Diverse entangled metal-organic framework materials incorporating kinked organodiimine and flexible aliphatic dicarboxylate ligands: Synthesis, structure, physical properties, and reversible structural reorganization

Article abstract of DOI:10.1021/ic070291d

Hydrothermal synthesis has afforded a family of divalent metal adipate (adp) coordination polymers incorporating the kinked dipodal organodiimine 4,4′-dipyridylamine (dpa). As revealed by single-crystal X-ray diffraction, the structures of these materials are critically dependent on the metal coordination geometry, the carboxylate binding modes, and the conformations of the flexible adipate moieties. In all cases, hydrogen-bonding interactions imparted by the dpa tethers also play a structure-directing role. All materials were further characterized via infrared spectroscopy and elemental and thermogravimetric analysis. [Co(adp)(dpa)] (1) displays doubly interpenetrated three-dimensional (3-D) networks with a decorated α-Po-type (pcu) topology. In contrast, [Ni(adp)(dpa)(H₂O)] (2) possesses a triply interpenetrated binodal cooperite-type (pts) framework, the highest level of interpenetration yet reported for this structure type. [Zn(adp)(dpa)]·H₂O (3) presents mutually inclined polycatenated 2-D graphitic layers consisting of neutral dimeric [Zn ₂(μ₂-adp)₂] kernels conjoined by dipodal dpa ligands. Compound 1 exhibited weak antiferromagnetic coupling between its carboxylate-bridged Co atoms, following Curie-Weiss behavior with Θ = -3.3 K. Compound 3 manifested blue light emission under ultraviolet excitation, as well as a reversible structural reorganization upon dehydration/rehydration.

Full text of DOI:10.1021/ic070291d

Inorg. Chem. 2007, 46, 7362−7370
Diverse Entangled Metal−Organic Framework Materials Incorporating
Kinked Organodiimine and Flexible Aliphatic Dicarboxylate Ligands:
Synthesis, Structure, Physical Properties, and Reversible Structural
Reorganization
Matthew R. Montney,† Subhashree Mallika Krishnan,† 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 February 13, 2007
Hydrothermal synthesis has afforded a family of divalent metal adipate (adp) coordination polymers incorporating
the kinked dipodal organodiimine 4,4 -dipyridylamine (dpa). As revealed by single-crystal X-ray diffraction, the structures
′
of these materials are critically dependent on the metal coordination geometry, the carboxylate binding modes, and
the conformations of the flexible adipate moieties. In all cases, hydrogen-bonding interactions imparted by the dpa
tethers also play a structure-directing role. All materials were further characterized via infrared spectroscopy and
elemental and thermogravimetric analysis. [Co(adp)(dpa)] (1) displays doubly interpenetrated three-dimensional
(3-D) networks with a decorated
interpenetrated binodal cooperite-type (pts) framework, the highest level of interpenetration yet reported for this
structure type. [Zn(adp)(dpa)] H2O (3) presents mutually inclined polycatenated 2-D graphitic layers consisting of
neutral dimeric [Zn2( 2-adp)2] kernels conjoined by dipodal dpa ligands. Compound 1 exhibited weak antiferromagnetic
coupling between its carboxylate-bridged Co atoms, following Curie Weiss behavior with Θ ) −3.3 K. Compound
R-Po-type (pcu) topology. In contrast, [Ni(adp)(dpa)(H2O)] (2) possesses a triply
‚
µ
−
3 manifested blue light emission under ultraviolet excitation, as well as a reversible structural reorganization upon
dehydration/rehydration.
Introduction
hydrogen storage,1 shape-selective separations,2 ion-ex-
change,3 catalysis,4 and optical properties.5-7 In the construc-
tion of these materials, benzenedicarboxylate and benzene-
tricarboxylate ligands are frequently employed to connect
cationic metal nodes, providing the necessary charge balance
to permit construction of a wide variety of neutral frame-
works without incorporation of smaller anions that could
Interest remains high in functional metal-organic frame-
work materials (MOFs) because of their capabilities in
* To whom correspondence should be addressed. Mailing address:
Lyman Briggs College, E-30 Holmes Hall, Michigan State University, East
Lansing, Michigan 48825. E-mail: laduca@msu.edu.
† Michigan State University.
‡ King’s College.
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7362 Inorganic Chemistry, Vol. 46, No. 18, 2007
10.1021/ic070291d CCC: $37.00
© 2007 American Chemical Society
Published on Web 08/10/2007

Entangled Metal-Organic Framework Materials
inhibit formation of void spaces. An extremely diverse range
of structural motifs occur in these systems, predicated on
the disposition of the donor atoms within the organic
component and metal coordination preferences. The level
of structural complexity in benzenecarboxylate MOFs has
been enhanced through incorporation of neutral nitrogen-
donor-tethering ligands such as 4,4′-bipyridine (4,4′-bpy),
which can connect metal cations through its distal pyridyl
nitrogen donor atoms into structurally intriguing solids with
potentially useful properties.6-8 For example, the paratactic
layered phase {[Zn(isophthalate)(4,4′-bpy)2][Zn(isophthalate)-
(4,4′-bpy)]‚0.25H2O exhibits blue luminescence upon ultra-
violet irradiation,7 and the interpenetrated 3-D material
[Zn(terephthalate)(4,4′-bpy)0.5] can chromatographically sepa-
rate branched and linear hydrocarbons.8
Compared with benzenedicarboxylate MOFs, organodi-
imine-scaffolded coordination polymers based on longer
aliphatic R,ω-dicarboxylates have received less attention.9-14
While the structural rigidity of benzenedicarboxylate subunits
can prove advantageous for the construction of porous
materials, flexible aliphatic dicarboxylates can provoke novel
structural motifs because of their ability to access numerous
energetically similar conformations. For instance, a few
divalent metal adipate (adp) coordination polymers incor-
porating 4,4′-bpy or 1,2-di-4-pyridylethane (bpe) have been
reported, in many cases, manifesting doubly interpenetrated
3-D networks.9-11,14
structural patterns via supramolecular and covalent interac-
tions. The combination of dpa with appropriate metal
precursors under hydrothermal conditions has resulted in the
construction of extended solids with diverse structural
motifs.15-17 For example, {[Ni(dpa)2(succinate)0.5]Cl} ex-
hibits a unique 5-connected self-penetrated structure with a
uniform 610 topology.15 [CuMoO4(dpa)2]‚2H2O possesses 2-D
copper molybdate lamella strutted by dpa tethers, which in
turn, anchor waters of crystallization in incipient voids via
N-H‚‚‚O hydrogen bonding.16 [Mo4O13(dpaH)2] displays
hydrogen-bonded interdigitated 1-D molybdate chains and
is able to intercalate primary and secondary amines.17 Herein,
we report the hydrothermal synthesis and characterization
of divalent cobalt, nickel, and zinc dpa-tethered metal adipate
interpenetrated or polycatenated coordination polymers. In
this class of materials, metal coordination geometry, car-
boxylate binding mode, conformational flexibility of the
adipate subunits and dpa-promoted supramolecular interac-
tions appear to play a synergistic role in structure direction.
