Self-assembly of novel manganese (II) compounds based on bifunctional-group ligands: Synthesis, structures, and magnetic properties

Article abstract of DOI:10.1016/j.jssc.2018.03.035

Four manganese (II) compounds are obtained by the reaction of manganese salts, triazole-derivatives and auxiliary reagents in aqueous solution or mix-solvents by routine or hydrothermal reactions. X-ray crystal structure analyses reveal that a neutral 0D compound [Mn(Hmctrz)₂(H₂O)₂] (1) (H₂mctrz = 1H-1,2,4-triazole-3-carboxylic acid) displays a centro-symmetric mononuclear octahedral entity with two Hmctrz^? anions and two water molecules; two neutral 2D clusters [Mn(Hdctrz)(H₂O)₂]_n (2) (H₃dctrz = 1H-1,2,4-triazole-3,5-dicarboxylic acid) and [Mn₂(pbtrz)(btca)]_n·4nH₂O (3) (pbtrz = 1,3-bis(1,2,4-triazol-1-yl)-propane&H₄btca = benzene-1,2,4,5-tetracarboxylic acid) possess layer structures with Hdctrz^2? linkers (2) and Mn(II)-pbtrz-Mn(II) building blocks periodically extended by μ-btca^4? connectors (3); [Mn(pbtrz)]_n·nOAc·nOH (4) shows a 3D diamond-shaped cationic framework with the anion void volume of 49.2%. Nitrogenous bases are used as the auxiliary ligand in compound 3 and the temple ligand in compounds 1, 2, and 4. Compounds 1–4 show antiferromagnetic coupling that has been fitted by different models with the molecular field approximate with D = ? 0.129(1) cm^?1 for 1, J = ? 0.354(4) cm^?1 for 2 and J = ? 0.696(6) cm^?1 for 3, respectively. The magnetic differences can be related to different superexchange interactions transmitted by the crystal lattice and/or the zero field splitting (ZFS) of the ⁶A_1g single-ion states of 1 and the syn-anti-COO^? of 2 as well as the mixed magnetic bridges of μ₁-O and μ-pbtrz-μ-COO^? of 3.

Full text of DOI:10.1016/j.jssc.2018.03.035

Author’s Accepted Manuscript
Self-assembly of novel manganese (II) compounds
based on bifunctional-group ligands: synthesis,
structures, and magnetic properties
Juan-zhi Yan, Li-ping Lu, Miao-li Zhu, Si-si Feng
www.elsevier.com/locate/yjssc
PII:
S0022-4596(18)30124-5
https://doi.org/10.1016/j.jssc.2018.03.035
YJSSC20161
DOI:
Reference:
To appear in:
Journal of Solid State Chemistry
Received date: 31 January 2018
Revised date: 19 March 2018
Accepted date: 29 March 2018
Cite this article as: Juan-zhi Yan, Li-ping Lu, Miao-li Zhu and Si-si Feng, Self-
assembly of novel manganese (II) compounds based on bifunctional-group
ligands: synthesis, structures, and magnetic properties, Journal of Solid State
Chemistry, https://doi.org/10.1016/j.jssc.2018.03.035
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Self-assembly of novel manganese (II)
compounds based on bifunctional-group
ligands: synthesis, structures, and magnetic
properties
Juan-zhi Yana,b, Li-ping Lua, Miao-li Zhua,c*, Si-si Fenga,c*
aInstitute of Molecular Science, Key Laboratory of Chemical Biology and Molecular
Engineering of the Education Ministry, Shanxi University, Taiyuan, Shanxi, 030006,
PR China.
bTaiyuan University, Taiyuan, Shanxi, 030032, PR China.
cKey Laboratory of Materials for Energy Conversion and Storage of Shanxi Province;
Shanxi University, Taiyuan, Shanxi, 030006, PR China.
miaoli@sxu.edu.cn
ssfeng@sxu.edu.cn
*Corresponding authors. Tel: ++86-351-7017974; Fax: ++86-351-7011022.
Abstract
Four manganese (II) compounds are obtained by the reaction of manganese salts,
triazole-derivatives and auxiliary reagents in aqueous solution or mix-solvents by
routine or hydrothermal reactions. X-ray crystal structure analyses reveal that a

neutral
0D
compound
[Mn(Hmctrz)2(H2O)2]
(1)
(H2mctrz
=
1H-1,2,4-triazole-3-carboxylic acid) displays a centro-symmetric mononuclear
octahedral entity with two Hmctrz anions and two water molecules; two neutral 2D
clusters [Mn(Hdctrz)(H2O)2]n (2) (H3dctrz = 1H-1,2,4-triazole-3,5-dicarboxylic acid)
and [Mn2(pbtrz)(btca)]n4nH2O (3) (pbtrz = 1,3-bis(1,2,4-triazol-1-yl)-propane &
H4btca = benzene-1,2,4,5-tetracarboxylic acid) possess layer structures with Hdctrz2
linkers (2) and Mn(II)-pbtrz-Mn(II) building blocks periodically extended by -btca4
connectors (3); [Mn(pbtrz)]nnOAcnOH (4) shows a 3D diamond-shaped cationic
framework with the anion void volume of 49.2%. Nitrogenous bases are used as the
auxiliary ligand in compound 3 and the temple ligand in compounds 1, 2, and 4.
Compounds 1−4 show antiferromagnetic coupling that has been fitted by different
models with the molecular field approximate with D = –0.129(1) cm–1 for 1, J =
–0.354(4) cm–1 for 2 and J = –0.696(6) cm–1 for 3, respectively. The magnetic
differences can be related to different superexchange interactions transmitted by the
6
crystal lattice and/or the zero field splitting (ZFS) of the A1g single-ion states of 1
and the syn-anti-COO– of 2 as well as the mixed magnetic bridges of μ1-O and
μ-pbtrz-μ-COO– of 3.
Keywords
1,2,4-triazole; Mn(II) compounds; structures; magnetism.

