Two-dimensional perovskite chiral ferromagnets

Article abstract of DOI:10.1021/acs.chemmater.0c02729

Magnetic molecular materials with a chiral configuration are attractive candidates for sensing, information storage, and spintronics. Herein, we report the first example of two-dimensional hybrid perovskite chiral ferromagnets, (R-MPEA)₂CuCl₄ and (S-MPEA)₂CuCl₄. These two compounds exhibit strong oppositely signed circular dichroism signals and clear ferromagnetic behaviors. Magnetic measurements revealed high saturation magnetization up to 12.5 emu g^-1. The coexistence of strong chirality and ferromagnetism enabled successful study on their magneto-chiral dichroism spectra. These findings demonstrate a new materials platform for future magneto-optical and spintronic applications, providing insights to the structure-property correlation of chiral ferromagnetic perovskite.

Full text of DOI:10.1021/acs.chemmater.0c02729

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Article
Two-Dimensional Perovskite Chiral Ferromagnets
Bing Sun, Xiao-Fei Liu, Xiang-Yang Li, Yamin Zhang, Xiangfeng Shao, Dezheng Yang, and Hao-Li Zhang
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.0c02729 • Publication Date (Web): 26 Aug 2020
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Tw o -D im e n s i o n a l P e r ov s k it e C h ir a l Fe r rom a g n e t s
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Bing Sun,† Xiao-Fei Liu,† Xiang-Yang Li,† Yamin Zhang,† Xiangfeng Shao,*,† Dezheng Yang,*,§
and Hao-Li Zhang*,†,‡
†State Key Laboratory of Applied Organic Chemistry (SKLAOC), Key Laboratory of Special Function Materials and
Structure Design (MOE), College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.
R. China
§Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, School of Physical Science and
Technology, Lanzhou University, Lanzhou 730000, P. R. China
‡Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Collaborative Innovation Center of Chemical Science
and Engineering, Tianjin University, Tianjin 300072, P. R. China
ABSTRACT: Magnetic molecular materials with a chiral configuration are attractive candidates for sensing, information
storage and spintronics. Herein, we report the first example of two-dimensional (2D) hybrid perovskite chiral ferromag-
nets, (R-MPEA)2CuCl4 and (S-MPEA)2CuCl4. These two compounds exhibit strong oppositely signed circular dichroism
(CD) signals and clear ferromagnetic behaviors. Magnetic measurements revealed high saturation magnetization up to
12.5 emu g-1. The coexistence of strong chirality and ferromagnetism enabled successful study on their magneto-chiral
dichroism (MChD) spectra. These findings demonstrate a new materials platform for future magneto-optical and
spintronic applications, providing insights to the structure-property correlation of chiral ferromagnetic perovskite.
Great efforts have been devoted to the material systems
whose time-reversal and space-inversion symmetries are
simultaneously broken, i.e. in a medium with magnetism
and chirality.1 Magnetism and chirality are directly con-
nected through an antisymmetric exchange of
Dzyaloshinskii-Moriya interaction (DMI). In a chiral fer-
romagnet, chirality breaks the space inversion and mirror
symmetry,2 which contributes to new types of interesting
cross-effects, such as chiral magnetic effect (CME),3 chi-
ral-induced spin selectivity4 (CISS) and magneto-chiral
dichroism (MChD).5 Materials with both magnetism and
chirality properties can be central to fundamental ad-
vances in multiferroics, current-induced spin-orbit tor-
ques and topological magnetic structures.6
Recently, organic-inorganic hybrid perovskites have
been explored as a platform for developing new multi-
functional materials.16-20 Metal-halide octahedra form lay-
ers separated by the organic molecules, these materials
are commonly referred to as two-dimensional (2D) hybrid
perovskites.21 2D hybrid perovskites have been exploited
in a wide range of applications, owing to their multiple-
quantum-well structures, relatively high stability and im-
pressive compositional tunability. Very few ferromagnetic
perovskites have been prepared so far, which showed
some interesting properties, such as spin-reorientation22
and thermochromic ferromagnets.23 The unique structural
tunability of hybrid perovskites offers an unprecedented
