Structure, thermal stability and magnetic behavior of Mn(II) complexes with phenoxyacetic acid herbicides

Article abstract of DOI:10.1016/j.poly.2021.115370

The reaction of manganese(II) chloride with ammonium salt of 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-bromophenoxyacetic acid (4-Br) gave rise to the formation of hydrated complexes with formulas: Mn(MCPA)₂·2H₂O, Mn(2,4-D)₂·2H₂O and Mn(4-Br)₂·3H₂O. The compounds were characterized by elemental and thermal analyses, spectroscopic methods, as well as, by magnetic measurements. The complexes crystallize in monoclinic system. The Mn(II) ion is surrounded by oxygen atoms (from carboxylate groups and water molecules) in the octahedral arrangement. Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed that compounds obey the Curie-Weiss law and have the paramagnetic properties. Being heated up to 1173 K the complexes decompose in three steps - first to anhydrous compounds: Mn(MCPA)₂/Mn(2,4-D)₂/Mn(4-Br)₂ through intermediate products: MnO/Mn₂OCl₂/Mn₂OBr₂ to the following oxides: Mn₂O₃/Mn₃O₄/Mn₃O₄. The X-ray single crystal structure analysis was performed for Mn(II) complex with 4-bromophenoxyacetic acid after its recrystallization from N,N-dimethylformamide. The formation of hexanuclear cluster of manganese(II) carboxylate with a hydrophobic exterior was observed.

Full text of DOI:10.1016/j.poly.2021.115370

Polyhedron 207 (2021) 115370
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structure, thermal stability and magnetic behavior of Mn(II) complexes
with phenoxyacetic acid herbicides
,
Aleksandra Drzewiecka-Antonika *, Wiesława Ferencb, Barbara Mirosławb, Dariusz Osypiukb,
c
´
Jan Sarzynski
a Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland
b Faculty of Chemistry, Maria Curie-Skłodowska University, Sq. Maria Curie-Skłodowska 2, PL-20031 Lublin, Poland
c Institute of Physics, Maria Curie-Skłodowska University, Sq. Maria Curie-Skłodowska 1, PL-20031 Lublin, Poland
A R T I C L E I N F O
A B S T R A C T
Keywords:
The reaction of manganese(II) chloride with ammonium salt of 4-chloro-2-methylphenoxyacetic acid (MCPA),
2,4-dichlorophenoxyacetic acid (2,4-D) and 4-bromophenoxyacetic acid (4-Br) gave rise to the formation of
hydrated complexes with formulas: Mn(MCPA)2⋅2H2O, Mn(2,4-D)2⋅2H2O and Mn(4-Br)2⋅3H2O. The compounds
were characterized by elemental and thermal analyses, spectroscopic methods, as well as, by magnetic mea-
surements. The complexes crystallize in monoclinic system. The Mn(II) ion is surrounded by oxygen atoms (from
carboxylate groups and water molecules) in the octahedral arrangement. Variable-temperature (1.8–300 K)
magnetic susceptibility measurements showed that compounds obey the Curie-Weiss law and have the para-
magnetic properties. Being heated up to 1173 K the complexes decompose in three steps - first to anhydrous
compounds: Mn(MCPA)2/Mn(2,4-D)2/Mn(4-Br)2 through intermediate products: MnO/Mn2OCl2/Mn2OBr2 to the
following oxides: Mn2O3/Mn3O4/Mn3O4. The X-ray single crystal structure analysis was performed for Mn(II)
complex with 4-bromophenoxyacetic acid after its recrystallization from N,N-dimethylformamide. The formation
of hexanuclear cluster of manganese(II) carboxylate with a hydrophobic exterior was observed.
