Cyclic Structural Transformations from Crystalline to Crystalline to Amorphous Phases and Magnetic Properties of a Mn(II)-Based Metal-Organic Framework

Article abstract of DOI:10.1021/acs.cgd.8b00064

A three-dimensional Mn(II) framework, [Mn₂(H₂L)(L)_0.5(MeOH)(DEF)]·0.1MeOH·0.1DEF·1.4H₂O (1; H₄L = 2,3-dioxido-1,4-benzenedicarboxylic acid), was synthesized under solvothermal conditions in diethylformamide/methanol (DEF/MeOH), where the Mn centers adopt octahedral and unusual pentagonal bipyramidal geometries. The ligand H₄L was subject to deprotonation to create μ₄-H₂L^2- and μ₆-L^4- anionic bridges, leading to the construction of a coordination network. The MeOH exchange process of crystalline 1 allowed for another crystalline phase (1a), which reversibly returned to the original crystalline state upon resolvation in DEF/MeOH. After evacuation of 1a, the amorphous phase 1b was irreversibly formed, followed by the restoration of the original phase 1 upon resolvation in DEF/MeOH. Consequently, this framework underwent cyclic structural transformations from the crystalline (1) to crystalline (1a) to amorphous (1b) and back to crystalline (1) phase, which are unique transformations for soft coordination networks. Magnetic measurements demonstrated that antiferromagnetic interactions were operative between the Mn(II) ions and were effectively mediated by the oxygen moieties of the μ₆-L^4- bridge.

Full text of DOI:10.1021/acs.cgd.8b00064

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Cyclic Structural Transformations from Crystalline
to Crystalline to Amorphous Phases and Magnetic
Properties of a Mn(II)-Based Metal-Organic Framework
Han Geul Lee, Chang Seop Hong, Hyuna Jo, Sunhwi Eom, Dong Won
Kang, Minjung Kang, Jeremy Hilgar, Jeffrey D. Rinehart, and Dohyun Moon
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00064 • Publication Date (Web): 24 Apr 2018
Downloaded from http://pubs.acs.org on April 24, 2018
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Crystal Growth & Design
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Cyclic Structural Transformations from Crystalline to
Crystalline to Amorphous Phases and Magnetic
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Properties of a Mn(II)ꢀBased MetalꢀOrganic Framework
Han Geul Lee,†,‡ Hyuna Jo,†,‡ Sunhwi Eom,† Dong Won Kang,† Minjung Kang,† Jeremy Hilgar,§
Jeffrey D. Rinehart,§ Dohyun Moon⊥ and Chang Seop Hong*,†
†Department of Chemistry, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of
Korea.
§Department of Chemistry and Biochemistry, University of California – San Diego, 9500 Gilman Drive,
Mail Code 0358, La Jolla, CA 92093-0358, USA.
⊥Beamline Division, Pohang Accelerator Laboratory, Pohang, Kyungbuk 790-784, Republic of Korea.
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ABSTRACT:
A
threeꢀdimensional
Mn(II)
H4L
framework,
2,3ꢀdioxidoꢀ1,4ꢀ
conditions in
[Mn2(H2L)(L)0.5(MeOH)(DEF)]ꢁ0.1MeOHꢁ0.1DEFꢁ1.4H2O
benzenedicarboxylic acid), was synthesized
(1;
under
=
solvothermal
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diethylformamide/methanol (DEF/MeOH), where the Mn centers adopt octahedral and unusual
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pentagonal bipyramidal geometries. The ligand H4L was subject to deprotonation to create ꢀ4ꢀH2L2ꢀ and
ꢀ6ꢀL4ꢀ anionic bridges, leading to the construction of a coordination network. MeOH exchange process
of crystalline 1 allowed for another crystalline phase (1a), which reversibly returned to the original
crystalline state upon resolvation in DEF/MeOH. After evacuation of 1a, the amorphous phase 1b was
irreversibly formed, followed by the restoration of the original phase 1 upon resolvation in DEF/MeOH.