opportunity to directly incorporate chiral organic mole-
cules to enable perovskite’s chirality.24-28 It has been
demonstrated that spin-polarized photoluminescence
occurred in chiral perovskites without an external mag-
netic field.29 Spin transport in perovskite can be effective-
ly manipulated upon the chirality of the (R/S/rac-
MBA)2PbI4 via the CISS mechanism.4 Moreover, large
spin-orbit coupling (SOC),30 controllable Rashba split-
ting,31,32 large Stark effect33,34 and optical spin selection35
have been discovered in hybrid perovskites, highlighting
their potential in spin-based applications. Theoretical
investigations have predicted more attractive applications
of chiral perovskite in quantum informatics and spintron-
ics.36,37
Chiral ferromagnets may play a crucial role in spintron-
ic devices, as a spin-polarized current flowing through
chiral magnetic structures will cause a variety of excita-
tions or manipulations of the magnetization.7 The inter-
play between crystallographic chirality and magnetism
also enables physical insight into fundamental under-
standing of anomalous Hall effect (AHE), magnetization-
induced second-harmonic generation (MSHG) and MChD,
and can give rise to new quantum particles, such as skyr-
mions.8 Chiral ferromagnetic systems possess DMI are of
fundamental interest in the field of molecular mag-
netism,9 and is becoming more important for new appli-
cations in spintronics.10 However, the examples of chiral
ferromagnets are still very limited.11-15
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Despite the extensive investigations, perovskite chiral
above 450 K, while (rac-MPEA)2CuCl4 is thermally stable
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ferromagnet remains blank to date. Herein, for the first
time, we synthesized a pair of enantiomeric 2D hybrid
perovskites, (R-MPEA)2CuCl4 and (S-MPEA)2CuCl4. Circu-
lar dichroism (CD) and magnetic measurements confirm
that these two perovskites possess both chirality and fer-
romagnetism. MChD investigation on chiral perovskites
was carried out for the first time, which revealed potential
of these materials for future optomagnetic and spintronic
applications.
up to 440 K (Figure S1).
Figure 1c and 1d illustrate the single-crystal structures
of the (R-MPEA)2CuCl4 and (S-MPEA)2CuCl4. Both crys-
tals have 2D layered structures, in which successive cor-
ner-sharing inorganic [CuCl6]4- octahedral layer is interca-
lated by two layers of chiral organic cations. In such a way,
the multiple-quantum-wells structure is naturally formed
with the chiral molecules embedded in.38 Compounds (R-
MPEA)2CuCl4 and (S-MPEA)2CuCl4 are antisymmetrically
isostructural and crystallize in the chiral space group of
C2 assigned to the monoclinic crystal system. The lattice
parameters of (R-MPEA)2CuCl4 and (S-MPEA)2CuCl4 are a
= 35.470 Å, b = 5.4017 Å and c = 5.3432 Å; a = 35.450 Å, b =
5.4065 Å and c = 5.3466 Å, respectively.
It is known that the Cu2+ ions in the perovskite struc-
ture are strongly Jahn-Teller (JT) active, giving rise to
changes in the Cu-Cl bond lengths and hence to structur-
al distortions of the CuCl6 octahedra.39 The distortion
levels (Δd) of the individual [CuCl6]4- octahedron is calcu-
lated using Equation (1):
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(a)
(b)
50 μm
50 μm
(c)
(d)
ꢈ
∆ꢀ = ꢁꢂ
ꢃ
ꢆꢄꢇ
(1)
ꢄꢅ
∑
ꢄ
where d is the mean Cu-Cl bond length (Table S2 and
Table S3) and dn are the six individual Cu-Cl bond
length.40 The distortions of CuCl6 octahedral in the perov-
skite structure are listed in Table S4. The values of Δd is
calculated to be 3.3210-4 and 3.0710-4 for the (R-
MPEA)2CuCl4 and (S-MPEA)2CuCl4, respectively, indicat-
ing that there is no substantial difference in structural
distortion.
(e)
(f)
(S-MPEA)2CuCl4
experimental
calculated
(R-MPEA)2CuCl4
experimental
calculated
(a)
(b)
10
5
(
(
(
R-MPEA
)
2CuCl4
2.5
2.0
1.5
1.0
0.5
0.0
S-MPEA
)
2CuCl4
rac-MPEA 2CuCl4
)
Figure 1. Optical microscopic images of (R-MPEA)2CuCl4 (a)
and (S-PEA)2CuCl4 (b). Single crystal structures viewed along
the c-axis (R-MPEA)2CuCl4 (c) and (S-MPEA)2CuCl4 (d) with
color codes Cu (Indigo), Cl (Red), C (gray), N (blue). The
CuCl6-units are displayed as polyhedra, and H atoms are
omitted for clarity. Experimental and calculated powder X-
ray diffraction (PXRD) patterns of (e) (R-MPEA)2CuCl4, (f)
(S-MPEA)2CuCl4.
