Effect of pendant arm length and nitrogen donor disposition on the topology of luminescent cadmium phenylenedicarboxylate coordination polymers with bis(pyridylmethyl)piperazine co-ligands

Article abstract of DOI:10.1016/j.ica.2009.09.043

Hydrothermal synthesis has afforded divalent cadmium coordination polymers containing bis(pyridylmethyl)piperazine (bpmp) tethers and either phenylenediacetate (phda) or phenylenedipropionate (phdp) ligands. {[Cd(1,4-phda)(4-bpmp)]·1.5H₂O}_n (1) displays a (4,4)-grid layered structure based on 4-connected {Cd₂O₂} dimeric units. Extension of the pendant arms generated {[Cd(1,4-phdp)(H4-bpmp)](ClO₄)·3.5H₂O}_n (2, phdp = phenylenedipropionate), which possesses a rare (3,6) 2D trigonal lattice based on 6-connected {Cd₂O₂} dimers. Changing the nitrogen donor atom disposition by using 3-bpmp as the nitrogen co-ligand yielded [Cd(1,4-phdp)(3-bpmp)(H₂O)]_n (3), which crystallizes in a 3-fold interpenetrated achiral diamondoid lattice. [Cd(1,3-phda)(4-bpmp)]_n (4) adopts a very similar structure to that of 1. Complexes 1-4 undergo blue-violet luminescence upon exposure to ultraviolet radiation.

Full text of DOI:10.1016/j.ica.2009.09.043

Inorganica Chimica Acta 363 (2010) 88–96
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Effect of pendant arm length and nitrogen donor disposition on the topology
of luminescent cadmium phenylenedicarboxylate coordination polymers
with bis(pyridylmethyl)piperazine co-ligands
*
Karyn M. Blake, Gregory A. Farnum, Lindsey L. Johnston, Robert L. LaDuca
Lyman Briggs College and Department of Chemistry, Michigan State University, East Lansing, MI 48825, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 August 2009
Received in revised form 19 September 2009
Accepted 24 September 2009
Available online 3 October 2009
Hydrothermal synthesis has afforded divalent cadmium coordination polymers containing bis(pyridyl-
methyl)piperazine (bpmp) tethers and either phenylenediacetate (phda) or phenylenedipropionate
(phdp) ligands. {[Cd(1,4-phda)(4-bpmp)]ꢀ1.5H2O}n (1) displays a (4,4)-grid layered structure based on
4-connected {Cd2O2} dimeric units. Extension of the pendant arms generated {[Cd(1,4-phdp)(H4-
bpmp)](ClO4)ꢀ3.5H2O}n (2, phdp = phenylenedipropionate), which possesses a rare (3,6) 2D trigonal lat-
tice based on 6-connected {Cd2O2} dimers. Changing the nitrogen donor atom disposition by using 3-
bpmp as the nitrogen co-ligand yielded [Cd(1,4-phdp)(3-bpmp)(H2O)]n (3), which crystallizes in a 3-fold
interpenetrated achiral diamondoid lattice. [Cd(1,3-phda)(4-bpmp)]n (4) adopts a very similar structure
to that of 1. Complexes 1–4 undergo blue-violet luminescence upon exposure to ultraviolet radiation.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Cadmium
Dicarboxylate
Coordination polymer
Luminescence
1. Introduction
alkanes [11a]. Within these aromatic carboxylate ligands a modi-
cum of conformational flexibility is permitted through
r-bond
Coordination polymers constructed from tethering carboxylate
ligands have been shown to have promise in several technological
and industrial applications [1,2], such as gas storage [3], small mol-
ecule sorption and separation [4], ion-exchange [5], catalysis [6],
luminescence [7] and non-linear optical behavior [8]. Different me-
tal coordination environments and carboxylate group binding and
bridging modes promote a wide variety of structural topologies in
this class of materials [9]. Filled-shell d10 divalent zinc and cad-
mium ions often enhance structural diversity [10], as the lack of
crystal field stabilization allows the specific coordination environ-
ment to respond to the geometric and steric requirements of the
carboxylate ligands.
