Self-catenated and interdigitated layered coordination polymers constructed from kinked dicarboxylate and organodiimine ligands

Article abstract of DOI:10.1021/ic700931u

Hydrothermal combination of divalent nickel or cobalt nitrates with the kinked carboxylic acid 4,4′-oxybis(benzoic acid) (H₂oba) and the kinked and hydrogen-bonding capable organodiimine 4,4′-dipyridylamine (dpa) under basic conditions has afforded a pair of coordination polymers with a formulation of {[M(oba)(dpa)]·H₂O} (M = Ni, 1; M = Co, 2). Both materials were characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The structures of 1 and 2 are isomorphous and manifest intriguing self-catenated two-dimensional layered motifs with very rare non-diamond 6⁶ topology constructed from the direct covalent linkage of [M(oba)]_n double helices through [M(dpa)]_n undulating chains. Adjacent self-catenated layers engage in mutual interdigitation to form double-layer patterns that further aggregate via supramolecular hydrogen-bonding patterns imparted by the central amine of the dpa ligand. These coordination polymers are very thermally robust, with decomposition occurring only above 400°C.

Full text of DOI:10.1021/ic700931u

Inorg. Chem. 2007, 46, 7917−7922
Self-Catenated and Interdigitated Layered Coordination Polymers
Constructed from Kinked Dicarboxylate and Organodiimine Ligands
David P. Martin,† Ronald M. Supkowski,‡ and Robert L. LaDuca*,†
Lyman Briggs College and Department of Chemistry, Michigan State UniVersity,
East Lansing, Michigan 48825, and Department of Chemistry and Physics, King’s College,
Wilkes-Barre, PennsylVania 18711
Received May 14, 2007
Hydrothermal combination of divalent nickel or cobalt nitrates with the kinked carboxylic acid 4,4′-oxybis(benzoic
acid) (H2oba) and the kinked and hydrogen-bonding capable organodiimine 4,4
conditions has afforded a pair of coordination polymers with a formulation of [M(oba)(dpa)]
Co, 2). Both materials were characterized by single-crystal X-ray diffraction, infrared spectroscopy, and
′
-dipyridylamine (dpa) under basic
{
‚
H2O (M Ni, 1; M
}
)
)
thermogravimetric analysis. The structures of 1 and 2 are isomorphous and manifest intriguing self-catenated two-
dimensional layered motifs with very rare non-diamond 66 topology constructed from the direct covalent linkage of
[M(oba)]n double helices through [M(dpa)]n undulating chains. Adjacent self-catenated layers engage in mutual
interdigitation to form double-layer patterns that further aggregate via supramolecular hydrogen-bonding patterns
imparted by the central amine of the dpa ligand. These coordination polymers are very thermally robust, with
decomposition occurring only above 400 °C.
Introduction
unique topologies, such as a (12,3)-topology chiral 3-D
network in {[Ni(1,3,5-tri(4-pyridyl)triazine](NO3)2}4 and a
rare 8-connected framework in [Cd3(terephthalate)3(L1)2-
(H2O)2] (L1 ) 1,4-bis(1,2,4-triazol-1-yl)butane).5 This in-
triguing genre of materials can also display potentially useful
physical properties including photoluminescence6 and tem-
perature-dependent spin crossover behavior.7
One of the best approaches toward the self-assembly and
crystallization of self-penetrated/self-catenated coordination
polymer networks involves the use of one or more confor-
mationally flexible dipodal tethering ligands, usually
dicarboxylates.8-10 The relatively short conformationally
flexible succinate (suc) dianion has been one efficacious
choice. {[Cd(suc)(L2)]‚H2O} (L2 ) N,N′-bispyridin-4-yl-
methylsuccinamide) possesses [Cd(L2)] triple helices, linked
Mutual entanglement of structural motifs is a very com-
monly encountered feature in coordination polymer chem-
istry.1 Three-dimensional (3-D) coordination polymers can
exhibit varying degrees of interpenetration, with higher
numbers of distinct interpenetrated lattices promoted by long-
spanning tethering ligands that maximize void spaces within
a single covalently connected framework.2 While many
interpenetrated coordination polymers exhibit diamondoid
(dia) frameworks because of the potential for large apertures,
other 3-D structure types such as R-Po (pcu), cooperite (pts),
and SrAl2 (sra) can also display this behavior.3 However,
self-catenated coordination polymers, where rods of the same
framework penetrate through the shortest internodal circuits,
are much rarer.4-10 Self-catenated materials can manifest
(5) Wang, X.-L.; Qin, C.; Wang, E.-B.; Su, Z.-M. Chem.sEur. J., 2006,
12, 2680-2691.