0
-5
10
(
(
R-MPEA 2
)
CuCl4
CuCl4
S-MPEA 2
)
(
rac-MPEA)2CuCl4
200 400 600 800 1000 1200 1400
250
300
350
400
450
500
Wavelength (nm)
Wavelength (nm)
Figure 2. Absorbance and CD spectra of the chiral perov-
skites. UV-vis-NIR absorption spectra (a) and CD spectra (b)
of (R-MPEA)2CuCl4, (S-MPEA)2CuCl4 and (rac-MPEA)2CuCl4.
Direct combination of the chiral cations and
CuCl22H2O mixing in ultrapure water at 80 °C followed
by slow cooling of the solutions to room temperature
yields yellow flake crystals, as seen in Figure 1a and 1b.
Detailed synthesis procedures are listed in the experi-
mental section. The crystal structure and refinement data
are provided in Figure 1c, 1d and Table S1. Powder X-ray
diffraction (PXRD) patterns of (R-MPEA)2CuCl4 and (S-
MPEA)2CuCl4 all exhibit sharp peaks and show almost
identical features as simulated spectra based on their sin-
gle crystal structures, confirming the phase purity of the
as-synthesized crystals (Figure 1e and 1f). Thermogravi-
metric analysis (TGA) measurements indicate that (R-
MPEA)2CuCl4 and (S-MPEA)2CuCl4 possesses high ther-
mal stability, with identical decomposition temperature
UV-vis-NIR absorption spectra of (R-MPEA)2CuCl4, (S-
MPEA)2CuCl4 and racemic compound are shown in Figure
2a, which are nearly identical. The absorption peak at
~379 nm near the absorption edge corresponds to 2D per-
ovskite excitonic feature, which is characteristic for 2D
perovskites. The 2D hybrid perovskite structures are nat-
ural quantum wells with semiconducting slabs alternating
with dielectric slabs.41 Therefore, this absorption feature is
derived from quantum and dielectric confinement effects
of the carriers, previously shown in other 2D semiconduc-
tors such as the (CH3CH2NH3)4Pb3Br10−xClx series and
42,43
(PA)2(MA)n-1PbnI3n+1
.
The high energy absorption band
observed at ~274 nm is associated with π→π∗ transition
of the organic cations.44 The absorption edges of the chi-
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ral perovskites locate around 567 nm. A broad band ap-
transition from ferromagnet to paramagnet (Figure 3a). A
long-range ferromagnetic ordering below 6 K was ob-
served for (R-MPEA)2CuCl4, (S-MPEA)2CuCl4 and (rac-
MPEA)2CuCl4. The Curie temperatures of these 2D perov-
pears in the near-infrared spectrum ranging from 600 to
1200 nm, indicating the appearance of broad gap states.45
This weak, broad band centered at approximately 800 nm
in the absorption spectra results from Laporte forbidden
Cu2+ d-d transitions.46,47 Photoluminescence spectra of (R-
MPEA)2CuCl4, (S-MPEA)2CuCl4 and (rac-MPEA)2CuCl4 are
shown in Figure S2. A broad emission band peaking at 555
and 617 nm was observed for these three compounds, in-
dicating that nearly identical photoluminescence proper-
ties.
23
skites are similar to those observed on (BED)2CuCl6 and
CuCl4(C6H5CH2CH2NH3)2.49 The hysteresis loops confirm
the presence of spontaneous magnetization (Figure 3 b, c
and d). The magnetization nearly saturates at a value of
12.5 emu g-1 in a field of 2500 Oe at 2 K in all compounds.
Furthermore, the ferromagnetic hysteresis loops show a
quick saturation, therefore supporting the presence of
significant interactions below the magnetic ordering tran-
sition.50 When the temperature is higher than the Curie
temperature, the hysteresis loops gradually disappears. It
is noted that the saturated magnetization is the highest
value in the ever reported in perovskite materials.
