Cobalt(II) Bipyrazolate Metal-Organic Frameworks as Heterogeneous Catalysts in Cumene Aerobic Oxidation: A Tag-Dependent Selectivity

Article abstract of DOI:10.1021/acs.inorgchem.0c00481

Three metal-organic frameworks with the general formula Co(BPZX) (BPZX2- = 3-X-4,4′-bipyrazolate, X = H, NH2, NO2) constructed with ligands having different functional groups on the same skeleton have been employed as heterogeneous catalysts for aerobic liquid-phase oxidation of cumene with O2 as oxidant. O2 adsorption isotherms collected at pO2 = 1 atm and T = 195 and 273 K have cast light on the relative affinity of these catalysts for dioxygen. The highest gas uptake at 195 K is found for Co(BPZ) (3.2 mmol/g (10.1 wt % O2)), in line with its highest BET specific surface area (926 m2/g) in comparison with those of Co(BPZNH2) (317 m2/g) and Co(BPZNO2) (645 m2/g). The O2 isosteric heat of adsorption (Qst) trend follows the order Co(BPZ) > Co(BPZNH2) > Co(BPZNO2). Interestingly, the selectivity in the cumene oxidation products was found to be dependent on the tag present in the catalyst linker: while cumene hydroperoxide (CHP) is the main product obtained with Co(BPZ) (84% selectivity to CHP after 7 h, pO2 = 4 bar, and T = 363 K), further oxidation to 2-phenyl-2-propanol (PP) is observed in the presence of Co(BPZNH2) as the catalyst (69% selectivity to PP under the same experimental conditions).

Full text of DOI:10.1021/acs.inorgchem.0c00481

pubs.acs.org/IC
Article
Cobalt(II) Bipyrazolate Metal−Organic Frameworks as
Heterogeneous Catalysts in Cumene Aerobic Oxidation: A Tag-
Dependent Selectivity
Anna Nowacka, Rebecca Vismara, Giorgio Mercuri, Marco Moroni, Miguel Palomino,
Kostiantyn V. Domasevitch, Corrado Di Nicola, Claudio Pettinari, Giuliano Giambastiani,
́
Francesc X. Llabres i Xamena,* Simona Galli,* and Andrea Rossin*
Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Three metal−organic frameworks with the general
formula Co(BPZX) (BPZX2− = 3-X-4,4′-bipyrazolate, X = H, NH2,
NO2) constructed with ligands having different functional groups on the
same skeleton have been employed as heterogeneous catalysts for
aerobic liquid-phase oxidation of cumene with O2 as oxidant. O2
adsorption isotherms collected at pO2 = 1 atm and T = 195 and 273
K have cast light on the relative affinity of these catalysts for dioxygen.
The highest gas uptake at 195 K is found for Co(BPZ) (3.2 mmol/g
(10.1 wt % O2)), in line with its highest BET specific surface area (926
m2/g) in comparison with those of Co(BPZNH2) (317 m2/g) and
Co(BPZNO2) (645 m2/g). The O2 isosteric heat of adsorption (Qst)
trend follows the order Co(BPZ) > Co(BPZNH2) > Co(BPZNO2).
Interestingly, the selectivity in the cumene oxidation products was found to be dependent on the tag present in the catalyst linker:
while cumene hydroperoxide (CHP) is the main product obtained with Co(BPZ) (84% selectivity to CHP after 7 h, pO2 = 4 bar,
and T = 363 K), further oxidation to 2-phenyl-2-propanol (PP) is observed in the presence of Co(BPZNH2) as the catalyst (69%
selectivity to PP under the same experimental conditions).
reactions. For example, Zhang et al.4 used CuO nanoparticles
as the catalyst and O2 as oxidant at 358 K, attaining a very
1. INTRODUCTION
Oxidation of cumene (CM) to cumene hydroperoxide (CHP)
good selectivity to CHP (93.2%) at a relatively high conversion
is an interesting process from an industrial viewpoint, as CHP
level (44.2%). This catalyst could be reused up to six times
is an intermediate for the synthesis of phenol, an important raw
without activity loss. Hsu et al.5 studied various polymer-
material for phenol resins, perfumes, medicines, agricultural
supported transition-metal catalysts for CM oxidation at 353 K
chemicals, and many other industrial products with added
under an O2 atmosphere. The best results achieved featured a
value.1 CM oxidation (Scheme 1) is typically carried out in the
99% selectivity at a 6.8% conversion, with a reaction rate that
liquid phase, using O2 (or air) as oxidant in the absence of any
was 84% faster in comparison to the blank experiment
catalyst (the so-called thermal auto-oxidation process) and
(autoinitiated with CHP) under analogous conditions. None-
with small amounts of CHP or other substances added as
theless, the most widely exploited transition metal in CM
initiators. CM conversion is usually kept low to maximize the
oxidation catalysis is cobalt. Several literature examples
selectivity toward CHP (typically above 90−92%) and
minimize side products resulting from CHP decomposition,
featuring both homogeneous and heterogeneous cobalt-based
systems can be found. As a representative example, the
mainly 2-phenyl-2-propanol (cumyl alcohol, PP) and aceto-
[Co(N3Py2)(H2O)](ClO4)2 and [Co(N3Py2)(CH3CN)]-
phenone (AP) (Scheme 1, paths a and b).2 Despite these
(BPh4)2 complexes (N3Py2 = κ5N-pentadentate pyridine-
precautions, the productivity of the auto-oxidation process is
generally below the desired values.
To solve this problem, there is great interest in developing
Received: February 14, 2020
robust and reusable homogeneous and heterogeneous catalysts
for CM oxidation to increase CHP productivity without
compromising the high selectivity typically attained in the
auto-oxidation process.3 Most of these catalysts are based on
transition metals, which are active in several catalytic oxidation
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
© XXXX American Chemical Society
Inorg. Chem. XXXX, XXX, XXX−XXX
A

Inorganic Chemistry
pubs.acs.org/IC
Article
Scheme 1. Schematic Representation of CM Oxidation to
CHP and Its Further Oxidation to Yield 2-Phenyl-2-
propanol (PP, a) and Acetophenone (AP, b)
Scheme 2. Molecular Structure of the Three Spacers
Employed in This Work: 3-Amino-4,4′-bipyrazole
(H2BPZNH2, Left), 3-Nitro-4,4′-bipyrazole (H2BPZNO2,
Center), and 4,4′-Bipyrazole (H2BPZ, Right)
atm), together with the already known analogues Co(BPZ)
(H2BPZ = 4,4′-bipyrazole, Scheme 2) and Co(BPZNO2)
(H2BPZNO2 = 3-nitro-4,4′-bipyrazole, Scheme 2), sharing the
same structural motif. Different selectivities have been
observed, as a function of the nature of the chemical tag
present in the catalyst ligand. The selectivity trend found is
strongly connected with the ability of the scrutinized MOFs to
promote further CHP oxidation.
2. EXPERIMENTAL SECTION
based ligand) reported in 20176 belong to the former class.
The latter family is definitely larger, spanning from Co-salen
polymers,7 a Co(OAc)2/SiO2 xerogel composite,8 and simple
CoX2 salts (X− = Cl−, OAc−, acac−)9 to the mixed-valence
2.1. Materials and Methods. All of the reagents and solvents
used were acquired from commercial vendors and employed as
received, without purification. 4,4′-Bipyrazole,20 3-nitro-4,4′-bipyr-
azole,21 3-amino-4,4′-bipyrazole,19b Co(BPZ),19e and Co-
(BPZNO2)19c were prepared following previously published
procedures. Elemental analyses (C, H, N %) were carried out on a
Fisons Instruments 1108 CHNS-O elemental analyzer. IR spectra
were recorded as the neat species from 4000 to 600 cm−1 using a
PerkinElmer Spectrum One System instrument. Thermogravimetric
analysis (TGA) and differential scanning calorimetry (DSC) were
simultaneously carried out using a NETZSCH STA 409 PC analyzer
on the Co(BPZNH2)·DMF and the activated Co(BPZNH2)
compounds. For the former, ∼10 mg of as-synthesized Co-
(BPZNH2)·DMF was heated in an oven at 323 K for 4 h; then, it
was placed in an alumina crucible devoted to thermal analysis. For the
latter, ∼10 mg of as-synthesized Co(BPZNH2)·DMF was activated at
413 K under vacuum (10−3 bar) for 24 h; then, it was placed in an
alumina crucible. Under a N2 flow (40 mL min−1), the temperature
was increased from 303 to 1173 or 1073 K at a rate of 10 K min−1.
The raw data obtained were corrected on the basis of a background
curve. The nature and purity of all the samples used in this work were
evaluated by elemental analysis, IR spectroscopy, and powder X-ray
diffraction (PXRD). PXRD qualitative analyses were performed by
means of a Bruker AXS D8 Advance vertical-scan θ:θ diffractometer
equipped with an X-ray tube (Cu Kα, λ = 1.5418 Å), a Bruker
Lynxeye linear position-sensitive detector, a nickel filter in the
diffracted beam, and the following optical components: primary beam
Soller slits (2.5°), fixed divergence slit (0.5°), and antiscatter slit (8
mm). The generator was operated at 40 kV and 40 mA. PXRD data
were measured under room-temperature conditions in the 2θ range
5.0−105.0°, with steps of 0.02° and a time per step of 10 s, and
treated with whole powder pattern refinements, using the TOPAS-
Academic V6 software package.22 XPS spectra were recorded using a
SPECS spectrometer equipped with a Mg Kα (1253.6 eV) X-ray
source and a 150MCD-9 Phoibos detector. The spectra were
corrected using the sp2 graphitic component of the C 1s spectrum
as an internal reference (binding energy, BE, 284.6 eV). The
morphology of the samples was analyzed with a field emission
scanning electron microscope (FESEM) JEOL Model JSM-7001F.
