2D arrays of organic qubit candidates embedded into a pillared-paddlewheel metal-organic framework

Article abstract of DOI:10.1021/jacs.0c07251

The creation of ordered arrays of qubits that can be interfaced from the macroscopic world is an essential challenge for the development of quantum information science (QIS) currently being explored by chemists and physicists. Recently, porous metal?organic frameworks (MOFs) have arisen as a promising solution to this challenge as they allow for atomic-level spatial control of the molecular subunits that comprise their structures. To date, no organic qubit candidates have been installed in MOFs despite their structural variability and promise for creating systems with adjustable properties. With this in mind, we report the development of a pillared-paddlewheel-type MOF structure that contains 4,7-bis(2-(4-pyridyl)-ethynyl) isoindoline N-oxide and 1,4-bis(2-(4-pyridyl)-ethynyl)-benzene pillars that connect 2D sheets of 9,10-dicarboxytriptycene struts and Zn2(CO2)4 secondary binding units. The design allows for the formation of ordered arrays of reorienting isoindoline nitroxide spin centers with variable concentrations through the use of mixed crystals containing the secondary 1,4-phenylene pillar. While solvent removal causes decomposition of the MOF, magnetometry measurements of the MOF containing only N-oxide pillars demonstrated magnetic interactions with changes in magnetic moment as a function of temperature between 150 and 5 K. Variable-temperature electron paramagnetic resonance (EPR) experiments show that the nitroxides couple to one another at distances as long as 2 nm, but act independently at distances of 10 nm or more. We also use a specially designed resonance microwave cavity to measure the face-dependent EPR spectra of the crystal, demonstrating that it has anisotropic interactions with impingent electromagnetic radiation.

Full text of DOI:10.1021/jacs.0c07251

Subscriber access provided by UNIV OF DURHAM
Article
2D Arrays of Organic Qubit Candidates Embedded
into a Pillared-Paddlewheel Metal-Organic Framework
Marcus J Jellen, Mayokun Ayodele, Annabelle L. Cantu, Malcolm D. E. Forbes, and Miguel A. Garcia-Garibay
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c07251 • Publication Date (Web): 25 Sep 2020
Downloaded from pubs.acs.org on September 26, 2020
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 10
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
2D Arrays of Organic Qubit Candidates Embedded into a Pillared-
Paddlewheel Metal-Organic Framework
Marcus J. Jellen,†,= Mayokun J. Ayodele,‡,= Annabelle Cantu,† Malcolm D. E. Forbes,‡,* and Miguel A.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Garcia–Garibay†,*
†Department of Chemistry and Biochemistry, University of California, Los Angeles CA 90095–1569 USA
‡Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, OH
43403–0001 USA
ABSTRACT: The creation of ordered arrays of qubits that can be interfaced from the macroscopic world is an essential challenge
for the development of quantum information science (QIS) currently being explored by chemists and physicists. Recently, porous
metal-organic frameworks (MOFs) have arisen as a promising solution to this challenge as they allow for atomic-level spatial con-
trol of the molecular subunits that comprise their structures. To date, no organic qubit candidates have been installed in MOFs de-
spite their structural variability and promise for creating systems with adjustable properties. With this in mind, we report the devel-
opment of a pillared-paddlewheel-type MOF structure that contains 4,7–bis(2-(4-pyridyl)-ethynyl) isoindoline N-oxide and 1,4–
bis(2-(4-pyridyl)-ethynyl)-benzene pillars that connect 2D sheets of 9,10-dicarboxytriptycene struts and Zn2(CO2)4 secondary bind-
ing units. The design allows for the formation of ordered arrays of reorienting isoindoline nitroxide spin centers with variable con-
centrations through the use of mixed crystals containing the secondary 1,4-phenylene pillar. While solvent removal causes decom-
position of the MOF, magnetometry measurements of the MOF containing only N-oxide pillars demonstrated magnetic interactions
with changes in magnetic moment as a function of temperature between 150 and 5 K. Variable-temperature electron paramagnetic
resonance (EPR) experiments show that the nitroxides couple to one another at distances as long as 2 nm, but act independently at
distances of 10 nm or more. We also use a specially designed resonance microwave cavity to measure the face-dependent EPR
spectra of the crystal, demonstrating that it has anisotropic interactions with impingent electromagnetic radiation.
line meta–architectures with multiple functional features,8
including the opportunity to develop multiscale platforms to
INTRODUCTION
Quantum information science (QIS) has the potential to
revolutionize science and engineering by taking advantage of
counterintuitive quantum phenomena, such as entanglements
and superpositions of states, that will enable, for example,
large–scale applications in quantum computing, quantum sens-
ing, and quantum communications.1 While current computers
utilize classical bits existing in one of two states (0 or 1) in
order to carry out computations, quantum bits (qubits) harness
the nature of quantum particles, which allows them to exist in
a coherent superposition of two or more states and therefore,
are able to carry out multiple commands simultaneously.2
Early examples of qubits include photons,3 nuclear spins in
nitrogen doped diamonds,4 and superconducting states in Jo-
sephson–Junctions.5 The manipulation of electron spins on
molecules using pulsed microwave pulses comprises a rela-
tively new and promising pathway currently being explored in
the QIS and magnetic materials fields.6 Paramagnetic metal
centers with “spin free” ligands have already shown tremen-
dous promise for the development of qubits with coherence
times up to 150 µs.7 However, stable organic radicals also
comprise a useful subset of potential qubits due to their struc-
tural variability and synthetic accessibility, which makes it
possible to further engineer them into highly ordered crystal-
transduce molecular and supramolecular properties into the
macroscopic world.9,10
The first challenge of the organic approach comes from the
great difficulties related to the predictability and limited func-
tionality of close packed molecular crystals. Insight from re-
ticular chemistry offers promising solutions toward the crea-
tion of ordered arrays of organic qubits through the use of
metal-organic frameworks (MOFs). MOFs are porous materi-
als comprised of inorganic nodes connected by organic link-
ers. Careful selection of the metal and organic building blocks
allows structures with variable geometries and engineered
molecular dynamics to be constructed in a predictable fash-
ion.9 This control over structure will allow for the precise
placement of qubits with predetermined distances and orienta-
tions with respect to one another, with additional degrees of
freedom available by switching between alternative orienta-
tions.10 Well-characterized MOF structures containing static
qubits are reported in the literature, in particular those using
tetracarboxy porphyrin linkers.11 These studies show the pow-
er of reticular chemistry for the advancement of QIS by estab-
lishing a 50 Å coupling limit between neighboring qubits,12 as
well as developing qubits that maintain their coherence for up
1
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 10
to 14 µs13 and the preservation of spin coherence at room tem-
make it possible to study temperature– and concentration–
dependent anisotropic exchange interactions with electron
paramagnetic resonance (EPR) spectroscopy.
perature14 using Cu(II), Co(II) or VO(IV) metal centers, re-
spectively. However, relatively few examples of MOFs with
paramagnetic centers on organic linkers are known in the
literature as compared to their inorganic counterparts.15
1
2
3
4
RESULTS AND DISCUSSION
Synthesis. Nitroxide rotor 1 was synthesized via a modi-
fied procedure developed by Kitagawa and coworkers.21 The
key Sonogashira coupling reaction is illustrated in Scheme 2.
