Synthesis and characterization of [Mn(phen)(H2O)4]·SO4·2H2O

Article abstract of DOI:10.1016/j.molstruc.2018.04.027

Manganese(II) complex [Mn(phen)(H₂O)₄]·SO₄·2H₂O has been synthesized in aqueous methanol medium. The complex crystal was directly obtained from reaction of MnSO₄·H₂O in water with a mixture of methanol solution of disalicyaldehyde oxaloyldihydrazone and 1,10-phenanthroline. Its structure has been established by X-ray crystallography. It has also been characterized by thermogravimetry, TEM, magnetic moment, UV–visible, EPR and IR spectra. The complex is normal paramagnetic and shows a weak d-d band at 420 nm due to ⁶A_1g (F) → ⁴T_2g (G) transition and strong charge transfer bands. The EPR spectrum of the complex is indicative of decrease of metal-metal interaction with decrease in temperature. IR spectra of the complex is consistent with the coordination of 1,10-phenanthroline to the manganese(II) centre.

Full text of DOI:10.1016/j.molstruc.2018.04.027

Accepted Manuscript
Synthesis and characterization of [Mn(phen)(H O) ]·SO ·2H O
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4
4
2
Ibanphylla Syiemlieh, Arvind Kumar, Sunshine D. Kurbah, Ram A. Lal
PII:
S0022-2860(18)30458-7
10.1016/j.molstruc.2018.04.027
MOLSTR 25100
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 6 December 2017
Revised Date: 8 March 2018
Accepted Date: 5 April 2018
Please cite this article as: I. Syiemlieh, A. Kumar, S.D. Kurbah, R.A. Lal, Synthesis and
characterization of [Mn(phen)(H O) ]·SO ·2H O, Journal of Molecular Structure (2018), doi: 10.1016/
2
4
4
2
j.molstruc.2018.04.027.
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ACCEPTED MANUSCRIPT
Synthesis and characterization of [Mn(phen)(H2O)4].SO4.2H2O
Ibanphylla Syiemlieha, Arvind Kumarb, Sunshine D. Kurbaha and Ram A. Lala*
aCentre for Advanced Studies, Department of Chemistry, North-Eastern Hill University,
Shillong-793022, India.
bDepartment of Chemistry, Faculty of Science and Technology, The University of West-Indies,
St. Augustine, Trinidad and Tobago.
Abstract
Manganese(II) complex [Mn(phen)(H2O)4].SO4.2H2O has been synthesized in aqueous
methanol medium. The complex crystal was directly obtained from reaction of MnSO4.H2O in
water with a mixture of methanol solution of disalicyaldehyde oxaloyldihydrazone and 1,10-
phenanthroline. Its structure has been established by X-ray crystallography. It has also been
characterized by thermogravimetry, TEM, magnetic moment, UV-visible, EPR and IR spectra.
6
The complex is normal paramagnetic and shows a weak d-d band at 420 nm due to A1g
(F)→4T2g (G) transition and strong charge transfer bands. The EPR spectrum of the complex is
indicative of decrease of metal-metal interaction with decrease in temperature. IR spectra of the
complex is consistent with the coordination of 1,10-phenanthroline to the manganese(II) centre.
Introduction
Manganese compounds are not only used by nature in a variety of metalloenzymes
especially for oxidation reactions [1] but also they are low cost and environmental friendly. In
many microorganism, plants and animals, manganese plays a significant and diverse role. In the
biological systems, it plays a key role as a cofactor of proteins participating in processes
including metabolism and wound healing. The mitochondria requires, the enzyme manganese
superoxide dismutase (MnSOD) in the form of antioxidant [2] to discharge its function.
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Although manganese can function as a neurotoxin, yet it is preferred over the more toxic iron
and copper in metal-based SOD mimetics [3]. There are three major classes of MnSOD mimetics
such as a manganese(III) porphyrin compounds, manganese(III) salens, and manganese(II)
pentaazamacrocycles (MnPAM) also known as cyclic polyamines [4]. Besides, the biological
importance, manganese also plays significant roles in catalysis under homogeneous and
heterogeneous conditions [5]. Manganese complexes of functionalized N2O2 schiff bases
function as efficient peroxide disproportionation catalysts in acetonitrile [6]. Schiff base
complexes containing manganese(III) have been found to act as efficient catalysts for the
oxygenation of heteroatom containing organic compounds [7].
