The formation of a neutral manganese(III) complex containing a tetradentate Schiff base and a ketone - Synthesis and characterization

Article abstract of DOI:10.1080/00958972.2015.1073268

2-Benzoylphenolato-(2,2′-((2,2-dimethylpropane-1,3-diyl)bis((nitrilo)(phenylmethylidyne)))-diphenolato-manganese(III) methanol solvate, [Mn(C₃₁H₂₈N₂O₂)(C₁₃H₉O₂)]·CH₃OH

Full text of DOI:10.1080/00958972.2015.1073268

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The formation of a neutral
manganese(III) complex containing a
tetradentate Schiff base and a ketone –
synthesis and characterization
Agata Bartyzela & Agnieszka A. Kaczorbc
a Faculty of Chemistry, Department of General and Coordination
Chemistry, Maria Curie-Skłodowska University, Lublin, Poland
b Faculty of Pharmacy with Division of Medical Analytics,
Department of Synthesis and Chemical Technology of
Pharmaceutical Substances with Computer Modelling Lab, Medical
University of Lublin, Lublin, Poland
Click for updates
c Department of Pharmaceutical Chemistry, School of Pharmacy,
University of Eastern Finland, Kuopio, Finland
Accepted author version posted online: 21 Jul 2015.Published
online: 20 Aug 2015.
To cite this article: Agata Bartyzel & Agnieszka A. Kaczor (2015): The formation of a neutral
manganese(III) complex containing a tetradentate Schiff base and a ketone – synthesis and
characterization, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2015.1073268
To link to this article: http://dx.doi.org/10.1080/00958972.2015.1073268
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Journal of Coordination Chemistry, 2015
http://dx.doi.org/10.1080/00958972.2015.1073268
The formation of a neutral manganese(III) complex
containing a tetradentate Schiff base and a ketone – synthesis
and characterization
AGATA BARTYZEL*† and AGNIESZKA A. KACZOR‡§
†Faculty of Chemistry, Department of General and Coordination Chemistry, Maria Curie-Skłodowska
University, Lublin, Poland
‡Faculty of Pharmacy with Division of Medical Analytics, Department of Synthesis and Chemical
Technology of Pharmaceutical Substances with Computer Modelling Lab, Medical University of
Lublin, Lublin, Poland
§Department of Pharmaceutical Chemistry, School of Pharmacy, University of Eastern Finland,
Kuopio, Finland
(Received 16 October 2014; accepted 10 June 2015)
2-Benzoylphenolato-(2,2′-((2,2-dimethylpropane-1,3-diyl)bis((nitrilo)(phenylmethylidyne)))-dipheno-
lato-manganese(III) methanol solvate, [Mn(C31H28N2O2)(C13H9O2)]·CH3OH (1), was synthesized
and characterized by FTIR, UV–vis, TG-FTIR, TG/DSC, molar conductivity, magnetic moment mea-
surement, and quantum chemical calculations. During the synthesis, partial hydrolysis of ligand is
observed. The compound was obtained as amorphous, dark-brown powder. The effects of organic sol-
vents of various polarities on the UV–vis spectra of ligands and complex were investigated. In addi-
tion, the IR and UV–vis spectra were also calculated and compared with the experimental data. A
single crystal for analysis was obtained by dissolving the amorphous complex in methanol, and slow
evaporation of solvent at 4 °C. Single-crystal X-ray analysis indicated that the methanol molecules are
not incorporated into the crystal lattice after the recrystallization process ([Mn(C31H28N2O2)
(C13H9O2)] (2)). In the structure Mn(III) is surrounded by two nitrogens and four oxygens of deproto-
nated Schiff base and α-hydroxy ketone ligands, and adopts a distorted octahedral geometry.
Keywords: Tetradentate Schiff base; Manganese(III) complex; Crystal structure; Spectral analysis;
Thermal analysis; Quantum chemical calculations
*Corresponding author. Emails: adaxe13@wp.pl; agata.bartyzel@poczta.umcs.lublin.pl
© 2015 Taylor & Francis