After much tribulation, we discovered that this coupling only
proceeds in pure tetramethylpyridine as the solvent. Single
crystals, suitable for X–ray analysis, were grown from a su-
per–saturated solution of 1 in ethanol. The other UCLA–NO
components 2 and 4 were synthesized according to literature
methods, with slight modifications, (see SI).22
5
6
7
8
Here we describe the synthesis and characterization of
UCLA-NO/Ph, a multi-component pillared paddlewheel met-
al organic framework (Scheme 1) with paramagnetic isoindo-
line–N–Oxide rotors 1, and diamagnetic 1,4–bis(2-(4-pyridyl)-
ethynyl)-benzene, 2, linkers. These ligands connect impene-
trable 2–D sheets composed of Zn2(CO2)4 secondary binding
units (SBUs), 3, which are composed of Zn2+ metal clusters
and 9,10–dicarboxytriptycene struts, 4. The diamagnetic phe-
nylene linker 2 was chosen as an isostructural ligand to pre-
pare magnetically diluted mixed crystalline samples of
UCLA–NO/Ph, which maintain the original lattice geometry.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 2
Scheme 1
Finally, samples of the new MOF UCLA–NO were prepared
via a convenient solvothermal synthesis in DMF.23 All MOF
components were added to a 10 mL vial, covered in 3.0 mL of
anhydrous DMF and then placed in an oven overnight at 100
°C. Diluted samples were prepared by using the appropriate
molar ratio of 1:2 in the solvothermal synthesis. Samples of
UCLA–NO showed decomposition when heated under vacu-
um to remove solvent (Figure S9 and S10) and upon mechani-
cal grinding. We attribute this sensitivity to the weak dative
bond between pyridine and zinc, as well as the flexible alkyne
linker, which is prone to displacement by water.24 Flattened
rectangular prismatic crystals amenable to pan–powder X–ray
diffraction (PXRD) were washed with fresh DMF before fur-
ther investigation.
Our design has a few key features worth noting. A lattice
constant of ca. 10 Å can accommodate molecular rotors with a
radius of revolution of ca. 7 Å, making it possible for a nitrox-
ide radical to rotate and reorient without having to overcome
steric barriers. Furthermore, the nitroxide–bearing moiety is
suspended between two alkynes, which are known to have a
vanishingly low intrinsic activation barrier for axial rotation.9
In the absence of solvent, these features would allow the crys-
talline rotators to reorient, even at cryogenic temperatures (10
K or below),16 such that it would be possible to use external
electric fields to affect the macroscopic polarization10,17 arising
from the collective interactions of the nitroxide electric dipole
moments. Under these conditions, electric fields may be used
to alter magnetic order and QIS properties, including the po-
tential of encoding information within the shapes of standing
microwave cavity modes, and controlling the transmission of
magnetic information along rotary dipole chains.18 As a new
class of organic multiferroic materials with tetragonal order,
these systems would have the potential of undergoing sponta-
neous dipole–dipole–induced anti–ferromagnetic (AF) transi-
tions at the Néel temperature to create chains of spin–paired
nitroxides.19 Furthermore, the layered tetragonal nature of
UCLA–NO not only insulates the nitroxide rotors between the
2D-nets formed by 3 and 4, but it also allows for the applica-
tion of transverse magnetic fields along specific crystallo-
graphic faces of the MOF. Such features are vital for the
transmission of classical information along well-defined crys-
tal axes.20 And finally, the formation of mixed crystals utiliz-
ing diamagnetic moiety 2 to dilute the spin concentration will
Figure 1. PXRD traces of A) Zn–TDC crystals, B) UCLA–NO,
C) UCLA–Ph, D) 1:1 Diluted UCLA–NO.
X-ray Crystallography. The PXRD analyses were carried
out with Cu–Kα1 radiation (1.5406 Å). Samples were placed
on a zero–background plate at a fixed stage with a drop of
DMF to prevent crystal collapse by desolvation. Data was
collected from 2 theta angles of 5 to 50 degrees at room tem-
2
ACS Paragon Plus Environment

Page 3 of 10
Journal of the American Chemical Society
for a group that can undergo diffusional rotation (Figure 2A).
perature. The step width was 0.016 degrees, with the acquisi-
1
2
3
4
5
6
7
8
tion time being approximately 10 s at each step. We first ana-
lyzed crystals composed of only 3 and 4 as a control (Figure
1A) followed by analysis of crystals obtained with the addition
of pillars 1, and/or 2. Crystals with 100% pillar 1 or 2 are
shown in Figures 1B and 1C, respectively, which confirm the
formation of two isostructural crystal lattices. Crystals pre-
pared with a 50:50 mixture of 1 and 2 demonstrated that the
two pillars are able to form substitutional isoreticular solid
solutions that make it possible to dilute the nitroxide radical
(Figure 1D) throughout the MOF structure. Analysis of the
crystal structure of UCLA–NO and UCLA–Ph shows that the
distance between layers are slightly wider in the case of
UCLA–NO (20.492 Å vs. 20.364 Å), explaining the slight
shift to lower angles for UCLA–Ph (Figure S13 and S14).
Additionally, the broad peak from 15 to 30 degrees in figure
1D, and to a lesser extent, 1C and 1B, are attributed to the
presence of included solvent.