Preliminary physical property studies (thermal degradation,
magnetism, and luminescence) were also undertaken to gauge
the functional potential of this family of materials. The zinc
derivative also undergoes a reversible structural reorganiza-
tion upon dehydration and rehydration.
Experimental Section
General Considerations. CoCl2‚6H2O, NiCl2‚6H2O, ZnCl2
(Fisher), and adipic acid (Aldrich) were obtained commercially.
4,4′-Dipyridylamine (dpa) was prepared via a published procedure.17
Water was deionized above 3 MΩ in-house. Thermogravimetric
analysis was performed on a TA Instruments TGA 2050 thermo-
gravimetric analyzer with a heating rate of 10 °C min-1 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
Mattson Galaxy FTIR Series 3000 using KBr pellets. Powder X-ray
diffraction patterns were obtained via Θ-2Θ scans performed on
a Rigaku Rotaflex instrument. Variable-temperature magnetic
susceptibility data (2-300 K) was 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 temper-
ature for 5 min before magnetization measurement to ensure thermal
equilibrium. The susceptibility data was corrected for diamagnetism
using Pascal’s constants.18 Luminescence spectra were obtained with
a Hitachi F-4500 fluorescence spectrometer on solid crystalline
samples anchored to quartz microscope slides with Rexon Corpora-
tion RX-22P ultraviolet-transparent epoxy adhesive.
For some time we have been interested in the synthesis
and characterization of coordination polymers containing the
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
center, allowing it to promote the formation of novel
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Preparation of [Co(adp)(dpa)] (1). CoCl2‚6H2O (88 mg,
0.37 mmol), dpa (127 mg, 0.73 mmol), and adipic acid (54 mg,
0.37 mmol) were placed into 10 mL of distilled H2O in a 23 mL
Teflon-lined Parr acid digestion bomb. The bomb was sealed and
heated at 120 °C for 44 h, whereupon it was cooled slowly to
25 °C. Magenta blocks of 1 (83 mg, 60% yield based on Co) were
isolated after washing with distilled water, ethanol, and acetone
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Inorganic Chemistry, Vol. 46, No. 18, 2007 7363

Montney et al.
Table 1. Crystal and Structure Refinement Data for 1-3
and drying in air. Anal. Calcd for C16H17CoN3O4 (1): C, 51.35;
H, 4.58; N, 11.23%. Found: C, 51.09; H, 4.24; N, 11.11%. IR
(KBr, cm-1): 3450 s br, 3302 s, 3180 s, 3075 m, 2937 s, 2858 s,
1650 m, 1596 s, 1531 s, 1500 m, 1443 m, 1408 m, 1366 m, 1322
m, 1305 m, 1209 m, 1146 w, 1098 w, 1066 w, 1053 w, 1018 m,
975 w, 944 w, 926 w, 910 w, 857 w, 822 m, 780 w, 732 w, 681 w,
629 w, 591 w, 535 w.
1
2
3
empirical formula C16H17CoN3O4 C16H19N3NiO5 C16H19N3O5Zn
fw
374.26
173(2)
0.71073
monoclinic
C2/c
16.5935(18)
9.9693(11)
19.166(2)
90
95.781(2)
90
3154.4(6)
8
392.05
173(2)
0.71073
monoclinic
C2/c
23.157(3)
9.3556(13)
17.074(2)
90
119.455(2)
90
3220.9(8)
8
398.71
293(2)
0.71073
orthorhombic
Pbcn
21.472(5)
8.542(2)
18.807(5)
90
collection T (K)
λ (Å)
cryst syst
space group
a (Å)
Preparation of [Ni(adp)(dpa)(H2O)] (2). NiCl2‚6H2O (88 mg,
0.37 mmol), dpa (127 mg, 0.73 mmol), and adipic acid (54 mg,
0.37 mmol) were placed into 10 mL of distilled H2O in a 23 mL
Teflon-lined Parr acid digestion bomb. The bomb was sealed and
heated at 120 °C for 44 h, whereupon it was cooled slowly to
25 °C. Green blocks of 2 (91 mg, 63% yield based on Ni) were
isolated after washing with distilled water, ethanol, and acetone
and drying in air. Anal. Calcd for C16H19NiN3O5 (2): C, 49.02; H,
4.89; N, 10.72%. Found: C, 48.67; H, 4.66; N, 10.56%. IR (KBr,
cm-1): 3430 m, 3296 m, 3181 m, 3135 m, 3093 m, 3048 m, 2960
m, 2917 m, 2895 m, 1633 m, 1604 s, 1527 s, 1487 s, 1412 s, 1347
s, 1307 m, 1293 m, 1232 w, 1217 s, 1160 m, 1103 w, 1075 w,
1060 w, 1022 m, 977 w, 936 w, 899 w, 879 w, 815 m, 777 m, 727
w, 695 w, 680 w, 663 w, 641 w, 620 w, 596 m, 543 m, 467 w.
