New mononuclear manganese(II) complexes with 2,4,6-tris(2-pyridyl)-1,3,5- triazine (tptz) - Selective catalyst in UHP oxidation of sulfides

Article abstract of DOI:10.1016/j.poly.2011.12.027

A new manganese complex of the formula [Mn(tptz)(OH₂) ₃](CF₃SO₃)₂·EtOH, (1, where tptz = (2,4,6-tris(2-pyridyl)-1,3,5-triazine) is presented, exhibiting an excellent catalytic activity and selectivity in oxidation of various sulfides to the corresponding sulfoxides with UHP (urea hydrogen peroxide) as oxidant under air at room temperature. A modified preparation procedure produces another new manganese complex of the formula [Mn(tptz)(CH₃COO)(OH ₂)₂](CF₃SO₃)·3H₂O (2). X-ray structures of both Mn(II) complexes, properties (elemental analysis, electrochemistry, EPR, IR, Raman, and UV-Vis spectra), as well as DFT studies results are reported.

Full text of DOI:10.1016/j.poly.2011.12.027

Polyhedron 34 (2012) 202–209
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Polyhedron
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New mononuclear manganese(II) complexes with
2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) – selective catalyst in UHP oxidation of
sulfides
c,
d
e
Mohammad Mahdi Najafpour a, , Małgorzata Hołynska , Amir Nasser Shamkhali , Mojtaba Amini ,
⇑
⇑
´
Sayed Habib Kazemi a, Sasan Zaynalpoor a, Rahim Mohamadi a, Mojtaba Bagherzadeh e, Tadeusz Lis b
a Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, P.O. Box 45137-66731, Iran
b Department of Chemistry, University of Wrocław, 14 Joliot-Curie St., 50-383 Wrocław, Poland
c Fachbereich Chemie und Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein Strasse, D-35043 Marburg, Germany
d Department of Applied Chemistry, Faculty of Sciences, University of Mohaghegh Ardabili, Ardabil, P.O. Box 56199-11367, Iran
e Chemistry Department, Sharif University of Technology, P.O. Box 11155-9616, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A new manganese complex of the formula [Mn(tptz)(OH2)3](CF3SO3)2ꢀEtOH, (1, where tptz = (2,4,6-tris(2-
pyridyl)-1,3,5-triazine) is presented, exhibiting an excellent catalytic activity and selectivity in oxidation
of various sulfides to the corresponding sulfoxides with UHP (urea hydrogen peroxide) as oxidant under air
at room temperature. A modified preparation procedure produces another new manganese complex of
the formula [Mn(tptz)(CH3COO)(OH2)2](CF3SO3)ꢀ3H2O (2). X-ray structures of both Mn(II) complexes,
properties (elemental analysis, electrochemistry, EPR, IR, Raman, and UV–Vis spectra), as well as DFT
studies results are reported.
Received 24 September 2011
Accepted 26 December 2011
Available online 3 January 2012
Keywords:
Manganese
Triflate
2,4,6-Tris(2-pyridyl)-1,3,5-triazine
Crystal structures
Density Functional Theory
Oxidation of sulfides
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
(Urea hydrogen peroxide) as oxidant under air at room temperature.
Properties and DFT studies results are provided.
Manganese compounds are not only low cost and environmen-
tally friendly, but also used by Nature as catalytically active in a
variety of metalloenzymes [1–10]. Thus, manganese complexes
are among the transition metal complexes chiefly used as catalysts
to promote oxidation reactions. In fact, many catalytic studies have
been developed in recent years, where manganese complexes have
been found to catalyze a diversity of catalytic oxidation reactions
of organic substrates in organic solvents [11–20]. One of them,
the selective oxidation of sulfides, is an important transformation
in organic synthesis, leading to sulfoxides, playing the role of
essential intermediates [21–24].