Further analysis of the structure shows that neighboring pillars
are approximately 10.84 Å apart (Figure 2B), and using simple
models and geometric considerations one can determine that
the closest head–to–head distance between neighboring nitrox-
ides would have oxygen-oxygen distances of ca. 1.58 Å (Fig-
ure 2C). While this distance is shorter than the Van der Waal
radii of the two oxygen atoms (3.04 Å), and on the order of a
peroxide O–O single bond (ca. 1.45 Å), a bond is not expected
in this case due to unfavorable energetics and steric interac-
tions. However, this observation suggests the potential of
reaching configurations where neighboring radicals may have
strong magnetic dipole and exchange interactions (both terms
are present in the dipolar tensor for such structures, and the
exchange term may well be anisotropic). In fact, antiferro-
magnetic coupling of neighboring N–O functional groups has
been observed in adamantly nitroxide plastic crystals at tem-
peratures as low as 1.48 K, when the N–O to N–O distances
are ca. 4 Å apart,18 and as high as 260 K when antiparallel N-
O dimers can be formed with intermolecular N…O distances of
ca. 2.2 Å.25
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Zero-field cooling of UCLA–NO from 150 K to 5 K
illustrating the temperature dependence of χT.
The possibility of observing intermolecular magnetic inter-
actions was examined by measuring the temperature depend-
ence of the magnetic susceptibility (χ(T)) using a superconduct-
ing quantum interference device (SQUID) magnetometer.
While paramagnetic samples display magnetic susceptibilities
with a temperature dependence characterized by an Arrhenius
behavior, a sharp increase at the Curie temperature is observed
for ferromagnetic materials, and a sharp decrease for antifer-
romagnetic materials is observed at the analogous Neel tem-
perature.26 Samples of UCLA–NO were sealed in a quartz
tube under a 700 torr vacuum with a small amount of solvent
in order to prevent MOF decomposition. Zero–field cooling
(ZFC) results suggest at first sight a typical Arrhenius-type
behavior at all temperatures ranging from 150 K to 5 K (Fig-
ure S15). However, a plot of χ(T)T vs. T (Figure 3) shows that
χ(T)T gradually increases until it reaches a maximum value at
ca. 30 K. After this point, χ(T)T begins to decrease until 5 K,
the lowest temperature in the measurement. While proper di-
amagnetic corrections were not feasible with this sample due
to the included solvent, the observation that χ(T)T increases by
1.5 times its initial value before decreasing once again is in-
Figure 2. A) Crystal structure of UCLA–NO displaying no ni-
troxide rotator. B) Distance analysis between pillar agents in the
MOF. C) Distance between head–to–head nitroxide oxygen rotors
(distances in Å).
Single crystal X-ray diffraction data measured with Cu–Kα
radiation (λ = 1.5046 Å) were obtained from a solvent–
containing yellow crystal of UCLA–NO. Diffraction patterns
were collected at 200 K with an area detector and the structure
solved and refined with the SHELXTL program. While all
heavy atoms were refined anisotropically, the hydrogen atoms
were placed at the calculated positions. The diffraction data
were solved in the tetragonal space group p4/mbm with a
modest Rf= 6.05%. Unit cell dimensions a = 15.3316(6) and b
= 15.3316(6) are equivalent and shorter than c = 23.4500(13)
by approximately 8.11 Å. All angles are equal to the expected
tetragonal angle of 90°. Two notable features of the structure
are 1) the rotationally disordered pyridyl groups occupying
positions related by 90°, and 2) the “missing” nitroxide radi-
cal, indicating that it has no preferred orientation, as expected
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 10
dicative of weak high spin and pairing interactions between and the following additional nitroxide MOFs with varying
neighboring isoindoline nitroxides.27 Similar field-cooled (FC)
measurements carried out at 5000 Oe exhibited a much more
dramatic slope, due to the increased external field, but also
shows a slight curving below 30 K, demonstrating that these
coupling interactions are not blocked by increased magnetic
fields (Figure S15). A field–dependent measurements of
100% UCLA–NO run at 7 K exhibited no hysteresis, demon-
strating that the interactions leading to this change in χ(T)T are
either very weak or arise from very few interacting partners at
this temperature (Figure S15). EPR data below revealed traces
of Cu(II) ions in sample, but we are currently unable for ac-
count for them in the magnetometry data.
compositions of nitroxide to phenylene pillars (1:2) equaling
3:1, 1:1,1:3, 1:9, and 1:99, respectively (Figure 3).
1
2
3
4
5
6
7
8
At 50 °C, only the most diluted nitroxide MOF 1:99
showed the complete three-line spectra expected for an isolat-
ed nitroxide radical as a result of hyperfine coupling interac-
tions with the 14N nitrogen nucleus, which has a total nuclear
spin I = 1. At this high temperature, the isoindoline nitroxide
radical would have the freedom to rapidly reorient about its
axis, with an activation barrier determined by the solvent oc-
cluded within the pores of MOF. As the temperature decreases
from 50 °C to –150 °C, the nitroxide radical experiences in-
creasingly slower rotation, with longer rotational correlation
times that result in spectral broadening. In fact, an increase in
line broadening is observed in the spectra for all the MOF
compositions. Two additional peaks observed at low field in
the lower temperature spectra (–50 °C to –150 °C) for the 1:99
and 1:9 ratio samples are assigned to residual copper (II) ions,
which are found as trace impurities in the synthesis.28 These
signals did not appear in the 3:1, 1:1 and 1:3 samples where
the nitroxide radicals are present in much higher concentra-
tion. Moving from top to bottom in Figure 3B as the samples
change from low to high nitroxide concentrations, the spectra
become increasingly broadened. This broadening is due to
Heisenberg spin exchange as neighboring electrons with iden-
tical spin states are close enough to swap their spin infor-
mation at a rate that is much faster than the rate of the inverse
of the hyperfine interactions.29 In going from lower to higher
temperatures at intermediate concentrations, the line shapes
sharpen at higher temperatures as a result of motional narrow-
ing.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5 nm
1 nm
= 1
= 2
Figure 4. Schematic representation of the MOF layer indicating
the average distances between a nitroxide pillar at the center for
1:2=1:9 (center square, dave≈2 nm) and 1:2=1:99 dilutions (outer
square, dave ≈ 10 nm).
Figure 3. A) Single crystal photos of the nitroxide MOFs in this
study at ambient conditions. B) Variable temperature EPR meas-
urements ranging from –150 °C to 50 °C of UCLA–NO mixed
crystals with various concentrations of 1:2.
