A new 2-carboxylate-substituted 4,4′-bipyridine ligand: Coordination chemistry of 4,4′-bipyridine-2-carboxylic acid and its synthetic intermediate 2-methyl-4,4′-bipyridine

Article abstract of DOI:10.1039/b606280f

The first monocarboxylate-substituted 4,4′-bipyridine ligand, 4,4′-bipyridine-2-carboxylic acid (4-(pyridin-4-yl)pyridine-2-carboxylic acid (PPCAH)), has been successfully synthesized from 4,4′-bipyridine. Reactions with transition metals zinc and manganese were used to establish the coordination characteristics of the product, 4,4′-bipyridine-2-carboxylic acid, and of the synthetic intermediate, 2-methyl-4,4′-bipyridine, by single-crystal X-ray diffraction. The ligand PPCAH is useful for the formation of metal-containing building blocks that can be used in the assembly of mixed-metal framework materials. The synthesis and structure of one such mixed-metal coordination polymer, Cu(PPCA)₂HgI₂, is also presented. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b606280f

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www.rsc.org/dalton | Dalton Transactions
A new 2-carboxylate-substituted 4,4ꢀ-bipyridine ligand: coordination
chemistry of 4,4ꢀ-bipyridine-2-carboxylic acid and its synthetic
intermediate 2-methyl-4,4ꢀ-bipyridine
Chun-Long Chen,a,b Joseph M. Ellsworth,a Andrea M. Goforth,a Mark D. Smith,a Cheng-Yong Sub and
Hans-Conrad zur Loye*a
Received 3rd May 2006, Accepted 7th August 2006
First published as an Advance Article on the web 18th August 2006
DOI: 10.1039/b606280f
The first monocarboxylate-substituted 4,4ꢀ-bipyridine ligand, 4,4ꢀ-bipyridine-2-carboxylic acid
(4-(pyridin-4-yl)pyridine-2-carboxylic acid (PPCAH)), has been successfully synthesized from
4,4ꢀ-bipyridine. Reactions with transition metals zinc and manganese were used to establish the
coordination characteristics of the product, 4,4ꢀ-bipyridine-2-carboxylic acid, and of the synthetic
intermediate, 2-methyl-4,4ꢀ-bipyridine, by single-crystal X-ray diffraction. The ligand PPCAH is useful
for the formation of metal-containing building blocks that can be used in the assembly of mixed-metal
framework materials. The synthesis and structure of one such mixed-metal coordination polymer,
Cu(PPCA)2HgI2, is also presented.
the size of cavities in the resulting framework is limited by the
Introduction
length of the pyrazinecarboxylate ligand. Thus, to enable the
Due to rapid advances in the past several years, the field of
assembly of larger networks, we decided to synthesize a new,
supramolecular chemistry has progressed to the point where
longer ligand with coordination characteristics similar to those
specified supramolecular structures can often be obtained via the
assembly of judiciously selected building blocks under controlled
of the pyrazinecarboxylate ligand.
Although substituted bipyridyl ligands have been studied
reaction conditions.1 One aspect, in particular, that has greatly
for many years due to their utility in the formation of
supramolecular structures,6 only a few examples of the syn-
thesis of monomethyl-substituted 4,4ꢀ-bipyridine are recorded
in the literature,7 and no monocarboxylate-substituted 4,4ꢀ-
bipyridine has been reported to date. Consequently, the
coordination chemistry of the monomethyl-substituted 4,4ꢀ-
bipyridine and the monocarboxylate-substituted 4,4ꢀ-bipyridine
has yet to be investigated. As part of our continuing in-
vestigation of mixed-metal coordination compounds based on
pyrazinecarboxylate ligands, we present herein the synthesis
and coordination characteristics of the new 2-carboxylate-
substituted 4,4ꢀ-bipyridyl ligand, 4,4ꢀ-bipyridine-2-carboxylic acid
(PPCAH) (Scheme 1). The single-crystal structures of five com-
plexes: [Mn(2-Me-4,4ꢀ-bipy)(NO3)2(H2O)2] (1), [Mn(2-Me-4,4ꢀ-
bipy)2(CH3CN)2(H2O)2](ClO4)2 (2), [Mn(PPCA)2(H2O)2]·2H2O
(3), [Zn(PPCA)2(H2O)2]·2H2O (4) and Cu(PPCA)2HgI2 (5) show
that the ligand PPCA, and its synthetic intermediate 2-methyl-
4,4ꢀ-bipyridine (2-Me-4,4ꢀ-bipy), are promising supramolecular
reagents for the construction of hydrogen-bonded inorganic–
organic hybrid materials. Furthermore, we demonstrate that
PPCA has coordination characteristics similar to the pyrazinecar-
boxylate ligand, and that it is a useful ligand for the formation of
affected the field of supramolecular chemistry is ligand design
and synthesis, which continues to play an important role in
the formation of new supramolecular complexes with desired
structures and concomitant properties.2
Pyridyl ligands that contain carboxylate groups, such as
pyrazinecarboxylate or pyridinecarboxylate, exhibit the coordina-
tion characteristics of both the pyridyl donor and the carboxylate
group; and this dual functionality imparts these ligands with
special networking abilities. Consequently, they have received
increased attention by research groups for use in the synthesis
of new mono- and bi-metallic inorganic–organic materials.3 In
particular one group of pyridyl based ligands, the pyrazinecar-
boxylates, has proven to be extremely versatile for the construction
of new framework materials due to their ability to engage in
several different coordination modes.4 In fact, our recent studies
on copper–mercury and copper–cadmium pyrazinecarboxylate
systems, which have resulted in the formation of several intriguing
mixed-metal frameworks,5 demonstrate that 2-pyrazinecarboxylic
acid and 2-methylpyrazine-5-carboxylic acid are excellent ligands
for use in the assembly of extended mixed-metal structures. The
first step involves the formation of a metal-containing building
block by coordinating two ligands to one copper center, followed
by the reaction of this copper-containing building block with a
second metal cation. This strategy has resulted in numerous, new
mixed-metal framework structures. In all these cases, however,
aDepartment of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina, 29208, USA. E-mail: zurloye@mail.chem.sc.edu
bSchool of Chemistry and Chemical Engineering, Sun Yat-Sen University,
Guangzhou, 510275, China
Scheme 1
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metal-containing building blocks that can be used in the assembly
of mixed-metal framework materials.
