Substituent dependent topologies in cobalt isophthalate coordination polymers with bis(pyridylmethyl)piperazine coligands

Article abstract of DOI:10.1016/j.ica.2011.03.009

Divalent cobalt coordination polymers containing bis(4-pyridylmethyl) piperazine (4-bpmp) or bis(3-pyridylmethyl)piperazine (3-bpmp) ligands and 5-substituted isophthalate ligands have been hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. [Co(OHip)(4-bpmp)]_n (1, OHip = 5-hydroxyisophthalate) manifests a (4,4) grid 2D coordination polymer structure, with anti-syn bridged {Co ₂(OCO)₂} dimers serving as connecting nodes. Similar dinuclear {Co₂(OCO)₂} clusters are evident in [Co(OMeip)(4-bpmp)]_n (2, OMeip = 5-methoxyisophthalate). However, the lack of hydrogen-bonding capability of the methoxy substituent promotes formation of a rarer 6-connected (3,6) triangular net. {[Co(H₂O) ₄(H₂3-bpmp)](NO₂ip)₂·6H ₂O}_n (3, NO₂ip = 5-nitroisophthalate) possesses cationic [Co(H₂O)₄(H₂3-bpmp)]n4n+ chains connected into a supramolecular lattice by unligated NO₂ip dianions and water molecules of crystallization. The variable temperature magnetic susceptibility behavior of 1 and 2 is ascribed to cooperation between single-ion effects and weak ferromagnetic superexchange.

Full text of DOI:10.1016/j.ica.2011.03.009

Inorganica Chimica Acta 371 (2011) 71–78
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Inorganica Chimica Acta
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Substituent dependent topologies in cobalt isophthalate coordination polymers
with bis(pyridylmethyl)piperazine coligands
⇑
Amy M. Pochodylo, Robert L. LaDuca
Lyman Briggs College and Department of Chemistry, Michigan State University, East Lansing, MI 48825, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 October 2010
Received in revised form 21 February 2011
Accepted 3 March 2011
Available online 16 March 2011
Divalent cobalt coordination polymers containing bis(4-pyridylmethyl)piperazine (4-bpmp) or bis(3-pyr-
idylmethyl)piperazine (3-bpmp) ligands and 5-substituted isophthalate ligands have been hydrother-
mally prepared and structurally characterized by single-crystal X-ray diffraction. [Co(OHip)(4-bpmp)]n
(1, OHip = 5-hydroxyisophthalate) manifests a (4,4) grid 2D coordination polymer structure, with anti-
syn bridged {Co2(OCO)2} dimers serving as connecting nodes. Similar dinuclear {Co2(OCO)2} clusters
are evident in [Co(OMeip)(4-bpmp)]n (2, OMeip = 5-methoxyisophthalate). However, the lack of hydro-
gen-bonding capability of the methoxy substituent promotes formation of a rarer 6-connected (3,6) tri-
Keywords:
Cobalt
Dicarboxylate
Coordination polymer
Hydrogen bonding
Ferromagnetism
angular net. {[Co(H2O)4(H23-bpmp)](NO2ip)2ꢀ6H2O}n (3, NO2ip = 5-nitroisophthalate) possesses cationic
4nþ
½CoðH2OÞ4ðH23-bpmpÞꢁn
chains connected into a supramolecular lattice by unligated NO2ip dianions
and water molecules of crystallization. The variable temperature magnetic susceptibility behavior of 1
and 2 is ascribed to cooperation between single-ion effects and weak ferromagnetic superexchange.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
in tandem with dipyridyl nitrogen-base co-ligands in order to aug-
ment the in these materials topological diversity. For instance,
Crystalline coordination polymer solids possess important
industrially focused applications [1,2] such as gas storage [3],
selective absorption and separation [4], ion exchange [5], heteroge-
neous catalysis [6], luminescence [7], and non-linear optical
behavior [8]. Aromatic dicarboxylates such as terephthalate [9]
or isophthalate (ip) [10] are commonly employed ligands in the
molecular design of divalent metal coordination polymers, because
they can impart a rigid crystalline framework and necessary charge
balance. Interplay between metal ion coordination preference, geo-
metric disposition of the carboxylate groups on the aromatic ring,
carboxylate binding mode and the inclusion of any dipodal nitro-
gen-base tethering ligands [11] induces diverse structural topolo-
gies in these systems, although a priori prediction of coordination
polymer structure remains elusive in most cases. In coordination
polymer solids containing divalent cobalt ions, the presence of
multinuclear clusters or cobalt carboxylate chains can result in
intriguing magnetic behavior including spin-canting and single-
chain magnetism [12].