1. Introduction
Over the last decade, extensive researches have been carried out for the structures
and magnetic properties of coordination polymers [1−4]. Manganese compounds have
been especially investigated because the high spin ground states may be obtained
from the strong exchange interactions between the 3d electrons [5, 6]. Consequently,
manganese compounds show different types of magnetic behaviour such as
ferromagnetic [7, 8], antiferromagnetic [9−11], metamagnetic [12], spin-canting [13]
and etc. Besides the spin carrier, the judicious choice of bridging groups is also
crucial to the design of molecular magnets. As is well-known, the carboxylate group
not only transfers moderate or strong ferromagnetic or antiferromagnetic magnetic
interaction, but also constructs various interesting architectures with rich coordination
modes such as chelating, terminal and bridging syn–syn, anti–anti, or syn–anti [14,
15]. Meanwhile, 1,2,4-triazolyl groups as nitrogen-based donors have been strongly
recognized as the main factors for efficient magnetic super-exchange between the
nearest spin carriers [16] due to varied coordination characteristics [17−21], the
asymmetric tridentate bridging mode [22] as well as the well-suited distance [23−27].
Furthermore, the exocyclic substitutes of the 1,2,4-triazolate derivatives with end-on
coordination capacity, such as carboxylate-, mono- and/or di-amino, can also
synergistically assist the structural diversity [28] and magnetic interactions either by
coordination with spin carriers or by weak non-covalent interactions[19, 21, 29−31].
Up to now, most manganese complexes based on triazolate-carboxylate are reported
with either ferromagnetic or antiferromagnetic interactions [32−34]. However, it is

still full of challenges to develop structure/magnetism correlations in the design of
new magnetic materials [35]. Recently, we reported a 1D molecular chain via
tri-nuclear units [Mn3(dctrz)2(H2O)8]n, whose antiferromagnetic coupling was
transmitted by the alternating chain with μ1,2-N,N and μ1,1-O bridging magnetic chains
of H3dctrz [30]. Encouraged by the success of carboxylate and 1,2,4-triazolate bridges,
we employ chelating ligands of H3dctrz/H2mctrz/pbtrz (Scheme 1) associated with the
carboxylate or nitrogen-based ligands as the synthetic strategy to study new
manganese magnetic systems.
Here, we report the synthesis (Scheme 2), crystal structures, thermal stabilities, and
magnetic properties of four Mn(II) compounds containing 1,2,4-triazolate and
O
O
O
N
N
N
N
N
OH
OH
OH
N
N
HN
N
HN
N
N
1H-1,2,4-triazole-3,5-dicarboxylic acid 1H-1,2,4-triazole-3-carboxylic acid 1,3-bis(1,2,4-triazol-l-yl)-propane
ab. pbtrz
ab. H2mctrz
ab. H3dctrz
(I)
(III)
(II)
Scheme 1. 1,2,4-triazole derivatives
carboxylate groups, namely, [Mn(Hmctrz)2(H2O)2] (1), [Mn(Hdctrz)(H2O)2]n (2),
[Mn2(pbtrz)(btca)]n (3), and [Mn(pbtrz)]n∙nOAc∙nOH (4). In compound 1, the Mn(II)
cations are antiferromagnetically coupled via monomer model with a zero field
splitting. Compound 2 characterizes the Mn(II) chain with carboxylate bridges while
in compound 3, the mixed magnetic bridges of μ1-O and μ-pbtrz-μ-COO– present an
antiferromagnetic coupling with a long-range canted antiferromagnetic ordering.
Compound 4 shows a robust diamond-shaped framework with a larger anion void
volume.

2. Experimental
All chemicals were of standard commercial grade and were used directly without
further purification. The ligand H3dctrz was prepared and purified according to the
literature [36]. IR spectra data were recorded on a BRUKER TENSOR27
spectrometer with KBr disks. Elemental analyses for C, H and N were performed on a
CHN-O-Rapid instrument. Powder X-ray diffraction (PXRD) patterns were collected
on a Bruker D8 Advance X-ray diffractometer using Cu-Kα radiation (λ = 1.540598 Å)
at 30 kV and 15 mA. The simulated patterns of 14 were derived from free Mercury
Version 2.2 software. Thermogravimetric (TG) studies were carried out on a Dupont
thermal analyzer with temperature range 298−1073 K under N2 flow with a heating
rate of 20 K min−1. Variable temperature (1.8−300 K) magnetic susceptibilities of
crystalline samples of the complexes were measured on a Quantum Design MPMS
SQUID magnetometer with an applied field of 1000 Oe.
2.1. Synthesis of [Mn(Hmctrz)2(H2O)2] (1)
MnCl2·4H2O (0.198 g, 1.0 mmol) in 3.0 mL of aqueous solution was slowly added
into a flask containing H3dctrz (0.078 g, 0.5 mmol) and pbtrz (0.08 g, 0.5 mmol) in
10.0 mL of aqueous solution. The reacting solution was kept stirring for 6.0 h. The
precipitate was filtrated, and colourless crystals were isolated from the filtrate within
6 weeks. Yield: 0.164 g (52.2% based on Mn(II)). Elemental analysis (EA) for calcd.
1 (C6H8N6O6Mn, 315.12): C 16.96, H 1.78, N 22.25; found: C 17.34，H 1.94, N
21.22%. IR (cm−1, s = strong, m = medium, w = weak): 3361s, 3122s, 1625s, 1476s,
1411s, 1368w, 1353w, 1296s, 1162w, 1012m, 984w, 892w, 841m, 670m.

