Synthesis and characterization of s-triazine cored tripodal keto-oxime and its trinuclear complexes

Article abstract of DOI:10.1080/00397911.2010.521967

2,4,6-Tris(4-hydroxybenzimino)-1,3,5-triazine (II) has been synthesized by the reaction of 1equiv. melamine (I) and 3equiv. 4-hydroxybenzaldehyde and characterized by means of elemental analysis, 1H NMR, Fourier transform-infrared spectroscopy, and liquid

Full text of DOI:10.1080/00397911.2010.521967

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Synthesis and Characterization of S-
Triazine Cored Tripodal Keto-oxime and
Its Trinuclear Complexes
Şaban Uysal a
a Faculty of Science, Department of Chemistry, Selcuk University,
Konya, Turkey
Accepted author version posted online: 30 Jun 2011.Version of
record first published: 14 Sep 2011.
To cite this article: Şaban Uysal (2012): Synthesis and Characterization of S-Triazine Cored Tripodal
Keto-oxime and Its Trinuclear Complexes, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 42:1, 84-92
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Synthetic Communications1, 42: 84–92, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.521967
SYNTHESIS AND CHARACTERIZATION OF S-TRIAZINE
CORED TRIPODAL KETO-OXIME AND ITS TRINUCLEAR
COMPLEXES
S¸aban Uysal
Faculty of Science, Department of Chemistry, Selcuk University, Konya,
Turkey
GRAPHICAL ABSTRACT
Abstract 2,4,6-Tris(4-hydroxybenzimino)-1,3,5-triazine (II) has been synthesized by the
reaction of 1 equiv. melamine (I) and 3 equiv. 4-hydroxybenzaldehyde and characterized by
means of elemental analysis, 1H NMR, Fourier transform–infrared spectroscopy, and liquid
chromatography–mass spectrometry (LC-MS). 2,4,6-tris(4-(2-phenyl-2-keto-hydroxyimi-
noyloxy)benzimino)-1,3,5-triazine L (III) has been synthesized by the reaction of 1 equiv.
II and 3 equiv. chloroisonitrozoacetophenone and characterized by means of the same meth-
ods. Four novel trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases
N,N0-bis(salicylidene)ethylenediamine-(salenH2) or bis(salicylidene)-o-phenylenediamine-
(salophen H2) with L (III) have been synthesized and characterized by means of elemental
analysis, Fourier transform–infrared spectroscopy, LC-MS (ESIþ), and thermal analyses.
The metal ratios of the prepared complexes have been determined using atomic absorption
spectroscopy. The aim of the present study is to synthesize novel tridirectional-trinuclear
systems and to present their effects on magnetic behavior of [salen or salophenFe(III)=
Cr(III)] capped complexes. The complexes have also been characterized as low-spin dis-
torted octahedral Fe(III) and as distorted octahedral Cr(III) bridged by keton-oxime group.
Keywords Keton-oxime groups; melamine; salen; salophen; Schiff bases
Received August 15, 2010.
Address correspondence to S¸aban Uysal, Faculty of Science, Department of Chemistry, Selcuk
University, 42031 Konya, Turkey. E-mail: uysal77@hotmail.com
84