Numerous complexes of tridentate ligands with manganese
have been investigated because of their interesting structural, re-
dox, photochemical, catalytic and water oxidation properties
[25–27]. The ligand tptz (2,4,6-tris(2-pyridyl)-1,3,5-triazine),
which may function simultaneously as a tridentate and a bidentate
ligand, has gained considerable interest, because of its use as a
spacer for designing supramolecular complexes [28–35]. Examples
of manganese(II) complexes with tptz ligand have been reported.
Eighteen cases of such compounds are known, being mainly mono-
nuclear complexes in cationic (CCDC refcodes FIGGAE [32], GIH-
QEU [36], GIHQIY [36]) or neutral form (GIHQAQ [36], LIBWUP
[37], XIHSIR [35], XIHSOX [38] and YENSAM01 [39]). The remain-
ing tptz Mn(II) complexes display polymeric (e.g. ACOKIN [35]) or
dimeric structure (METKOM [40], XAZKUF [41]). There is one
example of a tptz and Mn(II)-containing salt, where no complex
is formed (pentachloridomanganate(III) chloride monohydrate of
protonated tptz cation [42]).
In this paper we present new mononuclear Mn(II) complexes
with tptz (2,4,6-tris(2-pyridyl)-1,3,5-triazine) as a ligand, one of
which exhibits excellent catalytic activity and selectivity for oxida-
tion of various sulfides to the corresponding sulfoxides using UHP
The Density Functional Theory (DFT) methods are recently
widely used to study the structure of transition metal complexes
as they yield reasonable results and lower computational cost
compared to the post Hartree–Fock methods [43]. Bendix et al.
⇑
Corresponding authors. Tel.: +98 241 415 3201; fax: +98 241 415 3232 (M.M.
Najafpour), tel./fax: +49 (0)6421 2825615 (M. Hołyn´ ska).
E-mail addresses: mmnajafpour@iasbs.ac.ir (M.M. Najafpour), mholynska@
gmail.com (M. Hołyn´ ska).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.12.027

M.M. Najafpour et al. / Polyhedron 34 (2012) 202–209
203
used DFT methods to study the structure, vibrational properties
and UV–Vis spectra of [Mn(N)(CN)5]3ꢁ, trans-[Mn(N)(CN)4(py)]2ꢁ
capillary column (phenyl methyl siloxane 30 m ꢂ 320 lm ꢂ
,
0.25 lm) and a flame-ionization detector.
and [Mn(N)(CN)4]2ꢁ complexes [44]. Ghosh et al. successfully used
DFT calculations for a variety of iron and manganese porphyrin
complexes with metal oxidation states of +III and above [45]. Carr-
asco et al. studied the charge transfer influence on the spin ground
state of manganese and iron superoxide dismutases and deter-
mined that metal-to-ligand charge transfers stabilize the S = 2
and S = 5/2 spin states as ground spin states for these model com-
plexes [46]. Jackson et al. used DFT method to examine the ther-
mochromic transition previously reported for the oxidized state
of Mn-dependent superoxide dismutase [47]. Chai et al. used DFT
calculations to indicate a strong spin–spin interaction of the two
Mn(I) ions with the open shell configuration 3d54s1 in
[(HC{CH3CN(2,6-iPr2C6H3)2})Mn]2 dinuclear complex [48]. Lu and
Peters performed DFT calculations to probe the electronic validity
of pseudotetrahedral manganese complexes supported by the an-
2.1. General procedure for sulfide oxidation
A typical reaction using the complex [Mn(tptz)(OH2)3](CF3-
SO3)2ꢀEtOH (1) as a catalyst and sulfides as substrates at a
1:20 M ratio is described as follows. To a solution of sulfide
(0.2 mmol), imidazole (0.1 mmol) as axial ligand, chlorobenzene
(0.2 mmol) as internal standard and the catalyst (0.01 mmol) in
an (1:1) mixture of CH3OH/CH2Cl2 (1 mL), UHP (0.4 mmol) was
added as an oxidant. The mixture was stirred at room temperature
and the progress of the reaction was monitored by GC, by removing
small samples of the reaction mixture. To establish the identity of
the products unequivocally, the retention times and spectral data
were compared to those of commercially available compounds.