Preparation of {[Zn(adp)(dpa)]‚H2O} (3). ZnCl2 (50 mg,
0.37 mmol), dpa (127 mg, 0.73 mmol), and adipic acid (54 mg,
0.37 mmol) were placed into 10 mL of distilled H2O in a 23 mL
Teflon-lined Parr acid digestion bomb. The bomb was sealed and
heated at 120 °C for 96 h, whereupon it was cooled slowly to
25 °C. Colorless blocks of 3 (97 mg, 66% yield based on Zn) were
isolated, after washing with distilled water, ethanol, and acetone
and drying in air. Anal. Calcd for C16H19N3O5Zn (3): C, 48.20; H,
4.80; N, 10.54%. Found: C, 47.91; H, 4.67; N, 10.52%. IR (KBr,
cm-1): 3376 s br, 3309 m, 2973 m, 2928 m, 2859 m, 1716 w,
1698 w, 1683 w, 1600 s br, 1522 s, 1490 m, 1445 m, 1429 m,
1408 m, 1351 s, 1317 m, 1278 w, 1209 m, 1152 m, 1062 m, 1000
s, 874 m, 855 w, 818 m, 741 w, 729 w, 645 m, 603 m, 537 m,
528 w.
X-ray Crystallography. A magenta block of 1 (0.20 mm ×
0.16 mm × 0.16 mm), a light green prism of 2 (with dimensions
0.28 mm × 0.22 mm × 0.20 mm), and a colorless rhomb of 3
(0.35 mm × 0.30 mm × 0.30 mm) were subjected to single-crystal
X-ray diffraction using a Bruker-AXS SMART 1k CCD instrument.
Reflection data was acquired using graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å). The data was integrated via
SAINT.19 Lorentz and polarization effect and empirical absorption
corrections were applied with SADABS.20 The structures were
solved using direct methods and refined on F2 using SHELXTL.21
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 hydrogen atoms
bound to the central nitrogen of the dpa moieties and any water
molecules in 1-3 were found via Fourier difference maps, then
restrained at fixed positions and refined isotropically. Relevant
crystallographic data for 1-3 is listed in Table 1; more detailed
information is available in the respective CIF files (see Supporting
Information).
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
3449.8(15)
8
1.535
1.456
0.0792
0.1034
D
calcd (g cm-3
)
1.576
1.114
0.0771
0.0862
1.617
1.239
0.0542
0.0744
µ (mm-1
R1a (all data)
wR2b (all data)
)
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) ∑{[w(Fo2 - Fc )2]/∑[wFo ]2}1/2
.
2
2
as single-phase crystalline products under hydrothermal
conditions via combination of the appropriate metal chloride,
4,4′-dipyridylamine, and adipic acid. The infrared spectra
of 1-3 were fully consistent with their formulations. Sharp,
medium intensity bands in the range of ∼1600-1200 cm-1
were ascribed to stretching modes of the pyridyl rings of
the dpa moieties.22 Features corresponding to pyridyl ring
puckering mechanisms were evident in the region between
820 and 600 cm-1. Asymmetric and symmetric C-O
stretching modes of the adipate carboxylate moieties were
evidenced by very strong, slightly broadened bands at ∼1600
and ∼1400 cm-1. Broad bands in the region of ∼3400-
3200 cm-1 in all cases represent N-H stretching modes
within the dpa ligands and O-H stretching modes within
either aquo ligands or water molecules of crystallization,
where present. The broadness of these latter spectral features
is caused by significant hydrogen-bonding pathways within
1-3.
Structural Description of [Co(adp)(dpa)] (1). The asym-
metric unit of 1 (Figure 1) possesses one Co atom, one dpa
ligand with an interring torsion angle of 25.9°, and two halves
of two different adipate moieties (A, denoted by atom sets
C21-C23 and O1-O2; B, denoted by atom sets C31-C33
and O3-O4). Co is ligated by two cisoid oxygen donors
(O1 and O2) from a single chelating carboxylate terminus
of A, by two cis-disposed oxygen atoms (O3 and O4A) from
two different B ligands, and by two trans-disposed nitrogen
atoms belonging to two crystallographically identical dpa
ligands. The Co atoms in 1 therefore manifest a distorted
octahedral [trans-CoO4N2] coordination environment, with
Co-N bond lengths ranging from 2.14 to 2.20 Å and Co-O
bond lengths from 2.01 to 2.27 Å. The bond lengths between
Co and the chelating carboxylate oxygen donors are markedly
longer than those to the monodentate carboxylate oxygen
atoms. The bond angles about Co range from ∼59° (the bite
Results and Discussion
Synthesis and Spectral Characterization. The coordina-
tion polymers 1-3 were prepared cleanly and in high yield
(19) SAINT, Software for Data Extraction and Reduction, version 6.02;
Bruker AXS, Inc.: Madison, WI, 2002.
(20) SADABS, Software for Empirical Absorption Correction, version 2.03;
Bruker AXS, Inc.: Madison, WI, 2002.
(21) Sheldrick, G. M. SHELXTL, Program for Crystal Structure Refinement;
University of Gottingen: Gottingen, Germany, 1997.
(22) Kurmoo, M.; Estournes, C.; Oka, Y.; Kumagai, H.; Inoue, K. Inorg.
Chem. 2005, 44, 217-224.