Mn(II) complexes
Phenoxyacetic herbicides
Magnetic properties
X-ray crystallography
hexanuclear Mn(II) carboxylate coordination
cluster
1. Introduction
photosynthetic organisms as it is involved in diverse processes such as (i)
photosynthesis, (ii) respiration, (iii) scavenging of reactive oxygen spe-
Manganese (Mn) is considered an essential element in most organ-
isms. In the human, it is absorbed through the gastrointestinal tract
(from food and water) and transported to organs such as liver, pancreas
or pituitary where it is rapidly accumulated. This biometal is involved in
(i) the synthesis and activation of enzymes including oxidoreductases,
transferases, hydrolases, lyases, isomerases, ligases etc., (ii) regulation of
the metabolism of glucose and lipids, (iii) the acceleration of the syn-
thesis of proteins and vitamins (B, C, E), (iv) catalysis of hematopoiesis,
(v) endocrine regulation and (vi) improving immune function [1].
Moreover, it is present in the active centers of several important en-
zymes like arginase, phosphoenolpyruvate decarboxylase, glutamine
synthetase and superoxide dismutase (MnSOD) that is involved in
mitochondrial oxidative stress to clear reactive oxygen species (ROS)
[1]. In plants, manganese is taken up from the soil by the active trans-
port system of epidermal root cells and translocated to the shoot [2]. It is
an important micronutrient for growth and reproduction of
cies, (iv) pathogen defense and (v) hormone signaling [2].
In soils, manganese can exist in eleven oxidation states: from ꢀ 3 to +7.
The most common ones are +2, +3 and +4. The Mn(III) and Mn(IV)
species form insoluble oxides that quickly sediment. Mn(II) is the most
soluble species and the only plant available form. Divalent manganese,
present in soil and plant tissues, can interact with anions as phenox-
yacetate herbicide [3]. The phenoxy herbicides can be introduced to the
environment as free acids, alkali and amine salts or esters. All these forms
are highly soluble in water, in which they dissociate into acid anions. They
persist around 1 month in soil [4] and are degraded by microorganisms.
However, before they are degraded by microbes, they can react with
metals present in soil and plants tissues, forming metal-organic complexes.
The aim of the research was to obtain, in laboratory conditions,
analogous systems with manganese cations only in +2 oxidation state
and then to study their structure, thermal stability and magnetic prop-
erties. Therefore, we synthesized Mn(II) complexes with 4-chloro-2-
* Corresponding author.
E-mail address: adrzew@ifpan.edu.pl (A. Drzewiecka-Antonik).
https://doi.org/10.1016/j.poly.2021.115370
Received 15 June 2021; Accepted 12 July 2021
Available online 16 July 2021
0277-5387/© 2021 The Authors.
Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).

A. Drzewiecka-Antonik et al.
Polyhedron 207 (2021) 115370
Table 1
The unit cell parameters for polycrystalline complexes.
Complex
Crystal system
a (Å)
b (Å)
c (Å)
α
(◦)
β (◦)
γ (◦)
V (Å3)
Mn(MCPA)2⋅2H2O
Mn(2,4-D)2⋅2H2O
Mn(4-Br)2⋅3H2O
Monoclinic
Monoclinic
Monoclinic
6.7839 ± 0.0077
8.0300 ± 0.0072
20.3700 ± 0.0056
17.3769 ± 0.0066
7.3310 ± 0.0063
3.8300 ± 0.0013
20.547 ± 0.030
17.679 ± 0.0083
5.1200 ± 0.0029
90
90
90
95.213 ± 0.035
94.233 ± 0.064
115.170 ± 0.075
90
90
90
2412.12 ± 0.05
1037.86 ± 0.02
399.44 ± 0.02
methylphenoxyacetic (MCPA), 2,4-dichlorophenoxyacetic (2,4-D) and
4-bromophenoxyacetic (4-Br) acids. The compounds were characterized
by elemental analysis, X-ray fluorescence spectroscopy (XRF), X-ray
powder diffraction (XRD), thermogravimetry method, attenuated total
reflection infrared spectroscopy (ATR-IR) and magnetic susceptibility
measurements. For the complex with bromo derivative, after its
recrystallization from N,N-dimethylformamide (DMF) solution, we were
able to receive crystals for X-ray single crystal structure analysis.
diffraction patterns of all complexes and the products of their decom-
position process were registered on a HZG-4 (Carl-Zeiss, Jena) diffrac-
tometer using Ni filtered CuKα radiation. The measurements were made
within the range of 2θ = 4-80◦ by means of Bragg-Brentano method. For
the interpretation of diffractograms (Figs. 1S-3S in the Supplementary
material) the Dicvol 06 programme was used.