All the reactions were run at least in duplicate.
i
ionic tris(phosphino)borate ligand [PhBP3 Pr] [49]. Liu et al. used
DFT calculations on binuclear Mn(II) complexes found in biological
systems [50]. The authors investigated such properties as the rela-
tive energy of the lowest and highest spin states, the Mn(II)–Mn(II)
distance, or effect of the kind of oxygen bridge presence. Adams
2.2. [Mn(tptz)(OH2)3](CF3SO3)2ꢀEtOH (1)
The complex was prepared by dissolving manganese(II) triflate
(2 mmol, 706 mg) and tptz (2 mmol, 624 mg) in ethanol (15 mL).
The mixture was stirred for about 2 h at room temperature. This
solution yielded yellow crystals of the complex 1 after 10 d.
et al. optimized the structure of CpFeMn2(CO)7(l3-S2)2 complex
by DFT and Fenske–Hall (FH) molecular orbital calculations, which
show that the unpaired electron occupies a low lying anti-bonding
orbital, that is located principally on the iron atom [51]. These and
other investigations emphasize the ability of DFT methods for the
prediction of geometry and electronic structure of complex com-
pounds [51–54].
C
22H24F6MnN6O10S2, 1.0 g, ꢃ65% yield). Anal. Calc. for the complex:
C, 34.52; H, 3.16; N, 10.98; Found: C, 34.32; H, 3.22; N, 10.72%.
2.3. [Mn(tptz)(CH3COO)(OH2)2](CF3SO3)ꢀ3H2O (2)
We now report the preparation and characterization of two new
manganese(II) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine
ligand. One of these complexes exhibits an excellent catalytic
activity and selectivity in oxidation of various sulfides to the corre-
sponding sulfoxides with UHP (urea hydrogen peroxide) as oxidants
under air at room temperature. Then the stable structures of these
complexes are calculated by a DFT method to rationalize the new
structures and their stability is discussed.
Slow addition of an aqueous solution of sodium acetate (4 mL,
1 mmol) to the solution of 1 (1 mmol, 765 mg in 5 mL ethanol)
yielded yellow crystals of the complex 2 after 10 d at room temper-
ature. C21H25F3MnN6O10S, 352 mg, ꢃ53% yield). Anal. Calc. for the
complex: C, 37.90; H, 3.79; N, 12.63; Found: C, 37.83; H, 3.52; N,
12.72%.
2.4. Crystal data and X-ray measurement
For monocrystals of 1 and 2 X-ray measurements were carried
2. Experimental
out with the aid of an Oxford Diffraction Xcalibur PX diffractome-
ter equipped with graphite-monochromatized Mo K
a radiation
All reagents and materials used for the synthesis were reagent
grade and used without further purification. Elemental analyses
were performed on a Perkin-Elmer 2400 CHNS/O elemental ana-
lyzer. IR spectra (400–4000 cmꢁ1) were measured on an FT-IR JASCO
460 spectrophotometer for KBr pellets and electronic spectra on a
JASCO 7850 spectrophotometer. EPR spectra were collected at 4 K
for frozen samples with an X-band Varian E-9 spectrometer
equipped with an Oxford ESR-900 liquid helium cryostat. Typical
instrument settings were the following: modulation amplitude of
20 G, modulation frequency of 100 kHz and microwave power of
2.0 mW. The FT Raman spectra for KBr pellets were recorded at room
temperature in the region from 400 to 3500 cmꢁ1, using a Bruker IFS
66/S spectrometer with FRA106/S FT-Raman attachment and with
1064 nm NdYAG laser excitation. Electrochemical studies were car-
ried out in a conventional three-electrode cell using a Pt electrode as
a counter electrode and Ag wire quasi reference electrode, and a
2 mm diameter glassy carbon disk electrode as a working electrode.
All potentials were reported versus an Ag/AgCl reference electrode.