7364 Inorganic Chemistry, Vol. 46, No. 18, 2007

Entangled Metal-Organic Framework Materials
Figure 3. View down b of 1 illustrating cross-linking of two 2-D [Co2-
(µ2-adp)(µ4-adp)] layers through dpa tethering ligands.
atom connects to a neighboring Co atom via a bischelating
bisbridging µ2-adipate moiety (type A), with a through-ligand
Co-Co distance of 9.448(1) Å. The bischelating adipate
dianions rest in a very twisted gauche-gauche-gauche
conformation (four-atom torsion angles ) 59.8, 64.1, and
59.8°). Each Co atom further connects to five other Co atoms
through two different exotetradentate µ4-adipate ligands (type
B), within which, each oxygen donor atom binds to cobalt
in a monodentate fashion. Type B adipate moieties exist in
an S-shaped conformation, with a gauche-anti-gauche
pattern (four-atom torsion angles ) 73.3, 180.0, and 73.3°).
Dimeric kernels are built from the bridging of two nearest-
neighbor Co atoms (Co-Co through-space distance of 3.966-
(1) Å) through two carboxylate termini on two different
B-type ligands, thereby forming 8-membered (CoOCO)2
rings. Both carboxylate termini of B adipates bridge adjacent
Co centers in a syn-syn conformation (Co-O‚‚‚O-Co
torsion angle ) 26.9°). Within the layer motif, dimeric
subunits linked by type B exotetradentate adipate anions tilt
in the same direction, while those linked through A-type
bisbridging adipate units tilt in the opposite direction. The
[Co2(µ2-adp)(µ4-adp)] 2-D layers can be viewed as a system
of conjoined 8-membered (CoOCO)2 and 36-membered
(CoOC6O)4 rings.
Figure 1. Expanded asymmetric unit of 1 with thermal ellipsoids at 50%
probability. Most hydrogen atoms have been removed for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1a
Co1-O4
Co1-O3#1
Co1-N3#2
Co1-O1
Co1-N1
Co1-O2
O1-C11
O2-C11
O4-C21
O3-C21
2.024(2)
2.033(2)
2.155(2)
2.156(2)
2.175(2)
2.270(2)
1.243(3)
1.253(3)
1.255(3)
1.244(4)
O4-Co1-O3#1
O4-Co1-N3#2
O3#1-Co1-N3#2
O4-Co1-O1
O3#1-Co1-O1
N3#2-Co1-O1
O4-Co1-N1
O3#1-Co1-N1
N3#2-Co1-N1
O1-Co1-N1
O4-Co1-O2
O3#1-Co1-O2
N3#2-Co1-O2
O1-Co1-O2
N1-Co1-O2
O3-C21-O4
O1-C11-O2
124.43(10)
84.85(9)
90.71(9)
93.33(9)
142.21(8)
91.21(9)
90.29(8)
93.68(9)
174.75(9)
87.08(9)
151.92(9)
83.53(8)
93.03(9)
58.67(8)
90.32(9)
124.8(3)
120.8(3)
a Symmetry transformations to generate equivalent atoms: #1 -x + 1/2,
-y + 5/2, -z; #2 x + 1/2, -y + 5/2, z + 1/2.
Each [Co2(µ2-adp)(µ4-adp)] layer connects to two other
identical layers through tethering dpa struts, with an interlayer
Co-Co distance of 12.063(1) Å, constructing a full covalent
3-D network with the general formulation [Co(adp)(dpa)],
depicted in Figure 3. The covalent connectivity of the 3-D
network is assisted by two types of supramolecular interac-
tion, as revealed by PLATON.23 Pyridyl rings belonging to
neighboring dpa ligands engage in π-π stacking interactions
with a centroid-to-centroid distance of 3.997(2) Å and an
interring dihedral angle of 7.6°. In addition, weak C-H‚‚‚O
interactions exist between the dpa moieties and carboxylate
oxygen atoms of adipate ligand type B (C1‚‚‚O4 )
2.925 Å, C10‚‚‚O4 ) 2.863 Å). If the 8-membered (CoO-
CO)2 rings are taken as a single connecting node, the short
topological symbol for the [Co(adp)(dpa)] coordination
polymer network is 41263, consistent with a 6-connected
decorated R-Po (pcu)24 net.
Figure 2. View down (1 0 1) of a neutral [Co2(µ2-adp)(µ4-adp)] layer in
1.
angle of the chelating carboxylate unit in A) to ∼124°.
Selected bond distances and angles for 1 are given in
Table 2.
(23) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 1998.
(24) The three-letter abbreviations for many common network topologies
can be found in Delgado Friedrichs, O.; O’Keeffe, M.; Yaghi, O. M.
Acta Crystallogr. 2003, A59, 22-27. A useful searchable database of
networks and tilings relevant to coordination polymer chemistry can
be found on the Internet at http://rcsr.anu.edu.au/.
Extension of the structure through both type of adipate
moieties along the (1 0 1) crystal plane results in a neutral
[Co(adp)] layer (Figure 2) similar to those seen in the related
4,4′-bpy-containing phase [Mn(adp)(4,4′-bpy)].11 Each Co
Inorganic Chemistry, Vol. 46, No. 18, 2007 7365

Montney et al.
Figure 5. Expanded asymmetric unit of 2 with thermal ellipsoids at 50%
probability. Most hydrogen atoms have been omitted for clarity. Hydrogen-
bonding interactions are indicated as dashed lines.
Figure 4. Framework perspective of 1 depicting its doubly interpenetrated
decorated pcu-type 3-D network structure. Only Co and terminal C atoms
of µ4-adipate ligands are shown.
