Pendant arm length control of dimensionality in cobalt dipyridylamine coordination polymers containing meta-benzenedicarboxylate ligands

Article abstract of DOI:10.1016/j.ica.2010.07.070

Hydrothermal synthesis has afforded a pair of divalent cobalt coordination polymers containing meta-substituted benzenedicarboxylate and 4,4′-dipyridylamine (dpa) ligands, in which the length of the pendant arms on the anionic components dictates the overall dimensionality. [Co(1,3-phda)(dpa)(H₂O)]_n (1, 1,3-phda = 1,3-phenylenediacetate) possesses a ruffled (4,4) rhomboid grid 2-D layered structure with an 5-connected sqp supramolecular net. Use of a meta-substituted benzenedicarboxylate with shorter pendant arms generated {[Co(1,3-bdc)(dpa)] ·3H₂O}_n (2, 1,3-bdc = 1,3-benzenedicarboxylate), which displays a 3-D network structure with 6⁵8 topology. Antiferromagnetic coupling, in conjunction with zero-field splitting, was evident across the supramolecular Co-O-H?O-Co patterns in 1 and the syn-syn bridged {Co(OCO)}₂ dimeric units in 2.

Full text of DOI:10.1016/j.ica.2010.07.070

Inorganica Chimica Acta 363 (2010) 3966–3972
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Pendant arm length control of dimensionality in cobalt dipyridylamine
coordination polymers containing meta-benzenedicarboxylate ligands
Karyn M. Blake a, Maxwell A. Braverman a, Joseph H. Nettleman a, Laura K. Sposato b, Robert L. LaDuca a,
⇑
a Lyman Briggs College, Department of Chemistry, Michigan State University, East Lansing, MI 48825, USA
b Department of Chemistry and Physics, King’s College, Wilkes-Barre, PA 18711, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Hydrothermal synthesis has afforded a pair of divalent cobalt coordination polymers containing meta-
substituted benzenedicarboxylate and 4,40-dipyridylamine (dpa) ligands, in which the length of the
pendant arms on the anionic components dictates the overall dimensionality. [Co(1,3-phda)(dpa)(H2O)]n
(1, 1,3-phda = 1,3-phenylenediacetate) possesses a ruffled (4,4) rhomboid grid 2-D layered structure with
an 5-connected sqp supramolecular net. Use of a meta-substituted benzenedicarboxylate with shorter
pendant arms generated {[Co(1,3-bdc)(dpa)]ꢀ3H2O}n (2, 1,3-bdc = 1,3-benzenedicarboxylate), which
displays a 3-D network structure with 658 topology. Antiferromagnetic coupling, in conjunction with
zero-field splitting, was evident across the supramolecular Co–O–Hꢀ ꢀ ꢀO–Co patterns in 1 and the syn–syn
bridged {Co(OCO)}2 dimeric units in 2.
Received 10 March 2010
Accepted 23 July 2010
Available online 3 August 2010
Keywords:
Cobalt
Dicarboxylate
Dipyridylamine
Coordination polymer
Antiferromagnetism
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
Employment of dipyridyl-type neutral co-ligands has further
enhanced the scope of these materials, for example, affording the
Coordination polymer solids constructed from aromatic dicar-
boxylate ligands show burgeoning use towards industrial applica-
tions [1,2] in gas storage [3], gas separation [4], ion-exchange [5],
catalysis [6], luminescence [7] and non-linear optical behavior
[8]. Additionally these phases often exhibit intriguing variable
temperature magnetic behavior, especially among those contain-
ing juxtaposed S = 3/2 divalent cobalt ions in distorted octahedral
coordination environments, in which magnetic superexchange,
spin–orbit coupling, and zero-field splitting play cooperative roles
[9]. Even within the narrower scope of cobalt-containing coordina-
tion polymers, the variety of accessible carboxylate-group binding
and bridging modes has been shown to instill a wide diversity of
underlying structural topologies and magnetic behavior.
