Evolution from discrete mononuclear complexes to trinuclear linear cluster and 2D coordination polymers of Mn(II) with dihydrazone Schiff bases: Preparation, structure and thermal behavior

Article abstract of DOI:10.1016/j.poly.2021.115329

Four Mn(II) coordination compounds based on the 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H₂L¹) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H₂L²), were prepared using different synthetic condition

Full text of DOI:10.1016/j.poly.2021.115329

Polyhedron 206 (2021) 115329
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Evolution from discrete mononuclear complexes to trinuclear linear cluster
and 2D coordination polymers of Mn(II) with dihydrazone Schiff bases:
Preparation, structure and thermal behavior
a
,
*
b
b
a,
b
a
Lilia Croitor , Maria Cocu , Ion Bulhac , Paulina N. Bourosh , Victor Ch. Kravtsov ,
b
,
c
b,*
Oleg Petuhov , Olga Danilescu
a
Institute of Applied Physics, Academiei 5, MD2028 Chisinau, Republic of Moldova
Institute of Chemistry, Academiei 3, MD2028 Chisinau, Republic of Moldova
b
c
Institute of Geology and Seismology, Gheorghe Asachi 60/3, MD2028 Chisinau, Republic of Moldova
A R T I C L E I N F O
A B S T R A C T
1
Keywords:
Four Mn(II) coordination compounds based on the 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H L ) and
2
Hydrazone Schiff bases
Mn(II) coordination compounds
Crystal structure
2
2
,6-diacetylpyridine bis(nicotinoylhydrazone) (H
2
L ), were prepared using different synthetic conditions and
1
starting manganese salts: discrete mononuclear [Mn(H
2
L )
(2) complexes and two 2D coordination polymers {[Mn
(3) and {[MnL ]⋅dmf} (4), where dmf = N,N-dimethylformamide. Single-crystal X-ray diffraction
L , which differ only by para- or meta- position of radicals with respect to the
nitrogen atoms in the terminal pyridyl fragments, demonstrate chelate or chelate-bridging coordination mode
with N , or N and N donor atoms, respectively. The planar-chelate coordination of these ligands
provides the pentagonal-bipyramidal surrounding of Mn(II) and the terminal pyridyl moieties promote bridging
function and structure expansion in 2–4 as well as octahedral Cl coordination geometry for one of Mn(II)
2
(H
2
2
O) ](NO
3
)
2
(1) and trinuclear
1
(L1)
[
Mn
.5C
study shows that H
3
(H
2
L )
2
(NCS)
2
Cl
4
(H
2
O)
2
]
3
3
2
(H O)
2
]⋅
IR spectroscopic studies
Thermal stability
2
1
2
H
5
OH}
n
n
1
2
L and H
2 2
3
O
2
4
O
2
5 2
O
2 4
N
atoms in the trinuclear complex 2. All compounds have been investigated in the solid state by IR spectroscopy
and thermal analysis in order to understand the influence of the inorganic anion presence/absence on the sta-
bility of synthesized compounds.
1
. Introduction
candidate for preparation of dihydrazone Schiff bases with multiple
coordination sites, giving rise to metal complex compounds with
Hydrazones (R
1
R
2
C = NNR
2
R
4
) represent a class of organic ligands
exclusive geometries. The opportunities for generating new molecular
architectures can be possible by condensation of dap with isonicotinic/
nicotinic acid hydrazides (Scheme 1) [12,13] and by suitable substitu-
tion of their pyridine rings in order to provide additional donor atoms.
capable to coordinate with diverse metal centers generating varied
molecular architectures. The possibility of keto-enol tautomerization
[
1–4], the conformational flexibility, pharmacological activity [5,6] due
to the presence of azomethine moiety and their use in medicine make
them being of great interest. Thus, the development of Schiff base li-
gands with the hydrazone fragment allowed the synthesis of new metal
complexes, which have been employed in numerous fields of scientific
research, due to their chemical, physical, biological and structural
properties, as well as their applications [7–10].
Coordination compounds with the 2,6-diacetylpyridine bis(iso-
1
nicotinoylhydrazone) (H
2
L ) ligand are obtained both from direct and
template synthesis. Analysis of the Cambridge Structural Database
(CSD) [11] revealed twenty coordination compounds of transition
3 2
metals where this ligand predominately acts as a pentadentate N O
ligand and surrounding metal ion in the equatorial plane. The exami-
nation of published examples showed that the L1 moiety forms homo-
and heterometallic complexes coordinating in the neutral, biprotonated
and bideprotonated fashions on nitrogen atoms of the terminal pyridine
The addition of functional groups with potentially donor atoms to
hydrazones leads to the new Schiff base ligands capable of forming
stable chelates [11]. The 2,6-diacetylpyridine (dap) is a suitable
*
Corresponding authors.
E-mail addresses: croitor.lilia@gmail.com (L. Croitor), mariacocu@gmail.com (M. Cocu), ionbulhac@yahoo.com (I. Bulhac), pavlina.bourosh@ifa.md
P.N. Bourosh), victor.kravtsov@ifa.md (V. Ch. Kravtsov), petuhov.chem@gmail.com (O. Petuhov), olgadanilescu@mail.ru (O. Danilescu).
(
https://doi.org/10.1016/j.poly.2021.115329
Received 14 May 2021; Accepted 11 June 2021
Available online 17 June 2021
0
277-5387/© 2021 Elsevier Ltd. All rights reserved.