2.2. Synthesis of Co(BPZNH2)·DMF. Co(NO3)2·6H2O (0.291 g,
1.00 mmol) was added to a N,N-dimethylformamide (DMF) solution
(15 mL) of 3-amino-4,4′-bipyrazole (0.149 g, 1.00 mmol). The
mixture was stirred at 393 K for 24 h. After slow cooling to room
temperature, a dark violet precipitate was formed. The precipitate was
filtered off, washed with hot DMF (2 × 10 mL), and dried under
vacuum. Yield: 73%. Co(BPZNH2)·DMF is insoluble in dimethyl
sulfoxide, alcohols, acetone, acetonitrile, chlorinated solvents, and
water. Anal. Calcd for Co(BPZNH2)·0.75DMF: C, 37.98; H, 3.96; N,
10
spinel Co3O4 and modified cobalt oxides.11
In addition to the production of CHP noted above, CM
oxidation is important for other applications as well. Indeed,
many catalysts that are highly active for CM oxidation are also
very active in converting CHP into its two main byproducts:
PP and AP. Like phenol, PP and AP are also valuable
intermediates in the production of resins, perfumes, and
pharmaceuticals.12 It is therefore interesting to learn how the
properties of a catalyst can be tuned to promote either the
selective formation of CHP or its further decomposition to the
target products PP and AP, while avoiding the accumulation of
CHP in the reaction mixture to reduce safety concerns.
Among the plethora of heterogeneous catalysts available, in
recent years metal−organic frameworks (MOFs) have gained
the stage as versatile and multifunctional catalysts in several
chemical processes.13 MOFs are crystalline porous materials
whose chemicophysical properties can be easily tuned through
a judicious combination of tailored organic linkers and metallic
nodes. Thus, MOFs may be superior heterogeneous catalysts
in comparison to the “classical” fully inorganic zeolites/oxides
or to fully organic carbon-based nanomaterials. In the specific
context of alkane and alkene oxidation catalysis, several
transition-metal-based MOFs have been scrutinized by differ-
ent research groups worldwide.14 Similarly to what observed
with other heterogeneous catalysts, the most exploited
transition metal for MOF construction in this applicative
context is cobalt.15
In previous investigations, we have shown that MOFs
containing transition metals of the 3d series such as Cu(2-
pymo)2,16 Cu(im)2,16 Cr,Fe-MIL-101,17 and the mixed-metal
NiCo-BTC series18 can be employed as catalysts for the
aerobic oxidation of alkanes, including cumene. In light of this,
and starting from our expertise in the preparation of transition-
metal-containing bipyrazolate MOFs with ligands decorated
with different chemical tags,19 we have isolated the new
cobalt(II) MOF Co(BPZNH2), containing the 3-amino-4,4′-
bipyrazole spacer (H2BPZNH2, Scheme 2), and we have tested
it as a heterogeneous catalyst in cumene oxidation under mild
conditions using oxygen as a green oxidant (T = 363 K, pO2 = 4
B
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Figure 1. Conditioned order in Co(BPZNH2): (a−c) possible mutual dispositions of the amino groups along the pore walls, assuming that the 3-
amino-4,4′-bipyrazolate ligand is not planar. (d) Portion of the packing as reference. Axis color code: a, red; b, green; c, blue. Atom color code:
carbon, gray; nitrogen, blue; zinc, violet. The hydrogen atoms have been omitted for clarity.
30.87. Found: C, 37.94; H, 3.94; N, 30.79. IR (neat, cm−1; Figure
S1): 3387 (w, br) [ν(N−H)], 3095 (w) [ν(C−Haromatic)], 2928 (w)
[ν(C−Haliphatic)], 1655 (vs) [ν(C = O)], 1500 (s) [ν(CC + C
N)], 1435 (w), 1384 (s), 1275 (m), 1250 (m), 1204 (w), 1163 (w),
1123 (s), 1093 (m), 1056 (s), 1014 (w), 946 (s), 839 (m).
successfully modeled via a whole powder pattern refinement by using
two Cccm unit cells with slightly different parameters (Figure S3 and
Table S1). The difference in the asymmetric unit volumes (∼4 Å3,
estimated as V/Z′; Table S1) cannot be explained in terms of two
phases with a different solvation degree. Indeed, ex situ activation (T
= 413 K, 10−3 Torr, 24 h) or in situ heating of an as-synthesized
sample at a temperature above that needed for complete solvent
removal (see Thermal Behavior) did not provide a unique phase.
Upon activation, the two powder patterns coalesce into one that can
be described only apparently by the unit cell parameters of one
orthorhombic C phase (Figure S4). Despite the adoption of various
models with different complexity to describe the peak profile (e.g.,
convolution, to a Lorentzian description, of hkl-class specific tanθ- or
1/cosθ-dependent spherical harmonics), some Bragg reflections are
still right-side anisotropically broadened. The issue could be fixed by
assuming that the sample is biphasic even after activation (Figure S5).
On the basis of recent seminal works on conditioned disorder in
MOFs,24 we propose that this experimental evidence can be explained
by the existence of two phases in which the ligands locally adopt
different conditioned orders of the NH2 substituents. In the
hypothesis that the bipyrazolate ligand is not planar (an occurrence
already observed in the literature even with unsubstituted
bipyrazolates19e,20,25), we can think of three mutual dispositions of
the NH2 groups (Figure 1) along the a and b axes.
2.3. Powder X-ray Diffraction Structural Characterization.
Samples of Co(BPZNH2)·DMF and Co(BPZNH2) were placed in
the cavity of a silicon-free background sample holder 0.2 mm deep
(Assing Srl, Monterotondo, Italy). PXRD data acquisitions were
carried out with the instrumentation described above in the 2θ range
5.0−105.0°, with steps of 0.02° and an overall scan time of about 12
h. Though they are retraceable to those of other M(bipyrazolate)
MOFs (M = Co, Zn)19b,c,e with orthorhombic Cccm crystallographic
symmetry, the PXRD patterns of all the as-synthesized samples of
Co(BPZNH2)·DMF that we handled showed doubling or right-side
anisotropic broadening of specific Miller index classes (e.g., [hhl],
[0kl], and [h0l]), with respect to the PXRD pattern calculated on the
basis of the supposed orthorhombic C crystallographic symmetry.
This was also witnessed by a whole powder pattern refinement
performed with the Le Bail method, using the TOPAS-Academic V6
software package (Figure S2). Lowering the crystallographic
symmetry (e.g., down to C2/c or P21/c, proper subgroups of Cccm)
did not lead to any improvement. Similarly, ab initio indexing (i.e.,
peak search followed by profile fitting to estimate the maximum
positions of low- to medium-angle peaks, which were then handled
through the singular value decomposition algorithm23 within TOPAS-
Academic V6) did not lead to trustable unit cells describing all the
observed reflections. In contrast, the powder pattern could be
Thus, phases featuring slightly different unit cell parameters can be
obtained, depending on the conditioned order adopted by the
dangling −NH2 groups. Heating promotes a disruption of this order
until the two phases coalesce almost completely. As a proof, a
C
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Figure 2. Representation of the crystal structure of Co(BPZNH2): (a) torsion angles between the two ligand pyrazolate rings in Phases 1 and 2
and their coordination mode through the 1-D chains along the [001] crystallographic direction; (b) portion of the packing of Co(BPZNH2) Phase
1 viewed in perspective along the [001] crystallographic direction. Color code: carbon, gray; hydrogen, light gray; cobalt, violet; nitrogen, blue. For
the sake of clarity, the solvent molecules have been omitted and an ordered model has been assumed for the position of the NH2 groups on the
skeleton of the ligand, by lowering the symmetry down to C2. Main bond distances and angles: Phase 1, Co−N 2.062(2), 2.081(2) Å, Co···Co,
3.611(2), 8.899(6) Å, N−Co−N, 109.6(6)−110.8(6)°; Phase 2, Co−N 2.051(5) Å, Co···Co 3.620(4), 8.941(6) Å, N−Co−N, 108(2)−
112.7(14)°.
structure refinement was carried out through the Rietveld method
using two orthorhombic Cccm phases, starting from the crystal
structure of Zn(BPZNO2).19c A rigid body was built up to model the
crystallographically independent portion of the ligand, assigning mean
values to bond distances and angles,26 without constraining the two
pyrazolate rings to be coplanar. The amino group was maintained
coplanar to the skeleton of the ligand. Even though for the final
structure refinement Co(BPZNH2) was preventively activated (413
K, 10−3 bar, 24 h) to eliminate the guest solvent, the MOF adsorbs
water vapor from the atmosphere simply during its transfer from the
vacuum apparatus to the alumina crucible for the thermogravimetric
analysis. This is witnessed by a thermal analysis performed on the
activated sample (Figure S6). To locate the adsorbed water
molecules, structure solution was carried out with TOPAS-Academic
V6 by a combined Monte Carlo/Simulated Annealing27 approach
using a number of oxygen atoms whose site occupation factors and
fractional coordinates were allowed to vary. During the final stages of
the Rietveld refinement, ligand bond distances (except the C/N−H
distances) were refined in a restrained range of values, on the basis of
a search in the Cambridge Structural Database (v. 2019) for room-
temperature crystal structures containing the M(pyrazolate) (M = 3d
transition metal) fragment. The background was modeled through a
Chebyshev-type polynomial function. A common, refined isotropic
thermal factor (Biso) was attributed to all atoms, except to the metal
center, whose isotropic thermal factor was calculated as Biso(M) = Biso
− 2.0 (Å2). The peak profile was modeled through the fundamental
parameters approach.28 The anisotropic peak profile of the two phases
was modeled by convoluting the same tanθ contribution of the
Stephens correction.29 The final Rietveld refinement plot is provided
as Figure S7 in the Supporting Information. The CIF file is cited in
Accession Codes (the CIF file of Phase 1 is provided as a
representative example). The final m/m ratio (%) of the two phases
found at the end of the refinement process is 66:34.