* To whom correspondence should be addressed. E-mail: laduca@
msu.edu.
(6) Bi, M.; Li, G.; Zou, Y.; Shi, Z.; Feng, S. Inorg. Chem. 2007, 46,
604-606.
† Michigan State University.
‡ King’s College.
(7) Niel, V.; Thompson, A. L.; Goeta, A. E.; Enachescu, C.; Hauser, A.;
Galet, A.; Munoz, M. C.; Real, J. A. Chem.sEur. J. 2005, 11, 2047-
2060.
(8) Lloyd, G. O.; Atwood, J. L.; Barbour, L. J. Chem. Commun. 2005,
1845-1847.
(9) Montney, M. R.; Mallika Krishnan, S.; Patel, N. M.; Supkowski, R.
M.; LaDuca, R. L. Crystal Growth Des. 2007, 7, 1145-1153.
(10) Wang, X. L.; Qin, C.; Wang, E.-B.; Li, Y.-G.; Su, Z.-M., Xu, L.;
Carlucci, L. Angew. Chem., Int. Ed. 2005, 44, 5824-5827.
(1) (a) Batten, S. R. CrystEngComm 2001, 3, 67-73. (b) Carlucci, L.;
Ciani, G.; Proserpio, D. M. Coord. Chem. ReV. 2003, 246, 247-289.
(2) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEng-
Comm, 2004, 6, 377-395.
(3) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460-
1494.
(4) Abraham, B. F.; Batten, S. R.; Grannas, M. J.; Hamit, H.; Hoskins,
B. F.; Robson, R. Angew. Chem., Int. Ed. 1999, 38, 1475-1477.
10.1021/ic700931u CCC: $37.00
Published on Web 08/16/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 19, 2007 7917

Martin et al.
Table 1. Crystal and Structure Refinement Data for 1 and 2
into a very rare two-dimensional (2-D) self-penetrated sheet
motif via tethering gauche conformation suc ligands.8 A
unique self-penetrated 3-D 5-connected net with a uniform
610 topology in {[Ni(dpa)2(suc)0.5]Cl} (dpa ) 4,4′-dipyridy-
lamine) was constructed by the linkage of quadruply
interpenetrated [Ni(dpa)2]n2n+ adamantoid frameworks through
gauche suc tethers.9 The longer kinked dicarboxylate ligand
4,4′-oxy(bisbenzoate) (oba) has also been used to promote
the formation of polycatenated and self-penetrated coordina-
tion polymers. For instance, {[Ni(oba)(4,4′-bpy)]‚2H2O}
exhibited a unique (3,5)-connected self-penetrated 3-D
structure with (4.82)(4.64.84.10) topology.10
This latter result and our own previous success in
promoting self-penetration by means of the dpa ligand has
inspired us to pursue mixed ligand coordination polymers
with both oba and dpa tethers. These efforts have proven
fruitful with the synthesis and crystallization of the isomor-
phous coordination polymers {[M(oba)(dpa)]‚H2O} (M )
Ni, 1; M ) Co, 2), which possess very rare 2-D self-catenated
layers with an uncommon topology constructed from the
junction of [M(oba)] double helices through dipodal dpa
tethers.
