One-dimensional nickel and cobalt phthalate coordination polymers incorporating the kinked dipodal organodiimine 4,4′-dipyridylamine: Hydrothermal synthesis, structural characterization and thermal properties

Article abstract of DOI:10.1016/j.ica.2006.12.004

Hydrothermal synthesis has afforded a family of three structurally related metal phthalate (pht) 1-D coordination polymers incorporating the kinked dipodal organodiimine 4,4′-dipyridylamine (dpa), with a general formulation of [L₂M(dpa)₂M(H₂O)₄] · H₂O (L = pht, M = Co, 1, M = Ni, 2; L = 4-methylphthalate (4-mpht), M = Co, 3). Single crystal X-ray diffraction of 1 and 2 revealed the presence of one-dimensional (1-D) polymeric chains consisting of [M(H₂O)₄]²⁺ and [M(pht)₂]^2- subunits linked through dpa tethers. These chains in turn conjoin into pseudo 2-D layers and 3-D networks via extensive supramolecular hydrogen bonding pathways. An extremely similar structure is observed for 3 despite the presence of the bulkier methyl group substituent. 1-3 were further characterized via infrared spectroscopy and elemental and thermogravimetric analysis. 1-3 represent the first dicarboxylate coordination polymers incorporating dpa tethering ligands.

Full text of DOI:10.1016/j.ica.2006.12.004

Inorganica Chimica Acta 360 (2007) 2353–2362
www.elsevier.com/locate/ica
One-dimensional nickel and cobalt phthalate coordination
polymers incorporating the kinked dipodal organodiimine
0
4
,4 -dipyridylamine: Hydrothermal synthesis,
structural characterization and thermal properties
a
b
a,
*
Maxwell A. Braverman , Ronald M. Supkowski , Robert L. LaDuca
a
Lyman Briggs School of Science, Department of Chemistry, E-30 Holmes Hall, Michigan State University, East Lansing, MI 48825, USA
b
Department of Chemistry and Physics, King’s College, Wilkes-Barre, PA 18711, USA
Received 2 November 2006; received in revised form 1 December 2006; accepted 1 December 2006
Available online 13 December 2006
Abstract
Hydrothermal synthesis has afforded a family of three structurally related metal phthalate (pht) 1-D coordination polymers incorpo-
0
rating the kinked dipodal organodiimine 4,4 -dipyridylamine (dpa), with a general formulation of [L M(dpa) M(H O) ] Æ H O (L = pht,
2
2
2
4
2
M = Co, 1, M = Ni, 2; L = 4-methylphthalate (4-mpht), M = Co, 3). Single crystal X-ray diffraction of 1 and 2 revealed the presence of
2
+
2ꢀ
one-dimensional (1-D) polymeric chains consisting of [M(H
2
O)
4
]
and [M(pht) ] subunits linked through dpa tethers. These chains in
2
turn conjoin into pseudo 2-D layers and 3-D networks via extensive supramolecular hydrogen bonding pathways. An extremely similar
structure is observed for 3 despite the presence of the bulkier methyl group substituent. 1–3 were further characterized via infrared spec-
troscopy and elemental and thermogravimetric analysis. 1–3 represent the first dicarboxylate coordination polymers incorporating dpa
tethering ligands.
ꢀ
2006 Elsevier B.V. All rights reserved.
Keywords: Coordination polymer; Phthalate; Cobalt; Nickel; Dipyridylamine; Crystal structure; Thermogravimetric analysis
1
. Introduction
range of structural motifs occurs in these systems, predi-
cated on the disposition of the donor groups within the
dicarboxylate moieties, coordination geometry preferences,
and an array of available binding carboxylate modes. A
remarkable 26 distinct binding modes have been observed
in coordination polymers bearing the phthalate (pht, 1,2-
benzenedicarboxylate) dianion [6]. More recently, elabora-
tion of dicarboxylate-containing inorganic/organic hybrid
materials has been achieved through the incorporation of
neutral organodiimine tethering ligands such as the rigid-
Over the past decade many researchers have undertaken
significant effort towards the synthesis and characterization
of metal dicarboxylate and tricarboxylate coordination
polymers because of the burgeoning capability of these
materials in gas storage [1], small molecule shape-selectivity
[
2], ion-exchange [3], catalysis [4], and optical properties [5].