Consequently, this framework underwent cyclic structural transformations from the crystalline (1) to
crystalline (1a) to amorphous (1b) and back to crystalline (1) phase, which are unique transformations
for soft coordination networks. Magnetic measurements demonstrated that antiferromagnetic
interactions were operative between the Mn(II) ions, and were effectively mediated by the oxygen
moieties of the ꢀ6ꢀL4ꢀ bridge.
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Crystal Growth & Design
INTRODUCTION
Metalꢀorganic frameworks (MOFs) are crystalline platforms that are characterized by high surface
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area and porosity. Their applications include gas storage and separation, catalysis, proton conductivity,
sensing, drug delivery, and so on.1ꢀ5 Although MOFs frequently exhibit structural rigidity, they are
flexible upon external stimuli such as hostꢀguest interactions, photoꢀ and thermo responses, and
pressure.6 Such structural flexibility emerges as a result of breathing, swelling, linker rotation, and
subnetwork displacement within the framework structure.
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In terms of hostꢀguest interactions, solvent molecules incorporated into the interior of the framework
trigger structural flexibility of the dynamic soft crystals. Substantial structural variations in soft
coordination networks are accompanied by changes in the ligand conformation and deformation of the
metal nodes when guest molecules enter or exit the pores of the framework.7ꢀ9 Solvent inclusion in or
removal from the framework often engenders single crystalꢀtoꢀsingle crystal transformations.10ꢀ12 The
structural dynamics in flexible coordination systems also promotes crystalꢀtoꢀamorphous structural
conversions upon solvationꢀdesolvation.13ꢀ16 Thus, most structural transformations involve reversible or
irreversible phase exchange between two crystalline states or between crystalline and amorphous states.
In fact, structural nonrigidity of soft frameworks is more diverse and even three states are mutually
transformable upon various sample treatments (solvent exchange, activation, and resolvation, for
instance).17ꢀ19 In these examples, phase conversions from crystalline to another crystalline to other
crystalline states occur upon incorporation of guest solvent molecules into the frameworks or
elimination of the introduced solvent molecules. Based on these observations, it was envisioned that
more extensive framework dynamics could be achieved in association with the creation of new multiple
phases under different external conditions.
Herein, we report the synthesis, crystal structure, multiꢀstructural flexibility, and magnetic properties
of the threeꢀdimensional (3D) network of [Mn2(H2L)(L)0.5(MeOH)(DEF)]ꢁ0.1MeOHꢁ0.1DEFꢁ1.4H2O (1;
H4L = 2,3ꢀdioxidoꢀ1,4ꢀbenzenedicarboxylic acid). This network exhibits significant structural flexibility
in connection with extensive cyclic conversions from one crystalline phase to another crystalline phase
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to an amorphous phase to the original crystalline state during solvent inclusion and removal. It is
remarkable that these phase transformations take place among three states, including an amorphous
phase, which has not been demonstrated before to the best of our knowledge. Antiferromagnetic
coupling occurs between the Mn(II) ions, mediated by the oxygen atoms of the organic ligand.
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EXPERIMENTAL SECTION
Reagents. All chemicals and solvents used in the synthesis were of reagent grade and were used as
received. All manipulations were performed under aerobic conditions.
2,3-Dioxido-1,4-benzenedicarboxylic acid (H4L). 1,2,4ꢀTrichlorobenzene (5 mL) was added to a
mixture of pyrocatechol (1.00 g, 9.08 mmol) and KHCO3 (2.91 g, 29.06 mmol), and the mixture was
placed in a 23ꢀmL autoclave. The bomb was sealed after adding dry ice (5.836 g, 132.6 mmol) and
placed in an oven heated to 225 °C for 14 h. The resulting mixture was washed with diethyl ether by
stirring for 30 min and collected by vacuum filtration. The crude product was dissolved in 600 mL of
water by stirring for 30 min and filtered through a Celite® filter aid. Hydrochloric acid was slowly
added to the solution until the pH reached 1–2. The precipitate was collected by filtration and washed
with water. A beige color solid was obtained and dried at 70 oC. Yield = 73%. 1H NMR (DMSOꢀd6, 500
MHz) δ(ppm): 7.28(s). Anal. Calcd for C8H7.9O6.95 (H4L·0.95H2O): C, 44.64; H, 3.70. Found: C, 44.69;
H, 3.72.