2
A. Bartyzel and A.A. Kaczor
1. Introduction
The chemistry of manganese has been the subject of many studies, since this metal is a
constituent or a cofactor for a number of important enzymes, e.g. superoxide dismutase,
catalase, oxalate oxidase, arginase, cholinesterase, phosphoglucomutase, etc. [1]. There is
further interest in the study of manganese compounds due to their magnetic [2], photolumi-
nescence [3], antifungal, antibacterial [4], and catalytic properties [5]. Special attention has
been paid to the studies of manganese complexes with ligands containing N and/or O
donors, due to their interesting coordination chemistry [3(b), 6] and their role in inorganic
biochemistry [6(a, c, and h), 7], catalysis [3(b), 6(f–i), 7(e), 8], and optical [6(h), 9], or
magnetic materials [3(b), 6(c, j–k), 10]. For these reasons, synthesis and characterization of
manganese complexes with polydentate Schiff base ligands, particularly with salen-type
derivatives (tetradentate, N2O2), have been extensively examined [1(c), 2(a), 6(f–i), 7(a, e),
8(a–d)].
In this paper, we present the structure of a manganese(III) complex with mixed ligands.
To the best of our knowledge, few similar structures, i.e. containing salen-type Schiff base
and aldehyde- or ketone-phenolate anions, have been described [11]. The complex pre-
sented here is the first described structure of this kind containing a Mn(III) center. Similar
complexes, but containing Co(III), were prepared by Fukuhara et al. in the reaction of
previously synthesized Co(II)-Schiff base compounds and appropriate phenyl aldehyde or
ketone ligands [11(a)]. Gupta and co-workers synthesized a mononuclear, neutral Co(III)
complex using the direct (where both ligands, a ketone and Schiff base, were used) and
template methods [11(b)]. In our case, similar to the synthesis of Co(III) complex reported
by Kia et al. [11(c)], the Mn(III) complex was prepared by the direct method using man-
ganese(II) salt and Schiff base ligand in 1 : 1 ratio. During synthesis, the partial hydrolysis
process is observed and the final complex contains a tetradentate Schiff base and a ketone
coordinated to Mn(III). We report synthesis, thermal and spectroscopic characterization of
the mononuclear manganese(III) complex (Mn(C31H28N2O2)(C13H9O2)]·CH3OH (1)) with a
tetradentate Schiff base and a ketone (scheme 1). Complex 1 has also been characterized
with molar conductivity and magnetic moment studies. The molecular structure of the
recrystallized complex ([Mn(C31H28N2O2)(C13H9O2)] (2)) was also determined by X-ray
crystallography. Furthermore, quantum chemical calculations were performed to address the
structure of 2 and to compute IR and UV–vis spectra.
2. Experimental
2.1. Materials
The 2,2-dimethyl-1,3-propanediamine and 2-hydroxybenzophenone (K) (scheme 1) used for
preparation of a Schiff base were obtained from Aldrich Chemical Company. The metal salt
Mn(NO3)2·4H2O was purchased from Merck. The organic solvents (MeOH, EtOH, ACN,
DMF, and THF) were purchased from Polish Chemical Reagents in Gliwice (Poland). All
solvents and chemicals were reagent grade and used without purification.

Manganese(III) Schiff base complex
3
2.2. Synthesis
2.2.1. Preparation of 2,2′-((2,2-dimethylpropane-1,3-diyl)bis((nitrilo)(phenylmethyli-
dyne)))-diphenol (SchB). The Schiff base (scheme 1) was synthesized according to the
method described in previous papers [12]. A solution of 10 mmol 2-hydroxybenzophenone
and 5 mmol 2,2-dimethyl-1,3-propanediamine in 60 mL of methanol was refluxed for 5 h.
The excess of the solvent (ca. 50 mL) was then evaporated. After cooling to 4 °C, a yellow
solid was produced. The polycrystalline product was collected by filtration, washed with
methanol, and dried (74.5% yields). Elemental analysis of C31H30N2O2, Calcd (%): C,
80.49; H, 6.54; N, 6.06. Found: C, 80.41; H, 6.63; N, 5.98.
2.2.2. Preparation of 1 and 2. A mixture of stoichiometric amounts of manganese(II)
nitrate (1 mmol) and Schiff base (1 mmol) in 15 mL of methanol was placed in a 100-mL
Teflon vessel. The reaction mixture was heated to 50 °C for 20 min and kept at that tem-
perature for 1.5 h. The content of the vessels was stirred during the whole time of the syn-
thesis and then cooled. The solution was left in air allowing complete evaporation of
solvent. A solid, dark-brown product (2-benzoylphenolato-(2,2′-((2,2-dimethylpropane-1,3-
diyl)bis((nitrilo)(phenyl-methylidyne)))-diphenolato-manganese(III) methanol solvate (1))
was washed with cold methanol until pH of the filtrate was 5. The residue was dried in air
and later recrystallized from methanol. The yield of the purified complex was 44.6%. Ele-
mental analysis of [Mn(C31H28N2O2)(C13H9O2)]·CH3OH (M = 744.75 g mol−1). Calcd (%):
C, 72.57; H, 5.55; N, 3.76. Found: C, 72.19; H, 5.41; N, 3.78. After dissolving the pure
recrystallized compound (50 mg) in methanol and slowly evaporating the solvent at 4 °C, a
few single crystals suitable for X-ray analysis were obtained (2-benzoylphenolato(2,2′-((2,
2-dimethylpropane-1,3-diyl)bis((nitrilo)(phenyl-methylidyne)))-diphenolato-manganese(III)
(2)). The yield of 2 was 11.6%. Elemental analysis of [Mn(C31H28N2O2)(C13H9O2)]
(M = 712.71 g mol−1). Calcd (%): C, 74.15; H, 5.23; N, 3.93. Found: C, 74.43; H, 5.12; N,
4.01.
2.3. Methods and physical measurements
The microwave oven used in this study was a CEM MARS-5 system equipped with tem-
perature and pressure controllers. Elemental analysis for C, H, and N was performed using
a Perkin-Elmer CHN 2400 analyzer. Magnetic susceptibility measurement was conducted at
295 K using a magnetic susceptibility balance MSB-MKI, Sherwood Scientific Ltd,
Cambridge. The data were corrected for diamagnetic susceptibilities [13]. The effective
magnetic moment was calculated from the equation µeff = 2.828(χcorT)1/2. The molar con-
ductivities were measured at 25 °C using a PHYWE 13701.93 conductivity meter. The
infrared spectra were obtained using a Thermo Scientific Nicolet 6700 FTIR with a Smart
iTR diamond ATR accessory. The data were collected between 4000 and 600 cm−1 with a
resolution of 4 cm−1 for 16 scans (figures S1–S4, see online supplemental material at http://
dx.doi.org/10.1080/00958972.2015.1073268). The UV–vis spectra were obtained by a
Genesys 10s spectrophotometer (Thermo Scientific) using 1.0 cm quartz cells. Thermal sta-
bility and decomposition of the analyzed complexes were determined by a Setaram Setsys
16/18 derivatograph, recording TG, DTG, and DSC curves. The samples [5.33 mg (1) and
2.65 mg (2)] were heated in a ceramic crucible between 30 and 850 °C in flowing air

