be found. The reactions of equimolar
amounts of the protonated ligand and Cd(OAc)2·2H2O in
H2O/MeCN (1:1, v/v) under solvothermal conditions or by
simple reflux lead to phase-pure compound 3 (see Figure SI-14
in the Supporting Information). If the solvent mixture is
replaced by dimethylformamide (DMF), the three-dimensional
(3D) coordination polymer 4 is obtained.
Whereas 3 crystallizes in the triclinic space group P1 (No. 2)
̅
with one formula unit per unit cell, 4 crystallizes in the
D
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a
Table 3. Selected Bond Lengths and Angles of 3 and 4
a
Symmetry codes for 3: a: 1 − x, −y, −z; b: 1 − x, 1 − y, −z; c: x, −1 + y, z. Symmetry codes for 4: a: −1 + x, 1 − y, −0.5 + z; b: 1 + x, 2 − y,
−0.5 + z.
Scheme 2. Reaction Conditions for the Syntheses of 3 and 4
nonporous coordination polymer with only 5% solvent acces-
sible voids.26 Cobalt and zinc frameworks isomorphous to 4
were presented recently.27
Similar to the conversion of 1 into 2, 4 can be obtained by
loss of 3 equivalents of water upon heating of the 1D coordination
polymer 3. (See Scheme 2.) As can be seen from TD-PXRD
measurements, 3 is stable up to 230 °C. Above this tempera-
ture, again, an amorphous phase is observed. When the
sample is heated up to 290 °C, discrete reflections occur,
indicating a crystalline phase with stability of the framework
up to 380 °C. The powder patterns of 4 and the crystalline
high-temperature phase of 3 are in perfect agreement. (See
Figure 5.) Therefore, it can be concluded that the 1D polymer 3
is converted to the 3D diamondoid network of 4 within the tem-
perature range of 230−290 °C. Again, this conversion is accom-
panied by a rearrangement in the Cd2+ coordination sphere.
Whereas in 3, the pyridine groups of the (Me-3py-trz-pba)− ligands
coordinate, in 4 the triazole units bind to the metal ions.
E
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Figure 5. (Left) Comparison of the powder patterns of 3, 4, and the high-temperature phase of 3 (room-temperature measurements). (Right)
Temperature-dependent powder patterns (Guinier−Simon diagram) of 3.
Figure 6. DTA/TG-MS analysis of 3. Black trace represents the TG signal, while the blue trace represents the DTA signal and the green trace
represents the MS signals.
The conversion is evidenced by the loss of water molecules
retraced by DTA/TG-MS analysis. Up to 230 °C, a mass loss of
7.8% is observed, which correlates well with the calculated mass
loss of 7.5% for three water molecules per formula unit (m/z = 18).
The phase transition from crystalline 3 to the amorphous
phase and the decomposition of 4 at ∼390 °C (m/z =
44 [CO2]+) are found to be endothermic. The exothermic peak
at 290−300 °C in the DTA curve (black square, Figure 6) can
be interpreted as the crystallization of 4 from the amorphous
material.
measurements, the water content was determined to be four
water molecules per formula unit (see Figure SI-18 in the
Supporting Information). In the crystal structure of 5, the Zn2+
ion is coordinated in a distorted tetrahedral fashion by two
monodentate carboxylate groups and two triazole rings (see
Table 4). Phase-pure 5 can only be obtained by reacting
equimolar amounts of Zn(OAc)2·2H2O and H(H-Me-trz-pba)
in H2O/MeOH (1:1, v/v) by diffusion at room temperature
(see Scheme 3). Whereas 2 and 4 show an interpenetration of
type Ia (FIV), 5 can be assigned to be of type IIIa, since the
interwoven nets are not only connected by simple translation.
In addition to the translation interpenetration vector (TIV) in
[001] with a length of 1288 pm, the c glide plane (NISE) acts
as a second independent symmetry element between two pairs
of networks. Despite the 4-fold interpenetration, 5 possesses
pore channels along the crystallographic c-direction with
squarish windows of 400 pm × 400 pm and a solvent-accessible
volume of ∼34%.26 (See Figure 7.)
