Parallel chain polyrotaxane, layer, and diamondoid divalent metal coordination polymers containing para aromatic dicarboxylate and bis(4-pyridylmethyl)piperazine ligands

Article abstract of DOI:10.1016/j.ica.2013.07.002

Hydrothermal reaction of a closed-shell divalent metal salt, a para aromatic dicarboxylate precursor, and the long-spanning dipyridyl ligand bis(4-pyridylmethyl)piperazine (4-bpmp) afforded three new coordination polymers, which were structurally characte

Full text of DOI:10.1016/j.ica.2013.07.002

Inorganica Chimica Acta 406 (2013) 65–72
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Parallel chain polyrotaxane, layer, and diamondoid divalent metal
coordination polymers containing para aromatic dicarboxylate
and bis(4-pyridylmethyl)piperazine ligands
⇑
Gregory A. Farnum, Nathan H. Murray, 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:
Hydrothermal reaction of a closed-shell divalent metal salt, a para aromatic dicarboxylate precursor, and
the long-spanning dipyridyl ligand bis(4-pyridylmethyl)piperazine (4-bpmp) afforded three new coordi-
nation polymers, which were structurally characterized by single-crystal X-ray diffraction. [Cd(tere)(4-
bpmp)(H2O)]n (1, tere = terephthalate) exhibits a simple non-interpenetrated 66 diamondoid 3D network
with pentagonal bipyramidally coordinated cadmium ions. [Zn2(tere)(4-bpmp)2Cl2]n (2), which possesses
tetrahedrally coordinated zinc atoms, manifests an exceptionally rare 1D + 1D ? 1D parallel interpene-
trated threaded-loop polyrotaxane structure. Extension of the para aromatic dicarboxylate pendant arms
by employing the 1,4-phenylenediacetate (1,4-phda) ligand generated [Zn(1,4-phda)(4-bpmp)(H2O)2]-
ꢀ2H2O}n (3), which shows a simple stacked (4,4) grid structure. Luminescent properties of these materials
are also discussed.
Received 22 May 2013
Accepted 2 July 2013
Available online 11 July 2013
Keywords:
Cadmium
Zinc
Coordination polymer
Luminescence
Polyrotaxane
Diamondoid net
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
Variation of an ancillary coligand can instill substantial struc-
tural and physical property diversity in d10 configuration divalent
The synthesis and study of transition metal benzenedicarboxyl-
ate coordination polymers has consistently remained an active
area of research over the past decade, because of their burgeoning
and significant potential in gas storage applications [1], as selective
absorbents [2], as stationary phases for ion-exchange [3], in indus-
trially applicable heterogeneous catalysis [4], and in non-linear
optical devices [5]. The palpable aesthetic beauty of many inter-
penetrated and self-penetrated coordination polymer structures
is undeniable, adding to the appeal of these investigations [6].
The simplest aromatic dicarboxylate ligands, namely the ortho
phthalate [7], meta isophthalate [8], and para terephthalate (tere)
ligands [9–16], have certainly been very effectively employed in
the construction of functional crystalline metal–organic solids.
metal terephalate coordination polymers. [Zn2(tere)2(dabco)]n
(dabco = 1,4-diazabicyclo[2.2.2]octane) shows a primitive cubic
type lattice with 62% solvent accessible void space, high hydrogen
uptake capability, and unexpected unit cell shrinkage upon inclu-
sion of guest molecules [12]. Use of a long-spanning, flexible bisim-
idazole ligand afforded a 2-fold parallel interpenetrated (4,4) grid
structural motif in {[Zn(tere)(bimx)]ꢀ1.5H2O}n (bimx = 1,4-bis(imi-
dazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene) [13]. In this mate-
rial, close stacking of the interpenetrated layers permits the
formation of only small water-bearing cavities. The thermochroic
material {[Cd(tere)(bpybc)1.5]ꢀ10H2O}n (bpybc = 1,10-bis(4-carb-
oxybenzyl)-4,40-bipyridinium) shows 1D chain motifs with loops
of bpybc pairs and bpybc rods, polythreaded into a complicated
polypseudorotaxane 1D + 1D ? 2D structural pattern [14]. {[Cd4
(tere)4(4-bpfp)3(H2O)2]ꢀ8H2O}n (4-bpfp = bis(4-pyridylformyl)
piperazine) manifests a complicated 3D 3,4,8-connected trinodal
self-penetrated network topology [15]. [(CH3)2NH2]2[Cd5(tere)4
(trz)2(btrz)2]n (Htrz = 1,2,4-triazole; btrz = benzotriazole) possesses
For example, the 3D interpenetrated phase [Zn(tere)(4,40-bpy)0.5
]
(4,40-bpy = 4,40-bipyridine) can absorb significant amounts of car-
bon dioxide [9a], showing proof of concept for the amelioration
of global warming-causing gases via this class of materials. The
well-studied porous phase [Zn4O(tere)3]n has versatile absorptive
behavior [10] and has recently been impregnated with palladium
nanoparticles with an aim towards selective heterogeneous catal-
ysis [11].