SYNTHESIS AND CHARACTERIZATION OF S-TRIAZINE
85
INTRODUCTION
Melamine resins have been used in many applications, including the manufacture
of plastic dishes under the trade name Melmac. 1,3,5-Triazine derivatives are widely
used as herbicides,[1] drugs,[2] and spolymers,[3] such as melamineformaldehyde, which
has excellent thermal and electrical properties.[4] Interest in the metal coordination
environment has prompted the study of oxime ligands because of their variable geome-
tries and the tunability of their substituents. Oxime ligands are used as analytical
reagents and serve as models for biological systems (e.g., vitamin B12 and dioxygen
carriers) as well as catalysts in chemical processes.[5]
The anions of salen or salen-type ligands and their complexes have been
regarded as interesting varieties in many fields of chemical research because of certain
specific properties. Fe(salen) complexes have been extensively studied in solid state
and in solution. Barone et al.[6] showed that such systems exhibited catalytic activity
toward the blend oxidation of hydrocarbons and their electron-transfer reactions,
mimicking the catalytic functions of peroxidases. Woldemariam et al.[7] synthesized
a water soluble Fe(III)-salen complex and studied its biochemical effects on DNA
in vitro and on cultured human cells. We have also reported that the synthesis and
characterization of mono-=tri-=multi-carboxylato or mono-=tri-catechol bridges with
[salen or salophenFe(III)=Cr(III)].[8–13] Singh and Gupta[14] have also studied
synthesis, structure, and physicochemical properties of melamine-based dendrimers.
We have especially preferred chromium complexes because chromium is a unique
transition-metal ion, which is biologically significant at all the levels of living
organisms.[15] Chromium(III)-salen complexes in the homogeneous phase have also
been used for the epoxidation of olefins.[16,17]
The aim of the present study is to synthesize novel tridirectional-trinuclear sys-
tems and to present their effects on magnetic behavior of [salen or salophenFe(III)=
Cr(III)] capped complexes. We also report that synthesized tridirectional melamine
Schiff bases present a new scaffold. Melamine (C3N6H6) was reacted with 3 equiv. of
4-hydroxybenzaldehyde in benzene and bolied under reflux, and the desired tris-
iminophenol (II) 2,4,6-tris(4-hydroxybenzimino)-1,3,5-triazine was obtained in a one
step.[18,19] Then, as dry Cl2 gas was bubbled through a suspension of isonitrosoaceto-
phenone in chloroform under sunlight for 30min, chloroisonitrozoacetophenone was
obtained. Compound II was reacted with 3 equiv. of chloroisonitrozoacetophenone
in acetone at room temperature, and the targed ligand (L) 2,4,6-tris(4-(2-phenyl-2-
ketohydroxyiminoyloxy)benzimino)-1,3,5-triazine was obtained in one step. Their
structures are characterized by Fourier transform–infrared (FT-IR), 1H NMR, liquid
chromatography–mass spectroscopy (LC-MS), thermal gravimetric analysis (TGA),
and magnetic suscebtibility. The metal ratios of the prepared complexes have been
determined using atomic absorption spectroscopy (AAS).
RESULTS AND DISCUSSION
The target ligand L (III) was synthesized in two steps from melamine. The con-
version of melamine to the triarmed-melamine-oxime derivative was accomplished
with 68% yield. The structural formula of L (III) was verified by elemental analyses,
1H NMR, FT-IR, and mass spectral data[20] (Fig. 1, Tables 1 and 2). The ligand is

86
S¸. UYSAL
Figure 1. Synthetic routes for the preparation of ligand III.
soluble in common organic solvents. The synthetic strategy for preparing L (III)
utilizes a complex as a ligand that contains a potential donor group capable of coor-
dinating to another ligand. Therefore, we chose [Fe=Cr(salen or salophen)]2O as
ligand complexes.[21] These complexes are the first examples of melamine-based
trinuclear complexes bridged to the iron=chromium centers by keton and oxime
groups (Fig. 2). All compounds are stable at room temperature in the solid state,
and they are only soluble in organic solvents such as ethylacetate, dimethylsulfoxide
(DMSO), dimethylformamide (DMF), and are insoluble in water. The results of
Table 1. Some physical properties, molecular weight (g=mol) data, elemental analyses, and AAS analyses
of the ligands and complexes
Found and Calculated (%)
Mp
(ꢀC)
Yield
(%)
Color
[MW (g=mol)]
Compounds
mB
C
H
N
Fe
—
Cr
—
C24H18N6O6
(II)
—
142
196
72
68
54
56
45
48
White
[438]
65.67
65.75
64.98
65.53
61.94
62.56
65.03
65.27
62.43
62.95
65.12
65.65
4.12
4.14
3.56
3.75
4.61
4.91
3.48
3.63
3.85
3.93
3.44
3.65
19.15
19.17
14.21
14.33
11.27
11.40
10.36
10.58
11.35
11.48
10.36
10.64
C48H33N9O9
L (III)
—
White
[880]
—
—
—
C96H72N15O15Fe3
L(FeSalen)3 (IV)
1.73
1.75
3.72
3.78
243a
276a
226a
248a
Brown
[1842]
Brown
[1986]
Green
[1830]
Green
[1974]
9.02
9.10
8.29
8.44
—
C
108H72N15O15Fe3
—
L(FeSalophen)3 (V)
C96H72N15O15Cr3
L(CrSalen)3 (VI)
9.23
9.62
8.71
8.92
C108H72N15O15Cr3
L(CrSalophen)3 (VII)
—
aDecomposition.