Table 4. Selected Bond Distances (Å) and Angles (deg) for 2a
Table 3. Classical Hydrogen-Bonding Distances (Å) and Angles (deg)
for 1-3
Ni1-N3 (×2)
Ni1-O3#1,#2 (×2)
Ni1-O4#1,#2 (×2)
Ni2-O1 (×2)
Ni2-O5 (×2)
Ni2-N1 (×2)
O1-C11
2.0313(17)
2.0699(14)
2.1956(15)
2.0410(14)
2.0502(15)
2.1204(17)
1.264(2)
1.255(3)
1.268(2)
1.266(2)
N3#3-Ni1-N3
N3-Ni1-O3#1
N3-Ni1-O3#2
O3#1-Ni1-O3#2
N3-Ni1-O4#1
O3#1-Ni1-O4#1
O3#2-Ni1-O4#1
N3-Ni1-O4#2
O4#1-Ni1-O4#2
O1-Ni2-O1#4
O1-Ni2-O5#4
O1-Ni2-O5
97.71(10)
96.38(6)
94.15(6)
163.97(8)
91.61(6)
61.47(5)
106.26(6)
154.82(6)
89.68(8)
180.00(7)
88.78(6)
91.22(6)
180.0
symmetry
transformation for A
D-H‚‚‚A
d(H‚‚‚A)
DHA d(D‚‚‚A)
1
N2-H2N‚‚‚O1
1.879
172.50
2.738
-x, -y + 3, -z
O2-C11
2
O3-C16
O4-C16
O5-H5A‚‚‚O2
O5-H5B‚‚‚O3
N2-H2N‚‚‚O4
1.868
1.994
2.013
151.45
175.89
172.00
2.624
2.825
2.855
x, y - 1, z
x - 1/2, -y - 3/2, z - 1/2
O5#4-Ni2-O5
O1-Ni2-N1#4
O5-Ni2-N1#4
O1-Ni2-N1
3
O1W-H1WA‚‚‚O2
O1W-H1WB‚‚‚O3
N3-H3N‚‚‚O1W
1.992
1.980
1.944
161.98
173.98
173.58
2.812
2.823
2.821
x, y - 1, z
91.24(6)
92.78(7)
88.76(6)
87.22(7)
180.0
x, -y, z - 1/2
O5-Ni2-N1
The apparent void space within a single [Co(adp)(dpa)]
pcu framework is occupied by an identical 3-D framework
(Figure 4), with a full interpenetration vector (FIV)25 in the
(1/2, 1/2, 0) direction with a translation distance of 9.68 Å
(calculated by TOPOS software26) in a fashion very similar
to that of the previously reported [Mn(adp)(bpe)] phase.14
The Class Ia (translation-only) double interpenetration25 of
the independent networks in 1 is assisted by interframework
hydrogen bonding between the central N-H unit of the dpa
moieties to ligated carboxylate oxygen atoms of type O1
belonging to bischelating type A adp ligands. Metrical
parameters for these supramolecular interactions are listed
in Table 3. No residual void space exists within the structure
of 1.
Structural Description of [Ni(adp)(dpa)(H2O)] (2). The
asymmetric unit of 2 (Figure 5) was revealed to contain two
crystallographically distinct Ni atoms sited on inversion
centers, one doubly deprotonated dianionic adipate, one
neutral dpa ligand, and one aquo ligand bound to Ni2. Ni2
manifests [NiO4N2] octahedral coordination. The dpa nitro-
gen donors are oriented in a trans fashion at Ni2, as are the
two symmetry-related aquo ligands. The two remaining trans
coordination sites are occupied by oxygen donors from
monodentate carboxylate subunits belonging to two sym-
N1#4-Ni2-N1
O2-C11-O1
O4-C16-O3
125.11(19)
118.90(18)
a Symmetry transformations to generate equivalent atoms: #1 -x + 1/2,
y - 3/2, -z + 3/2; #2 x - 1/2, y - 3/2, z; #3 -x, y, -z + 3/2; #4 -x +
1/2, -y - 3/2, -z + 1.
metry-related adipate ligands. Ni1 possesses a distorted
[NiO4N2] octahedral coordination sphere featuring two
symmetry-related chelating adipate carboxylate subunits
(with O-Ni-O bite angle of 61.5°) and two cis-disposed
dpa nitrogen termini (N-Ni-N angle of 97.6°). The che-
lation of the adipate moiety is asymmetric, with each
carboxylate subunit instigating one short (2.070 Å) and one
long (2.196 Å) Ni-O bond. The deviation from an idealized
octahedral coordination geometry at Ni1 can be ascribed to
the requirements imposed by carboxylate chelation. The Ni2
to adipate oxygen bond distances (∼2.04 Å) are slightly
shorter than those to Ni1, reflective of the monodentate
carboxylate binding mode at Ni2. The trans-disposed nitrogen
donors at Ni2 atoms have noticeably longer Ni-N distances
(by ∼ 0.1 Å) than the cis-oriented dpa nitrogen atoms at
Ni1, perhaps because of the more congested chelation-free
coordination environment at Ni2. Selected bond data for 2
are given in Table 4.
Unlike in 1, the adipate moieties in 2 serve only as
exobidentate µ2-bridging ligands. The adipate ligand has one
carboxylate terminus chelating to Ni1, while the other end-
capping carboxylate coordinates to Ni2 in a monodentate
(25) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEngComm
2004, 6, 378-395.
(26) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl.
Crystallogr. 2000, 33, 1193.
7366 Inorganic Chemistry, Vol. 46, No. 18, 2007

Entangled Metal-Organic Framework Materials
Figure 6. Single sinusoidal 1-D [Ni(adp)(H2O)] ribbon in 2. Intrachain
hydrogen bonding is shown as dashed lines.
fashion. This adipate binding mode stands in contrast to that
observed in the 1-D coordination polymer [Ni(adp)(H2O)4],27
wherein the adipate ligands link neighboring Ni ions in a
bis-monodentate bridging fashion. To accommodate this
monodentate/chelating bridging mode, which is unprec-
edented to the best of our knowledge for the adipate ligand,
the adipate dianions in 2 adopt a “hairpin” anti-gauche-
gauche conformation (torsion angles 171.1, 54.0, and 55.0°).