the unique example of a 10-connected
pentanuclear clusters [16].
c-Pu 3D topology, based on
Given the structural diversity seen in previously reported zinc
and cadmium terephthalate phases, we aimed to extend this chem-
istry by employing the long-spanning, hydrogen-bonding capable
bis(4-pyridylmethyl)piperazine (4-bpmp) ligand (Scheme 1). The
4-bpmp ligand has proven extremely useful in our group [17–22]
⇑
Corresponding author. Address: Lyman Briggs College, E-30 Holmes Hall,
Michigan State University, East Lansing, MI 48825 USA. Tel.: +1 5174322268.
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.2013.07.002

66
G.A. Farnum et al. / Inorganica Chimica Acta 406 (2013) 65–72
to air cool to 25 °C. Colorless blocks of 2 (42 mg, 48% yield based on
Zn) were isolated after washing with distilled water and acetone,
and drying in air. Anal. Calc. for C40H44Cl2N8O4Zn2 2: C, 53.23; H,
4.91; N, 12.42. Found: C, 52.87; H, 4.48; N, 12.07%. IR (cmꢁ1):
2812 (w), 2779 (w), 1621 (s), 1599 (s), 1558 (w), 1498 (w), 1429
(m), 1386 (m), 1351 (s), 1326 (m), 1290 (m), 1227 (m), 1202 (w),
1174 (w), 1139 (m), 1122 (w), 1095 (w), 1065 (m), 1031 (m),
1010 (s), 934 (w), 892 (w), 855 (m), 838 (s), 828 (s), 808 (s), 753
(s), 728 (m), 669 (w).
Scheme 1. Ligands used in this study.
and in other groups [23–25] in producing coordination polymers,
many with intriguing novel topologies. [Co3(oba)3(4-bpmp)2]n
(oba = oxybis(benzoate)) shows a striking 8-connected self-pene-
trated net composed of multiple sets of interlocked helical patterns
[17]; {Zn2(Hpyro)2(H24-bpmp)]ꢀ4H2O}n (pyro = pyromellitate)
exhibits a very simple yet self-penetrated net with a 3,4-connected
(4.82)(4.8210) topology [18]. {[Co3(5-(4-carboxybenzyloxy)-iso-
phthalate)2(4-bpmp)2(H2O)6]ꢀ10H2O}n also has a 3,4-connected
binodal topology, but with a very rare jeb (63)(658) network [23].
In this contribution we hereby report the single crystal struc-
tures and luminescent properties of [Cd(tere)(4-bpmp)(H2O)]n (1)
and [Zn2(tere)(4-bpmp)2Cl2]n (2). In order to probe the structural
effect of lengthening the para carboxylate pendant arms, we also
utilized the related 1,4-phenyelenediacetate (1,4-phda) ligand to
prepare [Zn(1,4-phda)(4-bpmp)(H2O)2]ꢀ2H2O}n (3).
2.4. Preparation of [Zn(1,4-phda)(4-bpmp)(H2O)2]ꢀ2H2O}n (3)
Zn(ClO4)2ꢀ6H2O (22 mg, 0.06 mmol) and 1,4-phenylenediacetic
acid (12 mg, 0.06 mmol) were dissolved in 1.5 mL H2O in a small
glass vial. A 0.75 mL aliquot of a 1:1 ethanol:water solution was
placed on top, followed by
a solution of 4-bpmp (17 mg,
0.06 mmol) in 1.5 mL ethanol. The vial was allowed to stand undis-
turbed for 14 d. Clear, colorless blocks of 3 were observed, en-
trained in a white powdery solid. Manual separation of enough
bulk 3 for additional studies was not feasible.
