A chain of changes: Influence of noncovalent interactions on the one-dimensional structures of nickel(II) dicarboxylate coordination polymers with chelating aromatic amine ligands

Article abstract of DOI:10.1021/ic049341u

Five one-dimensional coordination polymers, Ni(BDC)(1,10-phen) (1), Ni(BDC)(2,2′-bipy).O.75H₂BDC (2), Ni(BDC)(1,10-phen)(H ₂O) (3), Ni(BDC)(1,10-phen)(H₂O)·O.5H ₂BDC (4) and Ni(BDC)(2,2′-bipy)(H₂O) (5) [where BDC = 1,4-benzenedicarboxylate, 2,2-bipy = 2,2′-bipyridine, and 1,10-phen = 1,10-phenanthroline] that have the same topology but markedly different geometry and packing of the chains have been synthesized by hydrothermal reactions. The results of variations of synthesis conditions and substitutions of 1,10-phenanthroline with 2,2′-bipyridine indicate that incorporation of the coordinating water molecule, which affects the degree of bending of the chain, is primarily influenced by the amine ligand size, suggesting a substantial structural role of aromatic-aromatic interactions and amine ligand steric effects. The incorporation of the guest H₂BDC molecules was found to be favored by lower pH conditions. Crystal data: 1, monoclinic, space group P2₁/n, a = 9.5589(6) A, b = 12.6776(8) A, c = 13.5121(9) A, β = 95.437(1)°, Z = 4; 2, monoclinic, space group P2₁/c, a = 20.532(3) A, b = 21.505(3) A, c = 18.872(3) A, = 93.86(1)°, Z = 16; 3, triclinic, space group P1, a = 8.618(3) A, b = 10.058(4) A, c = 11.353(4) A, α = 115.31(1)°,β = 92.33(1)°, γ = 94.03(1)°, Z = 2; 4, triclinic, space group P1, a: 9.7682(12) A, b = 10.6490(13) A, c = 11.2468(14) A, α = 76.685(2)°, β = 65.309(2)°, γ = 85.612(2)°, Z = 2; 5, monoclinic, space group P2₁/c, a = 13.9683(9) A, b = 17.4489(11) A, c = 13.7737(9) A, β = 99.12(1)°, Z = 8.

Full text of DOI:10.1021/ic049341u

Inorg. Chem. 2004, 43, 5360−5367
A Chain of Changes: Influence of Noncovalent Interactions on the
One-Dimensional Structures of Nickel(II) Dicarboxylate Coordination
Polymers with Chelating Aromatic Amine Ligands
YongBok Go, Xiqu Wang, Ekaterina V. Anokhina, and Allan J. Jacobson*
Department of Chemistry, UniVersity of Houston, Houston, Texas 77204-5003
Received May 19, 2004
Five one-dimensional coordination polymers, Ni(BDC)(1,10-phen) (1), Ni(BDC)(2,2′-bipy)‚0.75H BDC (2),
2
Ni(BDC)(1,10-phen)(H O) (3), Ni(BDC)(1,10-phen)(H O)‚0.5H BDC (4) and Ni(BDC)(2,2′-bipy)(H O) (5) [where BDC
2
2
2
2
) 1,4-benzenedicarboxylate, 2,2-bipy ) 2,2′-bipyridine, and 1,10-phen ) 1,10-phenanthroline] that have the same
topology but markedly different geometry and packing of the chains have been synthesized by hydrothermal reactions.
The results of variations of synthesis conditions and substitutions of 1,10-phenanthroline with 2,2′-bipyridine indicate
that incorporation of the coordinating water molecule, which affects the degree of bending of the chain, is primarily
influenced by the amine ligand size, suggesting a substantial structural role of aromatic−aromatic interactions and
amine ligand steric effects. The incorporation of the guest H BDC molecules was found to be favored by lower pH
2
conditions. Crystal data: 1, monoclinic, space group P21/n, a ) 9.5589(6) Å, b ) 12.6776(8) Å, c ) 13.5121(9)
Å, â ) 95.437(1)°, Z ) 4; 2, monoclinic, space group P21/c, a ) 20.532(3) Å, b ) 21.505(3) Å, c ) 18.872(3)
Å, â ) 93.86(1)°, Z ) 16; 3, triclinic, space group P1h, a ) 8.618(3) Å, b ) 10.058(4) Å, c ) 11.353(4) Å, R )
115.31(1)°, â ) 92.33(1)°, γ ) 94.03(1)°, Z ) 2; 4, triclinic, space group P1h, a ) 9.7682(12) Å, b ) 10.6490(13)
Å, c ) 11.2468(14) Å, R ) 76.685(2)°, â ) 65.309(2)°, γ ) 85.612(2)°, Z ) 2; 5, monoclinic, space group
P21/c, a ) 13.9683(9) Å, b ) 17.4489(11) Å, c ) 13.7737(9) Å, â ) 99.12(1)°, Z ) 8.