2-D phase [Co(1,3-bdc)(bpee)]n (bpee = trans-1,2-bis(4-pyridyl)
ethylene)) [14] and the 1-D phase {[[Co(H2O)4]( -dpa)[Co(1,2-
bdc)2](
-dpa)]ꢀH2O}n (1,2-bdc = 1,2-benzenedicarboxylate, dpa = 4,
40-dipyridylamine) [15]. Within commonly used aromatic dicar-
boxylate ligands, conformational flexibility is restricted to -bond
rotation of the carboxylate groups. In an effort to promote wider
topological diversity, the meta-substituted 1,3-phenyldiacetate
(1,3-phda) and its ortho- and para-substituted isomers have at-
tracted some recent interest as anionic ligands for coordination
polymer synthesis [16–20]. Dual-ligand divalent cobalt coordina-
tion polymers containing different phda isomers and the tethering
ligand bis(4-pyridylmethyl)piperazine show (4,4) grid, 5-con-
nected Archimedean layer, and 3-D primitive cubic network
topologies [20]. Despite this recent study, the use of conforma-
tionally agile phenylenediacetate dianions towards the prepara-
tion of cobalt-containing coordination polymers remains
underdeveloped.
In the present study we have probed the effect of pendant arm
length on the dimensionality and topology of divalent cobalt coor-
dination polymers containing both the kinked and hydrogen-bond-
ing capable dpa and meta-substituted aromatic dicarboxylate
ligands, with the successful synthesis of [Co(1,3-phda)(dpa)(H2O)]n
(1, 1,3-phda = 1,3-phenylenediacetate) and {[Co(1,3-bdc)(dpa)]ꢀ
3H2O}n (2). The variable temperature magnetic properties of and
thermal degradation behavior of both 1 and 2 are also presented
herein.
l
l
r
Rigid phenyl rings within aromatic dicarboxylate ligands have
provided the necessary structural scaffolding for the production
of many cobalt-containing coordination polymers, including
{KCo7(OH)3(1,3-bdc)6(H2O)4ꢀ12H2O}n (1,3-bdc = 1,3-benzenedicar-
boxylate, isophthalate) [10], {[(CH3)2NH2]2[Co6(l3-OH)2(l-H2O)
(1,3-bdc)6]ꢀ2.5H2O}n [11], [Co(1,4-naphthalenedicarboxylate)]n
[12], and {Co(4,40-biphenyldicarboxylate)(H2O)2ꢀH2O}n [13].
⇑
Corresponding author. Address: Lyman Briggs College, E-30 Holmes Hall,
Michigan State University, East Lansing, MI 48825, USA. Tel.: +1 517 432 2268.
E-mail addresses: laduca@msu.edu, laduca@chemistry.msu.edu (R.L. LaDuca).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.07.070

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 3966–3972
3967
constants [22]. Thermogravimetric analysis was performed on a
TA Instruments TGA 2050 Thermogravimetric Analyzer with a
heating rate of 10 °C/min up to 900 °C. Elemental Analysis was
carried out using a Perkin Elmer 2400 Series II CHNS/O Analyzer.
2. Experimental
2.1. General considerations
Cobalt salts and dicarboxylic acids were obtained commercially
from Aldrich. 4,4-Dipyridylamine was prepared via a published
2.2. Preparation of [Co(1,3-phda)(dpa)(H2O)]n (1)
procedure [21]. Water was deionized above 3 M
X cm in-house.
Cobalt nitrate hexahydrate (108 mg, 0.37 mmol), dpa (63 mg,
0.37 mmol), 1,3-phenylenediacetic acid (72 mg, 0.37 mmol) and
10 mL deionized water were placed into a 23 mL Teflon-lined acid
digestion bomb. The bomb was sealed and heated in an oven at
120 °C for 48 h, and then cooled slowly to 25 °C. Pink blocks of 1
(64 mg, 0.15 mmol, 40% yield based on Co) were isolated after
washing with distilled water, ethanol, and acetone and drying in
air. Anal. Calc. for C20H19CoN3O5 1: C, 54.55; H, 4.35; N, 9.54.
Found: C, 54.12; H, 4.05; N, 9.48%. IR (cmꢁ1): 3200 w br, 1590 s,
1513 m, 1486 m, 1439 w, 1411 w, 1385 s, 1342 m, 1266 w, 1210
s, 1088 w, 1014 s, 904 w, 843 w, 821 s, 716 s, 679 w.