Further, manganese(III) salen complexes are amongst the most extensively studied class
during their utility as catalysts in the Jacobson-Katsuki epoxidation [8-10]. They also find
application in important reactions such as benzylic C-H fluorination both stoichiometrically and
catalytically [11] and nitrene transfer to electron-rich olefins [12]. Mn-salen complexes are also
used as starting materials in the preparation of other transition metal nitride complexes [13, 14].
Fuji and coworkers established structural and reactivity differences between Mn(IV)-phenolate
and Mn(III)-phenoxyl radical electronic structures as potential intermediates involved in the
Jacobson-Katsuki epoxidation reaction and found that there is a clear reactivity difference as a
consequence of a change in electronic structure from Mn(III)-phenoxyl radical to Mn(IV)-
phenolate. Manganese(III) porphyrins have been employed as electrocatalyst in the epoxidation
of olefins [15] as electrocatalyst. The water soluble manganese porphyrin Mn(III)-(TMPyP) has
also been found to electrolyze the oxidation of alkenes in aqueous media [16, 17]. Apart from
manganese porphyrins, manganese - Schiff base complexes were also employed as
electrocatalysts for alkene epoxidation [18] in acetonitrile medium, was reported the use of
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[MnIII(salen)] complex and other manganese(III) complexes containing modified salen were used
as electrocatalyst in electrochemical epoxidation of olefins in the presence of dioxygen and
benzoic anhydride [19]. The modified [MnIII(salen)] complexes gave better turnovers and current
efficiencies that based on the unsubstituted [MnIII(salen)] complex. The use of chiral manganese
Schiff base complexes for enantioselective electrocatalytic epoxidation of olefins was reported
by Wong and co-workers [20]. A similar electrocatalytic system for asymmetric epoxidation was
also reported by Tanaka et al. in CH2Cl2/aqueous NaCl biphasic medium [21].
Besides the above importance of manganese(II) in different fields, manganese metal-
organic frameworks (MnMOFs) have attracted great attention due to their intriguing
architectures [22]. They have found potential applications in the field of gas storage, catalysis,
separation, drug delivery, nonlinear optic and sensors as functional materials [23]. As a result of
these efforts, a variety of functional materials have been obtained and employed in the above
material fields [24]. Further, the continuous search for new materials exhibiting higher
performance than those used currently are necessity of time in order to meet the requirements of
daily improving technology. In this regard, the design and synthesis of functional materials with
interesting geometric configurations depends upon the sensible choice of suitable ligands with
fixed geometry and flexible coordination capacity. In this connection, 1, 10-phenanthroline has a
rigid framework as chelating donor ligand and exhibits excellent coordination ability with
transition metal ions. [25]. Hydrazones are potential multidentate ligands [26, 27], in particular
those derived from oxaloyldihydrazides are capable of stabilizing metal ions in higher oxidation
states [28, 29] and in combination with 1, 10-phenanthroline ligand are capable of providing
more amazing and interesting compounds because of the significantly different nature of N and
O donor sites. Thus, 1, 10-phenanthroline nitrogen atoms are soft donor atoms and are capable of
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stabilizing lower oxidation states of transition metals but the hydrazone ligands possess relatively
hard donor atoms and stabilize transition metal ions in their higher oxidation states [29].
It is imperative to mention that much work has been done on the bis and tris complexes
of 1,10-phenanthroline and 2,2'-bipyridine [30]. Yet the corresponding work on mono complexes
of these ligands are quite limited [31-33] because they cannot be prepared as readily as the bis
and tris complexes. Moreover, the synthesis of mono complexes by usual methods in solution is
a matter of chance. Most of these complexes have been prepared by thermal decomposition of
bis and tris complexes only [34].