L. Croitor et al.
Polyhedron 206 (2021) 115329
1
2
2 2
Scheme 1. Graphic representation of the H L and H L ligands synthesis.
fragments (Fig. S1) in consequence providing eleven mononuclear and
two binuclear compounds, as well as one 2D coordination polymer. It is
noteworthy that only five coordination compounds [8,14] were pre-
Thermal analysis was performed on Derivatograph Q-1000 system in
3
◦
nitrogen atmosphere (100 cm /min) at a heating rate of 10 C/min in
the temperature range of 20 – 1000 ◦C. Thermogravimetric (TG), de-
rivative weight loss (DTG) and differential thermal (DTA) curves were
simultaneously registered.
pared through one-pot template synthesis, while the rest of the com-
1
pounds - by direct reaction between H
2
L and transition metal salts.
Our previous study of transition metals coordination compounds
2
with 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H
2
L ) ligand
2.2. Synthesis
[
14–18] also showed that this ligand can coordinate in neutral, bipro-
L1 and H
L .
2
tonated, mono- and bideprotonated modes (Fig. S2), revealing six
mononuclear, two binuclear, and one tetranuclear coordination com-
pounds, as well as one 1D and five ꢀ 2D coordination polymers. Six
compounds [15,18] were obtained by exploring direct synthetic
method, while the others were obtained by template synthesis.
2.2.1. Synthesis of H
2
2
1
The ligands 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H
2
L )
2
and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H
2
L ) were pre-
pared by the condensation of the respective carbonyl compound and
amines using similar methods as described earlier [12,13].
The interest in Mn(II)-based coordination compounds arise not only
from its biomimetic roles [16,19] or as a cofactor for some enzymes
1
2.2.2. Synthesis of [Mn(H
2
L )
2
(H
2
O)
2
](NO
3
)
2
(1)
(
decarboxylase, hydrolase and kinase) [20–23], but also because they
2,6-diacetylpyridine (0.16 g, 1 mmol) in ethanol (10 mL), iso-
nicotinic acid hydrazide (0.14 g, 1 mmol) in ethanol (10 mL) and KSCN
are good precursors for magnetic materials (due to a large number of
unpaired electrons of manganese complexes) [24–28], as well as for its
intricate structures. This transition metal ion easily coordinates with
nitrogen, oxygen and chloride atoms that provide versatile coordination
abilities with the preparation of exciting mono- and polynuclear com-
(0.1 g, 1 mmol) in ethanol (10 mL) were added to Mn(NO
3
)
2
⋅4H
2
O (0.25
g, 1 mmol) in ethanol (10 mL). The yellow solution was refluxed on a
water bath for 3 h until the solution was coloured in orange. After 24 h
yellow crystals were obtained (0.209 g). The product was filtered off and
washed with ethanol and air dried. Yield: 34%. Anal. Calcd. for 1,
pounds [11] with effective biomedical applications [29].
1
The crystals of discrete coordination compounds [Mn(H
2
L )
2
(H
2
O)
2
]
C
21
H
23MnN
9
O
10: C, 40.92; H, 3.76; N, 20.45. Found: C, 40.85; H, 3.80;
1
ꢀ 1
(
NO
3
)
2
(1) and [Mn
(H
3 2
L )
2
(NCS)
2
Cl
(H
4 2
O)
2
] (2) suitable for single-
N, 20.35. IR data (cm ): 3500-3600br, 1656m, 1645m, 1604m, 1556m,
1492w, 1323vs, 1299s, 1230m, 1137m, 1074m, 1041w, 1014m,
1006m, 844m, 826m, 752m, 666w, 552w, 524w, 473w.
crystal diffraction analysis were obtained by template assembly of
1
components, while 2D coordination polymers {[Mn
3
(L )
(4) by the direct reaction between
ligands and manganese sulfate salt.
3
(H
2
O)
2
]⋅
2
1
.5C
2
5
H OH}
n
(3) and {[MnL ]⋅dmf}
n
1
2
1
pre-synthesized H
2
L
and H
2
L
2.2.3. Synthesis of [Mn
3
(H
2
L )
2
(NCS)
2 4 2 2
Cl (H O) ] (2)
Compounds were characterized by single crystal X-ray diffraction
method, IR spectroscopy and thermal analysis.
The mixture of MnCl
2
⋅4H
2
O (0.011 g, 0.05 mmol), KSCN (0.004 g,
0.025 mmol), isonicotinic acid hydrazide (0.007 g, 0.05 mmol) and 2,6-
diacetylpyridine (0.009 g, 0.05 mmol) was dissolved in ethanol (8 mL)
◦
2
. Experimental
was sealed in a Teflon-lined autoclave and heated at 80 C for 72 h under
◦
autogenous pressure. Cooling to room temperature at the rate of 0.6 C/
2
.1. Materials and methods
min afforded the product as yellow acrylic crystals were collected by
filtration (0.001 g) and washed with ethanol and ethylic ether. Yield:
All reagents (dap, inaH, naH, all Mn(II) salts, KSCN) and solvents
2 8 3
~3%. Anal. Calcd. for 2, C22H21Cl Mn1.50N O S: C, 41.89; H, 3.36; N,
ꢀ 1
(
ethanol, dmf) were obtained from commercial sources and were used
17.76. Found: C, 41.23; H, 3.13; N, 17.70. IR data (cm ): 3610-3290br,
3193br, 2070vs, 1693s, 1623s, 1605s, 1491m, 1462m, 1235m, 1171s,
1064m, 1012s, 846s, 814s, 751m, 655m, 559m, 528w, 467m, 441w.
without further purification. Elemental analysis was performed on an
Elementar Analysen systeme GmbH Vario El III elemental analyzer. The
ꢀ 1
IR spectra were obtained in Vaseline oil (400–4000 cm ) and ATR
ꢀ 1
(
650–4000 cm ) on a FT IR Spectrum-100 Perkin Elmer spectrometer.