Many zinc and cadmium coordination polymers are based on
aromatic di- and tricarboxylate ligands such as isophthalate
[10a], terephthalate [10b], or trimesate [10c], wherein the rigidity
of the phenyl rings provides stable structural scaffoldings. The
inclusion of bifunctional nitrogen-base co-ligands has been a suc-
cessful tactic to develop the structural complexity and utility of
this class of materials [11]. An especially curious example is the
interpenetrated three-dimensional (3D) phase [Zn(terephthal-
ate)(4,40-bpy)0.5]n, which possesses cavities that can be used for
the gas-chromatographic separation of linear and branched
rotation of the carboxylate groups. A more recent approach in
coordination polymer design and construction has been the use
of flexible linking ligands [12], including aromatic dicarboxylates
with conformationally agile pendant arms such as phenylenediac-
etate (phda) [13–15] or phenyenedipropionate (phdp) [16]
ligands.
In this contribution we report our synthetic explorations towards
cadmium phda or phdp coordination polymers containing long-
spanning, hydrogen-bonding capable bis(pyridylmethyl)piperazine
(bpmp) ligands, resulting in the isolation and structural character-
ization of {[Cd(1,4-phda)(4-bpmp)]ꢀ1.5H2O}n (1), {[Cd(1,4-phdp)-
(H4-bpmp)](ClO4)ꢀ3.5H2O}n (2), [Cd(1,4-phdp)(3-bpmp)(H2O)]n (3),
and [Cd(1,3-phda)(4-bpmp)]n (4). Within this group of materials,
either extending the length of the pendant arms on the dicarboxyl-
ate ligands or altering the disposition of the nitrogen donors in the
bpmp ligands forces substantial changes in the overarching coordi-
nation polymer topologies. In addition, compounds 1–4 undergo
visible light emission upon exposure to ultraviolet light.
2. Experimental
2.1. General considerations
* Corresponding author. Address: Lyman Briggs College, E-30 Holmes Hall,
Michigan State University, East Lansing, MI 48825 USA. Tel.: +1 517 432 2268.
E-mail address: laduca@msu.edu (R.L. LaDuca).
Cadmium salts and dicarboxylic acids were obtained commer-
cially from Aldrich. The isomeric bis(pyridylmethyl)piperazine
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.09.043

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
89
ligands were prepared via a published procedure [17]. Water was
deionized above 3 M -cm in-house. Elemental analysis was car-
2807 w, 1612 m, 1565 s, 1500 w, 1460 w, 1426 m, 1390 s, 1354 m,
1322 w, 1299 w, 1272 w, 1224 w, 1157 m, 1131 m, 1062 w, 1016
m, 956 w, 930 w, 842 m, 799 m, 750 m, 733 w, 725 w, 697 w, 661
m.
X
ried out using a Perkin Elmer 2400 Series II CHNS/O Analyzer. IR
spectra were recorded on powdered samples on a Perkin Elmer
Spectrum One instrument. The luminescence spectra were ob-
tained with a Hitachi F-4500 Fluorescence Spectrometer on solid
crystalline samples anchored to quartz microscope slides with Rex-
on Corporation RX-22P ultraviolet-transparent epoxy adhesive.
