Transformation of maleato manganese(II): Temperature effect and coordination modes

Article abstract of DOI:10.1016/j.poly.2004.01.005

Two maleato bipyridine manganese(II) coordination polymers [Mn(male)(bpy)(H₂O)]_n·2nH₂O (1) and [Mn(male)(bpy)]_n (2) (H₂male=maleic acid, bpy=2,2 ^′-bipyridine) were prepared in an ice-bath and at room temperature respectively, and were spectroscopically and structurally characterized. Complex 1 obtained at low temperature, possesses a one-dimensional helical chain in the solid state with hepta-coordination number at the manganese center. At room temperature, the hydrated complex 1 was irreversibly converted into the thermodynamically stable dehydrated product 2 with octahedral coordination. A similar dehydration effect was observed for the maleato manganese(II) complex with a more conjugated phenanthroline (phen) ligand. The maleato manganese(II) coordination polymer [Mn(male)(phen)] _n·nH₂O (3) can be converted into the dehydrated product [Mn(male)(phen)]_n (4) upon heating, while the resultant product retains a similar pattern of coordination mode.

Full text of DOI:10.1016/j.poly.2004.01.005

Polyhedron 23 (2004) 987–991
www.elsevier.com/locate/poly
Transformation of maleato manganese(II): temperature effect
and coordination modes q
*
Hong-Bin Chen, Hui Zhang, Jin-Mei Yang, Zhao-Hui Zhou
Department of Chemistry and State Key Laboratory for Physical Chemistry of Solid State Surface, Xiamen University, Xiamen 361005, China
Received 20 July 2003; accepted 11 December 2003
Abstract
Two maleato bipyridine manganese(II) coordination polymers [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O (1) and [Mn(male)(bpy)]n (2)
(H2male ¼ maleic acid, bpy ¼ 2,20-bipyridine) were prepared in an ice-bath and at room temperature respectively, and were spec-
troscopically and structurally characterized. Complex 1 obtained at low temperature, possesses a one-dimensional helical chain in
the solid state with hepta-coordination number at the manganese center. At room temperature, the hydrated complex 1 was irre-
versibly converted into the thermodynamically stable dehydrated product 2 with octahedral coordination. A similar dehydration
effect was observed for the maleato manganese(II) complex with a more conjugated phenanthroline (phen) ligand. The maleato
manganese(II) coordination polymer [Mn(male)(phen)]n ꢀ nH2O (3) can be converted into the dehydrated product [Mn(male)(phen)]n
(4) upon heating, while the resultant product retains a similar pattern of coordination mode.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Manganese maleate; Coordination polymer; Temperature effect; Helical architecture; Hydrogen bonds; p–p interactions
1. Introduction
sembled in the crystalline phase. This is because the self-
assembly processes are heavily influenced by subtle
factors, such as templates [2], choice of solvents and
counterions [3], and pH values [4]. When the reaction
conditions are deliberately controlled, infinite networks
with novel topologies can be gained. Though it was clear
long ago that temperature can dramatically affect the
extended structure of the networks, the influence of
temperature in the formation of coordination polymers
is less well understood and systematic studies are rare [5].
It is known that in the self-assembly of both synthetic
and biological systems the thermodynamic product is
usually favored, the kinetic product may also be ob-
tained if the shape of the energy hypersurface is such that
the system becomes trapped in local minima [6]. To de-
velop the better understanding of temperature effects on
the formation of coordination polymers, in the present
contribution, two new maleato manganese(II) polymers
formulated as [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O (1) and
[Mn(male) (bpy)]n (2) were temperature-dependently
prepared and structurally characterized. Irreversible
conversion from kinetic maleato manganese 1 to the
dehydrate product 2 was investigated.
Metal-directed self-assembly of coordination poly-
mers with well-defined architectures has presently been
one topic of intense interest in the field of supra-molec-
ular chemistry owing to their original topologies, desired
properties and potential applications in multidisciplinary
areas, e.g., catalysis, nonlinear optics, magnetism, lumi-
nescence, gas storage and chemical absorption [1].
