M.J. Wudkewych, R.L. LaDuca / Journal of Molecular Structure 1120 (2016) 156e162
161
ꢁ
each zinc atom are filled by single carboxylate oxygen donor atoms
from two 2,4-pdc ligands. Slight differences in the metrical pa-
rameters (Table 3) result in the crystallographic distinction be-
tween Zn1 and Zn2 atoms.
The remaining water ligands were lost between 210 and 365
C
(total observed mass loss 16.1%, calc’d 16.0%). Combustion of the
organic ligands occurred above 365 C. of Compound 3 underwent
loss of its bound water molecules between 70 and 110 C, with a
ꢁ
ꢁ
Individual [Zn(H
2
O)
2
] fragments are connected by 2,4-pdc li-
(H O) coordination polymer chains
mass loss of 7.7% closely aligned with the predicted value of 7.5%.
Ligand combustion occurred above 110 C. The TGA traces for 1e3
ꢁ
gands into [Zn (2,4-pdc)
2
2
2
4
]
n
oriented along the c crystal direction. The bis(monodentate) 2,4-
pdc carboxylate connections between adjacent zinc atoms mea-
sure 9.1908(15) and 9.1917(15) Å, for Zn1$$$Zn1 and Zn2$$$Zn2
are shown in Figs. S7eS9, respectively.
4.6. Luminescent properties of 1e3
connections, respectively. In turn parallel [Zn
coordination polymer chains are pillared into [Zn
pdc) (H O) (3-pna)] layered motifs parallel to the bc crystal
2
(2,4-pdc)
2
(H
2
O)
4
]
n
2
(2,4-
Polycrystalline samples of 1e3 were exposed to ultraviolet light
to probe their possible photoluminescence. Excitation spectra were
acquired to determine the optimum wavelength for inducing
photoluminescence, by monitoring any emission at a wavelength of
400 nm. For 1 and 3, the maximum excitation occurred at 230 nm.
Broad and weak violet light emission (Fig. S10) was observed, with
maximum wavelengths of 434 nm and 415 nm respectively. Com-
pound 2 only showed extremely weak emission when excited with
ultraviolet light. It is plausible that the fluorescent behavior of 1 and
2
2
4
n
planes (Fig. 4a) by twisted anti-conformation 3-pna ligands
ꢁ
(
N$$$C$$$C$$$N torsion angle ¼ 139.5 ). Incipient void space within
the zig-zag layer motifs is filled by an identical [Zn
pdc) (H O) (3-pna)] layer (Fig. 4b).
2
(2,4-
2
2
4
n
Treating the zinc atoms as three-connected nodes results in a
two-fold parallel interpenetrated 2D þ 2D / 2D (6,3) herringbone
net (Fig. 5). Solvent accessible cavities within each system of two-
fold interpenetrated layers in 2 comprise 14.0% of the unit cell
volume as calculated by PLATON [23], and contain short three-
molecule discrete water chains with D(3) classification [24].
These are connected to the coordination polymer framework by
accepting hydrogen bonds from 3-pna amide NeH groups, and
donating hydrogen bonds to the 3-pna carbonyl oxygen atoms
3 is caused by
pep* or pen molecular orbital transitions in the
aromatic rings of the 2,4-pdc and dipyridylamide ligands [25].
5. Conclusions
As seen previously in cadmium succinate coordination polymers
containing 3-pina, 3-pna [11], or 3-pmna [26] ligands, nitrogen
donor disposition and tether lengths play a marked role in instilling
topologies during self-assembly of zinc coordination polymers
based on 2,4-pyridinedicarboxylate. In the case of 3-pina, a simple
salt was obtained, but in the cases of the nicotinamide derivatives,
coordination polymers were obtained. The longer ligand 3-pmna
resulted in a 1-D chain motif, while the shorter 3-pna ligand pro-
moted formation of a two-fold parallel interpenetrated herring-
bone layer net. The 2-D 3-pna containing phase 2 showed the
highest level of thermal robustness, consistent with the increase in
dimensionality.
(Table S1). Adjacent sets of two-fold interpenetrated [Zn
2
(2,4-
pdc) (H O) (3-pna)] layers aggregate (Fig. S5) by hydrogen
2
2
4
n
bonding donation from bound water molecules to unligated 2,4-
pdc oxygen atoms (Table S1).
2 2 n
4.4. Structural description of {[Zn(2,4-pdc)(H O) (3-pmna)] (3)
The asymmetric unit of compound 3 contains a divalent zinc
atom, a 2,4-pdc ligand, two aqua ligands, and a 3-pmna ligand. A
ZnN } coordination octahedron is evident at zinc, with merid-
{
3 3
O
ional disposition of the nitrogen and oxygen donor atoms (Fig. 6).
Two 3-pmna pyridyl nitrogen atoms in a cis disposition and a 2,4-
pdc pyridyl nitrogen atom occupy one set of mer positions. Two cis-
disposed aqua ligands and a single oxygen donor atom from the
Acknowledgements
2
,4-pdc ligand occupy the other set of mer positions. Metrical pa-
Lyman Briggs College and the Honors College of Michigan State
University provided the financial support for this work. R.L.L.
thanks Dr. Awan Afuqya for assistance within the luminescence
spectrophotometer.
rameters within the coordination environment are listed in Table 4.
Three of the 2,4-pdc oxygen atoms remain unligated.
Dipodal 3-pmna ligands connect neutral [Zn(2,4-pdc)(H
fragments into {[Zn(2,4-pdc)(H O) (3-pmna)] 1-D coordination
polymer chains (Fig. 7), with a Zn$$$Zn contact distance of
.887(2) Å. This distance denotes the b lattice parameter, as the
2 2
O) ]
2
2
n
Appendix A. Supplementary data
9
chain motifs are arranged parallel to the b crystal axis. Adjacent
chains are connected into the 3-D supramolecular crystal structure
of 3 (Fig. S6) by extensive hydrogen bonding pathways (Table S1).
The aqua ligands in one chain donate hydrogen bonds to unligated
References
2
,4-pdc oxygen atoms, while the amide NeH groups of the 3-pmna
ligands donate hydrogen bonds to the ligated 2,4-pdc oxygen
atoms. According to PLATON, there is no incipient void-space
within the supramolecular structure of 3.
4.5. Thermal properties
[
[
Compound 1 underwent loss of its unligated water molecules
ꢁ
between 25 and 125 C, with a mass loss of 2.6% closely corre-
sponding to the calculated value of 2.8%. Loss of bound water
ꢁ
molecules took place between 125 and 195 C, with a mass loss of
6
.2% (5.5% calc’d). Ejection of the organic components occurred
ꢁ
above 200 C. Compound 2 underwent ejection of all water mole-
cules of crystallization and two equivalents of bound water be-
ꢁ
tween 160 and 210 C, marked by a mass loss of 12.3% (calc’d 11.5%).
Wudkewych, Megan J.