3. X-ray crystallography
Single-crystal reflection data for 1–4 were collected using a Bru-
ker AXS Apex2 CCD instrument. Reflection data was acquired using
2.2. Preparation of {[Cd(1,4-phda)(4-bpmp)]ꢀ1.5H2O}n (1)
graphite–monochromated Mo Ka radiation (k = 0.71073 Å). The
reflection data were integrated with SAINT [18]. Lorentz and polari-
zation effect and empirical absorption corrections were applied
with SADABS [19]. The structures were solved using direct methods
and refined on F2 using SHELTXL [20]. The crystal of 3 was non-mer-
ohedrally twinned. The twin law was determined using CELL NOW
[21] and the refinement was carried out on reflection data from
only the major twin component. All non-hydrogen atoms were re-
fined with anisotropic thermal parameters. Hydrogen atoms bound
to carbon atoms were placed in calculated positions and refined
with isotropic thermal parameters using a riding model. Hydrogen
atoms bound to water molecules or piperazinyl nitrogen atoms
were located by Fourier difference map and restrained at fixed
positions, except for those in 2, and bound to the partially occupied
O2W position in 1. Two of the water molecules in 2 were disor-
dered across two positions each. One of the perchlorate ions in 2
was disordered over two positions, that each share two fully occu-
pied oxygen atom positions. Relevant crystallographic data for 1–4
are listed in Table 1.
Cd(NO3)2ꢀ4H2O (59 mg, 0.19 mmol), 4-bpmp (110 mg,
0.41 mmol), 1,4-phenylenediacetic acid (33 mg, 0.17 mmol) and
10 mL deionized water were placed into a 23 mL Teflon-lined acid
digestion bomb. The bomb was sealed and heated in an oven at
120 °C for 48 h, and then cooled slowly to 25 °C. Colorless blocks
of 1 (31 mg, 0.052 mmol, 27% yield based on 1,4-phda) were iso-
lated after washing with distilled water, ethanol, and acetone
and drying in air. Anal. Calc. for C26H31CdN4O5.5 1: C, 52.05; H,
5.21; N, 9.34. Found: C, 52.49; H, 4.87; N, 9.21%. IR (cmꢁ1): 3421
m br, 2920 w, 2815 w, 1612 m, 1565 s, 1547 s, 1477 w, 1424 s,
1399 s, 1374 w, 1356 w, 1324 w, 1298 w, 1255 w, 1220 w, 1157
m, 1128 m, 1012 m, 928 w, 898 w, 844 m, 799 m, 782 w, 736 m,
721 w, 689 w, 671 w.
2.3. Preparation of {[Cd(1,4-phdp)(H4-bpmp)](ClO4)ꢀ3.5H2O}n (2)
Cd(ClO4)2ꢀ6H2O (58 mg, 0.19 mmol), 4-bpmp (99 mg,
0.37 mmol),
and
1,4-phenylenedipropionic
acid
(41 mg,
0.19 mmol) and 5 mL deionized water were placed into screw-
cap vial. The vial was sealed and heated in an oil bath at 80 °C
for 72 h, and then cooled slowly to 25 °C. Colorless blocks of 2
(82 mg, 58% yield based on Cd) were isolated after washing with
distilled water, ethanol, and acetone and drying in air. Crystals of
2 partially lose their water molecules of crystallization upon stand-
ing at room temperature. Anal. Calc. for C56H80Cd2Cl2N8O23 (with
loss of five water molecules of crystallization) 2: C, 46.73; H,
4.90; N, 7.78. Found: C, 46.67; H, 5.03; N, 7.48%. IR (cmꢁ1): 3383
m br, 3012 w, 2925 w, 2918 w, 2845 w, 1701 m, 1646 w, 1613
m, 1561 m, 1540 s, 1435 s, 1425 s, 1403 m, 1364 w, 1314 m,
1273 w, 1223 m, 1191 w, 1171 w, 1087 s, 1015 m, 985 w, 974
w, 941 m, 892 m, 832 s, 806 m, 793 m, 721 w, 665 m.
4. Results and discussion
4.1. Synthesis and spectral characterization
Hydrothermal reaction of a cadmium salt, the requisite pheny-
lenedicarboxylic acid, and the appropriate bis(pyridyl-
methyl)piperazine isomer generated crystalline samples of 1–4.
