Full text of DOI:10.1002/1521-3765(20011015)7:20<4431::AID-CHEM4431>3.0.CO;2-P

FULL PAPER
A Reversible Structural Interconversion Involving [M(H2pdc)2(H2O)2] ´ 2H2O
(M ˆ Mn, Fe, Co, Ni, Zn, H3pdc ˆ 3,5-pyrazoledicarboxylic acid) and the Role
of A Reactive Intermediate [Co(H2pdc)2]
Long Pan, Nancy Ching, Xiaoying Huang, and Jing Li*[a]
Abstract: A new type of hydrogen
bonded networks [M(H2pdc)2(H2O)2] ´
2H2O [M ˆ Mn (1), Fe (2), Co (3), Ni
(4), Zn (5); H3pdc ˆ 3,5-pyrazoledicar-
boxylic acid] have been synthesized via
hydrothermal reactions and their struc-
tures have been characterized. Upon a
cooling-heating cycle, these com-
highly reactive. Further chemical reac-
tions of these reactive intermediates
show that they may act as effective
precursors towards assembly of new
supramolecular compounds that may
otherwise be inaccessible by other syn-
thetic routes. An interesting struc-
ture containing an ªopen-boxº mole-
isolated
by
using
dehydrated
[Co(H2pdc)2] as the precursor, and its
crystal structure has been analyzed.
Crystal data for 1 ± 6: monoclinic, space
group P21/c and Z ˆ 2 with a ˆ
10.186(2), b ˆ 12.473(2), c ˆ 6.831(1) Š,
b ˆ 108.80(3)8 (1); a ˆ 9.896(2), b ˆ
12.402(2), c ˆ 6.810(1) Š, b ˆ 108.15(3)8
(2); a ˆ 9.981(2), b ˆ 12.426(2), c ˆ
6.807(1) Š, b ˆ 108.23(3)8 (3); a ˆ
9.896(2), b ˆ 12.402(2), c ˆ 6.810(1) Š,
b ˆ 108.15(3)8 (4); a ˆ 10.001(2), b ˆ
12.430(2), c ˆ 6.834(1) Š, b ˆ 108.32(3)8
(5); a ˆ 9.9617(1), b ˆ 18.5080(2), c ˆ
28.4786(3) Š, b ˆ 93.076(1)8 (6).
pounds undergo
a
reversible struc-
cule
[Co4(Hpdc)4(py)12] ´ 4py ´ 2H2O ´
tural interconversion process via hydra-
2CH3OH (6) (py ˆ pyridine) has been
tion-dehydration: [M(H2pdc)2(H2O)2] ´
4 H2O
*
2H2O )
‡4 H2O
Keywords: carboxylate ligands ´ hy-
[M(H2pdc)2]. The process
drogen bonds
´
self-assembly
´
is associated with distinct color changes.
The dehydrated [M(H2pdc)2] (M ˆ Mn,
Fe, Co, Ni, and Zn) are amorphous and
structure elucidation ´ supramolec-
ular chemistry
pyrazole nitrogen atoms, which are highly accessible to
metals, to form both monodentate and/or multidentate
M O and M N bonds. The coordinated structural motifs
thus generated can then readily form hydrogen-bonded
networks.[4±5]
Introduction
Recent interest in the development of supramolecular net-
works organized and held by means of intermolecular
interactions, such as hydrogen bonding or p ± p interactions,
has attracted tremendous attention due to their fascinating
crystal structures, electronic and optical properties, and
potential applications as molecular devices such as sensors
and indicators.[1] Hydrogen bonding, as the strongest and most
directional intermolecular force, has been intensively inves-
tigated in organic crystalline solids,[2] but is relatively un-
explored in the coordination complexes.[3] In the search
for new functional hydrogen-bonded metal coordination
network structures, we have investigated a divalent metal
3,5-pyrazoledicarboxylate system involving Groups 7 ± 10
and Group 12 metal centers. The ligand, 3,5-pyrazoledi-
carboxylic acid (H3pdc), known both as a multiple proton
donor and acceptor, can use its carboxylate oxygen and
To date, the majority of known supramolecular assemblies
are synthesized by direct reactions of metal salts with various
ligands. Recently, a ªsecondary building blockº approach
introduces an alternative route that uses cluster molecules as
reaction precursors.[6±7] Due to their low solubility in most
common organic or inorganic solvents, very few examples are
known in which coordination compounds themselves are
employed as precursors.[5a] However, when a ligand (or an
ancillary solvent molecule) is removed from a coordination
complex, the metal coordination in the so-formed intermedi-
ate species becomes unsaturated, and the uncoordinated site
becomes highly reactive. These intermediate species can then
be used as reactive precursors for further reactions. Such
reactions often lead to new structures that retain certain
features of the intermediate species and that may not be
accessible by other routes. Herein, we report the hydro-
thermal synthesis and crystal structure of a new type of
hydrogen-bonded network [M(H2pdc)2(H2O)2] ´ 2H2O, M ˆ
[a] Prof. J. Li, Dr. L. Pan, N. Ching, Dr. X. Huang
Department of Chemistry, Rutgers University
Camden, NJ 08102 (USA)
Fax : (‡1)856-225-6506
E-mail: jingli@crab.rutgers.edu
Chem. Eur. J. 2001, 7, No. 20
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J. Li et al.
FULL PAPER
Mn (1), Fe (2), Co (3), Ni (4) and Zn (5), their reversible
structural interconversion associated with color change, and
the reactions of the dehydrated Co intermediate [Co(H2pdc)2]
with pyridine. A novel compound, [Co4(Hpdc)4(py)12] ´ 4py ´
2H2O ´ 2CH3OH (6), was produced from these reactions.
Attempts of synthesizing 6 by direct reactions of metal salts
and ligands were not successful.