3. X-ray crystallography
Single crystal reflection data for 1–3 were collected at 173 K
using a Bruker-AXS Apex II CCD instrument. Reflection data was
2. Experimental
acquired using graphite-monochromated Mo
Ka radiation
(k = 0.71073 Å). The data was integrated via SAINT [26]. Lorentz
and polarization effect and absorption corrections were applied
with SADABS [27]. The structures were solved using direct methods
and refined on F2 using SHELXTL [28]. 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. Crystals of 2 dif-
fracted poorly, resulting in an elevated Rint value due to weak
intensities. Structure solution and refinement were still satisfac-
tory when using all data. Relevant crystallographic data for 1–3
are listed in Table 1.
2.1. General considerations
Metal salts, aromatic dicarboxylic acids, and ligand precursors
were obtained from Aldrich. Bis(4-pyridylmethyl)piperazine [25]
was prepared using a literature procedure. Potassium terephthal-
ate was produced by the deprotonation of terephthalic acid with
excess potassium hydroxide in ethanol. Water was deionized
above 3 MX–cm in-house. IR spectra were recorded on a Perkin El-
mer Spectrum One DRIFT instrument on powdered samples. Ele-
mental Analysis was carried out using a Perkin Elmer 2400 Series
II CHNS/O Analyzer. The luminescence spectra were obtained with
a Hitachi F-4500 Fluorescence Spectrometer on solid crystalline
samples anchored to quartz microscope slides with Rexon Corpo-
ration RX-22P ultraviolet-transparent epoxy adhesive.
4. Results and discussion
2.2. Preparation of [Cd(tere)(4-bpmp)(H2O)]n (1)
4.1. Synthesis and spectral characterization
Cd(NO3)2ꢀ4H2O
(56 mg,
0.18 mmol),
4-bpmp
(51 mg,
0.18 mmol) and potassium terephthalate (44 mg, 0.18 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 (32 mg, 32% yield
based on Cd) were isolated after washing with distilled water and
acetone, and drying in air. Anal. Calc. for C24H26CdN4O5 1: C, 51.21;
H, 4.66; N, 9.95. Found: C, 50.98; H, 4.41; N, 9.71%. IR (cmꢁ1): 3381
(w), 2811 (w), 2772 (w), 1659 (w), 1610 (w), 1561 (m), 1545 (s),
1505 (m), 1449 (w), 1389 (s), 1334 (m), 1293 (s), 1263 (m), 1223
(m), 1144 (m), 1124 (m), 1095 (m), 1065 (w), 1008 (s), 998 (m),
935 (w), 889 (m), 852 (s), 839 (s), 793 (s), 752 (s).
Compounds 1 and 2 were prepared by the hydrothermal reac-
tion of cadmium nitrate (for 1) or zinc chloride (for 2), potassium
terephthalate and 4-bpmp. Compound 3 was prepared by slow dif-
fusion of an aqueous solution of zinc perchlorate and 1,4-pheny-
lenediacetic acid with an ethanolic solution of 4-bpmp.
Unfortunately analytically pure samples of 3 could not be obtained,
whether via solvent diffusion or hydrothermal methods. The infra-
red spectra of all of the compounds were consistent with their
crystal structures.
Bands between 2800 and 3100 cmꢁ1 in all spectra represent
C–H stretching modes. Asymmetric and symmetric C–O stretching
modes of the tere ligands are present as broadened, stronger bands
at 1545 and 1389 cmꢁ1 (1), and 1599 and 1351 cmꢁ1 (2). A nar-
2.3. Preparation of [Zn2(tere)(4-bpmp)2Cl2]n (2)
rower Dm gap between the C–O stretching bands has been ascribed
to chelating carboxylate binding mode [29], consistent with the
bis(chelating) tere binding mode seen in 1 and the bis(monoden-
tate) tere binding mode in 2. Medium intensity bands in the range
of ꢂ1600 to ꢂ1200 cmꢁ1 are caused by stretching modes of the
pyridyl rings of the 4-bpmp and the aromatic rings of the tere