4,4ꢀ-Bipyridine-2-carboxylic acid (PPCAH). 2-Methyl-4,4ꢀ-
bipyridine (0.85 g, 5 mmol) was dissolved in 50 mL distilled
water. Potassium permanganate (2.37 g, 15 mmol) was added
while stirring, and the resulting mixture was heated at reflux
for 12 h (Scheme 3). A brown precipitate (MnO2) was isolated
by filtration, and the filtrate was extracted with ether to remove
unreacted 2-methyl-4,4ꢀ-bipyridine starting material. Addition of
concentrated hydrochloric acid precipitated a white powder, which
was recrystallized from water. Yield: 23.9%. H1 NMR (d) (DMSO-
d6) 8.89 (dd, H2, H6, H6ꢀ), 8.44 (d, H3ꢀ, H5ꢀ), 8.14 (dd, H5); mp
218–219 ◦C.
Experimental
All starting materials and solvents were obtained from commercial
1
sources and used without further purification. H NMR spectra
were collected at room temperature on a Varian Mercury/VX 300
spectrometer with chemical shifts reported in d relative to CDCl3
or DMSO-d6. Melting point determinations were made on samples
in sealed glass capillaries using an Electrothermal 9100 apparatus.
X-Ray powder diffraction (XRD) patterns were acquired on a
Rigaku D/Max-2200 powder X-ray diffractometer with graphite-
monochromatized Cu-Ka radiation (k = 0.15148 nm).
Complex 1: [Mn(2-Me-4,4ꢀ-bipy)(NO3)2(H2O)2]. Mn(NO3)2·
6H2O (0.05 mmol) dissolved in CH3CN (3 mL) was layered onto
a solution of 2-methyl-4,4ꢀ-bipyridine (0.05 mmol) in CH2Cl2
(2 mL) to give colorless plate crystals (58% yield) suitable for
X-ray analysis.
CAUTION! Perchlorate salts are potentially explosive and should
only be used in small quantities and handled with the necessary
precautions.
Complex 2: [Mn(2-Me-4,4ꢀ-bipy)2(CH3CN)2(H2O)2](ClO4)2.
Mn(ClO4)2·6H2O (0.05 mmol) dissolved in CH3CN (3 mL) was
layered onto a solution of 2-methyl-4,4ꢀ-bipyridine (0.05 mmol) in
CH2Cl2 (2 mL) to give colorless plate crystals (53% yield) suitable
for X-ray analysis.
Synthesis
2-Methyl-4,4ꢀ-bipyridine. The method used to synthesize 2-
methyl-4,4ꢀ-bipyridine is similar to that (Scheme 2) reported in the
literature.7a 4,4ꢀ-Bipyridine (31.24 g, 0.2 mmol) was dissolved in a
solution of 98% sulfuric acid (11 mL) in distilled water (140 mL)
. Subsequently, acetic acid (60 g, 1.0 mol) and a solution of
silver nitrate (3.40 g, 0.02 mmol) in water (20 mL) were added
to the bipyridine solution. The resultant mixture was heated to
Complex 3: [Mn(PPCA)2(H2O)2]·2H2O. Na2CO3 (0.025 mmol)
was added to 4,4ꢀ-bipyridine-2-carboxylic acid (PPCAH)
(0.05 mmol) in H2O (3 mL). Once the solution became clear,
Mn(NO3)2·6H2O (0.1 mmol) in CH3CN (3 mL) was layered onto
it. Two days later, yellow prismatic crystals (42% yield) suitable for
X-ray analysis were harvested.
◦
110 C and maintained at that temperature for 30 min, at which
point ammonium persulfate (45.64 g, 0.2 mol) was added portion-
wise as a solid. Once the vigorous evolution of carbon dioxide
had ceased, the solution was heated at reflux for an additional
30 min, allowed to cool, and made alkaline to a pH value of
about 8. The reaction products were then extracted with ether
and identified by TLC. The combined extracts were dried over
CaCl2 and evaporated in vacuo, to yield a solid yellow mixture
(27.19 g). The yellow mixture was introduced as a solution in
chloroform onto a column of alumina packed in hexanes. Elution
with hexane–acetone (5 : 1) gave four bands. The third band was
identified as 2-methyl-4,4ꢀ-bipyridine, H1 NMR (d, CDCl3) 2.64 (s,
CH3), 7.32–7.51 (m, H3,3ꢀ,5,5ꢀ aromatic protons), 8.59–8.72 (m,
H2ꢀ, 6,6ꢀ aromatic protons); mp 92–93 ◦C.