1
2
empirical formula
fw
C24H19N3NiO6
504.16
C24H19CoN3O6
504.36
temp (K)
λ (Å)
cryst syst
space group
a (Å)
293(2)
293(2)
0.71073
monoclinic
C2/c
23.100(5)
11.865(3)
17.365(4)
107.886(3)
4529.3(17)
8
1.473
0.903
0.823
-30 e h e 29
-15 e k e 15
-22 e l e 21
23 750
5140
0.0237
0.71073
monoclinic
C2/c
22.849(7)
11.832(4)
17.514(6)
108.324(5)
4495(2)
8
1.485
0.810
0.849
-30 e h e 29
-15 e k e 15
-23 e l e 22
24 772
5216
0.0439
b (Å)
c (Å)
â (deg)
V (Å3)
Z
D
calcd (g cm-3
)
µ (mm-1
)
min/max T
hkl ranges
total reflns
unique reflns
R(int)
params/restraints
309/1
0.0430
0.0351
0.0972
0.0931
0.449/-0.419
1.066
309/1
0.0693
0.0432
0.1148
0.1038
0.457/-0.304
1.044
R1a (all data)
R1a (I > 2σ(I))
R2b (all data)
R2b (I > 2σ(I))
max/min residual (e- Å-3
GOF
)
Experimental Section
b
2
2
2
General Considerations. Metal nitrates were obtained com-
mercially from Fisher and 4,4′-oxy(bisbenzoic acid) was purchased
from Aldrich. 4,4′-dipyridylamine (dpa) was prepared via a
published procedure.11 Water was deionized above 3 MΩ in-house.
Thermogravimetric analysis was performed on a TA Instruments
TGA 2050 Thermogravimetric Analyzer with a heating rate of
10 °C min-1 up to 600 °C. Elemental Analysis was carried out
using a Perkin-Elmer 2400 Series II CHNS/O Analyzer. IR spectra
were recorded on a Mattson Galaxy FTIR Series 3000 using KBr
pellets.
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. R2 ) ∑{[w(Fo - Fc )2]/∑[wFo ]2}1/2
.
X-ray Crystallography. A green rhomb of 1 (with dimensions
0.75 mm × 0.30 mm × 0.25 mm) and a magenta rhomb of 2 (with
dimensions 0.65 mm × 0.30 mm × 0.25 mm) were subjected to
single-crystal X-ray diffraction using a Bruker-AXS SMART 1k
CCD instrument at 293(2) K. Reflection data were acquired using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). The
data were integrated via SAINT.12 Lorentz and polarization effect
and multiscan absorption corrections were applied with SADABS.13
The structures were solved using direct methods and refined
on F2 using SHELXTL.14 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms bound to carbon atoms were
placed in calculated positions and refined isotropically with a
riding model. The dpa amine hydrogen atoms in both materials
were found via Fourier difference maps, then restrained at fixed
positions and refined isotropically. The disordered water molecule
positions in 1 and 2 were successfully modeled with partial
occupancy ratios and were refined isotropically. Hydrogen atoms
could not be found for the disordered water molecules. Relevant
crystallographic data for 1 and 2 are listed in Table 1. Supramo-
lecular contact information and incipient void space volumes were
computed with PLATON software.15 Network topologies were
calculated or verified using the OLEX16 and TOPOS17 software
programs.
Preparation of {[Ni(oba)(dpa)]‚H2O} (1). A mixture of Ni-
(NO3)2‚6H2O (81 mg, 0.28 mmol), 4,4′-oxy(bisbenzoic acid) (72
mg, 0.28 mmol), and dpa (95 mg, 0.56 mmol), along with 0.6 mL
of a 1.0 M NaOH solution, was suspended in 10 g of H2O (555
mmol) in a 23 mL Teflon-lined acid digestion bomb which was
placed in a 120 °C oven for 48 h. The bomb was allowed to cool
slowly to room temperature; then 93 mg (66% yield based on Ni)
of green crystals of 1 were isolated after washing with distilled
water, ethanol, and acetone and drying in air. Anal. Calcd for
C24H19N3NiO6: C, 57.18; H, 3.80; N, 8.33%. Found: C, 57.47; H,
3.25; N, 8.43%. IR (KBr, ν, cm-1): 3450 vw b, 3250 vw, 3150
vw, 3000 vw, 2900 vw, 1595 s, 1519 s, 1500 m, 1419 s, 1342 m,
1234 m, 1213 m, 1180 m, 1156 m, 1080 w, 1064 w, 1023 m, 903
w, 880 m, 849 m, 820 m, 781 m, 772 m, 724 m, 663 m.
