Divalent metal homophthalate coordination polymers with long-spanning dipyridyl ligands containing piperazine moieties

Article abstract of DOI:10.1016/j.ica.2013.01.005

Hydrothermal reaction of a metal nitrate salt, homophthalic acid (H ₂hmph), and a long-spanning dipyridyl ligand bearing a central piperazine moiety afforded three new divalent metal homophthalate coordination polymers, which were structurally characterized by single-crystal X-ray diffraction. [Zn₂(hmph)₂(3-bpmp)]_n (1, 3-bpmp = bis(3-pyridylmethyl)piperazine) exhibits a 2D (4,4) grid topology formed from the 3-bpmp linkage of [Zn₂(hmph)₂]_n 1D chains featuring{Zn₂(OCO)₄} paddlewheel clusters. {[Co(H ₂O)₄(4-bpfp)][Co(hmph)₂(4-bpfp)]·6H ₂O}_n (2, 4-bpfp = bis(4-pyridylformyl)piperazine) possesses alternating anionic [Co(hmph)₂(4-bpfp)]_n ^2n- and cationic [Co(H₂O) ₄(4-bpfp)]_n²ⁿ⁺ chains. [Ni(hmph)(4-bpfp)(H₂O)]_n (3) manifests [Ni(H ₂O)(hmph)]_n chains formed through anti-syn carboxylate bridging. In turn these are connected into a (4,4) grid via tethering 4-bpfp ligands. Variable temperature magnetic susceptibility data indicates weak ferromagnetic superexchange along the embedded [Ni(OCO)]_n chain subunits (g = 2.272(4), J = 0.25(1) cm^-1). The d¹⁰ derivative 1 undergoes ligand-centered blue-violet luminescence upon exposure to ultraviolet light (λ_max = 417 nm). Thermal decomposition behavior is also explored.

Full text of DOI:10.1016/j.ica.2013.01.005

Inorganica Chimica Acta 403 (2013) 78–84
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Divalent metal homophthalate coordination polymers with
long-spanning dipyridyl ligands containing piperazine moieties
Ciana M. Rogers b, Curtis Y. Wang a, Gregory A. Farnum b, Robert L. LaDuca b,
⇑
a Diamond Bar High School, Diamond Bar, CA 91765, USA
b 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:
Available online 20 January 2013
Hydrothermal reaction of a metal nitrate salt, homophthalic acid (H2hmph), and a long-spanning dipyr-
idyl ligand bearing a central piperazine moiety afforded three new divalent metal homophthalate coor-
dination polymers, which were structurally characterized by single-crystal X-ray diffraction.
[Zn2(hmph)2(3-bpmp)]n (1, 3-bpmp = bis(3-pyridylmethyl)piperazine) exhibits a 2D (4,4) grid topology
formed from the 3-bpmp linkage of [Zn2(hmph)2]n 1D chains featuring{Zn2(OCO)4} paddlewheel clusters.
{[Co(H2O)4(4-bpfp)][Co(hmph)2(4-bpfp)]ꢀ6H2O}n (2, 4-bpfp = bis(4-pyridylformyl)piperazine) possesses
Coordination Polymers Special Issue
Keywords:
Zinc
Cobalt
2nꢁ
2n+
alternating anionic [Co(hmph)2(4-bpfp)]n
and cationic [Co(H2O)4(4-bpfp)]n
chains. [Ni(hmph)
(4-bpfp)(H2O)]n (3) manifests [Ni(H2O)(hmph)]n chains formed through anti–syn carboxylate bridging.
In turn these are connected into a (4,4) grid via tethering 4-bpfp ligands. Variable temperature magnetic
susceptibility data indicates weak ferromagnetic superexchange along the embedded [Ni(OCO)]n chain
subunits (g = 2.272(4), J = 0.25(1) cmꢁ1). The d10 derivative 1 undergoes ligand-centered blue-violet lumi-
nescence upon exposure to ultraviolet light (kmax = 417 nm). Thermal decomposition behavior is also
explored.
Nickel
Coordination polymer
Luminescence
Magnetism
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
[Cd(phthalate)(dpa)(H2O)]ꢀ4H2O}n (dpa = 4,40-dipyridylamine) has
a simple 4-connected self-penetrated yyz net with 7482 topology
The synthesis and characterization of divalent metal benzenedi-
carboxylate coordination polymers remains an extremely active
research focus, as this class of materials has significant potential
as gas storage systems [1], selective molecular absorbents [2],
ion-exchange substrates [3], heterogeneous catalysts [4], and in
non-linear optical applications [5]. The aesthetic appeal of many
coordination polymer structures is undeniable, adding to the impe-
tus for further investigations [6].