2.3. Thermal characterization of complexes
2. Experimental part
The thermal stability and decomposition process of complexes were
studied in air using a Setsys 16/18 (Setaram) TG, DTG and DSC instru-
ment. The experiments were carried out under air flow in the temper-
ature range of 293 – 1173 K at a heating rate of 5 K⋅minꢀ 1. The initial
masses of samples changed from 5.42 to 5.01 mg. The compounds were
heated in Al2O3 crucibles.
2.1. Synthesis of complexes
The solvents and all chemicals used for the synthesis were of
commercially available reagent grade and were applied without further
purification. 4-Chloro-2-methyl-; 2,4-dichloro-, and 4-bromo-phenoxya-
cetates of ammonium (pH ~ 5) of 0.1 mol/L concentration were pre-
pared by the addition of NH3 (aq) solution (25% pure) to respective
phenoxyacetic acids in water solution (99% pure).
2.4. Magnetic characterization of complexes
Magnetic susceptibilities of samples were investigated at 1.8 – 300 K
with the use of Quantum Design SQUID-VSM magnetometer. The
superconducting magnet was operated at a field strength ranging from
0 to 7 T. Measurements of samples were made at magnetic field of 0.1 T.
The SQUID magnetometer was calibrated with the palladium rod sam-
ple. Correction for diamagnetism of the constituent atoms was calcu-
lated by the use of Pascal’s constants. The effective magnetic moment
The complexes were synthesized by the addition of equivalent
quantities of 0.1 mol/L ammonium salt of respective acid (pH ~ 5) to a
warm solutions of MnCl2⋅4H2O and by crystallizing at 293 K. To reach of
equilibrium state the solids were constantly stirred for 1 h. Next they
were filtered off, washed with warm water to remove ammonium and
chloride ions and dried at 303 K to a constant mass.
values were calculated from the equation: µ = 2.83 (χm⋅T)1/2, where:
Mn(MCPA)2⋅2H2O
eff
Yield: 53.84%, pinkish solid
µeff - effective magnetic moment, χm – magnetic susceptibility per
ATR-IR: 3471, 3264 (
ν
OHwater), 1631 (νasCOO–), 1593 (νasCOO–),
molecule and T - absolute temperature.
1557 (νasCOO–), 1334 (νsCOO–),1223 (
ν
Car–Oether), 1054 (
ν
Car–Cl) cmꢀ 1
Anal. Calc. for Mn(C9H5O3Cl)2⋅2H2O: C, 44.49; H, 4.08; Cl, 14.49;
Mn, 11.21% Found: C, 44.08; H, 4.07; Cl, 14.40; Mn, 11.00%
Mn(2,4-D)2⋅2H2O
2.5. Single crystal X-ray diffraction of the recrystallized complex
The X-ray diffraction intensities for the single crystal of the Mn(II)
complex with 4-bromophenoxyacetic acid (recrystallized from DMF)
were collected at 120 K on SuperNova X-ray diffractometer equipped
with Atlas S2 CCD detector using the mirror-monochromatized CuKα
Yield: 63.42%, white solid
ATR-IR: 3554, 3292 (
ν
OHwater), 1606 (νasCOO–), 1579 (νasCOO–),
1560 (νasCOO–), 1341 (νsCOO–), 1230 (
νCar–Oether), 1049 (
ν
Car–Cl) cmꢀ 1
Anal. Calc. for Mn(C8H5O3Cl2)2⋅2H2O: C, 36.16; H, 2.64; Cl, 26.74;
Mn, 10.36% Found: C, 36.18; H, 2.64; Cl, 26.68; Mn, 9.82%
Mn(4-Br)2⋅3H2O
radiation (λ = 1.54184 Å). Data were collected using the
ω scan tech-
nique, with an angular scan width of 1.0◦. The programs CrysAlis CCD,
CrysAlis Red and CrysAlisPro [5,6] were used for data collection, cell
refinement and data reduction. The analytical numeric absorption
correction based on indexing of crystal faces was applied [7]. The
structure was solved by direct methods using SHELXS-97 and refined by
the full-matrix least-squares on F2 using the SHELXL-97 [8]. The H-
atoms were positioned geometrically and allowed to ride on their parent
atoms, with Uiso(H) = 1.5 Ueq(C) for methyl groups and 1.2 Ueq(C) for the
rest groups. The DMF molecule has high thermal ellipsoids due to weak
intermolecular interactions. Crystallographic data are given in Tables 1S
in the Supplementary Material.