2

L. Croitor et al.
Polyhedron 206 (2021) 115329
Table 1
Crystallographic data and structure refinement details for compounds 1–4.
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
Z
C
21
H
23MnN
O
9 10
C
22
H
21Cl
2
Mn1.50N
8
O
3
S
C
66
H
64Mn
3
N
21
O
9.50
C
24
H
24MnN
527.45
Orthorhombic
8 3
O
616.42
630.84
Monoclinic
1468.20
Triclinic
P-1
Monoclinic
P2
1
/c
C2/c
1 1
P2 2 2
2
4
4
2
a(Å)
8.3541(5)
10.2910(6)
16.2970(9)
73.649(5)
83.224(5)
73.874(5)
19.741(3)
8.1600(10)
17.245(2)
90
25.6486(10)
9.4136(3)
28.4353(11)
90
12.9449(4)
9.5117(4)
9.9745(4)
90
b(Å)
c(Å)
α(deg)
β(deg)
γ(deg)
112.140(10)
90
99.968(4)
90
90
90
3
V (Å )
1290.32(14)
1.587
2573.1(6)
1.628
6761.9(4)
1.442
1228.14(8)
1.426
–
3
D
c
(g/cm
)
ꢀ
1
μ
(mm
)
0.585
1.079
0.626
0.581
F(000)
634
1282
3032
546
3
Crystal size (mm )
0.30 × 0.20 × 0.07
0.30 × 0.20 × 0.02
0.40 × 0.40 × 0.30
12951/6285
[R(int) = 0.0328]
4896
0.40 × 0.40 × 0.20
3030/1825
Reflections collected/unique
7848/4535
5922/5922
[
R(int) = 0.0237]
[R(int) = 0.0259]
1688
Reflections with [I > 2
σ
(I)]
3662
2371
Data/restraints/parameters
4535/0/386
0.999
5922/72/348
0.918
6285/9/470
1.000
1825/0/155
1.003
2
GOF on F
R
R
1
, wR
, wR
2
[I > 2
σ
(I)]
0.0505, 0.1329
0.0647, 0.1449
0.0629, 0.0875
0.1646, 0.0968
0.0485, 0.1195
0.0661, 0.1290
0.0412, 0.1097
0.0460, 0.1136
1
2
(all data)
2
.2.4. Synthesis of {[Mn
A mixture of MnSO
3
(L1)
⋅5H O (0.012 g, 0.05 mmol), 2,6-diacetylpyr-
3
(H
2
O)
2
]⋅1.5C
2
H
5
OH}
n
(3)
area detector and a graphite monochromator using MoK
α
radiation.
4
2
Determination of the unit cell parameters and processing of experi-
mental data were performed using the CrysAlis Oxford Diffraction Ltd.
[30]. All calculations to solve the structures and to refine the proposed
models were carried out with the SHELXS97 [31] and SHELXL2014
program packages [32]. All non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms attached to carbon and nitrogen atoms were
positioned geometrically and treated as riding atoms. The O-bounded H-
atoms in water molecule in 1–3 were found from differential Fourier
maps at the intermediate stages of the refinement. Compound 2 was
refined as a non-merohedral twin with the component ratio 0.785:0.215.
idine bis(isonicotinoylhydrazone) (0.03 g, 0.075 mmol), dime-
thylformamide (5 mL), ethanol (3 mL) and water (1 mL) was sealed in a
◦
Teflon-lined autoclave (10 mL) and heated at 120 C for 48 h under
◦
autogenous pressure. Cooling to room temperature at the rate of 0.6 C/
min afforded the product as ruby crystals and separated (0.011 g). Yield:
~
3 21
5%. Anal. Calcd. for 3, C66H64Mn N O9.50: C, 53.99; H, 4.39; N,
ꢀ 1
2
1
7
0.03. Found: C, 53.80; H, 4.32; N, 20.12. IR data (cm ): 3245m,
668m, 1602m, 1567s, 1500m, 1219m, 1158s, 1087w, 1066w, 1007m,
99m, 761m, 670m, 586w, 518w, 461w.