The extent of through-space exchange and dipole-dipole
radical–radical interactions between nitroxides in the layers
will depend on their distance (dRR). Assuming the formation of
a random solid solution, the average value dRRave should be
statistically determined by the nitroxide concentration. For
example, a nitroxide in a 1:99 sample (represented with a red
dot in the 10 x 10 array in Figure 4), will be surrounded by
phenylene pillars 2 (blue dots). One may expect that their
nearest next neighbors will be on average ca. 10 nm away with
others at shorter and longer distances with varying probabili-
ties. However, at dilutions 1:9 and lower, one may expect that
there will be a significant fraction of nitroxides within closest
neighboring distances of ca. 1 nm and 1.4 nm. We assume
that radical–radical interactions occurring among layers along
Variable-Temperature EPR Analysis. Wet crystals of
the nitroxide–containing MOF were filtered and immediately
inserted into a quartz capillary tube, and sealed at both ends.
The sealed tube was then placed into a JEOL EPR resonant
cavity (TE011) connected with a liquid nitrogen dewar system.
Steady state electron paramagnetic resonance (SSEPR) exper-
iments were carried out at different temperatures ranging from
–150 °C to +50 °C using a sweep width of 50 mT and a 100
kHz modulation amplitude of 0.1 mT, except for the 1:99 di-
luted Nitroxide MOF, for which 0.8 mT modulation amplitude
was used. We collected EPR data for UCLA–NO (Figure S16)
4
ACS Paragon Plus Environment

Page 5 of 10
Journal of the American Chemical Society
Single-Crystal EPR Analysis. Further EPR analyses were
the crystal c axis will not be significant. Our results indicate
1
2
3
4
5
6
7
8
that nitroxides begin to lose communication when they are on
average ca. 2 nm apart, and they behave as independent mono-
radicals at a separation of about 10 nm. Similar limits have
been experimentally observed for both electron–nuclear spin
dipolar interactions and electron–electron exchange interac-
tions.30 This finding demonstrates that the nitroxide rotors in
this structure may be sensitive to both environmental changes
and to paramagnetic impurities.
carried out on a single crystal of the 1:1 diluted nitroxide using
a specially designed microwave resonator that allowed for
coarse crystal rotations, to explore the angular dependence of
the applied external magnetic field. A 200 x 150 x 100 µm
sized single crystal shaped as a flattened cuboid was selected,
covered with mineral oil, and placed on a microscope slide
that was inserted and held rigid in the center of an JEOL EPR
wafer cavity (TM110), specially designed for solid and flat
samples.
9
The starting position for the crystal rotation was arbitrary,
but to define a laboratory frame of reference, an arbitrary x–
axis was chosen to lie along the longer side of the crystal and
parallel to the surface of the sample holder, but perpendicular
to the direction of the magnetic field that aligns with a relative
z–axis of the crystal. The crystal was then flipped to an upright
position making a new, relative, y–axis lie along the sample
holder while the initial x–axis now perpendicular to both sam-
ple holder plane and magnetic field direction. Finally, the
crystal was tilted sideways about the y–axis such that it re-
mains parallel to the sample holder plane and places the arbi-
trary z–axis perpendicular to the magnetic field. Experiments
were carried out at 30° rotation intervals over a 360˚ rotation
with each axis aligned with the sample holder plane under
ambient conditions. A sweep width of 20 mT and a modula-
tion amplitude of 1.0 mT were used for each 4–minute scan.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Close analyses of the dataset in Figure 5 shows that the
spectra obtained by rotation along the y and z axes are similar,
but inversed (starting with angle 30° of z is the same as start-
ing at angle 330° of y). However, rotation about the x axis
yields distinct spectra. We know that in many cases, the crys-
tal habit approaches the symmetry of the unit cell. Based on
this data, we conclude that rotation about the x axis of the
laboratory frame reflects rotation about the approximate 4–
fold symmetry axis of the crystal, which is a unique axis and
lies along the shorter edge of the crystal as illustrated in Figure
6. This observation is confirmed as the spectra repeats at 90º
intervals. Rotation along the y and z axis is similar and their
spectra repeat at 10° intervals, indicating that they are the
crystallographic 2–fold axes. These both lie along the longer
edges of the crystal.
Magnetic Field
4-fold axis: 90o repeat
2-fold axis
2-fold axis: 180o repeat
4-fold axis
2-fold axis
2-fold axis
Figure 6. Rotational symmetry of crystal sample placed in
the EPR cavity.
As expected for a low density amphidynamic crystal with a
static frame linked to axially rotating radicals, the EPR spectra
of UCLA-NO were not characterized by a single sharp line
due to exchange narrowing, as it is commonly observed in
close packed crystalline nitroxides such as crystals of pure
pillar 1 (Figure S17). By contrast, one can see broadened
three–line spectra determined of the hyperfine splitting of the
radical with the 14N nucleus with I = 1. An additional set of
peaks are apparent in both the low field and mid field signals
Figure 5. Single–crystal EPR measurements of a 1:1 diluted crys-
tal of UCLA–NO analyzing each orientation of the crystal from
0o to 330o in 30o increments.
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 10
of all three axes at angles; 0°, 30°, 90°, 150°, 180°, 210°, 270°, lines and the spectral amplitude. This is consistent with the
1
2
3
4
5
6
7
8
300°, and 330°, suggesting that there are two or more popula-
tions of nitroxides within the MOF cavity that have different
chemical environments. Interestingly, the high field line of
these signals shows a broadening effect not present in the oth-
er two resonances, as expected from the cumulative effect of
the field-dependent g-factor and A (hyperfine coupling) aniso-
tropies (tensors). These two non–equivalent nitroxide types
might be due to the slight deviation from tetragonal packing in
the crystal structure, which is reduced to the monoclinic space
group C2/c. This would cause different orientations of the 2pz
orbital of the N atom to exist relative to the crystal frame, but
not relative to the symmetric molecular backbone. It is good to
bear in mind that we are dealing with pillared MOFs in which
we have a 2–D framework joined together by an orthogonal
pillar linker with the attached nitroxide (Figure 7). This means
that the molecular rotation is restricted to one degree of free-
dom and along one of the crystallographic axes. Along the x–
axis dataset, there is overlap of split peaks at 30°, 60°, 120°,
150°, 210°, 240°, 300° and 330° which suggests the two in-
equivalent nitroxides might experience similar positioning at
these angles.