Prior to all measurements the acetonitrile or water electrolyte was
degassed at least for 10 min and throughout the measurement the
cell was kept under nitrogen gas atmosphere to avoid oxygen inter-
ference. Electrochemical measurements were run using a Zahner–
Zennium potentiostat–galvanostat under ambient temperature.
The products of oxidation were identified and analyzed with an
HP Agilent 6890 gas chromatograph equipped with an HP-5
source at 120(2) K (see Table 1 for the selected experimental data).
For the obtained datasets intensities were extracted and corrected
(including absorption correction) with the use of CrysAllisRED soft-
ware [55].
2.5. Refinement
Both crystal structures were solved by direct methods with
SHELXS program [56] and refined with the use of SHELXL [56].
In 1 both triflate anions were found to be considerably disor-
dered. The disorder model was approximated as two positions of
the whole anion (the refined occupancy factors of 0.52(2) and
0.48(2), 0.70(2) and 0.30(2), for major and minor components with
C111 and C211 atom, respectively). Soft SADI restraints were used
to keep all corresponding bond lengths within these anions equiv-
alent. Subsequently, SAME restraints were used. Ethanol molecule
of solvation was modeled as disordered in two positions differing
with the position of the whole ethyl group. The occupancy factors
of the two disorder components were refined to 0.54(1) and
0.46(1), respectively. Hydroxyl H1E atom was found on difference
Fourier map and refined with DFIX restraint to keep the O–H bond
length at 0.82 Å and Ueq = 1.5 Ueq (parent O atom). Subsequently
AFIX 3 constraint was applied to the H1E atom. The tptz ligand H
atoms were generated based on known geometry and refined with
Ueq = 1.2 Ueq (parent atom). All water H atoms were found on the

204
M.M. Najafpour et al. / Polyhedron 34 (2012) 202–209
Table 1
X-ray data for 1 and 2.
1
2
Formula
Formula weight
Temperature (K)
k (Å)
Crystal system
Space group
a (Å)
[(C18H12N6)(H2O)3Mn] 2(CF3O3S)ꢀC2H5OH
[(C18H12N6)(CH3COO) (H2O)2Mn][CF3O3S]ꢀ3H2O
765.53
665.47
120(2)
120(2)
0.71073
Monoclinic
P21/c
11.317(3)
15.961(5)
17.410(5)
90.50(3)
3145(2)
0.71073
Monoclinic
C2/c
13.762(4)
29.239(9)
13.987(4)
91.86(3)
5625(2)
b (Å)
c (Å)
b (Å)
V (Å3)
Z, qcalc (g cmꢁ3
)
4, 1.617
0.65
1556
8, 1.572
0.63
2728
l
(mmꢁ1
F(000)
)
Crystal size (mm)
h range(°)
Reflections: total/unique
Rint
0.42 ꢂ 0.28 ꢂ 0.23
4.7–38.7
13810/7104
0.034
0.41 ꢂ 0.19 ꢂ 0.11
4.5–35.0
65688/12332
0.046
Absorption correction
Minimum and maximum transmission factors
Data/restraints/parameter
GOF on F2
Analytical
0.790, 0.894
13810/128/575
1.02
Analytical
0.740, 0.895
12332/0/390
0.948
R1 [I > 2
r
(I)]
0.039
0.039
wR2 (all data)
Maximum, minimum
0.071
0.67, ꢁ0.58
0.079
0.43, ꢁ0.35
D
qelect (eÅꢁ3
)
difference Fourier maps and refined setting DFIX restraints to O–H
bond lengths (0.82 Å), as well as Ueq = 1.5 Ueq (parent atom). Subse-
quently, AFIX 3 constraints were applied to these H atoms. The
highest peak on the final difference Fourier map of 0.67 e/Å3 was
located 0.16 Å from Mn1 atom.