Elemental Analysis was carried out using a Perkin Elmer 2400 Ser-
ies II CHNS/O Analyzer. IR spectra were recorded on powdered
samples on a Perkin Elmer Spectrum One instrument. Variable
temperature magnetic susceptibility data (2–300 K) for 1 and 2
were collected on a Quantum Design MPMS SQUID magnetometer
at an applied field of 0.1 T. After each temperature change the
sample was kept at the new temperature for 5 min before magne-
tization measurement to ensure thermal equilibrium. The suscep-
tibility data was corrected for diamagnetism using Pascal’s
Table 1
2.3. Preparation of {[Co(1,3-bdc)(dpa)]ꢀ3H2O}n (2)
Crystal and structure refinement data for 1 and 2.
Compound
1
2
Cobalt nitrate hexahydrate (108 mg, 0.37 mmol), dpa (63 mg,
0.37 mmol), isophthalic acid (61 mg, 0.37 mmol), 1 mL methanol
and 9 mL deionized water were placed into a 23 mL Teflon-lined
acid digestion bomb. The bomb was sealed and heated in an oven
at 120 °C for 48 h, and then cooled slowly to 25 °C. Pink blocks of 2
(76 mg, 0.17 mmol, 46% yield based on Co) were isolated after
washing with distilled water, ethanol, and acetone and drying in
air. Anal. Calc. for C18H19CoN3O7 (with loss of one molar equivalent
of H2O) 2: C, 50.25; H, 3.98; N, 9.77. Found: C, 50.09; H, 3.62; N,
9.84%. IR (cmꢁ1): 3258 w, 3168 w, 3067 w, 1596 s, 1543 w, 1519
s, 1479 m, 1442 m, 1393 s, 1341 s, 1273 w, 1211 m, 1157 w,
1099 w, 1058 w, 1014 s, 905 w, 858 w, 810 s, 740 s, 718 s, 678
w, 657 w.
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
20H19CoN3O5
C18H19CoN3O7
448.30
monoclinic
C2/c
15.787(2)
12.3934(16)
20.928(3)
102.886(2)
3991.5(9)
8
1.479
0.904
0.771
ꢁ19 6 h 6 20
ꢁ16 6 k 6 16
27 6 l 6 26
21 651
4570
0.0239
440.31
monoclinic
P21/c
8.8309(11)
14.8164(18)
14.8547(18)
106.645(1)
1862.2(4)
4
1.571
0.961
0.633
ꢁ10 6 h 6 10
ꢁ17 6 k 6 17
ꢁ17 6 l 6 17
17 953
3408
0.0239
b (Å)
c (Å)
b (°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
Minimum/maximum transmission
hkl ranges
3. X-ray crystallography
Total reflections
Unique reflections
R(int)
Single-crystal reflection data for 1 and 2 were collected using a
Bruker AXS Apex2 CCD instrument. Reflection data was acquired
Parameters/restraints
271/4
0.0263
0.0226
0.0604
298/4
0.0545
0.0455
0.1606
R1 (all data)a
(I))a
using graphite-monochromated Mo K
a radiation (k = 0.71073 Å).
R1 (I > 2
wR2 (all data)b
wR2 (I > 2
(I))b
r
The reflection data were integrated with SAINT [23]. Lorentz and
polarization effect and empirical absorption corrections were
applied with SADABS [24]. The structures were solved using direct
methods and refined on F2 using SHELTXL [25]. All non-hydrogen
atoms were refined with anisotropic thermal parameters. Hydro-
gen atoms bound to carbon atoms were placed in calculated posi-
r
0.0580
0.1523
Maximum/minimum residual (eꢁ/Å3)
Goodness-of-fit (GOF)
0.250/ꢁ0.216
1.281/ꢁ1.024
1.054
1.104
a
R1
wR2 = {
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
2
1=2
[w(F2o ꢁ F2c Þ<ce : sup > 2 < =ce : sup >ꢂ=
R
½wF2oꢂ g
.
b
R
Fig. 1. Coordination environment of 1 with thermal ellipsoids shown at 50% probability and partial atom numbering scheme. Symmetry codes are given in Table 2.

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K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 3966–3972
Table 2
tions and refined with isotropic thermal parameters using a riding
Selected bond distance (Å) and angle (°) data for 1.
model. Hydrogen atoms bound to water molecules or dpa nitrogen
atoms were located by Fourier difference map and restrained at
fixed positions. Relevant crystallographic data for 1 and 2 are listed
in Table 1.