[7b], while {[Cu2(pht)2(dpa)]ꢀH2O}n has a hexagonal 1D nanotubu-
lar structure with open pores [7c]. Thus, metal coordination prefer-
ence can play
a very significant role in instilling the final
coordination polymer topology and dimensionality in these dual-
ligand systems.
In comparison to the numerous coordination polymers contain-
ing short-arm benzenedicarboxylate ligands, related phases con-
taining the potentially more flexible homophthalate ligand
(hmph, Scheme 1) are much rarer [10–13]. The extra degrees of
conformational freedom can instill diverse coordination polymer
topologies in response to the presence of a dipyridyl co-ligand with
a particular donor disposition. {[Cd(hmph)(4-bpmp)1.5]ꢀ4H2O}n
Aromatic dicarboxylate ligands such as phthalate [7], isophthal-
ate [8], and terephthalate [9], have proven very efficacious in the
construction of crystalline coordination polymer solids with func-
tional properties or with unprecedented topologies. By way of
example, the 3D interpenetrated phase [Zn(terephthalate)
(4-bpmp = bis(4-pyridylmethyl)piperazine)) manifests
a
new
(4,40-bpy)0.5
]
(4,40-bpy = 4,40-bipyridine) can absorb significant
3-fold interpenetrated 5-connected 3D net with a simple 4466
topology, significantly different from the usual, common sqp topol-
ogy. The different steric and supramolecular environment provided
by bis(4-pyridylformyl)piperazine (4-bpfp) afforded [Cd2(hmph)2
(4-bpfp)]n, which displays a rarely encountered 4,5-connected bin-
odal tcs net with (4462)(4466) topology [10]. [Zn2(hmph)2(4-bpfp)]n
has a decorated (4,4) grid topology with embedded [Zn2(OCO)4]
paddlewheel clusters [10]. [Cd(hmph)(4,40-bpy)] shows a simple
(4,4) grid topology, and is reported to emit red visible light upon
ultraviolet excitation [11], while {[Ni(hmph)(dpa)]ꢀ1.33H2O}n
possesses a (6,3) herringbone grid topology [12].
amounts of carbon dioxide [9a]. [Co(Hphthalate)2(4,40-bpy)]n pos-
sesses a unique 6-connected self-penetrated 3D network with
510647 topology built from a diamondoid [Co(Hphthalate)2]n sub-
net with crossing bpy tethers [7a]. Furthermore, the topological
scope of these phases can be enhanced by the inclusion of different
dipyridyl-type tethering ligands besides the rigid-rod tether 4,40-bpy.
⇑
Corresponding author. Address: Lyman Briggs College, E-30 Holmes Hall,
Michigan State University, East Lansing, MI 48825, USA. Tel.: +1 0016168369968.
E-mail address: laduca@msu.edu (R.L. LaDuca).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.005

C.M. Rogers et al. / Inorganica Chimica Acta 403 (2013) 78–84
79
were placed into 5 mL distilled H2O in a 15 mL screw-cap glass vial.
The vial was sealed as tightly as possible by hand and heated at
80 °C in an oil bath for 48 h. It was then withdrawn from the oven
and allowed to air cool to 25 °C. Orange blocks of 2 (42 mg, 48%
yield based on Co) were isolated after washing with distilled water
and acetone, and drying in air. Anal. Calc. for C25H32CoN4O11 2: C,
48.16; H, 5.17; N, 8.99. Found: C, 48.12; H, 5.17; N, 8.86%. IR
(cmꢁ1): 3300 (w, br), 2923 (w), 1650 (m), 1603 (m), 1530 (s),
1465 (w), 1433 (m), 1397 (s), 1290 (m), 1260 (m), 1210 (w),
1156 (m), 1053 (w), 1007 (s), 869 (w), 842 (m), 797 (w), 741
(m), 700 (s), 673 (s).
Scheme 1. Ligands used in this study.
2.4. Preparation of [Ni(hmph)(4-bpfp)(H2O)]n (3)
In this study we have aimed to extend the presently limited
scope of known divalent metal homophthalate long-spanning
dipyridyl coordination polymers with the synthesis, structural
characterization, and physical property determinations of [Zn2
(hmph)2(3-bpmp)]n (1), {[Co(H2O)4(4-bpfp)][Co(hmph)2(4-bpfp)]ꢀ
6H2O}n (2), and [Ni(hmph)(4-bpfp)(H2O)]n (3). Luminescent prop-
erties are recorded for the d10 derivative 1, while variable temper-
ature magnetic susceptibility experiments were carried out to
investigate spin communication between juxtaposted paramag-
netic centers in 3. Thermal decomposition behavior has been
probed for all three new materials.