2.4. Variable-Temperature Powder X-ray Diffraction. In
order to complete the thermal analysis, the thermal behavior of
Co(BPZNH2)·DMF was studied in situ by means of variable-
temperature PXRD. A ∼20 mg sample of as-synthesized Co-
(BPZNH2)·DMF was heated in air from 303 K up to 623 K by
employing a custom-made sample heater (Officina Elettrotecnica di
Tenno, Ponte Arche, Italy), with steps of 20 K; a PXRD pattern was
measured at all steps in the 2θ range 9.0−24.5°, with a step of 0.02°
and a time per step of 1.5 s.
2.5. Gas Adsorption. Approximately 40 mg samples of the three
MOFs were activated at 403 K under high vacuum (10−6 Torr) for 24
h prior to every measurement. The textural properties of Co-
(BPZNH2) were estimated by volumetric adsorption carried out with
an ASAP 2020 Micromeritics instrument, using N2 as the adsorbate at
77 K. For the Brunauer−Emmett−Teller (BET) specific surface area
calculation, the 0.01−0.1 p/p0 pressure range of the isotherm was
used for data fitting to satisfy all the Rouquerol consistency criteria.30
The pore size distribution was determined by means of the BJH
method (Halsey thickness equation) for the mesopores and by the
density functional theory method (DFT; slit-like pore shape typical of
carbon-based materials) for the micropores. The micropore volume
was estimated by applying the Dubinin−Astakhov model to the N2
adsorption isotherm in the pressure range 0 ≤ p/p0 ≤ 0.02.31 The O2
isosteric heat of adsorption (Qst) of the Co(BPZX) MOFs was
calculated from the O2 isotherms measured at 273 and 195 K by
applying a variant of the Clausius−Clapeyron equation:32
i
j
j
j
j
y
z
z
z
z
p
T − T
1
2
1
ln
= Q
st
j
j
z
z
p2
RTT
1
2
(1)
k
{
where pn (n = 1, 2) is the pressure value for the nth isotherm; Tn (n =
1, 2) is the temperature value for the nth isotherm, and R is the gas
constant (8.314 J K−1 mol−1).
Crystal data for Co(BPZNH2)·2.5H2O, Phase 1: C6H10CoN5O2.5,
FW = 251.1 g mol−1, orthorhombic, Cccm, a = 12.350(7) Å, b =
12.815(8) Å, c = 7.2225(14) Å, V = 1143.1(10) Å3, Z = 16, Z′ = 4, ρ
= 1.460 g cm−3, F(000) = 512, Rp = 0.014, Rwp = 0.018, RBragg = 0.006,
for 4826 data and 44 parameters in the 2θ range 8.5−105.0°. CCDC
Number: 1962311.
Crystal data for Co(BPZNH2)·0.8H2O, Phase 2: C6H6.6CoN5O0.8,
FW = 220.5 g mol−1, orthorhombic, Cccm, a = 12.530(12) Å, b =
12.758(13) Å, c = 7.2400(11) Å, V = 1157.4(16) Å3, Z = 16, Z′ = 4, ρ
= 1.265 g cm−3, F(000) = 444, Rp = 0.014, Rwp = 0.018, RBragg = 0.007,
for 4826 data and 44 parameters in the 2θ range 8.5−105.0°.
2.6. Oxidation of Cumene. Caution! The reaction conditions of
cumene oxidation have been carefully selected to avoid flammable
mixtures. Any deviation from these conditions must be carefully
evaluated. In a typical experiment, 1 mL of cumene (7.14 mmol, 99%,
Sigma-Aldrich) and the solid catalyst (Co(BPZ), Co(BPZNO2) or
Co(BPZNH2), with a cumene to metal molar ratio of 150) were
placed inside a glass tube microreactor (volume 6 mL) with a
magnetic stirrer, a manometer, a gas inlet, and a valve for liquid
sampling. The reactor was connected through a cannula to an O2
supply system fixed at pO2 = 4 bar. The reservoir continuously
restocks the O2 consumed during the oxidation reaction, to keep the
D
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
concentration of O2 constant during the reaction. The reactor was
placed on an iron hot plate preheated at 363 K. To monitor the time
evolution of the products, we used GC analysis (Agilent Technologies
7890A, capillary column 10 m × 320 μm × 0.1 μm) on aliquots taken
at fixed time intervals. To minimize the possible decomposition of the
hydroperoxide at the injector, the samples were injected directly on-
column. The metal content of the reaction filtrate was determined by
ICP-OES on a Varian 715-ES instrument.
2.7. Cumene Hydroperoxide Decomposition. For CHP
decomposition experiments, the same glass tube microreactors
descried above were used, containing 1 mL of cumene (7.14
mmol), 14 mg of catalyst (Co(BPZ), Co(BPZNO2) or Co-
(BPZNH2)) and diphenyl ether as internal standard (50 μL). After
the reactor was flushed with N2, CHP was added (110 μL) and the
reaction vessel was placed in an iron heating block at 363 K. The
conversion of CHP was determined by GC.
2.8. Heat of Immersion Experiments. A precisely weighed mass
of catalyst was placed in a glass bulb with a brittle end and outgassed
under high vacuum (10−5 mbar) for 24 h at 333 K. The bulb was then
sealed and transferred to a Setaram Calvet-type C80 calorimeter
equipped with a mixing cell containing 4.00 g of the wetting liquid
(either CM or CHP) and tightly sealed by an O-ring. The system was
placed into the calorimeter block and left for temperature
equilibration (303 K). When thermal equilibrium was reached, the
cell rod was gently pressed to break the brittle end of the bulb with
the bottom of the calorimeter cell. The wetting liquid entered into the
sample, and the evolution of the released heat was monitored as a
function of time. The total experimental heat of immersion was then
calculated by integrating this signal, after correcting by measuring
empty (reference) cells under the same conditions to account for bulb
breaking (exothermic event) and the heat of vaporization of the
wetting liquid filling the empty volume of the bulb with the vapor at
the corresponding vapor pressure (endothermic event).
Figure 4. O2 adsorption isotherms measured at 195 K on Co(BPZX).
a
Table 2. Aerobic Oxidation of Cumene
selectivity (%)
time
(h)
conversn
b
entry
catalyst
blank
Co(BPZ)
(%)
CHP PP
AP CMD
1
2
2a
3
3a
4
4a
4b
5
7
1
7
1
7
1
7
24
7
12
5
8
94
90
84
74
74
18
16
7
6
10
15
22
22
71
69
73
30
57
0
0
0
0
0
1
1
3
4
6
0
34
10
32
39
72
84
49
59
1
3
Co(BPZNO2)
Co(BPZNH2)
3
8
11
14
1
18
c
,
Co3(BTC)2
Co-salen-
69
37
6
d
polymer7
,
3. RESULTS AND DISCUSSION
3.1. Synthesis of Co(BPZNH2)·DMF and Crystal
Structure Analysis. The synthesis of Co(BPZNH2)·DMF
10
e
,
7
Co3O4
60
40
a
Reaction conditions unless specified otherwise: 1 mL (7.14 mmol)
of cumene, catalyst (cumene to metal molar ratio 150), pO2 = 4 bar, T
b
c
= 363 K. Conversion (mol %), determined by GC. BTC3−
=
d
benzene-1,3,5-tricarboxylate. Conditions: pO2 = 1 bar; T = 383 K.
Conditions: pO2 = 1 bar; T = 353 K.
e
Table 3. Decomposition of CHP over the Co(BPZX)
a
MOFs
b
CHP decomposition (%)
entry
catalyst
blank
Co(BPZ)
Co(BPZNO2)
Co(BPZNH2)
at 7 h
at 24 h
1
2
3
4
2.8
4.4
11.5
26.6
4.4
7.1
17.2
55.3
a
Reaction conditions: 1 mL of cumene, ca. 14 mg of catalyst (CM to
Co2+ molar ratio 150), 110 μL of CHP, diphenyl ether as internal
standard (50 μL), N2 atmosphere, 363 K. CHP decomposition (%)
b
Figure 3. N2 adsorption isotherm measured at 77 K on Co-
(BPZNH2). The desorption branch is drawn with empty symbols.
determined by GC.
Table 1. Collective Data on BET Areas, as Retrieved from the N2 Adsorption Isotherm, O2 Uptake (at p = 1 bar and T = 273,
195 K), and Oxygen Isosteric Heat of Adsorption (Qst) of the Co(BPZX) MOFs Presented in This Work
O2 adsorbed (mmol/g)
BET area (m2/g)
273 K
195 K
Qst(O2) (kJ/mol)
Co(BPZ)
Co(BPZNO2)
Co(BPZNH2)
92619e
64519c
317
0.6 (2.0 wt %)
1.1 (3.5 wt %)
0.5 (1.6 wt %)
3.2 (10.1 wt %)
2.8 (9.1 wt %)
1.8 (5.9 wt %)
17.7
13.7
15.9
E
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
confidently attributed to the water vapor adsorbed by the
sample during its transfer from the oven to the thermal
analyzer. The second loss can be reasonably explained as the
loss of 0.7 mol of DMF per mole of MOF (calculated weight
loss 19.6%). In situ variable-temperature PXRD performed in
air on a sample of Co(BPZNH2)·DMF shows that the MOF is
permanently porous (Figure S8). The two Cccm phases are
clearly visible (in terms of peak doubling) up to 423 K (blue
traces in Figure S8b); starting from 443 K, their PXRD
patterns coalesce and right-side anisotropic broadening of
specific classes of Miller indexes is evident (see the
Experimental Section). At 623 K, crystallinity loss is complete.