{[Co(OHip)(dpp)]ꢀH2O}n (dpp = 1,3-di(4-pyridyl)propane) shows a
fourfold interpenetrated diamondoid topology, while its nickel
derivative [Ni(OHip)(dpp)1.5(H2O)]n displays interdigitated sets of
1D ribbon motifs [13]. {[Co(3-bpt)(NO2ip)(H2O)2]ꢀ(H2O)}n
(3-bpt = 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole) has
a simple
(4,4) grid topology [19] but {[Co(NO2ip)(dpee)]ꢀ0.5dpeeꢀH2O}n
(dpee = 1,2-di(4-pyridyl)ethylene) exhibits a 2D bilayer structure
with nanoscale rectangular channels that encapsulate organic spe-
cies [20]. Despite some exploratory synthesis of individual coordi-
nation polymer phases, studies that systematically investigate
size-dependent steric effects imparted by substituted isophthalate
ligands on coordination polymer topology have been less common,
especially in divalent cobalt systems. Yang and co-workers
performed one such study in a divalent zinc system [24], prepar-
ing the coordination polymers [Zn4(H2O)(isophthalate)4(py)6]n
(py = pyridine), {[Zn2(OHip)2(py)4]2ꢀ(py)}n, and [Zn(tBuip)(py)2]n
(tBuip = 5-tert-butylisophthalate). In this series increasing the ste-
ric hindrance imparted by the 5-position substituent caused a de-
crease in coordination polymer dimensionality, from a 2D grid-like
layer to 1D single- and double-stranded chains.
Isophthalate ligand derivatives with substituents at their mutu-
ally meta-disposed 5-positions, such as 5-hydroxyisophthalate
(OHip) [13–16], 5-methoxyisophthalate (OMeip) [17,18], and
5-nitroisophthalate (NO2ip) [19–23] (Scheme 1), have been used
In this study we have investigated the preparation of divalent co-
balt coordination polymers containing a 5-position substituted iso-
phthalate ligand and bis(pyridylmethyl)piperazine (bpmp) isomers
3-bpmp or 4-bpmp (Scheme 1). The 4-bpmp ligand has afforded
topologically interesting nets such as the 8-connected 4451767 self-
penetrated net in [Co3(oba)3(4-bpmp)2]n (oba = oxybisbenzoate)
⇑
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 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.009

72
A.M. Pochodylo, R.L. LaDuca / Inorganica Chimica Acta 371 (2011) 71–78
cooled slowly to 25 °C. Magenta blocks of 1 (48 mg, 26% yield
based on Co) were isolated after washing with distilled water, eth-
anol, and acetone and drying in air. Anal. Calc. for C48H48Co2N8O10
1: C, 56.81; H, 4.77; N, 11.04. Found: C, 56.55; H, 4.29; N, 10.85%. IR
(cmꢂ1): 3300 (w, br), 3079 (w), 2940 (w), 2818 (w), 1616 (w), 1582
(s), 1532 (m), 1456 (m), 1422 (m), 1380 (s), 1347 (w), 1319 (w),
1296 (w), 1272 (w), 1231 (w), 1158 (m), 1133 (m), 1066 (w),
1010 (s), 975 (m), 931 (w), 888 (w), 838 (m), 817 (w), 799 (w),
784 (s), 722 (s), 670 (w).
2.3. Preparation of [Co(OMeip)(4-bpmp)]n (2)
Co(NO3)2ꢀ6H2O (108 mg, 0.369 mmol), 4-bpmp (99 mg, 0.37
mmol), 5-methoxyisophthalic acid (73 mg, 0.37 mmol) and 10 mL
deionized water were placed into a 23 mL Teflon-lined acid diges-
tion bomb. The bomb was sealed and heated in an oven at 120 °C
for 48 h, and then cooled slowly to 25 °C. Magenta blocks of 2
(18 mg, 9 % yield based on Co) were isolated after washing with
distilled water, ethanol, and acetone and drying in air. Anal. Calc.
for C25H23CoN4O5 2: C, 57.59; H, 5.03; N, 10.74. Found: C, 57.78;
H, 4.94; N, 10.43%. IR (cmꢂ1): 3047 (w), 2941 (w), 2816 (w),
1620 (w), 1579 (s), 1540 (w), 1456 (s), 1412 (m), 1385 (s), 1344
(w), 1322 (w), 1293 (m), 1267 (m), 1231 (w), 1151 (w), 1130 (s),
1060 (s), 1008 (s), 942 (w), 924 (s), 889 (w), 858 (w), 840 (m),
816 (w), 787 (s), 721 (s), 669 (w).