Ni(NO3)2ꢀ6H2O (41 mg, 0.14 mmol), 4-bpfp (41 mg, 0.14 mmol),
homophthalic acid (25 mg, 0.14 mmol), and 0.5 mL 1.0 M NaOH
were placed into 5 mL distilled H2O in a 15 mL screw-cap glass vial.
The vial was sealed as tightly as possible by hand and heated at
80 °C in an oil bath for 48 h. Blue needles of 3 (67 mg, 87% yield
based on Ni) were isolated after washing with distilled water and
acetone, and drying in air. Anal. Calc. for C25H24N4NiO7 3: C,
54.48; H, 4.39; N, 10.16. Found: C, 53.74; H, 4.38; N, 9.80%. IR
(cmꢁ1): 3500 (w, br), 2961 (w), 1660 (m), 1614 (m), 1582 (m),
1561 (s), 1547 (s), 1412 (s), 1385 (s), 1289 (m), 1260 (s), 1221
(w), 1151 (w), 1086 (w), 1050 (w), 1003 (s), 842 (m), 790 (m),
777 (w), 767 (w), 735 (s), 709 (s), 663 (s).
2. Experimental
2.1. General considerations
3. X-ray crystallography
Metal salts, homophthalic acid, and ligand precursors were ob-
tained from Aldrich. Bis(3-pyridylmethyl)piperazine [14] and
bis(4-pyridylformyl)piperazine [15] were prepared using literature
Single crystal reflection data for 1–3 were collected at 173 K
using a Bruker-AXS Apex II CCD instrument. Reflection data was
acquired using graphite-monochromated Mo
Ka radiation
procedures. Water was deionized above 3 MX-cm in-house. IR
(k = 0.71073 Å). The data was integrated via SAINT [17]. Lorentz
and polarization effect and absorption corrections were applied
with SADABS [18]. The structures were solved using direct methods
and refined on F2 using SHELXTL [19]. 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. Where possible, hydrogen atoms belonging to
water molecules were found by Fourier difference map and refined
with isotropic thermal displacement parameters. Relevant crystal-
lographic data for 1–3 are listed in Table 1.
spectra were recorded on a Perkin Elmer Spectrum One DRIFT
instrument on powdered samples. Elemental Analysis was carried
out using a Perkin Elmer 2400 Series II CHNS/O Analyzer. The lumi-
nescence spectrum of 1 was obtained with a Hitachi F-4500
Fluorescence Spectrometer on a solid crystalline sample anchored
to quartz microscope slides with Rexon Corporation RX-22P ultra-
violet-transparent epoxy adhesive. Variable temperature magnetic
susceptibility data (2 K to 300 K) for 3 were collected on a Quan-
tum Design MPMS SQUID magnetometer at an applied field of
0.1 T. After each temperature change the sample was kept at the
new temperature for 5 min before magnetization measurement
to ensure thermal equilibrium. The susceptibility data was cor-
rected for diamagnetism using Pascal’s constants [16].
4. Results and discussion
4.1. Synthesis and spectral characterization
2.2. Preparation of [Zn2(hmph)2(3-bpmp)]n (1)
Compounds 1–3 were prepared by the hydrothermal reaction of
the appropriate metal salt, homophthalic acid, and the requisite
dipyridyl ligand, with the addition of aqueous base for 2–3. The
infrared spectra of all of the compounds were consistent with their
crystal structures.
Zn(NO3)2ꢀ6H2O (42 mg, 0.14 mmol), 3-bpmp (38 mg, 0.14 mmol)
and homophthalic acid (25 mg, 0.14 mmol) were placed into 5 mL
distilled H2O in a 15 mL screw-cap vial. The vial was sealed as tightly
as possible by hand and heated at 80 °C in an oil bath for 48 h. It was
then withdrawn from the oil bath and allowed to air cool to 25 °C.
Colorless blocks of 1 (50 mg, 95% yield based on Zn) were isolated
after washing with distilled water and acetone, and drying in air.
Anal. Calc. for C34H32N4O8Zn2 1: C, 54.06; H, 4.12; N, 5.73. Found:
C, 53.52; H, 3.79; N, 5.31%. IR (cmꢁ1): 2921 (m), 2852 (m), 1629
(s), 1598 (m), 1460 (m), 1404 (s), 1300 (w), 1187 (w), 1148 (w),
1064 (w), 1004 (w), 936 (w), 801 (m), 741 (s), 704 (s), 674 (s),
658 (m).