3.3. N2 Adsorption. The textural properties of Co-
(BPZNH2) were investigated through N2 adsorption at 77 K
after thermal activation (403 K, 10−6 Torr, 24 h). As shown in
Figure 3, Co(BPZNH2) features a type IV isotherm with a
narrow hysteresis loop typical of a mainly microporous
material with slit-like pore shape; the calculated BET specific
surface area is 317 m2/g (Table 1). This value is similar to that
of Zn(BPZNH2) (395 m2/g)19b but lower than those of the
Co(BPZ) (926 m2/g)19e and Co(BPZNO2) (645 m2/g)19c
analogues. The total pore volume at p/p0 = 0.98 is 0.21 cm3/g.
The limiting micropore volume (0.14 cm3/g) estimated
through the Dubinin−Astakhov model to the N2 adsorption
isotherm is much lower than the pore volume calculated from
the crystal structure (∼0.38 cm3/g; vide supra). This suggests
that the real sample porosity is different from the crystallo-
graphic porosity obtained through purely geometrical consid-
erations. Indeed, this structural motif19b,c,e has already shown a
certain extent of framework flexibility that may vary the pore
size. The Dubinin−Astakhov analysis also revealed that the
micropore volume represents the main contribution to the
total pore volume (67%). In Co(BPZNH2) there are two
different micropore sizes (retrieved from the DFT analysis
slit pore shape of carbon-based materials) of 1.4 and 1.6 nm.
The narrow and extended hysteresis loop for p/p0 > 0.42 can
be ascribed to interparticle voids between crystallites in the
sample, as confirmed by the SEM analysis of a bulk sample of
the MOF (vide infra, section 3.5). The BJH analysis applied to
the desorption branch of the N2 isotherm did not find any
mesopores in the 5−50 nm pore width interval; the only peak
observed at w ≈ 3.9 nm is an artifact due to cavitation of the
liquid nitrogen meniscus at p/p0 = 0.42.35
Table 4. Heat of Adsorption for Selected MOFs in CM and
CHP
ΔHimm in CM
ΔHimm in CHP
J/g
J/m2
J/g
J/m2
Co(BPZ)
Co(BPZNH2)
−81
−219
−0.09
−0.69
−137
−283
−0.15
−0.89
Figure 5. SEM images of fresh (a) and used (b) Co(BPZNH2). No
morphological differences can be seen between the two samples.
does not require the application of solvothermal conditions. In
this case, the conventional synthetic path is equally viable using
N,N-dimethylformamide as solvent. Moreover, ligand depro-
tonation does not require the presence of a base. The MOF
precipitates out of the reaction mixture as a dark violet air-
stable powder insoluble in the most common organic solvents.
Co(BPZNH2) shows the same structural motif as Co(BPZ)19e
and Co(BPZNO2).19c A short description of the key structural
aspects is provided hereafter for the sake of completeness.
Co(BPZNH2) crystallizes in the orthorhombic space group
Cccm. As explained in the Experimental Section, in all of the
examined batches of Co(BPZNH2) two phases are present
with slightly different unit cell parameters and ligand
conformation. Indeed, the intrinsic asymmetry of the ligand
may create a locally different conditioned order of the amino
substituents (Figure 1). In Co(BPZNH2) Phase 1 a torsion
angle of ∼20° is present between the two pyrazolate rings,
while Co(BPZNH2) Phase 2 contains a planar ligand (Figure
2a). In the crystal structure of Co(BPZNH2), tetrahedral
CoN4 nodes and exo-tetradentate spacers build up a 3-D (4,4)-
connected open framework (Figure 2b), featuring 1-D
channels of rhombic shape parallel to the crystallographic
direction [001]. The channel aperture (distance between the
van der Waals sphere of the closest carbon atoms belonging to
parallel facing ligands = 5.0 and 5.5 Å for Phases 1 and 2,
respectively), and consequently the accessible volume, are
strictly dependent on the orientation of the ligand and the
torsion angle between its pyrazolate rings. At room temper-
ature and pressure conditions, the empty volume33 of the two
phases lies in the range 44−46%, which means a pore volume
of ∼0.37−0.39 cm3 g−1. The sra network type is unveiled by
the topological analysis carried out with TOPOS 4.0.34
3.4. O2 Adsorption. Given the use in catalysis of O2 as
green oxidant, the Co(BPZX) MOFs were tested as O2
adsorbents at T = 195, 273 K and pO2 up to 1 bar (Figure 4
and Figure S9, respectively). Table 1 collects the main O2
adsorption data. Co(BPZNO2) is the best O2 adsorbent at
high temperatures, while Co(BPZ) is the best O2 adsorbent at
low temperatures. In terms of weight percentage, the amount
of O2 adsorbed at 195 K is proportional to the respective BET
areas.
The isosteric heat of adsorption (Qst) of O2 was estimated
with a variant of the Clausius−Clapeyron equation (eq 1,
through the comparison of the O2 adsorption isotherms
recorded at 273 and 195 K). The results are shown in Table 1.
The isosteric heat of adsorption reflects the interaction
strength between O2 and the inner pore walls of the MOFs.
Co(BPZ) affords the highest value of 17.7 kJ/mol calculated at
zero coverage, while the Qst trend follows the order Co(BPZ)
> Co(BPZNH2) > Co(BPZNO2). The Qst values found for
these MOFs are higher than those found for the Co(II) MOFs
MFU-1 (11.1 kJ/mol) and MFU-2 (8.5 kJ/mol), built with the
3.2. Thermal Behavior. Before the simultaneous thermal
analysis (STA) was performed, a batch of as-synthesized
Co(BPZNH2)·DMF was maintained in an oven at 323 K for 4
h, to eliminate traces of humidity on the outer surface of the
material. As shown by the TGA trace (Figure S8a), the MOF is
stable under N2 up to ∼673 K (onset of the decomposition
temperature), showing a better thermal stability than Co-
(BPZ) (Tdec = 593 K)19e and Co(BPZNO2) (Tdec = 623
K).19c Before decomposition, two weight losses take place
(∼2.9% in the temperature range 303−351 K; ∼19.0% in the
temperature range 370−583 K). The first loss can be
F
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Figure 6. (a) XPS survey spectra recorded for fresh (blue curve) and used (red curve) Co(BPZNH2). XPS Co 2p (b, c) and N 1s (d, e) core level
regions of fresh and used Co(BPZNH2) along with their relative curve fittings.
1,4-bis[(3,5-dimethyl)pyrazol-4-yl]benzene ligand and having
much higher BET areas (1525 and 1474 m2/g, respectively).36
The thermodynamic affinity for O2 of Co(BPZ) is comparable
to that of PCN-9 (17.8 kJ/mol), a Co(II) MOF containing the
G
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
triazine-2,4,6-triyltribenzoate spacer and with a BET area of
1064 m2/g.37
Table 2) and PP selectivity (69% vs 57%). Our catalyst is also
better performing than the classical Co2+/Co3+ mixed-oxide
Co3O4 that shows only 40% selectivity for PP (entry 7 in
10
3.5. Oxidation of Cumene over Co(BPZX). The effect of
different ligand tags on the catalytic oxidation of cumene and
product distribution was evaluated. The results obtained with
Co(BPZ) are shown in Table 2, entries 2 and 2a, while the
whole time−conversion plot is presented in Figure S10 in the
Supporting Information. This MOF showed a good catalytic
activity for CM oxidation (34% conversion after 7 h) in
comparsion with the blank (autocatalyzed) process (5%
conversion under the same reaction conditions, entry 1).
Moreover, Co(BPZ) afforded a very high selectivity to CHP:
up to ∼90% at 8% conversion after 1 h, which is only slightly
lower than that of the autocatalytic process (94%). This
selectivity decreased slightly for longer reaction times, down to
84% at 34% conversion after 7 h, along with the formation of
PP and AP byproducts. These side products come from the
decomposition of CHP, which is catalyzed by the same active
sites (Co2+ ions) that are involved in CM oxidation.
We have recently reported on the catalytic activity of mono-
and bimetallic trimesate (benzene-1,3,5-tricarboxylate, BTC3−)
compounds prepared from aqueous solutions and employed in
the aerobic oxidation of CM.18 In particular, in comparison
with Co3(BTC)2 (Table 2, entry 5), a lower activity was found
for Co(BPZ) under the same experimental conditions (34% vs
49% conversion after 7 h, respectively), though the CHP
selectivity to was significantly higher: 84% vs 69%, respectively
(entries 2a and 5 in Table 2). These differences in catalysts
performance mirror the different chemical properties and
coordination environments of the Co2+ sites imposed by the
ligand nature and the crystal structure.
The introduction of −NO2 groups on the bipyrazolate
skeleton has no significant influence on the catalytic activity
(Table 2, entries 3 and 3a): a slightly higher activity was found
for Co(BPZNO2) at short reaction times in comparison to
Co(BPZ) (10% vs 8% conversion after 1 h, respectively), but
both compounds have practically the same activity at longer
reaction times, (32% vs 34% conversion after 7 h, respectively).
However, small changes were observed in product distribution:
a lower CHP selectivity (74%) and a higher formation of PP
and AP (Table 2, entries 3 and 3a) were observed for
Co(BPZNO2). Small traces (ca. 1%) of an additional heavier
product (CMD in Table 2) was also observed, identified as a
cumene dimer coming from the direct coupling of two cumyl
radicals (Scheme 1).38
More important changes are found when −NH2 groups were
introduced into the bipyrazolate linker (Table 2, entries 4 and
4b). In this case, dramatic changes of catalyst activity and
cumene oxidation products distribution were observed (see
Figure S10 in the Supporting Information): 39% conversion of
CM was reached with Co(BPZNH2) after only 1 h. After 7 h,
the conversion increased to 72%, while the selectivity to CHP
dropped to 16%. Interestingly, the resulting selectivity to PP
formation obtained over Co(BPZNH2) increased up to 69%.