The infrared spectra of 1–4 were consistent with their single crys-
tal structures. Sharp, medium intensity bands in the range of
ꢂ1600 cm–1 to ꢂ1200 cm–1 are attributed to stretching modes of
the pyridyl rings of the 4-bpmp or 3-bpmp ligands and the aro-
matic rings of the phenylenedicarboxylate moieties. Features cor-
responding to pyridyl ring puckering modes are evident in the
region between ꢂ930 and ꢂ600 cm–1. Asymmetric and symmetric
C–O stretching modes of the fully deprotonated dicarboxylate li-
gands were present as broadened strong bands at 1547 cm–1 and
1424/1399 cm–1 (1), 1540 cm–1 and 1435 cm–1 (2), 1544 cm–1
and 1406 cm–1 (3), and 1565 cm–1 and 1390 cm–1 (4). A strong
band at 1087 cm–1 in the spectrum of 2 marks the presence of
the unligated perchlorate ions.
2.4. Preparation of [Cd(1,4-phdp)(3-bpmp)(H2O)]n (3)
The procedure for the synthesis of 2 was followed, but with the
substitution of 3-bpmp (99 mg, 0.37 mmol) for 4-bpmp. Colorless
blocks of 3 (61 mg, 53% yield based on Cd) were obtained. Anal.
Calc. for C28H34CdN4O5 3: C, 54.33; H, 5.54; N, 9.05. Found: C,
54.28; H, 5.66; N, 8.66%. IR (cmꢁ1): 3370 w br, 2939 w, 2857 w,
2819 w, 1673 w, 1599 w, 1576 w, 1544 s, 1480 m, 1456 m, 1406
s, 1372 w, 1352 w, 1327 w, 1302 w, 1269 w, 1221 w, 1188 w,
1156 w, 1124 w, 1098 m, 1043 w, 1016 m, 1006 m, 969 w, 952
w, 934 w, 921 w, 840 m, 813 w, 791 w, 703 s
4.2. Structural description of {[Cd(1,4-phda)(4-bpmp)]ꢀ1.5H2O}n (1)
Compound 1 has an asymmetric unit containing a divalent cad-
mium atom, a 1,4-phda ligand, a complete 4-bpmp ligand, and two
water molecules of crystallization, one of whose positions is 50%
occupied (Fig. 1). The coordination environment at cadmium is a
{CdO5N2} distorted pentagonal bipyramid, with the equatorial
plane containing two chelating carboxylate groups from two 1,4-
phda ligands and a fifth oxygen donor, from a third 1,4-phda li-
gand. In the apical positions are pyridyl nitrogen donor atoms from
two different 4-bpmp ligands. Bond lengths and angles are con-
sisted with double chelation in this coordination environment,
and are given in Table S1.
2.5. Preparation of [Cd(1,3-phda)(4-bpmp)]n (4)
Cd(NO3)2ꢀ4H2O
(59 mg,
0.19 mmol),
4-bpmp
(51 mg,
0.19 mmol), 1,3-phenylenediacetic acid (36 mg, 0.19 mmol) and
6 mL deionized water were placed into a borosilicate glass tube
that had been flame-sealed at one end. The tube was flame-sealed
and heated in an oil bath at 80 °C for 48 h, and then cooled slowly
to 25 °C. Straw-colored blocks of 4 (15 mg, 14% yield based on Cd)
were isolated after washing with distilled water, ethanol, and ace-
tone and drying in air. Anal. Calc. for C26H28CdN4O4 4: C, 54.51; H,
4.93; N, 9.78. Found: C, 53.94; H, 4.97; N, 9.65%. IR (cmꢁ1): 2934 w,
The 1,4-phda ligands in 1 are exotridentate, in which each car-
boxylate endgroup chelates to a single cadmium atom, but an

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K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
Table 1
Crystal and structure refinement data for 1–4.
