Synthesis and crystal structures of manganese(III) complexes derived from bis-Schiff bases with antibacterial activity

Article abstract of DOI:10.1007/s11243-018-00296-x

Two mononuclear Mn(III) complexes, [MnL¹(N₃)(OH₂)] (1) and [MnL²L′] (2), where L¹ and L² are the dianionic forms of N,N′-bis(3-ethoxysalicylidene)-1,2-ethanediamine (H₂L¹

Full text of DOI:10.1007/s11243-018-00296-x

Transition Metal Chemistry
https://doi.org/10.1007/s11243-018-00296-x
Synthesis and crystal structures of manganese(III) complexes derived
from bis‑Schiꢀ bases with antibacterial activity
Heng‑Yu Qian · Nan Sun2
1
©
Springer Nature Switzerland AG 2019
Abstract
Two mononuclear Mn(III) complexes, [MnL (N )(OH )] (1) and [MnL L′] (2), where L and L are the dianionic forms of
1
2
1
2
3
2
1
2
N,N′-bis(3-ethoxysalicylidene)-1,2-ethanediamine (H L ) and N,N′-bis(3,5-dichlorosalicylidene)-1,4-butanediamine (H L ),
2
2
respectively, and L′ is the deprotonated form of 2,4-dichloro-6-(dimethoxymethyl)phenol (HL′), have been synthesized and
characterized. The complexes were characterized by physico-chemical and spectroscopic methods. The Mn atoms in the
structures are in octahedral coordination. In the crystal structure of complex (1), molecules are linked through intermolecular
O–H···O hydrogen bonds to form dimers. In both complexes, there exist π···π interactions among molecules. The complexes
and the Schiꢀ bases were assayed for antibacterial activities by MTT method.
1
Introduction
two new manganese(III) complexes, [MnL (N )(OH )] (1)
3
2
2
1
2
and [MnL L′] (2), where L and L are the dianionic forms
1
Schiꢀ bases represent one of the most widely utilized classes
of ligands in metal coordination chemistry. They oꢀer ver-
satile and ꢁexible ligands capable of binding various metal
ions to give complexes with versatile structures and proper-
ties [1–5]. Over the past few decades, considerable study has
been made on the chemistry of manganese(III) complexes
derived from Schiꢀ base ligands due to their important role
in catalytic, magnetic and biological applications [6–10]. In
addition, manganese plays an important role in metalloen-
zymes such as catalase [11], superoxide dismutase [12, 13]
and photosystem II of green plants [14, 15]. An important
aspect of Mn(III)-salen-type complexes is their antibacte-
rial application [16–18]. Complexes with mixed ligands
usually have versatile and interesting structures [19, 20].
In order to prepare new manganese complexes and explore
their biological application, we report here the synthesis and
characterization including single crystal X-ray structures of
of N,N′-bis(3-ethoxysalicylidene)-1,2-ethanediamine (H L )
2
and N,N′-bis(3,5-dichlorosalicylidene)-1,4-butanediamine
2
(H L ), respectively, and L′ is the deprotonated form of
2
2,4-dichloro-6-(dimethoxymethyl)phenol (HL′). The anti-
bacterial activity against three Gram-positive bacterial
strains (B. subtilis, S. aureus and St. faecalis) and three
Gram-negative bacterial strains (E. coli, P. aeruginosa and
E. cloacae) by MTT method was studied.
Experimental
Materials and physical methods
1
2
The Schiꢀ base compounds H L and H L were prepared
2
2
by 2:1 condensation of 3-ethoxysalicylaldehyde with ethane-
1,2-diamine, and 3,5-dichlorosalicylaldehyde with butane-
1
,4-diamine, respectively, in methanol, according to the lit-
erature method [21]. All the other reagents and solvents were
purchased from Aldrich with AR grade. FT-IR spectra were
recorded as KBr pellets on a Bruker Tensor-27 spectrometer.
Elemental (C, H and N) analyses were performed on a Perki-
nElmer 2400 II analyzer. Single crystal X-ray diꢀraction was
carried out with a Bruker Apex II CCD diꢀractometer. Elec-
tronic spectra were obtained with Lambda 35 spectropho-
tometer. Molar conductivity of the complexes in acetonitrile
was measured with a DDS-11A molar conductivity meter.