Longer reaction times only produced a slight increase in
conversion and selectivity to PP (up to 84% CM conversion
and 73% PP selectivity after 24 h), but the amount of CMD
increased significantly (6%) as well. The catalytic performance
of Co(BPZNH2) is better than that observed under similar
experimental conditions for the Co-Na heterodinuclear
polymer complex based on a Salen Schiff base and a crown
ether reported by Wang et al. in 2006,7 in terms of both
conversion (72% after 7 h vs 59% after 12 h, entries 4a and 6 in
Table 2).
As mentioned in the Introduction, CHP is the primary
product of CM oxidation, while PP and AP come from CHP
decomposition. Therefore, PP and AP formation depends on
the ability of the Co2+ sites to decompose the CHP formed in
the main reaction. In line with this observation, for other
MOFs16,18 we have observed that an increase in CHP
decomposition rate translates into a faster CM conversion
and a lower CHP selectivity. Therefore, the differences in
product distribution observed in Table 2 for the Co(BPZX)
MOFs reflect the ability of the catalyst to oxidize CM to CHP
and to decompose the formed CHP. To address this point, we
designed additional experiments of CHP decomposition over
the Co(BPZX) samples. The results obtained are summarized
in Table 3.
From a comparison of the data shown in Tables 2 and 3, it is
evident that the final CHP selectivity attained in the aerobic
oxidation of CM decreases as the ability of the catalyst to
decompose CHP increases. Thus, CHP decomposition over
Co(BPZ) was only slightly faster than in the blank experiment
(thermal CHP decomposition, Table 3, entries 1 and 2): 7.1%
vs 4.4% decomposition after 24 h, respectively. Conversely, the
decomposition of CHP was much faster over Co(BPZNH2),
attaining 55.3% decomposition after 24 h (Table 3, entry 4).
Meanwhile, the activity of Co(BPZNO2) for CHP decom-
position lies between the other two MOFs, as does the final
CHP selectivity (Table 3, entry 3). Co(BPZNO2) is slightly
more active than Co(BPZ) at short reaction times (<1 h), but
it also deactivates more quickly, due to the formation of the
bulky cumene dimers.
It has been reported39 that the presence of O2 during CM
oxidation can minimize CHP decomposition pathways, thus
increasing the final selectivity to CHP. Therefore, the higher
affinity of Co(BPZ) for O2 in comparison with Co(BPZNO2)
and Co(BPZNH2) according to the estimated isosteric heat of
adsorption (Qst, Table 1) might also contribute to some extent
to the higher selectivity to CHP observed for Co(BPZ).
In summary, the activity of the scrutinized MOFs for CM
conversion and CHP decomposition follows the trend
Co(BPZNH2) ≫ Co(BPZNO2) > Co(BPZ), which is also
the opposite trend observed for the CHP selectivity. Therefore,
the presence of amino (and, to a minor extent, nitro) groups in
the MOF linkers determines the catalytic properties of the
solids, inducing a clear tag-dependent selectivity. In particular,
the amino groups in the 4,4′-bipyrazolate ligand can play a dual
role: a local change in the electronic density on Co2+ and the
introduction of additional adsorption sites for CHP (through
hydrogen bonds between CHP and the solid catalyst) that may
accelerate CHP decomposition. Although the former effect
cannot be ruled out, we think that the latter may have a higher
impact on the catalytic properties of the scrutinized MOFs. In
this sense, Liao et al. have used carbon nanotubes (CNTs) and
nitrogen-doped carbon nanotubes (NCNTs) as catalysts for
the aerobic oxidation of CM.40 NCNTs were significantly
more active than CNTs for this reaction (74% vs 16%
conversion), yielding PP as the main product (96.7%
selectivity), while CNTs were highly selective toward CHP
(90%). On the basis of DFT calculations, the authors
concluded that the high catalytic activity and PP selectivity
of NCNTs is due to a strong interaction with CHP. Thus, once
H
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
CHP is formed, it remains strongly adsorbed onto the catalyst
surface, where it is easily overoxidized and decomposes to PP.
Conversely, the calculated interaction energy between CHP
and undoped CNTs was much lower, so that desorption of
CHP is more likely to occur. This minimizes CHP
decomposition events, thus increasing the final CHP
selectivity.
To determine whether the amino groups in Co(BPZNH2)
play a similar role in determining the catalytic properties for
CM oxidation, we have evaluated the strength of the
interaction between the catalyst and CM or CHP by measuring
their heat of immersion. This technique provides information
related to the surface area available to the liquid and, more
importantly, to the specific interaction between the solid
surface and the wetting liquid.41 The enthalpy of immersion
(ΔHimm) is the enthalpy change at constant temperature
arising when a solid is immersed into a wetting liquid in which
it does not dissolve or react.42 Moreover, immersion in the
pure liquid can closely mimic the catalytic conditions used in
this work. The results of the heat of immersion experiments are
collected in Table 4.
The heat of immersion in CHP is clearly much higher in the
case of Co(BPZNH2) than for Co(BPZ): 283 vs 137 J/g,
respectively. This difference is still higher if the specific surface
area of each compound is taken into account (0.89 vs 0.15 J/
m2, respectively). This is possibly due to the existence of the
amino groups in the linkers as additional (stronger) adsorption
sites for CHP, reasonably through N−H···O hydrogen
bonding interactions between the −NH2 group of BPZNH2
and the −OOH moiety of CHP. Moreover, the heat of
immersion in CHP is higher than that in CM for both
Co(BPZ) and Co(BPZNH2). This suggests that both MOFs
tend to decompose CHP, as already demonstrated in the CHP
decomposition experiments summarized in Table 3.
Finally, it is worth mentioning that all of the Co(BPZX)
compounds are stable under the adopted reaction conditions,
according to the PXRD patterns recorded after the catalysis.
Additional SEM and XPS comparative characterizations of
Co(BPZNH2) before and after catalysis have been carried out,
to check for structural or morphological changes occurring to
the MOF during the catalytic process. Both SEM images
(Figure 5) and the Co 2p and N 1s XPS spectra (Figure 6) of
fresh and used Co(BPZNH2) have confirmed its stability
under the oxidative catalytic conditions used. The Co 2p XPS
spectra can be fitted with only one main component with
related satellite peaks at BE ≈ 781, 796 eV (Figure 6b,c).
These peaks are typical of Co2+ ions for their 2p3/2 and 2p1/2
electronic states, respectively.43 No Co3+ ions are detected,
normally associated with bands at lower BE ≈ 767 (2p3/2), 769
(2p1/2) eV.44 The N 1s XPS spectra can be fitted with one
main component and a minor shoulder in a roughly 4:1 ratio at
BEs between 399 and 400 eV (Figure 6d,e). While the former
component at lower BE can be unambiguously ascribed to N
pyrazole atoms from the linker,45 peaks centered at 400 eV are
likely due to the −NH2 tag.46 The curve fitting has ruled out
the presence of oxidized functional groups such as −NO2
(whose N(1s) peak is normally centered around 404 eV).44
Analysis of the filtrates after the reaction by ICP-OES
revealed that the amount of Co2+ ions leached from the solid
catalysts was almost negligible, in all cases below 2% of the
total amount of Co2+ used in the reaction. Moreover, the
MOFs maintained their catalytic activity and CHP (or PP)
selectivity practically unmodified for at least five consecutive
cycles (see Figure S11).
4. CONCLUSIONS
A series of Co(II) MOFs containing 4,4′-bipyrazolate linkers
with different chemical tags have been exploited as
heterogeneous catalysts in cumene oxidation. The obtained
results have shown that simple ligand functionalization is a
good solution to tune the reaction outcome toward the desired
product (tag-dependent selectivity). Among the tested 4,4′-
bipyrazolate materials, Co(BPZ) presents good catalytic
activity and the best selectivity to CHP, while Co(BPZNH2)
features high activity. More importantly, Co(BPZNH2) turned
out to be a good candidate for PP production as the main
product. This mirrors the results obtained in CHP
decomposition tests and heat of immersion measurements
carried out on the scrutinized catalysts. The O2 affinity of the
materials has been quantified through the evaluation of the O2
isosteric heat of adsorption (Qst), with the trend Co(BPZ) >
Co(BPZNH2) > Co(BPZNO2). To the best of our knowl-
edge, this is the first example of the employment of pyrazolate
MOFs as catalysts for cumene oxidation and the first case of
tag-dependent selectivity ever observed in a MOF. A detailed
computational analysis of the reaction mechanism and of the
tag-dependent selectivity will be carried out soon, also
including other types of chemical tags on the bipyrazolate
linker not considered here. The in silico screening of the best-
performing bipyrazolate MOF for this reaction will allow us to
focus our future experimental synthetic efforts. Consequently,
other 3d-metal-based MOFs containing pyrazolate spacers will
be prepared and tested in cumene oxidation, in a search for
better-performing heterogeneous catalysts for this important
industrial reaction.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00481.
■
sı
IR spectrum of Co(BPZNH2)·DMF, graphical results of
the whole powder pattern refinements for Co-
(BPZNH2)·DMF under the assumption of the existence
of a monophasic or biphasic sample, graphical result of
the final stage of the Rietveld refinement for Co-
(BPZNH2), TGA and DSC traces of Co(BPZNH2)·
DMF, VT-PXRD patterns of Co(BPZNH2)·DMF, O2
adsorption isotherms measured on Co(BPZX) at 273 K,
Time−conversion plots for cumene oxidation with the
three MOF catalysts vs blank test, and results of the
reusability tests of Co(BPZ) and Co(BPZNH2) in five
consecutive catalytic cycles (PDF)
Accession Codes
CCDC 1962311 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
́
́
Francesc X. Llabres i Xamena − Instituto de Tecnologia
́
̀
̀
Quimica, Universitat Politecnica de Valencia, Consejo Superior
I
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
́
de Investigaciones Cientificas, 46022 Valencia, Spain;
orcid.org/0000-0002-4238-5784; Email: fllabres@
itq.upv.es
(Catalysts for Transition to Renewable Energy Future) ref.