Scheme 1. Ligands used in this study.
[25] and the rare threaded-loop self-penetrated layer seen in
{[Zn3(tca)2(4-bpmp)(H-4-bpmp)2](ClO4)2ꢀ5H2O}n (tca = tricarbally-
late) [26]. Although the 3-bpmp ligand has tended to promote lower
dimensionalities [27], it has allowed generation of some rare 3D net-
works [28]. We report here the synthesis and structural character-
ization of the coordination polymer solids [Co(OHip)(4-bpmp)]n
(1) and [Co(OMeip)(4-bpmp)]n (2), whose topologies depend criti-
cally on the steric bulk and hydrogen bonding capability of the iso-
2.4. Preparation of {[Co(H2O)4(H23-bpmp)](NO2ip)2ꢀ6H2O}n
Co(NO3)2ꢀ6H2O (108 mg, 0.369 mmol), 3-bpmp (99 mg, 0.37
mmol), 5-nitroisophthalic acid (78 mg, 0.37 mmol) and 10 mL
deionized water were placed into a 23 mL Teflon-lined acid diges-
tion 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 3
(101 mg, 30% yield based on the acid) were isolated after washing
with distilled water, ethanol, and acetone and drying in air. Anal.
Calc. for C32H48CoN6O22 3: C, 41.43; H, 5.22; N, 10.74. Found: C,
41.98; H, 4.78; N, 11.10%. IR (cmꢂ1): 3300 (w, br), 2994 (w, br),
2357 (w), 1598 (s), 1530 (s), 1452 (m), 1437 (w), 1418 (w), 1361
(w), 1344 (s), 1277 (w), 1197 (w), 1092 (w), 1071 (m), 1043 (w),
989 (w), 958 (w), 931 (m), 916 (w), 846 (w), 789 (s), 756 (w),
732 (m), 698 (s).
phthalate 5-position substituent.
A series of attempts were
undertaken to prepare divalent cobalt substituted isophthalate
coordination polymers containing the isomeric 3-bpmp ligand, in
order to explore the effect of nitrogen donor geometric disposition.
Unfortunately only H2NO2ip afforded any crystalline product,
resulting in the isolation of the 1D chain complex {[Co(H2O)4
(H23-bpmp)](NO2ip)2ꢀ6H2O}n (3). Magnetic superexchange and sin-
gle-ion effects within the dinuclear units formed in compounds 1
and 2 were also investigated.
2. Experimental
2.1. General considerations
3. X-ray crystallography
Cobalt salts and substituted isophthalic acids were obtained
commercially from Aldrich. Bis(4-pyridylmethyl)piperazine (4-
bpmp) and bis(3-pyridylmethyl)piperazine (3-bpmp) were pre-
pared via modification of a published procedure [29]. Water was
Single-crystal reflection data for 1–3 were collected using a Bru-
ker-AXS Apex2 CCD instrument. Reflection data was acquired using
graphite-monochromated Mo K
a radiation (k = 0.71073 Å). The
deionized above 3 MX cm in-house. Elemental analysis was per-
reflection data were integrated with SAINT [31]. Lorentz and polari-
zation effect and empirical absorption corrections were applied
with SADABS [32]. The structures were solved using direct methods
and refined on F2 using SHELTXL [33]. All non-hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen atoms
bound to carbon atoms were placed in calculated positions and re-
fined with isotropic thermal parameters using a riding model.
Hydrogen atoms bound to water molecules were located by Fou-
rier difference map and restrained at fixed positions. Relevant crys-
tallographic data for 1–3 are listed in Table 1.
formed by Micro-Analysis, Inc., Wilmington, Delaware, USA. IR
spectra Infrared spectra were recorded on powdered samples on
a Perkin Elmer Spectrum One instrument. Variable temperature
magnetic susceptibility data (2 K to 300 K) for 1 and 2 were col-
lected on a Quantum Design MPMS SQUID magnetometer at an ap-
plied field of 0.1 T. After each temperature change the sample was
kept at the new temperature for 5 min before magnetization mea-
surement to ensure thermal equilibrium. The susceptibility data
was corrected for diamagnetism using Pascal’s constants and for
the diamagnetism of the sample holder [30].