4
A. Bartyzel and A.A. Kaczor
atmosphere (v = 1 dm3 h−1) with a heating rate of 10 °C min−1. The TG–FTIR of the title
compound was recorded using the TGA Q5000 analyzer TA Instruments, New Castle,
Delaware, USA, interfaced to the Nicolet 6700 FTIR spectrophotometer (Thermo
Scientific). About 16.36 mg of 1 was put in an open ceramic crucible and heated from 30
to 1000 °C. The analysis was carried out at a heating rate of 20 °C min−1 under nitrogen at
a flow rate of 50 mL min−1. To reduce the possibility of gasses condensing along the trans-
fer line, the temperature in the gas cell and transfer line was set to 250 and 240 °C, respec-
tively. Gas analysis was performed by matching the spectra against those from the spectrum
library Nicolet TGA Vapor Phase of the software Ominic together with the literature
sources.
2.4. X-ray crystallographic studies
Single-crystal diffraction data were collected using an Oxford Diffraction Xcalibur CCD
diffractometer with graphite-monochromated MoKα radiation (λ = 0.71073 Å). The tem-
perature for the experiment was maintained at 100 K with an Oxford Cryosystem N2 gas-
stream cooling device. The programs CrysAlis CCD and CrysAlis Red [14(a)] were used
for data collection, cell refinement, and data reduction. A semi-empirical absorption–correc-
tion based on the intensities of equivalent reflections was applied, and the data were cor-
rected for Lorentz and polarization effects. The structure was solved by direct methods
using SHELXS-2013 and refined by full-matrix least squares on F2 using SHELXL-2013
[14(b)], both operating under WinGX [14(c)]. All non-hydrogen atoms were refined with
anisotropic displacement parameters. Hydrogens residing on carbon were positioned geo-
metrically and refined applying the riding model [C–H = 0.95–0.98 Å and with Uiso(H) =
1.2 or 1.5 Ueq(C)]. The molecular plots were drawn with ORTEP3 for Windows [14(d)],
Mercury [14(e)] and Diamond [14(f)]. The geometrical calculations were performed using
the PLATON program [14(g)].
2.5. Quantum chemical calculations
The energy and geometry of the ketone, Schiff base, and 2 were optimized using the
Hartree–Fock and B3LYP DFT [15(a) and (b)] methods and 6-311++G(3df,3pd) basis set
of Gaussian09 [15(c)]. The simulations of manganese compounds, in particular carried out
using DFT methods, often reveal a very poor convergence of the iterative procedure for
finding the solution of the Kohn–Sham equations [15(d)]. Thus, we employed a step-by-
step procedure of complex optimization, starting with the semi-empirical PM6 method, then
HF/6-31G(d,p) optimization and finally HF/6-311++G(3df,3pd) and B3LYP/6-311++G
(3df,3pd). The selection of the final basis set was a compromise between the accuracy of
the computations and the available resources. Visualization of data was performed with
Discovery Studio v. 3.1 [15(e)] and Gabedit v. 2.4.8 [15(f)]. Next, IR spectra were com-
puted for the ketone, Schiff base, and complex using the Hartree–Fock and B3LYP method
and 6-311++G(3df,3pd) basis set of Gaussian09. Preliminary vibrational band assignment
was performed using ChemCraft v. 1.7 software [15(g)] and based on the literature (see
table 1, Supplementary data). Moreover, the computed vibrational frequencies have been
unambiguously assigned by means of the potential energy distribution analysis of all the
fundamental vibration modes using VEDA 4 program [15(h–i)] as described previously
[15(j–l)] (tables S2–S4, Supplementary data). Chemissian v. 4.01 [15(m)] was used for
visualization of UV–vis spectra.