Introduction
ligand, 1,4-benzenedicarboxylate (BDC) has been studied
extensively.3 Polycyclic aromatic bidentate ligands such as
2,2′-bipyridyl (2,2′-bipy) and 1,10-phenanthroline (1,10-
phen) are frequently used in combination with polycarboxy-
lates, leading to novel architectures where they facilitate
supramolecular self-assembly through aromatic-aromatic
(π-π and CH-π) interactions.4 Compared to face-to-face
π-π stacking interactions that, until recently, were the
primary focus in the descriptions of aromatic supramolecular
contacts, edge-to-face CH-π interactions did not receive
significant attention. In the past decade, however, their
comparable importance in the crystal chemistry of coordina-
tion compounds is becoming more recognized.5 Several
Inorganic-organic hybrid materials have been studied for
potential applications in gas storage, catalysis, separations,
and molecular recognition.1 The organic components con-
taining N- or O-donors in the framework offer great potential
for chemical and structural diversity.2 Polycarboxylates are
widely used as bridging ligands for designing new inorganic-
organic hybrid materials. As a rigid and versatile bridging
* To whom correspondence should be addressed: E-mail: ajjacob@uh.edu.
Telephone: (713) 743-2785. Fax: (713) 743-2787.
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K. Nature 2000, 404, 982 (c) Kahn, O.; Martinez, C. Science 1998,
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5360 Inorganic Chemistry, Vol. 43, No. 17, 2004
10.1021/ic049341u CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/27/2004

Influences on 1D Structure of Coordination Polymers
(0.50 mmol, 84.0 mg), KOH (0.76 mmol, 42.5 mg), 2,2′-bipyridine
(0.42 mmol, 65.4 mg), and H2O (0.5 mL) was heated in a 23 mL
stainless steel reactor with a Teflon liner at 160 °C for 48 h. The
green rod-shaped crystals were filtered and washed with water and
acetone. Yield: 51% based on Ni. Anal. Calcd for
C24H16.5N2NiO7: C, 57.24; H, 3.30; N, 5.56. Found: C, 56.83; H,
3.23; N, 5.53. IR (KBr): 3430.76m(br), 3068.21m, 1695.13s,
1604.49w, 1575.56w, 1533.14s, 1509.99m, 1473.35w, 1456.00w,
1407.78s, 1278.58m, 1176.37w, 1132.01w, 1105.01w, 1054.87w,
1018.23w, 923.74w, 902.52w, 881.31w, 846.60m, 765.60m, 730.89m,
coordination polymers with BDC and 2,2-bipy or 1,10-phen
ligands, most of which are one-dimensional, have been
reported for divalent cations Mn2+, Co2+, Cu2+, Zn2+, and
Cd2+,6-8 but in the case of Ni2+, only mono- or dinuclear
molecular complexes containing a combination of these
ligands have been described to date.9,10 Herein, we present
the syntheses and structures of five new one-dimensional
coordination polymers of Ni2+: Ni(BDC)(1,10-phen) (1),
[Ni(BDC)(2,2′-bipy)]‚0.75H2BDC (2), Ni(BDC)(1,10-phen)-
(H2O) (3), [Ni(BDC)(1,10-phen)(H2O)]‚0.5H2BDC (4), and
Ni(BDC)(2,2′-bipy)(H2O) (5).
This new series of coordination polymers is based on
topologically identical chains where the nickel centers
chelated by amine ligands are linked by BDC bridges. The
coordination modes of the BDC ligands, geometry of the
chains (zigzag vs crankshaft configuration as well as the
angles between the individual links), and chain packing,
however, are substantially different among these compounds
and were found to be primarily influenced by noncovalent
interactions.
671.11m, 651.82w, 532.26m 474.40w, 441.62w, 418.47w cm-1
.
Synthesis of Ni(BDC)(1,10-phen)(H2O) (3). This compound
was prepared under the same conditions as 1 except for lower
synthesis temperature (160 °C). The product in the form of blue
crystals was filtered and washed with water and acetone. Yield:
57% based on Ni. Anal. Calcd for C20H14N2NiO5: C, 57.05; H,
3.35; N, 6.65. Found: C, 56.62; H, 3.41; N, 6.64. IR (KBr):
3363.26m(br), 3060.49w(br), 1689.34w, 1625.7w, 1583.28m,
1548.56s, 1513.85m, 1496.49w, 1423.21m, 1403.93s, 1380.79s,
1295.93w, 1222.65w, 1143.58w, 1103.09w, 1085.73w, 1049.09w,
1014.38m, 885.17w, 871.61w, 848.53m, 838.88m, 794.53m, 765.60w,
744.39m, 727.03m, 644.11w, 541.90m, 516.83m cm-1
.