2.2. Preparation of [Co(OHip)(4-bpmp)]n (1)
4. Results and discussion
Co(NO3)2ꢀ6H2O (108 mg, 0.369 mmol), 4-bpmp (99 mg, 0.37
mmol), 5-hydroxyisophthalic acid (67 mg, 0.37 mmol) and 10 mL
deionized water were placed into a 23 mL Teflon-lined acid diges-
tion bomb, along with 1.0 mL of a 1.0 M NaOH solution. The bomb
was sealed and heated in an oven at 120 °C for 72 h, and then
4.1. Synthesis and spectral characterization
Hydrothermal reaction of cobalt nitrate, the requisite dicarbox-
ylic acid, and the appropriate bis(pyridylmethyl)piperazine isomer
generated crystalline samples of 1–3. The infrared spectra of 1–3

A.M. Pochodylo, R.L. LaDuca / Inorganica Chimica Acta 371 (2011) 71–78
73
Table 1
Crystal and structure refinement data for 1–3.
Compound
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
48H48Co2N8O10
C25H26CoN4O5
521.43
monoclinic
P21/c
12.670(3)
10.095(3)
18.237(5)
90
91.786(4)
90
C32H48CoN6O22
927.69
1014.80
triclinic
P1
triclinic
ꢀ
ꢀ
P1
11.6902(9)
13.6397(10)
14.0927(10)
87.051(1)
89.268(1)
80.615(1)
2214.1(3)
2
8.6581(7)
10.5948(9)
11.1721(9)
75.964(1)
83.826(1)
89.243(1)
988.37(14)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
2331.5(10)
4
1.485
Z
Dcalc (g cmꢂ3
)
1.522
0.821
1.559
0.530
l
(mmꢂ1
)
0.781
Minimum/maximum transmission
hkl ranges
0.8889/0.9524
ꢂ14 6 h 6 14, ꢂ16 6 k 6 16,
ꢂ16 6 l 6 16
32 441
8056
0.0714
0.8179/0.9052
ꢂ15 6 h 6 15, ꢂ11 6 k 6 11,
ꢂ21 6 l 6 21
13 778
4153
0.0458
0.9101/0.9679
ꢂ10 6 h 6 10, ꢂ12 6 k 6 12,
ꢂ13 6 l 6 13
14 345
3590
0.0613
Total reflections
Unique reflections
Rint
Parameters/restraints
619/0
0.0694
0.0447
0.1237
0.1092
0.303/ꢂ0.603
317/0
0.0542
0.0434
0.1205
0.1124
0.500/ꢂ0.684
298/16
0.0901
0.0708
0.2002
0.1825
1.331/ꢂ1.453
R1 (all data)a
R1 (I > 2
wR2 (all data)b
wR2 (I > 2
(I))b
r
(I))a
r
Maximum/minimum residual (eꢂ/
Å3)
Goodness-of-fit (GOF)
1.040
1.063
1.078
a
R1
wR2 ¼ f
=
R
||Fo| ꢂ |Fc||/
R|Fo|.
2
2
1=2
R
½wðF2o ꢂ F2c Þ ꢁ=
R
½wF2oꢁ g
.
b
were consistent with their single crystal structures. Medium inten-
sity bands in the range of ꢃ1600–ꢃ1200 cmꢂ1 are attributed to
stretching modes of the pyridyl rings of the bpmp ligands and
the aromatic rings of the substituted isophthalate ligands. Features
corresponding to pyridyl ring puckering modes are evident in the
region between ꢃ930 and ꢃ600 cmꢂ1. Asymmetric and symmetric
C–O stretching modes of the fully deprotonated dicarboxylate li-
gands are present as strong bands at 1531 and 1380 cmꢂ1 (1),
1579 and 1385 cmꢂ1 (2), and 1530 and 1360 cmꢂ1 (3). Broad, weak
spectral features at ꢃ3400 cmꢂ1 for 1 and 3 denote the presence of
O–H stretching modes in the bound or unbound water molecules,
or the hydroxy group in 1. The nitro substituent in 3 is evidenced
Table 2
Bond length (Å) and angle (°) data for 1.