Yield: 69.80%, pinkish solid
ATR-IR: 3507, 3348 (
ν
OHwater), 1646 (νasCOO–), 1589 (νasCOO–),
1580 (νasCOO–), 1341 (νsCOO–), 1231 (
νCar–Oether), 1054 (νC –Br)
ar
cmꢀ 1
Anal. Calc. for Mn(C8H6O3Br)2⋅3H2O: C, 33.62; H, 3.50; Br, 28.02;
Mn, 9.63% Found: C, 33.62; H, 3.25; Br, 28.00; Mn, 9.62%
The colourless crystals of Mn(II) complex with 4-bromophenoxyace-
tic acid (recrystallized from DMF) suitable for an X-ray single crystal
structure analysis, were obtained by a slow evaporation of the solvent
from DMF solution at room temperature.
Crystal Data for C114H114Br12Mn6N6O42 (M = 3528.66 g/mol):
trigonal, space group P-3 (no. 147), a = 16.9142(6) Å, c = 13.4364(6) Å,
2.2. Structural characterization of complexes
V = 3329.0(2) Å3, Z = 1, T = 120.01(10) K,
μ(Cu Kα) = 9.411 mm-1,
Dcalc = 1.76 g/cm3, 56,180 reflections measured (8.94◦ ≤ 2Θ ≤
154.92◦), 4662 unique (Rint = 0.0710, Rsigma = 0.0244) which were used
The contents of carbon and hydrogen in complexes were determined
by elemental analysis using CHN 2400 Perkin – Elmer analyser. The
amounts of metal and halogen atoms were established by X-ray fluo-
rescence (XRF) method using spectrophotometer with energy dispersion
ED XRF-1510 (Canberra – Packard). The ATR-IR spectra of complexes
and their parent ligands were recorded over the range of 4000 – 400
cmꢀ 1 using Thermo Scientific Nicolet iS5 spectrometer. The X-ray
in all calculations. The final R1 was 0.0432 (I>=2μ(I)) and wR2 was
0.1174 (all data).
CCDC 2,089,845 contains the supplementary crystallographic data,
which can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
2

A. Drzewiecka-Antonik et al.
Polyhedron 207 (2021) 115370
Fig. 1. The comparison of ATR-IR spectra of Mn(II) complexes (a,b) with initial acids (c,d) in two spectral ranges: 3700–2400 cmꢀ 1 (left) and 1800–1000
cmꢀ 1 (right).
1223–336–033; or e-mail: deposit@ccdc.cam.ac.uk.
article describing the Co(II), Ni(II) and Cu(II) coordination compounds
with MCPA and 2,4-D [9]. As for these three cations, connections with
Mn(II) showed low cytotoxicity against studied cells, therefore the
biological research will not be discussed further.
3. Results and discussion
The complexes were synthesized by the reaction of manganese(II)
chloride with ammonium salt of 4-chloro-2-methylphenoxyacetic acid
(MCPA); 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-bromophenoxy-
acetic acid (4-Br) according to the procedure described in the experi-
mental section. The compounds were obtained in the form of
microcrystalline powders and were initially characterized by X-ray
powder diffraction technique and infrared spectroscopy. The formulas of
the complexes were determined based on the results of elemental and X-
ray fluorescence analyses. The structural changes of substances during
thermal treatment were studied in the range of 293–1173 K. In order to
estimate the nature of metal–ligand bonding and to study the sur-
roundings of metal ions the magnetic susceptibility of complexes was
measured in temperature range of 1.8–300 K.
For manganese(II) complex with 4-bromophenoxyacetic acid, dis-
solved in the DMF solution, it was possible to obtain single crystals
suitable for X-ray crystallography. The X-ray crystal structure analysis
showed the formation of new hexanuclear compound with solvent
molecules included in the metal coordination sphere.