SYNTHESIS AND CHARACTERIZATION OF S-TRIAZINE
87
Table 2. Decomposition steps with the temperature range and weight loss for ligand and complexes
Temp.
range (ꢀC)
Weight loss
found (calcd.) (%)
Compound
96H72N15O15Fe3
L(FeSalen)3 (IV)
Step
Fragment
C
I
II
III
I
165–260
295–365
560–675
170–275
315–375
560–672
125–240
275–325
560–676
132–248
286–335
560–670
25.76 (26.34)
42.54 (43.48)
15.98 (16.71)
23.86 (24.44)
46.65 (47.57)
14.89 (15.50)
25.82 (26.55)
42.91 (43.74)
16.44 (16.81)
23.97 (24.62)
47.11 (47.83)
14.93 (15.59)
3C6H6, 3NO2, 3CO
3C2H4, 3 N2, 6CO, 6C6H6
3=2 N2, 3=2C2H2, 3C6H6
3C6H6, 3NO2, 3CO
C108H72N15O15Fe3
L(FeSalophen)3 (V)
II
III
I
3 N2, 6CO, 9C6H6
3=2 N2, 3=2C2H2, 3C6H6
3C6H6, 3NO2, 3CO
C96H72N15O15Cr3
L(CrSalen)3 (VI)
II
III
I
3C2H4, 3 N2, 6CO, 6C6H6
3=2 N2, 3=2C2H2, 3C6H6
3C6H6, 3NO2, 3CO
C108H72N15O15Cr3
L(CrSalophen)3 (VII)
II
III
3 N2, 6CO, 9C6H6
3=2 N2, 3=2C2H2, 3C6H6
the elemental analyses, given in Table 1, are in a good agreement with the structures
suggested for the ligands and their complexes. The results show that all complexes
are trinuclear.
When chloroisonitrosoacetophenone was added to tripodal Schiff base ligand
II, the phenolic OH band at 3338 cmꢁ1 disappeared. In the FT-IR spectra of L III,
=
the vibrations of the triazine C N (a), azomethine C N (b), oxime C N (c), carbonyl
=
=
=
C O, and CꢁOꢁC of the free ligands were observed at 1576, 1622, 1653, 1694, and
1372 cmꢁ1 range, respectively.[22–24] The bands at 3258 cmꢁ1 and 958 cmꢁ1 can be
assigned to the oxime-O-H and oxime N-O group vibrations, respectively.[25] IR
bands at 1658–1654 cmꢁ1 for complex IV–VII were assigned to C N (c) stretching
=
vibrations, 1008–1004 cmꢁ1 were assigned to N-O stretching vibrations, and 1538–
1544 cmꢁ1 were assigned to C N (d) stretching vibrations for complexes IV–VII,
=
ꢁ1
=
whereas C N (d) stretching vibration bands were found at 1560–1567 cm for
[Fe=Cr(salen or salophen)]2O complexes.[8–13,22,23,26] In the FT-IR spectra of
tripodal-trinuclear complexes IV–VII, the oxime OH band disappeared, and oxime
N-O bands shifted upward, suggesting chelation of oxygen atoms to the metal. Bands
Figure 2. Synthetic routes for the preparation of complexes.