Atoms Mn(2), Cl(2) and one pyridine ring of isonicotinic fragment in the
2
1
2
.2.5. Synthesis of {[MnL ]⋅dmf}
n
(4)
H
2
L
molecule in 2 is disordered over two positions with the 0.54 and
A mixture of MnSO
4
⋅5H
2
O (0.012 g, 0.05 mmol), 2,6-diacetylpyr-
0.46 probabilities. The outer sphere ethanol molecule in 3 is disordered
over three positions. The X–ray data and the details of the refinement for
1–4 are summarized in Table 1. Selected geometric parameters for 1–4
are given in Tables S1 and S2. The Figures were produced using the
Mercury program [33]. The solvent accessible voids (SAVs) were
calculated using PLATON [34]. Crystallographic data of the compounds
reported herein were deposited with the Cambridge Crystallographic
Data Centre and allocated the deposition numbers CCDC
2082304–2082307.
idine bis(nicotinoylhydrazone) (0.03 g, 0.075 mmol), dimethylforma-
mide (5 mL), ethanol (3 mL) and water (1 mL) was sealed in a Teflon-
◦
lined autoclave and heated at 120 C for 48 h under autogenous pres-
◦
sure. Cooling to room temperature at the rate of 0.6 C/min afforded the
product as garnet crystals were separated (0.013 g). Yield: 52%. Anal.
Calcd. for 4, C24
H
8 3
24MnN O : C, 54.65; H, 4.59; N, 21.24. Found: C,
ꢀ 1
5
1
5
4.59; H, 4.60; N, 21.30. IR data (cm ): 1672s, 1651m, 1594m, 1582m,
551m, 1495m, 1257m, 1156s, 1136m, 1095m, 1049s, 818m, 754s,
62w, 534w, 418w.
3
. Results and discussion
2
.3. X-ray crystallography
A coherent variation of the synthetic methods (direct or template)
Diffraction measurements for compounds 1–4 were carried out at
room temperature on an Xcalibur E diffractometer equipped with CCD
and the reaction conditions, such as reflux the reactants at room tem-
perature or under solvothermal conditions, taking into account the
Scheme 2. Experimental procedure for the preparation of the obtained coordination compounds.
3

L. Croitor et al.
Polyhedron 206 (2021) 115329
1
2+
cation in 1 with partial atomic numbering scheme (a). Perspective view of the fragment of the H-
Fig. 1. View of the structure of mononuclear [Mn(H
2
L )(H
2 2
O) ]
bonded supramolecular network in 1 in which C-bound H atoms are omitted for clarity (b).
–
(C N) stretching vibration bands in pure organic li-
nature of the solvent and the anion has been undertaken. One-pot syn-
thesis involving Mn(II) salts, dap, and iaH ligands, in C OH solution
presence of the
ν
–
ꢀ 1
ꢀ 1
2 5
H
gands was documented at 1569 cm and 1568 cm while in complexes
ꢀ ꢀ 1
1
results in orange and yellow crystals (Fig. S3) of mono- and trinuclear
Mn(II) compounds 1 and 2 (Scheme 2). In both these cases, the reactions
were carried out in the presence of the KSCN salt. When the corre-
these bands were observed at 1656 cm in 1, 1623 cm in 2, 1567
ꢀ 1
ꢀ 1
–
–
C) absorption bands of the
cm in 3, and 1551 cm in 4. The
ν
(C
ꢀ 1
1
aromatic ring are manifested at 1601, 1495 and 1444 cm in H
2
L , and
2
in H L . These vibrations are observed in
ꢀ
1
2
sponding Schiff base and the MnSO
4
⋅5H
2
O salt were taken as reagents
1594, 1484, 1443 cm
ꢀ 1
complexes at 1604, 1556, 1492 cm in 1, at 1605, 1491 and 1462 cm
ꢀ 1
under solvothermal conditions, ruby/garnet crystals of compounds 3
and 4 were obtained (Scheme 2, Fig. S3).
ꢀ
1
ꢀ 1
in 2, at 1602, 1591, 1500 cm in 3, and at 1594, 1582, 1495 cm in 4
–
The results of this study and our recent publications showed that the
addition of dmf solvent in the synthesis plays a significant role in the
dimensionality extension of coordination compounds: reactions in the
absence of dmf carry to the mononuclear coordination compounds for-
mation (1, 2 and [14,17,35]), while the addition of dmf led to the
fabrication of coordination compounds with higher dimensionality (3, 4
and [15,18]). It has been also observed that the chosen reaction con-
ditions affect the obtaining of pure crystals: in the result of the sol-
vothermal synthesis are obtained crystals with lower yield but with high
purity (2–4), while the refluxing or stirring of the reactants leads to
obtaining of impure crystals, which require additional recrystallization
[36,37]. The solvent dmf molecule in 4 are represented by
ν
(C O) band
–
ꢀ
1
at 1672 cm
.
ꢀ 1
The highest intensity bands from 1323 and 1297 cm , as well as the
band from 826 cm 1 in spectrum 1 are attributed to the NO
ꢀ
ꢀ
anions
3
-
oscillations [36,38]. The coordinated NCS anions through nitrogen
ꢀ
1
atom are manifested via:
the spectrum 2),
ν(CN) – 2070 cm (the most intensive band in
ꢀ 1
ꢀ 1
.
ν
(CS) – 814 cm and δ(NCS) – 467 cm
The type of substitutions in aromatic rings are distinguished by ab-
sorption bands that are manifested by δ(CH)planar oscillations (in region
ꢀ 1
ꢀ 1
1275–1000 cm for 1,4- and 1175–1000 cm for 1,2,3- substitution
ꢀ 1
ꢀ 1
type) and δ(CH)nonplanar (860–800 cm for 1,4- and 810–750 cm for
1,2,3-substitution type) [36,37]. In our compounds the oscillations
(
1). Compounds 2–4 were aimed to be obtained by the same method as 1
ꢀ 1
and unfortunately, it failed.