In these phases dianionic dicarboxylate ligands not only
serve to link metal cations into higher dimensionalities
but also provide necessary charge balance, thereby permit-
ting formation of a wide variety of neutral coordination
polymer frameworks without concomitant incorporation
of porosity-curtailing smaller anions. An extremely diverse
0
0
rod 4,4 -bipyridine (4,4 -bpy), which can connect metal cat-
ions through its distal pyridyl nitrogen donor atoms into a
host of structurally intriguing solids with potentially useful
properties [7–10]. For example, the 2-D layered phase
0
[
Zn O(isophthalate) (4,4 -bpy)] manifested intense blue
4
3
0
*
luminescence [8], [Fe(2,5-pyridyldicarboxylate)(4,4 -bipy)] Æ
Corresponding author.
E-mail address: laduca@msu.edu (R.L. LaDuca).
H O displayed reversible solvent absorptive behavior [9],
2
0
020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.12.004

2354
M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
and the interpenetrated 3-D material [Zn(terephthal-
ate)(4,4 -bpy)0.5] exhibited a remarkable ability to chro-
were added to 10 mL of distilled H O in a 23 mL Teflon
2
0
lined Parr acid digestion bomb. The bomb was sealed,
heated to 120 ꢁC for 43 h, and then gradually cooled to
23 ꢁC. Light pink prisms of 1 (145 mg, 89% yield based
on Co) were obtained after filtration, washing with distilled
water and acetone, and drying in air. Crystals of 1 were sta-
ble indefinitely in air. Anal. Calc. for C H Co N O (1):
matographically separate linear and branched alkanes [10].
For some time we have been interested in the synthesis
and characterization of coordination solids containing the
0
0
organodiimine 4,4 -dipyridylamine (dpa). Unlike 4,4 -bpy,
dpa possesses a kinked disposition of its terminal nitrogen
donor atoms as well as a hydrogen bonding locus at its cen-
tral secondary amine subunit that can promote the forma-
tion of novel structural patterns. Neighboring dpa entities
can also interact with each other or with other aromatic
subunits through supramolecular p–p stacking interac-
tions. Prior results from our laboratory have shown that
combination of dpa with appropriate metal oxide precur-
sors under hydrothermal conditions can result in the con-
struction of extended solids with diverse structural motifs
3
6
36
2
6
13
C, 49.21; H, 4.13; N, 9.57. Found: C, 49.00; H, 3.95; N,
ꢀ1
9.38%. IR (KBr, cm ): 3254 br vs, 3166 br vs, 1949 w,
1853 w, 1604 s, 1589 s, 1550 s, 1520 s, 1478 m, 1443 m,
1401 s, 1351 m, 1328 m, 1210 m, 1083 w, 1064 w, 1022
m, 972 w, 903 w, 861 w, 827 m, 815 w, 769 m, 731 m,
700 m, 654 m, 593 m, 536 m, 440 w.
2.3. Preparation of [Ni (pht) (H O) (dpa) ] Æ H O (2)
2
2
2
4
2
2
0
[
11–13]. [M(Hdpa) V O ] (M = Co, Ni) manifests 2-D
NiCl Æ 6H O (88 mg, 0.37 mmol), 4,4 -dipyridylamine
2 2
2
4
12
metal oxide layers consisting of serpentine 1-D anionic
(127 mg, 0.74 mmol) and phthalic acid (62 mg, 0.37 mmol)
2
+
vanadate chains linked through protonated [M(Hdpa)2]
cationic subunits [11]. [NiMoO (dpa) ] displays a striking
were added to 10 mL of distilled H O in a 23 mL Teflon
2
lined Parr acid digestion bomb. The bomb was sealed,
heated to 120 ꢁC for 92 h and then gradually cooled to
23 ꢁC. Green prisms of 2 (110 mg, 68% yield based on
Ni) were obtained after filtration, washing with distilled
water and acetone, and drying in air. Crystals of 2 were sta-
ble indefinitely in air. Anal. Calc. for C H Ni N O (2):
4
2
3
-D starburst network comprised of nickel molybdate 1-
D chains tethered by neutral dpa moieties, assisted by
hydrogen bonding between the central N–H subunit of
the ligands and molybdate oxygen atoms in neighboring
chains [12]. [Mo O (Hdpa) ], whose structure contains
4
13
2
36 36
2
6
13
hydrogen bonded, interdigitated 1-D molybdate chains,
was shown to intercalate primary and secondary amines
C, 49.24; H, 4.13; N, 9.57. Found: C, 48.89; H, 3.86; N,
ꢀ1
9.36%. IR (KBr, cm ): 3454 br vs, 3248 br vs, 1945 w,
1849 w, 1746 w, 1719 w, 1704 m, 1692 m, 1646 m, 1638
s, 1596 s, 1581 s, 1550 s, 1520 s, 1483 m, 1435 m, 1397 s,
1350 m, 1215 m, 1095 w, 1064 w, 1018 w, 953 w, 899 w,
876 w, 857 w, 834 w, 830 w, 815 w, 765 w, 650 w, 589 w,
535 w, 504 w, 432 w.