Results and Discussion
The crystal structures of [M(H2pdc)2(H2O)2] ´ 2H2O (M ˆ
Mn, Fe, Co, Ni, Zn): Five new compounds were synthesized
by stoichiometric mixing of divalent metal salts M(NO3)2/
M'Cl2 (M ˆ Co, Ni, Zn; M' ˆ Mn), H3pdc, and H2O. The
reactions were carried out in 23 mL acid-digestion bombs at
1508C for three days. For the iron compound, Fe(NH4)2(SO4)2
was used since FeCl2/Fe(NO3)2 as starting material resulted in
an unknown powder. Low pHs were observed in all reactions
(final pH ˆ 1.5 ± 2). Single-phase samples were obtained for
compounds 1, and 3 ± 5 as confirmed by powder X-ray
diffraction (PXRD) analysis, although most yields were not
particularly high due to the complex redox process involved in
the reactions.[8] Orange-yellowish, beige, and powder blue
polycrystalline samples were isolated for Fe, Co, and Ni
phases, respectively. The Mn and Zn compounds were color-
less.
Single-crystal X-ray diffraction analysis on selected crystals
showed that all five compounds 1 ± 5 are isostructural, and
crystallize in the monoclinic crystal system, space group P21/c
(No. 14). The structure contains undulating sheets of
[M(H2pdc)2(H2O)2] ´ 2H2O. Figure 1 shows a view of structure
3. Within each layer, the metal atoms are located at the
inversion center and are six-coordinate. Each metal center is
bonded to two 3,5-pyrazoledicarboxylate ions at equatorial
positions through the chelating carboxylate oxygen O1 and its
adjacent pyrazole nitrogen N1, with the Co O and Co N
bond lengths of 2.1062(19) and 2.108(2) Š. These bond
lengths are consistent with those found in comparable
structures.[9] In addition, each metal center is also coordinated
to two water molecules at apical positions with a Co O bond
length of 2.058(2) Š, which is stronger compared to those in
Cu ± pdc compounds of a similar structure.[10] The two H2pdc
ions are attached to the metal centers in a trans manner, each
forming a stable five-membered ring with acute O-Co-N
angles (76.91(8)8).
Figure 1. View of the basket-weave-like, two-dimensional hydrogen-
bonded network of [M(H2pdc)2(H2O)2] ´ 2H2O, M ˆ Mn (1), Fe (2), Co
(3), Ni (4), and Zn (5) along the c axis. Large cross-shaded circles are metal
atoms, small cross-shaded, open, and partially shaded circles are O, C, and
N atoms, respectively. Large solid circles represent the two solvated water
molecules. Hydrogen bonds are indicated by dotted lines.
quet is a 36-membered H-bonded ring known as graph set
R44(36).[13] Two solvated water molecules are found inside each
ring and are held in place through three types of hydrogen
bonds; one formed by its oxygen atom with a protonated
pyrazole nitrogen atom (N2 H2 ´´´ O6 ˆ 2.707(3) Š), and the
other two by the two hydrogen atoms with two different
carboxylic oxygen atoms to give O6 H4 ´´´ O3ii ˆ 2.919(3) Š
and O6 H5 ´´´ O1i ˆ 2.832(3) Š. The interlayer interactions
are through hydrogen bonding between the coordinated water
O5 in one sheet and the 3,5-pyrazoledicarboxylic oxygen
atoms O2iii, O3iv in the adjacent sheet with two hydrogen
bonds O5 H2 ´´´ O2iii ˆ 2.728(3) and O5 H3 ´´´ O3iv ˆ
2.855(3) Š. This gives rise to a hydrogen-bonded, undulating,
three-dimensional structure (Figure 2). Selected bond lengths
and angles for all structures are given in Tables 1 and 2. The
hydrogen bonds are listed in Table 3.
The corresponding bond lengths of metal with carboxylic
oxygen atoms (Mn O ˆ 2.179(3), Fe O ˆ 2.161(2), Ni O ˆ
2.079(3), Zn O ˆ 2.1202(19) Š) and with nitrogen atoms
The reversible structural interconversion: To assess the
thermal stability of compounds 1 ± 5 and their structural
variation as a function of the temperature, thermogravimetric
analyses (TGA) were performed on single-phase polycrystal-
line samples of 1 and 3 ± 5. For example, the onset of the
weight loss of the four (two solvated and two coordinated)
water molecules in 3 occurred at about 908C and completed at
2208C (obsd 16.4%, calcd 16.3%). The loss of the 3,5-
pyrazoledicarboxylate ligands began at about 2508C. PXRD
on the final residues at 8008C indicated that the remainder of
the sample was elemental Co with some minor cobalt oxide.
(Mn N ˆ 2.207(4),
Fe N ˆ 2.139(3),
Ni N ˆ 2.041(4),
Zn N ˆ 2.100(2) Š) fall in the same range as analogous
chelating M O and M N bonds.[11] All C O, C C, and N N
bonds, and pyrazole ring angles in the H2pdc (or pdc) ligand
are consistent with those reported previously.[4] As shown in
Figure 1, a two-dimensional network with a rare parquet
(basket weave) pattern[12] is formed through strong hydrogen
bonds between the carboxylate oxygen (O2) and hydrogen
(H1) of the neighboring 3,5-pyrazoledicarboxylate ions
(O4 H1 ´´´ O2ii ˆ 2.529(3) Š). The building-block of the par-
4432
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Chem. Eur. J. 2001, 7, No. 20

Basket-Weave-Like Complexes
4431±4437
Figure 2. View along the a axis showing hydrogen-bonded (wave-like) three-dimensional structure. The interlayer interactions are through hydrogen
bonding between the coordinated water molecules (at apical positions) in one layer and the 3,5-pyrazoledicarboxylate ions in the adjacent layer.
Table 1. Selected bond lengths [Š] and angles [8] for 1, 2, 3, 4, and 5.