Synthesis of [Ni(BDC)(1,10-phen)(H2O)]‚0.5H2BDC (4). This
compound was prepared similarly to 2 except for the use of 1,10-
phen instead of 2,2′-bipy and the reaction temperature of 180 °C.
The blue crystalline product was filtered and washed with water
and acetone. Yield: 57% based on Ni. Anal. Calcd for
C27H17N2NiO7: C, 57.18; H, 3.40; N, 5.56. Found: C, 57.01; H,
3.41; N, 5.64. IR (KBr): 3377.73m(br), 3066.76m(br), 1688.86s,
1586.17w, 1542.30vs, 1516.74m, 1507.52m, 1425.62m, 1404.89s,
1378.38s, 1260.00w, 1246.76w, 1147.44w, 1123.82w, 1105.5w,
1088.62w, 1016.79w, 853.35s, 796.46m, 774.28m, 744.39m, 726.07s,
Experimental Section
Materials and Methods. All the reactants were reagent-grade
and were used as purchased without further purification. The
infrared spectra were measured on a Galaxy Series FTIR 5000
spectrometer with pressed KBr pellets. Thermal analyses were
performed on a TGA V5.1A Dupont 2100 instrument from room
temperature to 600 °C with a heating rate of 3 °C/min in air.
Synthesis of Ni(BDC)(1,10-phen) (1). A mixture of NiCl2‚6H2O
(0.42 mmol, 100 mg), 1,4-benzenedicarboxylic acid (0.63 mmol,
104.7 mg), KOH (1.68 mmol, 94.3 mg), 1,10-phenanthroline (0.42
mmol, 75.8 mg), and H2O (0.5 mL) was heated in a 23 mL stainless
steel reactor with a Teflon liner at 170 °C for 48 h. The blue
crystalline product was filtered and washed with water and acetone.
Yield: 57% based on Ni. Anal. Calcd for C20H12N2NiO4: C, 59.60;
H, 3.00; N, 6.95. Found: C, 59.68; H, 3.13; N, 7.04. IR (KBr):
3367.05m(br), 3079.78w, 3056.63w, 1623.77w, 1585.20w, 1552.42s,
1536.99s, 1506.14s, 1425.14m, 1400.07s, 1340.29w, 1315.12w,
1299.79w, 1253.51w, 1222.65w, 1195.65w, 1141.65m, 1103.09w,
1085.73w, 1020.16m, 889.02w, 869.74w, 850.45s, 842.74s, 779.10w,
750.17m, 728.96s, 646.04m, 549.61w, 536.11m, 499.47m, 482.11w,
603.13m, 534.67m, 516.83m cm-1
.
Synthesis of Ni(BDC)(2,2′-bipy)(H2O) (5). This compound was
prepared as deep-blue crystals under the same reaction conditions
as 1 except for the use of 2,2′-bipy instead of 1,10-phen. Yield:
69% based on Ni. Anal. Calcd for C18H14N2NiO5: C, 54.46; H,
3.55; N, 7.06. Found: C, 54.34; H, 3.58; N, 7.16. IR (KBr):
3316m(br), 3104.85m, 1577.49w, 1570.23w, 1548.56s, 1523.49w,
1506.14m, 1475.28m, 1444.43s, 1411.64s, 1378.86s, 1311.36w,
1253.51w, 1174.44w, 1153.23w, 1056.80w, 1027.87w, 1016.30w,
098.31w, 887.1w, 844.67s, 806.10m, 759.82s, 734.75w, 653.75w,
634.46w, 522.61m, 441.62w, 418.47w cm-1
.
453.19w, 428.12w cm-1
.
Crystallographic Studies. Single crystals of suitable dimensions
for 1-5 were used for the structure determinations. All measure-
ments were made with a Siemens SMART platform diffractometer
equipped with a 1K CCD area detector. A hemisphere of data (1271
frames at 5-cm detector distance) was collected for each phase by
a narrow-frame method with scan widths of 0.3° in ω and an
exposure time of 30-40 s/frame. The first 50 frames were
remeasured at the end of data collection to monitor instrument and
crystal stability, and the maximum correction applied to the
intensities was <1%. The data were integrated by use of the
Siemens SAINT program,11 with the intensities corrected for
Lorentz factor, polarization, air absorption, and absorption due to
variation in the path length through the detector faceplate. The
structures were solved by direct methods and refined on F2 by full-
matrix least-squares with SHELXTL.12 All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were refined isotro-
Synthesis of [Ni(BDC)(2,2′-bipy)]‚0.75H2BDC (2). A mixture
of NiCl2‚6H2O (0.42 mmol, 100 mg), 1,4-benzenedicarboxylic acid
(5) (a) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885. (b) Waters,
M. L. Curr. Opin. Chem. Biol. 2002, 6, 736. (c) Hunter, C. A.; Sanders,
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T.; Umezawa, Y.; Tsuboyama, S.; Nishio, M. Eur. J. Inorg. Chem.
2002, 3148.