Complex 4: [Zn(PPCA)2(H2O)2]·2H2O. Na2CO3 (0.025 mmol)
was added to 4,4ꢀ-bipyridine-2-carboxylic acid (PPCAH)
(0.05 mmol) in H2O (3 mL). Once the solution became clear,
Zn(BF4)2·6H2O (0.1 mmol) in CH3CN (3 mL) was layered onto
it. Two days later, colorless plate crystals (46% yield) suitable for
X-ray analysis were harvested.
Complex 5: [Cu(PPCA)2HgI2]. PPCAH (0.5 mmol), HgI2
(0.5 mmol), and Cu(NO3)2·3H2O (0.5 mmol) were placed in a
23 mL Teflon-lined autoclave with 10 mL ◦water. The autoclave
was subsequently sealed and heated to 160 C at 1 ◦C min−1 and
held at that temperature for 72 h. At the end of this period, the
◦
autoclave was cooled to 80 ◦C at 0.1 C min−1 and held at that
temperature for 12 h before cooling to room temperature at the
same rate. Rectangular turquoise crystals (32% yield) suitable for
X-ray analysis were harvested.
X-Ray crystallography
X-Ray intensity data for 1–5 were measured at 150 K on a Bruker
SMART APEX CCD-based diffractometer (Mo-Ka radiation,
Scheme 2
Scheme 3
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8
˚
k = 0.71073 A). For 1, initial unit cell indexing was ambiguous.
Results and discussion
The data are metrically consistent with an unusual C-centered
Synthesis
˚
˚
orthorhombic unit cell with a = 19.331 A, b = 43.975 A, c =
˚
7.245 A. After raw data frame integration and Lp corrections
The synthesis of the intermediate, 2-methyl-4,4ꢀ-bipyridine, was
similar to the method reported in the literature.7a 4,4ꢀ-Bipyridine
was mixed with sulfuric acid, silver nitrate and ammonium persul-
fate in an aqueous solution. The resulting yellow solid, a mixture
of 2,2ꢀ,6-trimethyl-4,4ꢀ-bipyridine, 2,2ꢀ-dimethyl-4,4ꢀ-bipyridine, 2-
methyl-4,4ꢀ-bipyridine and 4,4ꢀ-bipyridine, was separated using an
alumina column before oxidation. It was found that oxidation of
the entire mixture made it difficult to isolate the desired product,
PPCAH, but that the product PPCAH can be isolated if a mixture
consisting of only 2-methyl-4,4ꢀ-bipyridine and 4,4ꢀ-bipyridine (the
fourth band off the column) is oxidized.
(SAINT+),8 examination of the intensity data with XPREP9
showed Rint = 0.079 for this cell. However the pattern of systematic
absences in the intensity data agreed with no space group. Process-
ing the data according to a primitive monoclinic cell (reported
below) with half the volume gave Rint = 0.053 and absences
corresponding to P21/c. A reasonable solution was obtained
in P21/c but resulted in high (>20%) R-factors and several
unacceptable displacement parameters. An excellent refinement
was obtained in P21/c by treating the crystal as being twinned by
pseudo-merohedry, i.e., the primitive monoclinic crystal is twinned
to emulate the C-centered orthorhombic cell. The twin law applied
is {1 0 1/0 1 0/0 0 1}, derived analogously to a previously reported
example of this form of twinning.10 The major twin fraction
refined to 0.553(1). The crystal system and space group choice
were further verified by ADDSYM/PLATON.11 For 1–5, the
raw data frame integration and Lp corrections were performed
with SAINT+.8 For all complexes, analysis of the data showed
negligible crystal decay during collection and no absorption
correction was applied for 1–4, while an absorption correction
using SADABS8 was used for 5; direct methods structure solu-
tion, difference Fourier calculations and full-matrix least-squares
refinement against F2 were performed with SHELXTL.9 All
non-hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms bound to carbon were placed in
geometrically idealized positions and included as riding atoms.
All water hydrogens were located in difference maps and refined
with a common isotropic displacement parameter with the O–
H distances restrained to be approximately equal. Crystal data
are summarized in Table 1, selected bond lengths and angles are
given in Table 2 and all hydrogen bonds involved are tabulated in
Table 3.
¯
¯
Structures
The two crystallographically independent molecules of complex
1, [Mn(2-Me-4,4ꢀ-bipy)(NO3)2(H2O)2], are shown in Fig. 1. The
2-Me-4,4ꢀ-bipy ligand is coordinated in a monodentate fashion
CCDC references numbers 267236–267239 and 601017.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b606280f
Fig. 1 Thermal ellipsoid plot of the two crystallographically independent
molecules in complex 1 with atomic labeling scheme. Displacement
ellipsoids are drawn at the 50% probability level.