In view of the above importance of manganese complexes in different fields and
importance of 1, 10-phenanthroline and hydrazone ligands in coordination chemistry, we aimed
to prepare series of manganese complexes of some dihydrazones i.e., Schiff bases, such as
disalicyaldehydeoxaloyldihydrazone
(H4slox)
and
bis(2-hyroxy-1-
naphthaldehyde)oxaloyldihydrazone (H4nph) in combination with 1, 10-phenanthroline and 2, 2-
bipyridine with manganese metal ions and characterize them by various physicochemical and
spectroscopic methods and establish their structure by X-ray crystallography. Accordingly, we
have carried out reactions of above ligands with MnSO4.H2O in methanolic-water medium under
reflux at 100 °C and the undissolved material was rejected by filtration. The filtrate was kept for
crystallization which yielded a crystal of a mono complex of 1,10-phenanthroline with
manganese(II) ion along with four coordinated water molecules within a month. In the present
communication, the compound described is insoluble in water and most of the organic solvents,
including DMSO and DMF, hence it has been characterized in the solid state only. So we
describe herewith, the synthesis, characterization and crystal structure of the mono complex of
manganese(II) with 1,10-phenanthroline.
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Experimental section
Solvents were reagents grade and used as received. MnSO4.H2O, diethyloxalate,
hydrazine hydrate, salicyaldehyde, 2-hydroxy-1-naphthaldehyde, 2, 2-bipyridine and 1, 10-
phenanthroline were obtained from E-Merck, Himedia, or equivalent grades.
Analytical studies
Manganese was determined by standard literature method [35].
CHN analysis
Carbon, hydrogen and nitrogen analyses were carried out on a Perkin-Elmer 2400
CHNS/O analyser.
Mass loss study
The mass loss of the complex was determined by heating the compound at 110 °C and
180 °C for 4 hours in an electronic oven.
Transmission electron microscopy (TEM)
Transmission electron microscopy (TEM) images were measured on JEOL-TEM-
2100CX electron microscope operated at 200 kV without addition of a contrast agent, since the
presence of the ion provides enough contrast. For TEM images, a drop of sample solution was
cast out on a carbon coated and allowed to dry.
Thermal analysis
The thermogravimetric analysis of the complex was carried out on the perkin-Elmer STA
6000 (Simultaneous Thermal Analyzer) model in a ceramic crucible under dynamic nitrogen
atmosphere. The heating rate of the complex was maintained at 20 °C/min-1. The DTA standard
used in the experiment is Pt 10 % Rh.
Magnetic susceptibility
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Sherwood Magnetic Susceptibility Balance MSB-Auto was used to measure magnetic
susceptibility at room temperature.
Electronic spectroscopy
The electronic spectrum of the complex in solid state was measured from 200-1100 nm
on a Perkin Elmer Lamda 25 UV/Vis Spectrophotometer at room temperature.
Infrared spectroscopy
Infrared spectrum was recorded in the range 4000 – 400/500 cm-1 on Perkin-Elmer,
model 983 spectrophotometer with samples investigated as KBr discs.
ESR spectroscopy
The ESR spectrum of the complex was recorded in powder form at room temperature and
LNT at X-band frequency on Varian, E-112E line century series, ESR spectrometer using TCNE
(g = 2.0027) as an internal marker.
X-ray crystallography
A pale yellow crystal suitable for X-ray analysis was obtained from methanol-water
solution at room temperature. The intensity measurement was made on Gemini-co-mounted fine
focus dual source single Crystal X-Ray diffractometer using graphite- monochromated Mo Kα
radiation (λ = 0.7107 Å) at 292 K. Crysalispro Agilent technology software were used for data
collection, indexing reflection and determination of lattice constant, empirical absorption
correction. The structure was solved by direct method (SHELXT-2014) [36] and refined full
matrix least square using SHELXL-2014 based on F2 [36]. Anisotropically thermal parameters
were employed for the non-hydrogen atom and isotropic parameter for all hydrogen atoms. The
position of the hydrogen atoms was placed at a geometrical position after the final refinements.
Preparation of disalicyaldehydeoxaloyldihydrazone (H4slox)
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The disalicyaldehydeoxaloyldihydrazone (H4slox) was prepared according to the procedure
described in the literature [28a].