[Mn2(H2L)(L)0.5(MeOH)(DEF)]·0.1MeOH·0.1DEF·1.4H2O (1). MnCl2·4H2O (534.3 mg, 2.7
mmol) and H4oꢀdobdc (178.3 mg, 0.9 mmol) were dissolved in a mixed solvent comprising N,Nꢀ
diethylformamide (DEF)/MeOH (5/1, v/v, 9 mL) by sonication. The filtered brownish solution and
hydrochloric acid (0.09 mL) were transferred to a 23ꢀmL glass vial and sealed tightly. The vial was
placed in an oven preꢀheated to 120 °C for 1 day. The resulting solid was washed with DEF/MeOH (5/1,
v/v, 120 mL) mixed solvent (mother liquor) and then with MeOH (30 mL). The solid was collected by
filtration, followed by drying in Ar for 1 h, affording a brownish solid. Yield = 53%. Anal. Calcd. for
C
18.6H24.3Mn2N1.1O12.6: C, 38.87; H, 4.26; N, 2.68. Found: C, 38.73; H, 3.92; N, 2.94.
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Crystal Growth & Design
Reversible Phase Conversion between 1 and 1a upon MeOH Exchange and DEF/MeOH
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Resolvation. 1 was soaked in MeOH for 5 days, where the solvent was refreshed every day. The solid
was collected by filtration and Arꢀdried for 1 h to produce the MeOHꢀexchange sample of
[Mn2(H2L)(L)0.5(MeOH)2]·1.8H2O (1a). Anal. Calcd. for C14H16.6O12.8: C, 33.66; H, 3.35. Found: C,
33.74; H, 3.16. 1a was immersed in DEF/MeOH (5/1, v/v) mixed solvent for 3 d, where the solvent was
refreshed every day. The solid was collected by filtration, followed by drying in Ar for 1 h to give the
regenerated sample of [Mn2(H2L)(L)0.5(MeOH)1.28(DEF)0.72]·1.1H2O. Anal. Calcd. for
C16.88H20.24Mn2N0.72O12.1: C, 37.78; H, 3.80; N 1.88. Found: C, 37.48; H, 3.58; N, 1.89. These processes
were monitored by powder Xꢀray diffraction (PXRD) and infrared (IR) analyses.
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Phase Transformation from Crystalline 1a to Amorphous 1b upon Activation. 1a was evacuated
for 1 h to generate the activated solid [Mn2(H2L)(L)0.5]ꢁ2.4H2Oꢁ0.6MeOH (1b). Anal. Calcd. for
C
12.6H12.2Mn2O12: C, 32.51; H, 2.64. Found: C, 32.67; H, 2.86. This process was monitored by PXRD
and IR.
Phase Transformation from Amorphous 1b to Crystalline 1 upon DEF/MeOH Resolvation. 1b
was soaked in DEF/MeOH (5/1, v/v) mixed solvent for 3 d, where the solvent was refreshed every day.
Filtration and Ar drying of the resulting solid afforded the resolvated phase of
[Mn2(H2L)(L)0.5(MeOH)0.5(DEF)0.82(H2O)0.68]·1.72H2O. Anal. Calcd. for C16.6H20.82Mn2N0.82O12.72: C,
36.57; H, 3.85; N 2.11. Found: C, 36.19; H, 3.45; N, 2.48. This process was monitored by PXRD and
IR.
Physical Measurements. Proton nuclear magnetic resonance spectra (1H NMR) were recorded with a
500 MHz NMR spectrometer. Infrared spectra were obtained with an ATR module using a Nicolet iS10
FTꢀIR spectrometer. Powder XRD (PXRD) patterns were recorded on a Rigaku Ultima III
diffractometer using CuꢀKα (λ = 1.5406 Å) radiation, with a scan speed of 2°/min and a step size of
0.01°. Elemental analyses for C, N, and H were performed at the Elemental Analysis Service Center of
Sogang University. Gas sorption measurements were carried out on a ASAP2020 instrument at 77 K
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(N2). Magnetic data for 1 were acquired with a Quantum Design SQUID susceptometer. Diamagnetic
corrections for 1 were estimated from Pascal’s Tables.