Table 1 Crystallographic data for 1–5
Empirical
1
2
3
4
5
Formula
Mr
C11H14MnN4O8
385.20
C26H30Cl2MnN6O10
712.40
C22H22MnN4O8
525.38
C22H22N4O8Zn
535.81
C22H14CuHgI2N4O4
916.30
Crystal system
Monoclinic
24.007(3)
7.2451(9)
19.331(2)
113.671(2)
3079.5(7)
P21/c
Monoclinic
11.1520(8)
13.1262(9)
11.6168(8)
112.855(1)
1567.00(19)
P21/n
Monoclinic
19.3775(10)
7.6358(4)
15.1202(7)
93.305(1)
2233.50(19)
I2/a
Monoclinic
19.4456(12)
7.6438(4)
14.8027(9)
93.582(1)
2195.9(2)
I2/a
Monoclinic
30.3812(18)
5.0478(3)
16.3401(9)
108.268(1)
2379.6(2)
C2/c
˚
a/A
˚
b/A
˚
c/A
◦
b/
3
˚
V/A
Space group
Z
8
2
4
4
4
Dc/g cm−1
1.662
1.9–50.3
0.908
1.510
4.3–52.8
0.656
1.562
4.2–52.7
0.649
1.621
4.2–52.7
1.178
2.558
2.8–52.7
9.970
◦
2h Range/
l(Mo-Ka)/mm−1
Refl. meas.
29733
16385
11586
8881
12484
Indep. refl.
5505
461
0.0452, 0.0500
0.0958, 0.0980
1.125
+0.51/−0.31
3214
215
0.0384, 0.0421
0.1008, 0.1032
1.053
+0.58/−0.48
2292
182
0.0344, 0.0391
0.0833, 0.0860
1.045
+0.32/−0.20
2263
182
0.0277, 0.0302
0.0742, 0.0753
1.077
+0.46/−0.28
2444
156
0.0310, 0.0353
0.0782, 0.0806
1.083
+1.95/−1.01
No. param. refined
R1 [I > 2r(I), all data]
wR2 [I > 2r(I), all data]
GOF
Dqmax/min/e−
−3
˚
A
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˚
Table 3 Hydrogen bonds for complexes 1–4 [distances (d) in A and angles
(∠) in ◦
]
D–H · · · A
Complex 1
d(D–H)
d(H · · · A)
d(D · · · A)
∠(DHA)
O(1)–H(1A) · · · O(17)#1
O(1)–H(1B) · · · O(20)#2
O(2)–H(2A) · · · N(2)#3
O(2)–H(2B) · · · O(22)#4
O(3)–H(3A) · · · O(13)#5
O(3)–H(3B) · · · O(14)
0.83(2)
0.83(2)
0.83(2)
0.83(2)
0.83(2)
0.83(2)
0.83(2)
0.84(2)
2.11(3)
2.26(4)
1.93(3)
2.11(2)
2.02(3)
2.05(2)
1.88(3)
2.25(3)
2.929(5)
3.000(5)
2.718(4)
2.930(4)
2.795(5)
2.877(5)
2.689(5)
3.044(5)
167(6)
147(5)
159(6)
170(5)
155(5)
173(6)
164(6)
159(5)
O(4)–H(4A) · · · N(4)#6
O(4)–H(4B) · · · O(16)#7
Complex 2
O(1)–H(1A) · · · O(11)
O(1)–H(1B) · · · N(2)#2
0.79(2)
0.81(2)
2.02(2)
1.92(2)
2.814(2)
2.729(2)
176(3)
175(3)
Complex 3
Fig. 2 Thermal ellipsoid plot of complex 2 with atomic labeling scheme.
Displacement ellipsoids are drawn at the 50% probability level and
hydrogen bonds are shown in dotted black lines. The suffix “a” (lower
case) refers to symmetry equivalent atoms (symmetry code −x, −y, 1 − z).
O(3)–H(3A) · · · O(4)
O(3)–H(3B) · · · O(2)#2
O(4)–H(4A) · · · O(1)#3
O(4)–H(4B) · · · N(2)#4
0.809(14)
0.796(13)
0.808(14)
0.805(14)
1.866(16)
1.956(14)
1.960(14)
2.041(17)
2.6560(19)
2.7490(18)
2.7665(18)
2.780(2)
165(3)
174(2)
176(2)
152(3)
Complex 4
bipy)2(H2O)4][ClO4]2.14 Again, however, the N2 pyridyl nitrogen is
sterically protected by the adjacent methyl group, which prevents
the formation of an extended coordination polymer structure.
Complexes 3 and 4 are isomorphous. As shown in Fig. 3, two
symmetric PPCA ligands are each chelated to the metal center via
one nitrogen atom and one oxygen atom. The asymmetric unit
contains half of the M(C11H7N2O2)2(H2O)2 [M = Mn (3) or Zn
(4)] complex located on a two-fold axis of rotation, and one
independent uncoordinated water molecule. The M(PPCA)2 unit
in 3 or 4 with two uncoordinated terminal nitrogen atoms is similar
to the M(pyrazinecarboxylato)2 unit where, however, the terminal
N · · · N separation in 3 or 4 is significantly longer than those found
in metal containing building blocks based on pyrazinecarboxylate
ligands.5,15 In complex 3 or 4, two water molecules complete the
distorted octahedral coordination environment around the metal,
while two uncoordinated water molecules are connected to the
Mn(PPCA)2(H2O)2 unit via O–H · · · O hydrogen bonds.