δ(CH)planar manifested at: 1230, 1014 and 1006 cm in 1, 1235 and
1012 cm in 2, 1219 and 1066 cm in 3, 1257 and 1049 cm in 4
illustrate the 1,4- substitution (two neighbour hydrogen atoms), while
ꢀ
1
ꢀ 1
ꢀ 1
Despite the low yields of some compounds, all syntheses are easily
reproducible. The obtained crystals were checked on a single-crystal X-
ray diffractometer, which demonstrates their reproducibility through
the coincidence of the unit cell parameters.
ꢀ 1
ꢀ 1
those at 1137, 1074 and 1041 cm in 1, 1171, 1064 and 1012 cm in
ꢀ 1
ꢀ 1
2, 1158, 1087, 1007 cm in 3, and 1136, 1095, 1049 cm in 4 show
the 1,2,3- substitution (three neighbour hydrogen atoms)) in the aro-
matic ring [36]. The absorption bands of the δ(CH)nonplanar oscillation
from the benzene rings are more pronounced and are manifested in the
3
.1. IR spectroscopy
ꢀ 1
ꢀ 1
The IR spectra of compounds 1–4 confirm the coordination of
range 860–750 cm for 1,4- and 1,2,3- substitutions: at 826 cm in 1,
846 cm in 2, at 799 cm in 3, and at 818 cm in 4 for two neighbour
1
2
–
ꢀ 1 ꢀ 1 ꢀ 1
organic ligands H
2
L
and H
2
L
to Mn(II) ions (Fig. S4). The
ν
(C
–
O)
ꢀ 1
ꢀ 1
ꢀ 1
stretching vibration bands represent the most important vibration bands
hydrogen atoms and at 753 cm in 1, 751 cm in 2, at 761 cm in 3,
ꢀ 1
1
ꢀ 1
and characteristic for the Schiff base ligands at 1671 cm in H
2
ꢀ 1
L and
and at 754 cm in 4 for 1,2,3- substitution type [36,37].
ꢀ
1
2
ꢀ 1
1
666 cm in H
2
L [12]. These bands are observed at 1645 cm in 1,
In the 700–400 cm region of all IR spectra
ν
(M-N) and
ν(M–O)
ꢀ 1
ꢀ 1
ꢀ 1
1
693 cm in 2, 1668 cm in 3, and 1651 cm in 4.
oscillations have been partially revealed [38,39]. Thus, the
ν
(Mn-Npyr-
In the IR spectrum of compound 1, the strong absorption in the
idine) oscillations are manifested to 552 (1), 559 (2), 586 (3) and 562
ꢀ
1
ꢀ 1
ꢀ 1
3
500–2600 cm region, represented by peaks at 3124, 3075 and 2731
cm (4), and
ν(Mn-Nazomethine) – 524 (1), 528 (2), 518 (3) and 534 cm
ꢀ
1
cm , indicates the stretching vibrations
hydrogen bonds formation, as well as
ν
(OH) and
ν
(NH) associated by
(4). The oscillations
ν
(Mn-Ocarbohydrazide) are revealed by the absorption
ꢀ 1
ν
(CH). The absorptions in the
bands 473 (1), 441 (2), 461 (3) and 418 cm (4), while the (Mn-
ν
ꢀ 1
ꢀ 1
ꢀ 1
region 3610–3290 cm and the broad band at 3193 cm in spectrum 2
are attributed to
δ(NH) oscillations are manifested to 1623 cm
In the spectra of complexes 3 and 4 is absent the band
Owater) oscillations are observed at 666 (1), 655 (2) and 670 cm (3)
ν
(OH) and
ν
(NH) oscillations, while the δ(OH) and
[38].
ꢀ 1
.
ν
(NH)
3.2. X-ray study
ꢀ 1
ꢀ 1
observed in free ligands at 3184 cm and 3186 cm , which demon-
strates the dianionic nature of the ligands in compounds. In 3, the wide
The crystal structures of compound 1 comprises mononuclear com-
ꢀ 1
1
2+
ꢀ
absorption bands at 3510–3110 cm can be attributed to
ν
(OH) vi-
plex cation [Mn(H
2
L )(H
2
O)
2
]
and NO
pentagonal bipyramid provided
3
anions. The coordination
brations of coordinated water and lattice ethanol molecules. The
polyhedron of the metal attains an N
3 4
O
4

L. Croitor et al.
Polyhedron 206 (2021) 115329
1
Fig. 2. View of the molecular structure of trinuclear [Mn
3
(H
2
L )
2
Cl
4
(NCS)
2
(H
O)
2 2
] compound with partial atomic numbering scheme (a). The fragments of H-
bonded supramolecular layer (b) and network (c) in 2. C-bound H atoms are omitted for clarity.
◦
by the pentadentate ligand in the equatorial plane and water molecules
in the axial vertices (Fig. 1a). The Schiff base acts as a neutral penta-
dentate ligand coordinating through pyridyl nitrogen atom (N4), two
azomethine nitrogen atoms (N3 and N5) and two carbohydrazide oxy-
gen atoms (O1 and O2), at usual for Mn(II) bond distances (Table S1).