Weak, highly broadened features above ꢂ3200 cmꢁ1 in the
spectrum of 2 and 3 indicate the presence of the bound and/or
unligated water molecules. Bands between 2800 and 3100 cm–1
in all spectra represent C–H stretching modes. Asymmetric and
symmetric C–O stretching modes of the hmph ligands are present
as broadened, stronger bands at 1629 and 1404 cmꢁ1 (1), and 1530
and 1397 cmꢁ1 (2), 1561 and 1385 cmꢁ1 for the monodentate car-
boxylate group in 3, and 1547 and 1412 cmꢁ1 for the bridging car-
boxylate group in 3. A narrower
Dm gap between the C–O
2.3. Preparation of {[Co(H2O)4(4-bpfp)][Co(hmph)2(4-bpfp)]ꢀ6H2O}n (2)
stretching bands has been ascribed to a bridging or chelating car-
boxylate binding mode [20]. Medium intensity bands in the range
of ꢂ1600 to ꢂ1200 cmꢁ1 are caused by stretching modes of the
pyridyl rings of the 3-bpmp or 4-bpfp ligands and the aromatic
Co(NO3)2ꢀ6H2O (41 mg, 0.14 mmol), 4-bpfp (41 mg, 0.14 mmol),
homophthalic acid (25 mg, 0.14 mmol), and 0.5 mL 1.0 M NaOH

80
C.M. Rogers et al. / Inorganica Chimica Acta 403 (2013) 78–84
Table 1
Crystal and structure refinement data for 1–3.
Data
1
2
3
Empirical Formula
Formula weight
Crystal system
Space group
a (Å)
C
34H32N4O8Zn2
C25H32CoN4O11
623.48
C25H24N4NiO7
551.19
monoclinic
P21/c
16.411(3)
16.687(3)
8.7009(16)
90
91.587(2)
90
2381.9(8)
4
1.537
0.870
755.38
triclinic
P1
triclinic
ꢀ
ꢀ
P1
7.775(2)
10.371(3)
10.484(3)
92.643(3)
107.411(3)
106.529(4)
765.3(4)
1
7.4031(9)
11.9709(14)
16.4265(19)
97.706(1)
96.661(1)
100.489(1)
1365.0(3)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.639
1.629
1.517
0.696
l
(mmꢁ1
)
Min./max. transmission
hkl ranges
Total reflections
Unique reflections
Rint
0.6997/0.8807
0.7557/0.8744
0.7488/0.9777
19 6 h 6 19, 0 6 k 6 20, 0 6 l 6 10
50075
ꢁ10 6 h 6 10, ꢁ13 6 k 6 13, ꢁ13 6 l 6 13
8 6 h 6 8, ꢁ14 6 k 6 14, ꢁ19 6 l 6 19
13340
3615
0.0474
217/0
22162
4958
4365
0.1171
340/3
0.0930
0.0643
0.1647
0.1507
0.584/ꢁ1.074
1.117
0.0261
403/15
0.0271
0.0243
0.0620
0.0601
0.270/ꢁ0.303
1.045
Parameters/restraints
a
R1 (all data)
0.0452
0.0335
0.0784
0.0731
0.393/ꢁ0.342
1.043
a
R1 (I > 2
r
(I))
b
wR2 (all data)
b
wR2 (I > 2r(I))
Max/min residual (eꢁ/Å3)
Goodness-of-fit (GOF) on F2
a
R1
wR2 = {
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
b
2
R
[w(Fo ꢁ Fc2)2]/
R .
[wFo2]2}1/2
rings of the hmph ligands [21]. The C–O carbonyl stretching bands
gen donor atom from a 3-bpmp ligand. Bond lengths and angles
within the coordination environment are listed in Table 2.
of the 4-bpfp ligands appeared at 1650 cmꢁ1 (2) or 1660 cmꢁ1 (3).