(6) (a) Sun, D.; Cao, R.; Liang, Y.; Shi, Q.; Su, W.; Hong, M. J. Chem
Soc., Dalton Trans. 2001, 2335. (b) Cano, J.; De Munno, G.; Sanz,
J.; Ruiz, R.; Lloret, F.; Faus, J.; Julve, M. J. Chem. Soc., Dalton Trans.
1994, 3465. (c) Zhu, L. G.; Xiao, H. P.; Lu, J. Y. Inorg. Chem.
Commun. 2004, 7. 94. (d) Zhang, L. J.; Zhao, X. L.; Cheng, P.; Xu,
J. Q.; Tang, X.; Cui, X. B.; Xu, W.; Wang, T. G. Bull. Chem. Soc.
Jpn. 2003, 76, 1179. (e) Shi, X.; Zhu, G.; Fang, Q.; Wu, G.; Tian, G.;
Wang, R.; Zhang, D.; Xue, M.; Qiu, S. Eur. J. Inorg. Chem. 2004,
185.
(7) Zhang, X.-M.; Tong, M.-L.; Gong, M.-L.; Chen, X.-M. Eur. J. Inorg.
Chem. 2003, 138.
(8) Xu, H. B.; Su, Z. M.; Shao, K. Z.; Zhao, Y. H.; Xing, Y.; Liang, Y.
C.; Zhang, H. J.; Zhu, D. X. Inorg. Chem. Commun. 2004, 7, 260.
(9) Deng, Z. L.; Shi, J.; Jiang, Z. H.; Liao, D. Z.; Yan, S. P.; Wang, G.
L.; Wang, H. G.; Wang, R. J. Polyhedron 1992, 11, 885.
(10) Xiao, H. P.; Shi, Z.; Zhu, L. G.; Xu, R. R.; Pang, W. Q. Acta
Crystallogr. 2003, C59, m82.
(11) SAINT, Program for Data Extraction and Reduction, Siemens Analyti-
cal X-ray Instruments Inc., Madison, WI, 1996.
(12) SHELXTL, Program for Refinement of Crystal Structures, Siemens
Analytical X-ray Instruments Inc., Madison, WI, 1994.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5361

Go et al.
Table 1. Crystallographic Data for Compounds 1-5
1
2
3
4
5
chemical formula
FW
C20H12N2NiO4
403.03
C24H16.5N2NiO 7
503.19
C20H14N2NiO 5
421.04
C24H17N2NiO 7
504.11
C18H14N2NiO5
397.02
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/n
9.5589(6)
12.6776(8)
13.5121(9)
monoclinic
P21/c
20.532(3)
21.505(3)
18.872(3)
triclinic
P1h
triclinic
P1h
monoclinic
P21/c
13.9683(9)
17.449(1)
13.7737(9)
8.618(3)
10.058(4)
11.353(4)
115.31(1)
92.33(1)
94.03(1)
884.7(6)
2
9.768(1)
10.649(1)
11.247(1)
76.685(2)
65.309(2)
85.612(2)
1034.1(2)
2
R, deg
â, deg
95.437(1)
93.86(1)
99.12(1)
γ, deg
V, Å3
1630.1(2)
4
8314(2)
16
3314.6(4)
8
Z
temp, K
223(2)
1.642
1.221
0.0289, 0.0700
0.0403, 0.0744
293(2)
1.604
0.986
0.0573, 0.1032
0.2134, 0.1465
223(2)
1.580
1.133
0.0454, 0.0984
0.0699, 0.1072
293(2)
1.570
0.991
0.0306, 0.0790
0.0349, 0.0817
293(2)
1.591
1.204
0.0291, 0.0747
0.0404, 0.0798
Fc, g cm-3
µ(Mo KR), mm-1
R1, wR2 [I > 2σ(I)]a
R1, wR2 (all data)a
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
2
2
2
pically with geometric constrains. Crystal data for the compounds
1-5 are summarized in Table 1.
resulting in change of a coordination mode of one of the
two BDC ligands from chelating to monodentate (Table 2).
A simultaneous presence of chelating and monodentate
coordination modes of BDC ligands is quite rare and is
found, to our knowledge, in only two recent examples:
[Ni(BDC)(py)3]6‚(DMF)6‚(H2O)9,13 where the bis-chelating
and bis-monodentate BDC ligands alternate throughout the
chain as in 3 and 4, and [Cd(BDC)(2,2′-bipy)]‚H2O,8 where
one carboxylic group in each BDC ligand is chelating and
the other is monodentate. Compared to the chains in 1 and
2, the incorporation of the water molecule in 3 and 4 causes
an increase in the Ni-Ni-Ni angle to an idealized value of
135°, leading to less bent chains. The observed Ni-Ni-Ni
angles within the chains are 139.26(1)° in 3 and 136.57(1)°
in 4. The Ni-Ni distances for nickel atoms bridged by bis-
chelating BDC ligands [10.663(5) Å in 3 and 10.63(1) Å in
4] are similar to those in 1 and 2, while bis-monodentate
BDC bridges lead to longer Ni-Ni distances [11.23(4) Å in
3 and 11.37(1) Å in 4].
