Crystal Growth & Design
Article
destructive self-oxidation (both of which can seriously hamper
16,17
catalytic efficacy),
along with the necessary separation of
otherwise homogeneous catalysts from the reaction mixture. In
addition to the proposed facile separations, these catalysts can
be easily recycled and used multiple times without significant
decay in performance or leeching of structural compo-
1
8,19
nents.
The choice of manganese for the synthesis of
these MMPFs is based on the great diversity of topologies
possible as well as for its functionality in the targeted catalysis
2
0,21
reaction.
Recent reports of Mn-based MOFs functioning as CO2
cycloaddition catalysts, including a one-pot transformation of
olefins into cyclic carbonates utilizing an imidazolium bromide
Figure 1. Porphyrin ligand that serves as the organic linker in MMPF-
12 and MMPF-13:5,15-bis(3,5-dicarboxyphenyl)-10,20-bis(2,6-
22
functionalized MOF and a visible-light-assisted cycloaddi-
2
3
tion, provide valuable insight into designing systems that
offer novel means to a similar end. Though MMPF-12 and -13
affect high efficiencies with relatively low catalyst loading and
mild conditions, a comparison is warranted. In the former
work, considering only the conversion of styrene oxide to
styrene carbonate, a much higher ratio of catalyst and
cocatalyst is required at higher pressure and temperature to
affect yields like those observed with MMPF-12 and -13, in a
quarter of the time. In the latter work, a more rigid comparison
is drawn as substrate and cocatalyst are identical: under
ambient temperature and 1 atm with additional catalyst
loading (and less cocatalyst) complete conversion of
epichlorohydrin is achieved in the same amount of time, this
result being clearly attributed in some part to the light used.
Additionally, comparisons are drawn between several hetero-
dibromophenyl)porphyrin (H dcdbp).
4
three days, deep purple crystals of MMPF-12 were isolated in 58%
yield based on the Mn. MMPF-13 was prepared in a similar manner as
that of MMPF-12 with the exception of DMA being replaced by N,N-
dimethylformamide (DMF) and methanol with ethanol. The
modified reaction produced purple crystals of MMPF-13 in 54%
yield based on Mn.
Single-crystal X-ray diffraction analysis revealed that compound
MMPF-12 crystallizes in the orthorhombic space group Pnma.
Manganese seated in the porphyrin core with a near-perfect
tetrahedral {N } geometry, coordinating with the four nitrogen
4
analysis (Figure S1). Additionally, the metal center appears to possess
trans-axial ligation of one hydroxo group and one solvent molecule
(DMA, methanol, or water) based on single-crystal X-ray diffraction
data. The length of Mn−N bonds range from 1.9730 to 2.0970 Å.
MMPF-12 exhibits one Mn O (CO ) dimer secondary building unit
geneous catalysts, including MOFs, for cycloaddition of CO
to epoxides in a review by Marciniak et al.
2
24
2
3
2 4
−
(
SBU) and two isostructural Mn O (HCO )(CO ) trimer SBUs.
3 5 2 2 4
Recent statistics in 2018 have revealed that carbon dioxide
As presented in Figure 2, in the dimer SBUs, Mn1 ions coordinate
(
CO ) emission has accounted for 81% of greenhouse gases.
2
with five oxygen atoms from three bidentate bridging μ -η η
2
1 1
Though it is sequestered naturally in several environmental
compartments, these sinks have not kept up with changes in
anthropogenic emission, leading to an overall increase in
carboxylates and two water molecules with a square pyramidal
geometry. Mn2 ions exhibit the same geometry as Mn1; yet, Mn2 ions
are instead coordinated with three carboxylate groups from three
different dcdbp ligands, one μ -η carboxylate, and one OH group.
25
atmospheric CO2. Carbon capture through the chemical
1
1
fixation of CO is an appealing approach in addressing and
Consequently, two pentacoordinated Mn atoms linked by three μ
-
2
2
η η carboxylate groups construct the dimer SBUs. Three crystallo-
mending the environmental impact of anthropogenic CO2
emission, particularly, conversion of CO2 into useful
compounds, thereby adding economic value for the byproducts
1 1
graphically distinct Mn ions could be observed in the
−
Mn O (HCO )(CO ) trimer. In the trimer SBUs, Mn4 is
3
5
2
2 4
2
6,27
surrounded by six oxygen atoms from two bidentate bridging μ
-
2
of sequestration.
This can be achieved effectively through
η η carboxylates, two μ -η carboxylates, a water molecule, and
1
1
1
1
the application of MMPFs toward the catalytic cycloaddition of
−
oxygen from HCO . Mn5 is coordinated with two carboxylate
oxygen atoms, one HCO2 group, and two oxygen atoms to complete
2
CO to epoxides, yielding dioxolanones, which are a class of
−
2
compounds utilized in polycarbonate materials, electrolytes in
lithium batteries, pharmaceutical production, antifungal agents,
a square pyramidal geometry. Importantly, as shown in Figure 2, the
−
difference between two Mn O (HCO )(CO ) trimers was that
3
5
2
2 4
28−30
and as polar solvents.
Mn6 connected by an oxygen atom as well as two μ -η η
2 1 1
carboxylates. Further structural analysis revealed that all of the
nodes in the structure of MMPF-12 are 4-connected; thus, MMPF-12
exhibits an nbo topology.
Single-crystal X-ray diffraction analysis revealed that MMPF-13
crystallizes in the orthorhombic space group Pbca. The low occupancy
In view of these demanding challenges and as a continuation
of our interest in the MOFs research, we offer in this
contribution a facile approach for the synthesis and detailed
structural characterization of two manganese-based MMPFs,
namely, MMPF-12 and MMPF-13, and their applications in
(determined by analysis of XRD data to be about 92% freebase) of
both selective (CO /CH ) gas sorption and catalytic cyclo-
2
4
Mn in the porphyrin macrocycle indicates that the linker is primarily a
freebase porphyrin. Interestingly, the dihedral angles between the
porphyrin plane and the attached dicarboxylate benzene rings are
different, 58.9 and 65.6 deg. The ligand dcdbp in this case exhibits
multimodal coordination. The asymmetric unit of MMPF-13 consists
of two crystallographically unique Mn ions. Mn1 is fully coordinated
to the dcdbp ligand with seven oxygen atoms from one bridging μ2-
η η carboxylate, one bidentate bridging μ -η η carboxylate, one μ -η
1
addition of CO to epoxides as an access to a series of
2
important compounds.
EXPERIMENTAL SECTION
■
With slight modification of the solvents and temperature used in the
syntheses, two porous porphyrinic manganese MMPFs, denoted as
MPPF-12 and MPPF-13, were obtained. MMPF-12 was synthesized
via a hydrothermal method using Mn(NO ) ·4H O (0.28 mmol),
2
1
2
1
1
1
carboxylate, monodentate chelating μ -η carboxylate, and three
1
2
oxygen atoms from free water molecules and an OH group. Mn2 is
coordinated with five oxygen atoms from two bidentate bridging μ2-
η η carboxylates, two water molecules, and one oxygen from DMF.
3
2
2
(
H dcdbp, Figure 1) (0.002 mmol), dimethylacetamide (DMA)
4
(0.009 mmol), methanol (0.005 mmol), and water (3.7 mmol). After
1
1
2
787
Cryst. Growth Des. 2021, 21, 2786−2792
Magnuson, Zachary L.
