Metal complexes of a new class of polydentate Mannich bases: Synthesis and spectroscopic characterisation

Article abstract of DOI:10.1016/j.ica.2011.10.013

A new class of polydentate Mannich bases featuring an N₂S ₂ donor system, bis((2-mercapto-N-phenylacetamido)methyl)phosphinic acid H₃L¹ and bis((2-mercapto-N-propylacetamido)methyl) phosphinic acid H₃L², has been synthesised from condensation of phosphinic acid and paraformaldehyde with 2- mercaptophenylacetamide W1 and 2-mercaptopropylacetamide W2, respectively. Monomeric complexes of these ligands, of general formula K₂[Cr ^III(Lⁿ)Cl₂], K₃[M′ ^II(Lⁿ)Cl₂] and K[M(Lⁿ)] (M′ = Mn(II) or Fe(II); M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The structures of new ligands, mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) and Fe(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Co(II), Zn(II), Cd(II) and Hg(II) complexes. Complex formation studies via molar ratio in DMF solution were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1).

Full text of DOI:10.1016/j.ica.2011.10.013

Inorganica Chimica Acta 379 (2011) 163–170
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Note
Metal complexes of a new class of polydentate Mannich bases: Synthesis
and spectroscopic characterisation
⇑
Mohamad J. Al-Jeboori , Fahad A. Al-Jebouri, Muayed A.R. Al-Azzawi
Department of Chemistry, College of Education, Ibn Al-Haitham, University of Baghdad, P.O. Box 4150, Adamiyah, Baghdad, Iraq
a r t i c l e i n f o
a b s t r a c t
Article history:
A new class of polydentate Mannich bases featuring an N2S2 donor system, bis((2-mercapto-N-pheny-
lacetamido)methyl)phosphinic acid H3L1 and bis((2-mercapto-N-propylacetamido)methyl)phosphinic
acid H3L2, has been synthesised from condensation of phosphinic acid and paraformaldehyde with
2-mercaptophenylacetamide W1 and 2-mercaptopropylacetamide W2, respectively. Monomeric com-
Received 11 September 2010
Received in revised form 25 August 2011
Accepted 1 October 2011
Available online 10 October 2011
II
plexes of these ligands, of general formula K2[CrIII(Ln)Cl2], K3[M0 (Ln)Cl2] and K[M(Ln)] (M0 = Mn(II) or
Fe(II); M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The structures of new ligands,
mode of bonding and overall geometry of the complexes were determined through IR, UV–Vis, NMR, and
mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conduc-
tance. These studies revealed octahedral geometries for the Cr(III), Mn(II) and Fe(II) complexes, square
planar for Ni(II) and Cu(II) complexes and tetrahedral for the Co(II), Zn(II), Cd(II) and Hg(II) complexes.
Complex formation studies via molar ratio in DMF solution were consistent to those found in the solid
complexes with a ratio of (M:L) as (1:1).
Keywords:
Mannich bases
Bis((2-mercapto-N-
phenylacetamido)methyl)phosphinic acid
Bis((2-mercapto-N-
propylacetamido)methyl)phosphinic acid
Transition metal complexes
Structural study
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
system [14–16]. There has been great interest in designing com-
plexes with N2S2 system that may serve as become functional mod-
The design and study of complexes with N2S2 ligands is an inter-
esting area of research for both inorganic and bioinorganic chemists
[1,2]. Compounds bearing N and S donors have been extensively
investigated with regard to their numerous applications in different
fields including organic synthesis [3]. The soft-hard nature of
ligands with N and S donor atoms facilitate the coordination of
these ligands with a wide range of metal ions which have a poten-
tial applications in biomedical [4–6], biomimetic [7] and catalytic
system [8,9]. One significant application of complexes with N2S2
ligands is their use in the medical fields for therapeutic and diag-
nostic purposes [10]. These include the complexation of N2S2 sys-
tem with a range of soft metals such as 64Cu, and 99mTc in
diagnostic imaging and 186/188Re in targeted radiotherapy [11,12].
In addition, aliphatic N2S2 chelates of hard metals such as 67/68Ga
and 111In radionuclides are widely used in diagnostic imaging
[13]. Furthermore, N2S2 ligands played a vital role in the develop-
ment of metal-sulfur complexes with characteristic redox proper-
ties. These involve the design and synthesis of polydentate
ligands with sulfur and nitrogen cores to achieve a metal environ-
ment in simple complexes directly analogous to the biological
els (biomimetics) of the active sites of the metalloenzymes. These
covered the preparation of Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) com-
plexes with N2S2 donor ligands. The choice of these metals was gov-
erned by their relevance in the active sites of various oxygenases
and peroxidises and their ability to react with CO2, CO, NO or CH3
moieties [7,17,18]. Compounds of phosphinic acid and its deriva-
tives are also of interest due to their pharmaceutical applications
and biological activity which include enzyme inhibition
[19–21]. Recently, we have investigated the preparation of the
potentially tetradentate Mannich base ligands system and their
metal complexes [22,23]. These ligands system based on the use
of semi- and thiosemicarbazide derevatives to prepare the Mannich
ligands, Scheme 1. As part of our continuing efforts to synthesis and
characterise transition metal chelates using polydentate ligands,
we were interested to see if amide derivatives could be used to
obtain new type of Mannich bases could form metal complexes
with the ligands coordinated in the required fashion. The ligands
have been specifically designed in which a tetradentate chelate
N2S2 system could be used to bind metal ion upon complex
formation. We describe here the synthesis and spectral
investigation of two Mannich bases, bis((2-mercapto-N-phenylace-
tamido)methyl)phosphinic acid H3L1 and bis((2-mercapto-N-pro-
pylacetamido)methyl)phosphinic acid H3L2 (see Scheme 2) and
some of their metal complexes.
⇑
Corresponding author.
E-mail address: mohamadaljeboori@yahoo.com (M.J. Al-Jeboori).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.10.013