Similarly to 3 and 4, compound 5 is based on Ni(BDC)-
(L)(H2O) chains where the nickel atoms are bridged by
alternating bis-chelating and bis-monodentate ligands (Table
2). The orientation of the coordinating water molecule with
respect to the amine ligand in 5 (cis to both nitrogens),
however, is different from that in 3 and 4 (trans to one of
the nitrogens and cis to the other) and leads to a more bent
chain with idealized Ni-Ni-Ni angle of 90° as opposed to
135°. The observed Ni-Ni-Ni angles in 5 are 87.05(1)°
and 88.01(1)°. The Ni-Ni distances [10.657(4) Å for bis-
chelating and 11.305(4), 11.151(1) for bis-monodentate
BDC-bridged pairs, respectively] are similar to those in 3
and 4. In contrast to compounds 1-4 and most other 1D
coordination polymers with BDC bridges, the chain config-
uration in 5 is crankshaft rather than zigzag. This feature is
not a direct result of a different local environment around
the nickel atoms, since the alternative zigzag configuration
(derived from the crankshaft chain by 180° rotations around
the bis-chelating BDC bridges) does not lead to any steric
Results
Crystal Structures. Compounds 1-5 are all formed by
one-dimensional chains where octahedrally coordinated Ni(II)
centers are linked by BDC bridges. These structures signifi-
cantly differ, however, in coordination modes of the BDC
ligands, geometry of the chains (Table 2), and chain packing
(Table 3).
Structures of Individual Chains in 1-5. The simplest
coordination pattern is observed in compounds 1 and 2 (Table
2), where each nickel atom has an octahedral environment
formed by three chelating bidentate ligands: one aromatic
amine ligand (1,10-phen in 1 and 2,2′-bipy in 2) and two
carboxylic groups from two BDC ligands. As generally found
in complexes with chelating carboxylate ligands, the nickel
octahedra are highly distorted [O-Ni-O angles formed by
chelating carboxylate range between 62.11(5) and 63.2(1)]
due to the short O-O separation in the carboxylate group
[2.182(5)-2.199(5) Å]. The angles between the “blades”
(Ni-O-C-O and Ni-N-C-C-N planes) in these pro-
pellerlike units, however, are closer to the ideal value of 120°
(108-128° for 1 and 115-125° for 2). The Ni-O bond
distances range from 2.038(1) to 2.211(2) Å in 1 and from
2.054(4) to 2.128(3) Å in 2, and Ni-N bond distances are
2.045(2) and 2.059(2) Å in 1 and range from 2.040(5) to
2.065(5) Å in 2, which are typical values for the correspond-
ing Ni-L distances. Each BDC ligand connects two nickel
centers leading to a zigzag chain where the Ni-Ni-Ni
angles, defined by the orientation of the two BDC ligands
in the Ni(BDC)2L building units (L ) 1,10-phen in 1 and
2,2′-bipy in 2), are close to the ideal value of 120°
[121.52(1)° in 1 and 126.30(1) and 127.19(1)° in 2]. The
Ni-Ni distances within the chains are 10.647(3) Å for 1
and 10.535(2) and 10.576(2) Å for 2. A chain similar to that
in 2 with M-M-M angles of 128.52(1)° is found in
Zn(BDC)(2,2′-bipy)‚(2,2′-bipy).7
In compounds 3 and 4, the environment of nickel atoms
is modified by incorporation of a coordinating water
molecule into a trans position to one of the nitrogen atoms,
(13) Ohmura, T.; Mori, W.; Hasegawa, M.; Takei, T.; Ikeda, T.; Hasegawa,
E. Bull. Chem. Soc. Jpn. 2003, 76, 1387.
5362 Inorganic Chemistry, Vol. 43, No. 17, 2004

Influences on 1D Structure of Coordination Polymers
Table 2. Structures of the Chains and Synthesis Conditions Summary for Compounds 1-5
a Angles shown in the figures correspond to Ni-Ni-Ni angles. b Molar ratio of reactants (NiCl2:H2BDC:KOH:amine). c Temperature range for the formation
of the compound. Optimized synthesis temperatures are given in the Experimental Section. d Final pH.
hindrance within the individual chain, suggesting that the
less common crankshaft configuration in 5 is preferred on
the basis of optimization of interchain noncovalent interac-
tions and packing considerations.
Chain Packing and Supramolecular Interactions in
1-5. The structures of individual chains in compounds 1
and 2 are essentially the same and differ only in the size of
the amine ligand (Table 2). The chain packing in these struc-
tures, however, is significantly different (Table 3). In com-
pound 1, the chains form two types of layers so that the chain
axes in adjacent layers are almost perpendicular to each other.