[
13]. Herein we report the first extension of our explora-
tions of dpa-containing extended solids into a dicarboxy-
late system with the hydrothermal synthesis and
characterization of three hydrated divalent metal phthalate
(
pht) and 4-methylphthalate (4-mpht) coordination poly-
mers. Thermal properties of these new materials are also
discussed.
2.4. Preparation of [Co (4-mpht) (H O) (dpa) ] Æ H O
2
2
2
4
2
2
(
3)
2
. Experimental
0
CoCl Æ 6H O (88 mg, 0.37 mmol), 4,4 -dipyridylamine
2
2
2
.1. General considerations
(127 mg, 0.74 mmol) and 4-methylphthalic acid (65 mg,
.37 mmol) were added to 10 mL of distilled H O in a
0
2
CoCl Æ 6H O, NiCl Æ 6H O (Fisher), phthalic acid and
23 mL Teflon lined Parr acid digestion bomb. The bomb
was sealed, heated to 120 ꢁC for 44 h, and then gradually
cooled to 23 ꢁC. Light pink plates of 3 (90 mg, 54% yield
based on Co) were obtained after filtration, washing with
distilled water and acetone, and drying in air. Crystals of
2
2
2
2
4
-methylphthalic acid (Aldrich) were obtained commer-
0
cially. 4,4 -dipyridylamine (dpa) was prepared via a pub-
lished procedure [13]. Water was deionized above 3 MX
in-house. 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. IR spectra were recorded on a Matt-
son Galaxy FTIR Series 3000 using KBr pellets. Powder X-
ray diffraction on ground samples of 1–3 for phase purity
verification were obtained via H–2H scans performed on
a Rigaku Rotaflex instrument.
3
were stable indefinitely in air. Anal. Calc. for
C H Co N O (3): C, 50.34; H, 4.48; N, 9.27. Found:
3
8
40
2
6
13
ꢀ
1
C, 50.12; H, 4.09; N, 9.22%. IR (KBr, cm ): 3234 s,
3155 s, 2992 m, 2364 w, 1937 w, 1600 s, 1546 s, 1521 s,
1437 m, 1397 s, 1349 m, 1208 m, 1158 w, 1085 w, 1064
w, 1019 m, 899 w, 853 m, 825 m, 795 m, 770 m, 732 m,
675 m, 640 m, 591 m, 531 m, 448 m.
3. X-ray crystallography
2
.2. Preparation of [Co (pht) (H O) (dpa) ] Æ H O (1)
2 2 2 4 2 2
A light pink prism of 1 (0.35 mm · 0.30 mm · 0.15 mm),
a light green prism of 2 (with dimensions 0.74 mm · 0.28
mm · 0.18 mm), and a pink plate of 3 (0.60 mm · 0.50
0
CoCl Æ 6H O (88 mg, 0.37 mmol), 4,4 -dipyridylamine
2
2
(
127 mg, 0.74 mmol) and phthalic acid (62 mg, 0.37 mmol)

M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
2355
mm · 0.05 mm) were subjected to single crystal X-ray dif-
4. Results and discussion
fraction using a Bruker-AXS SMART 1k CCD instrument.
Reflection data were acquired using graphite-monochro-
mated Mo Ka radiation (k = 0.71073 A). The data were
4.1. Synthesis and spectral characterization
˚
integrated via SAINT [14]. Lorentz and polarization effect
and empirical absorption corrections were applied with
SADABS [15]. The structures were solved using direct meth-
The coordination polymers 1–3 were prepared cleanly
under hydrothermal conditions via combination of a
hydrated cobalt (1, 3) or nickel (2) chloride, phthalic acid
2
0
ods and refined on F using SHELXTL [16]. All non-hydrogen
(1, 2) or 4-methylphthalic acid (3), and 4,4 -dipyridylamine.
atoms were refined anisotropically. Hydrogen atoms bound
to carbon atoms were placed in calculated positions and
refined isotropically with a riding model. The hydrogen
atoms bound to the central nitrogen of the dpa moieties
and all aquo ligands in 1–3 were found via Fourier differ-
ence maps, restrained at fixed positions, and then refined
isotropically with thermal parameters 1.2 times the average
Attempts to prepare a dpa-containing phthalate coordina-
tion polymer with divalent cadmium salts resulted in the
formation of the known layered orthorhombic phase
[Cd(pht)(H O)] [5c]. No tractable materials resulted from
2
several attempts to prepare zinc analogues to 1–3. The
infrared spectra of 1–3 were fully consistent with their for-
mulations. Sharp, medium intensity bands in the range of
ꢀ
1
U values of the atoms to which they are bound. The crys-
ꢁ1600 to ꢁ1200 cm were ascribed to stretching modes
of the pyridyl rings of the dpa moieties [17]. Features cor-
responding to pyridyl ring puckering mechanisms were evi-
ij
tallographically disordered unligated water molecule posi-
tions in 1 and 2 were modeled using partial occupancies.
