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N.E. Greig et al. / Journal of Solid State Chemistry 225 (2015) 402–409
vibrational modes (1610–1475 cmꢁ1). Singlet and triplet state
values are reported as the 0–0 transitions from linker emission.
The structure contains two crystallographically unique FDC
linkers. The first FDC coordinates to both lanthanides of the dimer
and provides one oxygen to each lanthanide center in a mono-
dentate fashion from only one of its carboxylate moieties, O3 and
O4. This coordination is mirrored by a symmetrically equivalent FDC
ligand at an angle of 134.041. The remaining carboxylate moiety of
this FDC remains uncoordinated and is protonated, and lies in
between and nearly orthogonal to the sheets. FTIR spectroscopy
shows both protonated and deprotonated FDC (see SI). The second
FDC linker acts to propagate the sheets and is entirely coordinated to
the lanthanides through all carboxylate oxygen atoms. Bridging the
two lanthanide ions of the dimer is a bidentate oxygen atom, O2,
of a carboxylate group. The remaining oxygen of this carboxylate
group, O1, is coordinated to one Eu, while the other dimer receives
coordination through O10 with a symmetrically equivalent ligand on
the opposite side of the dimer, along with an O20 bridge repeated on
the other side. The other carboxylate of this linker operates to
connect two neighboring dimer groups, with O8 bonding to a Eu of
one dimer, and O7 coordinating to a Eu of the next nearest dimer.
The last coordinated moiety, the bound water, O9, is in roughly the
same plane as O2 and O3. Table 2 notes selected bond lengths for
the title compounds. Fig. 3 shows a ball-and-stick representation of
the dimer unit, and Fig. 4 shows the thermal ellipsoid plots for the
crystallographically unique atoms.
Table 3 shows the hydrogen bonding in the Eu-CP. First, there is
a hydrogen bond between the bound water ligand O(9) and O(1) of
the fully deprotonated FDC that forms the dimer. The second
interaction in the table is between O(10), which is a carboxylic acid
moiety of one sheet dangling in the channel, and O(9), which is a
bound water of a dimer on a neighboring sheet. This interaction
aids in stacking the sheets. The next interactions involve weaker
C–H-Acceptor hydrogen bonds. There is a weak intersheet inter-
action between C(8)–H(8) of the dangling furan moiety of one
sheet to a coordinated oxygen of a dimer in a neigboring sheet,
O(1). There is another weak H-bond between C(9) and O(10),
occurring in the channels and is between two furan moieties of
different sheets, further aiding in the stacking of the sheets. Lastly,
there is a weak intrasheet hydrogen bond between C(11)–H(11)
and the bound water molecule, O(9).
2.4. Further characterization
Thermogravimetric analysis was conducted on the Eu-analog of
1 using a Mettler-Toledo TGA/DSC 1 from 30 to 600 1C at 10 1C/min
under a nitrogen gas flow. FTIR spectroscopy was likewise con-
ducted on the Eu-analog of 1 to establish the vibrational modes
present within the crystalline lattice. A ThermoScientific Nicolet iS5
FT-IR was used for this analysis.
3. Results and discussion
3.1. Structural description
The following structural description will focus specifically on that
of the Eu-FDC CP. The other FDC CPs were found to have the same
structure, as confirmed with single and/or powder X-ray diffraction.
The title material is a two-dimensional compound constructed from
EuO8 polyhedra in a distorted square antiprism geometry that edge
share to form a dimer. Surrounding each Eu, there are five mono-
dentate oxygen atoms, which belong to carboxylate moieties (O1,
O3, O4, O7, O8), two symmetry equivalent oxygen atoms (O2, also a
carboxylate oxygen) bridging the Eu ions to form the dimer unit, and
one bound water molecule (O9).
The Eu dimers form 2D sheets that expand along the [100] and
[010] (Fig. 1) directions, propagated by the organic linker. These
sheets (Fig. 2) stack along [001]. Fully protonated carboxylic acid
groups are found dangling between the sheets, with carbon(C5)-
oxygen bond distances of 1.223 Å (C¼O) and 1.312 Å (C–OH) for O10
and O11, respectively. H-bonding and
stacking of the sheets.
π–π interactions facilitate the
There is a
π–π interaction between two neighboring centroid
Cg(2)–Cg(2) (calculated using PLATON [34] where Cg¼ring center
of gravity; values provide center to center distances) rings in
which O6, C11, C10, C13, and C12 make up Cg(2). This interaction
occurs at a distance of 3.560 Å, and is between two neighboring
dimers within the sheet. A weak interaction between centroids Cg
(1) and Cg(2), where Cg(1) is formed from the ring made up from
atoms O5, C8, C4, C3, and C9. This intersheet interaction occurs at a
distance of 4.014 Å and aids in the stacking of the sheets.
This structure is remarkably similar to a CP constructed by 2,
3-pyridinedicarboxylate (pydc) anions [14] instead of FDC ions. Both
compounds are 2-D CPs constructed from Ln dimers with one fully
deprotonated linker, one partially deprotonated linker, and one aqua
ligand, just as with the title compound. The layers stack through
similar hydrogen bonding interactions as well. The pydc compound
displayed an interesting thermal decomposition, which seems to
be mirrored within compound 1 as well (see SI for thermogram).
Beginning at 100 1C, compound 1 (Eu) loses 10.1% of its mass, which
can be attributed to the loss of the bound water ligand and a CO
molecule (calculated loss of 9.6%). The CO is lost from the partially
protonated linker. This linker continues to degrade over two nearly
indistinguishable mass losses of 9.4% and 17.6% beginning at around
330 1C, corresponding to loss of a CO2 moiety followed by the rest of
the linker (calculated losses: CO2¼9.2%; C4H3O2¼17.3%). The com-
pound continues to degrade immediately after these two mass loses
to remove the rest of the organic species (experimental¼27.9%;
theoretical¼27.1%). Overall, a mass loss of 65.0% was observed. This
Fig. 1. View of the title compound down [010], showing the stacking of the layers.
Note the uncoordinated FDC in between the layers. Orange polyhedra represent Eu
(III), black lines are carbon, and red spheres are oxygen. Hydrogens have been
omitted for clarity. (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)