Compound
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C26H31CdN4O5.5
599.95
C56H80Cd2Cl2N8O23
1528.98
C28H34CdN4O5
618.99
monoclinic
C2/c
16.2998(17)
6.2571(7)
26.351(3)
90
92.578(1)
90
C26H28CdN4O4
572.92
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
9.431(3)
11.545(4)
12.924(5)
89.603(4)
68.964(5)
77.068(6)
1275.9(8)
2
11.1197(19)
14.804(3)
21.356(5)
102.460(3)
100.433(3)
106.730(2)
3174.2(10)
2
9.4666(19)
11.085(2)
12.577(3)
87.42(3)
82.61(3)
72.12(3)
1245.7(4)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
2684.9(5)
4
1.531
Z
Dcalc (g cm–3
)
1.562
0.902
1.600
0.839
1.527
0.916
l
(mm–1
)
0.859
Min./max. trans.
0.854
0.897
0.887
0.924
hkl ranges
ꢁ11 6 h 6 11, ꢁ13 6 k 6 13,
ꢁ15 6 l 6 15
18 691
ꢁ13 6 h 6 13, ꢁ17 6 k 6 17,
0 6 l 6 25
81 236
–19 6 h 6 19, –7 6 k 6 7,
–31 6 l 6 31
8016
–11 6 h 6 11, –13 6 k 6 13,
–12 6 l 6 15
30 208
Total reflections
Unique reflections
Independent reflections
4675
0.0990
11 761
0.0860
2443
0.0313
4566
0.0198
(Rint
)
Parameters/restraints
334/3
0.0807
0.0501
0.1140
0.1011
1.116/ꢁ0.876
830/4
0.0873
0.0565
0.1451
0.1332
1.103/ꢁ1.015
176/3
0.0281
0.0248
0.0608
0.0590
0.344/ꢁ0.264
316/0
0.0173
0.0167
0.0429
0.0424
0.265/ꢁ0.268
R1 (all data)a
R1 (I > 2
wR2 (all data)b
wR2 (I > 2
(I))b
Maximum/minimum
residual (e Åꢁ3
Goodness-of-fit (GOF)
r
(I))a
r
)
0.996
1.054
1.062
1.048
a
R1
wR2 = {
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
b
2
R
[w(Fo ꢁ Fc2)2]/
R .
[wFo2]2}1/2
Fig. 1. Coordination environment of 1 with thermal ellipsoids shown at 50% probability and partial atom numbering scheme.
oxygen atom (O3) at one of the carboxylates also bridges to a third
cadmium atom. Each pair of cadmium atoms is bridged by a pair of
O3 oxygen atom to form a rhomboid {Cd2O2} dimeric unit; the
CdꢀꢀꢀCd and OꢀꢀꢀO distances across this kernel are 3.856 and
2.831 Å, respectively. This rhomboid unit is quite pinched in
appearance, with O–Cd–O and Cd–O–Cd angles subtending
72.57(14) and 107.43(14)°. The 1,4-phda ligands connect the
{Cd2O2} dimers into [Cd(1,4-phda)]n ribbon motifs that are aligned
along the b crystal direction (Fig. 2). The CdꢀꢀꢀCd distance across the
1,4-phda ligands through the chelating carboxylate groups is
11.545 Å, marking the b lattice parameter.
Individual [Cd(1,4-phda)]n ribbon motifs are connected into a
[Cd(1,4-phda)(4-bpmp)]n 2D slab (Fig. 3) by the tethering 4-bpmp
ligands, with a CdꢀꢀꢀCd inter-ribbon distance of 17.270 Å. If the
{Cd2O2} dimers are treated as 4-connected nodes, the slab motif
of 1 can be construed as a standard (4,4) coordination polymer
grid. Within the slab are apertures of 12.923 ꢃ 25.184 Å, as defined
by through-space CdꢀꢀꢀCd distances. The Cd(1,4-phda)(4-bpmp)]n
2D slabs stack along the a crystal direction (Fig. S1), through supra-
molecular hydrogen-bonding mechanisms provided by the water
molecules of crystallization, piperazinyl nitrogen atoms, and car-
boxylate oxygen atoms (Table S2).The unligated water molecules
occupy 8.9% of the unit cell volume, according to PLATON [22].