Preparation of bis(2-hydroxy-1-napthhaladehyde)oxaloyldihydrazone
Oxaloyldihydrazine was prepared by reacting diethyloxalate (20 mL) and hydrazine
hydrate (13 mL) in 1:2 molar ratios under stirring for 30 minutes. The product thus isolated was
recrystallized from H2O.
Bis(2-hydroxy-1-napthhaladehyde)oxaloyldihydrazone (H4nph) was prepared by
condensing oxaloyldihydrazine (3 g, 25.42 mmol), in hot H2O (100 mL) with 2-hydroxy-1-
naphthaladehyde (8.75 g, 50.84 mmol) in ethanol (20 mL) over hot plate at 70 °C with constant
stirring for 1 h. The yellow precipitate thus obtained was washed with hot H2O-ethanol and dried
over anhydrous CaCl2.
Preparation of [Mn(phen)(H2O)4].SO4.2H2O
A mixture of H4slox (0.326 g, 1 mmol) in 10 mL methanol and and 1,10-phenanthroline
(0.198 g, 1 mmol) in 10 mL methanol was added to a solution of MnSO4.H2O (0.169 g, 1 mmol)
in 50 mL water and stirred for 30 min. The reaction mixture was refluxed for 6 hours at 100 °C
which gave a light yellow precipitate. The precipitate was filtered and washed with methanol-
water solution [35 mL, 1:2.5 (v:v)], then with methanol (30 mL) and finally with ether (30 mL)
to remove last traces of water and dried over anhydrous CaCl2. The filtrate so obtained was kept
for crystallization at room temperature. Within a fortnight, a pale yellow crystal was obtained.
Yield: 20 %. Decomp. pt: >300. Colour: Pale Yellow. Anal (%), Calcd for C12H20MnN2O10S
(MW 439.30): C, 32.81; H, 4.59; N, 6.38; Mn, 12.50; Found: C, 33.15; H, 4.57; N, 6.01; Mn,
12.78. IR data (cm-1, KBr): 3434 (vs) ν(OH), 1635 (w), 1623 (s), 1592 (m) ν(1,10-
phenanthroline), 864 (m), 845 (s) ω(CH), 1126 (vs) ν(SO). UV/Vis (solid state) nm: 365, 420.
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We tried to prepare the corresponding pyridine/substituted pyridine complexes by similar
method by adding pyridine/substituted pyridines in the filtrate of the reaction mixture keeping
H4slox:1,10-phenanthroline:MnSO4.H2O:pyridines molar ratio at 1:1:1:10 but only the original
aquo complex crystallized out from the solution.
A similar method was also used to isolate the corresponding 2,2'-bipyridine complex, but
we failed.
Results and Discussion
The complex was obtained by crystallizing the filtrate obtained from reaction of H4slox
and 1, 10-phenanthroline in 1:1 molar ratio in methanol-water solution with MnSO4.H2O in
water under reflux at higher temperature. Pale yellow coloured crystals were obtained within a
fortnight. The complex is insoluble in water and common organic solvents such as methanol,
ethanol, acetone, acetonitrile, DCM, CHCl3, CCl4, benzene and also in highly coordinating
solvents like DMF and DMSO. The complex decomposes above 410 °C without melting as is
evident from thermogram. Complex showed a mass loss of 8.59 % at 110 °C which corresponds
to loss of two water molecules (theo: 8.20 %) present in the lattice. Further, a mass loss of 14.61
% is observed at 180 °C which corresponds to loss of four water molecules (theo: 16.40 %) but
no mass loss was observed at 220 °C. The loss of four water molecules at 180 °C indicates that
they are coordinated to manganese(II) centre. No loss of mass at 220 °C dismissed the possibility
of loss of any high melting donor group from the coordination sphere of manganese complex.
We were interested to prepare the corresponding pyridine/2-picoline/3-picoline/4-picoline
complexes by substitution of coordinated water but in no case pyridine/substituted pyridine
complex was obtained. In all cases only original aqua complex crystallized out from the solution.
This revealed that that aquo complex is highly stable.