The coordinated ligand provides a pentagonal arrangement with four
360.23 which indicates a coplanar arrangement of donor atoms. The
axial water molecules and the metal ion demonstrate about a linear
◦
arrangement with O(1w)–Mn(1)–O(2w) angle 176.58(11) . The coor-
dinated pyridine ring forms dihedral angles with the two terminal pyr-
◦
idine rings equal to 9.92(12) and 15.24(13) . In the crystal structure of
1, the components form a 3D supramolecular network (Fig. 1b) by three
◦
chelate angles in the range from 67.93(9) to 70.21(8) and the non-
types of intermolecular hydrogen bonds: O
–
H⋯O between a water
H⋯N between the same water molecule
◦
chelate O–Mn–O angle 84.16(8) . The sum of these angles equals
molecule and nitrate anion; O
–
5

L. Croitor et al.
Polyhedron 206 (2021) 115329
Fig. 3. Fragment of 2D polymer in 3 with partial atomic numbering scheme illustrates the connectivity of the Mn(II) ions (a); Topology of the layer in the 3: top view
b), view along two-fold screw axis (c) and simplified topology of net based only on Mn(2) atoms and considering Mn(1) atoms as a bisconnector (e).The packing of
layers with the mode of enclathration of C OH molecules in 3; view along the b (b) and c (c) axis.
(
2 5
H
with the nitrogen atom of one terminal pyridine moiety, and N
–
H⋯O
Compound 3 {[Mn
polymer isostructural to the solvatomorphic {[Mn
2dmso} [8]. In this compound were distinguished two crystallograph-
3
(L1)
3
(H
2
O)
2
]⋅1.5C
2 5 n
H OH} is a 2D coordination
1
between the amide nitrogen atom and nitrate anion (Table S2).
3
(L )
3
(H
2
O)
2
]⋅
The structure of compound 2 consists of discrete centrosymmetric
n
1
trinuclear [Mn
3
(H
2
L )
2
(NCS)
2
Cl
4
2
(H O)
2
] complexes (Fig. 2a). The Mn
ically different Mn(II) ions, Mn(1) – in general position and Mn(2) – on
two-fold axis (Fig. 3a). All manganese atoms have pentagonal bipyra-
(
1) cation adopts an N
3
O
3
Cl pentagonal bipyramidal geometry going
from the pentadentate Schiff base ligand in the equatorial plane, while
4 3 5 2
midal geometry with N O and N O environment for Mn(1) and Mn(2),
ꢀ
1
the axial vertices are occupied by Cl anion and water molecule. The
H
2
L1 coordinates to Mn(1) in neutral form as a pentadentate ligand like
respectively, provided by L ligand in equatorial plane and two mono-
dentate ligands in axial positions which differ for these metal centres.
The axial positions of Mn(1) are occupied by an oxygen atom of water
in compound 1, and the environment of this metal presents an pentag-
onal arrangement, chelate N–Mn(1)–N/O bond angles in the equatorial
1
2-
molecule and an nitrogen atom from isonicotinic ring of the (L ) co-
ordinated to Mn(2), while the Mn(2) apical positions are occupied by the
◦
plane are in the range from 67.9(2)-68.1(2) (Table S1), the non-chelate
◦
◦
1 2-
O(1)–Mn(1)–O(2) bond angle is 86.68(18) , sum of these angles 359.17
symmetry related nitrogen atoms N(7) of isonicotinic rings of the (L )
1
2-
and Mn(1) atom displace on 0.157(3) Å from the mean plane of donor
atoms in the direction of chloride anion (Table S1). The water molecule
and chloride anion in the axial positions and the Mn(1) metal ion deviate
ligand coordinated to Mn(1). Thus, the (L ) ligands show a hex-
adentate and heptadentate coordination mode, (Fig. 3a) and result in 2D
coordination polymer with Mn⋯Mn separation 9.5538(7) and 9.6021
(7) Å.
◦
from linearity, O(1w)–Mn(1)–Cl(1) 170.01(14) . The coordinated cen-
1
tral pyridine ring of H
2
L
forms dihedral angles with the terminal pyr-
The topology of this 2D layered polymer is shown in Fig. 3b and 3c,
the Mn(1) serves as a bisconnected node, similar to Mn(2) in cluster 2,
while Mn(2) serves as a four connected nodes. This layer can also be
thought of as fused helices of the same chirality with common Mn(2)
nodes (Fig. 3c), but if one considers the Mn(1) nodes as a linear bis-
connector the topology of the layer may be simplified up to 4,4-net
(Fig. 3d).
◦
◦
idine rings equal to 22.3(3) and 28.6(3) or 48.48(3) for two positions
1
of disordered pyridine ring, respectively. In this structure the H
molecule act as a hexadentate ligand, involving one of the terminal ni-
trogen atoms to coordinate to Mn(2) of [MnCl (NCS) ] moiety. The Mn
2) atom is six-coordinated with N Cl square bipyramidal geometry
provided by two nitrogen atoms from two H L ligands and another two
2
L
2
2
(
4
2
2
-
-
N atoms from NCS anions in the equatorial plane, and two Cl anions in
the apical positions. The self-association of trinuclear aggregates in 2
occurs via O(1w)–H⋯S and N(2)/(6)–H⋯Cl hydrogen bonds with the
formation of the 2D supramolecular layer (Fig. 2b), which is further
assembled into a 3D supramolecular network (Fig. 2c) through O(1w)–
H⋯N hydrogen bonds (Table S2).