4.3. Structural description of {[Cd(1,4-phdp)(H4-
bpmp)](ClO4)ꢀ3.5H2O}n (2)
Compound 2 has an asymmetric unit consisting of two crystal-
lographically independent cadmium atoms, 1,4-phdp ligands, and
4-bpmp ligands each protonated at one piperazinyl nitrogen atom,
along with two unligated perchlorate anions and seven total water
molecules of crystallization (Fig. 4). Both cadmium atoms possess a
{CdO5N2} distorted pentagonal bipyramidal coordination environ-
ment, with two chelating 1,4-phdp carboxylate groups and another

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
91
oxygen donor atom from a third 1,4-phdp ligand. The axial sites are
taken up by pyridyl nitrogen donor atoms from two different H4-
bpmp ligands. Bond lengths and angles about cadmium are given
in Table S3.
Sets of crystallographically identical cadmium atoms are con-
nected into parallel 1D [Cd(1,4-phdp)]n ribbons, situated parallel
to the a crystal direction, by exotridentate 1,4-phdp ligands
(Fig. 5). The dicarboxylate ligands have the same bis(chelating)/
Fig. 2. A single [Cd(1,4-phda)]n chain in 1, highlighting the presence of {Cd2O2} rhomboid dimers.
Fig. 3. A view down a of the [Cd(1,4-phda)(4-bpmp)]n slab in 1. Each {Cd2O2} dimer connects to four others, forming a (4,4) grid topology.
Fig. 4. Coordination environments of 2 with thermal ellipsoids shown at 50% probability and partial atom numbering scheme. Only the hydrogen atoms at the protonated
piperazinyl groups are shown.

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K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
bridging binding mode seen in 1, creating {Cd2O2} rhomboid units.
Within the [Cd(1,4-phdp)]n ribbons based on Cd1, the CdꢀꢀꢀCd and
OꢀꢀꢀO cross-rhomboid distances are 3.757 and 2.874 Å, respectively.
The respective comparable distances for the ribbons based on Cd2
are 3.914 and 2.838 Å. As a result of the longer Cd2ꢀꢀꢀCd2 distance,
the {(Cd2)2O2} rhomboids are compressed to a greater degree than
the {(Cd1)2O2} dimers (108.2° and 71.8° angles as opposed to
105.2° and 74.8°). The pendant propyl arms of the 1,4-phda ligands
adopt gauche conformations, providing a ‘‘staple-like” orientation
that bridges adjacent cadmium atoms through its chelating car-
boxylate termini at a distance of 8.667 Å. This distance is almost
3 Å closer than the comparable distances in 1, despite the extra
Fig. 5. The crystallographically distinct [Cd(1,4-phdp)]n ribbons in 2. The Cd1- and Cd2-based ribbons are shown on the top and bottom, respectively.
Fig. 6. A view of the coordination polymer layer of 2. Each The parallel [Cd(1,4-phdp)]n ribbons are oriented up and down within the image. Each {Cd2O2} dimer connects to
six others, constructing a (3,6) grid topology.

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
93
methylene group at each pendant arm of the dicarboxylate
components.
The anion- and water-filled interlamellar regions occupy 24.3% of
the unit cell volume.
Adjacent [Cd(1,4-phdp)]n ribbons are linked by tethering H4-
bpmp ligands to construct 2D [Cd(1,4-phdp)(H4-bpmp)]n coordi-
nation polymer slabs. However, the connectivity pattern between
the ribbons is substantially different from that of its 1,4-phda ana-
logue 1. In compound 1, each {Cd2O2} rhomboid unit connects to
two others, in different [Cd(1,4-phda)]n chains, through 4-bpmp li-
gands; thus each {Cd2O2} dimer is a four-connected node. In the
case of 2, each {Cd2O2} unit connects via the crystallographically
distinct H4-bpmp ligands to four others, two each in two neighbor-
ing [Cd(1,4-phdp)]n ribbons (Fig. 6). Taking the inter-ribbon con-
nections into account, every {Cd2O2} dimer in 2 is a six-connected
node. As a result, the underlying topology of the coordination poly-
mer slab is a (3,6) trigonal grid (Fig. 7), relatively uncommon in
coordination polymer chemistry [23] when compared to the pleth-
ora of ‘‘standard” (4,4) grids.