In 2 one of the water molecules of solvation was found to be dis-
ordered in two positions (O51W/O52W with occupancy factors of
0.63(2) and 0.37(2), respectively); H atoms positions were the
same for both components). All water H atoms were found on
the difference Fourier maps and refined setting DFIX restraints to
O–H bond lengths (0.82 Å), as well as Ueq = 1.5 Ueq (parent atom).
Subsequently, AFIX 3 constraints were applied to these H atoms.
The remaining tptz and acetate ligand H atoms were generated
based on the known geometry and refined with Ueq = nUeq (parent
atom) (where n = 1.2 or 1.5 for tptz ligand or acetate anion, respec-
tively). The highest peak on the final difference Fourier map (of
0.43 e/Å3 was located at 0.62 Å from N11 atom).
2.6. Studies of properties
In ESI the following studies are presented: the use of DFT
calculations to interpret the UV–Vis spectra, analysis of hydrogen
Scheme 1. Two possible conformers of tptz, considered in literature [41,42].

M.M. Najafpour et al. / Polyhedron 34 (2012) 202–209
205
bonding network in the crystal structures, IR/Raman/UV–Vis spec-
troscopy, EPR, electrochemistry.
conditions, on crystallization of tptz (obtained in situ by trimeriza-
tion of 2-cyanopyridine) from the methanol solution B form is ob-
tained [67]. Moreover, in almost all tptz metal complexes (e.g.
[64,65]) and in its protonated forms (e.g. [68,69]) tptz adopts this
stable conformation. However, on trimerization of 2-cyanopyridine
in the presence of magnesium phthalocyanine reported to be cata-
lytic [66], crystals of tptz containing A conformers are obtained.
3. Results and discussion
3.1. DFT calculations
All DFT calculations were performed with the use of a B3LYP hy-
brid functional [57] in Firefly quantum chemistry package [58],
which is partially based on the GAMESS (US) [59] source code.
First, structures of tptz ligand in both configurations A and B
(Scheme 1) were optimized with the use of TZVP [60] and SBKJC
(with effective core potentials for inner shell electrons) [61,62] ba-
sis sets, and the related details are given in Tables S2a and S2b,
respectively. On the basis of DFT studies, B configuration is 13.5
and 13.2 kJmolꢁ1 more stable than A (B3LYP/TZVP and B3LYP/
SBKJC methods, respectively). This instability of configuration A
can be described in terms of more repulsive interactions among
the lone pairs of non-bonding electrons located on three N atoms
(N11, N12, and N13). However, in the case of conformation A the
repulsive interactions could be reduced due to hydrogen bonding
involving N centres as acceptors and if water molecules acting as
donors are present in the crystal structure.
(a)
Another result is the negligible difference of calculated geomet-
ric parameters between two mentioned basis sets (see Tables S2a
and S2b). Since, using effective core potentials (ECPs) for transition
metals reduces computational cost of the calculations, the results
collected in Tables S2a and S2b imply that the SBKJC basis set with
lower computational cost may be used without introducing any
considerable error. Moreover, the use of a TZVP basis set for both
of the complexes causes convergence problems. Then geometries
of the complexes 1 and 2 were optimized by the B3LYP/SBKJC
method. The selected optimized structural parameters of these
complexes in gas phase are given in Tables S2a and S2b, in compar-
ison with experimental X-ray data. DFT calculations lead to the
conclusion that the molecular structure of 1 in gas phase is very
similar to the corresponding structure in solid phase. In the case
of 2, one of the acetate ligands is not coordinated to the manganese
central atom in gas phase and forms a strong hydrogen bond to a
coordinated water molecule. This coordinated water molecule in
the crystal structure participates in hydrogen bonds to other water
molecules and an acetate ligand from a symmetry-related mole-
cule. Thus, geometric parameters from the DFT calculation and
an X-ray experiment differ significantly for 2 (e.g. the O2W–
Mn1–O25 angle). For 1, as it is obvious from Tables S2a and S2b,
the calculated results are in good agreement with experimental
data, except for the Mn1–O25 bond length. This difference be-
tween gas and solid phases is reasonable, especially in the case
of Mn1–O25 bond length – the existence of an intramolecular
hydrogen bonding between O25 and H2W2 atoms could lead to
weakening of the Mn1–O25 bond with higher bond length in gas
phase. The Mulliken charges for selected atoms in the complexes
1 and 2, as well as in the free ligand in A form, are given in Table S3.