Considerable efforts have been made to construct such
extended solid materials with manipulated and tunable
functionalities. The most common used strategy is to
employ appropriate organic building blocks with several
metal centers through direct bond formation. However,
it still remains a challenge for synthetic chemists to pre-
dict and control the way of molecular components as-
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.poly.2004.01.005.
* Corresponding author. Tel.: +86-592-2184531; fax: +86-592-
2183047.
E-mail address: zhzhou@xmu.edu.cn (Z.-H. Zhou).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.01.005

988
H.-B. Chen et al. / Polyhedron 23 (2004) 987–991
2. Experimental
diffraction were obtained after a few weeks. Yield: 90%.
Anal. Calcd. for C14H10N2O4Mn: C, 51.7; H, 3.1; N, 8.6.
Found: C, 52.2; H, 3.2; N, 8.9%. IR (KBr, cmꢁ1):
mas(C@O) 1593s, 1547vs, ms(C@O) 1429m, 1398m, m(Mn–
O) 774m.
All chemicals were commercially available and used
without further purification. Elemental microanalyses
(C, H and N) were performed on an EA 1100 elemental
analyzer. Infrared spectra were recorded from KBr
pellets on a Nicolet FT-IR 360 spectrophotometer in the
2.3. Conversion of [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O
(1) to [Mn(male)(bpy)]n (2)
range of 4000–400 cmꢁ1
.
The crystals of 1 were picked out and put in a beaker
with some mother liquid at ambient temperature. A few
days later, the block-like yellow crystals segmented into
ÔchaosÕ and IR spectra justified it was converted into
thermodynamic product 2.
2.1. Preparation of [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O
(1)
Manganese maleate was prepared in situ at 0 °C by
mixing MnCl2 ꢀ 4H2O (0.99 g, 5 mmol) and an equi-
molar amount of sodium maleate, dissolving in 20 ml
double distilled water. After stirring the mixture for 15
min, an equimolar amount of 2,20-bipyridine (0.780 g, 5
mmol), dissolved in 10 ml methanol, was slowly added
and stirring was continued for another 10 min. The so-
lution was kept in the refrigerator. Block-like crystals
suitable for single crystal diffraction analysis were ob-
tained a few days later. Yield: 85%. Anal. Calcd. for
C14H16N2O7Mn: C, 44.3; H, 4.2; N, 7.4. Found: C, 43.0;
H, 4.1; N, 7.3%. IR (KBr, cmꢁ1): m(O–H) 3377vs,
mas(C@O) 1578vs, ms(C@O) 1439s, m(Mn–O) 773s.
2.4. Conversion of [Mn(male)(phen)]n ꢀ nH2O (3) to
[Mn(male)(phen)]n (4)
The maleato phenanthroline manganese complexes 3
and 4 were prepared as reported very recently [7].
Crystals of 3 (0.37g, 1 mmol) in 5 ml water were warmed
in a 50 °C warm bath for 8 h. The resultant product was
showed to be the dehydrated maleato manganese com-
plex 4 by IR spectra.
2.5. X-ray data collection, structure solution and
refinement
2.2. Preparation of [Mn(male)(bpy)]n (2)
Intensity data were collected on a Bruker SMART
ꢀ
The preparation of 2 was similar to the hydrate prod-
uct 1 except the reaction was proceeded at ambient tem-
perature. Plate single crystals suitable for X-ray
APEX CCD using Mo Ka radiation (k ¼ 0:71073 A).