The chelating carboxylate terminus is situated at the anti
conformation side of the aliphatic chain. Neutral sinusoidal
1-D [Ni(µ2-adp)(H2O)] ribbons propagate along the (1 0 1)
direction of the crystal (Figure 6). The Ni1-Ni2 distance
within these ribbons is 8.397(1) Å, shorter by ∼1.1 Å than
the corresponding µ2-adipate bridged Co-Co distance in 1.
This substantial decrease can be ascribed to the hairpin
adipate conformation in 2. The “wavelength” of the sinu-
soidal ribbon motifs is ∼ 21 Å, as determined by the second
nearest-neighbor Ni1-Ni1 distance. Within each [Ni(µ2-adp)-
(H2O)] ribbon motif, the aquo ligands attached to Ni2 engage
in hydrogen-bonding donation to the unligated adipate
carboxylate oxygen atoms, thus stabilizing the monodenticity
of the carboxylate subunit on each adipate ligand and
preventing the bischelating binding mode seen in 1. Adjacent
[Ni(µ2-adp)(H2O)] ribbons are connected into a pseudo 2-D
layer via hydrogen-bonding donation from the Ni2-bound
aquo ligands to chelating carboxylate oxygen atoms bound
to Ni1, as shown in Figure 7.
Figure 7. Pseudo-2-D layer composed of hydrogen-bonded 1-D [Ni(adp)-
(H2O)] ribbons in 2. Interribbon hydrogen bonding is shown as dashed lines.
Figure 8. Zigzag 1-D [Ni(dpa)] chain motif in 2, highlighting alternating
cis and trans dpa coordination.
Figure 9. Framework perspective of the unprecedented triply interpen-
etrated pts net 3-D structure of 2. Each independent framework is depicted
in a different color. Ni atoms are shown as spheres, while the rods represent
the adp and dpa ligands.
The ribbon motifs are covalently connected into the full
3-D crystal structure of 2 by means of infinite [Ni(dpa)]
chains, which course in a perpendicular direction. These
structural subunits form via the connection of Ni1 and Ni2
atoms in different [Ni(adp)(H2O)] ribbons through tethering
dpa moieties. Because of the alternating cis and trans
orientations of dpa nitrogen donors at Ni1 and Ni2, respec-
tively, these infinite [Ni(dpa)] chains adopt a zigzag-style
arrangement (Figure 8). The Ni-Ni contact distance within
this second type of chain motif in 2 is 11.482(1) Å; the
“wavelength” of the zigzag repeat pattern is nearly 35 Å.
nected nodes (at Ni1, caused by trans dpa coordination),
affording a cooperite-type (pts)24 structure with 4284 topol-
ogy.28 The long vertex symbols for the 4-connected Ni1 and
Ni2 nodes are 4.4.82.82.88.88 and 4.4.87.87.87.87. The pts
networks in 2 are 3-fold interpenetrated (Figure 9), repre-
senting the highest level of interpenetration observed for this
structure type to date; the FIV25 relating the Class Ia
translation-only interpenetrated networks is (0,1,0) with a
translation distance of 9.36 Å, as calculated by TOPOS.26
The 3-D covalent connectivity of 2 is augmented by
hydrogen bonding between the central N-H unit of the two
distinct dpa ligands and carboxylate oxygen atoms, in
The covalent cross-linking of the [Ni(µ2-adp)(H2O)] rib-
bons and [Ni(dpa)] chains results in a 3-D network based
on the linking of tetrahedral 4-connected nodes (at Ni1,
caused by cis dpa coordination) and square planar 4-con-
(27) Bakalbassis, E. G.; Korabik, M.; Michailides, A.; Mrozinski, J.;
Raptopoulou, C.; Skoulika, S.; Terzis, A.; Tsaousis, D. Dalton Trans.
2001, 850-857.
(28) Carlucci, L.; Ciani, G.; Gudenberg, D. W. v.; Proserpio, D. M. New
J. Chem. 1999, 23, 397-401.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7367

Montney et al.
Figure 10. Expanded asymmetric unit of 3 with thermal ellipsoids at 50%
probability. Most hydrogen atoms have been omitted for clarity.
Table 5. Selected Bond Distances (Å) and Angles (deg) for 3
Zn1-O1
Zn1-O2
Zn1-N2
Zn1-N1
O1-C11
O2-C16
O3-C11
O4-C16
1.950(2)
1.969(2)
2.030(2)
2.037(2)
1.270(4)
1.292(4)
1.232(4)
1.234(4)
O1-Zn1-O2
O1-Zn1-N2
O2-Zn1-N2
O1-Zn1-N1
O2-Zn1-N1
N2-Zn1-N1
O3-C11-O1
O4-C16-O2
97.73(10)
110.81(10)
105.60(10)
115.03(10)
112.98(10)
113.30(10)
123.4(3)
Figure 11. [Zn2(adp)2] 18-membered ring bimetallic kernel in 3. Nitrogen
atoms bound to Zn are also shown.
122.3(3)
addition to π-π stacking interactions between neighboring
dpa pyridyl rings (centroid-to-centroid distance ) 3.754(1)
Å with an interring dihedral angle of 20.2°). Supramolecular
hydrogen-bonding distances and angles for 2 are given in
Table 3.
Structural Description of [Zn(adp)(dpa)]‚H2O (3).
Single-crystal X-ray diffraction revealed that 3 contains an
asymmetric unit (Figure 10) consisting of one zinc atom,
one adipate ligand in an S-shaped gauche-anti-gauche
conformation (torsion angles of 61.6, 175.3, and 56.9°), one
dpa ligand, and one water molecule of crystallization
hydrogen bonded to the secondary amine group of the dpa
ligand. In contrast to the octahedral coordination geometries
at the metal atoms in 1 and 2, Zn manifests a [ZnO2N2]
slightly distorted tetrahedral coordination sphere with bond
angles ranging between 97.7 and 115.0°. The Zn-N bond
lengths are slightly longer than the Zn-O bond lengths. The
adp ligands adopt a bismonodentate bisbridging binding
mode, with the ligated carboxylate oxygen atoms exhibiting
C-O bond distances ∼0.06 Å longer than the unligated
carboxylate oxygen atoms. Selected bond distance and angle
information for 3 is given in Table 5.