*
Heng-Yu Qian
hengyu_qian@126.com
1
Key Laboratory of Surface and Interface Science of Henan,
School of Material and Chemical Engineering, Zhengzhou
University of Light Industry, Zhengzhou 450002,
People’s Republic of China
2
College of Chemistry, Chemical Engineering and Material
Science, Shandong Normal University, Jinan 250014,
People’s Republic of China
Vol.:(0
1
123456789)
3

Transition Metal Chemistry
Caution! Perchlorate and azide complexes of metal ions
are potentially explosive. Only a small amount of mate-
rial should be prepared, and they should be handled with
caution.
(15,270), 417 (8180). Magnetic moment: 4.72 B.M. Λ
M
−
3
−1
2
−1
(10 M in acetonitrile): 43 Ω cm mol .
Synthesis of complex (2)
2
Synthesis of complex (1)
To a stirred suspension of H L (0.432 g, 1.00 mmol) and
2
3
,5-dichlorosalicylaldehyde (0.190 g, 1.00 mmol) in meth-
1
To a stirred suspension of H L (0.356 g, 1.00 mmol)
anol (20 mL) was added dropwise a methanol solution
(10 mL) of manganese(II) perchlorate hexahydrate (0.254 g,
1.00 mmol). After a few minutes, a brown solution was
formed. The solution was ꢂltered, and the ꢂltrate was kept
for slow evaporation. The diꢀraction quality deep brown sin-
gle crystals that deposited over a period of a few days were
collected by ꢂltration and washed with methanol. The yield
was 275 mg (38%). Anal. Calc. (%) for C H Cl MnN O :
2
and sodium azide (0.065 g, 1.00 mmol) in methanol
(
20 mL) was added dropwise a methanol solution (10 mL)
of manganese(II) perchlorate hexahydrate (0.254 g,
.00 mmol). After a few minutes, a brown precipitate
1
started to deposit. This was dissolved by adding the requisite
amount of acetonitrile. After 1 h stirring, the solution was
ꢂltered and the ꢂltrate was kept for slow evaporation. The
diꢀraction quality deep brown single crystals that depos-
ited over a period of a few days were collected by ꢂltration
and washed with methanol. The yield was 272 mg (58%).
Anal. Calc. (%) for C H MnN O : C, 51.2; H, 5.2; N, 14.9.
2
7
23
6
2
5
C, 44.8; H, 3.2; N, 3.9. Found (%): C, 44.7; H, 3.2; N, 4.0. IR
−
1
data (KBr, cm ): 1637 s, 1612 s, 1472 w, 1443 m, 1381 m,
1285 m, 1263 w, 1175 w, 1102 m, 1080 m, 952 m, 873 m,
771 w, 735 w, 644 w, 532 w, 478 w. UV–Vis data [metha-
20
24
5
5
−
1
−1
−1
Found (%): C, 51.3; H, 5.3; N, 14.7. IR data (KBr, cm ):
nol, λ/nm (ε/L mol cm )]: 275 (16,740), 315 (12,385),
−
3
3
1
378 w, 2031 s, 1606 s, 1445 m, 1372 m, 1257 w, 1185 m,
077 s, 943 m, 862 s, 765 w, 634 w, 551 w, 439 w. UV–Vis
445 (7232). Magnetic moment: 4.72 B.M. Λ (10 M in
M
−
1
2
−1
acetonitrile): 20 Ω cm mol .