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Thermogravimetric analysis
Thermogram of the complex reveals that it decomposes in three major steps in the
temperature ranges 60 - 176 °C, 410 - 522 °C and 750 - 890 °C, respectively. The mass loss in
the temperature range 60-176 °C is 23.20 % which corresponds to loss of six water molecules
(theo: 24.60 %) present in the lattice and coordination sphere [37]. In this temperature range, the
mass loss occurs in two substeps (Fig. 1). In the first step, 10.23 % of mass is lost while in the
second step 13.00 % of mass is lost. The total mass together corresponds to loss of six water
molecules from the complex. But in none of the substeps, mass loss corresponds to either two
water molecules (first step) or four water molecules (second step), respectively. This may be
indicative of the presence of H-bonding between lattice held water molecules and either
coordinated water molecules or lattice held SO42- ions [38]. These steps indicate that lattice and
coordinated water molecules are lost simultaneously one after another. This has also been
confirmed by studying the structure of the complex by X-ray crystallography. At a temperature
of 176 °C, the residue left is 76.54 % which corresponds to mass of [Mn(phen)SO4] [39].
Subsequently, the complex remains stable in the temperature range 176-410 °C showing a
negligible mass loss of 0.22 % at a temperature interval of 20 °C. The second decomposition step
commences at 410 °C and continues upto 522 °C. The mass loss in this temperature range is
39.18 %. This corresponds to loss of one 1,10-phenanthroline molecule (theo: 37.59 %) from the
complex [40]. The residue obtained at 522 °C is 35.44 % which corresponds to the mass of
MnSO4 (theo: 34.40 %) [41]. After 522 °C, the residue remains stable upto 750 °C showing a
negligible mass loss in this temperature interval. Again, the third decomposition step is initiated
at 782 °C which continues upto 890 °C, when the heating process comes to stop. In this
temperature range 18.81 % of mass is lost which suggests loss of SO3 (theo: 18.22 %) from
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decomposition of MnSO4 [41]. The final residue obtained is 15.57 %. This mass corresponds to
the formation of MnO (theo: 16.17 %). However, when IR spectrum of the residue is recorded, it
is found to match with that of an authentic sample of MnO2. This revealed that the final residue
is MnO2. The loss of residual mass obtained may be due to evaporation of MnO2 at higher
temperature.
Transmission electron microscopy
Transmission electron microscopy (TEM) has become a convenient and widely employed
method for the elucidation of the shape and size of particles (Fig. 2). Nanoparticles dispersed in
ethanol/acetone by ultrasonification and TEM plots of the complex, revealed the presence of
large number of particles of various dimensions and different shapes. Selected area diffraction
(SAED) pattern confirmed the crystalline nature of the complex.
This compound shows particles of different shapes and sizes. Particles having ellipsoid,
cylindrical, palm and thumb, half shirt and socket types of shapes are clearly visible. Majority of
the particles have ellipsoid shape. Major axes of big and small ellipsoid fall in the range 130-250
nm while the minor axes fall in the range 90-130 nm. The large cylindrical particles have their
dimension, length of the order of 800 nm and a diameter of the order of ~180 nm while the small
particles have their length and diameter of the order of 320 nm and 140 nm, respectively. The
hexagonal particles are similar to HR-TEM (High
Resolution
Transmission
Electron
Micrographs) of MWNT structures (multi-walled nanotube) [42]. The particles are composed of
ordered sheets. HR-TEM of this complex shows image that are somewhat like carbon nanotube
which are closed at their ends. At high resolution (2 nm), the presence of metal lattice is clearly
visible. The distance between the layers in this structure is 0.27 nm [43]. Its SAED shows a
weakly diffused rings [44]. More diffraction spots are seen rather than the rings.
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Crystal structure description
The crystal structure of complex reveals a centrosymmetric complex molecule. The
ORTEP view of the complex molecule is shown in Fig. 3 and the packing diagram of the
complex is shown in Fig. 4. The crystal refinement parameter has been given in Table 1 and
selected bond distances and angles are given in Tables 2 and 3.