ligands [30]. A weak, broad band at 3380 cmꢁ1 in the spectrum
ZnCl2 (25 mg, 0.18 mmol), 4-bpmp (99 mg, 0.37 mmol), and
potassium terephthalate (44 mg, 0.18 mmol) 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 oil bath and allowed

G.A. Farnum et al. / Inorganica Chimica Acta 406 (2013) 65–72
67
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
24H26CdN4O5
C40H44Cl2N8O4Zn2
529.26
monoclinic
P21/c
10.672(5)
18.341(8)
10.097(5)
90
C26H32N4O8Zn
593.93
562.89
monoclinic
C2/c
18.4608(7)
6.0615(2)
21.3052(8)
90
triclinic
ꢀ
P1
5.7160(2)
10.6104(3)
12.8179(4)
87.251(2)
b (Å)
c (Å)
a
(°)
b (°)
93.544(2)
90
2379.50(15)
4
1.571
0.960
95.375(16)
90
1967.7(16)
2
1.523
1.408
79.799(2)
81.568(2)
756.64(4)
1
1.303
0.861
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
Minimum/maximum transmission
0.6697/0.7452
0.6575/0.8702
0.7785/0.8639
hkl ranges
ꢁ22 6 h 6 22, ꢁ6 6 k 6 7, ꢁ25 6 l 6 25
ꢁ14 6 h 6 13, ꢁ22 6 k 6 22, ꢁ13 6 l 6 13
ꢁ6 6 h 6 6, ꢁ12 6 k 6 12, 15 6 l 6 15
Total reflections
Unique reflections
Rint
10304
22742
12511
2192
0.0316
158/1
0.0249
0.0222
0.0536
0.0521
0.432/–0.233
1.060
4587
0.2049
253/0
0.1465
0.0639
0.1898
0.1403
0.567/–0.830
1.011
2764
0.0290
188/3
0.0533
0.0517
0.1770
0.1758
1.177/–0.437
1.223
Parameters/restraints
a
R1 (all data)
a
R1 (I > 2
r
(I))
b
wR2 (all data)
b
wR2 (I > 2r(I))
Max/min residual (eꢁ/Å3)
Goodness-of-fit
P
P
a
R1
=
||Fo| – |Fc||/ |Fo|.
P
P
b
wR2 = { [w(Fo2 – Fc2)2]/ [wFo2]2}1/2
.
of 1 is consistent with the aqua ligands bound to cadmium. As
there is no ligated or unligated water in 2, such a band is absent.
(1,4-phdp) with the same metal ion and dipyridyl pillar results in
the same diamondoid topology as seen in 1, but with a dramatic in-
crease in interpenetration level and solvent-accessible void space
[19]. {[Cd(1,4-phdp)(4-bpmp)]ꢀ5H2O}n adopts a threefold interpen-
etrated diamondoid net, with void space in a single net facilitated by
the long span of the anti and gauche conformation phdp ligands.
{[Cd(1,4-phda)(4-bpmp)]ꢀ1.5H2O}n has a (4,4) layer structure based
on {Cd2O2} dimeric units [20]. Thus, tuning of the final structure is
possible by altering the length of para-dicarboxylate pendant arms
in cadmium coordination polymers containing 4-bpmp ligands.
4.2. Structural Description of [Cd(tere)(4-bpmp)(H2O)]n (1)
Compound 1 crystallizes in the monoclinic space group C2/c,
with an asymmetric unit consisting of a divalent cadmium atom
and an aqua ligand on a crystallographic 2-fold axis, half of a tere
ligand whose ring centroid sits on a crystallographic inversion cen-
ter, and half of a 4-bpmp whose piperazinyl ring is sited over an-
other crystallographic inversion center. The coordination
environment is a distorted {CdO5N2} pentagonal bipyramid, with
the aqua ligand and chelating carboxylate groups from two tere li-
gands in the equatorial plane (Fig. 1a). Pyridyl nitrogen donors
from two 4-bpmp ligands fill the axial sites. Bond lengths and an-
gles within the coordination sphere are listed in Table 2.
4.3. Structural Description of [Zn2(tere)(4-bpmp)2Cl2]n (2)
The asymmetric unit of compound 2 contains a divalent zinc
atom, a chloro ligand, a full 4-bpmp ligand, and half of a tere ligand
sited over a crystallographic inversion center. In contrast to the
pentagonal bipyramidal geometry at Cd in 1, 2 shows a distorted
{ZnN2OCl} tetrahedral coordination environment (Fig. 2a) because
of the smaller ionic radius of Zn relative to Cd. Bond lengths and
angles within the tetrahedral coordination environment of 2 are gi-
ven in Table 4.