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Crystallographic Structure Determination. Xꢀray data for a single crystal of 1 were acquired with a
cryoloop, where the crystal was mounted on a goniometer head under a cold stream of liquid nitrogen.
The diffraction data were acquired by applying synchrotron radiation on a 2D SMC MX ADSC
Quantumꢀ210 detector with a silicon (111) doubleꢀcrystal monochromator at the Pohang Accelerator
Laboratory, Korea. The ADSC Quantumꢀ210 ADX program (Ver. 1.92) was used for data collection,
while HKL3000 (Ver. 0.98.699) was used for cell refinement, reduction, and absorption correction. The
structure was solved by direct methods and refined by fullꢀmatrix leastꢀsquares analysis using
anisotropic thermal parameters for nonꢀhydrogen atoms with the SHELXTL program. The lattice solvent
molecules in 1 were significantly disordered and could not be modeled properly, thus the program
SQUEEZE, a part of the PLATON crystallographic software package, was used to calculate the solvent
disorder area and remove its contribution to the overall intensity data. All hydrogen atoms, except for
those bound to water molecules, were calculated at idealized positions and refined with the riding
model. Crystal data for 1: empirical formula = C31H49Mn4NO22, Mr = 1007.47, monoclinic, space group
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C2/c, a = 21.180(4) Å, b = 11.551(2) Å, c = 19.602(4) Å,
= 1.452 g cmꢀ3, = 1.146 mmꢀ1, 21520 reflections collected, 6287 unique (Rint = 0.0514), R1 = 0.0648,
β
= 106.06(3)o, V = 4608.4(16) Å3, Z = 4, Dcalc
ꢀ
wR2 = 0.1752 [I > 2σ(I)]. CCDC 1814445 (1) contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
RESULTS AND DISCUSSION
Description of Crystal Structure. Two types of Mn atoms (Mn1 and Mn2) are present in the
asymmetric unit of the crystal structure (Figure 1a). Mn1 is surrounded by seven oxygens from H2L2ꢀ,
L4ꢀ, and a DEF molecule, whereas Mn2 adopts a distorted octahedral geometry consisting of six oxygens
from H2L2ꢀ, L4ꢀ, and a MeOH molecule (Figure S1). To determine the exact coordination environment
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Crystal Growth & Design
around heptacoordinate Mn1, we performed a continuous shape measures (CShM) analysis.20ꢀ22 The
ideal geometry for heptacoordination involves a pentagonal bipyramid (PBPY, D5h), a capped
octahedron (COC, C3v), and a capped trigonal prism (CTPR, C2v). We calculated the SX (X = PBPY,
COC, CTPR) terms, resulting in values of 1.386, 6.497, and 5.525, respectively. From the obtained
values, we concluded that Mn1 adopts a distorted pentagonal bipyramidal geometry, which is rarely
encountered in coordination chemistry, except in sixꢀfold coordination (Figure S2).
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In terms of the structural parameters, the Mn1ꢀO lengths range from 2.141(3) to 2.488(2) Å, while the
Mn2ꢀO distances span from 2.103(2) to 2.192(2) Å. The bond angles of MnꢀOꢀMn are 99.54(9)o for
Mn1aꢀO1aꢀMn2, 110.37(9)o for Mn1aꢀO3ꢀMn2, and 117.82(10)o for Mn1ꢀO2ꢀMn2. The MnꢀMn
distances bridged by the carboxylates and oxygen atoms are 3.7876(7) Å for Mn1ꢀMn2 and 3.5645(6) Å
for Mn2ꢀMn1a. In the Mn1aꢀMn2 connection, the Mn1a atom is linked to Mn2 via two carboxylates and
one oxygen (O2) atom.