88
S¸. UYSAL
at 1709–1704 cmꢁ1 for complexes IV–VII, in which the IR bands for C O vibrations
=
=
of tripodal complexes have shifted upward, were also assigned to C O groups
because of coordination of [Fe=Cr(salen or salophen)]2O to keton-oxime groups.
For the tripodal-trinuclear complexes IV–VII, the bands in the 544–532 and
478–468 cmꢁ1 ranges can be attributed to the M-N and M-O stretching modes.[27]
To identify the structures of the ligand III, the 1H NMR spectra were recorded
1
in DMSO-d6.[28,29] In the H NMR spectra of chloroisonitrosoacetophenone, the
absence of a singlet at d ¼ 8.40 ppm showed that this compound was formed. In the
1H NMR spectra of II, the presence of a singlet at d ¼ 6.08 ppm for three phenolic
=
OH and of a singlet at d ¼ 9.77 ppm for Mel–N CH-Ph showed that a three-
directional link to melamine had occurred.[18,19,24] Then, also H NMR spectra of
1
the confirmed structures of the synthesized compounds III revealed that the value
(at d ¼ 6.08 ppm) of OH chemical shift disappeared. The signal in 1H NMR spectrum
of III at d 11.50 ppm corresponded to the oxime –OH proton resonances.
The magnetic moments of the complexes given in Table 1 were measured at
room temperature. On the basis of spectral evidence, the Fe(III) and Cr(III) com-
plexes have trinuclear structures in which the Fe(III) and Cr(III) cations have an
approximately an octahedral environment. The magnetic behavior of Fe(III) and
Cr(III) complexes are good harmony with the proposed trinuclear structures.[29]
The magnetic moment per trinuclear complexes, which were constructed from
[Fe=Cr(salen or salophen)] and III, shows a paramagnetic property with a magnetic
susceptibility value per atom of 1.73–1.75 B.M. and 3.72–3.78 B.M., respectively. It
was seen that the [Fe=Cr(salen or salophen)]–containing compounds were represented
by the electronic structure of t25geg0 and t23ge0g. The magnetic data for the [Fe=Cr(salen
or salophen)] triarmed complexes showed good harmony with the low-spin d5 (S ¼ 1=2)
Fe(III) and d3 (S ¼ 3=2) Cr(III) ion in an octahedral structure. This consequence was
supported by the results of the elemental analyses suggesting that these trinuclear
complexes are six coordinate structures.[8–13,25,29,30]
All the complexes have also been thermally investigated, and their plausible
degradation schemes are presented in Table 2.[31,32] Thermal decomposition of the
three-armed complexes IV–VII have started in range of the first step 125–275 ꢀC,
and the anhydrous [Fe=Cr(salen or salophen)] complexes detached from ligand III.
The thermal analyses (TG, DTA) of complexes IV–VII showed weight losses theore-
tically calculated to be 26.34%, 24.44%, 26.55%, and 24.62%; experimentally they were
observed to be 25.76%, 23.86%, 25.82%, and 23.97%, respectively. It can be attributed
to decomposition of keton-oxime groups in this step. The second decomposition step
was observed in the range 275–375 ꢀC. The thermal analyses (TG, DTA) of complexes
IV–VII showed weight losses theoretically calculated to be 43.48%, 47.57%, 43.74%,
and 47.83%; experimentally they were observed to be 42.54%, 46.65%, 42.91%, and
47.11%, respectively. It can be attributed to decomposition of salen or salophen groups
in this step. The final decomposition step was completed in the range of 560–676 ꢀC.
The final decomposition products were metals and triazine ring. The observed weight
losses for all ligands and complexes are in good harmony with the calculated values.
LC-MS (ESIþ) spectrum of all ligand and their complexes were investigated. The
calculated molecular weights of all ligand and complexes have been given in Table 1.
Molecular peaks of the cations are observed with the same isotope distribution as the
calculated ones, theoretically. That is, from the investigation of LC-MS spectra of the