O(3)–H(3A) · · · O(4)
O(3)–H(3B) · · · O(2)#2
O(4)–H(4A) · · · O(1)#3
O(4)–H(4B) · · · N(2)#4
0.799(8)
0.792(8)
0.781(8)
0.789(8)
1.884(11)
1.971(9)
2.004(9)
2.031(12)
2.6562(17)
2.7564(17)
2.7753(17)
2.777(2)
162(3)
171(2)
169(2)
158(2)
Symmetry codes: complex 1: (#1) x, y − 1, z; (#2) x, −y + 1/2, z − 1/2;
(#3) −x + 1, y + 1/2, −z + 3/2; (#4) x, −y + 3/2, z − 1/2; (#5) x, −y +
1/2, z + 1/2; (#6) −x, y + 1/2, −z + 3/2; (#7) x, y + 1, z; complex 2: (#1)
−x, −y, −z + 1; (#2) x − 1, y, z − 1; complex 3: (#1) −x + 1/2, y, −z +
1; (#2) −x + 1/2, −y + 1/2, −z + 1/2; (#3) x, y + 1, z; (#4) x − 1/2, y +
1/2, z + 1/2; complex 4: (#1) −x + 1/2, y, −z + 1; (#2) −x + 1/2, −y +
1/2, −z + 1/2; (#3) x, y + 1, z; (#4) x − 1/2, y + 1/2, z + 1/2; complex 5:
(#1) −x, y, −z + 1/2; (#2) −x + 1/2, −y − 1/2, −z.
to each of the Mn(II) atoms, leaving one pyridyl coordination
site open. In this respect, this complex is quite different from
many related complexes consisting of M(NO3)2 and 4,4ꢀ-bipyridine
ligands, where the bipyridine ligand is typically coordinated to a
metal center on both ends, thus affording extended structures.12
In the case of the 2-Me-4,4ꢀ-bipy ligand, however, the open
coordination site is sterically protected by the adjacent methyl
group which, apparently, blocks further coordination, and thus
prevents the formation of an extended coordination polymer
structure.12 In complex 1, two nitrate anions and two water
molecules complete the coordination environment around each
manganese atom.
When the anion was changed to ClO4−, complex 2 was
obtained. As shown in Fig. 2, 2 is a mononuclear complex
of composition [Mn(2-Me-4,4ꢀ-bipy)2(CH3CN)2(H2O)2](ClO4)2, in
which the manganese atom resides on a crystallographic center of
symmetry and is surrounded by two oxygen atoms from water
molecules, two nitrogen atoms from acetonitrile molecules and
two nitrogen atoms from two different 2-Me-4,4ꢀ-bipy ligands,
forming a pseudo-octahedral coordination environment. The
uncoordinated perchlorate anions are connected to the two
coordinated water molecules via O–H · · · O hydrogen bonds. Here
also, the 2-Me-4,4ꢀ-bipy ligand is coordinated to Mn via only one
pyridine nitrogen to form a ML2 mononuclear complex, which
is comparable to some known monodentate 4,4ꢀ-bipyridine based
complexes, such as [Cu(4,4-bipy)2(H2PO4)2(H2O)2],13 and [Mn(4,4-
Compared to related complexes based on 4,4-bipyridine,12–15
the introduction of the 2-carboxylate functional group enables the
PPCA ligand to chelate to the metal center, enabling it to readily
form ML2 metal containing building block as has been observed
for M(pyrazinecarboxylate)2 complexes.5
Hydrogen bonding is one of the important supramolecular
forces in biological macromolecules and coordination chemistry;
and, as such, it has received increasing interests in recent years. In
fact, hydrogen bonding has become a key concept in the emerging
field of crystal engineering because of the combination of strength
and directionality attributable to this class of interaction.16 In
complexes 1–4, there exist a large number of hydrogen bonding
donors and acceptors that further connect the complexes into
networks of higher dimensionality. Specifically, in complex 1,
each coordinated H2O molecule affords two hydrogen bonding
−
donors (OH). Three oxygen atoms from the two NO3 anions act
as hydrogen bonding acceptors, and the uncoordinated second
pyridine nitrogen also acts as a hydrogen bonding acceptor
(Fig. 4(a)). As shown in Fig. 4(b), the O–H · · · O hydrogen
bonds connect the Mn(2-Me-4,4ꢀ-bipy)(NO3)2(H2O)2 units into
2D layers. These layers are further connected through the 2-Me-
4,4ꢀ-bipy ligand via Mn–N coordination bonds and N · · · H–O
5282 | Dalton Trans., 2006, 5278–5286
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Fig. 3 Thermal ellipsoid plot of [Mn(PPCA)2(H2O)2]·2H2O (3) with atomic labeling scheme. Displacement ellipsoids are drawn at the 50% probability
level. The suffix “a” (lower case) refers to symmetry equivalent atoms (symmetry code 1/2 − x, y, 1 − z).
volved in hydrogen bonding interactions with the second pyridine
nitrogen. Unlike in complex 1, the hydrogen bonding in 2 does
not increase the dimensionality of the structure beyond a 1-
D chain (Fig. 5(a)). As shown in Fig. 5(b), each Mn(2-Me-
4,4ꢀ-bipy)2(CH3CN)2(H2O)2 unit is connected to two adjacent
complexes via four O–H · · · N hydrogen bonds, forming Mn2(2-
Me-4,4ꢀ-bipy)2(H2O)2 metallamacrocycles. Two adjacent metalla-
macrocycles share a manganese(II) ion, thus generating an infinite
1D chain (Fig. 5(b)).
Fig. 5 (a) Hydrogen bonding donors and acceptors in 2. (b) Hydrogen
bonded 1D chain in 2. Hydrogen bonds are indicated by dotted red lines.
As shown in Fig. 6, there are three types of hydrogen
bonds present in complex 3: one between adjacent
Fig. 4 (a) Hydrogen bonding donors and acceptors of one of the
two independent molecules in 1. Hydrogen bonds are indicated by
Mn(PPCA)2(H2O)2 complexes (O–H · · · O, labeled a) and
two between Mn(PPCA)2(H2O)2 units and uncoordinated H2O
dotted red lines. (b) 2D O–H · · · O hydrogen bonded inorganic layer;
2-methyl-4,4ꢀ-bipyridine and hydrogen atoms are omitted for clarity.