(b)
3.2. Crystal structures
tptz is an interesting ligand, the flexibility of which has already
been utilized in the design of transition metal complexes [63–65].
The molecule of tptz consists of a triazine ring, which is substituted
with three 2-pyridyl rings in positions 2,4,6. There are two crystal
structure reports available [66,67]. In these reports two conforma-
tions of tptz molecule are considered (Scheme 1): conformation A
and conformation B with a threefold symmetry axis and based
on ab initio calculations, the first conformation (A) should be high-
er-energetic. This is confirmed by experimental data as at ambient
Fig. 1. Complex cation in 1 (a) and 2 (b) with atom labeling scheme. Thermal
ellipsoids are drawn at 30% probability level.

206
M.M. Najafpour et al. / Polyhedron 34 (2012) 202–209
Table 2
Selected geometric parameters (°, Å) for the cationic Mn(II) complexes in 1 and 2: experimental
(X-ray diffraction – solid phase) and calculated (DFT – different species than in solid phase).
1: Geometric parameter
Experimental
Geometric parameter
Experimental
Mn1–O1W
Mn1–O2W
Mn1–O3W
2.150 (2)
2.146 (2)
2.095 (1)
86.9 (1)
88.4 (1)
170.6 (1)
172.6 (1)
90.1 (1)
95.5 (1)
102.6 (1)
94.6 (1)
Mn1–N11
Mn1–N12
Mn1–N13
O1W–Mn1–N12
N11–Mn1–N12
O3W–Mn1–N13
O2W–Mn1–N13
O1W–Mn1–N13
N11–Mn1–N13
N12–Mn1–N13
2.208 (2)
2.308 (2)
2.326 (2)
94.4 (1)
70.8 (1)
115.6 (1)
86.7 (1)
88.0 (1)
71.0 (1)
141.8 (1)
O3W–Mn1–O2W
O3W–Mn1–O1W
O2W–Mn1–O1W
O3W–Mn1–N11
O2W–Mn1–N11
O1W–Mn1–N11
O3W–Mn1–N12
O2W–Mn1–N12
1: Geometric parameter
DFT
Geometric parameter
DFT
Mn1–O1W
Mn1–O2W
Mn1–O3W
2.197
2.196
2.263
81.3
Mn1–N11
Mn1–N12
Mn1–N13
O1W–Mn1–N12
N11–Mn1–N12
O3W–Mn1–N13
O2W–Mn1–N13
O1W–Mn1–N13
N11–Mn1–N13
N12–Mn1–N13
2.147
2.322
2.345
100.1
73.8
119.4
85.9
85.9
O3W–Mn1–O2W
O3W–Mn1–O1W
O2W–Mn1–O1W
O3W–Mn1–N11
O2W–Mn1–N11
O1W–Mn1–N11
O3W–Mn1–N12
O2W–Mn1–N12
81.6
154.2
168.1
100.5
100.2
94.3
72.5
146.3
100.2
2: Geometric parameter
Experimental
Geometric parameter
Experimental
Mn1–O1W
Mn1–O2W
Mn1–N11
Mn1–N12
2.168 (2)
2.136 (2)
2.282 (1)
2.415 (2)
172.8 (1)
84.2 (1)
88.8 (1)
92.4 (1)
93.2 (1)
153.4 (1)
98.0 (1)
88.8 (1)
150.1 (1)
56.4 (1)
89.1 (1)
Mn1–N13
Mn1–O15
Mn1–O25
2.384 (2)
2.327 (1)
2.295 (2)
89.8 (1)
68.9 (1)
137.6 (1)
81.4 (1)
87.2 (1)
88.9 (1)
68.7 (1)
84.8 (1)
141.0 (1)
137.6 (1)
O1W–Mn1–N13
N11–Mn1–N13
O25–Mn1–N13
O15–Mn1–N13
O2W–Mn1–N12
O1W–Mn1–N12
N11–Mn1–N12
O25–Mn1–N12
O15–Mn1–N12
N13–Mn1–N12
O2W–Mn1–O1W
O2W–Mn1–N11
O1W–Mn1–N11
O2W–Mn1–O25
O1W–Mn1–O25
N11–Mn1–O25
O2W–Mn1–O15
O1W–Mn1–O15
N11–Mn1–O15
O25–Mn1–O15
O2W–Mn1–N13
2: Geometric parameter
DFT