SYNTHESIS AND CHARACTERIZATION OF S-TRIAZINE
89
compounds, it has been seen that molecular weights of ligands and complexes are in
good harmony with the intensity values observed in LC-MS spectra.
CONCLUSIONS
In this study, novel tri-directional and melamine cored Schiff base L III was
synthesized. The strategy of synthesis for preparing tripodal-trinuclear used a com-
plex as a ligand that contained a potential donor group capable of coordinating to
the other ligand. We chose [Fe=Cr(salen or salophen)]2O as ligand complexes
because they could coordinate to the other ligand. These complexes were the first
examples of tripodal-trinuclear complexes bridged by keton-oxime groups to the
iron and chromium centers. Their structures were characterized by means of elemen-
tal analysis, 1H NMR, FT-IR spectroscopy, LC-MS, thermal analyses, and magnetic
susceptibility measurements. The magnetic data for the tripodal-trinuclear com-
plexes showed good harmony with the low spin d5 (S ¼ 1=2) Fe(III) and d3
(S ¼ 3 ꢂ 1=2) Cr(III) ion in an octahedral structure.
EXPERIMENTAL
Materials and Methods
Melamine, 4-hydroxybenzaldehyde, and all other reagents were purchased from
Merck and used without further purification. 2,4,6-Tris(4-hydroxybenzimino)-1,3,5-
triazine used in this study was synthesized in a previous study.[18,19] [Fe=Cr(salen or
salophen)]2O was prepared according to previously published methods.[30,33,34]
1H NMR spectra were taken using a Varian-Mercury 200 NMR spectrometer. The
chemical shifts for NMR spectra were ascribed in relation to the external tetramethyl-
silane (TMS) standard. IR spectra were recorded using a Perkin-Elmer 1600 FT-IR
spectrometer using KBr pellets. Elemental analyses were carried out using a
Hewlett-Packard 185 analyzer. Metal contents in complexes were determined using
a Unicam 929 AAS spectrometer. Mass spectra of the compounds were obtained on
a Varian MAT 711 spectrometer. pH values were measured on a WTW 537 pH meter.
Magnetic susceptibilities of metal complexes were determined using a Sheerwood
Scientific MX Gouy magnetic susceptibility apparatus carried out using the Gouy
method with Hg[Co(SCN)4] as calibrant. The effective magnetic moments, meff, per
pffiffiffiffiffiffi
metal atom were calculated based on the expression leff ¼ 2:84 vMT B.M., where
v
M is the molar susceptibility.
Preperation of Ligand Complexes
[Fe=Cr(salen or salophen)]2O was prepared by adding concentrated ammonia
solution (26% w=w) to a stirred hot EtOH solution of [Fe=Cr(salen or salophen)Cl],
until it became alkaline.[30,33,34]
Synthesis of Chloroisonitrozoacetophenone
Dry Cl2 gas was bubbled through a suspension of isonitrosoacetophenone
(3.58 g, 24 mmol) in chloroform under sunlight for 30 min, and the suspended