Co1–O2#1
Co1–O4#2
Co1–O3
2.013(2)
2.0193(19)
2.037 (2)
2.189(3)
2.216(2)
2.0072(19)
2.013(2)
2.080(2)
2.157(2)
2.175(2)
O3–Co1–N1
88.61(9)
88.25(8)
95.73(9)
85.50(9)
173.67(9)
104.99(8)
152.30(8)
102.32(8)
89.87(8)
89.17(8)
85.94(8)
96.66(9)
91.18(9)
87.29(8)
173.13(9)
O2#1–Co1–N5
O4#2–Co1–N5
O3–Co1–N5
Co1–N1
Co1–N5
N1–Co1–N5
Co2–O6#3
Co2–O5#4
Co2–O7
O6#3–Co2–O5#4
O6#3–Co2–O7
O5#4–Co2–O7
O6#3–Co2–N8#5
O5#4–Co2–N8#5
O7–Co2–N8#5
O6#3–Co2–N4
O5#4–Co2–N4
O7–Co2–N4
Co2–N8#5
Co2–N4
O2#1–Co1–O4#2
O2#1–Co1–O3
O4#2–Co1–O3
O2#1–Co1–N1
O4#2–Co1–N1
103.86(8)
109.18(9)
146.96(9)
91.50(8)
90.47(9)
by a strong N–O stretching band at 1343 cmꢂ1
.
N8#5–Co2–N4
4.2. Structural description of [Co(OHip)(4-bpmp)]n (1)
Symmetry equivalent positions: #1 ꢂx, ꢂy + 1, ꢂz; #2 x ꢂ 1, y, z + 1; #3 x + 1, y + 1,
z; #4 ꢂx + 2, ꢂy + 2, ꢂz ꢂ 1; #5 x + 2, y + 1, z ꢂ 1.
The asymmetric unit of compound 1 contains two crystallo-
graphically distinct divalent cobalt atoms, two doubly deproto-
nated OHip ligands, and two 4-bpmp ligands. About each cobalt
atom, the coordination environment is a distorted {CoN2O3} square
pyramid with pyridyl nitrogen donor atoms from two 4-bpmp
ligands occupying trans positions within the basal plane. Oxygen
donor atoms from three different OHip ligands fill the remaining
three coordination sites. Different deviations from idealized square
(OCO)2} dimeric kernels, which have a CoꢀꢀꢀCo contact separation
of 4.557 Å. These are connected into 1D [Co(OHip)]n ribbons
(Fig. 1), which are oriented parallel to the [0 1 1] crystal direction.
The [Co(OHip)]n ribbons are connected into [Co(OHip)
(4-bpmp)]n 2D coordination polymer layers (Fig. 2a) by 4-bpmp
ligands that conjoin Co1 and Co2 atoms in neighboring ribbons,
with a CoꢀꢀꢀCo through-ligand distance of 15.843 Å. Individual
[Co(OHip)(4-bpmp)]n layers are oriented parallel to the (1 ꢂ1 1)
crystal planes. The angle between the pyridyl nitrogen atoms and
pyramidal geometry (s = 0.445 and 0.347 for Co1 and Co2, respec-
tively [34]) enforce the crystallographic distinction between the
cobalt atoms. Weaker semi-ligating interactions [35] between
OHip carboxylate oxygen atoms and cobalt (Co1ꢀꢀꢀO1, 2.578 Å;
Co2ꢀꢀꢀO8, 2.431 Å) give rise to ‘‘5+1’’ expanded secondary coordina-
tion environments. Relevant bond information for 1 is listed in
Table 2.
the piperazinyl ring centroid (defined as
j) is 170.4°. This slight
kink results in a smaller through-ligand metal–metal distance than
seen in other coordination polymers with ‘‘splayed-open’’ 4-bpmp
ligands [36]. If the {Co2(OCO)2} dimers are considered to be the
simplest connecting nodes, the underlying topology of the 2D net
of 1 is that of a standard (4,4) rhomboid grid (Fig. 2b). Interlayer
hydrogen bonding interactions (Table 3) between the hydroxy
Each OHip moiety bridges three cobalt atoms in a j3O:O0:O00
ligating mode, with one of its carboxylate arms linking a Co1 and
a Co2 atom in an anti-syn arrangement. Pairs of Co1 and Co2 atoms
are linked by two anti-syn carboxylate bridges to construct {Co2

74
A.M. Pochodylo, R.L. LaDuca / Inorganica Chimica Acta 371 (2011) 71–78
Fig. 1. [Co(OHip)]n ribbon in 1.
Fig. 2. (a) [Co(OHip)(4-bpmp)]n coordination polymer layer in 1. (b) Schematic perspective of the underlying (4,4) grid topology of 1, with the dimeric {Co2(OCO)2}
connecting nodes represented as spheres.
Table 3
Hydrogen bonding distance (Å) and angle (°) data for 1–3.
