Synthesis and Spectroscopic
Study of Some Transition Metal Complexes with 8-Methyl-11-oxo-Indeno(1, 2-b)
Quinoxaline
Mahmoud
Najim A. Al-jibouri,
Afnan Emad abdul Munim
Chemistry Department, College of Science, Al-Mustansiriya University,
Baghdad, Iraq
*Corresponding Author E-mail: mahmoudnajim71@yahoo.com
A new quinoxaline derivative
(L)8-methyl-11-oxo-Indeno (1, 2-b) quinoxaline was synthesized by a one
step reaction between ninhydrin and 4-methyl-phenylenediamine . It formed metal
complex when reacted with hydrated chlorides of Cr(III), Mn(II), Co(II),
Ni(II), Cu(II) and Zn(II) in
ethanol–chloroform medium. The quinoxaline derivative (L) has, characterized on
the basis of IR, NMR and UV-VIS spectral data. The metal complexes were
characterized by analytical, conductivities, spectral (F.A.A.S, IR, UV-VIS) and
magnetic data. Involvement of exocyclic carbonyl oxygen and one of the
quinoxaline nitrogen in coordination was concluded, such that the ligand behaves as a neutral bi dentate. Conductance measurements
indicate the electrolytic behavior of the complexes in 1:2 ratio except 1:1
ratio for chromium(III) complex .Electronic spectral and magnetic
susceptibility data suggest square planar geometry for [NiL2 ]Cl2complex,tetrahedral
symmetry for [ZnLCl2].H2O while the complexes of Cr(III),
Mn(II),Co(II), and Cu(II) of general formul were octahedral with molecular
formula [CrL2Cl2]Cl. H2O and [ML2(H2O)2]Cl2,M=Mn,Co
and Cu(II) ions respectively.
KEYWORDS: Transition metal complexes, quinoxaline
ligands, benzopyrazine
INTRODUCTION:
Quinoxalines are
benzo-fused six membered heterocycles prepared by condensation of o-phenylenediamine
with 1,2-dicarbonyl compounds.1,2 Quinoxaline derivatives are
interesting class of compounds possessing a broad spectrum of biological
activity.3 Interest in the design and synthesis of new metal
complexes with quinoxalines partially derived from their existence in
biological systems6 and for their potential to act as catalysts for
numerous chemical reactions.4,5 The electronic and geometric
features of the ligand impart on the metal ion the specific properties that
facilitate the binding of small molecules and catalytic action. Schiff bases
with an electron withdrawing heterocyclic ring system derived from
quinoxaline-2-carboxaldehyde would be interesting as their ligand field
strengths are expected to be weaker than the Schiff bases containing only
aromatic rings, like naphthaldehyde.
Bidentate heteroatom sites of
quinoxalines are important building blocks in constructing bimetallic
coordination compounds, e.g. 2,3-bis(2-pyridyl)quinoxaline and
2,3-bis-(2-furyl)quinoxaline complexes with transition metals (Cu, Co, Ru, Rh,
Pt),3 or binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes with
tetradentate Shiff bases derived from 2,6-diformyl-4-methylphenol and
2-hydroxy-3-hydrazino quinoxaline are characterized in detail.8 The
catalytic behavior of Mn(II), Fe(II),and Ni(II) chelates with
quinoxaline-2-carboxylidine-2-amino-5-methylphenol in oxidative recovery of
organic pollutants was studied by Sebastian et al.7
Owing to the importance of the
above ligand and as part of our earlier studies on similar types of systems,8,9
we report here results on our studies on a series of complexes formed by
8-methyl-11H-indeno[1,2-b]quinoxalin-11-one derived from ring closure of
ninhydrin with 3,4-diamino toluene.