2.2. Synthesis of [Mn(Hdctrz)(H2O)2]n (2)
NaHCO3 (0.042 g, 0.5 mmol) in 5.0 mL of aqueous solution was added into a flask
containing aqueous solution of H3dctrz (0.078 g, 0.5 mmol) with stirring,
MnCl2·4H2O (0.198 g, 1.0 mmol) powder was directly added, and then a 4.0 mL of
phen (0.10 g, 0.5 mmol) ethanol solution was added dropwise. The resulting solution
was kept stirring for 6.0 h. The precipitate was filtrated, and colourless crystals were
isolated from the filtrate within 4 weeks. Yield: 0.114 g (46.4% based on Mn(II)). EA
calcd. for 2 (C4H5N3O6Mn, 246.05): C 19.53, H 2.05, N 17.08. Found: C 19.72, H
2.59, N 16.87%. IR (cm−1): 3221s, 3101s, 1619s, 1517m, 1496m, 1454m, 1404s,
1356w, 1300s, 1162w, 1056s, 905w, 828m, 813w, 729m, 661m, 600w.
2.3. Synthesis of [Mn2(pbtrz)(btca)]n4nH2O (3)
A 5.0 mL methanol solution of MnCl2·4H2O (0.396 g, 2.0 mmol) was added into a
10.0 mL aqueous solution of pbtrz (0.179 g, 1.0 mmol) in a flask with stirring and
then a 5.0 mL aqueous solution of H4btca (0.051 g, 0.2 mmol) and N(C2H5)3 (50.0 μL)
was dropped to the above mixture. After 4h, the resulting solution was filtrated, and
colorless crystals were isolated from the filtrate within 4 weeks. Yield: 0.290 g
(43.7% based on Mn(II)). EA calcd. for 3 (C17H26N6O15Mn2, 664.32): C 30.74, H 3.94,
N 12.65. Found: C 31.25, H 4.07, N 11.57%. IR (cm−1): 3400s, 3200m, 3108m,
2295w, 1625s, 1420m, 1384s, 1340s, 1131m, 981w, 809m, 668m, 538m.
2.4. Synthesis of [Mn(pbtrz)]nnOAcnOH (4)
A mixture of pbtrz (0.090 g, 0.5 mmol), C6H4(NH2)(SO3H) (0.017 g, 0.1 mmol),
Mn(OAc)2·4H2O (0.245 g, 1.0 mmol), KOH (2.0%, 30 uL), CH3OH (8.0 mL) and

DMF (1.0 mL) was sealed in a 25.0 mL Teflon-lined stainless steel autoclave and
heated at 383 K for 3 days, and then slowly cooled to room temperature. Colourless
crystals of 4 were obtained, and the yield was 0.174 g (56.3% based on Mn(II)). EA
calcd. for 4 (C9H14N6O3Mn, 309.20): C 34.96, H 4.56, N 27.18. Found: C 35.12, H
4.09, N 26.87%. IR (cm−1): 3433m, 3108s, 1670s, 1524s, 1384s, 1280m, 1218w,
1139s, 1103w, 1043w, 981w, 885w, 668m.
2.5. X-ray crystallography
Single-crystal X-ray diffraction data for compounds 1, 4 were collected in Beijing
Synchrotron Radiation Facility (BSRF) beamline 3W1A which mounted with a
MARCCD-165 detector (λ = 0.72000 Å) with storage ring working at 2.5 GeV. In the
process, the crystal was protected by liquid nitrogen at 100(2) K. Data were collected
by the program Marccd and processed using HKL 2000 [37]. The data of the
compounds 2, 3 were collected on a Bruker Smart Apex II with CCD area detector
diffractometer Mo-Kα (λ = 0.71073 Å) at room temperature. Cell parameters were
determined using SMART software [38]. Data reduction and corrections were
performed using SAINTPlus. Absorption corrections were applied by using the
multi-scan program SADABS [38]. All the structures were solved by the direct
methods and refined by the full-matrix least-squares technique using the
SHELXS-2014 [38]. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms except those of water molecules were generated geometrically and
refined isotropically using the riding model. Due to the highly disordered OH– and
CH3COO– in 4, their contribution to densities was modelled using the SQUEEZE

routine in PLATON [39]. The crystallographic data for the four compounds are listed
in Table 1, and the selected bond lengths and angles are shown in Tables S1 and
hydrogen bonding data are given in Table S2.
Table 1. Crystal data and structure refinement parameters for compounds 1−4
Compounds
1
2
3
4
CCDC
1060382
1060383
1060384
1060385
Formula
Fw
C6H8N6O6Mn
315.12
C4H5N3O6Mn
246.05
C17H26N6O15Mn2 C27H42N18O9Mn3
664.32
296(2)
927.60
100(2)
0.72000
Cubic
T/K
100(2)
298(2)
Wavelength/Å
Crystal system
Space group
a /Å
0.72000
Monoclinic
P21/c
0.71073
Monoclinic
P21/c
0.71073
Triclinic
Ia3d
P1
9.177(2)
8.775(2)
6.855(1)
90
7.160(1)
10.212(1)
10.518(1)
90
9.696(2)
26.600(3)
26.600(3)
26.600(3)
90
b /Å
11.612(1)
11.637(1)
85.406(1)
89.370(1)
75.167(1)
1262.37(5)
2
c /Å
α/°
β/°
93.13(3)
90
95.256(1)
90
90
γ/°
V/Å3
90
551.2(1)
2
765.7(1)
4
18821(6)
16
Z
Dc /g∙cm−3
μ/mm−1
1.899
2.134
1.748
1.309
1.236
1.736
1.086
0.879
F(000)
318
492
680
7632
Rint
0.0315
0.0363
0.038
0.0533
0.1022/0.3079
0.1109/0.3246
1.520
R1/wR2(I> 2σ(I))a
R1/wR2(all data)b
GOF on F2
ρmax, min,/eÅ−3
0.0372/0.1308
0.0427/0.1466
1.041
0.0242/0.0590
0.0306/0.0620
1.074
0.0420/0.0943
0.0714/0.1047
1.002
0.569, −0.655
0.247, −0.253
0.899, −0.732
2 2
0.941, −0.663
a
b
2
o
2
o
2
o
1/ 2