1(Mn) 2(Fe) 3(Co) 4(Ni) 5(Zn)
2.152(4) 2.089(3) 2.058(2) 2.047(4) 2.096(2)
Table 2. Selected bond lengths [Š] and angles [8] for 6.[a]
Co1 O8i
Co1 O1
Co1 N1
Co1 N7
Co1 N6
Co1 N5
Co2 O4
Co2 N3
Co2 O5
Co2 N10
Co2 N9
Co2 N8
O1 C1
2.071(2)
2.087(2)
2.109(2)
2.146(3)
2.161(3)
2.167(3)
2.052(2)
2.097(3)
2.108(2)
2.135(3)
2.178(3)
2.184(3)
1.277(4)
1.234(4)
1.243(4)
1.261(4)
1.271(4)
1.247(4)
O7 C10
O8 C10
O8 Co1i
N1 N2
N1 C2
N2 C4
N3 N4
N3 C7
N4 C9
C1 C2
C2 C3
C3 C4
C4 C5
C6 C7
C7 C8
C8 C9
C9 C10
1.244(4)
1.263(4)
2.071(2)
1.338(3)
1.341(4)
1.356(4)
1.338(3)
1.341(4)
1.352(4)
1.496(4)
1.399(4)
1.377(4)
1.489(4)
1.489(4)
1.395(4)
1.380(4)
1.488(4)
M O5i
M O5
M O1
M O1i
M N1
M N1i
O1 C1
O2 C1
O3 C5
O4 C5
N1 C2
N1 N2
N2 C4
C1 C2
C2 C3
C3 C4
C4 C5
2.152(4)
2.179(3)
2.179(3)
2.207(4)
2.207(4)
1.257(5)
1.250(5)
1.209(5)
1.288(6)
1.333(6)
1.338(5)
1.351(6)
1.489(6)
1.399(6)
1.378(6)
1.473(6)
2.089(3)
2.161(2)
2.161(2)
2.139(3)
2.139(3)
1.247(4)
1.261(4)
1.204(4)
1.302(4)
1.341(4)
1.326(4)
1.351(4)
1.486(5)
1.389(5)
1.378(5)
1.469(5)
2.058(2)
2.1062(19)
2.1062(19)
2.108(2)
2.108(2)
1.263(3)
1.251(3)
1.207(3)
1.301(3)
1.336(3)
1.327(3)
1.351(3)
1.489(4)
1.400(4)
1.370(4)
1.485(4)
2.047(4)
2.079(3)
2.079(3)
2.041(4)
2.041(4)
1.248(6)
1.262(6)
1.196(6)
1.315(6)
1.351(6)
1.325(5)
1.340(6)
1.494(6)
1.386(6)
1.385(6)
1.461(6)
2.096(2)
2.1202(19)
2.1202(19)
2.100(2)
2.100(2)
1.249(3)
1.257(3)
1.208(3)
1.302(3)
1.336(3)
1.328(3)
1.350(3)
1.492(4)
1.394(4)
1.371(4)
1.477(4)
O2 C1
O3 C5
O4 C5
O5 C6
O6 C6
O8i-Co1-O1
O8i-Co1-N1
O1-Co1-N1
O8i-Co1-N7
O1-Co1-N7
N1-Co1-N7
O8i-Co1-N6
O1-Co1-N6
N1-Co1-N6
N7-Co1-N6
O8i-Co1-N5
O1-Co1-N5
N1-Co1-N5
N7-Co1-N5
N6-Co1-N5
175.81(8)
98.46(9)
77.52(9)
92.06(9)
91.99(9)
169.38(10)
89.34(10)
89.42(10)
89.42(11)
92.15(11)
89.28(10)
91.85(10)
89.20(11)
89.50(11)
177.94(9)
O4-Co2-N3
O4-Co2-O5
N3-Co2-O5
O4-Co2-N10
N3-Co2-N10
O5-Co2-N10
O4-Co2-N9
N3-Co2-N9
O5-Co2-N9
N10-Co2-N9
O4-Co2-N8
N3-Co2-N8
O5-Co2-N8
N10-Co2-N8
N9-Co2-N8
100.89(10)
177.94(9)
77.10(9)
O5i-M-O5 180.0
180.0
180.0
180.0
180.0
O5i-M-N1i
O5-M-N1i
O5i-M-N1
O5-M-N1
91.57(15)
91.00(11)
89.00(11)
89.00(11)
91.00(11)
180.0
88.60(11)
91.40(11)
75.50(10)
90.89(9)
89.11(9)
89.11(9)
90.89(9)
180.0
88.74(9)
91.26(9)
76.91(8)
90.29(16)
89.71(16)
89.71(16)
90.29(16)
180.0
89.67(14)
90.33(14)
78.77(13)
90.89(9)
89.11(9)
89.11(9)
90.89(9)
180.0
88.91(9)
91.09(9)
77.30(8)
88.43(15)
88.43(15)
91.57(15)
89.00(10)
170.06(11)
93.01(10)
90.40(12)
89.13(12)
89.11(11)
91.77(12)
90.58(12)
90.89(12)
89.92(11)
88.04(13)
179.00(12)
N1-M-N1i 180.0
O5i-M-O1i
O5-M-O1i
O1i-M-N1i
87.08(15)
92.92(15)
73.93(13)
O1i-M-N1 106.07(13) 104.50(10) 103.09(8)
101.23(13) 102.70(8)
90.33(14)
89.67(15)
O5i-M-O1
O5-M-O1
92.92(15)
87.08(15)
91.40(11)
88.60(11)
91.26(9)
88.74(9)
91.09(9)
88.91(9)
O1-M-N1i 106.07(13) 104.50(10) 103.09(8)
101.23(13) 102.70(8)
O1-M-N1
73.93(13)
75.50(10)
180.0
76.91(8)
180.0
78.77(13)
180.0
77.30(8)
180.0
O1-M-O1i 180.0
[a] Symmetry transformations used to generate equivalent atoms: i x ‡ 1,
y ‡ 1, z ‡ 1.