Co1–O5
2.0817(11)
2.0984(11)
2.1121(13)
2.1749(11)
2.1801(13)
2.1845(11)
91.39(4)
92.43(5)
91.47(5)
111.01(4)
85.88(4)
N1–Co1–O1
156.45(5)
90.42(5)
173.82(5)
94.36(5)
87.95(5)
170.45(4)
91.58(4)
96.57(5)
60.19(4)
85.71(5)
Co1–O4#1
Co1–N1
O5–Co1–N3#2
O4#1–Co1–N3#2
N1–Co1–N3#2
O1–Co1–N3#2
O5–Co1–O2
Co1–O1
Co1–N3#2
Co1–O2
4. Results and discussion
O5–Co1–O4#1
O5–Co1–N1
O4#1–Co1–N1
O5–Co1–O1
O4#1–Co1–O1
O4#1–Co1–O2
N1–Co1–O2
4.1. Synthesis and spectral characterization
O1–Co1–O2
N3#2–Co1–O2
Hydrothermal reaction of a cobalt salt, the requisite dicarbox-
ylic acid, and 4,40-dipyridylamine generated crystalline samples
of 1 and 2. The infrared spectra of both materials were consistent
with their crystal structures. Features corresponding to pyridyl or
phenyl ring flexing and puckering modes were observed in the re-
gion between 600 and 820 cmꢁ1. Medium intensity bands in the
range of ꢃ1600–1200 cmꢁ1 arise from stretching modes of the aro-
matic rings of the dicarboxylate ligands and pyridyl rings within
the dpa ligands [26]. Asymmetric and symmetric C–O stretching
modes of the benzenedicarboxylate moieties were evidenced by
very strong, slightly broadened bands at 1590/1513 and 1385/
1342 cm–1 for 1 and 1596/1519 and 1393/1341 cm–1 for 2. The
Symmetry equivalent positions: #1 ꢁx + 1, y ꢁ 1/2, ꢁz + 1/2; #2 ꢁx, y + 1/2, ꢁz + 1/2.
Table 3
Hydrogen-bonding distance (Å) and angle (°) data for 1–2.
D–Hꢀ ꢀ ꢀA
d (Hꢀ ꢀ ꢀA) <DHA
d (Dꢀ ꢀ ꢀA)
Symmetry
transformation
for A
1
O5–H5Aꢀ ꢀ ꢀO1
1.826(14) 178.0(18) 2.6933(15) ꢁx + 1, ꢁy + 1, ꢁz
1.740(15) 164.1(18) 2.5894(17) ꢁx + 1, y ꢁ 1/2,
ꢁz + 1/2
O5–H5Bꢀ ꢀ ꢀO3
Dm values for each pair of asymmetric and symmetric C–O stretch-
N2–H2Nꢀ ꢀ ꢀO4
2.030(15) 174.0(18) 2.8888(17) ꢁx, y ꢁ 1/2,
ꢁz + 1/2
ing frequencies are consistent with monodentate and chelating
coordination of the carboxylate units [27], respectively. Weak,
broad spectral features in the region of ꢃ3400 cm–1 represent
O–H stretching modes within the aqua ligands in 1, and the N–H
stretching mode for dpa central amine in both 1 and 2.
2
O1W–H1WAꢀ ꢀ ꢀO3
0.858(19) 157(5)
2.818(4)
3.00(2)
2.888(5)
ꢁx, ꢁy + 2, ꢁz
x, y ꢁ 1, z
O1W–H1WAꢀ ꢀ ꢀO3W 0.856(19) 177(5)
N2–H2Nꢀ ꢀ ꢀO1W
0.871(19) 170(4)
Fig. 2. View of the (4,4) rhomboid grid layer in 1. Hydrogen-bonding is indicated as dashed lines.

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 3966–3972
3969
4.2. Structural description of [Co(1,3-phda)(dpa)(H2O)]n (1)
The asymmetric unit of compound 1 contains a divalent cobalt
atom, one doubly deprotonated 1,3-phda ligand, one dpa moiety,
and one bound water molecule (Fig. 1). With a distorted {CoN2O4}
coordination sphere, each cobalt atom is ligated in a cis manner by
nitrogen atoms from two dpa ligands, which are both situated cis
to the aqua ligand. Two coordination sites are occupied by a chelat-
ing 1,3-phda terminus, with the remaining sites filled by an oxygen
atom donor from a monodentate carboxylate group of another
1,3-phda ligand. Bond parameters at cobalt are consistent with sin-
gly chelated octahedral coordination geometry (Table 2), with
bond lengths ranging from 2.0807(14) to 2.1847(15) Å and bond
angles ranging from 60.30(5) (for the chelating carboxylate) to
156.66(6)°.