Manganese(III) Schiff base complex
5
Table 1. Molar conductivity data of
1
(concentration
1.0 × 10−3, T = 25 °C).
Complex
Solvent
Λ
m [Ω−1 cm2 mol−1
]
MeOH
EtOH
DMF
ACN
THF
92.30
39.40
78.80
54.80
0.85
3. Results and discussion
The most common synthesis of metal complexes is the reaction of metal salts with Schiff
base ligand (direct method) or with ketone/aldehyde and amine (template method) in a
refluxing organic solvent [11, 16]. Here, we applied the microwave technique because it
allows improving product yields, reducing reaction times, making it appropriate for green
chemistry, and energy-saving processes. The new complex of manganese(III) was synthe-
sized by the reaction of Mn(II) salt and SchB. During the synthesis, a partial hydrolysis of
Schiff base ligand is observed. As a result, one product of hydrolysis (ketone) is bound to
the metal center to give a complex [Mn(C31H28N2O2)(C13H9O2)]·CH3OH (1). Complex 1
is stable at room temperature, both isolated and in solution. The room temperature magnetic
moment of the complex is 5.17 µB, confirming that Mn2+ was oxidized to Mn3+. The value
is close to the literature ones (4.80–5.00 µB) for high-spin (S = 2) magnetically dilute d4
manganese(III) ion with an octahedral geometry. It is characteristic of monomeric Mn(III)
complexes, where metal ion indicates little or no antiferromagnetic interaction [6(j–k),
7(e)]. X-ray structure analysis confirmed the formation of a monomeric complex. The molar
conductivities of 1 were measured in different solvents (table 1) at 10−3 mol L−1. The molar
conductivity of 1 performed in THF (0.85 Ω–1 cm2 mol–1) indicates the non-electrolytic
nature. In the case of complex solution in ACN, the molar conductivity is
54.80 Ω–1 cm2 mol–1. This value is lower than that characteristic of uni-univalent (1 : 1)
electrolyte (120–160 Ω–1 cm2 mol–1) [17], but it indicates that complex is partially
dissociated. In remaining solvents, the complex behaves as a uni-univalent (1 : 1) electrolyte
[17] which also indicate that in solution ketone ligand coordinating to Mn(III) ion is
replaced by appropriate solvent molecules.
3.1. Infrared spectra
In the solid state, SchB exists in the enolimine form [18]. Similar to previous reports [16],
the ν(O–H) band is not observed due to the presence of a strong intramolecular hydrogen
bond O–H. . .N [19]. For a similar reason, ν(O–H) band is not detected in the spectrum of the
ketone because of the strong intramolecular hydrogen bonds O–HÁ Á ÁO [20]. The presence of
intramolecular hydrogen bonds in SchB and K ligands influences the electron density of the
C=N and C=O groups, which causes the corresponding stretching vibrations [ν(C=N) and
ν(C=O)] to be observed at lower frequency (at 1596 and 1626 cm−1, respectively). All these
results are consistent with the crystal structures and are in agreement with the literature
[18–20]. In spectra of 1 and 2, ν(C=N) band occurs at similar frequencies compared to the

6
A. Bartyzel and A.A. Kaczor
free Schiff base, i.e. 1595 cm−1 (for 1) and 1594 cm−1 (for 2). In the case of ν(C=O) band,
coordination of the carbonyl oxygen to Mn(III) has stronger influence on electron density of
the C=O and shifts the band to a lower wavelength (1620 cm−1 for 1 and 1608 cm−1 for 2).
Similar shifts to lower wavenumber have been reported in the mixed ligand complexes of Sr
(II) and Ba(II) containing 2-hydroxybenzophenone [20(a)]. The Schiff base and ketone
ligand also coordinate Mn(III) ion via deprotonated phenolic oxygen. In analogy to other
complexes, where a metal center is coordinated via the phenoxy group [16, 21], the phenolic
O–H deformation bands (1335, 1221, and 1202 cm−1 for K and 1331, 1218, and 1200 cm−1
for SchB) do not occur in the spectrum of complexes. In the case of 1, a molecule of metha-
nol is also included in the structure. The bands connected with the presence of CH3OH in 1
are observed at 3368 cm−1 [ν(O–H)], 1307 cm−1 [ν(C–O)], and 1095 cm−1 [ν(C–O)]. The
remaining bands characteristic of both ligands and 1 and 2 are listed in table S1
(Supplementary data).
The calculated ‘‘raw’’ HF and DFT frequencies are usually significantly overestimated in
comparison to the experimental values because of the lack of electron correlation, an
insufficient basis set and anharmonicity [22(a) and (b)]. Thus, we used the scaling factors
reported in the literature to enhance raw results. The raw IR spectra were scaled with
0.9010 scaling factor for HF/6-311++G(3df,3pd) calculations and with 0.9604 scaling factor
for B3LYP/6-311++G(3df,3pd) calculations [22(c) and (d)]. Owing to the scaling procedure,
we obtained good agreement between the experimental and calculated raw frequencies
(tables S2–S4, Supplementary data).
3.2. Crystal structure
The molecular structure of 2 is displayed in figure 1. The crystallographic and refinement
data for 2 are summarized in table 2. Selected bond distances and angles are listed in
table 3; the hydrogen bond parameters are given in table 4. RMSD measured on heavy
atoms between the X-ray structure and HF/6-311++G(3df,3pd) was 0.9368 Å and between
the crystal-ray structure and B3LYP/6-311++G(3df,3pd) was 0.5738 Å. The superposition
of X-ray structure, HF/6-311++G(3df,3pd) optimized structure, and B3LYP/6-311++G
(3df,3pd) optimized structure is shown in figure S5 (Supplementary data). The largest dif-
ferences between X-ray and computed structures were found for the coordination bonds
around the central Mn. However, the overall geometry of X-ray and computed structures is
similar as indicated by low RMSD values (1.4587 Å between the crystal structure and HF/
6-311++G(3df,3pd) optimized structure and 0.9846 Å between the crystal structure and
B3LYP/6-311++G(3df,3pd) optimized structure) and high correlation coefficients R2
(0.9615 for bonds, 0.9427 for angles and 0.9512 for torsion angles between the crystal
structure and HF/6-311++G(3df,3pd) optimized structure; 0.9889 for bonds, 0.9777 for
angles and 0.9623 for torsion angles between the crystal structure and B3LYP/6-311++G
(3df,3pd) optimized structure). During slow recrystallization, methanol molecules are not
included into the crystal structure of 2. Complex 2 crystallizes in the monoclinic space
group P21/n. The Mn center is in an octahedral environment consisting of O1, O2, N1, and
N2 donors (two phenoxo oxygens and two imine nitrogens) from the Schiff base ligand and
O3 and O4 donors (phenoxo and carbonyl oxygens) from the ketone. The manganese ion
has a tetragonally elongated octahedral coordination geometry (see figure 2) which is
typical of the Jahn–Teller distorted d4 high spin Mn(III) [1(c), 6(c) and (i), 10(b), 16, 23].
The equatorial plane is formed by three phenolate oxygens (both ligands) and one nitrogen