4.4. Structural description of [Cd(1,4-phdp)(3-bpmp)(H2O)]n (3)
The asymmetric unit of compound 3 consists of a divalent cad-
mium atom and an aqua ligand sited on a 2-fold crystallographic
rotation axis, along with one-half of a 1,4-phdp ligand and one-half
of a 3-bpmp molecule. Complete 1,4-phdp and 3-bpmp ligands are
generated by crystallographic inversion centers located with their
central phenyl and piperazinyl rings, respectively (Fig. 8). Two che-
lating carboxylate groups from different 1,4-phdp ligands, the aqua
ligand, and two pyridyl nitrogen donor atoms from two different 3-
bpmp ligands comprise the distorted {CdO5N2} pentagonal bipyra-
midal coordination sphere. Relevant bond lengths and angles are
given in Table S4.
Extension of the structure through the 1,4-phdp and 3-bpmp li-
gands reveals a three-dimensional [Cd(1,4-phdp)(3-bpmp)(H2O)]n
coordination polymer lattice, in which the 1,4-phdp ligands adopt
a bis(chelating) binding mode. Each cadmium atom serves as a
‘‘tetrahedral” four-connected node, connecting to two others
through 3-bpmp ligands (CdꢀꢀꢀCd distance = 15.873 Å) and two oth-
ers through the 1,4-phdp ligands (Cdꢀ ꢀ ꢀCd distance = 15.352 Å).
The long girth of the ligands results in the formation of large aper-
tures (ꢂ14.6 ꢃ ꢂ19.1 Å) that accommodate interpenetration of
two identical [Cd(1,4-phdp)(3-bpmp)(H2O)]n lattices (Fig. 9). Thus
the overall topology of 3 is that of a 3-fold interpenetrated dia-
mondoid lattice. In contrast to other chiral diamond-topology
coordination polymers with an odd number of interpenetrated lat-
tices [25], the structure of 3 is centrosymmetric and therefore
would not exhibit non-linear optical behavior. The crystallographic
inversion centers within both the 1,4-phdp and 3-bpmp ligands
prevent chirality in the present case.
Neighboring [Cd(1,4-phdp)(H4-bpmp)]n coordination polymer
slabs stack along the (0 1 1) crystal direction (Fig. S2) in an ABAB
pattern through a complex series of hydrogen-bonding interac-
tions involving protonated piperazinyl groups, carboxylate oxygen
atoms, unligated perchlorate ions, water molecule dimers, and
discrete eight-molecule water chains (D8 classification) [24].
4.5. Structural description of {[Cd(1,3-phda)(4-bpmp)]n (4)
Compound 4 crystallizes in the centrosymmetric triclinic space
group with an asymmetric unit comprising a divalent cadmium
atom, a fully deprotonated 1,3-phda ligand and a complete 4-bpmp
ligand (Fig. 10). The coordination environment at cadmium is best
considered a distorted {CdN2O5} pentagonal bipyramid, with the
axial positions occupied by trans nitrogen donor atoms from two
4-bpmp ligands. The equatorial sites are filled by four oxygen do-
nors from two chelating carboxylate termini from two different
1,3-phda ligands and a single oxygen atom donor from a third
1,3-phda unit. Bond lengths and angles are consistent with a
Fig. 7. A network perspective of the underlying (3,6) trigonal grid topology in 2. The
spheres represent the centroids of the {Cd2O2} dimers.
Fig. 8. Coordination environment of 3 with thermal ellipsoids shown at 50% probability and partial atom numbering scheme. Complete 3-bpmp and 1,4-phdp ligands are
shown.

94
K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
Fig. 9. A view down c of the 3-fold interpenetrated diamondoid lattices in 3.
doubly chelated pentagonal bipyramidal divalent cadmium ion
(Table S5).