Hydrogen atoms on waters of crystallization could not be
found for 1 and 2. Relevant crystallographic data for 1–3
are listed in Table 1.
ꢀ
1
dent in the region between 800 and 600 cm . Asymmetric
and symmetric C–O stretching modes of the phthalate car-
boxylate moieties were evidenced by very strong, slightly
Table 1
Crystal and structure refinement data for 1–3
Data
1
2
3
Empirical formula
Formula weight
Collection T (K)
C
878.58
293(2)
36
H
36
N
6
Co O
2 13
C
878.10
173(2)
36
H
36
N
6
Ni
2
O
13
38 2 6 13
C H42Co N O
908.65
293(2)
0.71073
˚
k (A)
0.71073
0.71073
Crystal system
Space group
a (A)
monoclinic
C2/c
19.177(8)
13.655(5)
15.808(6)
90
116.98(7)
90
3689(3)
4
monoclinic
C2/c
19.162(6)
13.386(4)
15.951(5)
90
115.220(5)
90
3701(2)
4
monoclinic
C2/c
19.899(12)
13.332(8)
16.054(10)
90
114.437(9)
90
3877(4)
4
˚
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
˚
3
V (A )
Z
ꢀ3
D
calc (g cm
)
1.578
0.975
1.572
1.093
1.553
0.931
ꢀ
1
l (mm
)
Minimum/maximum
transmission
0.889
0.82
0.798
hkl ranges
ꢀ21 6 h 6 25, ꢀ17 6 k 6 18,
ꢀ24 6 h 6 24, ꢀ17 6 k 6 17,
ꢀ25 6 h 6 26, ꢀ 17 6 k 6 17,
ꢀ
19 6 l 6 20
ꢀ 21 6 l 6 21
21778
ꢀ 20 6 l 6 20
20949
Total reflections
Unique reflections
R(int)
12548
4363
0.0327
289/7
0.0612
0.0446
0.1094
0.1023
0.963/ꢀ0.536
4467
0.0208
289/7
0.0404
0.0330
0.0967
0.0913
0.917/ꢀ0.320
4464
0.0470
288/8
0.0789
0.0487
0.1274
0.1147
1.155/ꢀ0.527
Parameters/restraints
a
R
R
1
(all data)
1
(I> 2r(I))
b
wR
wR
2
(all data)
2
(I > 2r(I))
Maximum/minimum residual
ꢀ
˚
3
(
e /A )
Goodness-of-fit (GOF)
1.076
1.068
1.059
P
P
a
R1 ¼
jjF oj ꢀ jF cjj= jF oj:
P
P
b
2
2
c
2
2
2 1=2
o
wR2 ¼ f½wðF o ꢀ F Þ ꢂ= ½wF ꢂ g
:

2356
M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
ꢀ
1
broadened bands at ꢁ1600 and ꢁ1520 cm . Broad bands
The resulting [CoO N ] coordination octahedra in 1 display
4 2
ꢀ1
in the region of ꢁ3400 to ꢁ3200 cm in all cases represent
N–H stretching modes within the dpa ligands and O–H
stretching modes within water molecules of crystallization.
The broadness of these latter spectral features is caused by
significant hydrogen bonding pathways within 1–3.
standard bond lengths and angles. The asymmetric unit of 2
is virtually identical but with slightly shorter bond lengths,
consistent with well-established ionic radius trends [20].