D–HꢀꢀꢀA
d(H. . .A)
DHA
d(D. . .A)
Symmetry transformation for A
1
O9–H9OꢀꢀꢀO1
O10–H10OꢀꢀꢀO8
3
2.07(3)
2.08(3)
168(4)
162(4)
2.799(3)
2.790(3)
ꢂx + 1, ꢂy + 1, ꢂz
ꢂx + 3, ꢂy + 2, ꢂz – 1
O1–H1AꢀꢀꢀO5
O1–H1BꢀꢀꢀO2
O1W–H1WAꢀꢀꢀO6
O2–H2AꢀꢀꢀO6
O2–H2BꢀꢀꢀO3W
O2W–H2WBꢀꢀꢀO1
O3W–H3WAꢀꢀꢀO8
O3W–H3WBꢀꢀꢀO3
N2–H2 NꢀꢀꢀO4
1.794(19)
2.28
1.94(2)
1.82(2)
1.96(2)
1.89
2.16
1.95
1.65(2)
175(3)
174.5
173(9)
176(5)
167(5)
161.3
179.1
179.0
171(5)
2.652(4)
3.096(5)
2.800(6)
2.661(4)
2.795(6)
2.724(7)
3.009(7)
2.798(6)
2.547(5)
ꢂx, ꢂy, ꢂz
ꢂx, ꢂy, ꢂz ꢂ 1
x, y, z ꢂ 1
x, y ꢂ 1, z
x + 2, y ꢂ 1, z + 1
groups of the OHip ligands and the semi-ligating carboxylate oxy-
gen atoms serves to aggregate the [Co(OHip)(4-bpmp)]n layers into
the pseudo 3D crystal structure of 1. The topology of 1 also con-
trasts with the fourfold interpenetrated 66 diamondoid net seen
in its dpp analog [13].
4.3. Structural description of [Co(OMeip)(4-bpmp)]n (2)
The asymmetric unit of compound 2 contains a divalent cobalt
atom, a fully deprotonated OMeip ligand, and a 4-bpmp ligand. The
coordination environment about cobalt is a distorted {CoN2O4}

A.M. Pochodylo, R.L. LaDuca / Inorganica Chimica Acta 371 (2011) 71–78
75
Table 4
octahedron with pyridyl nitrogen donor atoms from two 4-bpmp
ligands situated trans to each other. A chelating carboxylate group
from an OMeip ligand occupies two of the equatorial sites, while cis
disposed single carboxylate oxygen atom from two different
OMeip ligands fill the remaining two equatorial positions. The
six-coordinate geometry about cobalt in 2 contrasts with the
‘‘5+1’’ square pyramidal environment in its OHip analog 1. Perti-
nent bond data for 2 is listed in Table 4.
The OMeip ligands bridge three cobalt atoms, like in 1, but in a
j4O,O0:O00:O000 ligating mode because of the chelation of one carbox-
ylate terminus. As in 1, the other carboxylate arm bridges two
cobalt atoms in an anti-syn manner to construct {Co2(OCO)2} di-
meric kernels, which have a CoꢀꢀꢀCo contact separation of 4.527 Å.
The slight decrease in CoꢀꢀꢀCo distance in 2 is ascribed to the chelat-
Bond length (Å) and angle (°) data for 2.
Co1–O5
2.015(2)
2.047(2)
2.149(2)
2.180(2)
2.192(3)
2.194(3)
104.54(9)
98.03(9)
156.63(8)
158.91(9)
96.29(8)
O2#2–Co1–O1#2
O5–Co1–N4
60.92(8)
89.09(9)
97.05(9)
89.22(9)
91.63(9)
88.80(9)
88.17(9)
86.28(9)
88.60(9)
174.71(10)
Co1–O4#1
Co1–O2#2
O4#1–Co1–N4
O2#2–Co1–N4
O1#2–Co1–N4
O5–Co1–N3#3
O4#1–Co1–N3#3
O2#2–Co1–N3#2
O1#2–Co1–N3#3
N4–Co1–N3#3
Co1–O1#2
Co1–N4
Co1–N3#3
O5–Co1–O4#1
O5–Co1–O2#2
O4#1–Co1–O2#2
O5–Co1–O1#2
O4#1–Co1–O1#2
Symmetry equivalent positions: #1 ꢂx, ꢂy + 1, ꢂz; #2 ꢂx, ꢂy + 2, ꢂz; #3 x + 1,
ꢂy + 3/2, z ꢂ ½.
Fig. 3. [Co(OMeip)]n ribbon in 2.
Fig. 4. (a) [Co(OMeip)(4-bpmp)]n coordination polymer layer in 2. (b) Schematic perspective of the underlying (3,6) grid topology of 2, with the dimeric {Co2(OCO)2}
connecting nodes represented as spheres.