In contrast with 1 and 2, where the adipate ligands serve
to propagate the extended crystal structures in 2-D and 1-D,
respectively, two adipate anions in 3 simply connect neigh-
boring Zn atoms to form neutral [Zn2(adp)2] bimetallic
kernels bearing 18-membered (ZnOC6O)2 rings (Figure 11).
The Zn-Zn distance across the bimetallic unit is 5.932(1)
Å. Each [Zn2(adp)2] kernel connects to four others through
tethering dpa ligands, thereby forming infinite 2-D layers
(Figure 12). The through-ligand Zn-Zn distance through the
dpa tethers is 11.541(1) Å. If each Zn atom is considered as
a 3-connected node, with the double adipate bridge treated
as a single connection, a (6,3) graphitic layer can be invoked.
Covalent connectivity within the layer motif is augmented
by weak C-H‚‚‚O interactions between the pyridyl rings
and unligated adipate carboxylate oxygen atoms (C1‚‚‚O3
) 3.192 Å, C5‚‚‚O4 ) 3.091 Å). Water molecules of
crystallization lie within the layers, anchored into place via
hydrogen-bonding acceptance from the central N-H units
Figure 12. A single {[Zn(adp)(dpa)]‚H2O} 2-D layer in 3. Water
molecules of crystallization are shown in orange. Hydrogen-bonding
interactions are depicted as dashed lines.
of the dpa moieties (see Table 3 for supramolecular metrical
parameters). Removal of the uncoordinated water molecules
from the unit cell of 3 reveals small incipient void spaces
(1.9% of the cell volume as calculated by PLATON).
As seen in Figure 13, the full pseudo-3-D crystal structure
of 3 consists of two sets of mutually inclined polycatenated29
(2d + 2d f 3D) (6,3) graphitic [Zn(adp)(dpa)] layers, similar
to the [Cu2(pyrazine)3(SiF6)] prototype discovered by Zaworot-
ko.30 One set of layers (type A, in red) is oriented parallel
to the (1 1 0) crystal plane, and the other (layer type B, in
green) is parallel to (1 -1 0) plane. The angle subtended by
the intersection of one layer A and one layer B is ∼43.4°.
The closest Zn-Zn distance between layers of the same type
is 8.542(1) Å, while the corresponding Zn-Zn nearest
approach between layers of different type is 7.287(1) Å. The
[Zn2(adp)2] neutral bimetallic kernels from layers of type A
slot into the open incipient void spaces in neighboring type
B layers, assisted by hydrogen-bonding donation between
(29) Carlucci, L.; Ciani, G.; Proserpio, D. M. Coord. Chem. ReV. 2003,
246, 247-289.
(30) MacGillivray, L. R.; Subramanian, S.; Zaworotko, M. J. J. Chem. Soc.,
Chem. Commun. 1994, 1325-1326.
7368 Inorganic Chemistry, Vol. 46, No. 18, 2007

Entangled Metal-Organic Framework Materials
polymers with organoimine ligands.32 TGA traces for 1-3
are shown in Figures S1-S3.
Dehydration/Rehydration Behavior of 3. To further
probe the dehydration behavior of 3, a sample was heated
in air at 180 °C for 48 h. The powder XRD pattern of as-
synthesized 3 is shown in Figure S4. Powder XRD revealed
that a structural transformation to a new phase had occurred
upon dehydration, which exhibited an orthorhombic unit
cell with a ) 17.685(2) Å, b ) 21.161(1) Å, and c ) 16.691-
(3) Å (Figure S5). Unfortunately, this dehydrated phase was
polycrystalline, precluding single-crystal structure determi-
nation. It is plausible that the adipate ligands adopt a different
conformation in response to the loss of hydrogen bonding
imparted by the water molecules of crystallization, resulting
in structural reorganization. Immersion of the dehydrated
material in water for 48 h regenerated the structure of 3
according to powder XRD (Figure S6). Reversible guest-
induced crystal-to-crystal transformations have been reported
in several other coordination polymer systems.33 Attempts
to fully structurally characterize the dehydrated orthorhombic
phase are underway.
Magnetic Properties of 1. The magnetic susceptibility
of 1 was measured as a function of temperature to probe
any spin communication between carboxylate-bridged Co
atoms. The value of the ømT product was 5.62 cm3 K mol-1
Co2 dimeric units at 300 K, roughly consistent with the value
for two coupled S ) 3/2 Co2+ ions (6.00 cm3 K mol-1). The
ømT product decreased only slightly until 100 K (Figure 14),
whereupon a more rapid decrease was observed, with a value
of 1.00 cm3 K mol-1 at 2 K. This diminution in ømT is
consistent with antiferromagnetic coupling across the bi-
nuclear kernels in 1, although single-ion anisotropy (D
parameter) resulting from the distorted octahedral coordina-
tion about Co or spin-orbit coupling cannot be ruled out.
A plot of 1/øm versus T revealed that the magnetic suscep-
tibility of 1 follows the Curie-Weiss law (øm ) C/T - Θ)
between 100 and 300 K with a C value of 5.66 cm3 K mol-1
and Θ ) -3.3 K, again indicative of antiferromagnetic
coupling between Co centers in 1. Similar weak antiferro-
magnetic coupling was observed in the previously reported
related [Co(adp)(L)] (L ) 1,2-di-4-pyridylethane, trans-1,2-
di-4-pyridylethylene) phases.12 Given the small negative
value of Θ in 1, any spin communication between more-
remote Co atoms bridged by the bischelating adipate moieties
or the tethering dpa ligands can be considered negligible.