(c) Hydrogen bonded 3D inorganic–organic network; Mn coordination
spheres are represented as pink polyhedra.
molecules (O–H · · · O labeled b and O–H · · · N labeled c). The
a-type hydrogen bonds join the Mn(PPCA)2(H2O)2 units in the
c direction, where each coordinated water affords one hydrogen
bond donor (OH) and where the uncoordinated oxygen atom
from the PPCA ligand acts as hydrogen bond acceptor (Fig. 6(a)).
The b-type interactions connect Mn(PPCA)2(H2O)2 units via
pairs of uncoordinated H2O molecules in the b direction. Overall,
the two oxygen atoms from the carboxylate groups act as hydrogen
hydrogen bonds, to form a hydrogen bonded 3D inorganic–organic
network (Fig. 4(c)).
−
In complex 2, the uncoordinated ClO4 anions are hydrogen
bonded to the coordinated water molecules, which are also in-
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bonding acceptors, the two coordinated H2O molecules act
as two hydrogen bonding donors, and the uncoordinated H2O
molecules act as two hydrogen bonding donors and two acceptors
to form the 2D sheets (Fig. 6(b)). The 2D hydrogen bonded sheets
formed by a- and b-type O–H · · · O hydrogen bonds are further
linked into a 3D supramolecular network by c-type O–H · · · N
hydrogen bonds, where the uncoordinated pyridine nitrogen acts
as the hydrogen bond acceptor (Fig. 6(c)), similar to the situation
observed for complexes 1 and 2.
When the PPCAH ligand is reacted with Cu(NO3)2·3H2O
and HgI2, turquoise crystals of complex 5 are obtained. X-
Ray crystallographic analysis reveals that 5 is a mixed-metal
coordination polymer consisting of Cu(PPCA)2 units linked by
HgI2 groups. The square planar Cu(II) lies on a crystallographic
inversion center and is coordinated by two nitrogen atoms (Cu(1)–
˚
N(1) 1.972(5) A) and two oxygen atoms (Cu(1)–O(1) 1.933(4)
˚
A) from two inversion-related PPCA ligands (Fig. 7). The Hg(II)
atom lies on a two-fold axis of rotation in a distorted tetrahedral
˚
HgI2N2 environment (Hg(1)–N(2) 2.411(5) A, Hg(1)–I(1) 2.654(5)
˚
A), and links the Cu(PPCA)2 units into an infinite zigzag chain
by coordinating to two nitrogen atoms from two C2 axis-related
Cu(PPCA)2 building blocks (Fig. 8). These 1D zigzag chains
run along the crystallographic [10-1] direction, and the Cu · · · O
˚
weak interactions [Cu(1)–O(2)* distance is 2.677(5) A (symmetry
codes * = x, y − 1, z and 1/2 − x, 1/2 − y, −z)] expand the
coordination of Cu(II) into a 4 + 2 mode, thus linking these
chains into 2D layers parallel to the crystallographic ab plane
(Fig. 9). The Cu(PPCA)2 building block, as it exists in complex 5,
is similar to the Cu(pyrazinecarboxylato)2 building block,15 further
demonstrating that the PPCAH ligand is, as intended, an extended
pyrazinecarboxylcyclic acid analog.
Bulk phase purity was established by powder X-ray diffraction
for complexes 1, 3 and 4. As this requires grinding the sam-
ples, powder X-ray diffraction of complex 2, which contains a
perchlorate group, was not carried out in the interest of safety.
The agreement between the calculated and measured diffraction
patterns, shown in Fig. 10, supports phase purity of the complexes
and rules out the possibility of a second phase.
Phase pure samples of compounds 1 and 3 were subjected
to thermogravimetric analysis. The TGA curve for compound 1
displayed four consecutive weight loss intervals. The first of these,
occurring over the temperature range 100–150 ◦C, corresponds
to the loss of coordinated water molecules (10.05%; theoretical,
9.35%). Decomposition of the sample at approximately 150 ◦C is
indicated by an abrupt, large multiple step weight loss. Likewise
for compound 3, a 14.32% weight loss between room temperature
Fig. 6 (a) a-type O–H · · · O hydrogen bonded chain structure. )b) 2D
layer bonded by a and b-type O–H · · · O hydrogen bonds. (c) 3D hydrogen
bonded supramolecular structures in 3. a-, b-type O–H · · · O hydrogen
bonds and c-type O–H · · · N hydrogen bond are indicated by purple, red
and green dotted lines respectively.
Fig. 7 Thermal ellipsoid plot of the Cu(PPCA)2 unit in the polymeric chain of 5. Displacement ellipsoids are drawn at the 50% probability level. The
suffix “A” refers to symmetry equivalent atoms (symmetry code 1/2 − x, −1/2 − y, −z).
5284 | Dalton Trans., 2006, 5278–5286
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Fig. 8 View of the 1D zigzag chain of complex 5.
Fig. 9 The 2D layer parallel to the crystallographic ab plane, the Cu · · · O
weak interactions are indicated by dotted cyan lines.
and 140 ◦C is consistent with the loss of water molecules from the
compound (theoretical, 13.70%). However, compound 3 is much
more thermally stable than compound 1. Sample decomposition
as indicated by a large, abrupt weight loss occurs for compound
3 at approximately 360 ◦C. TGA on compound 5 was not carried
out due to problems with volatilizing mercury.