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Figure 2b reveals strong CD signals appear at the same
wavelengths (at 324, 372 and 436 nm) for the (R-
MPEA)2CuCl4 and (S-MPEA)2CuCl4 films but with oppo-
site signs, while (rac-MPEA)2CuCl4 shows a featureless
flat signal. The CD spectra indicate strong chirality of the
two new 2D perovskites. As shown in Figure S3, opposite
CD absorption features are observed in R-MPEAHCl and
S-MPEAHCl. The racemic blend of rac-MPEAHCl exhib-
its no absorption difference between left- and right-
handed polarized light. The CD signals for these chiral
organic ammonium salts mainly located before 300 nm.
However, when they are incorporated into the chiral per-
ovskite, the resulting perovskites exhibit strongly oppo-
site CD values in the visible region (Figure 2b). These ob-
servations indicate that the chirality of organic cations
directly transferred to the perovskite framework, thereby
endowing the corresponding 2D perovskites with intrinsic
chirality.48 Notably, the CD peaks were located before the
absorption edge at 567 nm, suggesting a lifting of the spin
degeneracy within the band edge electronic states in-
duced by the chiral molecules.4
To date, only a few perovskite compounds have been
reported to possess a ferromagnetic coupling. It is inter-
esting to study the Jahn-Teller activity of Cu-based com-
plexes in the hybrid perovskites. From the configuration
ꢊ
ꢊ
of Cu ꢀꢉ
orbitals in the Cu-Cl octahedral layer (Figure
ꢆꢋ
S4), each octahedron is prolonged along the Jahn-Teller
z-axis that lies in the CuCl plane. In an organic-inorganic
perovskite system, the magnetic spin originates from the
51
ꢊ
ꢊ
unoccupied Cu ꢀꢉ
orbital. For these hybrid perov-
ꢆꢋ
ꢊ
ꢊ
skites, the ꢀꢉ
type symmetry orbitals of the individual
ꢆꢋ
octahedra in the a-b basal plane are orthogonal to each
other. Jahn-Teller-active ions cause cooperative antiferro-
distortive arrangements of the neighboring orthogonal
octahedra, which produces ferromagnetic interactions. In
fact, the system shows characteristics of a 2D Heisenberg
ferromagnet.50 The 2D copper halide perovskites present-
ed herein are ideal model systems for the study of Jahn-
Teller activity in Heisenberg systems, which may enable
deeper understanding to the structure-magnetic relation-
ships.52
10
8
15
10
5
(a)
(b)
(
(
(
R-MPEA
S-MPEA 2
rac-MPEA 2
)
2CuCl4
CuCl4
CuCl4
2 K
5 K
10 K
15 K
)
)
6
0
4
10
0
-5
2
(
R-MPEA
S-MPEA
)
2CuCl4
2
1
-10
-150
Magnetic field
-10
0 150
0
(
)2CuCl4
-15
0
5
10
15
20
25
30
-10000 -5000
0
5000 10000
Temperature (K)
Magnetic field (Oe)
15
10
5
(c)
(d)
15
10
5
2 K
5 K
10 K
15 K
2 K
5 K
10 K
15 K
0
0
0
10
0
-5
10
0
-5
-10
-150
Magnetic field
-10
-10
-150
Magnetic field
-10
0 150
0 150
-15
-1
-2
-15
-10000 -5000
0
5000 10000
-10000 -5000
0
5000 10000
Magnetic field (Oe)
Magnetic field (Oe)
Figure 3. Magnetic properties of the (R-, S-, rac-
MPEA)2CuCl4. (a) Temperature dependence of the magneti-
zations of (R-MPEA)2CuCl4, (S-MPEA)2CuCl4 and (rac-
MPEA)2CuCl4 in applied fields of 100 Oe. (b, c, d) The hyste-
resis loops of (R-MPEA)2CuCl4, (S-MPEA)2CuCl4 and (rac-
MPEA)2CuCl4 at 2 K, 5 K, 10 K and 15 K.
200 300 400 500 600 700 800 900
Wavelength (nm)
Figure 4. MChD investigation and the energy level diagram
of d-orbitals for Cu2+. MChD recorded on (R-MPEA)2CuCl4
and (S-MPEA)2CuCl4 at 2 K.