3.1. Structural characterization
The synthesis gave rise to the formation of hydrated complexes: Mn
(MCPA)2⋅2H2O, Mn(2,4-D)2⋅2H2O and Mn(4-Br)2⋅3H2O. All compounds
were obtained as microcrystalline powders. The Mn(II) complexes
crystallized in monoclinic crystal system with different volumes of the
unit cell with the smallest value observed for the bromine derivative
(Table 1).
The toxicity of Mn(II) complexes with herbicides was tested using
Chinese hamster lung fibroblast (V79) and the human immortalized
keratinocyte cells (HaCaT) with the procedure presented in our previous
Despite of the differences in the unit cell parameters, phenox-
yacetates of Mn(II) had analogous infrared spectra (Fig. 1a and 1b). In
3

A. Drzewiecka-Antonik et al.
Polyhedron 207 (2021) 115370
Table 2
Temperature ranges of thermal stability in air at 293 – 1173 K and the enthalpy values of dehydration process for analysed complexes.
Complex
ΔT1 (K)
Mass loss (%)
calcd.
n H2O
ΔT2 (K)
Mass losses (%)
calcd.
ΔH1H2O
Found
Found
(kJ/mol)
Mn(MCPA)2⋅2H2O
Mn(2,4-D)2⋅2H2O
Mn(4-Br)2⋅3H2O
350–386
378–408
298–403
7.45
6.78
8.13
7.23
9.72
2
2
3
400–522
423–893
497–640
85.31
85.62
85.04
85.77
87.60
85.04
38.38
44.64
26.04
10.77
ΔT1 - temperature range of dehydration process, ΔT2 - temperature range of anhydrous complex degradation, n – number of water molecules lost in one stage, ΔH1H2O
-
enthalpy value for 1 molecule of dehydration process.
Fig. 2. Relationships of χmcorr and χcmorr-1 vs. T in the range of 1.8–300 K for Mn(II) complexes with a) 4-chloro-2-methylphenoxyacetic acid (MCPA), b) 2,4-dichlor-
ophenoxyacetic acid (2,4-D) and c) 4-bromophenoxyacetic acid (4-Br).
their ATR-IR spectra there was a broad band between 3600 and 2800
cmꢀ 1 indicating the presence of water molecules (confirmed by
elemental and thermal analyses, Fig. 1a). Additionally, several maxima
between 3100 and 2800 cmꢀ 1 correspond to the C–H stretching vibra-
tions. The infrared spectra of free ligands had also a broad band but in
different region, viz. 3200–2500 cmꢀ 1 assigned to the –OH (from
carboxyl group) stretching vibration (Fig. 1c). Several bands corre-
sponding to the C–H stretching modes were observed at the same posi-
tion (within the experimental error) for each pair of free organic ligand
and its Mn(II) complex.
compounds with octahedral molecular geometry.
The positions of bands, assigned to the C–Oether and C–Cl/Br
stretching vibrations were very similar in the IR spectra of parent ligands
and their Mn(II) complexes (Fig. 1b and 1d), which suggests that neither
O ether nor Cl/Br atoms had coordinated to the Mn(II).
3.2. Thermal characterization of complexes
Thermogravimetric measurements of analysed complexes were car-
ried out in air in the range of 293–1173 K (Table 2). TG, DTG and DSC
curves were recorded using the DSC/TG technique (Figs. 4S-6S in the
Supplementary material). Being heated up to 1173 K the Mn(II) com-
plexes decomposed in three steps. They were stable up to 298–378 K.