Each 1,10-phen ligand is involved in face-to-face π-π inter-
actions with a 1,10-phen ligand from the closest layer of
the same type. The 1,10-phen planes are parallel displaced as
typically found in coordination polymers with aromatic nitro-
gen-containing ligands.4,5a In addition, two rings of each 1,10-
phen ligand form close contacts with two hydrogens from one
of the two crystallographically distinct BDC ligands (BDC-1)
that is oriented almost perpendicular (ca. 88°) to the 1,10-
phen plane. Since these BDC ligands are located at inversion
centers, their other two hydrogens have equivalent CH-π
interactions with another 1,10-phen ligand, so that each
BDC-1 ligand is sandwiched between two parallel 1,10-phen
planes. The rings of the BDC-1 ligands, in turn, have π-CH
interactions with hydrogens from two BDC-2 ligands. Each
of these BDC-2 ligands interacts with two BDC-1 rings,
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Go et al.
Table 3. Chain Packinga and Details of Aromatic-Aromatic Interactions (π-π and CH-π) in Compounds 1-5
a Schematic representations of the Ni-BDC backbones and the corresponding full structure views are shown, with purple lines highlighting single chains.
b Interplanar distances.
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Influences on 1D Structure of Coordination Polymers
leading to the formation of columns of edge-to-face stacked
aromatic rings in the direction perpendicular to the chains.
In contrast to 1, the chains in compound 2 are arranged in
layers with the same directions of the chain axes (Table 3).
The layers are stacked so that the 2,2′-bipy ligand planes
form columns with face-to-face π-π interactions where each
2,2′-bipy ligand interacts with two 2,2′-bipy ligands from
adjacent layer. This stacking leads to the formation of
channels where the guest H2BDC molecules are located. The
guest H2BDC molecules form an extensive network of
aromatic-aromatic interactions with the chains: face-to-face
π-π stacking with BDC ligands, CH-π interactions with
BDC ligands, and π-CH interactions with 2,2′-bipy ligands.
In addition, the H2BDC molecules are linked to each other
through hydrogen bonding to form linear planar chains as
found in all polymorphs of pure terephthalic acid.14 A closely
similar packing of M(BDC)(2,2′-bipy) chains is found in
Zn(BDC)(2,2′-bipy)‚(2,2′-bipy).7 In contrast to 2, however,
the guest 2,2-bipy planes in this structure are oriented
perpendicular to the channel axes.
Compounds 3 and 4, which are based on almost identical
Ni(BDC)(1,10-phen)(H2O) chains (Table 2) and differ in the
presence of guest H2BDC molecules, have similar chain
packing (Table 3) and hydrogen-bonding patterns (Figure
1a,b). The water molecules in both compounds are hydrogen-
bonded to two noncoordinating carbonyl oxygen atoms from
bis-monodentate BDC ligands: an adjacent ligand from the
same chain [Ow-O distance 2.66(1) Å in 3 and 2.65(1) Å
in 4] and that from a neighboring chain [Ow-O distance
2.86(1) Å in 3 and 2.81(1) Å in 4]. The interchain hydrogen
bonding leads to the formation of layers of chains (Table
3). Additional interactions within the layers occur through
CH-π contacts between BDC ligands that form edge-to-
face stacked columns similar to those found in 1. The layers
interact through π-π contacts between the 1,10-phen ligands.
In compound 3, the 1,10-phen planes are inclined toward
the layers at ca. 65°, leading to a compact packing. In
compound 4, on the other hand, the 1,10-phen planes are
almost perpendicular (ca. 99°) to the layers, which increases
the interlayer separation and creates space to accommodate
the guest H2BDC molecules. Each H2BDC molecule has
π-π interactions with two 1,10-phen ligands and is hydrogen-
bonded to two other H2BDC molecules to form chains similar
to those in 2.
Figure 1. Perspective view of the Ni2+ coordination environment including
the H-bonds (dotted lines) for 3 (a), 4 (b), and 5 (c). Hydrogen atoms are
omitted for clarity, and thermal ellipsoids are at the 30% probability level.
the same chain [Ow10-O8 distance 2.812(2) Å] and with a
water molecule Ow9 from an adjacent chain [Ow10-Ow9
distance 3.057(2) Å]. Each 2,2′-bipy ligand has π-π
interactions with one 2,2′-bipy ligand and CH-π interactions
with a BDC ligand. In addition, one of the two crystallo-
graphically independent 2,2′-bipy ligands has π-CH interac-
tions with a BDC ligand.
Characterization: (a) Vibrational Spectra. The IR
spectra of 1 and 2 show typical chelating carboxylate
antisymmetric and symmetric stretching bands at 1536 and
1400 cm-1 for 1 and 1533 and 1407 cm-1 for 2, respectively.