[a] Symmetry transformations used to generate equivalent atoms: i x, y ‡ 1,
z.
collapsed and the sample became amorphous. While the long-
range order no longer exists, the local metal pdc bonds
remain and were confirmed by the strong characteristic
absorption band for the asymmetric stretching of the carbox-
Similar results were obtained for 1, 4, and 5 and are tabulated
in Table 4.
Some unique and intriguing phenomena were observed
upon heating of 1 ± 5. Figure 3a shows the PXRD pattern of 3
before heating. After heating it under an inert atmosphere to
2308C, all four water molecules were dissociated from the
sample and the color of the sample changed from the original
beige to violet; this suggests a coordination and geometry
change of the metal center from octahedral to tetrahedral.[14]
The PXRD pattern taken at this point is also shown in
Figure 3b, which clearly reflects that the crystal structure
ˆ
ylate C O seen in the FT-IR spectrum, which compared well
1
with that taken before heating (nas(C ˆ 1640 cm ). The
ˆ
O)
1
disappearance of the band at ꢀ3537 cm , which corresponds
to the vibration of the water O H bonds, is also in full
agreement with the observation of the water loss from TGA
experiments (Table 4). After the amorphous sample was
placed in the water for 30 minutes, its turned from violet back
to the original beige, and the powder pattern taken at this
Chem. Eur. J. 2001, 7, No. 20
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J. Li et al.
FULL PAPER
Table 3. Selected hydrogen bond lengths [Š] and angles [8] for 1, 2, 3, 4, and
5.[a,b]
stage (Figure 3c) is in excellent agreement with the original
one shown in Figure 3a. The FT-IR spectrum also showed
reappearance of a strong band at 3537 cm , indicative of the
1
D H ´´´ A
1
2
3
4
5
O4 H1 ´´´ O2ii
2.515(5)
175.5
2.713(6)
160.7
2.891(6)
161.9
2.908(6)
169.0
2.720(5)
163.1
2.886(5)
173.1
2.512(3)
174.7
2.704(4)
158.6
2.825(4)
168.6
2.921(4)
154.8
2.703(4)
156.6
2.854(4)
166.4
2.529(3)
174.4
2.707(3)
157.4
2.832(3)
155.2
2.919(3)
169.9
2.728(3)
160.6
2.855(3)
172.9
2.521(5)
160.0
2.710(5)
163.0
2.801(5)
166.3
2.935(5)
175.9
2.731(5)
145.3
2.870(5)
175.3
2.524(3)
173.5
2.709(3)
166.3
2.834(3)
170.1
2.931(3)
173.4
2.732(3)
165.7
2.874(3)
164.4
returning of water molecules into the structure. Such a
structure recovery process associated with a color change can
be readily repeated through the simple heating ± cooling
cycles described above. Figure 3d gives the PXRD pattern
taken after the same procedure was repeated five times on the
original sample, indicating a very high reversibility. This
reversible structure transformation involving a crystalline and
an amorphous state was also observed for all other com-
pounds. The observations are summarized in Table 4. Note
that the cooling ± heating (hydration ± dehydration) cycles
described here are different from the previously reported
reversible structural transformation between two crystalline
compounds.[15] In the case of the Ni compound (4), the process
was also associated with a color change from powder blue
(before water loss) to green bluish or aquamarine (after water
loss). Evidently, the key to the observed phenomenon is the
ability to break and reform the hydrogen-bonded network,
which in turn results in the change in the metal coordination
geometry.
N2 H6 ´´´ O6
O6 H5 ´´´ O1i
O6 H4 ´´´ O3ii
O5 H3 ´´´ O2iii
inter layer
O5 H2 ´´´ O3iv
inter layer
[a] Symmetry transformations used to generate equivalent atoms: i x, y ‡ 1,
z; ii x ‡ 1, y ‡ 1/2, z ‡ 1/2; iii x, y ‡ 1/2, z ‡ 1/2; iv x 1, y, z. [b] Bond
length ˆ d(D ´´´ A); bond angle ˆa(DHA).
Table 4. TGA and FT-IR data on polycrystalline samples of 1, 3 ± 5.[a]
1
3
4
5
T range [8C][b]
90 ± 190
16.8
16.5
90 ± 220
16.4
16.3
beige
violet
110 ± 230
16.5
16.3
powder blue white
green-blue white
80 ± 200
16.2
16.1
weight-loss (obsd) [%][c]
The reactive intermediate [Co(H2pdc)2] and its reactions: The
dehydrated [M(H2pdc)2] (M ˆ Mn, Fe, Co, Ni, Zn) are highly
reactive as they have unsaturated metal coordination sites. To
probe the reactivity of these intermediate complexes, we
selected [Co(H2pdc)2] as a reactive precursor for reactions
with pyridine, a ligand that is similar in a number of ways to
the water molecule. After being dissolved in methanol,
pyridine was added to the solution. The reactions produced
an interesting new compound 6. An X-ray analysis on 6
revealed a unique ªopen-boxº molecule[16] composed of four
CoII ions that form a square[17±18] and eight apical pyridine
molecules (four above and four below the Co4 plane), as
shown in Figure 4a. The
weight-loss (calcd) [%][d]
color (before loss of 4H2O) white
color (after loss of 4H2O) white
state (before loss of 4H2O) crystalline crystalline crystalline crystalline
state (after loss of 4H2O) amorphous amorphous amorphous amorphous
residue (major, at 8008C) Mn
Co
1640
3537
Ni
1645
3541
Zn
1635
3545
1
[e]
nas(C [cm
nO-H(sh) [cm
]
1653
3548
ˆ
O)
1
[e]
]
[a] No data listed for 2. See ref. [8]. [b] Temperature range for the weight loss of
four water molecules. [c] Observed percentage weight loss of four water
molecules. [d] Calculated percentage weigh loss of four water molecules.