fact that the nitroxide bond vector along the molecular Y axis
can occupy all possible orientations in the laboratory y–z
plane. This causes the hyperfine constant to become isotropic
with respect to rotation about this axis. By contrast, rotation
about the laboratory y and z axes modulates the orientation of
the nitroxide p-orbital and the N-O bond vector between paral-
lel and perpendicular orientations with respect to the direction
of the magnetic field. Based on these observations, we pro-
pose that the smallest hyperfine splitting is obtained when the
direction of the N-O bond vector (molecular Y-axis) is orthog-
onal to the external magnetic field, while the largest splitting
is observed when the magnetic field is in the orthogonal direc-
tion. This is consistent with a hyperfine splitting tensor where
the principal components have values in the order AYY > AXX
≈ AZZ, as the majority of the electron density is distributed in
molecular orbitals parallel to the molecular Z-axis. Therefore,
dipole-dipole interactions between the electrons and the prox-
imate nuclei are greatest when the largest components of g and
A tensors of the nitroxide are parallel to the N–O bond.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Similar observations have been reported in inclusion crys-
tals of di-tert-butyl-aminyloxyl (di-tert-butyl-nitroxide) and
2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) in hexagonal
channels of thiourea and tris(o-pheneylenedioxy)cyclotri-
phosphazene (TPP).32 Long needle–like crystals with hexago-
nal 1–D channels hosting the non–bonded nitroxides were
shown to support isotropic rotation about the channel direction
in a molecular orientation that places the N-O bond orthogonal
to the channel (i.e., rotation about the molecular Z axis in the
molecular frame in Figure 7). It was shown that hyperfine
splitting measured with the magnetic field aligned with the
needle axis (orthogonal to the N-O bond) was small, and also
isotropic as a result of fast rotation. Accordingly, hyperfine
splitting measured with the magnetic field orthogonal to the
needle axis (i.e., aligned with the N-O bond) is larger and an-
gular dependent. Thus, in agreement with our conclusions and
with reference to the molecular frame defined in Figure 7,
these studies indicate that AYY > AXX ≈ AZZ. Although com-
plications to determine the rotational dynamics in the case of
UCLA–NO arise from the fact that the solvent causes the rota-
tional motion to be diffusion-controlled, the amphidynamic
MOF structure retains the properties of an ordered crystal.
Furthermore, we observe significant spin–spin exchange inter-
action when the neighboring pillars are separated from each
other by the lattice constant of ~10.8Å, especially when one
considers rotational configurations leading to nitroxide O at-
oms separated from each other by as little as 1.56 Å, as seen in
Figure 2. However, spin exchange decreases as the spins are
placed farther away from each other in mixed crystals grown
with the diamagnetic phenylene ligands (2).
Furthermore, it can be observed in both the y and z da-
tasets that the hyperfine splitting changes significantly, as
judged by the spacing between the three lines. Spectra at 90°
and 270° show the smallest hyperfine splitting, while the larg-
est splitting is observed at 0° and 180°. By contrast, the hyper-
fine splitting on the spectra along the x–axis is relatively con-
stant, suggesting that internal rotation of the nitroxide partly
averages its anisotropy by sampling all orientations along the
y-z plane. With the molecular frame indicated in capital bold
letters, we define the Z–axis along the 2pz orbital of the N–O
bond. While it is common to define the molecular x-axis along
the direction of the N-O bond vector, for convenience we will
assume that the direction of the molecular X–axis coincides
with that of the laboratory x-axis, which corresponds to the
axis of rotation along C2 and C5 of the benzene ring (Figure
7). In this coordinate system, the N-O bond vector along the
molecular Y-axis can occupy all possible orientations in the
laboratory y-z plane.31
CONCLUSIONS
Figure 7. A) Nitroxide molecular coordinate and spherical coor-
dinates defining the direction of external magnetic field. B) The
nitroxide ring with a defined molecular frame: z (green), x (or-
ange) and y (blue).
In conclusion, we have described the preparation and char-
acterization of a layered MOF structure built with nitroxide
pillars as a starting point for the generation of crystalline ar-
rays of organic qubits. SQUID magnetometry revealed that
the MOF structure containing 100 % N-oxide pillars experi-
enced an effective increase in magnetic moment from 150 K
down to 30K, at which point begun to decrease, suggesting the
temperature-mediated population of high spin and pairing
interactions between adjacent nitroxides. Using VT EPR spec-
Having described the relation between molecular and la-
boratory frames of reference, we can analyze the spectra
shown in Figure 5 and draw general conclusions on the anisot-
ropy of the hyperfine splitting. We can see that rotation about
the laboratory four–fold x axis leads to a relatively constant
hyperfine interaction, as revealed by the spacing of the three
6
ACS Paragon Plus Environment

Page 7 of 10
Journal of the American Chemical Society
troscopy we have shown that magnetic interactions display
strong anisotropies with impingent electromagnetic radiation,
1
while exchange interactions can be modulated by changes in
the nitroxide concentration in diluted crystals prepared with a
diamagnetic pillar analog. Our results suggest that these sys-
tems will be useful for future QIS applications that will require
information to be passed along specific directions of a bulk
material while providing a chemical interface for read/write
actions. Studies in progress include spectral simulations to
explore the dynamics of internal rotation and the development
of structures where the solvent can be removed to explore the
formation of magnetically ordered phases arising from rota-
tionally ordered states.
2
3
4
5
6
7
8
9
yon, B. P.; Whitfield, J. D.; Gillett, G. G.; Goggin, M. E.; Al-
meida, M. P.; Kassal, I.; Biamonte, J. D.; Mohseni, M.; Powell, B.
J.; Barbieri, M.; Aspuru-Guzik, A.; White, A. G. Towards Quan-
tum Chemistry on a Quantum Computer. Nature Chem. 2010, 2,
106–111. (e) Degen, C. L.; Reinhard, F.; Cappellaro, P. Quantum
Sensing. Rev. Mod. Phys. 2017, 89, 035002.
2
(a) DiVincenzo, D. P. The Physical Implementation of Quantum
Computation. Fortschritte der Physik 2000, 48, 771–783.
(b) Ladd, T. D.; Jelezko, F.; Laflamme, R.; Nakamura, Y.; Mon-
roe, C.; Brien, J. L. O. Quantum Computers. Nature 2010, 464,
45–53.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
4
Chuang I. L.; Yamamoto Y. Spin Quantum Computer. Phys. Rev.
A: At., Mol., Opt. Phys. 1995, 52, 3489–3497.