Manganese(III) Schiff base complex
7
Figure 1. ORTEP view with the atom numbering scheme of 2. Displacement ellipsoids are drawn at the 50%
probability level. All hydrogens are omitted for clarity.
Table 2. Crystal data and structure refinement for 2.
Formula
[Mn(C31H28N2O2)(C13H9O2)]
712.70
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
100(2)
Monoclinic
P21/n
9.7096(3)
b (Å)
c (Å)
14.6783(6)
24.8962(7)
95.940(3)
β (°)
Volume (Å3)
Z
3529.2(2)
4
Calcd density (g cm−3
)
1.341
0.421
μ (mm−1
)
Absorption correction
F(0 0 0)
Multi-scan
1488
Crystal size (mm)
θ range (°)
Index ranges
0.20 × 0.10 × 0.10
2.59–27.48
−12 <= h <= 12
−19 <= k <= 19
−30 <= l <= 32
29,325/8093
0.0564
Reflections collected/unique
Rint
Data/restraints/parameters
6239/0/368
0.999
GooF on F2
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0443, wR2 = 0.0971
R1 = 0.0727, wR2 = 0.1114

8
A. Bartyzel and A.A. Kaczor
Table 3. Selected bond lengths [Å] and angles [°].
Bond lengths (Å)
O(1)–Mn(1)
O(2)–Mn(1)
O(3)–Mn(1)
O(4)–Mn(1)
N(1)–Mn(1)
N(2)–Mn(1)
1.894(2)
1.895(1)
1.942(2)
2.226(1)
2.029(2)
2.215(2)
C(1)–O(1)
C(7)–N(1)
C(14)–N(1)
C(16)–N(2)
C(19)–N(2)
C(21)–O(2)
C(32)–O(3)
C(38)–O(4)
1.324(2)
1.304(3)
1.481(2)
1.471(3)
1.284(2)
1.329(2)
1.324(2)
1.242(2)
Bond angles (º)
O(2)–Mn(1)–O(1)
O(2)–Mn(1)–O(3)
O(1)–Mn(1)–O(3)
O(2)–Mn(1)–N(1)
O(1)–Mn(1)–N(1)
O(3)–Mn(1)–N(1)
O(2)–Mn(1)–N(2)
O(1)–Mn(1)–N(2)
89.64(6)
92.80(6)
171.04(6)
173.59(6)
87.07(7)
91.28(6)
85.33(6)
101.61(6)
O(3)–Mn(1)–N(2)
N(1)–Mn(1)–N(2)
O(2)–Mn(1)–O(4)
O(1)–Mn(1)–O(4)
O(3)–Mn(1)–O(4)
N(1)–Mn(1)–O(4)
N(2)–Mn(1)–O(4)
87.19(6)
89.94(6)
93.76(6)
89.34(6)
81.90(5)
91.70(6)
169.00(6)
Table 4. Hydrogen bonding and C–HÁ Á Áπ interactions [Å, °].
Hydrogen bonds
D–HÁ Á ÁA
C10–H10Á Á ÁO2i
d(D–H)
0.95
0.95
d(HÁ Á ÁA)
2.45
2.49
d(DÁ Á ÁA)
3.364(2)
3.202(3)
∠DHA
162
131
C9–H9Á Á ÁO3i
C–H. . .π interactions
C–HÁ Á ÁCg
d(HÁ Á ÁCg)
2.95
2.74
d(CÁ Á ÁCg)
3.609(2)
3.682(2)
∠CHCg
126
172
C27–H27Á Á ÁCg6ii
C17–H17CÁ Á ÁCg9i
i
Symmetry codes: 1/2−x, 1/2+y, 1/2−z; ii 1/2−x, −1/2+y, 1/2−z
(N(1)), while the axial positions are occupied by carbonyl oxygen (O(4)) and nitrogen
(N(2)). In most octahedral, manganese complexes of the salen-type Schiff base, the
equatorial planes were generally defined by two N and two O of this ligand [6(c) and (k),
23(b)–(d), 24(a)–(d)]. As already mentioned, in this complex the four atoms (N1, N2, O2,
and O1) are not coplanar, with the torsion angle ∠N1–N2–O2–O1 −44.18(5)°. Similar
arrangement of the Schiff base around Mn(III) ion is observed in complexes reported by
Watkinson et al. [6(j)], Cheng et al. [ 8(d)] or Ha [24(e)] and is probably due to the pres-
ence of chelating ligand in the coordination sphere of a metal. Mn(III) ion lies 0.690 Å out
of the mean plane formed by N1N2O2O1 of the Schiff base ligand. The equatorial atoms
[N(1), O(1), O(2), and O(3)] are nearly planar with the largest deviation from the mean
plane being 0.123 Å for O1. The Mn(III) center lies in the mean N(1)O(1)O(2)O(3) plane
with deviation being only 0.028 Å. The equatorial bond angles at manganese(III) ion are
roughly equal and close to 90° for an ideal octahedron [O(2)–Mn(1)–O(1) 89.64(6)°,
O(2)–Mn(1)–O(3) 92.80(6)°, O(1)–Mn(1)–N(1) 87.07(7)° and O(3)–Mn(1)–N(1) 91.28
(6)°]. The axial bond angle [N(2)–Mn(1)–O(4) 169.00(6)°] departs significantly from linear-
ity. It is worth noting that the axial Mn–O bond is significantly longer than the equatorial
Mn–O bonds by 0.28–0.33 Å, as expected for Jahn–Teller distortion of Mn centers with a