The extended structure showing the evolution of the oneꢀdimensional chain is illustrated in Figure 1b.
An octahedron connects two adjacent pentagonal bipyramids via corner or edge sharing to form an AB
stacking sequence along the chain direction. In the chain, there are two types of bridging ligands, i.e.,
H2L2ꢀ and L4ꢀ. H2L2ꢀ simultaneously binds four Mn atoms with two unprotonated hydroxyl groups,
serving as a ꢀ4ꢀbridge, whereas L4ꢀ can act as a ꢀ6ꢀbridge to connect six Mn atoms (Figure S3). Notably,
the binding mode of L4ꢀ is unique and has never been demonstrated in framework structures to the best
of our knowledge.23, 24 An additional notable feature is that such direct incorporation of the H2L2ꢀ type
ligand into a framework is unprecedented because only postꢀsynthetic exchange or postꢀsynthetic
deprotection of a pristine framework with H4L could lead to the construction of an architecture with
H2L2ꢀ.23, 24 The bridging ꢀ6ꢀL4ꢀ ligands link Mn atoms to generate oneꢀdimensional (1D) chains and
subsequently form a twoꢀdimensional (2D) sheet (Figure 1c). The sheets are interconnected by H2L2ꢀ
bridges to give a 3D structure (Figure 1d and S4). Two types of solvent molecules (MeOH and DEF)
coordinated to Mn centers are located in the square window toward the pore. In the pore, one DEF
molecule takes up two sites with an occupancy of 0.5 (Figure 1e). To assess the topology of a
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framework, the Mn2 dimer (Mn1 and Mn2b) is represented by a node, and the organic linkers of H2L2ꢀ
and L4ꢀ are denoted by a stick. The 3D network features a fiveꢀconnected hexagonal BN net with a point
symbol of {46.64} (Figure S5).25
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Phase Transformations. The PXRD data of asꢀsynthesized 1 were acquired and compared with the
simulated pattern (Figure 2). The phase purity of 1 was confirmed based on the coincidence of the
experimental and simulated patterns. To examine the structural transformability, 1 was immersed in
MeOH for five days at room temperature. The solvent was refreshed every day to ensure the complete
replacement of DEF with MeOH. The PXRD profile of the MeOHꢀexchanged sample (1a) was different
from that of 1, which indicates the formation of a new crystalline phase. While the colors of 1 and 1a
were almost identical, the single crystallinity was almost lost in 1a as confirmed by scanning electron
microscopy (Figure S6). The cell dimensions of 1 shrank upon soaking in MeOH, where the peaks in the
profile of 1a were shifted to higher 2θ angles. In the IR spectrum of 1, the peak at 1644 cmꢀ1 is assigned
to the C=O stretching band of the DEF molecule (Figure 3). This band disappeared after immersion of 1
in MeOH, indicating the removal of DEF during the MeOH exchange process, as corroborated by
elemental analysis. The pristine phase of 1 was restored by soaking 1a in DEF/MeOH for three days, as
confirmed by PXRD. The presence of the C=O peak in the IR spectrum after resolvation indicates the
incorporation of DEF into the framework of resolvated 1. Furthermore, 1a was evacuated at several
temperatures (40, 60, 120, and 150 °C) to remove the solvent molecules (Figure S7). After 1 h of
evacuation, the framework collapsed, even at room temperature, to afford the activated phase 1b. The
PXRD pattern of 1b showed no distinct peaks, demonstrating structural amorphization during the
activation process. A crystalꢀtoꢀamorphous conversion occurs when the longꢀrange structural order of
the crystalline phase is lost.13, 26 Such structural disintegration is triggered by elimination of guest or
coordinated molecules from the coordination system. Thus, herein, the pore structure was disorganized
as elucidated from the 77 K N2 sorption isotherm, where no adsorption was observed (Figure S8). The
resolvation of 1b was attempted by immersing the sample in MeOH for five days. Under this solvation
condition, the MeOHꢀexchanged phase 1a was not recovered, but the amorphous state 1b was
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Crystal Growth & Design
maintained, as demonstrated by the PXRD pattern (Figure S9). This result implies that the conversion
from 1b to 1a is irreversible. To probe the role of the solvent molecules in the crystallization process, 1b
was soaked in a mixed solvent of DEF and MeOH. Notably, as long as DEF was introduced into the
mixed solvent system, the original crystalline phase of 1 was reformed. This is in contrast with the
MeOH solvation case. It appears that the inclusion of DEF molecules into the framework plays a key
role in this amorphousꢀtoꢀcrystalline phase transformation. From the crystal structure (Figure 1e), the
DEF molecules are bonded to Mn centers and located in the square channels. The recovery of the
crystalline state seems to be initiated by DEF coordination and pore packing in the framework structure.