Preparation of {[Co(oba)(dpa)]‚H2O} (2). Compound 2 was
prepared in a manner similar to that for 1 except for the use of
Co(NO3)2‚6H2O (81 mg, 0.28 mmol) as the metal precursor; 91
mg (65% yield based on Co) of 2 as magenta rhombs were isolated
after washing with distilled water, ethanol, and acetone and drying
in air. Anal. Calcd for C24H19CoN3O6: C, 57.15; H, 3.80; N, 8.33%.
Found: C, 57.30; H, 3.16; N, 8.28%. IR (KBr, ν, cm-1): 3450 vw
b, 3250 vw, 3150 vw, 3000 vw, 2900 vw, 1595 s, 1519 s, 1500 m,
1419 s, 1342 m, 1234 m, 1213 m, 1180 m, 1156 m, 1080 w, 1064
w, 1023 m, 903 w, 880 m, 849 m, 820 m, 781 m, 772 m, 724 m,
663 m.
(12) SAINT, Software for Data Extraction and Reduction, version 6.02;
Bruker AXS, Inc.: Madison, WI, 2002.
(13) SADABS, Software for Empirical Absorption Correction, version 2.03;
Bruker AXS, Inc.: Madison, WI, 2002.
(14) Sheldrick, G. M. SHELXTL, Program for Crystal Structure Refinement;
University of Gottingen: Gottingen, Germany, 1997.
(15) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 1998.
(16) Dolomanov, O. V.; Blake, A. J.; Champness, N. R.; Schroder, M. J.
Appl. Crystallogr. 2003, 36, 1283.
(11) Zapf, P. J.; LaDuca, R. L.; Rarig, R. S.; Johnson, K. M.; Zubieta, J.
(17) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl.
Crystallogr. 2000, 33, 1193.
Inorg. Chem. 1998, 37, 3411-3414.
7918 Inorganic Chemistry, Vol. 46, No. 19, 2007

Self-Catenated and Interdigitated Coordination Polymers
Table 2. Selected Bond Distance (Å) and Angle (deg) Data for 1
and 2a
1
2
Ni1-N1
Ni1-N3#1
Ni1-O1
Ni1-O3#2
Ni1-O4#2
Ni1-O2
O1-C23
O2-C23
O3-C24
O4-C24
2.0453(17)
2.0557(17)
2.0658(14)
2.0798(15)
2.1887(16)
2.1890(15)
1.258(2)
1.265(2)
1.271(2)
1.248(3)
Co1-N1
Co1-N3#1
Co1-O1
Co1-O2
Co1-O3#3
Co1-O4#3
O1-C23
O2-C23
O3-C24
O4-C24
2.074(2)
2.100(2)
2.338(2)
2.071(2)
2.2889(19)
2.0861(17)
1.243(3)
1.249(4)
1.260(3)
1.263(3)
Figure 1. Expanded asymmetric unit of 1 with thermal ellipsoids at 50%
probability and partial atom numbering scheme, showing complete coor-
dination at Ni. Most hydrogen atoms and the disordered water molecules
of crystallization are omitted. The asymmetric unit of compound 2 is very
similar.