Geometric parameter
DFT
Mn1–O1W
Mn1–O2W
Mn1–N11
Mn1–N12
2.234
2.105
2.196
2.326
152.8
107.0
100.1
44.4
108.4
151.5
84.7
68.1
168.3
40.2
Mn1–N13
Mn1–O15
Mn1–O25
2.332
2.175
3.467
92.2
O1W–Mn1–N13
N11–Mn1–N13
O25–Mn1–N13
O15–Mn1–N13
O2W–Mn1–N12
O1W–Mn1–N12
N11–Mn1–N12
O25–Mn1–N12
O15–Mn1–N12
N13–Mn1–N12
O2W–Mn1–O1W
O2W–Mn1–N11
O1W–Mn1–N11
O2W–Mn1–O25
O1W–Mn1–O25
N11–Mn1–O25
O2W–Mn1–O15
O1W–Mn1–O15
N11–Mn1–O15
O25–Mn1–O15
O2W–Mn1–N13
71.7
106.6
107.9
96.0
92.9
72.1
105.6
107.2
143.8
95.5
In this report two new manganese(II) complexes with the 2,4,6-
The symmetry-independent part of 1 comprises triaqua(g3-
tris(2-pyridyl)-1,3,5-triazine (tptz) ligand have been investigated.
The coordination chemistry of manganese(II) is dominated by the
coordination numbers four and six. Coordination numbers of five,
seven or eight are rarely observed [54–69]. The formation of seven-
or eight-coordinated Mn(II) compounds depends on the type of li-
gand used in the synthesis [70–75].
Both title complexes contain mononuclear cationic Mn(II) com-
plexes with tridentate tptz ligands with triflate anions as counteri-
ons. There are differences in the contents of Mn atoms
coordination sphere in 1 and 2.
2,4,6-tris(2-pyridyl)-1,3,5-triazine)manganese(II) cation (Fig. 1),
two disordered triflate anions and one ethanol molecule of solva-
tion. In the triaqua(g3-2,4,6-tris(2-pyridyl)-1,3,5-triazine)manga-
nese(II) cation the central Mn(II) atom is distorted-octahedral
hexacoordinate. Three coordination sites are occupied by water
molecules. The remaining coordination sites are occupied by the
tptz ligand N atoms: one triazine N atom (N11) and two pyridyl
N atoms (N12 and N13). Two water ligands (O1W and O2W) are
trans with respect to each other (Mn–O bond lengths of 2.150(2)
and 2.146(2) Å, respectively, Table 2). The third water molecule

M.M. Najafpour et al. / Polyhedron 34 (2012) 202–209
207
Table 3
Results of studies on the oxidation of sulfides catalyzed by [Mn(tptz)(OH2)3](CF3SO3)2ꢀEtOH (1).a
b,c
Entry
1
Substrate
Conversion (%
48(6)
)
Selectivity to sulfoxide (%)d
94
TONe
9.6
2
3
49(7)
56(8)
94
96
9.8
11.2
4
5
57(6)
52(5)
95
97
11.4
10.4
6
7
8
CH3CH2–S–CH2CH3
CH3(CH2)2–S–(CH2)2CH3
CH3(CH2)7–S–(CH2)7CH3
33(1)
31(0)
26(0)
100
100
100
6.6
6.2
5.2
a
The molar ratios for catalyst: imidazole:substrate:UHP are 1:10:20:40. The reactions were performed in (1:1) mixture of CH2Cl2/CH3OH (1 mL) under air at room
temperature.
b
The GC conversion rates (%) are measured relative to the starting sulfide after 60 min.
c
d
e
Oxidation of sulfide carried out in the absence of catalyst.