ANR-17-MPGA-0017 for support. C.P. thanks the University
of Camerino and the Italian MIUR throughout the PRIN 2015
Project Towards a Sustainable Chemistry (20154 ×
9ATP_002). This project has also received funding from the
European Union’s Horizon 2020 research and innovation
program under the Marie Sklodowska-Curie grant agreement
No. 641887 (project acronym: DEFNET) and the Spanish
Government through projects MAT2017-82288-C2-1-P and
Severo Ochoa (SEV-2016-0683). Professor Norberto Mas-
ciocchi (University of Insubria, Como, Italy) is acknowledged
for fruitful discussions. The authors are also grateful to Dr.
Giulia Tuci (CNR-ICCOM Florence, Italy) for help with the
XPS curve fitting. The Microscopy Service of the Universitat
Simona Galli − Dipartimento di Scienza e Alta Tecnologia,
Universita dell’Insubria, 22100 Como, Italy; Consorzio
̀
Interuniversitario Nazionale per la Scienza e Tecnologia dei
Materiali, 50121 Firenze, Italy; orcid.org/0000-0003-
0335-5707; Email: simona.galli@uninsubria.it
Andrea Rossin − Istituto di Chimica dei Composti
Organometallici (ICCOM-CNR), 50019 Sesto Fiorentino,
Italy; Consorzio Interuniversitario Nazionale per la Scienza e
Tecnologia dei Materiali, 50121 Firenze, Italy; orcid.org/
0000-0002-1283-2803; Email: a.rossin@iccom.cnr.it
Authors
Anna Nowacka − Instituto de Tecnologia Quimica, Universitat
́
́
̀
̀
Politecnica de Valencia is gratefully acknowledged for the
electron microscopy measurements.
̀
̀
Politecnica de Valencia, Consejo Superior de Investigaciones
́
Cientificas, 46022 Valencia, Spain
Rebecca Vismara − Dipartimento di Scienza e Alta Tecnologia,
REFERENCES
■
̀
Universita dell’Insubria, 22100 Como, Italy; orcid.org/
(1) Fortuin, J. P.; Waterman, H. I. Production of Phenol from
Cumene. Chem. Eng. Sci. 1953, 2, 182−192.
(2) (a) Luyben, W. L. Design and Control of the Cumene Process.
Ind. Eng. Chem. Res. 2010, 49, 719−734. (b) Matsui, S.; Fujita, T.
New Cumene-Oxidation Systems: O2 Activator Effects and Radical
Stabilizer Effects. Catal. Today 2001, 71, 145−152.
0000-0001-9474-7671
Giorgio Mercuri − Istituto di Chimica dei Composti
Organometallici (ICCOM-CNR), 50019 Sesto Fiorentino, Italy
Marco Moroni − Dipartimento di Scienza e Alta Tecnologia,
̀
Universita dell’Insubria, 22100 Como, Italy; orcid.org/
0000-0001-6167-3792
(3) (a) Opeida, I. A.; Kytsya, A. R.; Bazylyak, L. I.; Pobigun, O. I.
Silver Nanoparticle Catalysis of the Liquid-Phase Radical Chain
Oxidation of Cumene by Molecular Oxygen. Theor. Exp. Chem. 2017,
52, 369−374. (b) Liquid Phase Aerobic Oxidation Catalysis: Industrial
Applications and Academic Perspectives; Shannon, S. S., Paul, L. A.,
Eds.; Wiley: 2016. (c) Tsodikov, M. V.; Kugel, V. Y.; Slivinskii, E. V.;
Bondarenko, G. N.; Maksimov, Y. V.; Alvarez, M. A.; Hidalgo, M. C.;
Navio, J. A. Selectivity and Mechanism of Cumene Liquid-Phase
Oxidation in the Presence of Powdered Mixed Iron-Aluminum Oxides
Prepared by Alkoxy Method. Appl. Catal., A 2000, 193, 237−242.
(d) Ismail, S. M. Liquid Phase Oxidation of Cumene over
Heretogeneous Catalysts. J. Chem. Soc. Pak. 1986, 8, 43−47.
(4) Zhang, M.; Wang, L.; Ji, H.; Wu, B.; Zeng, X. Cumene Liquid
Oxidation to Cumene Hydroperoxide over CuO Nanoparticle with
Molecular Oxygen under Mild Condition. J. Nat. Gas Chem. 2007, 16,
393−398.
́
́
Miguel Palomino − Instituto de Tecnologia Quimica,
̀
̀
Universitat Politecnica de Valencia, Consejo Superior de
Investigaciones Cientificas, 46022 Valencia, Spain
́
Kostiantyn V. Domasevitch − Taras Shevchenko National
University of Kyiv, 01601 Kyiv, Ukraine; orcid.org/0000-
0002-8733-4630
Corrado Di Nicola − Scuola di Scienze e Tecnologie, Universita
di Camerino, 62032 Camerino, Italy; orcid.org/0000-0002-
0958-6103
Claudio Pettinari − Istituto di Chimica dei Composti
Organometallici (ICCOM-CNR), 50019 Sesto Fiorentino,
Italy; Scuola del Farmaco e dei Prodotti della Salute, Universita
di Camerino, 62032 Camerino, Italy; orcid.org/0000-0002-
2547-7206
̀
̀
Giuliano Giambastiani − Istituto di Chimica dei Composti
Organometallici (ICCOM-CNR), 50019 Sesto Fiorentino,
Italy; Institute of Chemistry and Processes for Energy,
Environment and Health (ICPEES), UMR 7515 CNRS-
University of Strasbourg (UdS), 67087 Strasbourg Cedex 02,
France; Consorzio Interuniversitario Nazionale per la Scienza e
Tecnologia dei Materiali, 50121 Firenze, Italy; Kazan Federal
University, Alexander Butlerov Institute of Chemistry, 420008
Kazan, Russian Federation; orcid.org/0000-0002-0315-
3286
(5) (a) Hsu, Y. F.; Cheng, C. P. Mechanistic Investigation of the
Autooxidation of Cumene Catalyzed by Transition Metal Salts
Supported on Polymer. J. Mol. Catal. A: Chem. 1998, 136, 1−11.
(b) Hsu, Y. F.; Cheng, C. P. Polymer Supported Catalyst for the
Effective Autoxidation of Cumene to Cumene Hydroperoxide. J. Mol.
Catal. A: Chem. 1997, 120, 109−116. (c) Ying Fang, H.; Mei Huei,
Y.; Cheu Pyeng, C. Autooxidation of Cumene Catalyzed by
Transition Metal Compounds on Polymeric Supports. J. Mol. Catal.
A: Chem. 1996, 105, 137−144.
(6) Narulkar, D. D.; Srivastava, A. K.; Butcher, R. J.; Ansy, K. M.;
Dhuri, S. N. Synthesis and Characterization of N3Py2 Ligand-Based
Cobalt(II), Nickel(II) and Copper(II) Catalysts for Efficient
Conversion of Hydrocarbons to Alcohols. Inorg. Chim. Acta 2017,
467, 405−414.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c00481
(7) Wang, R.-M.; Duan, Z.-F.; He, Y.-F.; Lei, Z.-Q. Heterogeneous
Catalytic Aerobic Oxidation Behavior of Co−Na Heterodinuclear
Polymeric Complex of Salen-Crown Ether. J. Mol. Catal. A: Chem.
2006, 260, 280−287.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
S.G., R.V., and M.M. acknowledge Universita dell’Insubria for
■
(8) Rogovin, M.; Neumann, R. Silicate Xerogels Containing Cobalt
as Heterogeneous Catalysts for the Side-Chain Oxidation of Alkyl
Aromatic Compounds with tert-Butyl Hydroperoxide. J. Mol. Catal. A:
Chem. 1999, 138, 315−318.
̀
partial funding. G.G. thanks the Italian MIUR through the
PRIN 2017 Project Multi-e: Multielectron Transfer for the
Conversion of Small Molecules: an Enabling Technology for
the Chemical Use of Renewable Energy (20179337R7) for
financial support. G.G. thanks the TRAINER project
́
́
(9) Konopinska, A.; Orlinska, B.; Gillner, D. N-Hydroxyphthalimide
as a Catalyst of Cumene Oxidation with Hydroperoxide. Modern
Chemistry 2017, 5, 29−34.
J
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(10) Varma, G. R.; Graydon, W. F. Heterogeneous Catalytic
Oxidation of Cumene (Isopropyl Benzene) in Liquid Phase. J. Catal.
1973, 28, 236−244.
(11) Collom, S. L.; Bloomfield, A. J.; Anastas, P. T. Advancing
Sustainable Manufacturing through a Heterogeneous Cobalt Catalyst
for Selective C−H Oxidation. Ind. Eng. Chem. Res. 2016, 55, 3308−
3312.
(12) Scognamiglio, J.; Jones, L.; Letizia, C. S.; Api, A. M. Fragrance
Material Review on 2-Phenyl-2-Propanol. Food Chem. Toxicol. 2012,
50, S130−S133.
Prepared by a Facile “Green” Aqueous Synthesis. ACS Sustainable
Chem. Eng. 2019, 7, 7708−7715.
(19) (a) Vismara, R.; Tuci, G.; Tombesi, A.; Domasevitch, K. V.; Di
Nicola, C.; Giambastiani, G.; Chierotti, M. R.; Bordignon, S.;
Gobetto, R.; Pettinari, C.; Rossin, A.; Galli, S. Tuning Carbon
Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis-
(pyrazolate) Ligands with N-Containing Tags. ACS Appl. Mater.