N1-Ni1-N3#1
N1-Ni1-O1
N3#1-Ni1-O1
N1-Ni1-O3#2
91.11(7)
94.60(6)
97.06(6)
96.43(7)
94.47(6)
163.86(6)
99.57(7)
154.59(7)
104.90(6)
61.62(6)
156.12(6)
91.90(7)
61.52(5)
106.93(6)
87.56(7)
117.63(17)
127.55(18)
O2-Co1-N1
O2-Co1-O4#3
N1-Co1-O4#3
O2-Co1-N3#1
N1-Co1-N3#1
O4-Co1-N3#1
O2-Co1-O3#3
N1-Co1-O3#3
O4-Co1-O3#3
N3#1-Co1-O3#3
O2-Co1-O1
112.69(9)
110.57(8)
96.33(7)
135.80(8)
93.18(8)
100.85(8)
84.13(8)
155.00(7)
59.49(6)
86.02(8)
58.69(8)
90.06(8)
169.13(7)
87.52(8)
114.84(8)
117.3(2)
126.8(2)
N3#1-Ni1-O3#2
O1-Ni1-O3#2
N1-Ni1-O4#2
N3#1-Ni1-O4#2
O1-Ni1-O4#2
O3#2-Ni1-O4#2
N1-Ni1-O2
Figure 2. [Ni(oba)]n double helix substructure in 1.
Results and Discussion
Synthesis and Infrared Spectra. Hydrothermal combina-
tion of divalent cobalt or nickel nitrate with 4,4′-oxy-bis-
(benzoic acid) (H2oba) and 4,4′-dipyridylamine (dpa) with
addition of base afforded single crystals of {[M(oba)(dpa)]‚
H2O} (M ) Ni, 1; M ) Co, 2) cleanly and in high yield.
While running these reactions at lower pH afforded micro-
crystalline 1 and 2 (according to powder XRD), basic
conditions are required for large single crystals. The infrared
spectra of compounds 1 and 2 were consistent with their
formulations. Features corresponding to pyridyl ring pucker-
ing mechanisms were observed in the region between 600
and 820 cm-1. Sharp, medium intensity bands observed in
the range of ∼1520 to ∼1200 cm-1 arise from stretching
modes of the pyridyl rings of the dpa moieties. Asymmetric
and symmetric carboxylate stretching modes were observed
at 1595 and 1419 cm-1, respectively. The ∆ν value of 176
cm-1 is indicative of the bisbridging bischelating binding
mode of the oba ligands.18 Bands between 3050 and 3150
cm-1 represent C-H stretching modes. A broad band at
∼3400 cm-1 represents the N-H subunit within the dpa
ligands, overlapping with O-H stretching modes within the
water molecules of crystallization. The broadness of these
latter spectral features can be ascribed to the presence of
hydrogen-bonding pathways (vide infra).
Structural Description of {[M(oba)(dpa)]•H2O}-
Coordination Polymers (M ) Ni, 1; M ) Co, 2). The
asymmetric units of 1 and 2 were virtually identical, with
both materials crystallizing in the centrosymmetric mono-
clinic space group C2/c. Both contain one divalent metal
atom, one dianionic oba ligand, and one dpa ligand, along
with one water molecule of crystallization disordered equally
over two positions. (Elemental analysis and thermogravi-
metric analysis also indicated the presence of unligated water
molecules.) The {MO4N2} coordination spheres are each
defined by two chelating oba carboxylate termini, with two
cis-oriented dpa nitrogen donors. Bond lengths and angles
about the metal centers in 1 and 2 are consistent with
N3#1-Ni1-O2
O1-Ni1-O2
N1-Co1-O1
O4#3-Co1-O1
N3#1-Co1-O1
O3#3-Co1-O1
C20-O5-C14
C3-N2-C8
O3#2-Ni1-O2
O4#2-Ni1-O2
C14-O5-C20
C3-N2-C8
a Symmetry equivalent atoms: #1 -x + 1/2, y + 1/2, -z - 1/2; #2 -x
+ 1, y - 1, -z + 1/2; #3 -x + 1, y + 1, -z + 1/2.