EXPERIMENTS:
Instruments
CHN elemental
analysis of 8-methyl-11H-indeno[1,2-b]quinoxalin-11-one and its solid complexes
were performed with using a Carlo-Erba 1106 Elemental analyzer. Electronic
spectra of DMF solutions of ligand and its metal complexes were measured using
a Shimadzu 670 spectrometer in the range 200-800 nm. Magnetic susceptibility
measurements were carried out using a magnetic balance at room temperature with
Guoy method with Hg[Co(SCN)4] as calibrate. The 1H and 13C
NMR spectra were recorded on a Bruker 300 MHZ spectrometer in DMSO-d6
solvent. Gas and Mass spectroscopy of free
ligand in chloroform solution was recorded on Shimadzu GC MS- P2010 model
spectrometer in assistance with specific column in 0-700m/e range and
vaporization in 100-450℃ range at Al-Yarmook
(Jordan).
Preparation of the ligand
Ninhydrin (1.35
g, 8.43 mmol) was dissolved in 15 ml ethanol and mixed with 3,4-diamino-toluene
(0.91 g, 8.43 mmol.) dissolved in 15 ml ethanol. The solution was stirred for
20 minutes. The resulting yellow precipitate was filtered off under suction and
repeatedly washed with ethanol. The product was then dried in an oven to 120 C
for two hours and storaged in a desiccator over pellets of CaCl2 The yield was
75 % (Scheme 1).
Preparation of
the complexes
The metal salts
(CrCl3.6H2O, MnCl2.4H2O, CoCl2.6H2O,
NiCl2.6H2O, CuCl2.2H2O, and ZnCl2)
(1 mmol,) were dissolved in 15 ml ethanol and mixed with the ligand (2 mmol,
0.594 g) dissolved in 15 ml chloroform. The mixtures were refluxed under
stirring for about 10-12 h. After cooling the mixtures, the solid precipitates
deposited were filtered off, washed with a mixture of ethanol and chloroform
(1:2, v/v, 20 ml) dried in air and stored in a desiccator over pellets of CaCl2
.The yields were varied between 50 and 70 %. The physical properties of
complexes are given in Table 1.
RESULTS AND DISCUSSION:
The analytical
and physical data of metal complexes are listed in Table 1. The percents of C,
H, N and M content are obtained from elemental and atomic absorption
spectroscopical data and are in good agreement with the general molecular
formulas proposed for the complexes.
Physical
properties of the ligand
The ligand is
stable at room temperature having yellow color. It is soluble in chloroform,
benzene and hot ethanol, but partially soluble in DMSO and acetonitrile.
1H and 13C NMR spectra of the
free ligand
The ¹H NMR
spectrum of the free ligand in DMSO-d6 showed singlet absorption in
the region 3.15 ppm corresponding to CH3 (3H) protons of methyl
group directly attached to of phenyl group. Multiple signals were observed at
δ 7.6-8.05 ppm that may be attributed to Ar-H and pyrazine hydrogens (7H)
(Figure 1)10.
The 13C NMR spectrum
of the ligand in DMSO-d6 showed signals at 122 ppm (s, C1-C4),
125ppm (s, C2), 130 ppm (s, C3), 135 ppm (s, C5), 137ppm (s, C6), 140 ppm (s,
C7), 143 and 145 (C8,C9) 180 ppm indicate the positions and numbers of carbon
atoms in the proposed structure of free ligand (Figure 2)10.
Scheme(1): Preparation of L ligand
Table (1). Physical
properties and elemental analysis of prepared complexes.
|
M%
Calc.(found)
|
N%
Calc.(found)
|
H%
Calc.(found)
|
C%
Calc.(found)
|
MP, °C
|
Colour
|
Symbol of compound.