Table 2
˚
Selected bond distance (A) and angle (ꢁ) data for 1–2
4
[
.2. Structural description of
M (pht) (dpa) (H O) ] Æ H O (1, M = Co; 2, M = Ni)
1
2
2
2
2
2
4
2
Co1–O6 (·2)
Co1–N1 (·2)
Co1–O5 (·2)
Co2–O4 (·2)
Co2–O1 (·2)
Co2–N2 (·2)
O1–C17
O2–C18
O3–C17
O4–C18
2.0362(19)
2.141(2)
2.175(2)
2.053(2)
2.1186(19)
2.168(2)
1.274(3)
1.245(3)
1.247(4)
1.259(3)
Ni1–O6 (·2)
Ni1–N2 (·2)
Ni1–O5 (·2)
Ni2–O1 (·2)
Ni2–O2 (·2)
Ni2–N1 (·2)
O1–C17
O2–C18
O3–C17
O4–C18
2.0405(15)
2.0924(17)
2.1097(15)
2.0362(16)
2.0819(15)
2.1001(18)
1.255(2)
1.271(3)
1.256(3)
1.244(3)
1
and 2 are isomorphous, both crystallizing in the mono-
clinic space group C2/c and possessing an asymmetric unit
consisting of two metal atoms sited on inversion centers,
one phthalate (pht) anion, one dpa ligand, two bound aquo
ligands and two crystallographically disordered (quarter-
occupied) water molecules of crystallization, one of which
(
O2W) is situated on a crystallographic two-fold axis. The
asymmetric unit of 1 along with symmetry equivalent atoms
is displayed in Fig. 1. One of the cobalt atoms (Co2) is
ligated by two bidentate phthalate dianions in chelating
#
1
#1
O6 –Ni1–O6
O6–Co1–O6
O6–Co1–N1
180.00(17)
91.73(8)
88.27(8)
180.00(13)
91.81(8)
88.19(8)
89.07(8)
90.93(8)
180.00(12)
180.00(8)
91.08(8)
88.92(8)
180.00(13)
93.08(8)
86.92(8)
89.05(7)
90.95(7)
180.0
180.00(8)
#1
#1
O6 –Ni1–N2
90.60(7)
89.40(7)
180.00(11)
87.12(6)
92.88(6)
90.28(7)
89.72(7)
180.00(8)
180.00(16)
89.48(7)
90.52(7)
180.00(6)
93.53(7)
86.47(7)
88.63(6)
91.37(6)
180.00(11)
121.4(2)
120.6(2)
117.99(19)
124.23(19)
O6–Co1–N1
N1 –Co1–N1
O6–Co1–O5
O6 –Co1–O5
N1 –Co1–O5
N1–Co1–O5
O6–Ni1–N2
2
ꢀ
#1
#1
1
,6-coordination mode to form an ‘‘X-shaped’’ [Co(pht)2]
N2–Ni1–N2
#
1
O6 –Ni1–O5
O6–Ni1–O5
N2–Ni1–O5
subunit. This monometallic bidentate binding mode of the
phthalate dianions, resulting in seven-membered Co–O–
C–C–C–C–O rings, is relatively uncommon [6], but it is sim-
#
1
#
1
#1
N2 –Ni1–O5
2
ꢀ
#
1
#1
ilar to that observed in the C -symmetric [Be(pht) ] anion
[
2
2
O5 –Co1–O5
O4 –Co2–O4
O5–Ni1–O5
4
+
#3
#2
18] and in a neutral Ti complex [19]. Due to the steric
O1 –Ni2–O1
O1 –Ni2–O2
#
3
#2
O4 –Co2–O1
O4–Co2–O1
requirements imposed by chelation, the two oxygen donor
atoms of type O1 and O4 belonging to a single phthalate
ligand are cis-disposed. The carboxylate moiety marked
by C17, O1 and O2 is twisted by ꢁ34ꢁ relative to the aro-
matic ring of the phthalate ligand. In order to achieve an
appropriate geometry for chelation, the second carboxylate
subunit (delineated by C18, O3 and O4) is tilted to a much
greater extent (ꢁ74ꢁ). The other cobalt atom (Co1) pos-
sesses four aquo ligands, thereby forming a cationic
O1–Ni2–O2
#
3
#2
O1–Co2–O1
O2–Ni2–O2
#3
#2
O4 –Co2–N2
O4–Co2–N2
O1–Co2–N2
O1 –Ni2–N1
O1–Ni2–N1
O2–Ni2–N1
#
3
#2
O1 –Co2–N2
O2 –Ni2–N1
#
3
#2
N2–Co2–N2
O2–C17–O1
N1–Ni2–N1
124.4(2)
116.9(2)
118.4(2)
121.7(3)
O1–C17–O3
O1–C17–C12
O3–C17–C12
O4–C18–O2
O2–C17–C16
O1–C17–C16
O3–C18–O4
2
+
[
Co(H O) ] moiety. The coordination spheres about both
2 4
types of cobalt atoms are filled out by pyridyl nitrogen
donors from two dpa ligands oriented in a transoid fashion.
Symmetry transformations to generate equivalent atoms: (#1) ꢀx, ꢀy + 1,
ꢀz; (#2) ꢀx ꢀ 1/2, ꢀy ꢀ 1/2, ꢀz; (#3) ꢀx + 1/2, ꢀy + 3/2, ꢀz.
Fig. 1. The asymmetric unit of 1 with thermal ellipsoids (50% probability) and atom numbering scheme. Complete coordination environments are shown.