Temperature-dependent magnetic susceptibility in a
100 Oe magnetic field for the (R-MPEA)2CuCl4, (S-
MPEA)2CuCl4 and (rac-MPEA)2CuCl4 show clearly the
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MChD is a magneto-optical effect in which the absorp-
ence ferromagnetic superexchange interaction between
Cu2+ (S = 1/2)65 (Figure S4). In the UV-Vis region, the
MChD is generally understood as an interference effect
between electric dipole (E1) and magnetic dipole transi-
tions (M1) resulting from the SOC.66,67 Based on these
mechanisms, the MChD signal of the d-d transition for
Cu2+ is expressed by the summation of the E1-M1 interfer-
ence term of optical transition from the Cu2+ ions.61 Addi-
tionally, the dissymmetry factor for MChD can be defined
as:
tion coefficient of a chiral compound for an unpolarized
light beam differs depending on whether an externally
applied magnetic field is parallel or antiparallel to the
propagation direction of the light beam.53 MChD is de-
scribed as a manifestation of magneto-chiral anisotropy,
which can be formalized by expanding the frequency de-
pendence (ω) of the absorption coefficient (ε) with mag-
netic field H and the light propagation vector k (Equation
(2)).
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⁄
⁄
(
)
(
)
ꢄ
ꢤ ꢎ↑↑ꢍ ꢆꢤ ꢎ↓↑ꢍ
ꢌꢍ, ꢎ, = ꢏꢐ(ꢌ)± ꢑ ꢒ(ꢌ )ꢍ ± ꢓ(ꢌ )ꢎ ± ꢔ ꢄ ꢒ(ꢌ )ꢍ ∙ꢎ (2)
ꢟꢠꢡꢢꢣ
=
ꢎ↑↑ꢍ ꢦꢤ ꢎ↓↑ꢍ ) = 2 ꢧꢤ
(3)
ꢨꢩꢪꢫ
ꢤ
(
)
ꢥ
ꢊ
(
)
(
)
(ꢤ
Here, ε0 is associated to the normal absorption of light at
zero field, αd/l to the natural circular dichroism, β to the
magnetic circular dichroism, and γd/l to the MChD, with d
and l that refer to right- and left-handed medium, and +/-
the right- and left-handed circularly polarized waves, re-
spectively.54 MChD signal is associated with spin excita-
tions and can be used to probe molecular magnetism sys-
tems for store and read the information.55,56 Investigation
on the microscopic origins of MChD from organ-
ic/inorganic hybrid materials is so far scarce and limited
to only a few examples.5,53,54,57-59
where A = (A− + A+)/2, A− and A+ are the absorbances for
LCP and RCP in the absence of a magnetic field, respec-
tively.59 An essential characteristic of MChD is that gMChD
should be of opposite sign for two enantiomers.59 We
have calculated gMChD between 250 nm and 500 nm ac-
cording to Equation (3). Figure S5 plots the experimental
results for gMChD against the wavelength for the two enan-
tiomers, and the absolute values of the gMChD are summa-
rized in Table S5. We observed absolute values of gMChD
=
0.51 T-1 for the (R-MPEA)2CuCl4 and gMChD = 0.59 T-1 for (S-
MPEA)2CuCl4 at 405 nm, confirming significant magneto-
chiral anisotropy.68 It is noted that these gMChD coeffi-
cients are much higher than that reported for Eu((±)tfc)3
complex (5 × 10-3 T-1)59 and chiral Ni nanomagnets68 (7.3 ×
10-4 T-1). This intense absolute configuration-dependent
signal is direct experimental proof of the existence of the
MChD effect in these two perovskite materials.5,54
Owing to the coexistence of chirality and ferromag-
netism, the two enantiomers of (R-MPEA)2CuCl4 and (S-
MPEA)2CuCl4 are suitable for MChD study. The wave-
length dependence of the optical transmission in the re-
gion of 200-900 nm with an applied magnetic field (B = 1
T) at 2 K was tested (Figure 4). Measurements performed
in the same conditions for (R-MPEA)2CuCl4 and (S-
MPEA)2CuCl4 provide several strong MChD signals with
opposite signs in their optical response, resulting in per-
fect mirror images. The maximum absolute ΔA value of
these perovskite chiral ferromagnets is around 1.910-3
cm-1, which is similar to that observed on Prussian blue
analogue.5
In summary, we report the first pair of 2D hybrid per-
ovskites that exhibit strong chirality and ferromagnetism
simultaneously. Magnetic measurements reveal that these
enantiomers have a saturation magnetization value up to
12.5 emu g-1, which is the highest in the ever reported per-
ovskite materials. Moreover, this work presents the first
successful MChD measurement in perovskite materials,
which indicates that large values of magneto-chiral ani-
sotropy can be obtained in perovskite chiral ferromagnets.