Bis(chelating) tere ligands link Cd atoms along the c crystal axis,
forming [Cd(tere)(H2O)]n chains with a Cdꢀ ꢀ ꢀCd contact distance of
11.172 Å (Fig. 1b). The carboxylate groups are tilted by 14.2° rela-
tive to the aromatic ring plane of the tere ligands. The [Cd(tere)(H2-
O)]n chains are linked into
a 3D [Cd(tere)(4-bpmp)(H2O)]n
coordination polymer network (Fig. 1c) by splayed-open conforma-
tion 4-bpmp ligands (Nꢀ ꢀ ꢀNꢀ ꢀ ꢀNꢀ ꢀ ꢀN torsion angle = 180°), which
span a Cdꢀ ꢀ ꢀCd distance of 15.867 Å. Thus, each Cd atom serves as
a 4-connected node, via two tere ligands and two 4-bpmp ligands.
Topological analysis with TOPOS [31] reveals the presence of a
non-interpenetrated 66 diamondoid net (Fig. 1d). Stability of the
diamondoid net is enhanced by hydrogen bonding donation from
the aqua ligands in one [Cd(tere)(H2O)]n chain to ligated tere car-
boxylate oxygen atoms in another [Cd(tere)(H2O)]n chain (Table 3).
The nature of the dipodal nitrogen-base coligand plays an impor-
tant role in dictating the dimensionality and topology of cadmium
terephthalate coordination polymers. The simple diamondoid net
of 1 contrasts greatly with its bpfp congener {[Cd4(tere)4(bpfp)3(H2-
O)2]ꢀ8H2O}n (bpfp = bis(4-pyridylformyl)piperazine), which dis-
plays a convoluted 3D 3,4,8-connected self-penetrated network
[15]. Use of the longer armed ligand 1,4-phenylenedipropionate
Operation of the inversion centers reveals dimeric [Zn2Cl2
(bpmp)2] rings, where the zinc atoms are bridged by pairs of
twisted cis conformation bpmp tethers, with a 10.1° Nꢀ ꢀ ꢀNꢀ ꢀ ꢀNꢀ ꢀ ꢀN
torsion angle across the bpmp ligands. Although the cis conforma-
tion of bpmp ligands is not common relative to the splayed-open
anti conformation, it has been seen previously in the self-pene-
trated coordination polymers {[Zn3(tca)2(4-bpmp)(H4-bpmp)2]
(ClO4)2ꢀ5H2O}n (tca = tricarballylate) [21] and [Co3(oba)3(4-
bpmp)2]n [17]. Neighboring [Zn2Cl2(bpmp)2] dimers are conjoined
into 1D neutral [Zn2Cl2(tere)(bpfp)2]n coordination polymer chains
(Fig. 2b) along the c crystal axis via bis(monodentate) tere ligands.
The rigid rod tere ligands span a Znꢀ ꢀ ꢀZn distance of 11.036 Å.
The ZnꢀꢀꢀZn through-space distance across each large [Zn2Cl2
(bpmp)2] rings within the [Zn2Cl2(tere)(bpmp)2]n chains measures
13.315 Å. These large apertures permit penetration of the rod-like tere
ligands of another [Zn2Cl2(tere)(bpmp)2]n chain in a polyrotaxane

68
G.A. Farnum et al. / Inorganica Chimica Acta 406 (2013) 65–72
Fig. 1. (a) Coordination environment at Cd in 1. (b) [Cd(tere)]n 1D chain in 1. (c) [Cd(tere)(4-bpmp)]n 3D coordination polymer net in 1, with [Cd(tere)]n 1D chains shown in
red in the online version of this article. (d) Simplified representation of the diamondoid net in 1.
Table 2
aggregate via weak supramolecular C–Hꢀ ꢀ ꢀCl interactions (Cꢀ ꢀ ꢀCl
Selected bond distance (Å) and angle (°) data for 1.
distance = 3.552 Å) to form the overall crystal structure of 2
Cd1–O5
2.233(2)
O1#1–Cd1–N1#1
O1–Cd1–N1#1
N1–Cd1–N1#1
O5–Cd1–O2
80.92(6)
101.40(6)
164.74(9)
135.94(3)
142.38(5)
54.82(5)
81.24(6)
87.79(6)
135.94(3)
54.82(5)
142.38(5)
87.79(6)
81.24(6)
88.13(7)
(Fig. S1).