76
A.M. Pochodylo, R.L. LaDuca / Inorganica Chimica Acta 371 (2011) 71–78
ing binding mode of the non-bridging carboxylate group, as op-
posed to the monodentate binding mode seen in the OHip deriva-
tive 1. The full span of the OMeip ligands connects neighboring
{Co2(OCO)2} dimers into 1D [Co(OMeip)]n ribbons (Fig. 3), which
are oriented parallel to the [0 1 0] crystal direction.
bpmp ligand protonated at its piperazinyl nitrogen atoms, an unli-
gated NO2ip dianion, and three water molecules of crystallization.
A {CoN2O4} coordination octahedron is present in 3, with trans pyr-
idyl nitrogen donor atoms from two H23-bpmp2+ ligands and four
aqua ligands. Bond lengths and angles within the coordination
sphere are consisted with octahedrally coordinated cobalt
(Table 5).
Parallel [Co(OMeip)]n ribbons are connected into [Co(OMeip)(4-
bpmp)]n 2D coordination polymer layers (Fig. 4a) by 4-bpmp
ligands that span a CoꢀꢀꢀCo through-ligand distance of 15.898 Å.
The H23-bpmp2+ ligands connect [Co(H2O)4]2+ fragments into
4nþ
Individual layers lie parallel to the (1 0 2) crystal planes. The
j
½CoðH2OÞ4ðH23-bpmpÞꢁn
coordination polymer chain motifs
angle between the pyridyl nitrogen atoms and the piperazinyl ring
centroid is 173.8°; this more open angle results in a slightly longer
CoꢀꢀꢀCo distance than seen in 1.
(Fig. 5a), with CoꢀꢀꢀCo contact distances of 13.594 Å. This distance
is much shorter than the related metal–metal contact distances
in 1 and 2, because of the kinked disposition of the 3-position pyr-
idyl nitrogen donors in the isomeric variant of 4-bpmp. The H23-
bpmp2+ ligands are restricted by crystallographic symmetry to
Similar to the pattern seen in 1, each {Co2(OCO)2} dimer con-
nects to two others along a single [Co(OMeip)]n ribbon. However,
in marked contrast to 1, 4-bpmp ligands connect each {Co2(OCO)2}
dimer to four others, two in each neighboring [Co(OMeip)]n ribbon.
Thus rarer (3,6) triangular grids (Fig. 4b) [37] are formed in 2, in
contrast to the (4,4) grids in 1. It is plausible that the increased ste-
ric bulk and lack of hydrogen-bonding ability of the methoxy sub-
stituent, in addition to the adjustment of carboxylate binding
mode, results in the significant change in underlying layer topol-
ogy between 1 and 2. A (3,6) triangular net is seen in [Co(ip)(4-
bpmp)]n, the unsubstituted analog of 2 [38], which also lacks
substituent induced hydrogen bonding. Adjacent [Co(OMeip)(4-
bpmp)]n layers stack in an AAA pattern along the a crystal direction
by crystal packing forces to generate the pseudo 3D structure of 2.
adopt an anti conformation (NꢀꢀꢀNꢀꢀꢀNꢀꢀꢀN dihedral angle = 180°).
4nþ
Parallel ½CoðH2OÞ4ðH23-bpmpÞꢁn
chains are organized into the
3D crystal structure of 3 by numerous hydrogen bonding pathways
involving unligated water molecules and NO2ip dianions (Fig. 5b).
A very similar chain motif was seen in {[Co(H2O)4(H23-bpmp)](1,3-
phda)2ꢀ8H2O}n (1,3-phda = 1,3-phenylenediacetate) [39], showing
a structural invariance to the nature of the unligated aromatic
dicarboxylate. The water molecules of crystallization in 3 occupy
15.0% of the unit cell volume, as determined with PLATON software
[40]. In contrast to two previously reported 2D cobalt coordination
polymers containing both NO2ip and dipyridine moieties, the
NO2ip ions do not engage in ligation in 3. It is plausible that the
surfeit of aqua ligands and water molecules of crystallization pro-
vide enough stability from supramolecular hydrogen bonding
pathways to prevent NO2ip ligation.
4.4. Structural description of {[Co(H2O)4(H23-bpmp)](NO2ip)2ꢀ6H2O}n
(3)
4.5. Variable temperature magnetic properties of 1 and 2
The asymmetric unit of compound 3 contains a cobalt atom on a
crystallographic inversion center, two aqua ligands, one-half of a 3-
Variable temperature magnetic data were recorded for poly-
crystalline samples of 1 and 2 in order to probe possible magnetic
superexchange within their respective {Co2(OCO)2} dimeric sub-
units. The phenomenological Rueff expression [41] (Eq. (1)) has
been successfully applied in the recent past to S = 3/2 dimers
[42]. This treatment is necessary because of the significant cooper-
ative effects of magnetic coupling (J) and single ion effects such as
zero-field splitting (D) on variable temperature magnetic behavior.