R1  Fo  Fc / Fo


wR 2 [ w(F  F ) / w(F ) ]
.

3 Results and discussion
3.1. Synthesis
H3dctrz is a simple planar hepta-dentate ligand with a delocalized multi--electron
backbone [30]. The ligand can not only be partially or fully deprotonated (H2dctrz−,
Hdctrz2−, & dctrz3−) under different pH values, but also decompose and lose one or
two carboxylates in synthesis reactions. In our previous work [30], we proposed a
nlm
hijk
M
pattern designator(
) to specify the rich coordination modes of H3dctrz, where
sign M for the number of coordinated metal atoms, nlm and hijk for the position and
the number of donors coordinated N and O atoms. The ligand H2mctrz in 1 is a
decarboxylate of H3dctrz, which loses one carboxylate to ingenious structures [6, 40,
41]. In compound 2, H3dctrz is partially deprotonated to form Hdctrz2−, and we find a
3001
new coordinated mode: 1110 , which is different from reported complexes
3110
2001
[Mn3(dctrz)2(H2O)8]n( 2001) [30] and [Mn(Hdctrz)(H2O)3)]n ( 0110) [42]. Compared with
H3dctrz, pbtrz is a flexible double triazole ligand, in which four potential coordination
sites can connect the metal cations to high-dimensional frameworks and –CH2 groups
can provide different conformations such as anti–anti, anti–gauche, and
gauche–gauche [43−45]. Both ligands can bridge metal cations through 1,2,4–triazole
or carboxylate groups to form diversity structures [33]. The second ligands such as
nitrogen-based one can result in the spatial extension to build more complicated
structures, and further change intra- and inter- magnetic interactions of the complexes.
Moreover, they can also act as the temples to bring out H4btca to employ eight oxygen
donors from carboxylate group to spread the structural unit and to form a 2D

coordination polymer. However, in compounds 1, 2 and 4 nitrogen-based ligands act
as the templates, without of which, the compounds cannot be obtained under the same
conditions. Compounds 13 are synthesized under ambient condition while 4 is
formed under the solvothermal reaction with mild temperature (383 K), indicating that
high temperature is favourable to form this structure.
Scheme 2. Synthesis routes of 14
Triazole
derivatives
Mangancse
salts
Nitrogenous
bases
Second
ligands
Products
Dimension
RT
1) H3dctrz
+
MnCl2
+
+
pbtrz
+
H2O
H2O
[Mn(Hmctrz)2(H2O)2]
[Mn(Hdctrz)(H2O)2]n
1
2
3
4
0D
2D
2D
3D
RT
RT
2)
+
H3dctrz
+
+
MnCl2
MnCl2
N
N
3) pbtrz
4) pbtrz
+
N(C2H5)3 + H4btca
[Mn2(pbtrz)(btca)]n.4nH2O
[Mn(pbtrz)]n.nOAc.nOH
383 K
+
Mn(OAc)2 +
H2N
SO3H
Solvothemal
3.2. FT-IR spectra
The IR spectra of these compounds display the characteristic bands of the hydroxyl,
trazole and carboxylate groups. Compounds 1–4 show strong broad bands around
3361, 3221, 3400 and 3442 cm–1, respectively, suggesting the presence of O–H and
N–H groups (Fig. S1). The strong absorption peaks, 1476 cm–1 (1), 1496 cm–1 (2),
1427 cm–1 (3) and 1524 cm–1 (4), are attributed to the C=N stretching vibration of the
triazole ring. In fact, the IR absorption of carboxylate group is very complicated due
to its coordination diversity with metal cations. The characteristic bands of the
carboxylate groups in 1–3 appear in the usual region. The characteristic multiple
bands for the asymmetric (νas) and symmetric (νs) stretching vibrations of the

carboxylate groups are observed between 1600 and 1400 cm−1, and their different
separations (Δν = νas − νs) suggest the presence of the mono-dentate, bi-dentate
chelating and bridging modes of the carboxylate groups [46]. Interestingly, in
compound 4, strong bands occurring at approximately 1670 cm–1 and 1384 cm–1
suggest that the CH3COO– anion is not involved in the coordination, which is in good
agreement with its structure from single crystal X-ray diffraction data.
3.3 Structure description
Crystal Structure of [Mn(Hmctrz)2(H2O)2] (1). H2mctrz is not in the initial recipes
(Scheme 2). It is formed by the decarboxylation reaction of H3dctrz under acidic
conditions. Compound 1 crystallizes in the monoclinic P21/c space group with
centrosymmetric mononuclear molecule (Fig. 1a). It is assembled into a 3D
supramolecular network by abundant hydrogen-bonding interactions (Fig. 1b). The
asymmetrical unit of 1 contains one crystallographic independent Mn(II) cation, one
deprotonated Hmctrz− and one terminal coordinated water molecule. Each Mn(II)
cation, locating on the inversion center, has octahedral coordination geometry
(MnN2O4) from two nitrogen (N1 & N1i) and two oxygen (O1 & O1i) of two
symmetry-related Hmctrz− ligands in the equatorial plane and two oxygen (O3 & O3i)
of two water molecules in the axial sites. All the bond distances and angles fall in the
normal range [18, 24, 47, 48]. The axial distance of Mn–O (2.190(2) Ǻ) is slightly
longer than that of isostructural compound [Zn(Hmctrz)2(H2O)2] (2.133(1) Ǻ), and
shorter than that of [Cu(Hmctrz)2(H2O)2] (2.400(3) Ǻ) [49] which is due to