Hydrogen atoms bound to C and disordered water molecules of crystallization are omitted for clarity.

M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
2357
Fig. 2. The 1-D chain polymeric motif in 1 and 2. Most hydrogen atoms have been omitted for clarity.
Selected bond lengths and bond angle parameters for 1 and
eties, perhaps induced by steric constraints within and
between the 1-D polymeric chains.
2
are located in Table 2.
The structures of 1 and 2 extend into one-dimensional
The 1-D subunits in 1 and 2 aggregate into pseudo 2-D
layers coincident with the ab crystal plane via two distinct
supramolecular hydrogen bonding pathways (Fig. 3).
Ligated carboxylate oxygens (O1) in one chain accept
hydrogen bonds from bound aquo ligands (at H5A) in a
neighboring chain. The second type of aquo ligand,
marked by O6 and disposed in a cisoid orientation relative
to O5, donates hydrogen bonds to an unligated carboxylate
oxygen atom belonging to a phthalate moiety in an adja-
cent chain. A virtually identical hydrogen bonding scheme
between coordinated water molecules and unligated phtha-
late carboxylate oxygen atoms has been seen previously in
the 1-D coordination polymers [M(pht)(4-methylimidaz-
ole) (H O)] (M = Co, Cu) [22]. The through-space Co–
2
ꢀ
(
[
1-D) chains via the connection of [M(pht) ]
and
2
2
+
M(H O) ] subunits through tethering dpa ligands, as
2
4
seen in Fig. 2 for 1. It is plausible that the supramolecular
hydrogen bonding (vide infra) imparted by the dpa ligands
in 1 and 2 prevents the unligated phthalate oxygen atoms
from acting as donor ligands to metal atoms. A non-bridg-
ing chelating binding mode of the phthalate ligands is
therefore enforced, contrasting with the bridging/chelating
phthalate moieties observed within the 2-D layered phase
0
[
Ni(pht)(4,4 -bpy)(H O)] Æ 3H O [21]. As a result, only the
2
2
dpa ligands are able to covalently link neighboring metal
ions, fomenting the 1-D coordination polymeric structures
of 1 and 2.
2
2
˚
The distance between neighboring Co atoms within the
Co distance (ꢁ5.9 A) between juxtaposed chain motifs in
˚
˚
chain motifs of 1 is ꢁ11.3 A, with the corresponding dis-
1 (ꢁ0.1 A longer than in 2) is significantly shorter than
˚
tance between adjacent Ni atoms in 2 ꢁ0.2 A shorter.
the metal–metal distance within the polymeric chains.
Neighboring pseudo 2-D layers further connect into the
full 3-D structures of 1 and 2 by means of alternative hydro-
gen bonding mechanisms (Fig. 4). The central N–H subunit
of the dpa moieties within one layer are hydrogen bonded to
unligated phthalate carboxylate oxygen atoms of type O2 in
the next layer. In addition, the unligated oxygen atoms
The kinked nitrogen donor dispositions imparts a ꢁ70ꢁ tilt
between neighboring metal coordination octahedra, which
in turn inculcates the marked undulations in the polymeric
chains within 1 and 2. A marked torsional twist (ꢁ96ꢁ for
1
, ꢁ88ꢁ for 2, as measured by the dihedral angle C2–C3–
C8–C7) is evident between the pyridyl rings of the dpa moi-
Fig. 3. Hydrogen bonding interactions (shown as dashed lines) between 1-D chain motifs in 1.

2358
M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
Fig. 4. Stacking of neighboring pseudo 2-D layers in 1. Hydrogen bonding interactions are shown as dashed lines.
belonging to different phthalate anions (O3) accept hydro-
gen bonds from the ligated aquo ligands (O6) in adjacent
lamellar motifs. The aggregation into layers is further
enhanced through p–p stacking between one type of pyridyl
ring within a dpa ligand and a phthalate aromatic ring in the
down the c crystal axis reveals incipient rhomboidal chan-
nels bearing crystallographically disordered water mole-
cules of crystallization. As calculated by the PLATON
software program [23], the small solvent-accessible void
spaces within 1 and 2 are 3.4% and 3.3% of the total unit cell
volume, respectively. The water molecules of crystallization
are held into the coordination polymer matrix through
hydrogen bonding to unligated phthalate oxygen atoms
and bound aquo ligands. Hydrogen bonding contact
parameters for 1 and 2 are listed in Table 3.