Conversions within the System of 3∞[Zn(H-Me-trz-
pba)2]. Also within the system of three diamondoid networks
(dia) of 3∞[Zn(H-Me-trz-pba)2] (5, 6, and 6-ht), thermal
treatment leads to conversions. Compound 3∞[Zn(H-Me-trz-
pba)2]·4H2O (5) crystallizes in the tetragonal space group P4nc
(No. 104) with four formula units per unit cell. The asymmetric
unit contains a (H-Me-trz-pba)− ligand and a Zn2+ ion residing
on a 2-fold axis. Furthermore, approximately two disordered
and partially occupied water molecules could be located during
the refinement process. Nevertheless, from TG-DTA-MS
As can be seen from TD-PXRD measurements (Figure 8), 5
undergoes a phase transition already at 70 °C. The high-temperature
F
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a
Table 4. Selected Bond Lengths and Angles of 5 and 6
a
Symmetry codes for 5: a: 1 − x, 2 − y, z; b: 1.5 − x, 0.5 + y, −0.5 + z; c: −0.5 + x, 1.5 − y, −0.5 + z. Symmetry codes for 6: a: −1 + x, 1 − y, 0.5 + z;
b: −1.5 + x, 0.5 − y, −0.5 + z.
Scheme 3. Reaction Conditions for the Syntheses of 5 and 6
phase can be assigned to compound 6 (Figure 8), a new
diamondoid network of 3∞[Zn(H-Me-trz-pba)2] without any
porosity.26 In contrast to the conversions between 1 and 2 or 3
and 4, no amorphous phase between 5 and 6 is observed.
G
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Figure 7. Space-filling models of 5 and 6 (views are along the crystallographic c-direction).
To the best of our knowledge, crystal-to-crystal transformations
combined with a change of the number of interpenetrating nets
are a very rare phenomenon. An example is [Ag6Cl(atz)4]-
OH·6H2O (atz = 3-amino-1,2,4-triazolate), which shows a
change in interpenetration between 5-fold and 6-fold.28
Further thermal treatment of 5 leads to a second phase
transition at 220 °C (Figure 8), during which certain reflections
become identical. Indexing of the powder pattern of this high-
temperature (ht) phase of 6 identifies it to be the isomorphous
3
zinc analogue ∞[Zn(H-Me-trz-pba)2] (6-ht) of the cadmium
coordination polymer 2. In contrast to the sharp phase transition
at 70 °C, the reversible conversion of 6 to 6-ht occurs more
gradually over a temperature range. As expected for this phase
transition, the space group Cc of the low-temperature phase 6 is
a subgroup of Fdd2 (6-ht). Based on the reversibility, and from
comparison with 2, it can be concluded that, for the transition
from 6 to 6-ht, the connectivity in the network is retained.
The 6-ht compound is thermally stable up to 420 °C. Whereas
the conversions of 1 to 2, 3 to 4, and 5 to 6 are initiated by the
entropically favored loss of water molecules, the crystallization of
2 and 4 from amorphous phases and the transformation from 6
to 6-ht can be regarded as enthalpy-driven.
Figure 8. Temperature-dependent powder X-ray diffraction (TD-
PXRD) pattern (Guinier−Simon diagram) of ∞[Zn(H-Me-trz-
pba)2]·4H2O (5).
3
Polymer 6 can directly be synthesized from Zn(NO3)2·
6H2O and H(H-Me-trz-pba) under hydrothermal conditions
(Scheme 3). In addition, microcrystalline material is accessible
in multigram scale by simple reflux of Zn(OAc)2·2H2O and the
protonated ligand in H2O/MeOH (1:1, v/v) (see Figure SI-15
in the Supporting Information).
Polymer 6 crystallizes in the monoclinic space group Cc
(No. 9) with four formula units per unit cell. Similar to 5, the
Zn2+ ions are distorted tetrahedrally coordinated by two
monodentate triazole units and two carboxylates (see Table 4),
forming a 3D network with dia topology.