Conclusions
We have successfully synthesized the 2-carboxylate-substituted
4,4ꢀ-bipyridyl ligand, 4-(pyridin-4-yl)pyridine-2-carboxylic acid
(PPCAH), and five complexes assembled from either PPCA or
its synthetic intermediate, 2-methyl-4,4ꢀ-bipyridine. The ligand
PPCAH, and its synthetic intermediate, 2-methyl-4,4ꢀ-bipyridine,
are promising supramolecular reagents for the construction of hy-
drogen bonded inorganic–organic hybrid materials. Furthermore,
we demonstrate that the PPCAH ligand is a good candidate for the
formation of metal-containing building blocks and mixed-metal
coordination polymers. As it is a longer ligand with coordination
characteristics similar to those of the pyrazinecarboxylate ligand,
we believe that PPCAH can be useful for the two-step assembly of
mixed-metal framework materials with large cavities.
Fig. 10 Observed powder X-ray diffraction patterns (above) and simu-
lated patterns (below) of complexes 1, 3 and 4.
Acknowledgements
This work was supported by the National Science Foundation
through Grant CHE:0314164 and by the NNSF of China (No.
20303027).
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5 (a) D. M. Ciurtin, M. D. Smith and H.-C. zur Loye, Chem. Commun.,
2002, 74; (b) Y.-B. Dong, M. D. Smith and H.-C. zur Loye, Inorg. Chem.,
2000, 39, 1943; (c) Y.-B. Dong, M. D. Smith and H.-C. zur Loye, Solid
State Sci., 2000, 2, 861; (d) Y.-B. Dong, M. D. Smith and H.-C. zur
Loye, Angew. Chem., Int. Ed., 2000, 39, 4271; (e) C. T. Chapman, D. M.
Ciurtin, M. D. Smith and H.-C. zur Loye, Solid State Sci., 2002, 4, 1187;
(f) D. M. Ciurtin, M. D. Smith and H.-C. zur Loye, Dalton Trans., 2003,
1245.
6 (a) S. A. Barnett and N. R. Champness, Coord. Chem. Rev., 2003, 246,
145, and references therein; (b) D. M. Ciurtin, Y.-B. Dong, M. D. Smith,
T. Barclay and H.-C. zur Loye, Inorg. Chem., 2001, 40, 2825; (c) N. G.
Pschirer, D. M. Ciurtin, M. D. Smith, U. H. F. Bunz and H.-C. zur
Loye, Angew. Chem., Int. Ed., 2002, 41, 583; (d) D. M. Ciurtin, N. G.
Pschirer, M. D. Smith, U. H. F. Bunz and H.-C. zur Loye, Chem. Mater.,
2001, 2743.
7 (a) J. A. Barltrop and A. C. Jackson, J. Chem. Soc., Perkin Trans. 2,
1984, 367; (b) K. J. Schmalzl and L. A. Summers, Aust. J. Chem., 1977,
30, 657–662.
8 SMART Version 5.628 and SAINT+ Version 6.22. Bruker Analytical
X-ray Systems, Inc., Madison, WI, USA, 2001.
9 G. M. Sheldrick, SHELXTL Version 6.1, Bruker Analytical X-ray
Systems, Inc., Madison, WI, USA, 2000.
10 http://shelx.uni-ac.gwdg.de/∼rherbst/pseudo.html.
11 (a) ADDSYM Algorithm: Y. LePage, J. Appl. Crystallogr., 1987, 20,
264; (b) A. L. Spek, J. Appl. Crystallogr., 1988, 21, 578–579.
12 (a) H. Gudbjartson, K. Biradha, K. M. Poirier and M. J. Zaworotko,
J. Am. Chem. Soc., 1999, 121, 2599; (b) X. Zhao, B. Xiao, A. J. Fletcher,
K. M. Thomas, D. Bradshaw and M. J. Rosseinsky, Science, 2004, 306,
1012; (c) J. Y. Lu, W. A. Fernandez, Z. H. Ge and K. A. Abboud,
New J. Chem., 2005, 29, 434; (d) K. Abu-Shandi, H. Winkler, H.
Paulsen, R. Glaum, B. Wu and C. Janiak, Z. Anorg. Allg. Chem., 2005,
631, 2705; (e) M. Fujita, Y. J. Kwon, S. Washizu and K. Ogura, J. Am.
Chem. Soc., 1994, 116, 1151; (f) S. A. Barnett and N. R. Champness,
Coord. Chem. Rev., 2003, 246, 145.
13 K. Abu-Shandi, C. Janiak and B. Kersting, Acta Crystallogr., Sect. C.,
2001, 57, 1216.
14 M.-L. Tong, H. K. Lee, X.-M. Chen, R.-B. Huang and T. C. W. Mak,
J. Chem. Soc., Dalton Trans., 1999, 3657.
15 C. L. Klein, R. J. Majeste, L. M. Trefonas and C. J. O’Connor, Inorg.
Chem., 1982, 21, 1891.
References
1 (a) O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi
and J. Kim, Nature, 2003, 705; (b) S. R. Seidel and P. J. Stang, Acc.
Chem. Res., 2002, 35, 972; (c) H. D. Selby, B. K. Roland and Z. P.
Zheng, Acc. Chem. Res., 2003, 36, 933; (d) M. Ruben, J. Rojo, F. J.