˚
next layer (ꢁ3.5 to ꢁ4.0 A) (Fig. 5). Juxtaposed pseudo 2-D
layers are offset from each other in order to maximize the
both the hydrogen bonding and p–p stacking supramolecu-
lar interactions. The interlayer through-space M-M separa-
˚
tions in 1 and 2 are ꢁ 8.0 A. Examination of the structure
Fig. 5. View down c of 1 illustrating p–p stacking between phthalate and pyridyl aromatic rings in adjacent pseudo 2-D layers. Water molecules of
crystallization are shown. Hydrogen atoms have been omitted for clarity.

M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
2359
Table 3
Hydrogen bonding distance (A) and angle (ꢁ) data for 1–3
˚
D–H
d(Hꢃ ꢃ ꢃA)
\DHA
d(Dꢃ ꢃ ꢃA)
Symmetry transformation for A
1
O5–H5Aꢃ ꢃ ꢃO1
O5–H5Bꢃ ꢃ ꢃO1WA
O5–H5Bꢃ ꢃ ꢃO1WB
O5–H5Bꢃ ꢃ ꢃO3
O6–H6Aꢃ ꢃ ꢃO2
O6–H6Bꢃ ꢃ ꢃO3
N3–H3Nꢃ ꢃ ꢃO2
1.908
2.212
2.231
2.484
1.895
1.800
2.166
171.10
148.64
142.12
134.58
172.52
167.15
163.49
2.735
2.958
2.937
3.128
2.755
2.597
3.011
ꢀx + 1/2, ꢀy + 1/2, ꢀz
ꢀx + 1, y ꢀ 1, ꢀz + 1/2
x + 1/2, y ꢀ 1/2, z
ꢀx + 1, y ꢀ 1, ꢀz + 1/2
ꢀx + 1/2, y ꢀ 1/2, ꢀz + 1/2
2
O5–H5Aꢃ ꢃ ꢃO2
O5–H5Bꢃ ꢃ ꢃO1WA
O5–H5Bꢃ ꢃ ꢃO1WB
O6–H6Aꢃ ꢃ ꢃO4
O6–H6Bꢃ ꢃ ꢃO3
N3–H3Nꢃ ꢃ ꢃO4
1.885
2.065
2.009
1.909
1.786
2.162
176.36
149.76
158.19
176.72
175.07
159.95
2.735
2.814
2.798
2.769
2.614
2.992
ꢀx ꢀ 1/2, ꢀy + 1/2, ꢀz
x + 1/2, y + 1/2, z
ꢀx, y + 1, ꢀz + 1/2
ꢀx ꢀ 1/2, y + 1/2, ꢀz + 1/2
3
O1–H1WBꢃ ꢃ ꢃO3
O5–H5Bꢃ ꢃ ꢃO1W
O5–H5Aꢃ ꢃ ꢃO1
O6–H6Aꢃ ꢃ ꢃO4
O6–H6Bꢃ ꢃ ꢃO3
N3–H3Nꢃ ꢃ ꢃO4
1.988
2.201
1.919
1.956
1.804
2.110
155.56
158.78
175.07
170.87
164.91
162.16
2.779
3.002
2.769
2.800
2.626
2.962
x, y + 1, z
ꢀx + 1/2, ꢀy ꢀ 1/2, ꢀz
x + 1/2, y + 1/2, z
ꢀx + 1, y + 1, ꢀz + 1/2
ꢀx + 1/2, y + 1/2, ꢀz + 1/2
2
+
2ꢀ
4
.3. Structural description of [Co (4-mpht) (dpa) -
2
2, neighboring [Co(H O) ] and [Co(4-mpht)2] subunits
2
2
2
4
(
H O) ] Æ H O (3)
connect via dpa tethers, forming a 1-D polymeric chain.
The methyl groups on the 4-mpht moieties bound to Co2
project into the empty regions above and below the dpa
ligands that join to both adjacent Co1 atoms, perhaps ste-
rically inducing the narrowing of the inter-ring torsion
angles within the dpa ligands (ꢁ59ꢁ). The dpa-bridged
2
4
2
As seen in Fig. 6, the asymmetric unit of 3 is very similar
to that of 1 and 2, except for the addition of the pendant
methyl substituent at the 4-position on each phthalate ring.
All bond lengths and angles are consistent with octahedral
coordination at divalent cobalt (Table 4). Similar to 1 and
˚
Co–Co distance is 11.2 A, very slightly shorter than in 1.
Fig. 6. The asymmetric unit of 3 with thermal ellipsoids (50% probability) and atom numbering scheme. Complete coordination environments are shown.
Hydrogen atoms bound to C are omitted for clarity.