Our results about MChD-featured chiral ferromagnets
suggest that these materials hold potentials for the devel-
opment of magneto-optical devices, magneto-resistive
sensors and spintronic devices. This work provides a new
strategy for creating novel chiral ferromagnets by exploit-
ing perovskite structure, which may lay a foundation for
the further development of magnetic materials for
spintronic applications.
Sharp MChD peaks are discernible at λ = 262 and 490
nm, as well as λ = 545 and 764 nm, corresponding to in-
tra-atomic d-d transitions in the Cu2+ ions.60,61 The inset
shows the energy level diagram of d-orbitals for Cu2+. Ac-
cording to ligand field theory, the ground state electronic
distribution of Cu2+ is tꢈꢕ6ꢖꢕ3 which yields 2ꢗꢕ term, where
the excited electronic state is tꢈꢕ5ꢖꢕ which corresponds
to ꢘꢈꢕ term.62 Due to Jahn-Teller effect, ꢗꢕ ground state
4
2
2
2
2
is split into 2Aꢁꢕꢙꢀꢉ
ꢚ and ꢛꢈꢕ ꢀꢜ whereas ꢘꢈꢕ splits
(
)
ꢊ
ꢊ
ꢊ
ꢆꢋ
into ꢝꢁꢕꢙꢀꢉꢋꢚ, 2ꢝꢈꢕ ꢀꢉꢜ and ꢝꢞꢕꢙꢀꢋꢜꢚ states. In our case,
the observed electronic transitions at 262, 490 and 764
nm for the two enantiomers can be assigned to the
2
2
(
)
E X P ER I M EN TA L S EC TI ON
2
2
2
2 Aꢁꢕꢙꢀꢉ
2Aꢁꢕꢙꢀꢉ
ꢚ → ꢝꢞꢕꢙꢀꢋꢜꢚ , Aꢁꢕꢙꢀꢉ
ꢚ → ꢝꢈꢕ ꢀꢉꢜ
(
)
,
ꢊ
ꢊ
ꢊ
ꢊ
Materials. R-MPEA = R-β-methylphenethylamine (97%, ee
98%), S-MPEA = S-β-methylphenethylamine (97%, ee 98%)
was purchased from Alfa Aesar. rac-MPEA =
methylphenethylamine (98%) was purchased from J&K Sci-
entific co., LTD. CuCl22H2O (99.99%) was purchased from
ALADDIN. Hydrochloric acid (36%-38%) was purchased
from Xilong chemical reagent co., LTD. All reagents and sol-
vent were used without further purification.
ꢆꢋ
ꢆꢋ
2
(
)
ꢊ
ꢊ
ꢊ
ꢚ→ ꢛꢈꢕ ꢀꢜ , respectively. Figure 4 shows that
ꢆꢋ
rac-β-
the different transitions produce MChD signal is different
in strength and lineshape. The MChD signal around 545
nm gives the strongest intensity, which is corresponding
2
2
ꢊ
ꢊ
to the Aꢁꢕꢙꢀꢉ
ꢚ→ ꢝꢁꢕꢙꢀꢉꢋꢚ transition,63,64 while the
ꢆꢋ
signals associated with the other transitions are less in-
tense.
As discussed above, the orbitals on neighboring Cu2+
ions are orthogonal to each other, and the spins experi-
Synthesis of R-MPEAHCl and S-MPEAHCl single crys-
tals. R-MPEAHCl was synthesized by reacting R-MPEA and
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hydrochloric acid with the molar ratio of 1:1. The hydrochlo-
quantum interference device magnetometer with a sensitivi-
ty better than 10-8 emu (Quantum Design MPMS-XL, USA).
ric acid was added dropwise into the R-MPEA in a single-
mouth flask with a round bottom in an ice bath. It takes an
hour to complete. Then, the resulting solution was evapo-
rated at 80 °C in a rotary evaporator to remove the solvent.
As the solvent is removed, a large number of solids appeared.
The crystal was recrystallized in anhydrous ethanol two
times, then dried in a vacuum oven at 60 °C for 12 h. For the
synthesis of S-MPEAHCl, the steps were conducted the
same procedure as above described.