[e] Observed absorption bands for carboxylate C O (asymmetric stretch) and
water O-H bonds.
ˆ
[Co4(Hpdc)4(py)12] molecule is
illustrated in Figure 4b with the
carbon atoms of apical pyri-
dines omitted for clarity. There
are two types of crystallograph-
ically independent CoII ions.
Each Co1 is six-coordinate. In
the equatorial plane, one
Hpdc2 forms a chelate bond
with the metal through its car-
boxylate oxygen O1 and its
adjacent pyrazole nitrogen N1,
while the second Hpdc2 uses its
carboxylate oxygen O8 to form
a monodentate bond with the
metal (Co O8i ˆ 2.071(2) Š).
The remaining equatorial posi-
tion is occupied by a pyridine
nitrogen N7 with a Co N bond
length of 2.146(3) Š. The two
Figure 3. PXRD patterns for a) a single-phase polycrystalline sample of 3; b) above sample after heated to
2308C, at which point all four water molecules are dissociated and the sample color changed from beige to violet;
c) sample in b) after placed in water for 30 minutes (the color turned back to beige); and d) sample after repeating
the above procedure a) ± c) five times.
pyridine molecules at the apical
positions bond to the metal
with Co1 N5 and Co1 N6
4434
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Chem. Eur. J. 2001, 7, No. 20

Basket-Weave-Like Complexes
4431±4437
this structure is the formation of a unique ªopen-boxº by a
Co4 plane and the eight pyridines perpendicular to this plane
(Figure 4a). Two guest pyridine molecules are encapsulated
between every two adjacent boxes. The dihedral angles
between these guest pyridine planes and the equatorial plane
composed of four metals and four Hpdc2 ligands are 83.408
and 57.438, respectively. Stacking of these ªopen-boxesº gives
rise to a one-dimensional structure as shown in Figure 5. One
group of apical pyridine rings bonded to Co1 is approximately
Figure 4. a) Schematic drawing representing
a {Co4(py)8} ªopen-boxº
molecule. X symbolizes a pyridine ring. b) The crystal structure of the
{Co4(Hpdc)4} square unit in 6 with the asymmetric unit labeled. Non-
hydrogen atoms are shown and represented by thermal ellipsoids drawn at
the 50% probability. Carbon atoms of the apical pyridines are omitted for
clarity.
Figure 5. View along the a axis showing the stacking of the ªopen-boxº
molecules in 6. The encapsulated pyridine guest molecules are also shown.
bond lengths of 2.167(3) and 2.161(3) Š, respectively. The
acute angle (O1-Co1-N1) in the five-membered chelate ring is
77.52(9)8, and other angles around Co1 (O-Co1-O, O-Co1-N,
and N-Co1-N) range from 89.28(10) ± 98.46(9)8.
The local coordination geometry around Co2 is very similar
to Co1, with both axial positions taken by two pyridines with
Co2 N8 and Co2 N9 bond lengths of 2.184(3) and
2.178(3) Š, respectively. The equatorial positions of Co2 are
occupied by O5 and N3 in a chelating mode with Co2 O5 and
Co2 N3 bond lengths of 2.108(2) and 2.097(3) Š, respective-
ly. The carboxylate oxygen O4 coordinates to Co2 in a
parallel to a guest pyridine ring, which is encapsulated
between the adjacent open boxes, with the pyridine ± pyri-
dine distance of ꢀ3.5 Š that is highly subject to p ± p
interactions. Two kinds of hydrogen bonds exist inside the
Co4 square involving pyrazole nitrogen atoms (N2, N4) and
the adjacent carboxylate oxygen atoms (O3, O7), giving
N2 H4 ´´´ O3 ˆ 2.735 Š and N4 H5 ´´´ O7 ˆ 2.725 Š. The
cross-section of the void in the square is 5.58  5.78 Š
(distance between the two carboxylate oxygen atoms at the
opposite sites, see Figure 4b). The dimensions of the box are
estimated to be approximately 9.9  8.7  8.7 Š. Other guest
species in 6 include another type of pyridine molecule located
between the one-dimensional chains and the solvent mole-
cules (MeOH and H2O).
monodentate fashion with
a Co2 O4 bond length of
2.052(2) Š. The bond angles around Co2 are similar to those
of Co1. However, a notable difference lies in the relative
orientation of the two axial pyridine rings bonded to the two
metals. For Co2, the two pyridine rings make an angle of
ꢀ69.98, whereas for Co1, they are approximately parallel
(2.48). Within a Co4 square, each pair of neighboring Co1 ±
Co2 atoms is bridged by a m3-Hpdc ligand. All pyrazole and
pyridine rings at the equatorial positions are within the Co4
plane. The metal ± metal distances within a square are nearly
identical (Co1 ± Co2 ˆ 8.67 Š, Co1 ± Co2i ˆ 8.70 Š). The eight
apical pyridine molecules are nearly perpendicular to the Co4
square, with N5-Co1-N6 and N8-Co2-N9 angles of 177.94(9)
and 179.00(12)8, respectively. A salient feature observed in
Conclusion
Hydrothermal reactions of transition metal salts (Mn, Fe, Co,
Ni, Zn) with 3,5-pyrazoledicarboxylic acid have afforded a
new family of coordination complexes with a parquet-
patterned (basket-weave) structure held by hydrogen bonds.