Interfaces 2019, 11, 26956−26969. (b) Vismara, R.; Tuci, G.; Mosca,
N.; Domasevitch, K. V.; Di Nicola, C.; Pettinari, C.; Giambastiani, G.;
Galli, S.; Rossin, A. Amino-Decorated Bis(Pyrazolate) Metal-Organic
Frameworks for Carbon Dioxide Capture and Green Conversion into
Cyclic Carbonates. Inorg. Chem. Front. 2019, 6, 533−545. (c) Mosca,
N.; Vismara, R.; Fernandes, J. A.; Tuci, G.; Di Nicola, C.;
Domasevitch, K. V.; Giacobbe, C.; Giambastiani, G.; Pettinari, C.;
Aragones-Anglada, M.; Moghadam, P. Z.; Fairen-Jimenez, D.; Rossin,
A.; Galli, S. Nitro-Functionalized Bis(Pyrazolate) Metal-Organic
Frameworks as Carbon Dioxide Capture Materials under Ambient
Conditions. Chem. - Eur. J. 2018, 24, 13170−13180. (d) Pettinari, C.;
(13) (a) Rossin, A.; Tuci, G.; Luconi, L.; Giambastiani, G. Metal−
Organic Frameworks as Heterogeneous Catalysts in Hydrogen
Production from Lightweight Inorganic Hydrides. ACS Catal. 2017,
7, 5035−5045. (b) Chughtai, A. H.; Ahmad, N.; Younus, H. A.;
Laypkovc, A.; Verpoort, F. Metal−Organic Frameworks: Versatile
Heterogeneous Catalysts for Efficient Catalytic Organic Trans-
formations. Chem. Soc. Rev. 2015, 44, 6804−6849. (c) Liu, J.;
Chen, L.; Cui, H.; Zhang, J.; Zhang, L.; Su, C.-Y. Applications of
Metal−Organic Frameworks in Heterogeneous Supramolecular
Catalysis. Chem. Soc. Rev. 2014, 43, 6011−6061. (d) Gascon, J.;
̌
̌
Tabacaru, A.; Galli, S. Coordination Polymers and Metal−Organic
Frameworks Based on Poly(Pyrazole)-Containing Ligands. Coord.
̌
̌
Chem. Rev. 2016, 307, 1−31. (e) Pettinari, C.; Tabacaru, A.; Boldog,
I.; Domasevitch, K. V.; Galli, S.; Masciocchi, N. Novel Coordination
Frameworks Incorporating the 4,4′-Bipyrazolyl Ditopic Ligand. Inorg.
Chem. 2012, 51, 5235−5245. (f) Colombo, V.; Montoro, C.;
Maspero, A.; Palmisano, G.; Masciocchi, N.; Galli, S.; Barea, E.;
Navarro, J. A. R. Tuning the Adsorption Properties of Isoreticular
Pyrazolate-Based Metal−Organic Frameworks through Ligand
Modification. J. Am. Chem. Soc. 2012, 134, 12830−12843.
́
Corma, A.; Kapteijn, F.; Llabres i Xamena, F. X. Metal Organic
Framework Catalysis: Quo Vadis? ACS Catal. 2014, 4, 361−378.
(14) (a) Luo, S.; Zeng, Z.; Zeng, G.; Liu, Z.; Xiao, R.; Chen, M.;
Tang, L.; Tang, W.; Lai, C.; Cheng, M.; Shao, B.; Liang, Q.; Wang,
H.; Jiang, D. Metal Organic Frameworks as Robust Host of Palladium
Nanoparticles in Heterogeneous Catalysis: Synthesis, Application and
Prospect. ACS Appl. Mater. Interfaces 2019, 11, 32579−32598.
(b) Deng, X.; Li, Z.; García, H. Visible Light Induced Organic
Transformations Using Metal-Organic-Frameworks (MOFs). Chem. -
Eur. J. 2017, 23, 11189−11209. (c) Dhakshinamoorthy, A.; Asiri, A.
M.; García, H. Metal−Organic Frameworks as Catalysts for Oxidation
Reactions. Chem. - Eur. J. 2016, 22, 8012−8024.
̌
̌
(g) Tabacaru, A.; Pettinari, C.; Masciocchi, N.; Galli, S.; Marchetti,
F.; Angjellari, M. Pro-porous Coordination Polymers of the 1,4-
Bis((3,5-dimethyl-1H-pyrazol-4-yl)-methyl)benzene Ligand with Late
Transition Metals. Inorg. Chem. 2011, 50, 11506−11513. (h) Colom-
bo, V.; Galli, S.; Choi, H. J.; Han, G. D.; Maspero, A.; Palmisano, G.;
Masciocchi, N.; Long, J. R. High Thermal and Chemical Stability in
Pyrazolate-Bridged Metal−Organic Frameworks with Exposed Metal
Sites. Chem. Sci. 2011, 2, 1311−1319. (i) Masciocchi, N.; Galli, S.;
Colombo, V.; Maspero, A.; Palmisano, G.; Seyyedi, B.; Lamberti, C.;
Bordiga, S. Cubic Octanuclear Ni(II) Clusters in Highly Porous
Polypyrazolyl-Based Materials. J. Am. Chem. Soc. 2010, 132, 7902−
7904. (j) Galli, S.; Masciocchi, N.; Colombo, V.; Maspero, A.;
(15) (a) Song, X.; Hu, D.; Yang, X.; Zhang, H.; Zhang, W.; Li, J.; Jia,
M.; Yu, J. Polyoxomolybdic Cobalt Encapsulated within Zr-Based
Metal−Organic Frameworks as Efficient Heterogeneous Catalysts for
Olefins Epoxidation. ACS Sustainable Chem. Eng. 2019, 7, 3624−
3631. (b) Zhang, T.; Hu, Y.-Q.; Han, T.; Zhai, Y.-Q.; Zheng, Y.-Z.
Redox-Active Cobalt(II/III) Metal−Organic Framework for Selective
Oxidation of Cyclohexene. ACS Appl. Mater. Interfaces 2018, 10,
15786−15792. (c) Ma, Y.; Peng, H.; Liu, J.; Wang, Y.; Hao, X.; Feng,
X.; Khan, S. U.; Tan, H.; Li, Y. Polyoxometalate-Based Metal−
Organic Frameworks for Selective Oxidation of Aryl Alkenes to
Aldehydes. Inorg. Chem. 2018, 57, 4109−4116. (d) Othong, J.;
Boonmak, J.; Ha, J.; Leelasubcharoen, S.; Youngme, S. Thermally
Induced Single-Crystal-to-Single-Crystal Transformation and Hetero-
geneous Catalysts for Epoxidation Reaction of Co(II) Based Metal−
Organic Frameworks Containing 1,4-Phenylenediacetic Acid. Cryst.
Growth Des. 2017, 17, 1824−1835. (e) Wang, J.-C.; Ding, F.-W.; Ma,
J.-P.; Liu, Q.-K.; Cheng, J.-Y.; Dong, Y.-B. Co(II)-MOF: A Highly
Efficient Organic Oxidation Catalyst with Open Metal Sites. Inorg.
Chem. 2015, 54, 10865−10872. (f) Tuci, G.; Giambastiani, G.; Kwon,
S.; Stair, P. C.; Snurr, R. Q.; Rossin, A. Chiral Co(II) Metal−Organic
Framework in the Heterogeneous Catalytic Oxidation of Alkenes
under Aerobic and Anaerobic Conditions. ACS Catal. 2014, 4, 1032−
1039. (g) Hamidipour, L.; Farzaneh, F. Cobalt Metal Organic
Framework as an Efficient Heterogeneous Catalyst for the Oxidation
of Alkanes and Alkenes. React. Kinet., Mech. Catal. 2013, 109, 67−75.
́
́
́
Palmisano, G.; Lopez-Garzon, F. J.; Domingo-García, M.; Fernandez-
Morales, I.; Barea, E.; Navarro, J. A. R. Adsorption of Harmful
Organic Vapors by Flexible Hydrophobic Bis-pyrazolate Based MOFs.
Chem. Mater. 2010, 22, 1664−1672.
(20) Boldog, I.; Sieler, J.; Chernega, A. N.; Domasevitch, K. V. 4,4′-
Bipyrazolyl: New Bitopic Connector for Construction of Coordina-
tion Networks. Inorg. Chim. Acta 2002, 338, 69−77.
̈
(21) Domasevitch, K. V.; Gospodinov, I.; Krautscheid, H.; Klapotke,
T. M.; Stierstorfer, J. Facile and Selective Polynitrations at the 4-
Pyrazolyl Dual Backbone: Straightforward Access to a Series of High-
Density Energetic Materials. New J. Chem. 2019, 43, 1305−1312.
(22) TOPAS-Academic 6; Bruker, by Coelho Software: Brisbane,
Australia, 2016.
(23) Coelho, A. A. Indexing of Powder Diffraction Patterns by
Iterative Use of Singular Value Decomposition. J. Appl. Crystallogr.
2003, 36, 86−95.
(24) (a) Cheetham, A. K.; Bennett, T. D.; Coudert, F.-X.; Goodwin,
A. L. Defects and Disorder in Metal Organic Frameworks. Dalton
Trans. 2016, 45, 4113−4126. (b) Cliffe, M. J.; Wan, W.; Zou, X.;
Chater, P. A.; Kleppe, A. K.; Tucker, M. G.; Wilhelm, H.; Funnell, N.
P.; Coudert, F.-X.; Goodwin, A. L. Correlated Defect Nanoregions in
a Metal−Organic Framework. Nat. Commun. 2014, 5, 4176.
(25) (a) Spirkl, S.; Grzywa, M.; Volkmer, D. Synthesis and
Characterization of a Flexible Metal Organic Framework Generated
from MnIII and the 4,4’-Bipyrazolate-Ligand. Dalton Trans. 2018, 47,
8779−8786. (b) Nazarenko, O. M.; Rusanov, B.; Chernega, A. N.;
Domasevitch, K. V. Cobalt(II) and Cadmium(II) Square Grids
Supported with 4,4’-Bipyrazole and Accommodating 3-Carboxyada-
mantane-1-Carboxylate. Acta Crystallogr., Sect. C: Cryst. Struct.