Magneto-chiral dichroism. Manual grinding powder form
(R-MPEA)2CuCl4 and (S-MPEA)2CuCl4 mm-sized crystals
were used for magneto-chiral dichroism investigation. Mag-
neto-chiral dichroism spectra measurements were made on
Applied Photophysics Chirascan Magnetic circular dichroism
spectrometer in the presence of a magnetic field with both
parallel and antiparallel fields. Unpolarized light was di-
rected onto the samples using optical fibers. The two beams
of circularly polarized light with left and right rotation are
monochromated and focused. After that, the sample has the
same energy, the same light intensity, the same circular de-
gree of polarization, the same spot size and the same posi-
tion. The wavelength dependence of the optical transmission
in the region of 200-900 nm with an applied magnetic field
(B = 1 T) at 2 K was measured. The sample is placed in a cryo-
stat and the cooling rate is 5 °C/min. The averaged magneto-
chiral dichroism spectra were obtained from the difference
between the parallel and antiparallel transmission spectra.
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Synthesis of (R-MPEA)2CuCl4 and (S-MPEA)2CuCl4 single
crystals. The synthesis of these enantiomeric crystals
through self-assembly crystallization from an aqueous solu-
tion of chiral ammonium salt (R-MPEAHCl and S-
MPEAHCl) and CuCl22H2O salts, by slowly cooling crystal-
lization. Take (R-MPEA)2CuCl4 as an example, R-MPEAHCl
and CuCl22H2O with the molar ratio of 2:1 were dissolved in
an aqueous solution (2 mmol/mL) and stirred at 80 °C for 20
min. Then, the clear solution was kept in a quiet environ-
ment without destabilization for slowly cooling from high
temperature to low temperature. After about two hours,
many yellow plate-like crystals as large as several millimeters
were obtained.
A S SO C IA TED CO N TE N T
Supporting Information.
Synthesis of rac-MPEAHCl and (rac-MPEA)2CuCl4 com-
pounds. For the synthesis of rac-MPEAHCl, the steps were
conducted the same procedure as the synthesis of R-
MPEAHCl and S-MPEAHCl. By applying the racemic rac-
MPEAHCl in the synthesis, we also obtained a racemic
compound (rac-MPEA)2CuCl4. Although the crystal quality
was not good enough for single-crystal structural analysis, we
confirmed that (rac-MPEA)2CuCl4 crystallizes in a different
structure from those of (R-MPEA)2CuCl4 and (S-
MPEA)2CuCl4 by comparing PXRD patterns (Figure S6).
This material is available free of charge via the Internet at
http://pubs.acs.org.
TGA; Photoluminescence spectra; CD spectra; Configuration
ꢊ
ꢊ
of Cu ꢀꢉ ꢆꢋ orbital; Crystal data and structure refinement of
(R-MPEA)2CuCl4 and (S-MPEA)2CuCl4; Distortions of CuCl6
octahedral; Summary of the |gMChD| (PDF); X-ray crystallo-
graphic file for (R-MPEA)2CuCl4 and (S-MPEA)2CuCl4 (CIF)
A U TH OR I N F O R M A TI O N
C or re s p o n d i n g A u t h o r
Thermogravimetric analyses (TGA). TGA was carried out
on a Linseis STA PT1600. A heating rate of 10 °C min-1 under
flowing N2 was used from room temperature to high temper-
ature to investigate the thermal stabilities.
*shaoxf@lzu.edu.cn
*yangdzh@lzu.edu.cn
*haoli.zhang@lzu.edu.cn
N ot e s
The authors declare no competing financial interests.
Powder X-ray diffraction (PXRD). The X-ray diffraction
data were obtained at X’Pert PRO made by Panalytical Com-
pany with a wavelength of 1.5406 Å.
A C K N OW L ED G M EN T
This work was supported by the National Key R&D Program
of China (2017YFA0204903), National Natural Science Foun-
dation of China (NSFC. 51733004, 51525303, 1522203), 111 Pro-
ject and the Fundamental Research Funds for the Central
Universities. The authors thank beamline BL14B1 (Shanghai
Synchrotron Radiation Facility) for providing the beam time.
Single crystal X-ray diffraction (SCXRD). Single crystals of
(R-MPEA)2CuCl4 and (S-MPEA)2CuCl4 with good quality
were carried out on a Bruker D8 VENTURE Kappa Duo
PHOTON II CPAD diffractometer with graphite-
monochromatized Cu Kα radiation (λ = 1.54184 Å), operating
at 50 kV and 40 mA under N2 flow. Crystal data were inte-
grated and corrected for absorption (numerical) using the
STOE X-AREA programs. Crystal structures were solved by
direct methods and refined by full-matrix least-squares on F2
using the OLEX2 program package.
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