The discrete complex molecule has a very simple structure consisting of one 1,10-
phenanthroline molecule, one Mn ion, four coordinated water molecules, two lattice water
molecules and one sulfate ion present in the lattice structure. Manganese is six coordinate in a
cis-conformation. The geometry about Mn ion is distorted octahedral. The central manganese ion
is bonded to four oxygen atoms of coordinated water molecules and two nitrogen atoms of 1,10-
phenanthroline molecule in a chelating fashion. The distance (Mn1-N1) and (Mn1-N2) are
2.258(3) and 2.281(3) Å, respectively, which are normal for MnII-N (imine) bonds [45]. The
distance (Mn1-O1), (Mn1-O2), (Mn1-O3), (Mn1-O4) are 2.197(2), 2.174(2), 2.164(2) and
2.212(2) Å, respectively, while the bond angles (N1-Mn1-N2), (N2-Mn1-O3), (O3-Mn1-O4),
(O4-Mn1-N1), (O1-Mn1-O2), (N2-Mn1-O4), (N1-Mn1-O3), are 73.23(10), 91.97(10),
97.87(10), 98.12(10), 168.01(9), 167.78(10), 162.13(10, respectively. These bond length and
bond angles confirm that the geometry around manganese centre in the complex is distorted
octahedral. The Mn-O distances 2.164(2) - 2.212(2) Å fall in the range commonly found for
Mn(II) complexes [45, 46].
Crystal packing diagram
The presence of coordinated, lattice water molecules and free sulfate group in the
complex results into extensive and strong hydrogen bond interaction which permeates the entire
2-
lattice. Free water molecules act as proton donors to SO4 group but as proton acceptors from
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coordinated water molecules. Eight molecules of the complex are present in one-unit cell. The
two 1,10-phenanthroline rings bonded to different manganese atoms oriented in opposite
directions are in different planes. However, there is no π-π interaction between the two. Two
such 1,10-phenanthroline rings are in series with other parallel rings and constitute two layers.
Lattice water molecules and sulfate ions appear inserted between the two layers. The carbon-
carbon distance between the 1,10-phenanthroline in one sheet and the next sheet is 11.403 Å.
The shortest intrasheet distance between corresponding carbon atoms of 1,10-phenanthroline
ring is 6.020 Å. The distance between two manganese atoms coordinated to oppositely oriented
1,10-phenanthroline rings is 8.542 Å while the distance between the intersheet manganese atoms
is 5.532 Å. On the other hand, the distance between two adjacent manganese atoms is 9.498 Å.
The SO42- ion is interacting with the same H-atom of 1,10-phenanthroline through its sulphur and
2-
one of its oxygen atom. The very same oxygen and sulphur atoms of the SO4 interact with
hydrogen atom of lattice water. All coordinated water molecules are H-bonded to oxygen atoms
2-
of SO4 group (O-H---O) with O-H---O distance falling in the region 1.854 – 2.084 Å.
Coordinated water molecules are strongly H-bonded to SO42- group as compared to lattice water
molecules.
Magnetic moment
The effective magnetic moment of the complex is 5.98 B.M which is characteristic of
presence of high-spin Mn(II) in the complex.
EPR study
The complex shows only isotropic spectra with the g-values equal to 2.050 and 2.040 at
RT and LNT (Fig. 5), respectively. Such spectral features arise due to metal-metal interaction in
the solid state and owes due to spin relaxation [47]. The complex shows no splitting either at RT
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or LNT due to hyperfine coupling. It is to be noted that ꢀH value at RT is 145 G while at LNT is
160 G. This suggests that the metal-metal interaction, if at all, in the solid state decreases in
going from RT to LNT.
UV-visible
Due to insolubility of the complex in water and common organic solvents and highly
coordinating solvents such as DMF and DMSO, the electronic spectrum of the complex was
recorded in the region 200-1100 nm in solid state. The complex shows a strong band at 365 nm
and a weak band at 420 nm (Fig. 6). This spectrum was compared with that of free 1,10-
phenanthroline in DMF solution. 1,10-phenanthroline showed two bands at 302 nm (39000 dm3
mol-1 cm-1) and 338 nm (1600 dm3 mol-1 cm-1), respectively. These bands may be attributed to
π→π* transitions centred on the free ligand. The band at 365 nm is very strong. It appears to
arise from transfer of charge from filled molecular orbital centred on 1,10-phenanthroline to
unoccupied molecular centred on the metal ion. However, this band may have contribution from
ligand band at 338 nm which might be red shifted by 27 nm on complexation and merged with
charge transfer band. Further, the complex shows a weak band at 420 nm. The d-d transition in
the high-spin Mn(II) complex are very weak because they are both spin as well as Laporte
forbidden. Further, crystal field of any symmetry cannot split a Mn(II) d5 high-spin configuration
6
with S ground term. Usually d-d transitions are rarely seen in high-spin Mn(II) complexes. In
6
view of the low intensity of the band at 420 nm in the present complex, it is assigned to A1g
(F)→4T2g (G) transition, as has been reported for high-spin Mn(II) octahedral complex [48].