Exotetradentate hmph ligands with a l4-
j4O:O0:O00:O000 binding
mode (Scheme 2) produce [Zn2(hmph)2]n 1D coordination polymer
chains aligned along the a crystallographic axis, with embedded
{Zn2(OCO)4} paddlewheel dimeric units (Fig. 1b). The Znꢀ ꢀ ꢀZn
through space distance across the dimeric kernel is 2.9258(9) Å;
the related distance across the hmph ligand is 7.775 Å, defining
the a lattice parameter. Parallel [Zn2(hmph)2]n chain motifs are
linked into [Zn2(hmph)2(3-bpmp)]n 2D coordination polymer
layers (Fig. 1c) by anti-conformation 3-bpmp ligands. These layers
4.2. Structural description of [Zn2(hmph)2(3-bpmp)]n (1)
The asymmetric unit of compound 1 contains a divalent zinc
atom, a fully deprotonated hmph dianion, and half of a 3-bpmp li-
gand whose piperazinyl ring centroid is situated at a crystallo-
graphic inversion center. A slightly distorted {ZnO4N} square
pyramidal coordination environment is present in 1 (Fig. 1a); the
zinc atom rests 0.35 Å above the plane defined by the four hmph
oxygen donor atoms in the equatorial positions. Two of these, in
trans positions, are provided by short hmph carboxylate arms.
The other two trans oxygen donors belong to long hmph carboxyl-
ate pendant arms. The axial position is taken up by a pyridyl nitro-
ꢀ
lie parallel to the (011) crystal planes. The Znꢀ ꢀ ꢀZn internuclear
distance through the 3-bpmp ligands is 14.097 Å. Very similar di-
mer-bearing [Zn2(hmph)2]n chains were seen in the related phase
[Zn2(hmph)2(4-bpfp)]n [10].
Fig. 1. (a) Coordination environment at Zn in 1. (b) [Zn2(hmph)2]n 1D chain in 1. (c) [Zn2(hmph)2(3-bpmp)]n layer in 1. (d) Stacking of [Zn2(hmph)2(3-bpmp)]n layers.

C.M. Rogers et al. / Inorganica Chimica Acta 403 (2013) 78–84
81
Table 2
If each {Zn2(OCO)4} paddlewheel dimer in 1 is treated as a 4-
connected node, the layer structure can be considered a simple
(4,4) grid. Adjacent [Zn2(hmph)2(3-bpmp)]n layers stack in an
AAA pattern along both the b and c directions via three different
Selected bond distance (Å) and angle (°) data for 1.
Zn1–N1
2.0274(19)
2.0393(17)
2.0403(17)
2.0443(17)
2.0704(16)
100.20(7)
99.21(7)
160.45(7)
103.18(7)
90.51(8)
Zn1–O1#1
Zn1–O2#2
interlayer interactions: non-classical C–Hꢀ ꢀ ꢀO interactions,
p–p
Zn1–O4
stacking between hmph aromatic rings, and
3-bpmp pyridyl rings (Fig. 1d).
p–p stacking between
Zn1–O3#3
N1–Zn1–O1#1
N1–Zn1–O2#2
O1#1–Zn1–O2#2
N1–Zn1–O4
O1#1–Zn1–O4
O2#2–Zn1–O4
N1–Zn1–O3#3
O1#1–Zn1–O3#3
O2#2–Zn1–O3#3
O4–Zn1–O3#3
4.3. Structural description of {[Co(H2O)4(4-bpfp)][Co(hmph)2(4-
bpfp)]ꢀ6H2O}n (2)
87.29(8)
96.40(7)
85.48(7)
90.11(7)
The asymmetric unit of compound 2 contains two divalent co-
balt atoms (Co1, Co2) on crystallographic inversion centers, two
aqua ligands, a hmph ligand, halves of two crystallographically dis-
tinct 4-bpfp ligands whose piperazinyl ring centroids are situated
on inversion centers, and three water molecules of crystallization.
Both Co1 and Co2 exhibit a {CoO4N2} octahedral coordination
sphere with trans pyridyl nitrogen donor atoms from 4-bpfp li-
gands. Co1 possesses two sets of cis hmph carboxylate oxygen
atom donors, in which both cis oxygen donors arise from the same
hmph ligand. Therefore the hmph ligands in 2 do not bridge metal
centers, but instead bind to a single cobalt atom with a chelating
j2O:O00 binding mode (Scheme 2). Donors from the long carboxyl-
ate pendant arms of two hmph ligands are disposed in a trans man-
ner, as are donors from the short carboxylate arms (Fig. 2a). On the
other hand, the coordination environment of Co2 shows four aqua
ligands in its equatorial plane (Fig. 2b). Metrical parameters within
the coordination spheres are given in Table 3.
160.41(7)
Symmetry equivalent positions: #1 x ꢁ 1, y, z; #2
ꢁx + 1, ꢁy ꢁ 2, ꢁz ꢁ 1; #3 ꢁx, ꢁy ꢁ 2, ꢁz ꢁ 1.
Scheme 2. Binding modes of the homophthalate ligands in 1–3.