−
1
−1
data [methanol, λ/nm (ε/L mol cm )]: 270 (18,355), 305
Table 1 Crystallographic data
(
1)
(2)
and reꢂnement details for
complexes (1) and (2)
Molecular weight
469.38
723.11
Crystal color, habit
Crystal size, mm
Crystal system
Space group
Brown, block
0.18×0.17×0.17
Monoclinic
Brown, block
0.25×0.23×0.23
Triclinic
P2 /c
P1̄
1
Unit cell dimensions
a, Ǻ
b, Ǻ
c, Ǻ
α, °
β, °
γ, °
14.2751(8)
22.2214(12)
13.6275(7)
90
91.6220(10)
90
4321.1(4)
8
1.443
10.3872(11)
11.3040(12)
13.9229(12)
108.271(2)
94.174(2)
100.946(2)
1508.7(3)
2
3
V, Ǻ
Z
−3
ρcalcd, g cm
1.592
1.009
μ, mm−
1
0.653
θ Range collected, deg
Tmin and Tmax
1.43–24.58
0.8916 and 0.8971
21,144/7215
4451
2.72–25.50
0.7864 and 0.8010
14,066/5582
4580
Reꢁections collected/unique
Observed reꢁections
(
I≥2σ(I))
Data/restraints/parameters
GOOF on F
7215/6/575
0.996
5582/0/372
1.038
2
R , wR (I≥2σ(I))
0.0413, 0.0934
0.0877, 0.1124
0.320/–0.315
0.0423, 0.0914
0.0559, 0.0996
0.354/–0.348
1
2
R , wR (all data)
1
2
−3
Largest diꢀerences in peak/hole, e Ǻ
1
3

Transition Metal Chemistry
X‑ray structure determination
Table 2 Selected bond distances (Å) and angles (°) for complexes (1)
and (2)
Intensity data of the complexes were collected at 298(2) K
on a Bruker Apex II CCD diꢀractometer using graphite-
(
1)
Mn(1)–O(1)
1.877(2) Mn(1)–O(2)
2.323(3) Mn(1)–N(1)
1.970(3) Mn(1)–N(3)
1.877(2) Mn(2)–O(7)
2.334(2) Mn(2)–N(6)
1.975(3) Mn(2)–N(8)
1.871(2)
1.978(3)
2.261(3)
1.881(2)
1.978(2)
2.269(3)
92.20(11)
monochromated MoK radiation (λ=0.71073 Å). For data
α
Mn(1)–O(3)
Mn(1)–N(2)
Mn(2)–O(6)
Mn(2)–O(8)
Mn(2)–N(7)
O(2)–Mn(1)–O(1)
processing and absorption correction, the packages SAINT
and SADABS were used [22]. Structures of the complexes
were solved by direct and Fourier methods and reꢂned by
2
full-matrix least-squares based on F using SHELXL-97
[
23]. The non-hydrogen atoms were reꢂned anisotropically.
93.45(9)
O(2)–Mn(1)–N(2)
The water H atoms in complex (1) were located from dif-
ference Fourier maps. The remaining hydrogen atoms have
been placed at geometrical positions with ꢂxed thermal
parameters. Crystallographic data of the complexes (1) and
O(1)–Mn(1)–N(2) 172.67(12) O(2)–Mn(1)–N(1) 174.71(12)
O(1)–Mn(1)–N(1)
O(2)–Mn(1)–N(3)
N(2)–Mn(1)–N(3)
O(2)–Mn(1)–O(3)
N(2)–Mn(1)–O(3)
N(3)–Mn(1)–O(3) 170.31(10) O(6)–Mn(2)–O(7)
O(6)–Mn(2)–N(7) 173.90(10) O(7)–Mn(2)–N(7)
O(6)–Mn(2)–N(6)
N(7)–Mn(2)–N(6)
O(7)–Mn(2)–N(8)
N(6)–Mn(2)–N(8)
O(7)–Mn(2)–O(8)
N(6)–Mn(2)–O(8)
91.66(11) N(2)–Mn(1)–N(1)
96.02(10) O(1)–Mn(1)–N(3)
90.99(11) N(1)–Mn(1)–N(3)
82.59(13)
93.04(10)
85.04(11)
90.75(9)
85.94(10)
93.86(9)
(
2) are summarized in Table 1. Selected bond lengths and
92.64(9)
O(1)–Mn(1)–O(3)
angles are listed in Table 2.