distorted octahedral geometry caused by the presence of two
chelating ligands and are given in Table 2. The largest trans-
L-M-L bond angles in both cases are marked by oxygen
donors from carboxylate termini from two different oba
ligands. The Ni-O bond lengths in 1 vary only by ∼0.01 Å
within each type of chelating carboxylate; the corresponding
arrangement in 2 is much less symmetric, with Co-O bond
lengths spanning a range from ∼0.2 to ∼0.3 Å. In general,
the bond lengths in 1 are shorter than those in 2, consistent
with well-known ionic radius trends.19 The inter-ring four-
carbon-atom torsion angles within the dpa ligands in 1 and
2 are ∼37.5 and ∼41.3°, respectively. Nevertheless, the gross
structural features of 1 and 2 are largely similar despite the
differences in their metrical parameters (vide infra).
Extension of the structures of 1 and 2 through the
bisbridging, bischelating oba ligands reveals the presence
of neutral [M(oba)]n one-dimensional (1-D) double helices
coursing parallel to the b crystal direction (Figure 2, shown
for 1). The helical substructure of a single metal dicarboxy-
late strand is likely imparted by the central ether kink within
the oba ligands, which displays an inter-ring twist of ∼78°
in both 1 and 2. The Ni-Ni contact distance through the
oba tether in 1 is 14.389 Å; because of the longer bond
lengths in 2, the corresponding Co-Co distance is slightly
extended, at 14.428 Å. To accommodate the asymmetric
chelating binding modes and longer Co-O bond lengths in
2, the two carboxylate groups are twisted relative to their
respective benzene rings by ∼1 and ∼23°. The carboxylate
groups within the oba ligands in 1 are twisted to a greater
(18) Nakamoto, K. Infra-red Spectra of Inorganic and Co-ordination
Compounds; John Wiley and Sons: New York, 1963.
(19) Shannon, R. D. Acta. Crystallogr. 1976, A32, 751.
Inorganic Chemistry, Vol. 46, No. 19, 2007 7919

Martin et al.
Figure 3. View down the a crystal axis of the self-catenated two-dimensional [Ni(oba)(dpa)] layered motif in 1. The oba ligands weave above and below
the plane of the layer. Water molecules of crystallization are shown in orange.
each belonging to a different strand within an adjacent double
helical motif. Thus, each single strand is connected to both
strands in an adjacent double helix. As a result the structures
of 1 and 2 are composed of self-catenated layers with a very
rare non-diamond 66 topology, with a long vertex symbol
of 62‚62‚63‚66‚64‚64 as determined by TOPOS. Feng and co-
workers have recently prepared a self-penetrated coordination
polymer, ([Cu4I4(DABCO)4]), that possesses a non-diamond
66 topology.6 However, Feng’s material has three-dimen-
sional covalent connectivity; to the best of our knowledge,
1 and 2 are the first examples of a two-dimensional 66
Figure 4. Magnified perspective of the self-catenation of two adjacent
six-node circuits within a layer in 1.
coordination polymer topology.
A magnified view of the intralayer self-catenation is
presented in Figure 4, in which individual interwoven (M-
oba-M-oba-M-dpa)2 6-node circuits (in green and blue)
are joined by the dpa ligands outlined in red. The longest
through-space contact distances across a single 6-node circuit
in 1 are 20.183 (Ni-Ni) and 25.070 Å (Oether-Oether); the
corresponding distances in 2 are 20.100 and 25.059 Å. Water
molecules of crystallization lie within incipient void spaces
inside the layers, held loosely by weak C-H‚‚‚O hydrogen-
bonding pathways provided by the dpa ligands (C‚‚‚O
distances ) ∼3.05-3.15 Å). The solvent-bearing void
volumes are comparable in both cases, occupying 7.9 (1)
and 8.1% (2) of the respective unit cell volumes.
extent (∼5 and ∼39° torsions) in response to their more
symmetric binding and slightly shorter Ni-Ni distance. The
closest M-M distances between individual helices are 8.140
(in 1) and 8.254 Å (in 2).