2360
M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
Table 4
Selected bond distance (A) and angle (ꢁ) data for 3
network, resulting in the formation of incipient rhomboidal
cavities containing water molecules of crystallization
(Fig. 7), which lie on the crystallographic twofold rotation
axes. These cavities are splayed open to a slightly greater
extent as compared with 1 and 2, likely in response to the
steric requirements imposed by the methyl groups. Despite
this, the size of the solvent-accessible void space within the
structure of 3, 0.8% of the unit cell volume, is over four
times smaller than the corresponding voids in the phthalate
congeners 1 and 2. This void shrinkage could presumably
be the origin of the lack of crystallographic disorder in
the water molecules of crystallization in 3. On the whole,
while some minor structural differences are noted, the 4-
methyl substituents on the phthalate subunits in 3 do not
demonstrably alter the coordination polymer chain motifs
or their supramolecular aggregation in the present case.
˚
Co1–O6 (·2)
Co1–N1 (·2)
Co1–O5 (·2)
Co2–O2 (·2)
Co2–O1 (·2)
Co2–N2 (·2)
O1–C17
O2–C18
O3–C18
O4–C17
2.064(2)
2.108(3)
2.184(2)
2.041(2)
2.118(2)
2.163(3)
1.268(4)
1.249(4)
1.257(4)
1.242(4)
N1–Co1–O5
N1 –Co1–O5
91.51(11)
88.49(11)
180.00(13)
180.00(12)
90.07(10)
89.93(10)
180.00(12)
86.70(10)
93.30(10)
87.66(9)
92.34(9)
180.00(14)
123.8(3)
121.8(3)
120.5(3)
#1
#
1
O5–Co1–O5
O2–Co2–O2
O2–Co2–O1
#2
#2
O2 –Co2–O1
#2
O1–Co2–O1
O2–Co2–N2
#2
O2 –Co2–N2
O1–Co2–N2
#2
O1 –Co2–N2
#
1
#2
O6 –Co–O6
180.0(2)
N2–Co2–N2
#
1
O6 –Co1–N1
O6–Co1–N1
91.36(11)
88.64(11)
180.00(17)
86.45(10)
93.55(10)
O4–C17–O1
O2–C18–O3
O2–C18–C16
O3–C18–C16
#
1
N1–Co1–N1
#
1
O6 –Co1–O5
O6–Co1–O5
117.6(3)
Symmetry transformations to generate equivalent atoms: (#1) ꢀx, ꢀy +
, ꢀz; (#2) ꢀx + 1/2, ꢀy ꢀ 3/2, ꢀz.
4.4. Thermal analysis of 1–3
1
In order to ascertain their thermal stability, 1–3 were
The torsion angles between the carboxylate groups and the
subjected to thermogravimetric analysis under flowing
N . 1 exhibited full dehydration in one step beginning at
2
ꢁ100 ꢁC and ending at ꢁ200 ꢁC (10.9% observed mass loss,
10.3% calculated for loss of all bound and unligated water
molecules). A further 10.7% mass loss by 310 ꢁC was con-
sistent with decarboxylation and loss of two molecules of
aromatic ring within the phthalate moieties (72ꢁ and 34ꢁ) in
3
are virtually identical to those in 1 and 2.
The hydrogen bonding connectivity patterns between
the 1-D chains in 3, into 2-D layers and then into the full
pseudo 3-D crystal structure, are largely the same as those
in 1 and 2. Metrical parameters for these supramolecular
interactions are given in Table 3. Once again, p–p stacking
interactions assist in the stabilization of the pseudo 3-D
CO
complete by 680 ꢁC, resulting in a remnant mass corre-
sponding to deposition of CoCO (29.5% mass remaining,
(10.0% calculated). Combustion of all organics was
2
3
Fig. 7. View down c of 3 illustrating p–p stacking between 4-methylphthalate and pyridyl aromatic rings. The methyl substituents can be seen projecting
into the incipient void spaces. Water molecules of crystallization are shown. Hydrogen atoms have been omitted for clarity.

M.A. Braverman et al. / Inorganica Chimica Acta 360 (2007) 2353–2362
2361
2
7.1% calculated). Continued heating resulted in likely
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. TGA traces for 1–3 are also available
via the Web edition of this journal. Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.ica.2006.12.004.
decarboxylation to form a final product of CoO (17.0%
observed mass remaining, 18.3% calculated). The thermal
decomposition of 2 proceeded similarly with some minor
differences. Here, a small mass loss (2.0%) between
1
00 ꢁC and 160 ꢁC corresponds to expulsion of the water
molecules of crystallization, followed immediately by a
rapid decline of a further 9.1% in mass by 215 ꢁC, consis-
tent with loss of all aquo ligands (8.3% calculated). A com-
plex series of overlapping mass loss steps between 215 and
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