84.33(10) N(1)–Mn(1)–O(3)
91.89(10)
Antibacterial activity
91.42(10) O(7)–Mn(2)–N(6) 173.13(10)
82.69(11) O(6)–Mn(2)–N(8)
99.09(10) N(7)–Mn(2)–N(8)
84.96(10) O(6)–Mn(2)–O(8)
93.37(10)
87.72(11)
89.51(9)
Antibacterial activity of the complexes was tested against B.
subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli and E.
cloacae using MTT medium. The minimum inhibitory con-
centrations (MICs) of the compounds were determined by a
colorimetric method using MTT dye [24]. A stock solution
92.72(9)
82.93(9)
N(7)–Mn(2)–O(8)
N(8)–Mn(2)–O(8) 167.61(10)
88.18(10)
(
2)
−1
of the compounds (50 μg mL ) in DMSO was prepared, and
quantities of the compounds were incorporated in speciꢂed
quantity of sterilized liquid medium. A speciꢂed quantity
of the medium containing the compounds was poured into
micro-titration plates. Suspension of the microorganism was
Mn(1)–O(1)
Mn(1)–O(3)
Mn(1)–N(1)
O(1)–Mn(1)–O(3)
1.8789(18) Mn(1)–O(2)
1.8860(19) Mn(1)–O(4)
2.178(2) Mn(1)–N(2)
1.9308(19)
2.3824(18)
2.037(2)
91.03(9)
O(1)–Mn(1)–O(2)
O(1)–Mn(1)–N(2) 174.46(9)
91.75(9)
O(3)–Mn(1)–O(2) 169.77(8)
5
−1
prepared to contain approximately 10 cfu mL and applied
to micro-titration plates with serially diluted compounds
in DMSO to be tested and incubated at 37 °C for 24 h for
bacteria. After the MICs were visually determined on each
micro-titration plate, 50 μL of phosphate buꢀered saline
O(3)–Mn(1)–N(2)
O(1)–Mn(1)–N(1)
O(2)–Mn(1)–N(1)
O(1)–Mn(1)–O(4)
O(2)–Mn(1)–O(4)
87.89(9)
90.24(8)
91.23(8)
87.98(7)
85.63(7)
O(2)–Mn(1)–N(2)
O(3)–Mn(1)–N(1)
N(2)–Mn(1)–N(1)
O(3)–Mn(1)–O(4)
N(2)–Mn(1)–O(4)
88.40(9)
98.60(8)
95.29(9)
84.63(7)
86.51(8)
−
1
(
PBS 0.01 mol L , pH 7.4: Na HPO 12H O 2.9 g, KH PO
2
4
2
2
4
N(1)–Mn(1)–O(4) 176.34(8)
0
.2 g, NaCl 8.0 g, KCl 0.2 g, distilled water 1000 mL) con-
−
1
taining 2 mg mL of MTT was added to each well. Incu-
bation was continued at room temperature for 4–5 h. The
content of each well was removed, and 100 μL of isopro-
3,5-dichlorosalicylaldehyde produced the mononuclear
manganese(III) complexes (Scheme 1). Clearly, aerial oxida-
tion of manganese(II) to manganese(III) and metal-assisted
deprotonation of the phenolic moieties takes place during
the formation of the complexes. The low solution conduc-
−
1
panol containing 5% 1 mol L HCl was added to extract
the dye. After 12 h of incubation at room temperature, the
optical density (OD) was measured with a microplate reader
at 570 nm.
−
1
2
−1
tivities of the complexes (20–43 Ω cm mol ) indicated
that the ligands are coordinated to the metal center and are
not dissociated in solution.
Results and discussion
Spectroscopy
Chemistry
The characteristic imine stretching of the complexes is
−
1
observed at 1606–1612 cm as a strong signal. In the spec-
Reactions of manganese(II) perchlorate and bis-
tra of (1), the stretching band of water ligand OH groups
−
1
Schiff bases in the presence of sodium azide or
is observed at 3378 cm , and the characteristic band of
1
3

Transition Metal Chemistry
(1)
(
2)
Scheme 1 Synthetic procedures for the complexes
−
1
the azide ligand is observed at 2031 cm . In the spectra of
axial ligand atoms, and O(1), O(2), N(1) and N(2), as well
as O(6), O(7), N(6) and N(7) form the equatorial plane.
The coordination environment of the Mn atoms is slightly
distorted, as evidenced from the bond lengths and angles.