Each [M(oba)]n double helix is then joined to two others
through exobidentate dpa ligands to construct a 2-D layer
motif resting parallel to the bc crystal plane (Figure 3). The
M-M contact distances through the dpa ligands measure
11.216 (1) and 11.136 Å (2), with a similar inverse trend
between dpa torsion angle and metal-metal contact distance
as in prior succinate-based coordination polymers.9 Each
metal atom therefore serves as a 4-connected node. Two of
these connections occur through oba ligands within a single
helical strand, which weave over and under each other and
project above and below the plane of the layer. The dpa
ligands then permit conjunction to two other metal atoms,
Abutting self-catenated [M(oba)(dpa)] layers interdigitate
with each other, stacking along the a crystal direction to
establish the pseudo-3-D structures of 1 and 2 (Figure 5).
7920 Inorganic Chemistry, Vol. 46, No. 19, 2007

Self-Catenated and Interdigitated Coordination Polymers
Thermogravimetric Analysis and Dehydration Behav-
ior. Compound 1 underwent slow dehydration between
ambient temperature and ∼410 °C (4.2% mass loss observed,
3.6% predicted for 1 equiv of water), upon which decom-
position commenced. A mass loss of 66.0% corresponding
to the loss of one equivalent of oba and a pyridine fragment
was complete by ∼480 °C (66.9% predicted for the combined
mass loss). A further mass loss denotes the combustion or
expulsion of the remaining organic components. The final
remnant at ∼895 °C of 11.7% of the original mass corre-
sponds to the deposition of Ni metal (11.6% calcd). To probe
the structural integrity of 1, a sample was heated at 180 °C
for 24 h. Powder XRD indicated that the self-catenated
layered coordination polymer stayed intact. Compound 2 also
dehydrated slowly between 25 and ∼410 °C (3.8% mass loss,
3.6% predicted for 1 equiv of water), at which point,
expulsion of the organic ligands occurred. A decrease in mass
corresponding to the loss of one equivalent of oba was
complete by ∼510 °C (49.4% mass loss observed, 51.2%
predicted). This was followed by a mass loss of 34.5%
between this temperature and ∼825 °C corresponding to the
removal of 1 equiv of dpa (33.9% mass loss predicted). The
remaining 12.5% of the original mass corresponds to residual
Co metal (11.6% predicted).
Figure 5. Interdigitation of self-penetrated [Ni(oba)(dpa)]n layers in 1.
Interlayer hydrogen bonding between dpa central amine units and ligated
carboxylate oxygen atoms is shown as dashed lines.
Table 3. Interlayer Hydrogen-Bonding Distance (Å) and Angle (deg)
Data for 1 and 2
symmetry
transformation
D-H
d(H‚‚‚A)
DHA d(D‚‚‚A)
for A
1
2
N2-H2N‚‚‚O2 1.93(2) 171(2) 2.761(3) x, -y + 1, z - 1/2
N2-H2N‚‚‚O3 1.86(3) 170(3) 2.739(5) -x + 1, -y - 1, -z
The interdigitation is promoted by hydrogen-bonding be-
tween dpa amine N-H groups in one layer and a ligated
carboxylate oxygen atoms in the next. Geometric parameters
for these supramolecular interactions are given in Table 3.
Interlayer aggregation is supplemented by relatively strong
π-π stacking (3.720(2) Å, as calculated by PLATON)
between dpa pyridyl rings and oba benzene rings in
juxtaposed layers. The interdigitation allows relatively tight
packing of the layers, causing nearest-neighbor interlayer
M-M contact distances of ∼5.5 Å, substantially closer than
any intralayer M-M interaction. Neighboring layers are
related by crystallographic inversion centers. Therefore the
helices within these layers are of opposite handedness,
eliminating the possibility of acentricity.