A strong ν(CO2) band at 1695 cm-1 in the spectrum of 2
confirms that the BDC guest molecule resides in the channel
in a protonated form. In the IR spectra of 3 and 4, νasym(CO2)
and νsym(CO2) stretching vibrations at 1548 and 1404, 1380
cm-1 for 3 and 1542 and 1404, 1378 cm-1 for 4, respectively,
show that the BDC ligand adopts both monodentate and
chelating coordination modes. A strong band at 1692 cm-1
in the spectrum of 4 is assigned to the guest H2BDC
molecule. The IR spectrum of 5 shows an unusually complex
pattern in the region of the characteristic bands for the
In compound 5, the chains are parallel to each other and
form a compact packing with a complex three-dimensional
network of aromatic-aromatic interactions (Table 3) and
hydrogen bonding (Figure 1c). One of the two crystallo-
graphically distinct water molecules (Ow9) is hydrogen-
bonded to two noncoordinating carbonyl oxygen atoms from
bis-monodentate BDC ligands: an adjacent ligand from the
same chain [a strong hydrogen bond with an Ow9-O6
distance of 2.561(2) Å] and that from a neighboring chain
[Ow9-O8 distance 2.844(2) Å]. The other water molecule
(Ow10) forms hydrogen bonds with a carbonyl oxygen from
(14) (a) Bailey, M.; Brown, C. J. Acta Crystallogr. 1967, 22, 387. (b) Sledz,
M.; Janczak, J.; Kubiak, R. J. Mol. Struct. 2001, 595, 77.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5365

Go et al.
dicarboxylate unit. The antisymmetric stretching bands
around 1550(vs) cm-1 appear as a broad septet instead of
the more usual single or double strong bands, and the
symmetric stretching bands appear at 1411 and 1378 cm-1.
The splitting of νasym(CO2) arises from a complex network
of hydrogen bonds as shown in Figure 1c. A broad band at
3316m cm-1 is assigned to OH stretching vibration from the
coordinated water molecule involved in relatively strong
hydrogen bonding.
Discussion
Comparative analysis of the structures of a new series of
one-dimensional Ni2+ coordination polymers indicates that
the incorporation of a coordinating water molecule plays a
major role in determining the coordination mode of BDC
ligands (chelating vs monodentate) and the degree of bending
of the chain. Analysis of the relationships between the
synthesis conditions and the product composition suggests,
however, that the presence of a coordinated water molecule
is predominantly determined by the size of the amine ligand
(Table 2). Under the range of the synthesis conditions
studied, substitution of 1,10-phenanthroline with 2,2′-bi-
pyridine leads to products with different water content, with
the exception of compounds 3, Ni(BDC)(1,10-phen)(H2O),
and 5, Ni(BDC)(2,2′-bipy)(H2O), that form from the same
reactant ratio (NiCl2:H2BDC:KOH:amine ) 1:1.5:4:1) at
temperatures below 160 °C. Even though these two com-
pounds have the same composition, Ni(BDC)(L)(H2O), the
pronounced differences in the corresponding chain structures
(stretched zigzag chain in 3 and bent crankshaft chain in 5)
clearly illustrate the influence of the amine ligand size.
Considering the ligand steric effects alone, however, one
might expect that the substitution of 1,10-phen in 3 with
smaller 2,2′-bipy would lead to a similar structure with
layered stacking of the chains (Table 3) and smaller interlayer
separation, as usually observed when the size of a ligand is
varied in the case of layered compounds pillared by aliphatic
ligands.15 Therefore, the substantial structural differences
between 3 and 5 can be attributed primarily to the effects of
aromatic-aromatic interactions. Moreover, as the synthesis
temperature increases above 165 °C, compound 3, Ni(BDC)-
(1,10-phen)(H2O), transforms to the anhydrous phase 1, while
the 2,2′-bipyridine derivative 5, Ni(BDC)(2,2′-bipy)(H2O),
remains the only product up to 200 °C. The significant
difference in the stability of the hydrated products with 2,2′-
bipy and 1,10-phen ligands (3 and 5) can be also seen in the
contrast between their dehydration temperatures (115 and
205 °C, respectively). While one of the reasons for this
difference could be a more hydrophobic nature of 1,10-phen
ligand compared to that of 2,2′-bipy, it is not a predominant
factor, since a reverse combination, a hydrated deriva-
tive for 1,10-phen, Ni(BDC)(1,10-phen)(H2O)‚0.5H2BDC
(4), and an anhydrous one for 2,2′-bipy, Ni(BDC)(2,2′-
bipy)‚0.75H2BDC (2), results from a reactant ratio corre-
sponding to a lower pH (NiCl2:H2BDC:KOH:amine )
1:1.2:1.8:1). The lower pH conditions seem to favor the
incorporation of the guest H2BDC molecules due to the
stabilization of their neutral diprotonated state.