Next, in the range of 298 – 408 K, all complexes underwent a one-step
dehydration with endothermic peaks (DSC curves) loosing 2–3 mole-
cules of water and formed anhydrous compounds. For dihydrate Mn(II)
complexes with MCPA and 2,4-D the energetic effects accompanying the
dehydration process were similar, whereas the enthalpy for the
Moreover, the carboxylic groups in free acids yielded absorption
double bands around 1700 cmꢀ 1 (Fig. 1d). After the deprotonation, the
bands corresponding to the asymmetric and symmetric carboxylate
stretching vibrations, vasCOO- and vsymCOO-, were observed in the
spectra of Mn(II) complexes with acid anions (Fig. 1b). In the IR spectra,
the position and the shape of bands corresponding to the carboxylate
stretching modes were similar to those reported in our previous papers
[9–11] for complexes of MCPA, 2,4-D and 4-Br with Co(II) and Ni(II) -
4

A. Drzewiecka-Antonik et al.
Polyhedron 207 (2021) 115370
Fig. 3. Molecular structure and atom labelling scheme of the asymmetric unit (left, displacement ellipsoids were drawn at 50 % probability level). The structure of
the coordination units composed of six manganese cores linked through oxygen bridges (right).
Table 3
Selected bond lengths and angles for Mn(II) complex with 4-bromophenoxyace-
tic acid recrystallized from DMF.
Bond
Length /Å
Bond
Length /Å
Mn1-O1
2.220(2)
2.223(2)
2.190(2)
Value/˚
89.15(8)
85.16(8)
95.87(8)
96.04(8)
85.38(8)
88.17(8)
90.45(8)
Mn1-O5iii
2.158(2)
2.141(2)
2.212(2)
Value/˚
Mn1-O1ii
Mn1-O4
Mn1-O2i
Mn1-O7
Angle
Angle
O2i–Mn1–O1ii
O2i–Mn1–O1
O5iii–Mn1–O1ii
O5 iii–Mn1–O1
O4–Mn1–O1ii
O4–Mn1–O2i
O4–Mn1–O5iii
O5 iii–Mn1–O2i
O4–Mn1–O1
O7–Mn1–O1ii
O7–Mn1–O1
O7–Mn1–O2i
O7–Mn1–O5iii
O7–Mn1–O4
174.68(8)
173.09(9)
171.10(8)
91.75(8)
87.69(8)
87.09(9)
86.21(9)
Symmetry codes: i y–x, –x, z; ii y, –x +y, 2–z; iii –y +x, x, 2–z.
trihydrate bromine compound was lower, which suggests weaker
bonding of water molecules (Table 2).
Further heating of anhydrous compounds led to the formation of
MnO in the case of Mn(MCPA)2⋅2H2O, while Mn2OCl2 and Mn2OBr2
were formed for Mn(2,4-D)2⋅2H2O and Mn(4-Br)2⋅3H2O, respectively.
The final product of decomposition of Mn(II) compound with MCPA
herbicide was Mn2O3 whereas Mn3O4 was formed for complexes with
2,4-D and 4-Br anions, respectively.
Fig. 4. Crystal packing of Mn6(4-Br)12⋅6DMF with the hexanuclear coordina-
tion units stacked in columns along the c crystallographic axis.
bromophenoxyacetic acid (recrystallized from DMF) suitable for an X-
ray single crystal structure analysis, were obtained. The asymmetric unit
of the new compound was composed of one metal cation, one DMF
molecule and two deprotonated 4-bromophenoxyacetate anions (Fig. 3).
The coordination unit occupied a special position of an inversion
three-fold axis. It was multiplied by this symmetry element and formed a
closed cyclic hexameric unit with Mn… Mn distances of 3.6772(6) Å
(Fig. 3).
3.3. Magnetic characterization of complexes
In order to investigate the coordination spheres of Mn(II) ion the
magnetic susceptibilities of complexes were measured. The relationships
of χcmorr and χmcorr-1 vs. T in the range of 1.8 – 300 K are presented in Fig. 2.
The experimentally determined values of magnetic moments were in the
ranges 4.89 – 5.94 µB for Mn(MCPA)2⋅2H2O; 3.99 – 5.97 µB for Mn(2,4-
D)2⋅2H2O and 5.37 – 5.78 µB for Mn(4-Br)2⋅3H2O. Those values are close
The carboxylic acid anions differ in the coordination mode. The li-
gands occupying the horizontal part of the complex coordinated to three
Mn(II) ions through one bifurcated O atom and one simple bridge. The
vertically located carboxylic acid anions served as bidentate ligands,
each bridging two metal cations. Around each Mn(II) the octahedron
was formed and the Mn–O bond distances ranged from 2.141(2) to 2.223
(2) Å (Fig. 3, Table 3).
to spin only values for the Mn(II) ion calculated from the equation µ
=
[4 s(s + 1)]1/2 in the absence of the magnetic interactions for preesfefnt
spin-system. Its theoretical value calculated at room temperature is
equal to 5.9 µB. For Mn(II) ion complexes the magnetic moments were
lower than the spin – only value. This is due to the fact that the vectors L
and S are aligned by the strong field of a heavy atom in opposite di-
rections and this diminishes the resultant magnetic moment.