Table 5
Bond length (Å) and angle (°) data for 3.
Co1–O2#1
Co1–O2
2.109(3)
2.109(3)
2.115(3)
2.115(3)
2.145(3)
2.145(3)
O2–Co1–O1#1
O1–Co1–O1#1
O2#1–Co1–N1
O2–Co1–N1
94.28(13)
180.0
Co1–O1
88.44(13)
91.56(13)
91.06(12)
88.94(12)
91.56(13)
88.44(13)
88.94(12)
91.06(12)
Co1–O1#1
Co1–N1
O1–Co1–N1
Co1–N1#1
O1#1–Co1–N1
O2#1–Co1–N1#1
O2–Co1–N1#1
O1–Co1–N1#1
O1#1–Co1–N1#1
v
mT ¼ A expðꢂD=kTÞ þ B expðJ=kTÞ; where A þ B þ C
O2#1–Co1–O2
O2#1–Co1–O1
O2–Co1–O1
O2#1–Co1–O1#1
180.0(2)
¼ ð5 Ng2b2=4kÞ
ð1Þ
94.28(13)
85.72(13)
85.72(13)
The best-fit values to Eq. (1) for the (4,4) grid topology OHip
coordination polymer 1 (Fig. 6a) were A = 1.06(4) cm3 K mol Coꢂ1
and B = 2.39(2) cm3 K mol Coꢂ1 giving g = 2.71(4), J = 0.32(3) cmꢂ1
Symmetry equivalent position: #1 ꢂx, ꢂy, ꢂz.
4nþ
Fig. 5. (a) ½CoðH2OÞ4ðH23-bpmpÞꢁn
coordination polymer chain in 3. (b) Stacking of chains in 3 via unligated NO2ip dianions and water molecules.

A.M. Pochodylo, R.L. LaDuca / Inorganica Chimica Acta 371 (2011) 71–78
77
5. Conclusions
The hydrogen-bonding capability of 5-position substituents on
isophthalate ligands appears to dictate topology during self-assem-
bly of divalent cobalt coordination polymers containing neutral
bis(pyridylmethyl)piperazine ligands. In both OHip and OMeip
cases, one-dimensional ‘‘infinite’’ [Co(dicarboxylate)]n ribbons
with embedded {Co2(OCO)2} dimeric kernels are formed. However,
the hydroxy group of the OHip ligands engages in hydrogen bond-
ing to an OHip carboxylate group in another coordination polymer
layer, enforcing adjustment of carboxylate binding mode. In turn a
conformational change in the 4-bpmp ligand results in each
{Co2(OCO)2} dimer acting as a 4-connected note. In the case of
the OMeip ligand, hydrogen bonding donation on the part of the
5-position substituent is no longer possible. The supramolecular
environment then more closely resembles that of the unsubstitut-
ed isopththalate ligand despite the added steric hindrance, result-
ing in a (3,6) triangular net with {Co2(OCO)2} dimers serving as
6-connected nodes. Because of their common {Co2(OCO)2} dimeric
units, both the OHip derivative 1 and OMeip derivative 2 display
similar cooperativity between single-ion effects and weak carbox-
ylate-mediated ferromagnetism. Both 1 and 2 and their unsubsti-
tuted isophthalate analog possess 2D topologies. In contrast,
compound 3 adopts a 1D chain motif, likely because of the differ-
ent nitrogen donor disposition within the 3-bpmp ligand.
Acknowledgements
The authors gratefully acknowledge the donors of the American
Chemical Society Petroleum Research Fund for financial support of
this work. We thank Mr. Chaun I.B. Gandolfo for acquiring the
infrared spectra.
Appendix A. Supplementary material
CCDC 793894, 793892, and 793893 contain the supplementary
crystallographic data for 1, 2, and 3. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.03.009.
Fig. 6. Variable temperature magnetic plots for (a) 1 and (b) 2. The best-fit to the
Rueff phenomenological expression (Eq. (1)) is shown as a thin line in each graph.
and
D = 52(5) cmꢂ1
,
with
R = 3.1 ꢄ 10ꢂ3 = {
R
[(v
mT)obs
ꢂ
(v
mT)calc]2/ mT)obs]2}). The decrease in
R[(v vmT product between
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