2nꢁ
Fig. 2. (a) Coordination environment at Co1 in 2. (b) Coordination environment at Co2 in 2. (c) Hydrogen-bonded pair of [Co(hmph)2(4-bpfp)]n
[Co(H2O)4(4-bpfp)]n
anionic chain and
2n+
cationic chain in 2. Hydrogen bonding is shown as dashed lines. (d) Stacking diagram for 2, with anionic chain motifs in green and cationic chain
motifs in red. The colors refer to the graphic in the online version of this article.

82
C.M. Rogers et al. / Inorganica Chimica Acta 403 (2013) 78–84
Table 3
Selected bond distance (Å) and angle (°) data for 2.
Co1–O6
Co1–O8
Co1–N4
Co2–O7
Co2–O5
Co2–N3
2.0430(10)
2.1441(10)
2.1471(12)
2.0512(11)
2.1059(11)
2.1622(13)
180.0
96.01(4)
83.99(4)
180.0
O8–Co1–N4
89.62(4)
90.39(4)
180.0
O6#1–Co1–N4
N4–Co1–N4#1
O7#2–Co2–O7
O7#2–Co2–O5
O7–Co2–O5
180.0
90.12(4)
89.88(4)
180.0
89.68(5)
90.32(5)
92.34(5)
87.66(5)
180.0
O6–Co1–O6#1
O6–Co1–O8
O6#1–Co1–O8
O8–Co1–O8#1
O6–Co1–N4
O6#1–Co1–N4
O5#2–Co2–O5
O7#2–Co2–N3
O7–Co2–N3
O5#2–Co2–N3
O5–Co2–N3
90.98(4)
89.02(4)
N3#2–Co2–N3
Symmetry equivalent positions: #1 ꢁx + 1, ꢁy + 1, ꢁz; #2 ꢁx + 2, ꢁy, ꢁz.
The anionic [Co(hmph)2]2ꢁ fragments based on Co1 are linked
2nꢁ
into anionic [Co(hmph)2(4-bpfp)]n
chains by anti-conformation
4-bpfp ligands. Similarly, cationic [Co(H2O)4]2+ fragments are con-
2n+
nected into [Co(H2O)4(4-bpfp)]n
chains by other anti-conforma-
tion 4-bpfp ligands. In both chain motifs, the through-ligand
Coꢀ ꢀ ꢀCo distance is 16.427 Å, defining the c lattice parameter. Pairs
of distinct coordination polymer chains are connected to each
other via hydrogen bonding between the aqua ligands in the cat-
ionic chains and ligated or unligated hmph carboxylate oxygen
atoms in the anionic chains (Fig. 2c). Trapped between pairs of
chains of each type, in 1D incipient channels, lie co-crystallized
water molecule trimers (Fig. 2d). These are held to the coordina-
tion polymer chains by hydrogen bonding patterns involving hmph
carboxylate oxygen atoms and aqua ligands (Table 4).
Fig. 3. (a) Coordination environment at Ni in 3. (b) [Ni(H2O)(hmph)]n chain in 3,
featuring anti–syn bridged [Ni(OCO)]n chain subunit. (c) [Ni(H2O)(hmph)(4-bpfp)]n
layers with [Ni(H2O)(hmph)]n chains drawn in blue (online version of the article).
4.4. Structural description of [Ni(hmph)(4-bpfp)(H2O)]n (3)
The asymmetric unit of compound 3 contains a divalent nickel
atom, a hmph ligand, a 4-bpfp ligand, and an aqua ligand. Nickel
atoms in 3 display a {NiO4N2} octahedral coordination environ-
ment, with trans pyridyl nitrogen donors from two 4-bpfp ligands
(Fig. 3a). Two carboxylate oxygen atoms from a single hmph ligand
occupy cis coordination sites in the equatorial plane. The other two
equatorial sites are filled by an aqua ligand and a carboxylate oxy-
gen atom from a second hmph ligand. Bond lengths and angles
within the coordination environment in 3 are given in Table 5.
Dissimilar to the exotetradentate binding mode in 1 and the
chelating binding mode in 2, the hmph ligands in 3 adopt an exo-
atoms are linked by carboxylate groups in an anti–syn fashion
(Fig. 3b). The Niꢀ ꢀ ꢀNi distance along the embedded [Ni(OCO)]n
chain subunits is 5.265 Å. Parallel [Ni(H2O)(hmph)]n chains are
aligned along the c crystallographic direction.