Fig. 1. (a) Coordination environment of Mn(II) in 1 with 30% thermal ellipsoids, symmetry code:
i 1–x, –y + 2, –z. (b) 2D supra-molecular layer structure via H-bonds of 1 (Cyan: Mn; Red: O;
Grey: C; Blue: N)
Jahn-Teller effect of Cu(II) cation.
As shown in Fig. 1b and Table S2, there are strong O–H···O hydrogen bonds [50]
(2.729(3) Ǻ, 2.714(3) Ǻ) between carboxylate oxygen and coordinated water
molecules. These O–H···O interactions assemble the basic [Mn(Hmctrz)2(H2O)2] unit
into 2D layer structures paralleling to the crystallographic ac plane. The neighboring
2D layers stack in ABAB mode (Fig. 1b). The N–H···O interactions with a distance
of 2.717(4) Ǻ between neighboring layers build 2D structures into a 3D
supramolecular architecture. The strong hydrogen bonds might prevent nitrogen
atoms of 1- and 2-positional triazole from coordinating to Mn(II) even though
nitrogen atoms are strong donors [49].
Crystal Structure of [Mn(Hdctrz)(H2O)2]n (2). Compound 2 crystallizes in the
monoclinic P21/c space group and displays a 2D network sheet which is constructed
by Mn(II)-Hdctrz2− layers, exhibiting a 2D 3-connected symbolized as 63 topological

structure. There is one crystallographic independent Mn(II) cation, one deprotonated
Hdctrz2− anion and two coordinated water molecules in the asymmetrical unit.
As shown in Fig. 2a, Mn(II) cation in 2 is surrounded by one nitrogen (N1) and
three oxygen (O1, O2i & O3ii) from two individual Hdctrz2− anions and two
coordination water molecules (O5 & O6), forming a distorted octahedral coordination
arrangement (MnNO5), in which the Mn–O distances of 2.124(1)–2.244(1) Å are
slightly shorter than that of Mn–N separations (2.260(1) Å,).
Each ligand Hdctrz2− connects three Mn(II) cations to construct a tetranuclear
cluster [Mn4(Hdctrz)4] in two different bridging fashions: the one syn-anti-2-η1:η1
Fig. 2. (a) Coordination environment of Mn(II) in 2 with 30% thermal ellipsoids, symmetry
codes: i x, –y + 5/2, z + 1/2; ii –x + 1, y + 1/2, –z + 3/2. (b) View of 2D polyhedrons of MnNO5
and network sheets (the red line shows the Mn–OCO–Mn chain). (c) 2D 3-c (63) topologic
network.
carboxylate with Mn1···Mn1i distances of 5.955(1) Å, and the other 2-N1,
O3-Hdctrz2− through(–N–C–C–O–) connection with Mn1···Mn1ii distances of

7.069(1) Å (Fig. 2a and relative symmetry codes). Then, [Mn4(Hdctrz)4] unit joins
each other via the Hdctrz2− to build 2D network sheets paralleling to the
crystallographic bc plane (Fig. 2b). Furthermore, together with the carboxylate O and
triazole N atoms, two coordinated water molecules reinforce the network by hydrogen
bonds to carboxylate oxygen. Taking Mn(II) cations as 3-connected nodes and two
parallel Hdctrz2− (Mn···Mn, 9.618(2) Å) and COO− (Mn···Mn, 5.955(1) Å) as linkers,
the 2D polymeric layer can be simplified to a 3-connected symbolized as (63)
topologic network (Fig. 2c).
Crystal Structure of [Mn2(pbtrz)(btca)]n4nH2O (3). X-ray diffraction analysis
indicates that compound 3 also forms a 2D network sheet in which µ2-pbtrz ligand
coordinate with Mn(II) forming subunits periodically, then they are extended by
µ6-btca4– connectors. The asymmetric unit of 3 contains two crystallographic
independent Mn(II) cations, one neutral pbtrz ligand, two half deprotonated btca4–
anions, three coordinated water molecules and four disordered lattice water
molecules.
As shown in Fig. 3a, both Mn(II) cations adopt distorted octahedral geometries with
MnNO5 donor sets. The Mn1 octahedron is well defined by one triazolyl nitrogen
(N1), two carboxylate oxygen (O3 & O8) from the different btca4– anions and three
oxygen atoms (O9, O10 & O11) from coordinated water molecules. The Mn2 cation
is coordinated by one triazolyl nitrogen (N6ii), four carboxylate oxygen atoms (O1,
O2, O7 & O2i) from two different btca4– anions and one sharing oxygen atom O9
from coordinated water. The bond lengths of Mn–N and Mn–O are comparable to