CONCLUSION
■
The mononuclear complex [Cd(H-Me-trz-pba)2(H2O)4] (1),
1
the one-dimensional (1D) coordination polymer ∞[Cd(Me-
The conversion of compound 5 into 6 occurs in a system of
interpenetrated networks, accompanied by a change in degree
of interpenetration already at 70 °C. In contrast to the
framework of 5 with four interwoven nets, a 5-fold inter-
penetration of type Ia is found for 6. This leads to the con-
clusion that coordinative bonds between the ligands and the Zn
ions must be broken in order to enable the observed phase
transition. This is confirmed by the coordination mode of the
triazole unit: in 5, the triazole coordinates with the sterically
more hindered, but electronically favored nitrogen atom; in 6,
the sterically favored nitrogen atom binds to the Zn2+ ion.
In comparison to 6, 5 shows significantly shorter Zn−Ntrz bond
lengths originating in the methyl group located in α-position
to the coordinating nitrogen atom. The driving force for
this conversion is mainly the loss of water molecules and
the formation of a crystalline network without any porosity.
3py-trz-pba)2(H2O)2]·H2O (3) and four zinc- and cadmium-
containing diamondoid frameworks (2, 4, 5, and 6) have been
synthesized from the protonated ligands and the respective
metal salts. A topological analysis reveals {66} diamondoid
(dia) topology in the case of all these networks, but varying
4-fold (4 and 5) and 5-fold (2 and 6) interpenetration. Such
highly interpenetrated networks are rarely observed (from
recent TOPOS statistics: 4-fold, 8.3%; 5-fold, 3.6%), in com-
parison with the regularly occurring 2-fold (60.6%) and 3-fold
interpenetration (21.5%). (Table 5 shows the crystallographic
data for compounds 1−6.)
Their thermal behavior show that suitable complexes or 1D
coordination polymers with aquo ligands such as 1 or 3 can be
converted to neutral, three-dimensional (3D), interpenetrated
coordination polymers during the loss of solvent molecules.
H
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Table 5. Crystallographic Data for [Cd(H-Me-trz-pba)2(H2O)4] (1), 3∞[Cd(H-Me-trz-pba)2] (2), ∞1 [Cd(Me-3py-trz-
pba)2(H2O)2]·H2O (3), 3∞[Cd(Me-3py-trz-pba)2] (4), ∞3 [Zn(H-Me-trz-pba)2]·4H2O (5), and ∞3 [Zn(H-Me-trz-pba)2] (6)29
compound
1
2
3
4
5
6
color
colorless
prism
colorless
needle
colorless
needle
colorless
prism
colorless
prism
colorless
needle
shape
crystal dimensions [mm]
0.08 × 0.20 × 0.50 0.11 × 0.13 × 0.50 0.11 × 0.13 × 0.31 0.18 × 0.21 × 0.22 0.50 × 0.50 × 0.50
0.14 × 0.16 × 0.50
formula
MW [g mol−1
CdC20H24N6O8
588.85
CdC20H16N6O4
516.79
CdC30H28N8O7
725.00
Cd C30 H22 N8 O4 ZnC20H20.25N6O6.125 ZnC20H16N6O4
]
670.92
508.04
469.76
temperature [K]
diffractometer
crystal system
space group
unit cell
180(2)
180(2)
213(2)
180(2)
213(2)
213(2)
STOE IPDS-2T
monoclinic
I2/a (No. 15)
STOE IPDS-2T
orthorhombic
Fdd2 (No. 43)
STOE IPDS-I
triclinic
STOE IPDS-2T
monoclinic
Pc (No. 7)
STOE IPDS-I
tetragonal
P4nc (No. 104)
STOE IPDS-I
monoclinic
Cc (No. 9)
P1 (No. 2)
̅
a [pm]
1896.9(2)
717.96(5)
1598.8(2)
1899.5(2)
3006.3(3)
709.04(6)
779.2(1)
935.7(2)
1169.5(2)
77.41(1)
71.00(1)
73.42(1)
765.3(2)
1
740.0(1)
1461.5(3)
1417.5(3)
1459.6(2)
1288.4(1)
664.74(9)
1916.7(2)
1536.6(3)
b [pm]
c [pm]
α [°]
β [°]
γ [°]
volume [× 106 pm3]
Z
density [g cm−3
μ(Mo Kα) [mm−1
93.636(9)
99.54(1)
98.54(1)
2173.0(4)
4
4048.9(7)
8
1511.8(5)
2
2744.7(5)
4