Manganese(III) Schiff base complex
9
Figure 2. Coordination environment of Mn(III) ion.
+3 oxidation state [1(c), 6(c) and (i), 10(b), 16, 23(a)–(c)]. The small effect on Mn–O bond
lengths can be associated with the nature of bonds as it has been suggested by Bermejo and
co-workers [25]. In the case of oxygen in the equatorial plane, there is an ionic bond
between the deprotonated phenol groups (negatively-charged O ions) and manganese(III)
cation whereas Mn–O(4) bond is a coordination one. The short bond length C(38)–O(4) of
1.242(2) Å is equal to that in the free ketone ligand (1.240(4) Å) [20(a)] and indicates that
O(4) is a ketone donor rather than a charged donor [25]. However, if we compare the pre-
sent Mn(III) complex with a similar type of cobalt(III) compounds, where the Jahn–Teller
effect is not observed, the differences between Co–Ocarbonyl and Co–Ophenoxy bonds are less
than 0.05 Å [11(b) and (c)]. This confirms that the elongation of Mn–O bond in the axial
position is mainly related to the Jahn–Teller effect. All bond lengths around Mn(III) centers

10
A. Bartyzel and A.A. Kaczor
are comparable to the analogs in the literature i.e. the manganese(III) Schiff base complexes
with octahedral metal ion surrounded by nitrogen and oxygen donors [1(c), 6(c, f and h–j),
10(b), 16, 23(a) and (b), 26]. Coordination of Schiff base to manganese(III) does not have a
significant effect on C=N bond lengths as can be seen in the complexes reported by Sang
et al. [23(c)] or Song et al. [26(c)] where shortening or extending of azomethine bond
length was observed. The C=N bond distances are 1.284(2) and 1.304(3) Å in 2 and 1.289
(3) and 1.296(3) Å in the free Schiff base [18]. The Schiff base ligand is tetradentate, form-
ing three fused six-membered chelate rings (A: Mn/O1/C1/C6/C7/N1; B: Mn/N1/C14/C15/
C16/N2; C: Mn/O2/C21/C20/C19/N2) around manganese(III), while the ketone is bidentate,
also forming a six-membered ring (D: Mn/O3/C32/C37/C38/O4). The A ring presents inter-
mediate conformation between envelope and screw-boat with the Cremer–Pople parameter
Q = 0.623(1) Å, θ = 64.4(2)° and φ = 15.4(2)°. The B ring adopts a chair conformation
[Q = 0.606(2) Å, θ = 3.7(2)° and φ = 193(3)°] while the C and D rings form distorted
screw-boats (Q = 0.652(2) Å, θ = 68.3(2)° and φ = 28.8(2)° for C; Q = 0.452(2) Å,
θ = 70.3(2)° and φ = 29.7(2)° for D) [27].
There are no strong hydrogen bonds and the structure is stabilized by weak intermolecu-
lar C–HÁ Á ÁO hydrogen bonds and C–HÁ Á Áπ(ring) interactions. Hydrogens of the benzene ring
interact with phenolic oxygens of neighboring molecules through a pair of Car–HÁ Á ÁO
hydrogen bonds, forming a cyclic hydrogen bonded motif with the graph set notation,
R22(7). Car–HÁ Á ÁO hydrogen bonds are found between C9–H9Á Á ÁO3i and C10–H10Á Á ÁO2i
[symmetry code (i): 1/2 − x, 1/2 + y, 1/2 − z (table 4)]. The lengths of these interactions
(CÁ Á ÁO) are 3.364(2) and 3.202(3) Å and on the basis of geometric considerations they can
be classified as weak hydrogen bonds [28]. Intermolecular C–HÁ Á ÁCg contacts (table 4,
figure 3) occur between centroids of the two phenyl rings (Cg6 and Cg9, centroid of the
phenyl formed by C8–C13 and C32–C37) and phenyl hydrogen [C27–H27Á Á ÁCg6ii,
symmetry code (ii): 1/2 − x, −1/2 + y, 1/2 − z] and methyl hydrogen [C17–H17CÁ Á ÁCg9i,
symmetry code (i): 1/2 − x, 1/2 + y, 1/2 − z]. The distances of C–HÁ Á ÁCg contacts are 3.609
(2) Å for C27–H27Á Á ÁCg6 and 3.682(2) Å for C17–H17CÁ Á ÁCg9. The intermolecular
C–HÁ Á ÁO hydrogen bonds and C–HÁ Á Áπ(ring) interactions link the molecules into chains run-
ning parallel to the [0 1 0] direction (see figure 3). Due to these supramolecular interactions,
the MnÁ Á ÁMn distance of 7.955 Å is too long to establish intermetallic interactions between
neighboring manganese ions. Similar to the related compounds reported by Biswas et al.
Figure 3. Part of the crystal structure of manganese(III) complex showing C–HÁ Á ÁO hydrogen bonds and
C–HÁ Á Áπ(ring) interactions as well as formation of 1-D chains along the b-axis.