Both structures were solved by direct methods and re-
fined by full-matrix least squares based on F 2 using
Table 1
Crystallographic data for [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O (1) and [Mn(male)(bpy)]n (2)
Compounds
1
2
Empirical formula
Formula weight
Crystal system
Space group
C14H16N2O7Mn
379.23
monoclinic
C14H10N2O4Mn
325.18
monoclinic
P21=c
8.0194(2)
P21=c
11.4546(3)
ꢀ
a (A)
ꢀ
b (A)
8.6486(1)
23.3306(4)
13.3064(4)
8.8076(3)
ꢀ
c (A)
b (°)
V (A )
92.059(1)
1617.09(5)
111.455(1)
1249.42(7)
3
ꢀ
Z
4
1.558
4
1.729
Dcalcd: (g cmꢁ3
Crystal size (mm)
)
0.061 ꢂ 0.051 ꢂ 0.035
0.066 ꢂ 0.200 ꢂ 0.216
660
F0 0 0
780
h range (°)
T (K)
1:75 6 h 6 28:82
296
0.855
1:91 6 h 6 28:94
296
1.075
l (mmꢁ1
)
R½I > 2rðIÞꢃ
R ¼ 0:0554, Rw ¼ 0:1499
R ¼ 0:0595, Rw ¼ 0:1553
wꢁ1 ¼ r2ðFo2Þ þ 0:1245P2 P ¼ ðFo2 þ 2Fc2Þ=3
R ¼ 0:0383, Rw ¼ 0:0816
R ¼ 0:0524, Rw ¼ 0:0865
wꢁ1 ¼ r2ðFo2Þ þ 0:0373P2 þ 0:1049P,
P ¼ ðFo2 þ 2Fc2Þ=3
1.027
R (all data)
Goodness-of-fit
Minimum and maximum
ꢀ
residual density (e A
0.912
)1.130 and 0.727
)0.345 and 0.335
ꢁ3
)

H.-B. Chen et al. / Polyhedron 23 (2004) 987–991
989
Table 2
Selected bond lengths (A) and angles (°) for 1 and 2b
a
ꢀ
[Mn(male)(bpy)(H2O)]n ꢀ 2nH2O (1)
Bond lengths
Mn1–O1
Mn1–O4i
Mn1–N2
2.3666(2)
2.3600(2)
2.2540(2)
Mn1–O2
Mn1–Ow1
2.2344(2)
2.1375(2)
Mn1–O3i
Mn1–N1
2.362(2)
2.2528(2)
Bond angles
O1–Mn1–O2
O1–Mn1–O1w
O2–Mn1–O3i
O2–Mn1–N1
O3–Mn1–O1wi
O4–Mn1–Ow1i
Ow1–Mn1–N1
56.67(5)
82.99(6)
84.96(6)
139.66(6)
84.23(7)
81.97(7)
99.23(7)
O1–Mn1–O3i
O1–Mn1–N1
O2–Mn1–O4i
O2–Mn1–N2
O3–Mn1–N1i
O4–Mn1–N1i
Ow1–Mn1–N2
137.79(6)
88.21(6)
139.62(6)
91.65(6)
133.59(7)
79.80(6)
171.69(7)
O1–Mn1–O4i
O1–Mn1–N2
O2–Mn1–O1w
O3–Mn1–O4
O3i–Mn1–N1i
O4–Mn1–N2i
N1–Mn1–N2
158.97(7)
97.58(6)
95.68(7)
54.67(7)
100.36(6)
94.97(7)
72.57(6)
Hydrogen bonding
Bond lengths
O1wꢀ ꢀ ꢀO2i
2.727(3)
2.756(3)
O1wꢀ ꢀ ꢀO3w
O2wꢀ ꢀ ꢀO2wii
2.730(2)
2.863(3)
O2wꢀ ꢀ ꢀO1ii
O3wꢀ ꢀ ꢀO4iv
2.810(3)
2.805(4)
O2wꢀ ꢀ ꢀO4iii
[Mn(male)(bpy)]n (2)
Bond lengths
Mn1–O1
2.1812(2)
2.1733(2)
Mn1–O2i
Mn1–N1
2.1499(2)
2.2688(2)
Mn1–O3
Mn1–N2
2.1157(2)
2.3286(2)
Mn1–O4ii
Bond angles
O1–Mn1–O2i
O1–Mn1–N1
O2i–Mn1–O4ii
O3–Mn1–O4ii
O4ii–Mn1–N1
94.16(7)
86.74(6)
84.15(6)
94.53(6)
96.14(6)
O1–Mn1–O3
O1–Mn1–N2
O2–Mn1–N1i
O3–Mn1–N1
O4ii–Mn1–N2
82.89(6)
93.61(6)
89.82(6)
166.42(6)
88.95(6)
O1–Mn1–O4ii
O2–Mn1–O3i
O2–Mn1–N2i
O3–Mn1–N2
N1–Mn1–N2
176.65(6)
99.63(6)
159.24(7)
100.42(6)
71.44(7)
a Symmetry transformation: (i) 1 ꢁ x; 1=2 þ y, 1=2 ꢁ z; (ii) 1 ꢁ x, ꢁy, ꢁz; (iii) ꢁ1 þ x, ꢁ1=2 ꢁ y, ꢁ1=2 þ z; (iv) x, 1 þ y, z.
b Symmetry transformation: (i) x, 1=2 ꢁ y, 1=2 þ z; (ii) 1 ꢁ x, ꢁy, 1 ꢁ z.