Framework flexibility triggered by removal and inclusion of solvent molecules commonly occurs in
concert with transformations between two crystalline states or between crystalline and amorphous
phases.13ꢀ16, 27 Furthermore, mutual interconversion among three crystalline states after treatment of
samples with different solvents and after evacuation has been reported.17ꢀ19, 28 Notably, the present
framework undergoes conversion from one crystalline state (1) to another crystalline state (1a) to an
amorphous phase (1b) and eventually back to the original crystalline state (1). Thus, such multiꢀstep
transformations including an amorphous phase are unique among solventꢀinduced phase transitions
because only phase changes between two states and among three crystalline states have been commonly
demonstrated to date.
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Magnetic Properties. The magnetic data for 1 were collected as a function of the temperature at Hdc
= 1000 Oe (Figure 4a). The
lower than the value (4.38 cm3 K molꢀ1) calculated using the parameters S = 5/2 and g = 2. As the
χ
mT value per MnII ion was 4.27 cm3 K molꢀ1 at 300 K, which is somewhat
temperature decreased, the
cm3 K molꢀ1 at 2 K.
χmT product underwent a slow downturn and then rapidly declined to 0.39
To understand the magnetic coupling between the paramagnetic centers, we probed the metric
parameters of the structure (Figure 1a). In the bridging pathway of Mn1aꢀO1aꢀMn2, the Mn1aꢀO1a bond
length is 2.488(2) Å, which is much longer than the Mn2ꢀO1a bond length of 2.174(2) Å. The longer
Mn1aꢀO1a bond length could make the magnetic contribution of the Mn1aꢀO1aꢀMn2 route negligible. In
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comparison, the Mn1aꢀO3ꢀMn2 path has shorter bond length parameters of Mn1aꢀO3 = 2.209(2) Å and
Mn2ꢀO3 = 2.132(2) Å, thereby generating an effective magnetic pathway. In this 2route, the Mn1aꢀO3ꢀ
Mn2 bond angle is 110.37(9)o. Regarding the Mn1 and Mn2 centers, the two carboxylate bridges
provide longer magnetic pathways through three atoms. Mn1ꢀO2ꢀMn2 bridged by one oxygen atom
provides a more efficient path. The relevant bond distances are 2.303(2) Å for Mn1ꢀO2 and 2.119(2) Å
for Mn2ꢀO2, and the bond angle of Mn1ꢀO2ꢀMn2 is 117.82(10)o. The metric parameters of the Mn1ꢀO2ꢀ
Mn2 route are similar to the corresponding counterparts in the Mn1aꢀO3ꢀMn2 linkage. Thus, these two
magnetic routes are considered effective pathways for magnetic coupling. From the similar bond lengths
and angles, the two magnetic paths are reasonably assumed to give an identical coupling constant.
On the basis of the structural analysis, we fitted the magnetic data of 1 to an infinite uniform chain
model with the spin Hamiltonian H = ꢀJ∑Si⋅Si+1. To include interchain interactions, the meanꢀfield
approximation (zj‘) was taken into account in the fitting process. The best result afforded values of J = ꢀ
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1.98 cmꢀ1 and zj’ = ꢀ0.2 cmꢀ1 with g fixed at 2.00. We also tried to analyze the magnetic data with two J
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(J1 and J2) systems based on H = ꢀJ1∑S2i⋅S2i+1 – J2∑S2i+1⋅S2i+2
.