|
|
__-
|
11.96(10.95)
|
4.27(4.00)
|
76.92(75.81)
|
145-147
|
Yellow
|
L
|
|
8.046(7.66)
|
8.33(8.77)
|
3.22(3.00)
|
57.48(56.99)
|
170-172
|
Green
|
[Cr(L)2Cl2]Cl.H2O
|
|
8.76(8.00)
|
9.11(10.044)
|
0.59(3.11)
|
58.71(58.09)
|
204d
|
Deep yellow
|
[Mn(L)2(H2O)2]Cl2
|
|
10.38(9.99)
|
8.88(9.06)
|
3.55(3.43)
|
58.11(57.22)
|
210d
|
Pale yellow
|
[Co(L)2(H2O)2]Cl2
|
|
9.54(9.11)
|
9.11(10.33)
|
3.94(2.77)
|
61.66(60.39)
|
165-167
|
Red
|
Ni(L)2]Cl2.H2O ]
|
|
10.35(10.18)
|
8.46 (9.11)
|
3.78(3.55)
|
57.90(57.21)
|
281d
|
Dark brown
|
[Cu(L)2(H2O)2]Cl2.H2O
|
|
15.36(14.32)
|
7.09(8.22)
|
3.21(2.71)
|
48.60(47.22)
|
159-161
|
Off-White
|
[Zn(L)Cl2].H2O
|
L=C16H10N2O
Table(2):H and C13 NMR.spectra
of L ligand
|
Group
|
|
|
|
Phenyl
ring
|
=
7.6-8.049ppm (m)
|
|
Methyl
group
|
 2.5ppm (s)
|
|
Group
|
|
|
|
Phenyl ring
|
 = 40ppm (d6-dmso)
122ppm(s,C1)
125ppm(s,C2)
130ppm(s,C3)
135ppm(s,C4)
137ppm(s,C5)
140ppm(s,C6),143,145(C7,C8)
|
|
Methyl group
|
 = 20 ppm
|
Figure(1)-H NMR
spectrum of L compound in d6-DMSO
Figure (2) -C13
NMR spectrum of L-compound in d6-DMSO.
GC-mass
spectrum of free ligand:
The figure(3) shows the molecular ion peak
at 246 belong to M+1 and the others fragments may be assigned to departure of
–CH3 at 232, this supports the expected weak points present in the indeno
quinoxaline moiety and agree well with the literature survey of mass spec tra
of annulated heterocyclic rings11-12.
Figure(3)-GC-mass spectra of L ligand in CHCl3
solution.
Table 3: The Characteristic Stretching Vibration
Frequencies (cm-1) Located at FT-IR of (L) and its Metal Complexes
|
Compounds
|
 C=O
|
C=N
|
C-N
|
M-N
|
M-O
|
M-Cl
|
|
L
|
1730-1677
|
1570-1604(s)
|
1363
(m)
|
-
|
-
|
-
|
|
[Cr(L)2Cl2]Cl.H2O
|
1729-1655
|
1590-1575(s)
|
1182
(m)
|
515-450
(m)
|
410
(m)
|
330
(vw),3480(br.)
|
|
[Mn(L)2(H2O)2]
Cl2
|
1737-1655(s)
|
1570-1606
|
11320
|
433-466
(w)
|
422
(m)
|
3610
(br.),833
|
|
[Co(L)2(H2O)2]
Cl2
|
1721-1688(s)
|
1541-1599(s)
|
1311
(m)
|
488-505(m)
|
419(w)
|
3200
(br.).830
|
|
[Ni(L)2]Cl2.
H2O
|
1734-1643(s)
|
1568-1606
|
1322
(m)
|
510-433(m)
|
403(m)
|
-
|
|
[Cu
(L)2(H2O)2]Cl2
|
1649-1690(s)
|
1585-1614(s)
|
1370
|
500-418(w)
|
407(m)
|
3500(br.),840
|
|
[Zn(L)Cl2]
. H2O
|
1734-1649(s)
|
1566-1606(s)
|
1309
|
420-433(w)
|
410(m)
|
277-330
|
Where : s=strong, m=medium, w=weak and vw=
very weak, br.=broad.
IR spectrum of the ligand
Ninhydrin shows three bands in
the C=O stretching region, 1768, 1754, and 1720 cm-1The 1754 and1720
cm-1 bands are characteristic of its 1,3 –dicarbonyl functional group and 1768
cm-1 band is characteristic of the intermediate carbonyl in the tricarbonyl
species which is in equilibrium with the dihydroxy species .The disappearance
of thetwo carbonyl bands and the appearance of only one band at 1730-1677 cm-1
indicates the involvement of two carbonyl groups of ninhydrin in azomethine
formation . On the other hand 1,2-phenylenediamine has sharp NH2 bands at 3386
cm-1and 3364 cm-1 that are assigned as asymmetric and symmetric
stretching vibration, respectively9. But these bands did not appear
in the spectrum which indicates the derivative of these groups. The strong absorptions
located at 1570-1604 cm-1 is assigned for C=N stretching mode of vibration.