(b) Thermal Analysis. Compound 1, Ni(BDC)(1,10-
phen), is stable up to 350 °C, above which it decomposes to
NiO in a single step (observed weight loss 80.43%; calcd
81.46%). Compound 3, Ni(BDC)(1,10-phen)(H2O), first loses
its coordinated water molecule (onset at 115 °C, completion
at 140 °C; obsd 4.12%, calcd 4.29%) to form 1, as was
identified by powder diffraction. Its further decomposition
behavior is, therefore, analogous to that of 1 [single-step
loss of organic ligands (obsd 79.75%, calcd 77.92%) starting
at 350 °C]. In contrast to 3, compound 5, Ni(BDC)
(2,2′-bipy)(H2O), dehydrates at a significantly higher tem-
perature (onset at 205 °C, completion at 220 °C; obsd 4.84%,
calcd 4.54%). Its subsequent single-step decomposition to
NiO begins at 350 °C (obsd 76.23%, calcd 76.74%) and is
completed at 400 °C.
The decomposition of compounds containing guest H2BDC
molecules is somewhat unusual. For compound 2,
Ni(BDC)(2,2′-bipy)‚0.75H2BDC, the weight loss correspond-
ing to the removal of the guest H2BDC is expected to be
24.75%. The observed weight loss in the first decomposition
step (onset at 300 °C, completion at 330 °C), however, is
significantly larger (34.56%). Consequently, the second
weight loss of 50.50% between 350 and 420 °C is lower
than the expected value for the removal BDC and 2,2′-bipy
ligands (60.42%). The overall weight loss (obsd 85.06%;
calcd 85.17%) and the chemical analysis data indicate that
the composition of the compound is correct. The discrepancy
in the two steps suggests that the loss of the guest H2BDC
molecules is accompanied by a partial decomposition of the
framework, in contrast to Zn(BDC)(2,2′-bipy)‚(2,2′-bipy),7
which loses its 2,2′-bipy guests with the framework being
intact. For compound 4, Ni(BDC)(1,10-phen)(H2O)‚0.5H2-
BDC, the expected weight losses for the removal of
coordinated water and H2BDC guests are 3.63%, and
15.08%, respectively. The observed first weight-loss step
between 210 and 270 °C corresponds to 11.47%, while the
loss in second step between 275 and 340 °C is 6.94%. The
sum of the two observed values (18.41%), however, is close
to the expected 18.71%. The weight loss in the third
decomposition step between 340 and 410 °C is consistent
with the removal of the organic ligands (obsd 67.42%, calcd
65.12%). Decreasing the heating rate to 0.1 °C/min did not
lead to significant changes in the values of weight losses,
indicating that the discrepancy between the calculated and
observed values for the first two steps is not due to the
diffusion effects.
Conclusions
Five new one-dimensional coordination polymers with the
general formula Ni(BDC)L(H2O)x‚yH2BDC (x ) 0, 1; y )
0, 0.5, 0.75; L ) 1,10-phenanthroline or 2,2′-bipyridine) have
been prepared and characterized, and their structural relation-
ships have been investigated. These polymers are based on
(15) Clearfield, A. Prog. Inorg. Chem. 1998, 47, 371.
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Influences on 1D Structure of Coordination Polymers
topologically identical chains where the nickel centers
chelated by amine ligands are linked by BDC bridges.
Substitution of 1,10-phenanthroline with 2,2′-bipyridine
resulted in significant differences in the composition of the
compounds and geometry and packing of the chains, which
indicates the predominant structural role of aromatic-
aromatic interactions and the steric effects of these ligands.
While the energy of each individual π-π or CH-π interaction
is low, their cooperative effects in compounds with poly-
cyclic ligands can become a decisive factor in the choice
between alternative structures with energetically close but
different patterns of covalent bonding. The high degree of
flexibility of the chains (Ni-Ni-Ni angles of ca. 90°, 120°,
and 135°), which allows them to adapt to the changes in the
amine ligand size, is achieved by the versatility of coordina-
tion modes of the BDC bridges: a switch from a chelating
to a monodentate coordination mode accompanied by
incorporation of a coordinating water molecule provides a
means to change the Ni-Ni-Ni angle from 120° to 90° or
135° without a significant perturbation in the geometry of
the nickel coordination environment. Another pathway to
adjust the M-M-M angles within the chains by modifying
the coordination number and/or coordination geometry
around the metal center is found in related one-dimensional
M(BDC)L(H2O)x (x ) 0, 1; L ) 1,10-phenanthroline or 2,2′-
bipyridine) compounds with divalent transition metal cations
that have less specific coordination preferences than nickel
(Co2+, Cu2+, Zn2+, Cd2+).6,8
Acknowledgment. We thank the National Science Foun-
dation (DMR-0120463) and the R. A. Welch Foundation.
Supporting Information Available: X-ray crystallographic
data, in CIF format, for the structure determination of 1-5.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC049341U
Inorganic Chemistry, Vol. 43, No. 17, 2004 5367