Oꢀ ꢀ ꢀO through-space distances across the dinuclear kernel measure
3.825 and 2.803 Å, respectively. These rhomboid subunits are
noticeably pinched, with Cd–O–Cd and O–Cd–O angles of
107.54(5)° and 72.46(5)°, respectively. They are linked by the
1,3-phda ligands through a Cdꢀ ꢀ ꢀCd distance of 11.085(2) Å, which
corresponds to the b lattice parameter. The torsion angles within
the flexible pendant acetate arms of the 1,3-phda ligands are
[Cd(1,3-phda)]n double chains, arranged parallel to the b crystal
direction, are formed (Fig. 11) through an exotridentate binding
mode of the 1,3-phda ligands. Within these chains are embedded
{Cd2O2} rhomboid subunits constructed by the chelating/bridging
carboxylate endgroups of the phda ligands. The Cdꢀ ꢀ ꢀCd and
Fig. 10. Coordination environment of 4 with thermal ellipsoids shown at 50% probability and partial atom numbering scheme. The symmetry codes refer to those in Table 6.

K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
95
Fig. 11. A single [Cd(1,3-phda)]n double chain in 4.
Fig. 12. A [Cd(1,3-phda)(4-bpmp)]n slab in 4.
ꢂ68.0° and ꢂ105.5°. Similar to the structure of 1, the 1D double
chains can be considered to be formed from the edge-sharing of
the {Cd2O2} rhomboids with 20-membered {CdOC7O}2 circuits.
The [Cd(1,3-phda)]n double chains are pillared by tethering 4-
bpmp ligands to establish [Cd(1,3-phda)(4-bpmp)]n 2D coordina-
tion polymer slab patterns that are arranged parallel to the
[1 0 1] crystal planes (Fig. 12). Diimine tethers link {Cd2O2} rhom-
boids in neighboring [Cd(1,3-phda)]n double chains through a
Cdꢀ ꢀ ꢀCd contact distance of 16.975 Å. If the centroids of the
{Cd2O2} rhomboids are considered connecting nodes, the slab pat-
tern of 4 can be represented as a (4,4) rectangular grid motif. As
determined by through-space Cdꢀ ꢀ ꢀCd distances, the apertures
within the grid measure 14.74 ꢃ 24.59 Å. Although the structures
of 1 and 4 are similar 2D slabs built from {Cd2O2} rhomboid dimers,
differences in the grid apertures reflect the alteration in the posi-
tion of the dicarboxylate pendant arms. Adjacent [Cd(1,3-
phda)(4-bpmp)]n slabs stack in a simple AA pattern along the a
crystal direction via packing forces (Fig. S3).
Fig. 13. Luminescence spectra of 1–4.
4.6. Luminescent properties
Polycrystalline samples of 1–4 all underwent fluorescence upon
excitation with ultraviolet light (kex = 300 nm). Emission spectra
are shown in Fig. 13. The emission spectrum of 1 shows a broad,
featureless tail into the visible light region, while that of 4 shows
a weak maximum at 482 nm. The phdp derivatives 2 and 3 show
emission maxima at 398 and 467 nm, respectively. The higher
emission wavelength value for 3 possibly arises from altered
non-radiative vibrational mechanisms in the more rigid 3D dia-
mondoid topology, as opposed to the 2D layered topology of 2.
*
The luminescent behavior in 1–4 is ascribed to intraligand
or
tion polymers constructed from aromatic ligands [26].
p– p
p
–n transitions, similar to that seen in other d10 metal coordina-

96
K.M. Blake et al. / Inorganica Chimica Acta 363 (2010) 88–96
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The authors gratefully acknowledge the donors of the American
Chemical Society Petroleum Research Fund for financial support of
this work; K.M.B. thanks the SUMR grant program of the American
Chemical Society for her participation in the research. We thank
Dr. Rui Huang for performing the elemental analyses.
Appendix A. Supplementary material
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