Fig. 3. Close up view of the Co–O–Hꢀ ꢀ ꢀO–Co interlayer supramolecular interactions
in 1. Hydrogen-bonding is indicated as dashed lines.
Through the bridging 1,3-phda ligands, which adopt a chelat-
ing/monodentate binding mode, [Co(1,3-phda)]n chain motifs are
Fig. 4. Network perspective of the 5-connected 4466 sqp supramolecular lattice in 1. In the online version of this article, the interlayer hydrogen-bonding patterns are shown
in red. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Coordination environment of 2 with thermal ellipsoids shown at 50% probability and partial atom numbering scheme. Symmetry codes are given in Table 4.

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K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 3966–3972
Table 4
Selected bond distance (Å) and angle (°) data for 2.
the inability of the aqua ligands to bridge two cobalt ions in 1 pre-
vents the exotridentate 1,3-phda bridging mode seen in the nickel
compound, thus altering coordination polymer topology.
Co1–O1#1
2.030(2)
2.065(2)
2.126(2)
2.139(2)
2.168(2)
2.277(2)
124.40(8)
90.38(9)
91.12(9)
87.84(9)
87.51(9)
176.62(10)
90.07(8)
144.74(8)
96.26(10)
86.62(10)
148.71(8)
86.73(8)
92.17(9)
90.84(9)
58.65(8)
Co1–O2#2
Co1–N3#3
Co1–N1
Co1–O4
Co1–O3
4.3. Structural description of {[Co(1,3-bdc)(dpa)]ꢀ3H2O}n (2)
The asymmetric unit of compound 2 consists of a single divalent
cobalt atom, one doubly deprotonated 1,3-bdc anion, and one dpa
ligand, along with three unligated water molecules (Fig. 5). The
cobalt atom manifests a distorted {CoN2O4} coordination sphere,
with trans nitrogen atom donors from two dpa ligands, dissimilar
to the cis arrangement seen in 1. Two coordination sites are filled
by a chelating 1,3-bdc carboxylate group, while the remaining
two positions are occupied by oxygen atoms from two different
1,3-bdc ligands. Pertinent bond lengths and angles for 2 are given
in Table 4.
O1#1–Co1–O2#2
O1#1–Co1–N3#3
O2#2–Co1–N3#3
O1#1–Co1–N1
O2#2–Co1–N1
N3#3–Co1–N1
O1#1–Co1–O4
O2#2–Co1–O4
N3#3–Co1–O4
N1–Co1–O4
O1#1–Co1–O3
O2#2–Co1–O3
N3#3–Co1–O3
N1–Co1–O3
O4–Co1–O3
Extension of the structure through the exotridentate chelating/
bridging 1,3-bdc anions generates neutral one-dimensional (1-D)
[Co(1,3-bdc)]n coordination polymeric ribbons (Fig. 6). The bisbrid-
ging and chelating carboxylate units are tilted by ꢃ6.1° and ꢃ16.7°
from the plane of the 1,3-bdc aromatic ring, respectively. A pair of
bisbridging carboxylate groups connect neighboring Co atoms in a
syn–syn fashion, creating 8-membered {CoOCO}2 rings with a
through-space Coꢀ ꢀ ꢀCo distance of ꢃ3.953 Å. These rings deviate
somewhat from co-planarity, with deviations from the plane rang-
ing from 0.030 to 0.113 Å. Linkage of the {CoOCO}2 rings through
the 1,3-bdc chelating carboxylate endgroups forms {CoOC5O}2
16-membered rings with a Coꢀ ꢀ ꢀCo contact distance of 7.466 Å.
Sets of parallel [Co(1,3-bdc)]n ribbons are arranged orthogonally
to each other, and are connected through pairs of dpa ligands to
construct a 3-D [Co(1,3-bdc)(dpa)]n coordination polymer net-
work. The Coꢀ ꢀ ꢀCo distance through the dpa ligands measures
11.618 Å. Each {CoOCO}2 ring can be considered as a square planar
connecting node, connecting to two others along a single [Co(1,3-
bdc)]n ribbon, and to two others through two pairs of dpa tethers.