SHELX-97 software [8]. All non-hydrogen atoms were
anisotropically refined. Hydrogen atoms were included
at geometrically calculated positions with thermal pa-
rameters derived from the parent atoms, except those
bonded to the water molecules. The water hydrogen at-
oms were located in the difference map and included at
these sites, with a fixed isotropic displacement factor of
UðHÞ ¼ 1:2Ueq(O). Crystal data, data collection and
refinement parameters are summarized in Table 1. Se-
lected bond lengths and bond angles are listed in Table 2.
carboxyl group is in a bidentate bridging or chelating
mode [9,10].
X-ray diffraction analysis reveals the maleato man-
ganese dihydrate 1 possesses 1D helical chains with the
basic building unit Mn(male)(bpy)(H2O). Each manga-
nese atom is primarily coordinated by four oxygen at-
oms from two bidentated maleates, two nitrogen atoms
from bpy and one water molecule, in an irregular pen-
tagonal-bipyramidal configuration (Fig. 1). The car-
boxyl oxygen atoms O1, O2 chelate to central
manganese with an O1–Mn1–O2 bond angle of 56.7°,
while O3, O4 of the other carboxyl group bind another
manganese center. Thus each maleato unit serves as a
bis(bidentate) ligand to link two manganese atoms and
yields a half turn of the helical structure. All the carbon
atoms of the maleato unit form a common plane, from
which both terminal carboxyl groups O1–C1–O3 and
O3–C4–O4 are twisted from the carbon backbone by
20.0° and 72.1°, respectively. The four Mn–O bond
distances are different from each other to some extent
(Table 2), with that to O2 being particularly short
3. Results and discussion
Based on IR spectra, we can deliberately diagnose the
coordination nature of the maleato group in complexes
1 and 2. Specifically, asymmetric stretching vibrations
mas(COO) appear near 1578 cmꢁ1 for 1 and between
1593 and 1547 cmꢁ1 for 2, and the symmetric stretching
vibrations ms(COO) are observed near 1439 cmꢁ1 for 1
and between 1429 and 1398 cmꢁ1 for 2. The separations
½masðCOOÞ–msðCOOÞꢃ of complexes 1 and 2 (139 and 118
cmꢁ1) are much smaller than the value of 200 cmꢁ1 for
the free maleato group, indicating that the coordinated
ꢀ
[2.2344(2) A]. Unexpectedly, the shortest bond distance
is that to the coordinated water molecule [Mn1–O1w
ꢀ
2.1375(2) A]. So far, a great majority of structurally
characterized Mn(II) complexes take invariably a

990
H.-B. Chen et al. / Polyhedron 23 (2004) 987–991
those on the other side (Fig. 2). The helical chains are
further extended through hydrogen bonds between wa-
ter molecules and carboxyl oxygen atoms into a two-
dimensional network.
The asymmetric unit of 2 consists of one manganese
center, one maleato group and one bpy ligand. Each
manganese center primarily coordinates to two nitrogen
atoms from 2,20-bpy and four carboxylate oxygen atoms
from three maleato groups, in a geometry which is best
described as a distorted octahedron (Fig. 3). The Mn1–
ꢀ
ꢀ
N1 bond distance [2.2688(2) A] is slightly shorter than the
Mn1–N2 bond [2.3286(2) A] in the same ligand, sug-
gesting some twist in the 2,20-bpy ligand (dihedral angle
11.5° between the two pyridyl rings). Cis-fashioned ox-
ygen atoms O1 and O3 at the two termini of the maleato
unit bind the manganese center into a seven-member
chelate ring with an O1–Mn1–O3 bond angle of 82.89°,
while O2 and O4 bind to the other two manganese atoms.