Upon hydration ± dehydration, these compounds undergo a
reversible structure interconversion process through a cool-
ing ± heating cycle. The process is associated with a distinct
Chem. Eur. J. 2001, 7, No. 20
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4435

J. Li et al.
FULL PAPER
Synthesis of [Mn(H2pdc)2(H2O)2] ´ 2H2O (1): Reaction of MnCl2 (0.0315 g,
0.25 mmol), H3pdc ´ H2O (0.087 g, 0.5 mmol) and deionized water (10 mL)
in the mole ratio of 1:2:2222 at 1508C for 3 days produced colorless
column-like crystals of 1 in yield of 58.5% (0.064 g) based on MnII. The
product was washed with water (3 Â 10 mL) and acetone (3 Â 10 mL), and
dried in air. The final pH value was 1.5.
color change (Co, Ni, Fe). To the best of our knowledge, such
a reversible structural interconversion between crystalline
and amorphous states accompanied by color changes has not
been previously reported. In addition, the dehydrated inter-
mediate [M(H2pdc)2] is highly unsaturated and can be used as
a reactive precursor in the synthesis of new compounds with
suitable ligands. An interesting open-box molecule containing
a Co4 square has been isolated. This compound can not be
assembled by direct reactions of metal salts with the ligands.
Continuing investigation of compounds of this type may be
potentially important in the development of new indicators
and sensors, and the continued use of reactive precursors may
provide alternative routes to the assembly of interesting and
unusual structures.
Synthesis of [Fe(H2pdc)2(H2O)2] ´ 2H2O (2): Reaction of Fe(NH4)2(SO4)2 ´
6H2O (0.982 g, 0.25 mmol), H3pdc ´ H2O (0.087 g, 0.5 mmol), and deionized
water (10 mL) in the mole ratio of 1:2:2222 at 1508C for 3 days yielded
0.062 g of products containing orange-yellow polyhedral crystals of 2
(ꢀ20%) and an unknown brown powder. The products were washed with
water (3 Â 10 mL) and acetone (3 Â 10 mL), and dried in air. The final pH
value was 2.0.
Synthesis of [Co(H2pdc)2(H2O)2] ´ 2H2O (3): Reaction of Co(NO3)2 ´ 6H2O
(0.0728 g, 0.25 mmol), H3pdc ´ H2O (0.087 g, 0.5 mmol), and deionized
water (10 mL) at 1508C for 3 days resulted in beige column-like crystals of
3 in high yield (88.8%, 0.098 g) based on CoII. The product was washed with
water (3 Â 10 mL) and acetone (3 Â 10 mL), and dried in air. The final pH
value was 1.5.
Experimental Section
Synthesis of [Ni(H2pdc)2(H2O)2] ´ 2H2O (4): Reaction of Ni(NO3)2 ´ 6H2O
(0.0727 g, 0.25 mmol), H3pdc ´ H2O (0.087 g, 0.5 mmol), and deionized
water (10 mL) in the mole ratio of 1:2:2222 at 1508C for 3 days resulted in
powder blue column-like crystals of 4 in yield of 79.9% (0.088 g) based on
NiII. The product was washed with water (3 Â 10 mL) and acetone (3 Â
10 mL), and dried in air. The final pH value was 1.5.
Materials and instruments: Reagent grade MnCl2, Fe(NH4)2(SO4)2 ´ 6H2O,
Co(NO3)2 ´ 6H2O, Ni(NO3)2 ´ 6H2O, and Zn(NO3)2 ´ 6H2O were purchased
from Fisher and Alfa Aesar. 3,5-Pyrazoledicarboxylic acid monohydrate
(97%) was purchased from Acros. All chemicals were used as received
without further purification. Thermogravimetric analyses (TGA) were
performed on a computer-controlled TA Instrument TGA2050 system
under nitrogen flow and with a scan rate of 58Cmin 1. Infrared spectra
were measured from a photoacoustics Model300 on a Bio-Rad FTS-6000
IR system. Powder X-ray diffraction (PXRD) experiments were performed
on a Rigaku D/M-2200T automated diffraction system at an operating
power of 40 kV/40 mA. The data were recorded at room temperature with
a step size of 0.02 in 2q and a scan speed of 1.78min 1. The analysis was
carried out using JADE (windows) software package. The simulated
powder patterns from single crystal data were generated for the phase
identification. All hydrothermal reactions were performed in 23 mLTeflon-
lined stainless steel bombs under autogenous pressure.
Synthesis of [Zn(H2pdc)2(H2O)2] ´ 2H2O (5): Reaction of Zn(NO3)2 ´ 6H2O
(0.074 g, 0.25 mmol), H3pdc ´ H2O (0.087 g, 0.5 mmol), and deionized water
(10 mL) in the mole ratio of 1:2:2222 at 1508C for 3 days generated
colorless polyhedral crystals of 5 in yield of 49.4% (0.055 g) based on ZnII.
The product was washed with water (3 Â 10 mL) and acetone (3 Â 10 mL)
and dried in air. The final pH value was 1.5.
Synthesis of [Co4(Hpdc)4(py)12] ´ 4py ´ 2H2O ´ 2CH3OH (6): After heating
compound 3 (51.89 mg) under nitrogen gas to remove the four water
molecules, a violet powder of [Co(H2pdc)2] (43.27 mg, calcd 43.43 mg) was
collected. The [Co(H2pdc)2] powder (6 mg) was dissolved in methanol
(3 mL) in a vial to give a pale pink solution. Pyridine (2.0 mL) was then
Table 5. Crystallographic data, details of the data collection and structure refinement for 1, 2, 3, 4, 5, and 6.