There is literature precedent for similar parallel 1D + 1D ? 1D
Cd1–O1#1
2.3560(14)
2.3561(14)
2.3832(19)
2.3832(19)
2.4358(15)
2.4358(15)
81.36(4)
81.36(4)
162.72(7)
97.63(4)
Cd1–O1
pseudopolyrotaxanes in the supramolecular nets of some molecu-
lar species [32,33], with hydrogen bonding patterns occurring
within the open loops. For instance, the cationic complex
[{(HO2CC6H4CH2)-(Bu2bipy)Me2Pt}3{(tris(4-pyridyl)triazine)}]3+
manifests hydrogen-bonding interactions between pendant car-
boxylic acid functional groups from neighboring supramolecular
chains occurring within the loops [32]. In the coordination com-
plex [Zn2(1-bromo-3,5-bis(imidazol-1-ylmethyl)benzene)2(OAc)4],
supramolecular Brꢀ ꢀ ꢀBr interactions between unligated bromo
groups spur the formation of the parallel polyrotaxane chain motif
[33].
Cd1–N1
Cd1–N1#1
O1#1–Cd1–O2
O1–Cd1–O2
Cd1–O2
Cd1–O2#1
N1–Cd1–O2
O5–Cd1–O1#1
O5–Cd1–O1
O1#1–Cd1–O1
O5–Cd1–N1
O1#1–Cd1–N1
O1–Cd1–N1
O5–Cd1–N1#1
N1#1–Cd1–O2
O5–Cd1–O2#1
O1#1–Cd1–O2#1
O1–Cd1–O2#1
N1–Cd1–O2#1
N1#1–Cd1–O2#1
O2–Cd1–O2#1
101.40(6)
80.92(6)
97.63(4)
Symmetry equivalent position: #1 ꢁx, y, ꢁz + 1/2.
The flexibility of the 4-bpmp ligands, resulting in their ability to
adopt a cis curled conformation, is essential to the production of
the 1D + 1D ? 1D parallel interpenetrated chains in 2. More rigid
linkers such as dabco or 4,40-bpy seem to promote 2-fold interpen-
etrated 3D pcu nets in zinc terephthalate coordination polymers,
arrangement (Fig. 2c). The stability of this parallel entanglement is
enhanced by interchain C–Hꢀ ꢀ ꢀO interactions (Cꢀ ꢀ ꢀO dis-
tance = 3.083 Å). This parallel 1D + 1D ? 1D polyrotaxane coordi-
nation polymer entanglement is apparently only the second
known example, with the other being seen within the related com-
pound [Zn2Cl2(tere)(bpfp)2]n (bpfp = bis(4-pyridylformyl)pipera-
zine) [15]. In contrast to this other compound, which shows a
‘‘boat’’ conformation of its bpfp piperazinyl rings, the bpmp ligands
in 2 adopt a standard ‘‘chair’’ conformation. Adjacent 1D + 1D ? 1D
entangled [Zn2Cl2(tere)(bpmp)2]n coordination polymer chain pairs
for example in [Zn2(tere)2(dabco)]n [12] and [Zn(tere)(4,40-bpy)0.5 n
]
[9]. A cadmium terephthalate coordination polymer with 1,10-
bis(4-carboxybenzyl)-4,40-bipyridinium (bpybc) coligands shows
1D chains with [Cd2(bpybc)2] loops not dissimilar from the
[Zn2(4-bpmp)2] loops in 2, with tere ligands penetrating through
the loops. However in that particular cadmium complex
{[Cd(tere)(bpybc)1.5]ꢀ10H2O}n, two parallel sets of single 1D chains

G.A. Farnum et al. / Inorganica Chimica Acta 406 (2013) 65–72
69
Fig. 2. (a) Coordination environment at Zn in 2. (b) A single [Zn2(tere)2(4-bpmp)Cl2]n chain in 2. (c) Parallel 1D + 1D ? 1D threaded-loop polyrotaxane [Zn2(tere)2(4-
bpmp)Cl2]n chains in 2.
Table 3
Hydrogen bonding distance (Å) and angle (°) data for 1 and 3.
D–H. . .A
d(Hꢀ ꢀ ꢀA)
\DHA
d(Dꢀ ꢀ ꢀA)
Symmetry transformation for A
ꢁx, y + 1, ꢁz + 1/2
1
O5–H5Cꢀ ꢀ ꢀO2
1.851(19)
160(3)
2.681(2)
3
O3–H3Aꢀ ꢀ ꢀO1
O3–H3Bꢀ ꢀ ꢀO2
2.01(3)
1.79(2)
158(5)
164(5)
2.822(4)
2.629(4)
ꢁx + 1, ꢁy + 2, ꢁz + 1
ꢁx, ꢁy + 2, ꢁz + 1
interpenetrate orthogonally, resulting in a 2D sheet with polyro-
taxane linkages [14].