In the equatorial plane, the metal–ligand bond distances
involving the imine nitrogens are slightly longer than the
bond lengths involving phenolate oxygens. As expected due
to Jahn–Teller distortion of high spin manganese(III), the
bond distances involving the axial donor atoms are signiꢂ-
cantly longer than the bond lengths involving the equatorial
atoms. The trans angles (167.61(10)°–174.71(12)°) and the
cis angles (82.59(13)°–99.09(10)°) deviate slightly from the
ideal values. The coordinate bond values are in agreement
with those observed in other manganese(III) complexes
with Schiꢀ bases [25–28]. The average deviation (0.029(5)
Å for Mn(1) and 0.021(5) Å for Mn(2)) of the equatorial
donor atoms and the displacement (0.048(3) Å for Mn(1)
and 0.051(3) Å for Mn(2)) of the metal center from the least-
squares plane deꢂned by the equatorial donor atoms indi-
cates that the N O cavity aꢀords an almost perfect plane
−
1
(
2), the strong band at 1637 cm indicates the presence of
the carbonyl group. The Schiꢀ base ligands coordination is
substantiated by the lowering of the phenolic C–O stretch-
−
1
ing band, which appears at 1180–1185 cm in the com-
−
1
plexes, while observed at about 1200 cm in the free Schiꢀ
bases. Coordination of the Schiꢀ bases is further conꢂrmed
by the appearance of weak bands in the low wave numbers
−
1
4
00–600 cm , corresponding to ν(Mn–N) and ν(Mn–O).
UV–Vis spectrum of the complexes exhibits two typical
bands centered at 410–445 and 305–315 nm which can be
assigned to phenolate→manganese(III) charge transfer and
manganese(III) → imine (d → π*) metal to ligand charge
transfer transitions, respectively. The observed magnetic
moment at 300 K of the complexes is 4.72 B.M., indicating
that the manganese(III) centers in the complexes exist in
high spin state.
Structure description of complex (1)
2
2
The molecular structure of complex (1) is shown in
to the metal center. The Schiꢀ base ligands are approximate
planar with dihedral angels between the benzene rings of
1.1(3)° and 2.3(3)°.
Fig. 1. The asymmetric unit of the complex contains two
1
[
MnL (N )(OH )] molecules. The Mn center is six coordi-
3
2
nated by four donor atoms (N O ) of the coordinated Schiꢀ
2
2
base ligand, one oxygen atom of a water ligand and one
nitrogen atom of an azide ligand. In the octahedral coor-
dination, O(3) and N(3), as well as O(8) and N(8) are the
1
3

Transition Metal Chemistry
Fig. 1 Molecular structure of
complex (1)
N(1) and O(4) are the axial ligand atoms, and O(1), O(2),
N(2) and O(3) form the equatorial plane. The coordination
environment of the Mn atom is slightly distorted, as evi-
denced from the bond lengths and angles. As expected due
to Jahn–Teller distortion of high spin manganese(III), the
bond distances involving the axial donor atoms are signiꢂ-
cantly longer than the bond lengths involving the equato-
rial atoms. The trans angles (169.77(8)°–176.34(8)°) and
the cis angles (84.63(7)°–98.60(8)°) deviate slightly from
the ideal values. The coordinate bond values are in agree-
ment with those observed in manganese(III) complexes with
Schiꢀ bases [25–28]. The average deviation (0.034(3) Å) of
the equatorial donor atoms and the displacement (0.128(2)
Å) of the metal center from the least-squares plane deꢂned
by the equatorial donor atoms indicates that the N O cav-
2
2
Fig. 2 Molecular structure of complex (2)
ity aꢀords an almost perfect plane to the metal center. The
dihedral angel between the two benzene rings of the Schiꢀ
base ligand is 74.2(5)°.