1
2
3
4
5
6
formula
Mr
C10H14MnN4O12 C10H14FeN4O12
C10H14CoN4O12
441.18
C10H14NiN4O12
440.96
C10H14ZnN4O12
447.62
C102H100Co4N24O20
2217.78
437.19
438.10
crystal system
space group
a [Š]
b [Š]
c [Š]
monoclinic
P21/c (No.14)
10.186(2)
12.473(2)
6.831(1)
108.80(3)
821.6(2)
2
monoclinic
P21/c (No.14)
10.023(2)
12.432(2)
6.813(1)
108.42(3)
805.4(2)
2
monoclinic
P21/c (No.14)
9.981(2)
12.426(2)
6.807(1)
108.23(3)
801.9(2)
2
monoclinic
P21/c (No.14
9.896(2)
12.402(3)
6.810(1)
108.15(3)
794.2(2)
2
monoclinic
P21/c (No.14)
10.001(2)
12.430(2)
6.834(1)
108.32(3)
806.5(2)
2
monoclinic
P21/c (No.14)
9.9617(1)
18.5080(2)
28.4786(3)
93.076(1)
5243.07(10)
2
b [8]
V [Š3]
Z
3
1calcd [gcm
m [mm
]
1.767
0.879
1.806
1.014
1.827
1.148
1.844
1.300
1.843
1.600
1.405
0.702
1
]
crystal size
T [K]
l [Š]
q range [8]
scan mode
0.15 Â 0.10 Â 0.10 0.18 Â 0.15 Â 0.08 0.45 Â 0.18 Â 0.15 0.16 Â 0.06 Â 0.03 0.20 Â 0.18 Â 0.15 0.48 Â 0.18 Â 0.12
293(2)
293(2)
293(2)
293(2)
0.71073
2.17 ± 25.98
w
293(2)
220(2)
0.71073
2.11 ± 26.00
w-2q
0.71073
2.14 ± 26.01
w-2q
0.71073
2.15 ± 25.99
w-2q
0.71073
2.15 ± 25.97
w-2q
0.71069
2.56 ± 25.35
image plate f oscillations
absorption type
min/max transmissions
reflections collected
independent reflections (Rint) 1618 (0.0345)
observed reflections [I > 2s(I)] 1114
Y scan
0.948/1.000
1748
Y scan
0.962/0.999
1710
1582 (0.0574)
1220
Y scan
0.892/1.000
1705
1577 (0.0368)
1307
Y scan
0.827/1.000
1692
1565 (0.0385)
1090
Y scan
0.933/1.000
1711
1583 (0.0155)
1290
none
none
32290
9344 (0.0408)
8274
parameters
R1 [I > 2s(I)][a]
wR2[b]
125
125
0.0426
0.0863
1.19
125
0.0468
0.0752
1.06
125
125
0.0303
0.0649
1.08
678
0.0542
0.1093
1.19
0.0500
0.0929
1.13
0.0595
0.1074
1.11
GOF
3
residual peak/hole [eŠ
]
0.49/-0.44
0.89/-0.46
0.50/-0.30
1.18/-0.45
0.52/-0.37
0.41/-0.43
[a] R1ˆSjjFo j jFc jj/SjFo j. [b] wR2ˆ[S[w(jFo2 j jFc2 j)2]/Sw(Fo2†2]1/2. Weighting: 1, wˆ1/s2[Fo2 ‡ 2.80P], where Pˆ(Fo2 ‡ 2Fc2†/3; 2, wˆ1/s2(Fo2
1.80P); 3, wˆ1/s2(Fo2 ‡ 1.80P); 4, wˆ1/s2[Fo2 ‡ 3.0P]; 5, wˆ1/s2[Fo2 ‡ 1.50P]; 6, wˆ1/s2[Fo2 ‡ (0.02p)2 ‡ 10.0P].
‡
4436
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Chem. Eur. J. 2001, 7, No. 20

Basket-Weave-Like Complexes
4431±4437
added to the open vial. The color of the solution changed to red-pink.
Orange-pink needle crystals of 6 (yield: ꢀ25%) were formed after a slow
evaporation of the solution for several days.
Soc. 1999, 121, 1752; e) T. Sawaki, T. Dewa, Y. Aoyama, J. Am. Chem.
Soc. 1998, 120, 8539.
[3] a) D. Braga, F. Grepioni, J. J. Byrne, A. Wolf, J. Chem. Soc. Chem.
Commun. 1995, 1023; b) A. D. Burrows, C. Chan, M. M. Chowdhry,
J. E. McGrady, D. Michael, P. Mingos, J. Chem. Soc. Rev. 1995, 329;
c) C. B. Aakeröy, A. M. Beatty, Chem. Chmmun. 1998, 1067; d) H. J.
Choi, M. P. Suh, J. Am. Soc. Chem. 1998, 120, 10622.
[4] a) L. Pan, X.-Y. Huang, J. Li, Y. G. Wu, N.-W. Zheng, Angew. Chem.
2000, 112, 537; Angew. Chem. Int. Ed. 2000, 39, 527; b) L. Pan, X.-Y.
Huang, J. Li, J. Solid State. Chem. 2000, 152, 236.
[5] a) L. Pan, N. Ching, X.-Y. Huang, J. Li, Inorg. Chem. 2000, 39, 5333;
b) L. Pan, N. Ching, X.-Y. Huang, J. Li, Inorg. Chem. 2001, 41, 1271.
[6] A. Mayr, L.-F. Mao, Inorg. Chem. 1998, 37 5776.
[7] Y.-B. Dong, M. D. Smith, H.-C. zur Loye, Solid State Sci. 2000, 2, 861.
[8] J. Y. Lu, M. A. Lawandy, J. Li, T. Yuen, C. L. Lin, Inorg. Chem. 1999,
38, 2695.
X-ray crystallography: Single-crystal structure analyses for compounds 1 ± 5
were performed on an automated Enraf-Nonius CAD4 diffractometer
equipped with graphite monochromatic MoKa radiation. Lattice parame-
ters were obtained from least-squares analyses of 25 computer-centered
reflections with 6.55 ꢁ q ꢁ 13.938 (1), 5.98 ꢁ q ꢁ 13.468 (2), 9.24 ꢁ q ꢁ 14.738
(3), 6.20 ꢁ q ꢁ 14.428 (4), and 8.15 ꢁ q ꢁ 14.768 (5). The data collections for
all crystals were monitored by three standard reflections every four hours.