Manganese(III) Schiff base complex
11
[29], the lack of bridging ligands [6(f and h), 26(b)] rather excludes any kind of
exchange interaction between manganese(III) ions, which confirms the result of the
magnetic study.
3.3. Electronic absorption spectra
The electronic absorption spectra data of 1 and ligands in protic and aprotic solvents are
summarized in table S3 and shown in figures S6–S11 (Supplementary data). The UV–vis
spectra of the Schiff base depend on the type of solvent used. The spectrum of free Schiff
base exhibits five (in protic solvents) or three bands (in aprotic solvents, except the
spectrum recorded in DMF). The bands which are observed in the range 209–229 nm and
258–286 nm can originate from π → π* transitions of the aromatic ring. The next band at
324–325 nm is due to π → π* transition of the azomethine group [16, 30]. Similar to other
Schiff bases [16, 30(c), 31], in protic solvents at 400–403 nm the band originating from
n → π* transition of the azomethine group is also observed. The appearance of the
additional band in polar protic solvents provides information about enolimine–ketoamine
tautomerism of the Schiff base ligand. In polar aprotic solvents, like in the solid state [18],
the ligand is present predominantly as enolimine. According to the literature [16, 31], the
additional band at 400–403 nm can be linked with the shift of the tautomeric equilibrium to
the ketoamine form. The intensity of this band increases with polarity of solvent used. This
confirms the stabilization of the more polar ketoamine form in the more polar solvent,
which was also observed for other Schiff bases [16, 30(c), 31]. UV–vis spectra of K ligand
in different solvents contain three bands (except the spectrum recorded in DMF). Similarly
for SchB ligand, the bands at 210–219 nm and 260–270 nm are due to π → π* transitions
of the aromatic ring. The bands at 334–339 nm originate from n → π* transition in the car-
bonyl group [31(a) and (b), 32]. The spectra of metal compounds contain bands characteris-
tic of both ligand and metal ion [16]. In the complex, the intense absorption bands at 204–
237 and 260–283 nm can be assigned to intraligand π → π* transitions which are typical of
complexes with this type of ligand [16, 30(c), 33]. Mn(III) complexes with octahedral
geometry often show one charge transfer band around 400 nm and a spin allowed d–d
transition band around 500 nm. In the studied complex, the charge transfer band is shifted
to a lower wavelength (358–367 nm) and is observed for the spectra recorded in protic and
DMF solvents. This band can be attributed to the phenolate O(pπ) → Mn(dπ*) ligand-to-
metal charge transfer by analogy with related manganese(III) complexes combined with
n → π* transitions of (C=N) and (C=O) [16, 33]. Similarly to the previously described
manganese(III) complex [16], the band characteristic of d–d transition is not observed in
the spectrum of the studied compound at the concentration used. In more concentrated solu-
tions (1 × 10−3 mol L−1), this band appears as a shoulder ca. 500–540 nm.
Additionally, we calculated UV–vis spectra using the CIS HF, CIS DFT, and TD DFT
methods. For the purpose of UV–vis spectra calculations, the energy and geometry of the
ketone, Schiff base, and the complex were first optimized in solvents using the Polarizable
Continuum Model solvent model [34(a)]. This approach creates a solute cavity via a set of
overlapping spheres. In the case of MeOH : H2O (1 : 1 v/v) mixture, it was assumed that
solvent component descriptors vary linearly; thus, a linear combination of their values may
be used [34(b)]. The values of dielectric constants used in computations were 78.3900 for
water and 32.6130 for methanol, thus the dielectric constant for a mixture of 0.6919 M
fraction of water (assuming density of 1.00 g cm−3) and 0.3081 M fraction of methanol

12
A. Bartyzel and A.A. Kaczor
(assuming density 0.7918 g cm−3) yields 64.2860. The UV–vis spectra were calculated
with the configuration interaction singles (CIS) method [34(c)] for HF- and B3LYP-
optimized structures and time-dependent (TD) approach [34(d)] for B3LYP-optimized
structures. The dielectric constants at infinite frequency, required for the excited state
calculation, were 1.7760 for water and 1.7580 for methanol, yielding the value of this
parameter 1.7704 for the mixture. Surprisingly, the CIS method resulted in better approx-
imation than the TD DFT approach. The UV–vis spectra were enhanced by a scaling proce-
dure according to the scaling factors as previously reported [34(e)]. We proposed scaling
factors for a given basis set, separately for each method and each compound (table 5). The
proposed scaling factors are comparable to those reported by Suendo and Viridi [34(e)].
The inaccuracy of the computed UV–vis spectra for the complex may be caused by insuffi-
cient basis set or insufficient theory level.
3.4. Thermal analysis (TG/DSC and TG/FTIR)
Thermal analyses of the complexes were made by the TG/DSC (air, for 1 and 2) and TG/
FTIR (nitrogen, for 1) techniques. The thermoanalytical curves TG/DTG and DSC for 1
and 2 are presented in figure 4. Complexes 1 and 2 are stable at room temperature. The first
changes in the mass on TG curves (endothermic peak on DSC) of 1 are found above 37 °C
(for air) and 35 °C (for nitrogen). The observed mass losses for this step are 4.13 and
4.53%, respectively, for air and nitrogen analysis. The values are similar, indicating that the
first stage is probably the same in both cases and is related to the release of methanol
(Calcd value 4.30%). The desolvation process is connected with an endothermic effect
recorded on the DSC curve of 1. The enthalpy of this process is equal to 34.4
0.1 kJ mol−1. The first stage, the desolvation process, is also reflected on the FTIR spectra
of the evolved gasses phase. The characteristic vibration bands of CH3OH appear at 3750–
3600, 3150–2750, and 1100–950 cm−1 [16, 35], which confirms the presence of solvent
molecules in the crystal structure of the polycrystalline complex. Further thermal
decomposition of 1 in air takes place in a similar way to that of 2 and includes three stages
during which destruction and combustion of ligands are observed. In the first two stages of
ligand decomposition, which occur between 123–183 °C and 188–345 °C, intermediate,
unstable products are formed; the weight losses are 8.37 and 25.35% for 1 and 3.21 and
21.36% for 2. The last stage above ~350 °C corresponds to complete destruction and com-
bustion of the remaining parts of the ligands and formation of a final product which can be
MnO2 (found and calculated total weight losses are 88.24 and 88.33% for 1; 87.80 and
87.81% for 2), similar to thermal decomposition of complexes reported by Filho et al. and
Goher et al. [36].
In nitrogen atmosphere, thermal decomposition of 1 occurs at the beginning as in air
(figure 4). The step between 120 and 174 °C is assigned to destruction and combustion of
the ligands. The experimental weight loss of this level is 9.36%. This stage is connected
with the release of CO2, CO, and NO and methyl isocyanate. The bands’ characteristic of
carbon dioxide is at 2450–2300 cm−1 and 750–600 cm−1 due to valence and deformation
Table 5. Scaling factors for improvement of calculated UV–vis spectra.
Compound
Schiff base
Ketone
Complex
Method
CIS HF CIS DFT TD DFT CIS HF CIS DFT TD DFT CIS HF CIS DFT TD DFT
Scaling factor 0.9276
0.8995 0.8735 0.9213 0.8877 0.9082 0.5360 0.5468 0.4924