Romero-Salguero, L. H. Uppadine and J.-M. Lehn, Angew. Chem., Int.
Ed., 2004, 43, 3644; (e) S. Kitagawa, R. Kitaura and S.-I. Noro, Angew.
Chem., Int. Ed., 2004, 43, 2334; (f) H. Hofmeier and U. S. Schubert,
Chem. Soc. Rev., 2004, 33, 373; (g) S. Leininger, B. Olenyuk and P. J.
Stang, Chem. Rev., 2000, 100, 853; (h) C.-L. Chen, B.-S. Kang and C.-Y.
Su, Aust. J. Chem., 2006, 59, 3; (i) S. L. James, Chem. Soc. Rev., 2003,
32, 276.
2 (a) M. J. E. Resendiz, J. C. Noveron, H. Disteldorf, S. Fisher and P. J.
Stang, Org. Lett., 2004, 6, 651; (b) P. J. Steel, Acc. Chem. Res., 2005, 38,
243; (c) M. Albrecht, I. Janser and R. Fro¨hlich, Chem. Commun., 2005,
157; (d) C.-L. Chen, A. M. Goforth, M. D. Smith, C.-Y. Su and H.-C.
zur Loye, Angew. Chem., Int. Ed., 2005, 44, 6673; (e) Y.-B. Dong, H.-
Y. Wang, J.-P. Ma, D.-Z. Shen and R.-Q. Huang, Inorg. Chem., 2005,
44, 4679; (f) K. Takaoka, M. Kawano, M. Tominaga and M. Fujita,
Angew. Chem., Int. Ed., 2005, 44, 2151; (g) S. J. Lee and W. B. Lin,
J. Am. Chem. Soc., 2002, 124, 4554; (h) S.-L. Zheng and X.-M. Chen,
Aust. J. Chem., 2004, 57, 703; (i) D. Maspoch, D. Ruiz-Molina and J.
Veciana, J. Mater. Chem., 2004, 14, 2713; (j) C. Janiak, Dalton Trans.,
2003, 2781; (k) S. R. Batten and K. S. Murray, Coord. Chem. Rev., 2003,
246, 103.
3 (a) B. Zhao, P. Cheng, X. Y. Chen, C. Cheng, W. Shi, D. Z. Liao, S. P.
Yan and Z. H. Jiang, J. Am. Chem. Soc., 2004, 126, 3012; (b) Y.-H. Liu,
Y.-L. Lu, H.-C. Wu, J.-C. Wang and K.-L. Lu, Inorg. Chem., 2002, 41,
2592; (c) S. K. Ghosh, G. Savitha and P. K. Bharadwaj, Inorg. Chem.,
2004, 43, 5495; (d) M. Kurmoo, C. Estourne`s, Y. Oka, H. Kumagai and
K. Inoue, Inorg. Chem., 2005, 44, 217; (e) X. J. Li, R. Cao, Y. Q. Sun,
W. H. Bi, X. Li and Y. Q. Wang, Eur. J. Inorg. Chem., 2005, 321; (f) S.-I.
Noro;, H. Miyasaka;, S. Kitagawa;, T. Wada;, T. Okubo, M. Yamashita
and T. Mitani, Inorg. Chem., 2005, 44, 133.
4 (a) L. M. Zheng, T. Whitfield, X. Q. Wang and A. J. Jacobson, Angew.
Chem., Int. Ed., 2000, 39, 4528; (b) J. H. Luo, B. Alexander, T. R.
Wagner and P. A. Maggard, Inorg. Chem., 2004, 43, 5537; (c) C. L.
Ma, Y. F. Han, R. F. Zhang and D. Q. Wang, Dalton Trans., 2004,
1832; (d) C.-M. Liu, D.-Q. Zhang, J.-L. Luo, N.-L. Wang, H.-M. Hu
and D.-B. Zhu, Eur. J. Inorg. Chem., 2003, 3618; (e) D. G. Huang,
X. F. Zhang, C. N. Chen, F. Chen, Q. T. Liu, D. Z. Liao, L. C. Li and
L. C. Sun, Inorg. Chim. Acta, 2003, 353, 284; (f) C.-X. Cai, Y.-Q. Tian,
X.-M. Ren, Y.-Z. Li and X.-Z. You, Transition Met. Chem., 2002, 27,
924; (g) Y.-C. Liang, M.-C. Hong, J.-C. Liu and R. Cao, Inorg. Chim.
Acta, 2002, 328, 152; (h) D. M. Ciurtin, M. D. Smith and H.-C. zur
Loye, Polyhedron, 2003, 3043.
16 (a) D. Dobrzynska and L. B. Jerzykiewica, J. Am. Chem. Soc., 2004,
´
126, 11118; (b) L. R. Falvello, R. Garde and M. Tomas, Inorg. Chem.,
2002, 41, 4599; (c) A. M. Beatty, Coord. Chem. Rev., 2003, 246, 131;
(d) L. J. Prins, D. N. Reinhoudt and P. Timmerman, Angew. Chem.,
Int. Ed., 2001, 40, 2382 and references therein; (e) G. R. Desiraju, Acc.
Chem. Res., 2002, 35, 565; (f) C.-L. Chen, J.-A. Zhang, X.-P. Li, Z.-N.
Chen, B.-S. Kang and C.-Y. Su, Inorg. Chim. Acta, 2005, 358, 4527.
´
5286 | Dalton Trans., 2006, 5278–5286
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The Royal Society of Chemistry 2006
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