other Mn(II) complexes mixed pbtrz and carboxylate ligands [1,3,22]. Each pair of
MnNO5 octahedron forms a dimer via corner-sharing, in which both Mn(II) cations
are bridged by one μ1,1-O9 water molecule and two μ1,3-OCO carboxylates group.
That is, two carboxylate groups with the μ2-η1:η1-OCO chelating fashion, together
with one μ1,1-O9 atom serving as two Mn(II) cations, and Mn1–O9–Mn2 angle is
109.03(1)°. The neighbor Mn(II) cations with the Mn2···Mn2i distance of 5.646(1) Å.
Thus, two dimers are linked by two pbtrz and two neighbor carboxylates (in the
μ1-η1:η0 coordination mode) from btca4– forming the Mn2btca-COOn– (Mn2N2O7)
closed loops (SBU-1) with the Mn1···Mn2 distance of 3.708(1) Å, and the ligands
together with four Mn(II) cations in the tetramer cage have a parallelogram
conformation with the Mn2···Mn2ii distance of 5.711(1) and Mn1···Mn2ii 7.338(3) Å.
Further these cages make up of a layered organic-inorganic sheet via meta- and
para-carboxylates in directions of a and b axis respectively to form 2D chair modes
(Fig. 3b).

Fig. 3. (a) Coordination environments of Mn(II) in 3 with 30% thermal ellipsoids and lattice
water are omitted for clarity, symmetry codes: i –x + 1, –y + 1, –z + 1; ii x, y, z + 1 (b) View of 2D
polyhedron MnNO5 and network sheets with chair modes. (c) View of 2D 4-c (42.62) topologic
network
From the topological point of view, each Mn(II) center can be regarded as a
4-connecting tetrahedral node, while btca4– and pbtrz ligands serve as linear linkers.
As a result, the whole framework of 3 is reduced to a 2D 4-connected (44.62)-net layer
(Fig. 3c), which is further extended by strong N–H···O and O–H···O hydrogen bonds
to form a 3D supramolecular architecture.
Crystal Structure of [Mn(pbtrz)]nnOAcnOH (4). Compound 4 crystallizes in the
cubic space group Ia3d , which is assembled into a 3D diamond shaped network with
1D channels. The asymmetric unit of 4 has one crystallographic independent Mn(II)
cation, a half neutral pbtrz ligand, one OH– and one CH3COO– (Fig. 4a). By contrast
with 1, 2 and 3, each Mn(II) is four-coordinated with the donor set MnN4 by two
individual pbtrz ligands with -N1,N4-trz cis-binding mode. The difference attributes
to 1,3-bis(1,2,4-triazol-1-yl)-propane in which flexible –(CH2)3– spacers allow the
triazolyl group to bend and rotate freely, then form the coordination geometries of
metal cations [51, 52]. The distortion angles (105.8(3)–112.6(3)°) around the Mn(II)
center indicate that the central Mn(II) cation lies in distorted tetrahedral geometry.
The Mn–N (2.028(5), 2.039(5) Å) bond lengths are comparable to those of reported
Mn(II) compounds [24, 53].

Each pbtrz ligand links three Mn(II) cations and each Mn(II) cation connects three
pbtrz ligands. As a result, the cubic networks are formed with two kinds of closed
channels, cross-sectional area about 5.92×14.3 and 7.2×13.6 Å2 respectively (ignoring
hydrogen atoms) (Fig. 4b). However, these channels are occupied with disordered
OH– and CH3COO– which act as counter anions to balance the charges (Fig. 4c).
PLATON calculations [39] after removal of the disordered anions show that the
potential anion exchange volume of 4 is estimated to 3068.3 Å3, which constitutes
approximately 49.2% of the unit cell volume. Due to the presence of
3
crystallographic symmetry, the packing of 4 along the crystallographic [111] axis
created windmill-like cavity is shown in Fig. 4d. Topologically, by depicting Mn(II)
cations as 4-connectors nodes, pbtrz ligands as linear linkers, the structure can be
described as a 3D 4-connected (42.62.82) network (Fig. 4e).

Fig. 4. (a) Coordination environments of Mn(II) in 4 with 15 % thermal ellipsoids. Part of H
atoms and non-coordinated OH– and CH3COO– are omitted for clarity. Symmetry codes: i 1/4 – x,
–1/4 + z, 1/4 + y; ii –1/2 + z, + x, 1/2 – y; iii 3/4 – z, 1/4 – y, 1/4 + x; iv –1/4 + z, 1/4 – y, 3/4 – x; v
1/4 – y, 1/4 –x,5/4 – z; vi 1/4 –y, 1/4 + x, 3/4 – z (b) Unit cell packing diagrams with polyhedron
MnN4 viewed a axis. (c) Showing the closed channels with the counter anions and the OH– anions
adopt ball mode. (d) The illustration of 3D supermolecular frameworks of 4 is shown with
windmill-like channel along the crystallographic [111] direction. (e) Schematic representation of
the 4-c (42.62.82) network.