The search in the Cambridge Structural Database showed that such
Mn(II) complex with hexameric structure is unusual, since the analogous
polynuclear manganese carboxylate clusters contain usually manganese
cations in two oxidation states simultaneously: +2 and +3 [15].
In the crystal net the hexanuclear coordination units were arranged
The experimental data showed that the studied Mn(II) compounds
are high – spin complexes with octahedral symmetry around the central
ion and weak ligand field. They obey the Curie-Weiss law showing the
paramagnetic properties. A very weak antiferromagnetic interaction
between Mn(II) cations within complex molecule or a weak intermo-
lecular hydrogen bonds in the crystal lattice may appear [12–14].
Table 4
Intermolecular interactions (Å, ◦).
D–H⋅⋅⋅A
D–H
H⋅⋅⋅A
D⋅⋅⋅A
<DHA
C2–H2A… O2i
C2–H2A… O3i
C7–H7… Brii
0.97
0.97
0.93
2.342
2.559
2.989
3.116(4)
3.435(3)
3.840(5)
136
150
153
3.4. Single crystal X-ray diffraction of the recrystallized complex
The colourless crystals of Mn(II) complex with 4-
Symmetry codes: i –x + y, –x, z; ii ×, 1 + y, –1 + z.
5

A. Drzewiecka-Antonik et al.
Polyhedron 207 (2021) 115370
in columns along the c crystallographic axis (Fig. 4). Between the mol-
ecules there were only weak intermolecular interactions (Table 4)
because of a hydrophobic exterior layer structure of complex. The most
pronounced intermolecular interaction was C7–H7… Br1i (symmetry
code: i × , 1 +y, ꢀ 1 +z). Additionally the halogen atoms formed short
Br… Br contacts at 3.665(1) Å distance.
to the financial support of the European Regional Development Fund in
the framework of the Operational Program Development of Eastern
Poland 2007-2013 (Contract No. POPW.01.03.00-06-009/11-00,
Equipping the laboratories of the Faculties of Biology and Biotech-
nology, Mathematics, Physics and Informatics, and Chemistry for studies
of biologically active substances and environmental samples.
Prof. Marta Struga (Medical University of Warsaw, Chair and
Department of Biochemistry) is acknowledged for cytotoxicity assess-
ment of selected complexes.
4. Conclusion
Three Mn(II) complexes with 4-chloro-2-methylphenoxyacetic acid
(MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-bromophenoxy-
acetic acid (4-Br) were synthesized and characterized. The thermal de-
compositions of obtained compounds proceeded in three steps as
follows:
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.poly.2021.115370.
Mn(MCPA)2⋅2H2O → Mn(MCPA)2 → MnO → Mn2O3
Mn(2,4-D)2⋅2H2O → Mn(2,4-D)2 → Mn2OCl2 → Mn3O4
Mn(4-Br)2⋅3H2O → Mn(4-Br)2 → Mn2OBr2 → Mn3O4
References:
[1] L. Li and X. Yang, Review Article: The Essential Element Manganese, Oxidative
Stress, and Metabolic Diseases: Links and Interactions, Oxidative Medicine and
Cellular Longevity, Volume 2018, Article ID 7580707, 11 pages.
The hydrated Mn(II) compounds are high – spin complexes with
octahedral symmetry around the central ion and weak ligand field. They
obey the Curie-Weiss law and are paramagnetic. The analysis of infrared
spectra indicated the similar bonding of phenoxyacetates anions to the
metal cation. The Mn(II) cations are surrounded by carboxylate oxygen
atoms and water molecules. The coordination sphere of metal center can
be rearranged, as was observed in the case of complex with 4-bromophe-
noxyacetic acid with the weakest bonding of water molecules. After its
recrystallization from dimethylformamide (DMF), the detachment of
water molecules and attachment of the DMF molecules were observed.