ASSOCIATED CONTENT
K. Saeedi, S. Simmons, J. Z. Salvail, P. Dluhy, H. Riemann, N. V.
Abrosimov, P. Becker, H.–J. Pohl, J. J. L. Morton and M. L. W.
Thewalt, Room–Temperature Quantum Bit Storage Exceeding 39
Minutes Using Ionized Donors in Silicon–28. Science, 2013, 342,
830–833.
Supporting Information
Synthesis, characterization, PXRD and EPR spectral data of
UCLA-NO (PDF). X-ray diffraction data from pillar 1 and from
MOF samples UCLA-NO and UCLA-Ph (cif). Magnetometer
measurements of UCLA-NO derivatives. The Supporting Infor-
mation is available free of charge on the ACS Publications web-
site.
5
6
Koch, J.; Yu, T. M.; Gambetta, J.; Houck, A. A.; Schuster, D. I.;
Majer, J.; Devoret, M. H.; Girvin, S. M.; Schoelkopf, R. J.
Charge–insensitive qubit design derived from the Cooper pair
box. Phys. Rev. A 2007, 76, 042319.
(a) Wasielewski, M. R.; Forbes, M. D. E.; Frank, N. L.; Kowalski,
K.; Scholes, G. D.; Baldo, M. A.; Freedman, D. E.; Goldsmith, R.
E.; Goodson, T. III; Kirk, M. L.; McCusker, J. K.; Ogilvie, J. P.;
Shultz, D. A.; Stoll, S.; Whaley, K. B.; Yuen-Zhou, J. Exploiting
Chemistry and Chemical Systems for Quantum Information Sci-
ence. Nat. Rev. Chem. 2020, 4, 490-504. (b) Sproules, S. Mole-
cules as Electron Spin Qubits. Electron Paramag. Reson. 2017,
25, 61–97. (b) Luis, F.; Hill, S.; Coronado, E. Molecular Spins for
Quantum Computation. Nat. Chem. 2019, 11, 301–309. (c) von
Kugelgen, S.; Freedman, D. E. A chemical path to quantum in-
formation. Science 2019, 366, 1070- 1071.
AUTHOR INFORMATION
Corresponding Author
* E-mail: forbesm@bgsu.edu
* E-mail: mgg@chem.ucla.edu
Author Contributions
= These authors contributed equally
7
(a) Yu, C.; Graham, M. J.; Zadrozny, J. M.; Niklas, J.; Krzyaniak,
M. D.; Wasielewski, M. R.; Poluektov, O. G.; Freedman, D. E.
Long Coherence Times in Nuclear Spin-Free Vanadyl Qubits. J.
Am. Chem. Soc. 2016, 138, 14678-14685. (b) Graham, M. J.;
Krzyaniak, M. D.; Wasielewski, M. R.; Freedman, D. E. Probing
Nuclear Spin Effects on Electronic Spin Coherence via EPR
Measurements of Vanadium(IV) Complexes. Inorg. Chem. 2017,
56, 8106-8113. (c) Graham, M. J.; Zadrozny, J. M.; Shiddiq, M.;
Anderson, J. S.; Fataftah, M. S.; Hill, S.; Freedman, D. E. Influ-
ence of Electronic Spin and Spin-Orbit Coupling on Decoherence
in Mononuclear Transition Metal Complexes. J. Am. Chem. Soc.
2014, 136, 7623-7626.
Funding Sources
MDEF: National Science Foundation award CHE-1900541.
MAGG: National Science Foundation award DMR-1700471
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
MDEF thanks the U.S. National Science Foundation for continued
strong support of his research program through grant CHE-
1900541. Work at UCLA was supported by National Science
Foundation grant DMR-1700471.
8
(a) Olshansky, J. H.; Kryaniak, M. D.; Young, R. M.; Wasielew-
ski, M. R. Photogenerated Spin-Entangled Qubit (Radical) Pairs
in DNA Hairpins: Observation of Spin Delocalization. J. Am.
Chem. Soc., 2019 141, 2152-2160. (b) Wu, Y.; Zhou, J.; Nelson,
J. N.; Young, R. M.; Krzyaniak, M. D.; Wasielewski, M. R. Co-
valent Radical Pairs as Spin Qubits: Influence of Rapid Electron
Motion between Two Equivalent Sites on Spin Coherence. J. Am.
Chem. Soc., 2018 140, 13011-13021. (c) Nelson, J. N.; Krzyani-
ak, M. D.; Horwitz, N. E.; Rugg. B. K.; Phelan, B. T.; Wasielew-
ski, M. R. Zero Quantum Coherence in a Series of Covalent Spin-
Correlated Radical Pairs. J. Phys. Chem. A 2017, 121, 2241-2252.
(d) Yoshina, T.; Nishida, S.; Sato, S.; Nakazawa, S.; Rahimi, R.
D.; Toyota, K.; Shiomi, D.; Morita, Y.; Kitagawa, M.; Takui, T.
REFERENCES
1
(a) Ladd, T. D.; Laflamme, R.; Nakamura, Y.; Monroe, C.; O'Bri-
en, J. L. Quantum Computers. Nature 2010, 464, 45-53 (b) Kas-
sal, I.; Whitfield, J. D.; Perdomo-Ortiz, A.; Yung, M.-H.; Aspuru-
Guzik, A. Simulating Chemistry Using Quantum Computers. An-
nu. Rev. Phys. Chem. 2011, 62, 185-207. (c) Simmons, S.; Brown,
R. M.; Riemann, H.; Abrosimov, N. V.; Becker, P.; Pohl, H.-J.;
Thewalt, M. L. W.; Itoh, K. M.; Morton, J. J. L. Entanglement in
a Solid-State Spin Ensemble. Nature 2011, 470, 69–72. (d) Lan-
1
ESR and H-, 19F-ENDOR/TRIPLE Study of Fluorinated Diphe-
nylnitroxides as Synthetic Bus Spin-Qubit Radicals with Client
Qubits in Solution. J. Phys. Chem. Lett. 2011, 2, 449-453. (e)
Nakazawa, S.; Nishida, S.; Ise, T.; Yoshino, T.; Mori, N.; Rahimi,
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 10
1
2
3
4
5
6
7
8
9
R. D.; Sato, K.; Morita, Y.; Toyota, K.; Shiomi, D.; Kitagawa,
13 Zadrozny, J. M.;
man, D. E. A
Gallagher, A. T.;
Porous Array
Harris, T. D.;
of Clock
Freed-
Qubits.