́
(16) Luz, I.; Leon, A.; Boronat, M.; Llabres i Xamena, F. X.; Corma,
A. Selective Aerobic Oxidation of Activated Alkanes with MOFs and
their Use for Epoxidation of Olefins with Oxygen in a Tandem
Reaction. Catal. Sci. Technol. 2013, 3, 371−379.
́
(17) Santiago-Portillo, A.; Navalon, S.; Cirujano, F. G.; Llabres i
Xamena, F. X.; Alvaro, M.; Garcia, H. MIL-101 as Reusable Solid
Catalyst for Autoxidation of Benzylic Hydrocarbons in the Absence of
Additional Oxidizing Reagents. ACS Catal. 2015, 5, 3216.
́
(18) Nowacka, A.; Briantais, P.; Prestipino, C.; Llabres i Xamena, F.
X. Selective Aerobic Oxidation of Cumene to Cumene Hydroperoxide
over Mono- and Bimetallic Trimesate Metal−Organic Frameworks
K
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
̌
̌
Commun. 2013, C69, 232−236. (c) Tabacaru, A.; Pettinari, C.;
Marchetti, F.; Di Nicola, C.; Domasevitch, K. V.; Galli, S.; Masciocchi,
N.; Scuri, S.; Grappasonni, I.; Cocchioni, M. Antibacterial Action of
4,4′-Bipyrazolyl-Based Silver(I) Coordination Polymers Embedded in
PE Disks. Inorg. Chem. 2012, 51, 9775−9788. (d) Sun, Q.-F.; Wong,
K. M.-C.; Liu, L.-X.; Huang, H.-P.; Yu, S.-Y.; Yam, V. W.-W.; Li, Y.-Z.;
Pan, Y.-J.; Yu, K.-C. Self-Assembly, Structures, and Photophysical
Properties of 4,4′-Bipyrazolate-Linked Metallo-Macrocycles with
Dimetal Clips. Inorg. Chem. 2008, 47, 2142−2154. (e) Lozan, V.;
Solntsev, P. Y.; Leibeling, G.; Domasevitch, K. V.; Kersting, B.
Tetranuclear Nickel Complexes Composed of Pairs of Dinuclear LNi2
Fragments Linked by 4,4′-Bipyrazolyl, 1,4-Bis(4′-pyrazolyl)benzene,
and 4,4′-Bipyridazine: Synthesis, Structures, and Magnetic Properties.
Eur. J. Inorg. Chem. 2007, 2007, 3217−3226.
Graphene Oxide Supported PtPd@Pt Porous Nanospheres. Adv.
Synth. Catal. 2018, 360, 932−941.
(39) Casemier, J. H. R.; Nieuwenhuys, B. E.; Sachtler, W. M. H. The
Oxidation of Cumene and the Decomposition of Cumene Hydro-
peroxide on Silver, Copper, And Platinum. J. Catal. 1973, 29, 367−
373.
(40) Liao, S.; Chi, Y.; Yu, H.; Wang, H.; Peng, F. Tuning the
Selectivity in the Aerobic Oxidation of Cumene Catalyzed by
Nitrogen-Doped Carbon Nanotubes. ChemCatChem 2014, 6, 555−
560.
́
́
(41) Silvestre-Albero, J.; Gomez de Salazar, C.; Sepulveda-Escribano,
A.; Rodríguez-Reinoso, F. Characterization of Microporous Solids by
Immersion Calorimetry. Colloids Surf., A 2001, 187−188, 151−165.
(42) Everett, D. H. Manual of Symbols and Terminology for
Physicochemical Quantities and Units, Appendix II: Definitions,
Terminology and Symbols in Colloid and Surface Chemistry. Pure
Appl. Chem. 1972, 31, 577.
(26) Bond distances and angles for the rigid body describing the
ligand: C−C and C-N of the pyrazole ring 1.36 Å; exocyclic C−C
1.40 Å; C−H of the pyrazole ring 0.95 Å; C−NNH2 1.40 Å; N−H 0.95
Å; pyrazole ring internal and external bond angles 108 and 126°,
respectively; angles at the nitrogen atom of the amino group 120°.
(27) Coelho, A. A. Whole-Profile Structure Solution from Powder
Diffraction Data Using Simulated Annealing. J. Appl. Crystallogr.
2000, 33, 899−908.
(28) Cheary, R. W.; Coelho, A. A. A Fundamental Parameters
Approach to X-Ray Line-Profile Fitting. J. Appl. Crystallogr. 1992, 25,
109−121.
(29) Stephens, P. W. Phenomenological Model of Anisotropic Peak
Broadening in Powder Diffraction. J. Appl. Crystallogr. 1999, 32, 281−
289.
(30) Rouquerol, J.; Llewellyn, P.; Rouquerol, F.; Llewellyn, P. L.;
Rodriquez-Reinoso, F.; Rouquerol, J.; Seaton, N. Is the bet equation
applicable to microporous adsorbents? Stud. Surf. Sci. Catal. 2007,
160, 49.
(31) Saeidi, N.; Parvin, M. Accuracy of Dubinin-Astakhov and
Dubinin-Radushkevich Adsorption Isotherm Models in Evaluating
Micropore Volume of Bentonite. Period. Polytech., Chem. Eng. 2015,
60, 123−129.
(43) (a) Liu, C.; Wang, T.; Ji, J.; Wang, C.; Wang, H.; Jin, P.; Zhou,
W.; Jiang, J. The Effect of Pore Size and Layer Number of Metal−
Porphyrin Coordination Nanosheets on Sensing DNA. J. Mater.
Chem. C 2019, 7, 10240−10246. (b) Gong, T.; Yang, X.; Fang, J.-J.;
Sui, Q.; Xi, F.-G.; Gao, E.-Q. Distinct Chromic and Magnetic
Properties of Metal−Organic Frameworks with a Redox Ligand. ACS
Appl. Mater. Interfaces 2017, 9, 5503−5512.
(44) The NIST X-Ray Photoelectron Spectroscopy (XPS) Database;
Wagner, C. D., Ed.; National Institute of Standards and Technology:
1991.
(45) (a) Yamada, Y.; Kim, J.; Matsuo, S.; Sato, S. Nitrogen-
Containing Graphene Analyzed by X-Ray Photoelectron Spectrosco-
py. Carbon 2014, 70, 59−74. (b) Singhbabu, Y. N.; Kumari, P.;
Parida, S.; Sahu, R. K. Conversion of Pyrazoline to Pyrazole in
Hydrazine Treated N-Substituted Reduced Graphene Oxide Films
Obtained by Ion Bombardment and their Electrical Properties.
Carbon 2014, 74, 32−43.
(46) Dementjev, A.P; de Graaf, A; van de Sanden, M.C.M;
Maslakov, K.I; Naumkin, A.V; Serov, A.A X-Ray Photoelectron
Spectroscopy Reference Data for Identification of the C3N4 Phase in
Carbon-Nitrogen Films. Diamond Relat. Mater. 2000, 9, 1904−1907.
(32) (a) Zhu, X.; Tian, C.; Veith, G. M.; Abney, C. W.; Dehaudt, J.;
Dai, S. In Situ Doping Strategy for the Preparation of Conjugated
Triazine Frameworks Displaying Efficient CO2 Capture Performance.
J. Am. Chem. Soc. 2016, 138, 11497−11500. (b) Zhu, X.; Mahurin, S.
M.; An, S.-H.; Do-Thanh, C.-L.; Tian, C.; Li, Y.; Gill, L. W.;
Hagaman, E. W.; Bian, Z.; Zhou, J.-H.; Hu, J.; Liu, H.; Dai, S. Efficient
CO2 Capture by a Task-Specific Porous Organic Polymer
Bifunctionalized with Carbazole and Triazine Groups. Chem.
Commun. 2014, 50, 7933−7936.
(33) The empty volume was estimated with the software PLATON:
Spek, A. L. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65, 148−
155.
(34) Blatov, V. A.; Shevchenko, A. P.; Proserpio, D. M. Applied
Topological Analysis of Crystal Structures with the Program Package
ToposPro. Cryst. Growth Des. 2014, 14, 3576−3586.
(35) Bertier, P.; Schweinar, K.; Stanjek, H.; Ghanizadeh, A.;
Clarkson, C. R.; Busch, A.; Kampan, N.; Prinz, D.; Amann-
Hildenbrand, A.; Krooss, B. M.; Pipich, V. On the Use and Abuse
of N2 Physisorption for the Characterization of the Pore Structure of
Shales. CMS Work. Lect. 2016, 21, 151−161.
(36) Tonigold, M.; Lu, Y.; Mavrandonakis, A.; Puls, A.; Staudt, R.;
Moellmer, J.; Sauer, J.; Volkmer, D. Pyrazolate-Based Cobalt(II)-
Containing Metal−Organic Frameworks in Heterogeneous Catalytic
Oxidation Reactions: Elucidating the Role of Entatic States for
Biomimetic Oxidation Processes. Chem. - Eur. J. 2011, 17, 8671−
8695.
(37) Ma, S.; Zhou, H.-C. A Metal-Organic Framework with Entatic
Metal Centers Exhibiting High Gas Adsorption Affinity. J. Am. Chem.
Soc. 2006, 128, 11734−11735.
(38) Wang, Z.-J.; Lv, J.-J.; Yi, R.-N.; Xiao, M.; Feng, J.-J.; Liang, Z.-
W.; Wang, A.-J.; Xu, X. Nondirecting Group sp3 C-H Activation for
Synthesis of Bibenzyls via Homo-coupling as Catalyzed by Reduced
L
https://dx.doi.org/10.1021/acs.inorgchem.0c00481
Inorg. Chem. XXXX, XXX, XXX−XXX