Structure description of complex (2)
Antibacterial activity of the compounds
Molecular structure of complex (2) is shown in Fig. 2. The
Mn center is six coordinated by four donor atoms (N O ) of
The complexes and the free Schiꢀ bases were screened for
antibacterial activities against three Gram-positive bacte-
rial strains (B. subtilis, S. aureus and St. faecalis) and three
Gram-negative bacterial strains (E. coli, P. aeruginosa and
2
2
the coordinated Schiꢀ base ligand, one phenolate oxygen
atom and one ether oxygen atom of the ligand 2,4-dichloro-6-
(dimethoxymethyl)phenolate. In the octahedral coordination,
−
1
Table 3 MICs (μg mL ) of
the compounds and related
materials
Tested material
Gram positive
Gram negative
B. subtilis
S. aureus
St. faecalis
P. aeruginosa
E. coli
E. cloacae
(
1)
2)
12.5
1.56
>50
25
1.56
0.39
6.25
0.78
25
6.25
1.56
1.56
>50
12.5
>50
>50
1.56
3.12
25
>50
6.25
>50
12.5
6.25
3.12
>50
25
>50
>50
3.12
1.56
(
3.12
>50
25
6.25
3.12
1
2
H2L
H2L
Penicillin
Kanamycin
1
3

Transition Metal Chemistry
E. cloacae) by MTT methods. The MICs of the compounds
against the bacteria are presented in Table 3. Penicillin and
Kanamycin were tested as reference drugs. Complex (1)
shows strong activity against S. aureus, medium activities
against B. subtilis and P. aeruginosa and no activity against
St. faecalis, E. coli and E. cloacae. Complex (2) shows
strong activities against B. subtilis, S. aureus, P. aeruginosa
3. Davis KJ, Richardson C, Beck JL, Knowles BM, Guedin
A, Mergny J-L, Willis AC, Ralph SF (2015) Dalton Trans
4
4:3136–3150
4
. Judy-Azar AR, Mohebbi S (2015) J Mol Catal A 397:158–165
5. Li H-H, Zhou X-X, You Z-L (2013) Chin J Inorg Chem
29:649–653
6
.
Sakiyan I, Ozdemir R, Ogutcu H (2014) Synth React Inorg Met-
Org Nano-Met Chem 44:417–423
7
.
Choubey S, Roy S, Bhar K, Mitra P, Ribas J, Ghosh BK (2014)
Polyhedron 74:134–143
and E. coli, medium activities against St. faecalis and E.
1
cloacae. H L shows medium activity against S. aureus,
8. Maiti M, Sadhukhan D, Thakurta S, Zangrando E, Pilet G, Bauza
A, Frontera A, Dede B, Mitra S (2014) Polyhedron 75:40–49
2
2
while no activity against the remaining bacteria strains. H L
2
9
. Erdem O, Guzel B (2014) Inorg Chim Acta 418:153–156
shows strong activity against S. aureus, medium and weak
activities against B. subtilis, P. aeruginosa and E. coli, while
no activity against the remaining bacteria strains. In general,
the antibacterial activities of the two complexes are obvi-
1
0. You Z-L, Liu T, Zhang N, Zhang M, Xian D-M, Li H-H (2012)
Inorg Chem Commun 19:47–50
11. Kar P, Drew MGB, Ghosh A (2013) Inorg Chim Acta
4
05:349–355
1
2. Grau M, Rigodanza F, White AJP, Soraru A, Carraro M, Bonchio
M, Britovsek GJP (2014) Chem Commun 50:4607–4609
ously higher than the free Schiꢀ bases. Complex (2) is more
2
active than complex (1). Similarly, H L is more active than
13. Lieb D, Kenkell I, Miljkovic JL, Moldenhauer D, Weber N, Fil-
ipovic MR, Grohn F, Ivanovic-Burmazovic I (2014) Inorg Chem
53:1009–1020
2
1
H L , which might be attributed to the contribution of the
2
2
chloro-substituent groups of H L .
2
1
4. Liao R-Z, Karkas MD, Lee B-L, Akermark B, Siegbahn PEM
(
2015) Inorg Chem 54:342–351
1
5. Hirahara M, Shoji A, Yagi M (2014) Eur J Inorg Chem
2014:595–606
Conclusion
1
1
6. Hao YM (2015) Russ J Coord Chem 41:25–30
7. Hassan K, Mozhdeh L-D, Majid R, Reza KH (2014) Chin J Inorg
Chem 30:1733–1740
In summary, two new manganese(III) complexes with bis-
Schiꢀ bases have been synthesized and characterized. Crys-
tal structures of the complexes are described. Antibacterial
assays of the free Schiꢀ bases and the complexes show that
the complexes, especially complex 2, are eꢀective against
most of the tested bacteria strains.
18. Sang Y-L, Li X-C, Xiao W-M (2013) J Coord Chem 66:4015–4022
19. Guo S, Sun N, Ding Y, Li A, Jiang Y, Zhai W, Li Z, Qu D, You Z
(
2018) Z Anorg Allg Chem 644:1172–1176
2
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