Luminescent Properties of 3. In the solid state at room
temperature, 3 exhibited blue-violet luminescence upon
ultraviolet excitation (λ ) 250 nm), displaying an emission
spectrum with a broad feature centered at λmax ≈ 350 nm
and an extensive tail protruding into visible wavelengths.
Emission and excitation spectra for 3 are shown in Figure
15. Unligated dpa is also luminescent, showing a weak broad
emission with λmax ) 420 nm at the same excitation
wavelength. Therefore, by comparison with other zinc and
Figure 13. Framework view of mutually inclined polycatenated (6,3) layer
motifs in 3. Zn atoms are shown as spheres, while the organic tethers are
drawn as rods.
the water molecules of crystallization within one layer and
ligated (O2) and unligated (O3) adipate carboxylate oxygens
belonging to adjacent layers. In addition, weak interlayer
C-H‚‚‚O interactions between dpa pyridine rings and
unligated adipate oxygen atoms play a supplemental stabiliz-
ing role (C10‚‚‚O4 distance ) 3.143 Å). The structural
pattern of 3 is unprecedented for organodiimine-tethered zinc
dicarboxylates, standing in stark contrast to [Zn(adp)(4,4′-
bpy)],31 which crystallizes in a doubly interpenetrated pcu
structure type similar to that of 1.
Thermogravimetric Analysis. All new phases were
subjected to thermogravimetric analysis to ascertain their
thermal robustness. Compound 1 was thermally stable until
∼280 °C, whereupon it underwent decarboxylation (5.8%
mass loss observed, 5.9% calculated for one molar equivalent
of CO2), followed by a subsequent 30.9% mass loss
beginning at ∼350 °C and ending at ∼450 °C, roughly
corresponding to the loss of one carboxylated and one
decarboxylated adipate (32.6% predicted). Loss of all dpa
ligands was complete by ∼680 °C (42.9% mass loss
observed, 45.7% predicted). The final mass was consistent
with the deposition of Co3O4 (21.9% mass remaining, 21.4%
calculated). Compound 2 lost its coordinated water at
∼130 °C (5.1% mass loss observed, 4.6% calculated).
Catastrophic degradation commenced at ∼330 °C (65.4%
mass loss, 68.6% predicted for two dpa ligands, one adipate
ligand, and decarboxylation of the other adipate ligand). At
∼590 °C, the remaining decarboxylated adipate was lost
(13.5% mass loss, 12.7% predicted). The final mass remnant
(19.0% of the original) correlated exactly with that calculated
for NiO. Compound 3 underwent dehydration between 120
and 175 °C (5.7% mass loss, 4.5% predicted). Its mass
remained stable until 240 °C, whereupon a series of mass
losses ensued corresponding to elimination of organic
fragments. The 34.3% mass remnant at 900 °C is roughly
consistent with Zn(CN)2 (29.4% calculated), a remnant seen
previously upon thermolysis of other zinc coordination
(32) Ouellette, W.; Hudson, B. S.; Zubieta, J. Inorg. Chem. 2007, 46, 4887-
4904.
(33) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43,
2334-2375 and references therein.
(31) Zheng, Y.-Q.; Ying, E.-B. Polyhedron 2005, 24, 397-406.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7369

Montney et al.
Figure 14. Plot of ømT vs T for 1.
(3) promotes the formation of inclined polycatenated 2D f
3D graphite-like coordination polymer layers. All structures
illustrate the capability of the adipate ligand to adopt
energetically similar binding modes and conformations,
wherein subtle variations can amplify and therefore assist
in the development of the observed varied topologies and
interpenetration or polycatenation. Hydrogen bonding and
π-π stacking supramolecular interactions imparted by the
dpa ligand also play an important structure-directing role in
the present case. Continued efforts to explore the construction
of novel coordination polymers incorporating both 4,4′-
dipyridylamine and flexible aliphatic dicarboxylate ligands
are underway in our laboratory and will be reported in due
course.
Figure 15. Solid-state excitation/emission spectrum of 3.
cadmium dicarboxylate organodiimine coordination poly-
mers,34 the luminescent behavior of 3 is best rationalized by
dpa ligand-centered π f π* or π f n orbital transitions.
Acknowledgment. The authors gratefully acknowledge
Michigan State University for financial support of this work.
We are indebted to Troy E. Knight for acquisition of the
fluorescence spectra. We thank Dr. Rui Huang for elemental
analysis, Maxwell Braverman and Guilherme Cavichioli for
experimental assistance, and Dr. Janice S. Pawloski (Grand
Valley State University) for helpful discussions. M.R.M.
thanks the MSU Introductory Chemistry Honors Program
for his participation in this research. We thank one of the
reviewers for very helpful suggestions.
Conclusions
Hydrothermal synthesis has cleanly afforded three divalent
metal coordination polymers incorporating both the kinked
organodiimine 4,4′-dipyridylamine and the conformationally
flexible adipate ligand. While the Co (1) and Ni (2)
derivatives both display octahedral coordination geometry,
the presence of coordinated water molecules in the latter
provokes a shift from a doubly interpenetrated pcu topology
in 1 to an unprecedented binodal triply interpenetrated pts
morphology in 2. Tetrahedral coordination in the Zn congener
Supporting Information Available: CIF files, TGA traces for
1-3, and powder XRD patterns for as-synthesized, dehydrated, and
rehydrated 3. This material is available free of charge via the
Internet at http://pubs.acs.org. Crystallographic data (excluding
structure factors) for 1-3 have been deposited with the Cambridge
Crystallographic Data Centre (nos. 636517-636519). 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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Chen, X. M.; Ng, S. W. Chem. Commun. 2000, 2043-2044. (c) Dai,
J. C.; Wu, X. T.; Fu, Z. Y.; Cui, C. P.; Hu, S. M.; Du, W. X.; Wu, L.
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7370 Inorganic Chemistry, Vol. 46, No. 18, 2007