A comparison of the structures of 1 and 2 with other
divalent metal oba/organodiimine coordination polymers
reveals the importance of both the kinked oba and dpa ligands
in the promotion of the observed unique 2-D self-catenated
morphologies. Employment of the flexible tethering diimine
1,2-di-4-pyridylethane (bpe) resulted in {[Ni(oba)(bpe)]‚
H2O} and [Co(oba)(bpe)], which displayed interpenetrated
but “standard” 2-D (4,4) rhomboid grid coordination polymer
layers.20 An attempt to prepare a similar cadmium derivative
afforded the one-dimensional coordination polymer [Cd-
(Hoba)2(bpe)].21 In these oba/bpe cases, the nitrogen donors
of the bpe ligands are disposed in a trans manner at the
respective metal atoms. It is plausible that the cis disposition
of the dpa nitrogen donors in 1 and 2 promotes a zigzag
[Ni(dpa)] chain-type motif that allows conjunction of the [Ni-
(oba)] double helices into the observed self-catenated layer
pattern. Although a cis arrangement of the organodiimine
ligands exists in {[Ni2(oba)2(4,4′-bpy)2(H2O)2]‚4,4′-bpy},20
1d f 2D polycatenation of “trainlike” box motifs is observed
instead of interpenetration. It is most likely that the two
kinked ligands, by imposition of a unique covalent and
supramolecular environment, act in tandem to instigate
formation of the novel structures of 1 and 2.
Conclusion
Employment of the kinked ligands 4,4′-oxy(bisbenzoate)
and 4,4′-dipyridylamine has permitted hydrothermal synthesis
of two isomorphous coordination polymers with a very
uncommon non-diamond 66 topology, which represent two
new entries in the extremely small list of 2-D self-catenated
layered structures.8,22,23 Synergistic interactions between
covalent bonding modes imparted by the kinked donor
dispositions of the mixed ligand system and supramolecular
hydrogen bonding and π-π stacking mechanisms in turn
promote interdigitation and aggregation of neighboring
layers. In addition, the self-catenated morphology provides
incipient voids within the coordination polymer matrices and
imputes a high degree of thermal stability. While substan-
tially more experimental work will be required to gain the
ability to deliberately design particular self-penetrated frame-
works, judicious variance of the conformational flexibility
and donor disposition of long flexible or kinked tethering
ligands is likely to advance this intriguing aspect of
coordination polymer structural chemistry.
Acknowledgment. The authors gratefully acknowledge
Michigan State University for financial support of this work.
The thermogravimetric analyzer at King’s College was
purchased with a grant from the Alden Trust. We thank Dr.
Rui Huang (MSU) for elemental analysis and Lindsey
Johnston for acquiring the infrared spectra.
Supporting Information Available: TGA traces for 1 and 2
(Figures S1 and S2) and the powder XRD spectrum after heat
(22) Carlucci, L.; Ciani, C.; Macchi, P.; Proserpio, D. M.; Rizzato, S.
Chem.sEur. J. 1999, 5, 237-243.
(23) Rizk, A. T.; Kilner, C. A.; Halcrow, M. A. CrystEngComm 2005, 7,
359-362.
(20) Sun, C.-Y.; Zheng, X.-J.; Gao, S.; Li, L.-C.; Jin, L.-P. Eur. J. Inorg.
Chem. 2005, 4150-4159.
(21) Yin, D.-W.; Xiao, H.-P. Acta Crystallogr. 2005, E61, m708-m710.
Inorganic Chemistry, Vol. 46, No. 19, 2007 7921

Martin et al.
treatment of 1 (Figure S3). This material is available free of charge
via the Internet at http://pubs.acs.org. Crystallographic data in CIF
format for 1 and 2 have been deposited with the Cambridge
Crystallographic Data Centre with nos. 642623 and 642624,
respectively. Copies of the data can be obtained free of charge via
the Internet at http://www.ccdc.cam.ac.uk/conts/retrieving.html or
by post at CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.
(fax: 44-1223336033; e-mail: deposit@ccdc.cam.ac.uk).
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7922 Inorganic Chemistry, Vol. 46, No. 19, 2007