M.; Hara, H.; Carl, P.; Höfer, P.; Takui, T. A Synthetic Two-Spin
Quantum Bit: G -Engineered Exchange-Coupled Biradical De-
signed for Controlled-NOT Gate Operations. Agnew. Chem. Int.
Ed. 2012, 51, 9860–9864. (f) Sato, K.; Nakazawa, S.; Rahimi, R.;
Ise, T.; Nishida, S.; Yoshino, T.; Mori, N.; Toyota, K.; Shiomi,
D.; Yakiyama, Y.; Morita, Y.; Kitagawa, M.; Nakasuji, K.; Naka-
hara, M.; Hara, H.; Cark, P.; Höfer, P.; Takui, T. Molecular elec-
tron-spin quantum computers and quantum information pro-
cessing: pulse-based electron magnetic resonance spin technology
applied to matter spin-qubits. J. Mater. Chem. 2009, 19, 3739-
3754. (g) McGuire, J.; Miras, H. N.; Donahue, J. P.; Richards, E.;
Sproules, S. Ligand Radicals as Modular Organic Electron Spin
Qubits. Chem. Eur. J. 2018, 24, 17598-17605.
J. Am. Chem. Soc. 2017, 139, 7089–7094.
14 T. Yamabayashi; M. Atzori; L. Tesi; G. Cosquer; F. San-
tanni; M.–E. Boulon; E. Morra; S. Benci; R. Torre; M. Chiesa
Scaling Up Electronic Spin Qubits into a Three–Dimensional
Metal–Organic Framework. J. Am. Chem. Soc. 2018, 140, 12090
–12101.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
15 (a) Faust, T. B.; D’Alessandro, D. M. Radicals in metal-organic
frameworks. RSC Adv. 2014, 4, 17498-17512. (b) Zwoliński, K.
M.; Chmielewski, M. J. Tempo-Appended Metal-Organic
Frameworks as Highly Active, Selective, and Mild Reusable Cat-
alysts for Mild Aerobic Oxidation of Alcohols. ACS Applied Ma-
terials & Interfaces 2017, 9, 33956-33967 (c) Souto, M.; Strutyn-
ski, K.; Melle-Franco, M.; Rocha, J. Electroactive Organic Build-
ing Blocks for the Chemical Design of Functional Porous Frame-
works (MOFs and COFs) in Electronics. Chem. Eur. J. 2020, 26,
10912-10935.
9
Howe, M. E.; Garcia-Garibay, M. A. The Roles of Intrinsic Barri-
ers and Crystal Fluidity on the Dynamics of Crystalline Molecular
Rotors and Molecular Machines. J. Org. Chem. 2019, 84, 9835-
9849.
10 Molecular rotation is currently being researched in a number of
areas to create organic and hybrid materials with tunable and con-
trollable properties: (a) Setaka, W.; Yamaguchi, K. Order-
Disorder Transition of Dipolar Rotor in a Crystalline Molecular
Gyrotop and Its Optical Change. J. Am. Chem. Soc. 2013, 135,
14560-14563. (b) Tsurunaga, M.; Inagaki, Y.; Momma, H.;
Kwon, E.; Yamaguchi, K.; Yoza, K.; Setaka, W. Dielectric Re-
laxation of Powdered Molecular Gyrotops Having a Thiophene
Dioxide-diyl as a Dipolar Rotor. Org. Lett. 2018, 20, 6934-6937.
(c) Hashimoto, H.; Inagaki, Y.; Momma, H.; Kwon, E.; Setaka,
W. Kinetic Stabilization of Carbazole Nitroxides by Inclusion in a
Macrocage and Their Electron Spin Resonance Characterization.
J. Org. Chem. 2019, 84, 11783-11789. (d) Masuda, T.; Arase, J.;
Inagaki, Y.; Kawahata, M.; Yamaguchi, K.; Ohhara, T.l Nakao,
A.; Momma, H.; Kwon, E.; Setaka, W. Molecular Gyrotops with
16 Vogelsberg, C. S.; Uribe–Romo, F. J.; Lipton, A. S.; Yang, S.;
Houk, K. N.; Brown, S. Ultrafast Rotation in an Amphidynamic
Crystalline Metal Organic Framework. PNAS, 2017, 114, 13613–
13618.
17 Vacek, J.; Michl, J. Molecular dynamics of a grid-mounted mo-
lecular dipolar rotor in a rotating electric field. Proc. Nat. Acad.
Sc. 2001, 98, 5481–5486.
18 DeLeeuw, S. W.; Solvaeson, D.; Ratner, M. A.; Michl, J. Molecu-
lar dipole chains: Excitations and dissipation. J. Phys. Chem. B.,
1998, 102, 3876–3885.
19 (a) Chiarelli, R.; Novakt, M. A.; Rassat, A.; Tholencet, J. L. A
Ferromagnetic Transition At 1.48 K in an Organic Nitroxide. Na-
ture 1993, 363, 147–149. (b) You, A.; Be, M. A. Y.; Ferromag-
netic and Antiferromagnetic Intermolecular Interactions of Organ-
ic Radicals, α– Nitronyl Nitroxides. II. J. Chem. Phys. 1989, 91,
2743.
a
Five-Membered Heteroaromatic Ring: Synthesis, Temper-
Dependent Orientation of Dipolar Rotors inside the Crystal and its
Birefringence Change. Cryst.Growth Des. 2016, 16, 4392-4401.
(e) Winston, E. B.; Lowell, P. J.; Vacek, J.; Chocholoušová, J.;
Michl, J.; Price, J. C. Dipolar molecular rotors in the metal-
organic framework crystal IRMOF-2. Phys. Chem. Chem. Phys.
2008, 10, 5188-5191. (f) Horinek, D.; Michl. J. Molecular Dy-
namics Simulation of an Electric Field Driven Dipolar Molecular
Rotor Attached to a Quartz Glass Surface. J. Am. Chem. Soc.
2003, 39, 11900-11910. (g) Vacek, J.; Michl, J. Molecular dy-
namics of a grid-mounted molecular dipolar rotor in a rotating
electric field. PNAS 2001, 98, 5481-5486. (h) Jin, M.; Yamamoto,
S.; Seki, T.; Ito, H.; Garcia-Garibay, M. A. Anisotropic Thermal
Expansion as the Source of Macroscopic and Molecular Scale
Motion in Phosphorescent Amphidynamic Crystals. Angew.