crystallographic inversion center, half of a 1,4-phda ligand whose
aromatic ring centroid is located on another inversion center, half
of a 4-bpmp whose piperazinyl ring centroid is positioned over yet
another inversion center, one aqua ligand, and one net water
molecule of crystallization which is disordered equally over four
positions. Enforced by the crystallographic symmetry, the coordi-
nation environment at zinc in 3 is that of a [ZnO4N2] octahedron
(Fig. 3a), in contrast to the tetrahedral environment seen in its tere
congener 2. Pairs of 4-bpmp pyridyl nitrogen donors, aqua ligands,
and 1,4-phda carboxylate oxygen atom donors are situated in
4.4. Structural Description of [Zn(1,4-phda)(4-bpmp)(H2O)2]ꢀ2H2O}n
(3)
Compound 3 was prepared in attempt to probe whether longer
and flexible para-disposed carboxylate arms would produce a
polyrotaxane structure related to that of 2. The asymmetric unit
of compound
3 contains a divalent zinc atom sited on a
Fig. 3. (a) Coordination environment at Zn in 3, showing complete 4-bpmp and 1,4-phda ligands. (b) [Zn(1,4-phda)(4-bpmp)(H2O)2]n (4,4) grid layer in 3.

70
G.A. Farnum et al. / Inorganica Chimica Acta 406 (2013) 65–72
Table 4
Selected bond distance (Å) and angle (°) data for 2.
Znꢀ ꢀ ꢀZn bridging distance of 11.290 Å. These chains are in turn pil-
lared into [Zn(1,4-phda)(4-bpmp)(H2O)2]n (4,4) grid coordination
polymer layers (Fig. 3b) by splayed-open conformation 4-bpmp li-
gands (Nꢀ ꢀ ꢀNꢀ ꢀ ꢀNꢀ ꢀ ꢀN torsion angle = 180°). The Znꢀ ꢀ ꢀZn contact
distance through the dipyridyl ligands is 16.699 Å. The resulting
pinched rhomboid apertures within the layer motif have through
space Znꢀ ꢀ ꢀZn distances of 12.818 Å by 25.463 Å, with Znꢀ ꢀ ꢀZnꢀ ꢀ ꢀZn
angles of 50.07° and 129.93°. Hydrogen bonding donation from the
aqua ligands to the unligated 1,4-phda carboxylate oxygen atoms
serves to stabilize the bis(monodentate) dicarboxylate binding
mode. This factor may also be implicated in providing impetus
for the formation of the layer motifs during self-assembly (see
Table 3).
Zn1–O1
1.957(4)
Zn1–N4
2.057(5)
Zn1–N1
2.058(5)
Zn1–Cl1
2.2360(19)
122.10(19)
112.53(19)
101.43(18)
105.81(14)
104.90(14)
109.52(15)
O1–Zn1–N4
O1–Zn1–N1
N4–Zn1–N1
O1–Zn1–Cl1
N4–Zn1–Cl1
N1–Zn1–Cl1
Adjacent [Zn(1,4-phda)(4-bpmp)(H2O)2]n layers stack in an AAA
pattern along the a crystal direction (Fig. S2), fostered by hydrogen
bonding from the aqua ligands to ligated 1,4-phda carboxylate
oxygen atoms in a neighboring layer. A view down a reveals the
presence of solvent-filled channels (Fig. S3), which occupy 23.5%
of the unit cell volume according to PLATON [34]. These are filled
with the disordered water molecules of crystallization.
The structure of 3 is isostructural with its previously reported
cobalt congener [Co(1,4-phda)(4-bpmp)(H2O)2]ꢀ2H2O}n [35]. It is
also similar in structure to two other zinc 1,4-phda coordination
polymers with shorter dipyridyl tethering ligands. [Zn(1,4-
phda)(dpa)]ꢀH2O}n (dpa = 4,40-dipyridylamine) also has a (4,4) grid
structure based on isolated zinc ions, but shows a sawtooth layer
pattern as opposed to the flatter disposition of the layers in 3; this
is likely an effect of the ‘‘V-shaped’’ kinked dpa ligands [36].
{Zn(1,4-phda)(4,40-bpy)]ꢀH2O}n has {Zn2(OCO)2} dimeric clusters
produced by the termini of two cis conformation 1,4-phda ligands,
in contrast to the isolated zinc ions in 3. However, treating the di-
mers as connecting nodes produces a similar (4,4) grid topology
[37]. Thus it appears that zinc 1,4-phda coordination polymers fre-
quently form 2D layers, regardless of whether the dipyridyl coli-
gand is short, kinked, or long.