3.4. PXRD and thermal analysis
PXRD patterns were obtained to check the purity of compounds 1−4 (Fig. S2). All
the peaks displayed in the experimental patterns are similar to those in the simulated
patterns generated from single-crystal diffraction data, demonstrating single phases.
TG analyses were performed on crystalline samples of compounds 1−4 to study
their thermal stability (Fig. S3). TG curve of 1 shows a weight-loss of 10.7% (calcd:
11.2%) from 405 to 486 K corresponding to the release of two coordinated water
molecules. Compound 1 begins to collapse at 895 K. Compound 2 exhibits a
continuous two-step weight-loss stage from 453 K to 718 K corresponding to the
collapse of the framework. Compound 3 displays a two-step weight-loss process. The
first one is located on 393 K to 420 K due to the loss of two disordered lattice water
molecules (calcd. 5.4%, found 5.6%). Once the temperature is higher than 643 K, the
layered framework of 3 is broken, accompanying the decomposition of the compound.
For 4, a weight-loss of 7.1% in 298–661 K range is consistent with the removal the
counter anions OH– and CH3COO– as the relevant H2O and CO2 molecules (calcd.
7.1%). The 3D framework begins to collapse above 661 K.
3.5. Magnetic properties
Variable-temperature magnetic susceptibilities of 1–4 were measured in the range
–1
of 1.8–300 K under 1000 Oe and plots as χmT, χm and χm vs. T of 1–4 are shown in
Figs. 5–8 Because of the various distinctions of topologies, their magnetic properties
are very different.

[Mn(Hmctrz)2(H2O)2] (1). As shown in Fig. 5, the χmT value of 1 is 4.91
cm3·K·mol–1 at 300 K, corresponding to the expected one Mn(II) cation for an
isolated S = 5/2 (4.38 cm3·K·mol–1). Upon cooling, the χmT product of 1 steadily
decreases from 300 to 20 K and then abruptly down to 3.33 cm3·K·mol–1 at 1.8 K.
The behaviour is consistent with dominant antiferro-magnetic interactions. The plot of
χm–1 vs. T shows that 1 follows the Curie-Weiss law with C = 4.94 cm3·K·mol–1 and θ
= –0.58 K, an indication of antiferromagnetic coupling between the Mn(II) units.
Although compound 1 characterises chains of Mn(II) cations through the hydrogen
bonds with Mn–OCO–Mn, the –OCO– bridge is very long (7.100 Å). Therefore, the
coupling through this bridge is negligible. Accordingly, the decrease of the χMT below
10 K is most likely due to weak antiferromagnetic interactions between Mn(II) ions
6
transmitted in the crystal lattice and/or the zero field splitting (ZFS) of the A1g
single-ion states.
Fig. 5. Temperature dependence of χm, χmT, and 1/χm collected in an applied field of 1000 Oe for
compound 1. The red solid line represents the best fittings.
To explain magnetic properties of compound 1 composed of mononuclear Mn(II),
we use Eq. (1) including ZFS effect within the S = 5/2 local ground states of the Mn(II)
cations corrected by the factor predicted from the molecular field (Eq. 2) [54−56]:

Ng2 2 1 9exp(2D/kT)  25exp(6D/kT)


(1)
(2)
ZFS



4kT
1 exp(2D/kT)  exp(6D/kT)


m
2zJ'
N 2g2
mcorr

1
 m
In the Eqs. (1) & (2), zJ’ is the intermolecular exchange parameter; z is the number
of nearest neighbour Mn(II) centers; D is the axial ZFS parameter for Mn(II), and the
other symbols have their usual meaning. A least-squares fitting of the experimental
data for 1 leads to g = 2.085(2), D = –0.129(1) cm–1, zJ’ = – 0.067(1) cm–1 and R =
2.24×10–4. The criterion used in determination of the best fit is based on minimization
of the sum of squares of the deviation: R = ∑[(χmT)obsd – (χmT)calcd]2/[(χmT)obsd]2. This
model reproduces very satisfactorily the magnetic properties of this compound in the
whole temperature range (Fig. 5). Note that although this D value is within the normal
range observed for isolated Mn(II) cations [57], it could include a very weak AF
interaction. The negative D and θ values indicate AF exchange interactions between
nearest-neighbour Mn cations in 1.
[Mn(Hdctrz)(H2O)2]n (2). The χmT product of 2 is 4.70 cm3·K·mol–1 at 300 K (Fig.
6), which is slightly higher than the excepted value (4.38 cm3·K·mol–1) for one
magnetically uncoupled Mn(II) cation with S = 5/2 and g = 2.0. The χmT value of 2 is
a slightly decrease to 4.44 cm3·K·mol–1 from 300 to 60 K. With a further decrease in
temperature, the value of the χmT product decreases sharply, reaching a minimum
value of 1.90 cm3·K·mol–1 at 1.8 K. The magnetic susceptibility data follow the
Curie–Weiss law above 2.0 K with a negative Weiss temperature θ = –4.59 K and
Curie constant C = 4.77 cm3·K·mol–1. The negative Weiss temperature suggests the
presence of antiferromagnetic exchange interactions inside the Mn(II) dimer.

5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.8
0.6
0.4
0.2
0.0
70
60
50
40
30
20
10
0

C = 4.77 cm3mol-1
 = - 4.59K

(2.0 - 300 K)

0
50 100 150 200 250 300
T / K
0
50
100
150
200
250
300
T / K
Fig. 6. Temperature dependence of χm, χmT, and 1/χm collected in an applied field of 1000 Oe
–1
for 2. The red solid lines represent the best fittings. Inset: temperature dependence of χm
.
To evaluate the exchange coupling, we have to identify the dominant interaction
pathways in the metal–organic framework. As described in Fig. 2, though compound
2 is a 2D structure, the shortest Mn···Mn distance (7.069(1) Å) through the H3dctrz
bridge is longer than that through –OCO– bridge. So we suppose that magnetic
interactions dominantly come from Mn–OCO–Mn chains, in which spin Heisenberg
model for a one-dimensional chain or Fisher Model [58, 59] as Eqs. (3) & (4) is
suitable for 2.
NA g2B2S(S 1) 1 u
(3)


chain




3kT
1 u

where u is the Langevin function:
JS(S 1)
kT
u  coth

kT
S(S 1)
(4)
In order to take into account the intramolecular interactions in the 2D structure, the
mean-field approximation zJ′ is introduced shown in the Eq.(5) [59].
chain
M