90
S¸. UYSAL
material dissolved and turned yellow. Bubbling of the Cl2 gas was sustained for a
further 1 h under ultraviolet (UV) radiation (254 nm), and the temperature of the
mixture reached 40 ꢀC. When the mixture was cooled to room temperature, white
crystals formed. Excess Cl2 was expelled in vacuum and then filtered, and the solid
was washed with diethylether. FT-IR (cmꢁ1) 3256 (OH), 1656 (C N c), 1696
=
1
=
(C O), 956 (N-O). H NMR (DMSO-d6) d 11.50 (s, broad, 1H), 7.94–7.91 (d, 2H),
7.66–7.63 (dd, 1H), 7.55–7.52 (dd, H). LC-MS (ESIþ) m=z ¼ 183 [100%, chloroisoni-
trozoacetophenone]. Molecular peaks of the cations are observed with the same
isotope distribution as the theoretical ones.
Synthesis of 2,4,6-Tris(4-(2-phenyl-2-keto-hydroxyiminoyloxy)
benzimino)-1,3,5-triazine L (III)
Choloroisonitrosoacetophenone (3 equiv., 27.54 g, 150 mmol) in 50 mL acetone
was added to a suspension of 2,4,6-tris(4-hydroxybenzimino)-1,3,5-triazine (21.92 g,
50 mmol) and triethylamine (8.93 g, 150 mmol) in 40 mL of acetone. The product
obtained was collected by filtration and dried in vacuo. The obtained mixture was
purified using colon chromotography and using 1:4 ethylacetate=n-hexane mixture
as eluent. The product was recrystallized from a mixture of methanol and water
(1:2). FT-IR (cmꢁ1) 3258 (OH), 2886 (CHar), 1576 (triazine C N a), 1622
=
1
=
=
=
(CH N b), 1653 (CH N c), 1694 (C O), 958 (N-O), 1372 (CꢁOꢁC). H NMR
(DMSO-d6) d 11.50 (s, broad, 3H), d 9.79 (s, 3H), 7.94–7.91 (d, 6H), 7.76–7.73
(d, 6H), 7.66–7.63 (dd, 3H), 7.55–7.52 (dd, 6H), 6.93–6.90 (d, 6H). LC-MS (ESIþ)
m=z: 879 [100%, III]. Molecular peaks of the cations are observed with the same
isotope distribution as the theoretical ones. Some physical properties and yield for
III are given in Table 1.
Preparation of L(FeSalen)3 (IV), L(FeSalophen)3 (V), L(CrSalen)3 (VI),
and L(CrSalophen)3 (VII) Complexes
A solution of L (1.76 g, 2.0 mmol) and [Fe=Cr(salen or salophen)]2O (3.0 mmol)
in 100 mL of absolute methanol was refluxed for 3 h. The mixture was allowed to
cool to room temperature. Then the mixture was filtered and dried in vacuum.
LC-MS (ESIþ) m=z: 1849 [100%, IV], m=z: 1993 [100%, V], m=z: 1837 [100%, VI],
and m=z: 1981 [100%, VII]. Molecular peaks of the cations are observed with the
same isotope distribution as the theoretical ones. Some physical properties and yields
for IV, V, VI and VII are given in Table 1. FT-IR (cmꢁ1) for complex IV: 2884
=
(CHar), 1575 (triazine C N a), 1625 (CH N b), 1658 (C N c), 1540 (C N d),
=
=
=
=
1709 (C O), 1008 (N-O), 1380 (CꢁOꢁC), 540 (M-N), 475 (M-O); for complex V:
=
2885 (CHar), 1568 (triazine C N a), 1622 (CH N b), 1654 (C N c), 1538 (C N
=
=
=
=
d), 1708 (C O), 1004 (N-O), 1378 (CꢁOꢁC), 542 (M-N), 477 (M-O); for complex
=
=
VI: 2888 (CHar), 1572 (triazine C N a), 1623 (CH N b), 1656 (C N c), 1542
=
=
=
(C N d), 1704 (C O), 1005 (N-O), 1381 (CꢁOꢁC), 543 (M-N), 474 (M-O); and
=
for complex VII: 2882 (CHar), 1574 (triazine C N a), 1622 (CH N b), 1655
=
=
=
=
(C N c), 1544 (C N d), 1706 (C O), 1006 (N-O), 1382 (CꢁOꢁC), 544 (M-N),
478 (M-O).

SYNTHESIS AND CHARACTERIZATION OF S-TRIAZINE
91
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