IR Spectra
The complex shows strong broad band in the region 3100-3700 cm-1 with its centre at
3434 cm-1. This band may be attributed to stretching vibration of -OH group of coordinated and
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lattice water molecules. The uncoordinated 1,10-phenanthroline shows medium intensity bands
at 1618, 1588 and 1567 cm-1 due to ring vibrations. These bands are shifted to higher frequency
in the complex and appear at 1635, 1623 and 1592 cm-1. The shift of these bands to higher wave
number suggests coordination of 1,10-phenanthroline to Mn(II) ion through the nitrogen atoms
[49]. When 1,10-phenanthroline ring nitrogen atoms are coordinated to the metal centre the
nitrogen atom lone pair of electrons is shifted towards metal centre. As a result, the bonding pairs
of electrons present in C-C and C-H bonds drift towards nitrogen atom. Consequently, the C-C,
C-H vibrations shift to higher wave number [50, 51]. The complex further shows medium
intensity bands at 864 and 845 cm-1 which correspond to strong peaks at 849 and 838 cm-1 in the
free 1,10-phenanthroline. These vibrations are also shifted to higher frequency on complexation
and are assigned to ring breathing mode of 1,10-phenanthroline ligand [52]. A strong band is
observed at 1126 cm-1 which is attributed to νSO stretching vibrations of uncoordinated sulfate
group [53].
Conclusion
In this manuscript, we have synthesized a mononuclear high-spin manganese(II) complex
of the composition [Mn(phen)(H2O)4].SO4.2H2O using MnSO4.H2O, disalicyaldehyde
oxaloyldihydrazone ligand and 1,10-phenanthroline as starting material. The complex has been
characterized by various physico-chemical techniques and its structure has been established by
X-ray crystallography. The manganese(II) centre in the complex, is present in distorted
octahedral geometry. The UV spectrum of the complex shows a weak d-d band at 420 nm. IR
spectrum of the complex is consistent with bonding of 1,10-phenanthroline to the manganese
centre, sulfate is present in anionic form in the complex. The complex has normal magnetic
moment corresponding to high-spin Mn(II). Its EPR spectrum suggest the present of metal-metal
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interaction which decreases in going from RT to LNT.
Acknowledgement
Authors are thankful to the Head, SAIF, IIT, Bombay for recording EPR Spectra, Head,
SAIF, NEHU for spectral analysis and also to the Head of Department, Chemistry, NEHU,
Shillong for X-ray crystallography. Two of the authors (I. Syiemlieh and S. D. Kurbah) would
also like to thank UGC, New Delhi for the award of NFHE Fellowship.