Topological analysis with TOPOS [28] reveals a 4-connected 658
topology (CdSO4 network) for the coordination polymer frame-
work in 2 (Fig. 7), with orthogonal sets of [Co(1,3-bdc)]n ribbons
cross-linked by dpa ligands. The co-crystallized solvent molecules
are located in narrow channels along the b crystal direction, which
occupy 23.1% of the unit cell volume as calculated by PLATON [30].
The previously reported phase [Co(1,3-bdc)(bpee)]n [14] pos-
sesses very similar [Co(1,3-bdc)]n ribbons to those seen in 2. How-
ever, parallel sets of [Co(1,3-bdc)]n ribbons are linked into 2-D (4,4)
grid-like layers in [Co(1,3-bdc)(bpee)]n, if each {CoOCO}2 ring is
treated as a square planar connecting node. It appears that the
rigid-rod nature of the bpee ligands, enforced by their central
Symmetry equivalent positions: #1 ꢁx, ꢁy + 2, ꢁz;
#2 x + 1/2, y ꢁ 1/2, z; #3 x + 1/2, ꢁy + 3/2, z + 1/2.
formed. With Coꢀ ꢀ ꢀCo through-ligand distances of 8.683 Å, these
chains are oriented parallel to the [1 0 0] crystal direction. The che-
lating and monodentate acetate arms of the 1,3-phda ligands are
twisted by 65.9 and 77.4° relative to the phenyl ring plane, respec-
tively. Unligated oxygen atoms of the monodentate 1,3-phda
acetate arms accept hydrogen bonds from the ligated water mole-
cules (Table 3).
Adjacent [Co(1,3-phda)]n chains are connected by the kinked
dpa tethers to construct a ruffled [Co(1,3-phda)(dpa)(H2O)]n (4,4)
rhomboid coordination polymer grid (Fig. 2), which lies parallel
to the ab crystal plane. The Coꢀ ꢀ ꢀCo distance across the dipodal
dpa ligands measures 11.515 Å. The through-space grid apertures
measure 8.8304 and 14.8156 Å, which denote the a and b lattice
parameters, respectively. Additional stabilization within the layer
motif is provided by hydrogen-bonding between the dpa central
amine and the ligated oxygen atoms belonging to monodentate
acetate groups. Neighboring layers are symmetry related by the
21 screw axis parallel to the b crystal direction, and interact along
the c direction with an ABAB repeat pattern by means of hydrogen-
bonding donation from the aqua ligands to oxygen atoms within
chelating 1,3-phda acetate groups (Supplementary Fig. S1). The
metal–metal contact distance across the resulting {Co2(OHO)2}
kernels (Fig. 3) measures 5.068 Å. If pairs of these supramolecular
interactions are treated as bonds, the Co atoms can be considered
as 5-connected nodes. The resulting lattice has 4466 (sqp) topology
(Fig. 4) as determined by TOPOS software [28].
C@C
p bonds, promotes a 2-D coordination polymer structure.
The kinked, but shorter, geometry of the dpa ligands permits
connection of [Co(1,3-bdc)]n ribbons into a 4-connected 658 3-D
topology. The 3-D topology of meta-dicarboxylate containing 2 also
contrasts with the 1-D chain structure of its ortho-dicarboxylate
The covalent 2-D dimensionality of 1 contrasts dramatically
with that of its nickel congener, [Ni(1,3-phda)(dpa)(
[29], which manifests an underlying 3-D 41263 primitive cubic-
type topology based on Ni2( -H2O) dimers. It is plausible that
l-H2O)0.5]n
analogue {[[Co(H2O)4](
l
-dpa)[Co(1,2-bdc)2](
l
-dpa)]ꢀH2O}n [15].
The underlying 658 3-D topology of 2 is similar to that seen in its
l
Fig. 6. A [Co(1,3-bdc)]n chain in 2, with embedded {Co(OCO)}2 8-membered rings.

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 3966–3972
3971
Fig. 7. Schematic representation of the 3-D 658 network in 2.
Fig. 9. Variable temperature magnetic susceptibility data for 2. The best fit to Eq.