No decay was observed except the statistic fluctuation. Data collections
were controlled by the CAD4/PC,[19a] the XCAD4-PC[19b] was used for data
reduction. The crystal structure of 6 was determined by single-crystal X-ray
diffraction analysis on an Rigaku R-AXISIIc area detector employing
graphite monochromatic MoKa radiation. Indexing was performed from a
series of 18 oscillation images with exposures of 400 s per frame. Hemi-
sphere of data were collected using 48 oscillation angles with exposures of
1500 s per frame and a crystal-to-detector distance of 82 mm. Oscillation
images were processed by using bioteX.[20] Raw intensities were corrected
for Lorentz and polarization effects. Direct phase determination and
subsequent difference Fourier map synthesis yielded the positions of all
nonhydrogen atoms, which were subjected to anisotropic refinement.
Hydrogen atoms were located from the difference Fourier map, but were
not refined; their thermal parameters were set equal to 1.2 Â Ueq of the
parent nonhydrogen atoms. The final full-matrix, least-squares refinement
on F 2 was applied for all observed reflections [I > 2s(I)]. All calculations
were performed by using the SHELX97 software package.[21] Analytic
expressions of atomic scattering factors were employed, and anomalous
dispersion corrections were incorporated.[22] Crystal data and details of the
data collection and structure refinement for 1 ± 6 are listed in Table 5.
[9] S. C. Chang, J. K. H. Ma, J. T. Wang, N. C. Li, J. Coord. Chem. 1972, 2,
31.
[10] B. Mernari, F. Abraham, M. Lagrenee, Adv. Mater. Res. 1994, 1 ± 2, 317.
[11] a) M. A. S. Goher, A. A. Youssef, Z.-Y. Zhou, T. C. W. Mak, Poly-
hedron 1993, 12, 1871; b) R. V. Thundathil, E. M. Holt, S. L. Holt, K. J.
Katson, J. Chem. Soc. Dalton Trans. 1976, 1438; c) I. N. Pdyakova,
T. N. Polynova, M. A. Porai-Khshits, Koord. Khim. 1981, 7, 1894; d) P.
Richard, D. T. Qui, E. G. Bertaut, Acta Crystallogr. Sect. B 1974, 30,
628.
[12] A similar covalent bonded parquet network has been reported by
Y. B. Dong, R. C. Layland, N. G. Pschirer, M. D. Smith, U. H. F. Bunz,
H. C. zur Loye, Chem. Mater. 1999, 11, 1413.
[13] J. Bernstein, R. E. Davis, L. Shimoni, N. Chang, Angew. Chem. 1995,
107, 1689; Angew. Chem. Int. Ed. Engl. 1995, 34, 1555; a graph set Rda
(n) stands for a pattern formed through hydrogen bonding, in which R
specifies a ring, a and d are the numbers of hydrogen-bond acceptors
and donors, respectively, and n is the number of atoms in the ring.
[14] J. D. Lee, Concise Inorganic Chemistry, 4th ed., Chapman & Hall,
New York, 1991.
[15] a) V. Kiritsis, A. Michaelides, S. Skoulika, S. Golhen, L. Ouahab,
Inorg. Chem. 1998, 37, 3407; b) K. Endo, T. Sawaki, M. Koyanagi, K.
Kobayashi, H. Masuda, Y. Aoyama, J. Am. Chem. Soc. 1995, 117, 8341.
[16] a) M. J. Hannon, C. L. Painting, W. Errington, J. Chem. Soc. Chem.
Commun. 1993, 307; b) R.-D. Schnebeck, E. Freisinger, B. Lippert,
Eur. J. Inorg. Chem. 2000, 1193.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication no. CCDC- CCDC
160413 (1), CCDC 160414 (2), CCDC 160415 (3), CCDC 160416 (4),
CCDC 160417 (5), and CCDC 160418 (6). Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk).
Acknowledgements
[17] S. Leininger, B. Olenyuk, P. Stang, Chem. Rev. 2000, 100, 853.
[18] M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusukawa, K.
Biradha, Chem. Commun. 2001, 509.
[19] a) Enraf-Nonius CAD4-PC Software, Version 1.1, Enraf-Nonius,
Delft (The Netherlands), 1992; b) K. Hrams, XCAD4, Program for
the reduction of CAD4 Diffractometer Data, University of Marburg
(Germany), 1997.
The support of the National Science Foundation (DMR-9553066) and the
REU supplemental funds are gratefully acknowledged.
[1] a) K. Miyamura, A. Mihara, T. Fujii, Y. Gohshi, Y. Ishii, J. Am. Chem.
Soc. 1995, 117, 2377; b) Comprehensive Supramolecular Chemistry,
Vol. 10 (Eds.: J.-M. Lehn, J. L. Atwood, J. E. D. Davies, D. D.
McNicol, F. Vögtle, D. N. Reinhoudt), Pergamon, Oxford, 1996;
c) M. Munakata, L. P. Wu, T. Kuroda-Sowa, M. Maekawa, Y. Suenaga,
K. Furuichi, J. Am. Chem. Soc. 1996, 118, 3305.
[2] See, for example: a) G. R. Desiraju, Crystal Engineering: The Design
of organic Solids, Elsevier, New York, 1989; b) P. Brunet, M. Simard,
J. D. Wuest, J. Am. Chem. Soc. 1997, 119, 2737; c) J. A. Swift, A. M.
Pivovar, A. M. Reynolds, M. D. Ward, J. Am. Chem. Soc. 1998, 120,
5887; d) A. Ranganathan, V. R. Pedireddi, C. N. R. Rao, J. Am. Chem.
[20] BioteX:
a suite of programs for the collection, redution and
interpretation of imaging plate data, Molecular Structure Corpora-
tion, 1995.
[21] G. M. Sheldrick, SHELX-97, Program for Structure Refinement,
University of Göttingen (Germany), 1997.
[22] International Tables for X-ray Crystallography, Vol. C, Kluwer Aca-
demic, Dordrecht, 1989, Tables 4.2.6.8 and 6.1.1.4.
Received: March 26, 2001 [F3150]
Chem. Eur. J. 2001, 7, No. 20
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4437 $ 17.50+.50/0
4437