The layers are additionally stabilized by intramolecular hydrogen
bonds between coordinated water molecules and the O-amide atoms of
1
2-
the (L ) ligands (Table S2). The disordered polar protic ethanol solvent
molecules are accumulated in the crystal compartments of 3, held there
by the electrostatic, van der Waals forces. The calculation of SAVs for the
3
simulated solvent-free network yields the volume of 979.3 Å or 14.5%
6

L. Croitor et al.
Polyhedron 206 (2021) 115329
Fig. 4. View of the coordination environment of the Mn(II) ion in 4 with partial numbering scheme (a). Fragment of polymeric layer (b) and packing of the layers
which afford the channels filled with the dmf solvent shown in space-filling mode (c), Topology of the layer, top (d) and side (e) views.
2ꢀ
of the total unit cell volume (Fig. 3b and c).
arrangement. The (L2) ligand shows a twisted conformation proved by
Compound 4 with 2,6-diacetylpyridine bis(nicotinoylhydrazone) L2
ꢀ
the dihedral angle between coordinated pyridine ring and nicotinic ring
◦
anion reveals
a
2D coordination polymer build-up from seven-
manganese(II) complexes with symmetrical
equal to 40.70(14) , and is responsible for the linking of Mn(II) cations
coordinated (N
5
O
2
)
in the 2D coordination layer with 4,4-net topology and the diagonal
dimensions of the meshes of 9.5117(4) × 12.9449(4) Å (Fig. 4b). The
Mn⋯Mn separations across the Schiff base ligand is 8.5867(6) Å. The
layers are parallel to (ab) crystallographic plane and stack along the
crystallographic c-axis forming the channels filled by the polar aprotic
dmf solvent molecules (Fig. 4c), bonded through weak C–H⋯O
pentagonal bipyramidal environment. The metal atoms reside on two-
fold axis. In the equatorial plane the 2,6-diacetylpyridine bis(nic-
otinoylhydrazone) ligand surrounds the Mn(II) atom just like 2,6-diace-
tylpyridine bis(isonicotinoylhydrazone) in compounds 1–3, and the
axial positions are occupied by two nitrogen atoms of terminal pyridine
2
2-
rings of adjacent symmetry related complexes (Fig. 4a). Similar to the
hydrogen bonds with the nicotinic rings of (L ) (Table S2). The SAVs
2
compounds discussed above, the coordinated Schiff base ligand H
2
L
calculated for the simulated solvent-free network gives a value of 317.5
3
provides an ideal pentagonal arrangement, chelate N–Mn(1)–N/O bond
Å
(~25.9% of the unit cell volume), thus indicating a high solvent
◦
angle are 67.58(9) and 69.79(12) (Table S1), the non-chelate O–Mn
uptake. It is noteworthy that compound 4 is isostructural and isomor-
phous with our recent presented homo-Zn(II)/Cd(II) and heterometallic
Zn(II)M(II) (M(II) = Mn, Cd) coordination layers [18] obtained in a
similar way and which show good luminescence responsiveness to the
◦
◦
(
1)–O bond angle is 85.72(16) , and in sum give 360.46 attesting to the
planarity of the structure. The axial nitrogen atoms of nicotinic rings and
◦
Mn(1) form
a
176.5(2) angle showing
a
little deviated linear
7

L. Croitor et al.
Polyhedron 206 (2021) 115329
Fig. 6. Thermoanalytical curves (TG-a, DTG-b and DTA-c) for compounds 1 (grey), 2 (green), 3 (red) and 4 (blue).
◦
removal of guest solvent molecules.
(2.45% calc.) and up to 255 C the total loss is 7.8% which corresponds
to the elimination of one ethanol molecule (7.20% calc.). Both processes
◦
are accompanied by endothermic effects. In the interval 255–370
C
3
.3. Thermal analysis
from the TG curve there is no mass loss, at the same time on the DTA
curve an exothermic maximum is observed which can be explained by
the restructuring of the compound after the elimination of the solvent
molecules. Decomposition of the ligand occurs in temperature interval
To examine the thermal stability and decomposition of coordination
compounds, simultaneous thermal analyses (TG-DTG-DTA) of the Schiff
1
2
base ligands (H
2
L
and H
2
L ) (Fig. S5) and all complexes were carried
71–496 ◦C, process accompanied by an endothermic peak. The mass
3
◦
◦
out from 20 C to 1000 C in nitrogen atmosphere (Fig. 6).
loss at this stage being 46.4%, which corresponds to 56.8% of the ligand
mass. Because the thermal analysis was performed in an inert atmo-
1
◦
◦
The H L ligand melts at 212 C, remaining stable up to 254 C when
2
it begins to decompose. This ligand undergoes two decomposition steps:
sphere, as a result of the thermal degradation, carbonic residue and Mn
◦
a loss of 42.4% of the mass is observed up to 382 C, and the second step
◦
(
III) oxide were formed, the latter decomposes at 820 C into Mn
3
O
4
and
◦
2
is up to 466 C when another 12.0% mass is eliminated. The H
2
L ligand
L as melts at 266 C and immediately after
melting it begins to decompose. As the previous ligand, the thermal
the removed oxygen partially oxidizes the carbon residue. As a result, on
1
◦
is slightly more stable that H
2
◦
the DTA curve an exothermic peak is observed in the range 820–905 C
and it is found a larger mass decrease (3.17%) than calculated only for
2
occurs in two steps: in the range 270–384 ◦C is
2
degradation of H L
the decomposition of Mn(III) oxide (0.56%) (Fig. 6b).