Neighboring [Ni(H2O)(hmph)]n chains are connected into
[Ni(H2O)(hmph)(4-bpfp)]n (4,4) coordination polymer grids
(Fig. 3c) by tethering 4-bpfp ligands with a slightly twisted anti
conformation (Oꢀ ꢀ ꢀNꢀ ꢀ ꢀNꢀ ꢀ ꢀO torsion angle = 152.2°). The Niꢀ ꢀ ꢀNi
distance across the 4-bpfp within the coordination polymer grid
bidentate l2 j3O,O00:O000 binding mode (Scheme 2). Both the short
-
is 16.411 Å, marking the a lattice parameter. Supramolecular
p–p
stacking between hmph aromatic rings and 3-bpmp pyridyl rings
serves an ancillary structure stabilization role within the layers.
Adjacent [Ni(H2O)(hmph)(4-bpfp)]n layers stack in an ABAB pattern
along the c crystal axis, anchored to each other through hydrogen
and long carboxylate arms of the hmph ligand chelate to a single
nickel atom, while the long carboxylate arm also binds to another
nickel atom. Via this binding mode, [Ni(H2O)(hmph)]n 1D coordi-
nation polymer chains are formed in which neighboring nickel
Table 4
Hydrogen bonding distance (Å) and angle (°) data for 2–3.
D–Hꢀ ꢀ ꢀA
d(H. . .A)
\DHA
d(Dꢀ ꢀ ꢀA)
Symmetry transformation for A
2
O1W–H1WAꢀ ꢀ ꢀO5
O1W–H1WBꢀ ꢀ ꢀO3
O2W–H2WAꢀ ꢀ ꢀO1W
O2W–H2WB. . .O2
O3W–H3WAꢀ ꢀ ꢀO2W
O3W–H3WB. . .O2
O5–H5Aꢀ ꢀ ꢀO1
2.106(17)
1.900(17)
1.890(17)
1.995(17)
1.94(2)
159(2)
161(2)
170(3)
174(3)
161(3)
159(3)
169.8(18)
165.4(18)
171.2(18)
174.3(18)
2.9160(17)
2.7225(17)
2.746(2)
2.8370(19)
2.759(2)
x ꢁ 1, y, z
x ꢁ 1, y ꢁ 1, z
x, y ꢁ 1, z
ꢁx + 1, ꢁy + 1, ꢁz + 1
2.13(2)
2.926(2)
1.780(14)
1.860(15)
1.826(15)
1.914(14)
2.6168(15)
2.6780(16)
2.6627(16)
2.7635(15)
x + 1, y, z
O5–H5Bꢀ ꢀ ꢀO1
ꢁx + 2, ꢁy, ꢁz
O7–H7Cꢀ ꢀ ꢀO3
x, y ꢁ 1, z
O7–H7Dꢀ ꢀ ꢀO8
ꢁx + 1, ꢁy, ꢁz
3
O7–H7Cꢀ ꢀ ꢀO3
2.73(5)
2.00(2)
103(3)
155(4)
3.041(4)
2.814(4)
x, ꢁy + 1/2, z – 1/2
x, ꢁy + 1/2, z – 1/2
O7–H7Dꢀ ꢀ ꢀO5

C.M. Rogers et al. / Inorganica Chimica Acta 403 (2013) 78–84
83
Table 5
lic acid (445 nm), while 3-bpmp showed very weak luminescence
under the same excitation wavelength. Via comparison with other
d10 metal coordination polymers with aromatic ligands [22], the
Selected bond distance (Å) and angle (°) data for 3.
Ni1–O5
2.053(3)
2.064(3)
2.065(3)
2.068(3)
2.091(4)
2.092(4)
101.97(12)
77.30(11)
179.21(12)
172.00(12)
85.98(12)
O3#1–Ni1–O7
O5–Ni1–N1#2
O4–Ni1–N1#2
O3#1–Ni1–N1#2
O7–Ni1–N1#2
O5–Ni1–N4
94.76(12)
91.05(13)
90.60(13)
89.71(13)
87.94(13)
89.98(13)
88.09(13)
91.61(13)
91.19(13)
178.48(14)
Ni1–O4
emissive properties of 1 likely arises from ligand-centered
or
rings of the hmph ligands. The blueshift of the emission maximum
p p
ꢁ
Ni1–O3#1
Ni1–O7
p
ꢁn molecular orbital electronic transitions within the phenyl
Ni1–N1#2
Ni1–N4
is likely caused by coordination of the hmph ligand to zinc.