A best simulation resulted in
parameters almost identical to the one J system. The negative J value suggests the existence of
antiferromagnetic coupling between the MnII ions. The experimental fieldꢀdependent magnetization data
were far below the saturation value expected from the Brillouin equation, indicating a paramagnetic
state with S = 5/2 (Figure 4b). This indicates that the Mn spins are antiferromagnetically coupled along
the chain. The overall magnetic trend of 1a is similar to that of 1, as shown in Figure S10.
CONCLUSIONS
A 3D Mn(II) framework incorporating octahedral and uncommon pentagonal bipyramidal geometries
around Mn was prepared. The organic ligands act as a ꢀ4ꢀbridge or a ꢀ6ꢀbridge depending on the degree
of deprotonation of the ligand, leading to the construction of a network structure. The framework is
highly flexible and uniquely transformable from crystalline to crystalline to amorphous to crystalline
phases upon solvent exchange, activation, and resolvation. The magnetic measurements indicate that
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antiferromagnetic interactions between the Mn spins are operative through the oxygen species of the ꢀ6ꢀ
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bridge.
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ASSOCIATED CONTENT
Supporting Information. Xꢀray crystallographic files in CIF format, additional structural data for the
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complexes. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Eꢀmail: cshong@korea.ac.kr
Author Contributions
‡These authors contributed equally.
ACKNOWLEDGMENT
This work was supported by the Korea CCS R&D Center (KCRC) grant funded by the Korean
government (the Ministry of Science, ICT, & Future Planning (MSIP)) (NRFꢀ2014M1A8A1049253),
the Basic Science Research Program (NRFꢀ2015R1A2A1A10055658), the Priority Research Centers
Program (NRFꢀ20100020209), and PAL.
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Figure 1. (a) Structure of 1 showing Mn coordination and binding modes of two types of organic
ligands (L4ꢀ and H2L2ꢀ). (b) 1D chain structure along the b axis showing two types of Mn coordination
spheres. Blue polyhedron indicates a distorted octahedron for Mn2 and pink polyhedron denotes a
distorted pentagonal bipyramid for Mn1. (c) 2D sheet formed by L4ꢀ in the bc plane. (d) 3D network
constructed by the 2D sheet in (c) and the intersheet connection of H2L2ꢀ and DEF ligands. (e)
Enlargement of the dotted box in (d) detailing the intersheet disposition of DEF molecules with
occupancy of 0.5.
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(b)
resolvated (1b -> 1)
activated (1a - > 1b)
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MeOH-exchanged (1 - >1a)
as-synthesized (1)
simulated
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θ / ο
Figure 2. (a) Schematic representation of the reversible structural transformations among 1, MeOH
exchanged, and activated samples. (b) PXRD profiles of the asꢀsynthesized, MeOHꢀexchanged,
activated, and resolvated samples.
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as-synthesized (1)
MeOH-exchanged (1->1a)
MeOH-exchanged
resolvated (1a->1)
activated (1a->1b)
resolvated (1b->1)
C=O stretching of DEF
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Wavenumber / cm-1
Figure 3. IR spectroscopic data for asꢀsynthesized, MeOHꢀexchanged, activated, and resolvated
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fitted result. (b) Fieldꢀdependence of the magnetization at 1.8 K. The solid line is the Brillouin curve for
the uncoupled Mn(II) ion.
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Synopsis
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Cyclic Structural Transformations from Crystalline to Crystalline to Amorphous Phases and Magnetic
Properties of a Mn(II)ꢀBased MetalꢀOrganic Framework
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Han Geul Lee, Hyuna Jo, Sunhwi Eom, Dong Won Kang, Minjung Kang, Jeremy Hilgar, Jeffrey D.
Rinehart, Dohyun Moon and Chang Seop Hong
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A threeꢀdimensional Mn(II) metalꢀorganic framework exhibits substantial structural flexibility
associated with phase transformations from crystalline to crystalline to amorphous states.
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