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Table 1. Crystal data and structure refinement parameters of complex
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
C12H20MnN2O10S
439.30
296.38(10)
orthorhombic
Pbca
8.8982(6)
b/Å
18.5435(10)
c/Å
22.1299(17)
α
/°
/°
90
β
90
γ
/°
90
Volume/Å3
3651.5(4)
Z
8
ꢀ
/mm-1
0.891
Reflections collected
8261
Independent reflections
3211 [Rint = 0.0279, Rsigma = 0.0361]
Data/restraints/parameters 3211/0/245
Goodness-of-fit on F2
1.103
Final R indexes [I>=2
σ
(I)] R1 = 0.0453, wR2 = 0.1022
Final R indexes [all data]
R1 = 0.0551, wR2 = 0.1070
Largest diff. peak/hole /e Å-3 0.52/-0.53
Table 2. Selected bond length (Å) of complex
Atom Atom Length/Å Atom Atom Length/Å
Mn1 O2 2.174(2) N1 C1 1.326(4)
Mn1 O1 2.197(2) C12 C11 1.441(5)
Mn1 O4 2.212(2) C12 C4 1.410(5)
Mn1 O3 2.164(2) C11 C7 1.418(5)
Mn1 N2 2.281(3) C10 C9 1.388(5)
Mn1 N1 2.258(3) C1 C2 1.404(5)
S1 O5 1.475(2) C4 C3 1.395(6)
S1 O6 1.481(2) C4 C5 1.436(6)
S1 O7 1.468(2) C7 C8 1.406(6)
S1 O8 1.470(2) C7 C6 1.419(6)
N2 C11 1.350(4) C8 C9 1.344(6)
N2 C10 1.328(4) C3 C2 1.367(6)
N1 C12 1.363(4) C6 C5 1.334(7)

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Table 3. Selected bond angles of complex
Atom Atom Atom Angle/˚ Atom Atom Atom Angle/˚
O2 Mn1 O1 168.01(9) C12 N1 Mn1 115.6(2)
O2 Mn1 O4 85.58(8)
O2 Mn1 N2 87.67(9)
C1 N1 Mn1 126.0(2)
C1 N1 C12 118.3(3)
O2 Mn1 N1 101.82(9) N1 C12 C11 117.8(3)
O1 Mn1 O4 84.92(8) N1 C12 C4 123.2(3)
O1 Mn1 N2 102.94(9) C4 C12 C11 119.0(3)
O1 Mn1 N1 86.77(9) N2 C11 C12 117.9(3)
O4 Mn1 N2 167.78(10) N2 C11 C7 122.4(3)
O4 Mn1 N1 98.12(10) C7 C11 C12 119.7(3)
O3 Mn1 O2 87.34(9)
O3 Mn1 O1 86.73(9)
N2 C10 C9 123.7(4)
N1 C1 C2 122.2(4)
O3 Mn1 O4 97.87(10) C12 C4 C5 118.7(4)
O3 Mn1 N2 91.97(10) C3 C4 C12 116.6(4)
O3 Mn1 N1 162.13(10) C3 C4 C5 124.8(4)
N1 Mn1 N2 73.32(10) C11 C7 C6 119.4(4)
O5 S1 O6 108.98(15) C8 C7 C11 116.9(4)
O7 S1 O5 109.86(15) C8 C7 C6 123.7(4)
O7 S1 O6 109.49(13) C9 C8 C7 120.2(4)
O7 S1 O8 109.82(15) C2 C3 C4 120.4(4)
O8 S1 O5 109.51(13) C3 C2 C1 119.3(4)
O8 S1 O6 109.16(15) C5 C6 C7 120.8(4)
C11 N2 Mn1 115.3(2)
C10 N2 Mn1 127.0(2)
C10 N2 C11 117.7(3)
C8 C9 C10 119.1(4)
C6 C5 C4 122.4(4)

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Fig. 1. Thermogravimetric curve of the complex [Mn(phen)(H2O)4].SO4.2H2O.
a
b
c
d
Fig. 2. TEM images and selected area electron diffraction (SAED) inset (d) images of complex
[Mn(phen)(H2O)4].SO4.2H2O.
Fig. 3. Thermal Ellipsoid plot of the complex [Mn(phen)(H2O)4].SO4.2H2O (50% probability
level).

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Fig. 4. Packing diagram of the complex [Mn(phen)(H2O)4].SO4.2H2O view along a-axis.
a
b
Fig. 5. ESR spectrum of complex [Mn(phen)(H2O)4].SO4.2H2O in polycrystalline state at RT (a)
and LNT (b), f (9.1GHz).

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1.0
0.8
0.6
0.4
0.2
0.0
360
380
400
420
440
Wavelength (nm)
Fig. 6. Electronic spectrum of complex [Mn(phen)(H2O)4].SO4.2H2O in solid state.

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Highlights
•
•
•
•
Manganese(II) complex was synthesized and characterized.
Its geometry has been established by X-ray crystallography.
Magnetic susceptibility shows the complex is normal paramagnetic.
The UV-visible studies shows a weak d-d band in the complex.