O5–Ni1–O4
O5–Ni1–O3#1
O4–Ni1–O3#1
O5–Ni1–O7
O4–Ni1–O7
O4–Ni1–N4
O3#1–Ni1–N4
O7–Ni1–N4
4.6. Magnetic properties of 3
N1#2–Ni1–N4
A variable temperature magnetic susceptibility experiment was
carried out in order to investigate spin communication along the
embedded [Ni(OCO)]n chain subunits in 3. A Curie–Weiss plot over
the entire temperature range (Fig. S1) gives C = 1.29 cm3 K molꢁ1
Symmetry equivalent positions: #1 x, ꢁy + 1/2, z ꢁ 1/2; #2 x ꢁ 1, y, z.
and
H
= 0.06 K, with the small, positive
H
value portending weak
ferromagnetic coupling. At 300 K, the
v
mT product was 1.30 cm3 -
K molꢁ1, somewhat higher than expected for an isolated S = 1 Ni2+
ion (1.00 cm3 K molꢁ1), indicative of possible ferromagnetic cou-
pling. This value remained largely steady upon cooling to 40 K. Be-
low this temperature,
vmT product increased more rapidly, thus
corroborating the presence of ferromagnetic superexchange
through the anti–syn carboxylate bridges. Fitting of the data
(Fig. 5) to Fisher’s expression [23] for a 1D chain of S = 1 ions
Eq. (1) gives g = 2.272(4) and J = 0.25(1) cmꢁ1 with R = {
R [(vmT)obs –
(v
mT)calc]2}1/2 = 1.23 ꢃ 10ꢁ3. The small, positive J value also indicates
weak ferromagnetic coupling of eg-like orbital unpaired electrons
through the carboxylate molecular orbitals.
Ng2
b
2SðSþ1Þ
3k
1þu
v
mT ¼ ð
Þð1ꢁuÞ
ð1Þ
u ¼ coth½JSðSþ1Þꢄ ꢁ ½JSðSþ1Þꢄ
kT
kT
Fig. 4. Emission spectrum of 1.
4.7. Thermal properties
Thermogravimetric analysis was undertaken to examine the
decomposition behavior of 1–3. Thermograms are shown in
Figs. S2–S4. The thermal degradation of compound 1 began at
135 °C via likely decarboxylation of the hmph ligands (11.7% calc’d,
12.8% obs’d), followed by ejection of the 3-bpmp ligands above
290 °C (35.5% calc’d, 39.9% obs’d). The final mass remnant of
26.8% at 475 °C is likely a mixture of ZnO (21.6% calc’d) and some
uncombusted organic material. Dehydration of compound 2 oc-
curred between 25 and 85 °C, with a 11.7% mass loss roughly con-
sistent with removal of most of the bound and all of the unbound
water molecules (14.4% calc’d). The remainder of the aqua ligands
were removed between 85 and 200 °C. Above 250 °C, the organic
ligands were ejected from the coordination polymer structure.
The final mass remnant of 32.8% at 475 °C is most likely a mixture
of CoCO3 (18.9% calc’d) and a fair amount of uncombusted organic
material. Compound 3 underwent slow dehydration via ejection of
bound water molecules between 25 and 250 °C, with the 3.3% mass
loss matching the predicted value for one molar equivalent of
water per nickel. Ligand combustion above 250 °C was marked
by a precipitous mass loss. The final remnant of 24.6% at 475 °C
is likely a combination of NiCO3 (21.4% calc’d) and a small amount
of uncombusted carbonaceous material.
Fig. 5. Variable temperature magnetic susceptibility data for 3. The best fit to Eq.
(1) is shown as a thin black line.
bonding donation from aqua ligands to unligated long hmph car-
boxylate group oxygen atoms (Table 4).
5. Conclusions
Related, long-spanning dipyridyl/piperazine ligands have affor-
ded new divalent coordination polymers with the seldom used
flexible-arm homophthalate ligand, thereby expanding the scope
of its coordination polymer structural chemistry. Using the
kinked-disposition 3-bpmp ligand gave a coordination polymer
with [Zn(homophthalate)]n layers featuring {Zn2(OCO)4} paddle-
wheel dimers, very similar to the structure of a previously synthesized
4.5. Luminescent properties of 1
Irradiation of a crystalline sample of complex 1 with ultraviolet
light (kex = 260 nm) caused moderately intense blue-violet visible
light emission with a maximum at k = 418 nm (Fig. 4). This emis-
sion profile matches reasonably well with that of free homophtha-

84
C.M. Rogers et al. / Inorganica Chimica Acta 403 (2013) 78–84
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The authors gratefully acknowledge the donors of the American
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Appendix A. Supplementary material
CCDC 904801, 904799, and 904800 contain the supplementary
crystallographic data for 1–3. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.ica.2013.01.005.
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