In this way, each maleato group acts as a tetradentate
ligand to coordinate three manganese atoms. The dihe-
dral angle (45.0°) between O1–C1–O3 and O3–C4–O4 is
much smaller than that in 1 (67.9°). Both terminal car-
boxyl groups O1–C1–O2 and O3–C4–O4 twist from the
carbon backbone C1–C2–C3–C4 by 45.9°and 1°, re-
spectively. The conformations of the maleato units in the
two complexes are so different that the explanation why
two different topological products were obtained be-
comes obvious. The coordination mode of the maleato
group is to some extent similar to those previously re-
ported for [Mn4(male)2(bpy)8](ClO4)4 ꢀ (MeOH)2(H2O)2
[12], [Mn(male)(l-4,40-bpy)]n ꢀ 0.5nH2O [13] and [Mn
(male)(phen)]n [7,14]. However, the extension of the basic
unit and the packing style are different from those related
compounds, thus giving rise to topologically different
products. In addition, dimeric [Mn2(male)2(bpy)2] may
Fig. 1. One of the asymmetric units of [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O
(1) in the K-configuration; hydrogen atoms and water molecules were
omitted for clarity; thermal ellipsoids are drawn at 30% probability.
six-coordinate octahedral geometry around the metal
atom. Complexes with coordination numbers exceeding
six are limited to a few examples [11]. To the best of our
knowledge, a helical coordination polymer based on a
hepta-coordinated manganese center has not yet been
documented hitherto. Extension of the basic building
unit along the crystallographic 21 axis in the b direction
gives an infinite 1D helical architecture with a long 0pitch
ꢀ
of 8.649 A. The helical chain is decorated by 2,2 -bpy
ligands alternatively at the two sides and the 2,20-bpy
planes on the same side are absolutely parallel one an-
other, while they have a dihedral angle of 42.8° with
Fig. 3. Asymmetric unit of [Mn(male)(bpy)]n (2) with atom numbering
scheme; hydrogen atoms were omitted for clarity; thermal ellipsoids
are drawn at 30% probability.
Fig. 2. One of the perspective views of a single helical chain of
[Mn(male)(bpy)(H2O)]n ꢀ 2nH2O (1) in the M-configuration.

H.-B. Chen et al. / Polyhedron 23 (2004) 987–991
991
be better as a secondary building unit (SBU) than mo-
4. Supplementary materials
nomeric [Mn(male)(bpy)] for clearly describing the
crystal structure. In the dimeric model, the extension
directions of O2 and O20, O200 and O2000 are opposite to
each other, respectively, linking and being linked by an-
other four SBUs into a two-dimensional zigzag structure.
p–p stacking interactions between bipyridyl planes fur-
ther extend the two-dimensional structure into a three-
dimensional network.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 215790 for compound 1 and
215791 for compound 2. Copies of this information may
be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
The formation of both maleato manganeses com-
plexes is temperature-dependent. When the reaction
proceeded at 0 °C, only the one-dimensional coordina-
tion polymer 1 was separated. Whereas at ambient
temperature, only the thermodynamic product 2 was
isolated. Furthermore, the irreversible conversion from
1 to 2 was observed when 1 was exposed to an ambient
temperature for a few days and this reaction could be
qualitatively traced by IR spectra. As to the details of
how the conversion proceeds requires further theoretical
deduction and kinetic measurements. Here the possible
mechanism of transformation is depicted as follows. In
the first step, the manganese maleate species
[Mn(male)(H2O)2]n ꢀ nH2O was formed according to
previous reports [15]. Addition of 2,20-bipyridine ligand
replaces the water molecules to complete the formation
of the kinetic product [Mn(male)(bpy)(H2O)]n ꢀ 2nH2O
(1) with hepta-coordination. On warming to room
temperature, the maleato manganese complex 1 was
further compelled into the thermodynamically stable
product [Mn(male)(bpy)]n 2 with dehydration. Very re-
cently, the stable maleato bipyridine manganese species
Acknowledgements
Financial supports from the Ministry of Science and
Technology (001CB108906) and the National Science
Foundation of China (No. 20171037, 20021002) are
gratefully acknowledged.
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Scheme 1. Transformations of maleato manganese complexes with 2,2-
bipyridine and phenanthroline groups.