Absorption frequencies observed at 1337, and 1185 cm-1 are assigned to C-N
stretching10. The negative shifts in υN=C and υO=C modes along
with the appearance of new bands in the region 448-530 and 412-430
cm-¹ assignable to υM-N and υM-O11,12-13 vibrations
respectively, suggest that the imine of nitrogen is coordinating to the metal
ions besides exocyclic oxygen atom of carbonyl in pyrazine ring.. Furthermore, the
Cr(III),Mn,Co and Cu(II) complexes showed broad absorptions in the
3500-3610cm-¹ regions and rocking modes in the 830-840cm-1regions,
which may be assigned to O-H vibrations of coordinated water molecules13-14,
figures (4-5).
Figure(4)-FTIR spectrum of L-compound in KBr disc.
Figure(5)-FTIR spectrum of [CrL2Cl2]Cl.H2O
in CsI disc.
Electronic spectrum:
The electronic spectra of the
ligand and its metal complexes were recorded in chloroform and D.M.F. The
electronic spectra measurements were very useful for assigning the
stereochemistry of the metal ion in the complex based on the position and
number of d-d transition peaks. The electronic absorption spectra of the
quinoxaline derivative L ligand and its complexes with Cr(III), Mn(II), Co
(II) ,Ni (II) ,and Zn(II), complexes were recorded at room temperature using
DMF as the solvent. As the spectrum of the ligand with its complexes were compared,
where the bathochromic shift of absorptions due to carbonyl and the azomethine group14-16, besides
this shift additional spin allowed d-d bands corresponding to d-d transition
are observed for the solutions of complexes, figures(5-6) . The green solution in DMF
showed two spin- allowed transitions in the region 433-630 nm which may be
assigned to A2g⁴→T2g⁴(F)
and A2g⁴→T1g⁴(F) transitions respectively(14) ,which agree well with peaks of
octahedral geometry around Cr(III) ion. The cobalt(II) complex exhibited two
distinct absorptions in the regions650 and 388nm assigned to 4T1g(F)
→4T2g(F) (ν1)
and 4T1g(F) → 4T1g(P) (ν3)
transitions, respectively, which suggests octahedral geometry around the Co(II)
ion17-19. The second band,ν2 is not observed, but it is
calculated by using relation ν2 = ν1 + 10Dq, which is very close to (ν3)
transition15.The 10Dq values for both cobalt(II) and chromium(III)
complexes were 522.8 and5974 cm-1 which investigates the high spin
d7 octahedral symmetry around metal ion. This is further supported by the magnetic
susceptibility value (4.35 B.M.).The UV-visible spectra of copper(II) complexes
in DMF solutions displayed a broad peak at ~530nm and a well-defined shoulder around 455
nm assignable to B1g² →A2g²,and B1g²
→B2g² transitions respectively, which strongly favors
distorted-octahedral geometries around copper ions(II)16. The
magnetic moment values for copper complexes 1.70 B.M, this strongly indicates distorted
octahedral copper(II) complex.
The diamagnetic Ni(II) complexes
solution of red colored in DMF showed a distinct peak in the regions(404,395nm) which are assigned to A1g¹→B1g¹
and A1g¹→B2g¹ transitions respectively as well as
the absence of any band below10000cm-1,rules out the possibility of
tetrahedral structures for these nickel(II)complexes. The band-fitting equations16,17,
have been used to calculate the ligand field parameters (Dq, B, β,
and β%) for Co(II) and Ni(II) complexes indicated significant
covalent character of metal ligand bonds (Table 3). The value of Rachah
parameter (B) is less than free ion value, suggesting an orbital overlap
and delocalization of electron on the metal ion18. The nephelauxetic
ratio (β) for the metal complexes is less than one suggesting
partial covalence in the metal ligand bond(18). In contrast, the pale yellow
solution of Zn(II) complex in DMF exhibited high intensity peaks at 220 and
330nm , which are assignable to ligand field
(π→π*,n→π*) and LMCT transitions , these
observations indicates the tetrahedral symmetry around Zn(II) ion(19).The molar conductance values
obtained for these complexes at the concentration of 10-3M. The
values are too low to account for any dissociation of the complexes in DMF,
hence these complexes can be regarded as non-electrolytes, in contrast
Cr(III),Ni(II) and Cu(II) complexes showed molar conductance’s in the range
(70-166) Ω-1 cm-dm-3 ,this agree with the electrolytic behavior of 1:1 and
1:2 ratios respectively20.