Due to the exchange of solvent molecules, the formation of a hex-
anuclear manganese(II) carboxylate coordination clusters with a hy-
drophobic exterior was observed in crystal.
¨
[2] S. Alejandro, S. Holler, B. Meier, E. Peiter, Review: manganese in plants: from
acquisition to subcellular allocation, Front. Plant Sci. 11 (2020) 300, https://doi.
org/10.3389/fpls.2020.00300.
[3] E. Skiba, J. Kobyłecka, W.M. Wolf, Influence of 2,4-D and MCPA herbicides on
uptake and translocation of heavy metals in wheat (Triticum aestivum L.), Environ.
Pollut. 220 (2017) 882–890.
[4] http://sitem.herts.ac.uk/aeru/iupac/ - PPDB Pesticide Properties Database;
EXTOXNET – Extension Toxicology Network.
[5] Oxford Diffraction, Xcalibur CCD System, CRYSALIS Software System, Version
1.171, Oxford Diffraction Ltd. 2009.
[6] CrysAlisPro, Agilent Technologies, Version 1.171.37.34 (release 22-05-2014
CrysAlis171.NET).
[7] R.C. Clark, J.S. Reid, The analytical calculation of absorption in multifaceted
crystals, Acta Cryst. A 51 (6) (1995) 887–897.
[8] G.M. Sheldrick, A short history of SHELX, Acta Cryst. A 64 (1) (2008) 112–122.
[9] A. Drzewiecka-Antonik, W. Ferenc, A. Wolska, M.T. Klepka, C.A. Barboza,
´
˜
´
B. Cristovao, D. Osypiuk, J. Sarzynski, B. Tarasiuk, E. Grosicka-Maciąg, D. Kurpios-
Piec, M. Struga, Structural characterization and cytotoxic evaluation of Cu(II), Co
(II) and Ni(II) complexes with herbicide 4-chloro-2-methylphenoxyacetic acid,
Polyhedron 165 (2019) 86–96.
CRediT authorship contribution statement
´ ˜
[10] A. Drzewiecka-Antonik, W. Ferenc, A. Wolska, M.T. Klepka, B. Cristovao,
Aleksandra Drzewiecka-Antonik: Conceptualization, Validation,
Investigation, Writing - original draft, Writing - review & editing,
Visualization. Wiesława Ferenc: Resources. Barbara Mirosław:
´
J. Sarzynski, P. Rejmak, D. Osypiuk, The Co(II), Ni(II) and Cu(II) complexes with
herbicide 2,4-dichlorophenoxyacetic acid - Synthesis and structural studies, Chem.
Phys. Lett. 667 (2017) 192–198.
´ ˜
[11] A. Drzewiecka-Antonik, W. Ferenc, A. Wolska, M.T. Klepka, B. Cristovao,
´
Investigation. Dariusz Osypiuk: Investigation. Jan Sarzynski:
´
B. Mirosław, J. Sarzynski, D. Osypiuk, Coordination environment of new Co(II), Ni
(II) and Cu(II) complexes with 4-bromophenoxyacetic acid: Structural,
spectroscopic and theoretical studies, Polyhedron 133 (2017) 54–62.
[12] A. Earnshaw, Introduction to Magnetochemistry, Academic Press, New York, 1968,
pp. 30–83.
Investigation.
Declaration of Competing Interest
[13] A.F. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, John Wiley and Sons,
New York, 1988, pp. 955–979.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[14] O. Kahn, Molecular Magnetism Vol. 47 (1993) 287–332.
[15] M. Darii, I.G. Filippova, J. Hauser, S. Decurtins, V.C. Shi-Xia Liu, S.G.B. Kravtsov,
Incorporation of Hexanuclear Mn(II, III) Carboxylate Clusters with a Mn6O2 Core
in Polymeric Structures, Crystals 8 100 (2018) 11pages.
Acknowledgment
The research was carried out with the equipment purchased thanks
6