2zJ'chain
1
Ng2 2
(5)
The best least-squares fitting of the magnetic susceptibility data presents g = 2.0898,
J = –0.354(4) cm–1, zJ′ = –0.413(2) cm–1, R = 1.26×10–4. The theoretical curves
match the experimental data very well. The J and zJ′ values confirm that the weak

antiferromagnetic couplings between intra- and interactions of Mn–OCO–Mn chains.
However, it should be noted that the fitted values for J and zJ′ are only qualitatively
valid, because their comparability in magnitude does not meet the requirement of the
molecular field approximation that zJ′ should be much smaller than J [12]. All of
these observations characterize the AF interactions in compound 2.
[Mn2(pbtrz)(btca)]n4nH2O (3). The experimental χmT value at 300 K is 9.65
cm3·K·mol–1 (Fig. 7), which is a little smaller than that expected for a non-interacting
pair antiferromagnetic interactions operating in 3. The temperature dependence of the
–1
reciprocal susceptibilities χm obeys the Curie–Weiss law above 2.0 K with a Weiss
constant θ = –10.17 K, Curie constant C = 10.0 cm3·K·mol–1, indicating
antiferromagnetic interactions in 3.
Fig. 7. Temperature dependence of χm, χmT , and 1/χm collected in an applied field of 1000 Oe for
–1
3. The red solid line represents the best fittings. Inset: temperature dependence of χm
.
Structurally, the Mn1···Mn2 separation within a pair of corner-sharing octahedron is
3.698(1) Å, which is smaller than those of 5.646(1) and 6.902(1) Å based on two
bridges (pbtrz & btca4–) with zigzag projection on the bc plane. It could be presumed

that the main magnetic interactions come from Mn1 and Mn2 cations of
corner-sharing octahedron, therefore, the magnetic interactions of 3 can be further
simplify to a binuclear model with spin Hamiltonian H = –2JS1S2, in which the
molecule field approximation can be introduced to evaluate the weak superexchange
interaction transmitted by pbtrz and btca4– bridges. The experimental molar magnetic
susceptibilities of 3 can be quantitatively fitted by the following Eqs. (6) & (7).
2Ng22 A
(6)
dimer

kT
B
A  55exp 30x30exp 20x14exp12x5exp 6xexp 2x
B 11exp 30x9exp 20x7exp12x5exp 6x3exp 2x1
x = J/kT
dimer
2zJ'dimer
Ng2 2
M

1
(7)
The best least-squares analysis of the magnetic susceptibilities data leads to g =
2.011(6), J = –0.696(6) cm–1, zJ′ = 0.006 (1) cm–1, R = 1.99×10–4. The negative J
value suggests weak antiferromagnetic interactions between the adjacent Mn(II)
cations in 3, which is also verified by the negative θ value.
[Mn(pbtrz)]nnOAcnOH (4) As shown in Fig. 8, the observed χmT value for per
Mn(II) unit of 4 is 34.22 cm3·K·mol–1. It decreases almost linearly to 0.31
cm3·K·mol–1 at 2.0 K when lowering the temperature. The behavior is clearly
indicative of strong antiferromagnetic interactions between the Mn(II) centers. The
result is similar to the previous magnetic study of 64 Fe3+ ions of
{[Fe8O3(tea)(teaH)3(HCOO)6]8(HCOO)12}(ClO4)123CH3OH36H2O
[60].
No
satisfactory fit of the data is obtained now.

Fig. 8. Temperature dependence of χm and χmT collected in an applied field of 1000 Oe for 4.
Apparently, interesting antiferromagnetic couplings with variable strengths are
observed in the compounds 1–4, which are significantly due to different
superexchange interactions transmitted by the crystal lattice and/or the ZFS of the
6A1g single-ion states of 1 and the syn-anti-COO– of 2 as well as the mixed magnetic
bridges of μ1-O and μ-pbtrz-μ-COO– of 3. As we known, the bridging ligand can
transfer magnetic exchange interactions through σ as well as π pathways, and a linker
with only σ-bonding is a significantly weaker mediator [61]. For the present two
compounds, the magnetic interactions are only mediated through σ pathway, which
will result in weak antiferromagnetic interaction as observed.
4. Conclusion
In summary, four manganese magnetic samples based on 1,2,4-triazole and/or
carboxylate bridges are designed and synthesized by control the temperature and/or
the addition of co-ligands or nitrogenous bases. The templates as well as the pH value
are key factors in determining the fundamental motifs and the dimensionality of the
compounds based on H3dctrz and the Mn(II) cation. It is found that the pbtrz can
change the angles to meet the requirements of coordination and H4btca has been
successfully trapped in the neutral Mn(II) compound 3. The antiferromagnetic

couplings with variable strength are observed in the nearest neighbours of 1–4. In
addition, compound 4 is a potential anion exchange material with the anion void
volume 49.2% calculated by PLATON.
Supporting Information
X-ray crystallographic data for compounds 1−4 in CIF format (CCDC
1060382–1060385), selected bond lengths and bond angles, the figures of IR, PXRD
and TG analysis are presented.
Acknowledgements
We acknowledge Zeng-Qiang Gao (BSRF) for the help of single-crystal X-ray
diffraction data collection of 1 and 4 (line 3W1A), and acknowledge the financial
support by the Natural Science Foundation of China (Grant Nos 21571118, 21201113
& 21671124). A portion of this work was performed on the Scientific Instrument
Center of Shanxi University of China.
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