1936.0(5)
4
]
1.800
1.696
1.573
1.474
1.229
1.612
]
1.068
1.120
0.774
0.771
0.936
1.311
θmin−θmax [°]
reflections measured
1.04−28.00
9747
1.15−28.00
3597
1.65−25.00
5489
0.96−26.00
7462
1.90−28.00
7131
1.90−27.00
4644
independent reflections
2620
1992
2546
4596
3019
3291
observed reflections
(I > 2σ(I))
2476
1827
2352
3383
1901
3141
Rint
0.0353
173
0.0525
143
0.0292
221
0.0451
391
0.0368
163
0.0448
182
parameters refined
R1 (I > 2σ(I))
0.0432
0.1178
0.0478
0.1289
0.02(1)
0.9/−1.5
0.0309
0.0818
0.0467
0.1349
−0.05(4)
0.8/−0.7
0.0541
0.1582
0.03(5)
0.8/−0.4
0.0280
0.0718
−0.01(1)
0.4/−0.4
wR2 (all data)
Flack-x parameter
max/min peak [× 10−6 pm−3
]
1.1/−0.8
1.3/−0.3
Both products 2 and 4 represent interpenetrated, nonporous
frameworks with dia topology.
ASSOCIATED CONTENT
■
S
* Supporting Information
As shown by compounds 5 and 6, conversions based on
thermal treatment can even take place within a system of inter-
penetrated frameworks. The driving force for the presented
conversions is mainly the formation of thermally stable, non-
porous, crystalline 3D coordination polymers. In the case of 2
and 4, a remarkable thermal stability up to 380 °C is reached.
In addition, the conversion of the hydrates 1, 3, and 5 is
entropically favored by the loss of water molecules.
Experimental details associated with this article can be found in
the online version. Cambridge Crystallographic Data Centre
(CCDC) File Nos. 751491 and 861641−861649 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif. This material is available free of charge via the
Internet at http://pubs.acs.org.
The observed transformations are accompanied by a change
in the coordination spheres of the metal ions. Remarkably,
different pathways for these solid-state reactions are detected.
Whereas the conversion from 5 to 6 occurs directly at 70 °C,
for the transitions of 1 to 2 and 3 to 4, an intermediate
amorphous phase is observed. After rearrangement of all
components in temperature ranges of 200−310 °C (1) and
230−290 °C (3), highly crystalline 3D materials are found.
Furthermore, the structural transformation from 6 to 6-ht was
found to be reversible.
As can be seen from the reaction schemes, the structures of
coordination polymers can be very sensitive, with respect to the
synthesis conditions applied. Compounds 1 and 5 verify that
milder reaction conditions, especially diffusion methods at
room temperature, allow the synthesis of thermodynamically
less-stable products than solvothermal reactions or synthesis
under reflux.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: Krautscheid@rz.uni-leipzig.de.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank M.Sc. Marcel Handke for the DTA/TG-MS analyses.
Financial support by Deutsche Forschungsgemeinschaft (DFG
SPP 1362 - Porose metallorganische Gerustverbindungen), the
̈
̈
University of Leipzig (PbF-1) and the graduate school
BuildMoNa is gratefully acknowledged. D.L. acknowledges
the fellowship of the Fonds der Chemischen Industrie, and J.L.
acknowledges the ESF fellowship. Funded by the European
Union and the Free State of Saxony.
I
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Inorganic Chemistry
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DEDICATION
■
Dedicated to Prof. Dr. Reinhard Kirmse on the occasion of his
65th birthday.
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