(1) is shown as a thin line.
mediated antiferromagnetic superexchange [34] between cobalt
ions in neighboring [Co(1,3-phda)(dpa)(H2O)]n layers. The best-fit
values to Eq. (1) (Fig. 8) were A = 1.44(3) cm3 K molꢁ1 and
B = 1.70(3) cm3 K molꢁ1 giving g = 2.59(3), J = ꢁ1.81(8) cmꢁ1 and
D = 31(2) cmꢁ1
,
with R = 2.53 ꢄ 10ꢁ3 = {
R
[(
v
mT)obs ꢁ (
v
mT)calc]2/
R
[(v
mT)obs]2}). The negative J value corroborates the activity of
interlayer antiferromagnetic superexchange mechanisms across
the hydrogen-bonded {Co2(OHO)2} kernels in 1, with cooperation
of single-ion effects (D). According to a previous theoretical study
[34a], the antiferromagnetic coupling can be mediated by valence
orbital overlap of the oxygen atoms involved in the hydrogen-
bonding patterns.
The magnetic data for 2 obeyed the Curie–Weiss law across the
entire temperature range from
2 to 300 K (Fig. S3), with
C = 2.72 cm3 K molꢁ1 and
H
= ꢁ2.84 K, indicating possible antifer-
romagnetic interactions across the {Co(OCO)}2 rings although a
deeper treatment is again necessary to separate magnetic superex-
change from single-ion effects. The
vmT(T) data were fit to Eq. (1),
with the best-fit values A = 0.90(8) cm3 K molꢁ1 and B = 1.92(9)
cm3 K molꢁ1 giving g = 2.45(9), J = ꢁ0.63(9) cmꢁ1 and D = 11(1)
cmꢁ1, with R = 3.5 ꢄ 10ꢁ3 (Fig. 9). The small negative J and positive
D value indicates the presence of weak antiferromagnetic superex-
change across the {Co(OCO)}2 rings in 2, acting cooperatively with
Fig. 8. Variable temperature magnetic susceptibility data for 1. The best fit to Eq.
(1) is shown as a thin line.
copper analogue {[Cu(1,3-bdc)(dpa)]ꢀ0.5H2O}n, despite distorted
trigonal bipyramidal coordination at copper [31].
zero-field splitting to reduce the
vmT(T) product value as temper-
ature decreases. It should be noted that the fit to Eq. (1) at higher
temperatures is relatively poor, so the best-fit values should be ta-
ken as only approximate.
4.4. Magnetic properties of 1 and 2
The variable temperature magnetic susceptibility of 1 and 2 was
studied to examine the possibility of magnetic superexchange
across the supramolecular {Co2(OHO)2} kernels in 1 and within
the {Co(OCO)}2 rings in 2. Recently it has been seen [32] that the
phenomenological Rueff expression [33] (Eq. (1)) can be applied
to S = 3/2 dimers in addition to S = 3/2 chains. Such a treatment
is necessary because of the predominant effect that zero-field split-
ting and/or spin–orbit coupling has on magnetic behavior in diva-
lent cobalt complexes with tetragonally distorted octahedral
coordination environments.
4.5. Thermogravimetric analysis
Compounds 1 and 2 were subjected to thermogravimetric anal-
ysis to probe their thermal stability and decomposition behavior.
For compound 1, the aqua ligands were slowly lost between
ꢃ100 and ꢃ200 °C, as evidenced by a weight loss of 4.0% (4.1%
calc’d). Pyrolysis of the organic components occurred above
ꢃ275 °C. The remaining weight percent (17.4% at 900 °C corre-
sponded well with a deposition of CoO (17.0% calc’d). Compound
2 lost one molar equivalent of co-crystallized water upon long
term storage, as indicated by elemental analysis. Loss of the
remaining water molecules of crystallization occurred upon heat-
ing between room temperature and ꢃ100 °C (8.5% mass loss ob-
served, 8.4% calc’d). Ejection of the organic components occurred
v
mT ¼ A expðꢁD=kTÞ þ B expðJ=kTÞ
ð1Þ
where A + B = C = (5Ng2b2/4k).
The magnetic data for 1 fit the Curie–Weiss law for tempera-
tures between 25 and 300 K (Fig. S2), with C = 3.11 cm3 K molꢁ1
and
H
= ꢁ20.4 K, a preliminary indication of hydrogen-bonding

3972
K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 3966–3972
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Acknowledgements
The authors gratefully acknowledge the donors of the American
Chemical Society Petroleum Research Fund for financial support of
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