◦
identified a loss of 42.4% and in the range 384–475 C is removed
1
◦
The compound 4 is thermally stable up to 282 C, when the thermal
0.2% of the mass of the compound. In both cases, the resulting residues
degradation of the ligand starts and occurs in two stages: first between
undergo transformations with subsequent heating, processes that last up
82 and 368 C and second in interval 410–516 ◦C. Both stages are
◦
2
◦
to 1000 C.
accompanied by endothermic effects and mass loss is 14.9% and 42.4%
respectively. As in case of compound 3, Mn and carbonaceous res-
◦
The compound 1 begins to decompose at 110 C by removing water
2 3
O
molecules, the mass loss being 5.93% (5.84% calc.). The process is
idue are formed as a result of thermal decomposition. Mn(III) oxide
◦
accompanied by endothermic effect in the range of 110–190 C. In the
◦
decomposes in the range of 830–925 C to form Mn
3 4
O and the oxygen
◦
range 220–280 C there is an oxidative thermal degradation with a
formed oxidizes the carbon residue. As a result, an exothermic peak is
observed on the DTA curve (Fig. 6c).
strong exothermic effect. This is explained by the presence of nitrate
anions in the structure. The mass loss at this stage is 53.9% and as a
result, a mixture of carbonaceous residue and Mn(III) oxide is obtained.
4
. Conclusion
◦
◦
Up to 840 C the residue formed is stable and in the interval 840–995 C
on the TG curve a decrease of the mass is observed as a result of the
Modifications of synthetic methods and reaction conditions led to the
3 4
transformation of the oxide of Mn(III) into Mn O . The process is
preparation of four Mn(II) samples, two discrete compounds and two
coordination polymers, with hydrazone Schiff bases derived from 2,6-
diacetylpyridine and isonicotinic/nicotinic hydrazides. Schiff bases
behave as neutral (1 and 2) and bideprotonated (3 and 4) ligands and
coordinate to the Mn(II) ion through azomethine and central pyridyl
nitrogen atoms, as well as through carbohydrazide oxygen atoms, while
isonicotinic/nicotinic pyridine rings increase the structure dimension-
ality in 2–4. The thermal analysis has been established the influence of
the inorganic anion on the stability of synthesized compounds, thus,
compound 1 which contains the nitrate anion begins to decompose at a
accompanied by a weak endothermic effect, possibly due to the fact that
the more reactive organic part of the ligand (aliphatic chains) has been
oxidized by the nitrate ions and the aromatic residue is not oxidized
during this temperature range (Fig. 6a).
◦
Compound 2 is thermally stable up to 110 C; subsequent heating
leads to the loss of two coordinated water molecules, a process that ends
◦
◦
at 180 C. The mass loss represents 2.85% (2.85% calc.). Up to 290 C
this compound does not undergo other transformations, and in the range
2
90–377 ◦C there is a mass loss of 6.7%, which corresponds to the
◦
elimination of two inaH molecules (6.8% calc.). In the range 377–434 C
has observed another 18.1% mass loss, a process caused by the thermal
◦
1
◦
lower temperature (220 C) than the H L ligand (254 C) due to the
2
nitrate ion oxidizing effect. The chloride ion, on the other hand, in-
1
◦
degradation of the H
2
L ligand. Heating to 480 C leads to a total loss of
creases the thermal stability of the coordination compound, so that 2 is
◦
4
0.5%, and the residue formed gradually degrades to 1000 C. In the
◦
the most thermally stable (290 C). In the absence of the inorganic an-
◦
DTA curve at 654 C is observed an endothermic effect without a mass
change, which can be explained by the melting of Mn(II) chloride ob-
tained at the decomposition of compound 2.
ions, it was noticed that compounds begin to decompose at a tempera-
◦
1
– 254 ◦C) or slightly higher
ture close (compound 3 – 255 C, H
2
L
◦
2
◦
(
compound 4 – 282 C, H
2
L
– 266 C) to the ligand.
◦
Compound 3 begins to lose mass at 65 C due to elimination of sol-
◦
vent molecules: up to 155 C the mass of the compound decreases by
2
.5% which corresponds to the elimination of 0.5 ethanol molecule
8

L. Croitor et al.
Polyhedron 206 (2021) 115329
CRediT authorship contribution statement
[3] M. Sutradhar, M.V. Kirillova, M.F.C. Guedes da Silva, C.-M. Liu, A.J.L. Pombeiro,
Dalton Trans. 42 (2013) 16578–16587.
[
4] M. Sutradhar, E.C.B.A. Alegria, K.T. Mahmudov, M.F.C. Guedes da Silva, A.J.
Lilia Croitor: Conceptualization, Investigation, Visualization,
Writing - original draft, Supervision. Maria Cocu: Methodology,
Investigation, Formal analysis, Writing - original draft. Ion Bulhac:
Conceptualization, Investigation, Writing - original draft. Paulina N.
Bourosh: Investigation, Visualization, Writing - original draft. Victor
Ch. Kravtsov: Investigation, Visualization, Writing - review & editing.
Oleg Petuhov: Investigation, Visualization, Writing - original draft.
Olga Danilescu: Methodology, Investigation, Formal analysis, Writing -
original draft.
L. Pombeiro, RSC Adv. 6 (2016) 8079–8088.
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The authors are grateful to projects financed by the National Agency
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[
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9