Table 5
Selected bond distance (Å) and angle (°) data for 3.
Zn1–O1#1
Zn1–O1
2.117(3)
2.117(3)
2.135(3)
2.135(3)
2.160(3)
2.160(3)
180
90.62(12)
89.38(12)
89.38(12)
90.62(12)
N1–Zn1–N1#1
180
O1#1–Zn1–O3#1
O1–Zn1–O3#1
N1–Zn1–O3#1
N1#1–Zn1–O3#1
O1#1–Zn1–O3
O1–Zn1–O3
87.90(11)
92.10(11)
93.15(13)
86.85(13)
92.10(11)
87.90(11)
86.85(13)
93.15(13)
180
Zn1–N1
Zn1–N1#1
Zn1–O3#1
Zn1–O3
O1#1–Zn1–O1
O1#1–Zn1–N1
O1–Zn1–N1
O1#1–Zn1–N1#1
O1–Zn1–N1#1
N1–Zn1–O3
N1#1–Zn1–O3
O3#1–Zn1–O3
Symmetry equivalent position: #1 ꢁx, ꢁy + 2, ꢁz + 1.
mutually trans positions across the coordination sphere. Bond
lengths and angles within the octahedral environment are listed
in Table 5.
In 3, the trans conformation 1,4-phda ligands adopt a bis(mono-
dentate) binding mode, similar to that seen in the tere analog 2.
These produce [Zn(1,4-phda)(H2O)2]n coordination polymer chains
that are oriented parallel to the [-1 1 0] crystal direction, with a
Fig. 4. Emission spectrum of 1.

G.A. Farnum et al. / Inorganica Chimica Acta 406 (2013) 65–72
71
Fig. 5. Emission spectrum of 2.
4.5. Luminescent properties of 1 and 2
ligand and octahedral coordination at zinc obviated any polyrotax-
ane behavior in 3, resulting in a common (4,4) grid topology de-
spite its identical bis(monodentate) carboxylate bridging mode.
Irradiation of crystalline samples of complexes 1 and 2 with
ultraviolet light (kex = 250 nm) caused rather intense blue-violet
visible light emission with maxima at k = 401 nm (Fig. 4 for 1)
and k = 403 nm (Fig. 5 for 2). As the free 4-bpmp ligands mani-
fested very weak luminescence at the same excitation wavelength,
Acknowledgements
The authors gratefully acknowledge the donors of the American
Chemical Society Petroleum Research Fund and Michigan State
University for financial support of this work.
it is most probable that the luminescent behavior arises from
or –n molecular orbital electronic transitions within the phenyl
p–
p ⁄
p
rings of the tere ligands [38]. The higher intensity emission of
the Cd compound 1 compared to the Zn compound 2 could arise
from the bis(chelating) binding mode of the tere ligands in 1,
which could minimize non-emissive vibrational relaxation more
effectively than the bis(monodentate) tere ligands in 2.
Appendix A. Supplementary material
CCDC 933699, 933701 and 933700 contains the supplementary
crystallographic data for 1–3. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2013.07.002.
5. Conclusions
Coordination geometry preferences appear to play a significant
role in dictating the dimensionality and topology of d10 configura-
tion aromatic para-dicarboxylate coordination polymers with
bis(4-pyridylmethyl)piperazine coligands. In the case of the larger
cadmium ion, a pentagonal bipyramidal coordination environment
allows a bis(chelating) terephthalate binding mode, and instills a
non-interpenetrated 4-connected diamondoid coordination poly-
mer topology in 1. A previously reported phase with the longer
para-dicarboxylate ligand 1,4-phenylenedipropionate showed the
same topology, but with 3-fold interpenetration. The shorter tere
ligand in 1 thus enforces a lack of interpenetration due to smaller
apertures in the net. Tetrahedral coordination in the zinc derivative
2 promotes a bis(monodentate) terephthalate binding mode. The
flexibility of the bpmp ligand results in large [Zn2(bpmp)2] loops,
which when threaded by the rigid rod bis(monodentate)
terephthalate ligands form the exceptionally rare 1D + 1D ? 1D
parallel polyrotaxane arrangement of coordination polymer chains
in 2. Longer para-dicarboxylate arms in the 1,4-phenylenediacetate
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