Magnetic
Moment
The magnetic moment values for
Cr(III), Mn(II),and Co(II), complexes of the ligand (L)are shown in Table 3. The magnetic moment of Cr(II)
complex was 3.45 B.M. corresponds to an octahedral geometry of d³-
configuration.
Co(II) complex is in the range of 4.35 BM indicating that the Co(II) complex
are typically high spin complex and having octahedral structure. The Mn(II)
complex exhibit the magnetic moment values in the range of 5.15 BM, indicating
octahedral co-ordination of the ligand around Mn(II) ion(21). The Ni(II)
complex exhibit diamagnetic property suggesting the low spin square planner geometry
around nickel(II) ion, and this may agree well with the other data of
electronic spectra21-22.
Table-4: UV-Visible (cm-1)
,molar conductance and the magnetic moments of prepared complexes.
|
Compound
|
|
|
assignment
|
Proposed
geometry
|
Conda.
|
µB.M
|
|
L
|
299
388
|
33444
25773
|
|
|
9
|
|
|
[Cr(L)2Cl2]Cl.H2O
|
263
348
355
460
|
38022
28735
28169
21739
|
INCT
A2g4 T1g4(P)
A2g4T1g4(F)
A2g4T2g4(F)
|
Octahedral
|
50
|
3.45
|
|
[Mn(L)2(H2O)2]Cl2
|
393
408
328
|
25444
24509
30487
|
A1g6T1g4
|
Octahedral
|
88
|
5.15
|
|
[Co(L)2(H2O)2]Cl2
|
295
388
650
|
33898
25773
15384
|
T1g4A2g4
T1g4T1g4(P)
T1g4T2g4
|
Octahedral
|
101
|
4.35
|
|
[NiL2]Cl2.H2O
|
296
395
404
|
33783
25316
24752
|
MLCT
A1g1B2g1
A1g1B2g1
|
Square
planner
|
122
|
0
|
|
[Cu(L)2(H2O)2]Cl2.H2O
|
455
530
|
21978
19752
|
INCT
Eg T2g2
|
Distorted
octahedral
|
98
|
1.70
|
|
[Zn(L)Cl2].H2O
|
249
263
357
|
40160
38022
28011
|
n
INCT
|
Tetrahedral
|
18
|
Dia.
|
INCT=intra-ligand charge
transfer absorptions, D=diamagnetic, T.h=tetrahedral and a=molar conductance
was measured at0.001Msolution of DMSO in ohm-1.cm2.mol.-1
|
|
|
|
Figure(6)-UV-Visible spectrum of
L-solution in CHCl3(10-3 M).
|
Figure(7)-UV-Visible spectra of [MnL2(H2O)2]Cl2
complex in DMF.
|
CONCLUSION:
In this study, the synthesis and
structural investigations of quinoxaline-containing indole ligand and their
transition metal(II) complexes are presented. Structures of the ligand and
complexes were confirmed by spectral and analytical techniques. The ligand-to
metal (L :M) stoichiometry is 1 : 2 in all formed complexes except
zinc((II)which showed 1:1 molar ratio confirming [ZnLCl2] formula. The results
obtained from IR spectra revealed that the ligand coordinate to metal through
nitrogen atom of C=N- of pyrazine ring and adjacent oxygen atom of exocyclic
carbonyl groups. According to the results from elemental analyses,IR,UV-Visible
spectra,molar conductance and magnetic moments,the proposed stereo chemical
structures of the prepared complexes may be shown as below in figure (8).
Figure(8)-Stereo chemical structures of metal
complexes
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