Manganese(III) Schiff base complex
13
Figure 4. TG, DTG and DSC curves for 1 and 2 in air and TG curve in nitrogen.
vibrations, respectively. The double peaks corresponding to CO are at 2275–2050 cm−1.
The bands with the maxima which appear between peaks characteristic of CO2 and CO
(2311, 2305 and 2294 cm−1) are probably due to methyl isocyanate. The weak bands corre-
sponding to NO are recorded at 1950–1750 cm−1 with a characteristic peak at 1875 cm−1
[1(b), 16, 35]. The next stage on the TG curve is at 180–340 °C with the mass loss
25.87%. During this interval, destruction and combustion of the next part of the ligands are
observed and an unstable product is formed. The gaseous products recorded on FTIR spec-
tra are: CO2, NH3, CH4, and methyl isocyanate. Major bands for NH3 are observed at 750–
1200 cm−1 with the characteristic double-peak bands of the maxima at 965 and 931 cm−1.
The weak bands characteristic of CH4 (in the range 3175–2900 cm−1 with the characteristic
maximum at 3016 cm−1) appeared at the end of this stage about 290 °C [1(b), 16, 35, 37].
The intermediate, formed during this stage, is unstable and immediately undergoes further
decomposition. The experimental weight loss of this stage is equal to 48.04%. The gaseous
products released during this step are similar to those observed in the previous one with
more intense bands corresponding to the presence of methane. The methane bands
disappear at 560 °C. The last stage above 600 °C corresponds to the final destruction and

14
A. Bartyzel and A.A. Kaczor
Scheme 1. Ketone (K) and Schiff base (SchB) ligands and manganese(III) complex in the single-crystal (2) form.
combustion of ligands. At the beginning of this step, CO2 and methyl isocyanate were
observed on FTIR spectra. At a higher temperature (ca. 820 °C), the peaks characteristic of
CO are recorded. It can be observed from the TG curve that the decomposition process was
not completed in nitrogen.
4. Conclusion
We synthesized and characterized
a manganese(III) complex ([Mn(C31H28N2O2)
(C13H9O2)]·CH3OH (1)). During the synthesis of 1, we expected that Mn(II) would be oxi-
dized to Mn(III) and the metal center would be coordinated through a tetradentate Schiff
base, solvent molecules, or/and nitrate ion similar to previously reported manganese complex
[16]. Surprisingly the Schiff base is partially hydrolyzed and one of its products, the ketone,
has coordinated to manganese(III). Compound 1 was obtained as an amorphous powder
containing solvent in the structure ([Mn(C31H28N2O2)(C13H9O2)]·CH3OH). After slow
recrystallization at low temperature (4 °C) a few single crystals were obtained. X-ray analy-
sis has revealed that after recrystallization methanol molecules were not incorporated into
the crystal lattice ([Mn(C31H28N2O2)(C13H9O2)] (2)). Thermal decomposition of 1 and 2,
after desolvation of the amorphous complex, takes place in the same way which can indicate
that there is the same coordination environment around manganese(III) (i.e. through two
phenoxo oxygens and two imine nitrogens from the Schiff base ligand and two oxygens
from ketone) in both forms. It should be also noted that in polar solvents (MeOH, EtOH)

Manganese(III) Schiff base complex
15
and DMF, ketone is probably replaced by appropriate solvent molecules causing the complex
to behave like a uni-univalent electrolyte.
Supplementary material
Crystallographic data have been deposited with the CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (Fax: +44 1223 366033; Email: deposit@ccdc.cam.ac.uk or www://www.
ccdc.cam.ac.uk) and are available on request, quoting the deposition number CCDC
1007872.
Acknowledgements
The presented research was partially performed during the postdoctoral stay of Agnieszka
A. Kaczor at the University of Eastern Finland, Kuopio, Finland, under a Marie Curie
fellowship. Calculations were made under a computational grant from the Interdisciplinary
Center of Mathematical and Computational Modelling (ICM) in Warsaw, Poland, grant
number G30-18 and under resources and licenses of CSC, Finland.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Interdisciplinary Center of Mathematical and Computational Modelling (ICM) in
Warsaw, Poland [grant number G30-18].
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