Selectivity to sulfoxide = (sulfoxide%/(sulfoxide% + sulfone%)) ꢂ 100.
TON = (mmol of sulfoxide + mmol of sulfone)/mmol of catalyst.
(O3W) is trans with respect to the triazine N11 atom (see Table 2
for the range of Mn–N(tptz) bond lengths, Mn–N11(triazine) bond
is slightly shorter than Mn–N(pyridyl) bonds, which is representa-
tive, as shown by a CCDC database [67] survey of all transition me-
tal tptz complexes with tptz ligand coordinated in a l3 mode). The
Mn–O3W bond is shorter in comparison to the Mn–O1W and
N13 atoms; triazine N11 atom; as observed in 1, the Mn–N11(tri-
azine) bond is slightly shorter than the Mn–N(pyridyl) bonds). An
identical cation, also with very similar geometry, has been reported
in form of perchlorate salt (FIGGAE [32]). Similar non-equivalence
in Mn–O bond lengths involving the acetate ligand was observed in
these compounds, as well as in other (acetato-O,O0)(
4,6-tris(2-pyridyl)-1,3,5-triazine)manganese(II) complexes with
bidentate acetate ligand coordinated trans to 3-tptz ligand, differ-
g3-2,
Mn–O2W bonds. This kind of cation has not been reported so far.
Similar cationic triaqua(
g
3-2,4,6-tris(2-pyridyl)-1,3,5-triazine)
g
complexes are known for nickel(II) [76,77]. The overall geometry
of these cations is comparable to the cation in 1, however, no such
variability in Ni–O bond lengths is observed as in the case of 1.
ing with ligands occupying the remaining two coordination sites
(YENSAM01 [39]).
The tptz ligand, as observed for other complexes, may be planar
or nearly planar (with pyridyl rings twisted with respect to the
central triazine ring [76–80]). In 1 the two pyridyl rings are almost
coplanar with the plane of triazine ring with dihedral angles of
2.7(1) and 1.5(1)° for rings with N12 and N13 atom, respectively
(14.9(1)° for the ring with N14 atom). These values are slightly dif-
ferent in case of 2 (3.6(1), 3.6(1) and 9.1(1)°, respectively). Similar
tptz ligand deformation was observed for triaqua(2,4,6-tris(2-pyri-
dyl)-1,3,5-triazine)nickel(II) dinitrate trihydrate, this compound
was compared with a similar salt with tptz ligand protonated
non-coordinated pyridyl ring [76]. This difference, changing hydro-
gen bonding scheme (the protonated pyridyl ring may act as a
The asymmetric unit contents of
2 comprise (acetato-
O,O0)diaqua(
g
3-2,4,6-tris(2-pyridyl)-1,3,5-triazine)manganese(II)
complex cation (Fig. 1), one triflate anion and three water mole-
cules, one of which (O5W/O6W) was modeled as disordered in
two positions. The Mn(II) cationic complex structure differs with
respect to its equivalent in 1 by substitution of one water ligand
(trans to triazine N11 ligand, Fig. 1), with acetate anion bonded
in a bidentate mode (the relevant Mn–O bonds differ slightly in
length, Table 2). The remaining ligands bonded to Mn(II) in 2 are
two water molecules (O1W and O2W) trans with respect to each
other and three N atoms from one tptz ligand (pyridyl N12 and

208
M.M. Najafpour et al. / Polyhedron 34 (2012) 202–209
hydrogen bond donor), leads to coplanarity of all rings constituting
tptz ligand.
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