Chem. Int. Ed. 2019, 58, 18003-18010. (i) Colin-Molina, A.; Ka-
rothu, D. P.; Jellen, M. J.; Toscano, R. A.; Garcia-Garibay, M. A.;
Naumov, P.; Rodriguez-Molina, B. “Thermosalient Am-
phidynamic Molecular Machines: Motion at the Matter Molecular
and Macroscopic Scales. 2019, 1, 1033-1046.
20 Gauyacq, J. P. & Lorente, N. Extremely long–lived magnetic
excitations in supported Fe chains. Physical Review B, 2016, 94,
045420.
21 Li, L.; Matsuda, R.; Tanaka, I.; Sato, H.; Kanoo, P.; Jeon, H.J.;
Foo, M.W.; Wakamiya, A.; Murata, Y.; Kitagawa, S., A Crystal-
line Porous Coordination Polymer Decorated with Nitroxide Rad-
icals Catalyzes Aerobic Oxidation of Alcohols. J. Am. Chem. Soc.
2014, 136, 7543–7546
22 Bajpai, A.; Lusi, M.; Zaworotko, M. J. The role of weak interac-
tions in controlling the mode of interpenetration in hybrid ultra-
microporous materials. Chem. Commun., 2017, 53, 3978–3981 (b)
Vagin, S. I.; Ott, A. K.; Hoffmann, S. D.; Lanzinger, D.; Rieger,
B. Synthesis and Properties of (Triptycenedicarboxylato)Zinc Co-
ordination Networks. Chem. Eur. J. 2009, 15, 5845–5853.
23 Jiang, X.; Duan, H–B.; Kahn, S.; Garcia–Garibay, M.A. Diffu-
sion–Controlled Rotation of Triptycene in a Metal–Organic
Framework (MOF) Sheds Light on the Viscosity of MOF–
Confined Solvent. ACS Cent. Sci. 2016, 2, 608–613
11 (a) Graham, M. J.; Zadrozny, J. M.; Fataftah, M. S.; Freedman, D.
E. Forging Solid-State Qubit Design Principles in a Molecular
Furnace. Chem. Mater. 2017, 29, 1885-1897. (b) Urtizberea, A.;
Natividad, E.; Alonso, P. J.; Andrés, M. J.; Gascón, I.; Goldmann,
M.; Roubeau, O. A Porphyrin Spin Qubit and Its 2D Framework
Nanosheets. Adv. Funct. Mater. 2018, 28, 1801695.
24 Yuan, S.; Feng, L.; Wang, K.; Pang, J.; Bosch, M.; Lollar, C.;
Sun, Y.; Qin, J.; Yang, X.; Zhang, P.; Wang, Q.; Zou, L.; Zhang,
Y.; Zhang, L.; Fang, Y.; Li, J.; Zhou, H. Stable Metal – Organic
Frameworksꢀ: Design, Synthesis, and Applications. Adv. Mater.
2018, 30, 1–35.
12 Yu, C.–J.; Krzyaniak, M.; Fataftah, M. S.; Wasielewski, M. R.;
Freedman, D. E. A Concentrated Array of Copper Porphyrin
Candidate Qubits. Chem. Sci. 2019, 10, 1702–1708.
25 (a) Matsumoto, S.; Higashiyama, T.; Akutsu, H.; Nakatsuji, S. A
Functional Nitroxide Radical Displaying Unique Thermochrom-
ism and Magnetic Phase Transition. Angew. Chem. Int. Ed.,
8
ACS Paragon Plus Environment

Page 9 of 10
Journal of the American Chemical Society
1
2
3
4
5
6
7
2011, 50, 10879-10883. (b) Hoshino, N.; Takeda, T.; Akutagawa,
T. Multifunctional Molecular Rotators with Dielectric Magnetic
and Optical Responses. RSC Adv. 2014, 4, 743-747.
tions Employing 15N and 14N. The Journal of Physical Chemis-
try A 2014, 118, 6154–6162.
30 (a) Graham, M. J.; Yu, C.; Krzyaniak, M.; Wasielewski, M.;
Freedman, D. E. Synthetic Approach to Determine the Effect of
Nuclear Spin Distance on Electronic Spin Decoherence.
J. Am. Chem. Soc. 2017, 139, 3196–3201. (b) Jeschke, G. Dis-
tance Measurements in the Nanometer Range by Pulse EPR.
Chem. Phys. Chem. 2002, 3, 927–932.
26 West, A. R. Solid State Chemistry and its Applications, 2nd edi-
tion; John Wiley & Sons: Chichester, 2014.
8
9
27 Oshio, H.; Watanabe, T.; Ohto, A.; Ito, T.; Masuda, H. Intermo-
lecular Ferromagnetic and Antiferromagnetic Interactions in Hal-
ogen–Bridged Copper ( I ) Imino Nitroxidesꢀ: Crystal Structures
and Magnetic Properties of [ Cu I ( µ –X )(Imino Nitroxide )] 2 (
X ) I or Br ). Inorganic Chemistry 1996, 35, 472–479.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
31 Junk, M. J. N. Electron Paramagnetic Resonance Theory. As-
sessing the Functional Structure of Molecular Transporters by
EPR Spectroscopy; Springer Berlin Heidelberg: Mainz 2012.
28 Abdrakhmanov, R. S.; Garif’yanov, N. S.; Semenova, E. I. An
EPR Study of Various Compounds of Copper (II) and Silver (II).
Theoretical and Experimental Chemistry 1971, 4, 250–254.
32 (a) Birrell, G. B.; Pong, S.; Griffith, V. & O.H. Electron Spin
Resonance of Spin Labels in Organic Inclusion Crystals. Models
for Anisotropic Motion in Biological Membranes. J. Am. Chem.
Soc. 1973, 95, 2451–2458. (b) Kobayashi, H.; Ueda, T.; Miyaku-
bo, K.; Eguchiab, T.; Tanib, A. ESR Study of Molecular Dynam-
ics and Orientation of TEMPO Included in Organic 1-D Na-
nochannel, Phys.Chem.Chem.Phys. 2008, 10, 1263–1269.
29 Bales, B. L.; Meyer, M.; Peric, M. EPR Line Shifts and Line
Shape Changes Due to Heisenberg Spin Exchange and Dipole–
Dipole Interactions of Nitroxide Free Radicals in Liquids: 9. An
Alternative Method to Separate the Effects of the Two Interac-
9
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10
ACS Paragon Plus Environment