164
M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
DMSO-d6 solution using Brucker AMX 400 MHz and Jeol Lambda
400 MHz spectrometers with tetramethylsilane (TMS) as an internal
standard for 1H NMR analysis and H3PO4 85% as an external standard
for 31P{1H} NMR analysis. Conductivity measurements were made
with DMF solutions using a Jenway 4071 digital conductivity meter
and room temperature magnetic moments were measured with a
magnetic susceptibility balance (Jonson Mattey Catalytic System
Division).
3. Synthesis
3.1. Preparation of 2-mercaptophenylacetamide W1
A 100 mL round-bottomed flask equipped with a magnetic stir-
ring bar was charged with 2-mercaptoacetic acid (0.38 mL,
5.5 mmol). The content of the flask was cooled to about (ꢀ5 °C)
in an ice-bath. Aniline (0.5 mL, 5.5 mmol) was added dropwise,
while stirring over a period of 30 min, and a white viscous liquid
was formed. Un-reacted starting materials and water were re-
moved under vacuum, and then the oil product was stored at
4 °C for 2 weeks to give a white solid. Yield: (0.63 g, 80%), mp
Scheme 1. Chemical structure of Mannich bases derived from semi- and thiosem-
icarbazide compounds.
93–94 °C. IR data (cmꢀ1), 3315, 3283
m
(N–H), 2583
(C@O), 1611 d(N–H), 1601, 1540 (C@C), 1203
(C–S). NMR data (ppm), dH (400 MHz, DMSO-d6) showed
m
(S–H), 1659,
1620
1025
m
m
m
m
(C–N),
2. Experimental
trans: cis-phenylacetamide isomers in the ratio ca. 90:10; trans iso-
mer 90%; trans isomer; 3.4 (1H, t, JHH 7.4 Hz, S–H); 3.8 (2H, d, JHH
7.6 Hz, C1–H); 7.1 (1H, dd JHH 7.6 Hz, C6–H), 7.3 (2H, d, JHH
8.5 Hz, C5,7–H), 7.7 (2H, d, JHH 8.5 Hz, C4,8–H), 10.83(1H, s, N–H);
cis isomer 10%; 3.1 (1H, S–H); 3.2 (2H, C1–H); 6.5 (Ar–H), 6.6
(Ar–H), 6.9 (Ar–H); dC (100.63 MHz, DMSO-d6): 28.3 (C1), 119.6
(C4,8), 123.6 (C6), 129.0 (C5,7), 138.4 (C3), 148.4 (C2, C@O; cis iso-
mer), 166.7 (C2, C@O; trans isomer). The positive (EI) mass spec-
trum of W1 showed the parent ion peak at m/z 167.15 (42.30%)
corresponding to (M)+ and the following fragments; 139.4 (22%)
[Mꢀ(C@O)]+, 91.4 (100%) [Mꢀ{(C@O)+HNCH2SH)}]+.
2.1. Materials
All reagents were commercially available and used without fur-
ther purification. Solvents were distilled from appropriate drying
agents immediately prior to use.
2.2. Physical measurements
Elemental analyses (C, H and N) were carried out on a Heraeus
instrument (Vario EL). Metals were determined using a Shimadzu
(A.A) 680 G atomic absorption spectrophotometer. Chloride was
determined using potentiometer titration method on a (686-Titro
processor-665Dosimat-Metrohm Swiss). Melting points were
obtained on a Buchi SMP-20 capillary melting point apparatus and
are uncorrected. IR spectra were recorded as KBr or CsI discs using
3.2. Preparation of 2-mercaptopropylacetamide W2
The method used to prepare 2-mercaptopropylacetamide was
similar to that used for 2-mercaptophenylacetamide but propyl-
amine (0.5 mL, 8.4 mmol) was used in place of aniline. The quanti-
ties of other reagents used were adjusted accordingly. An identical
work-up procedure was employed to give (0.61 g, 84%) of the title
a
Shimadzu 8300 FTIR spectrophotometer in the range
(4000–250) cmꢀ1. Electronic spectra were measured in the region
(200–900) nm using 10ꢀ3 M solutions in DMF at 25 °C using a
Shimadzu 160 spectrophotometer. Mass spectra were obtained by
positive Electron-Impact (EI) and Fast Atom Bombardment (FAB)
was recorded on a VG autospec micromass spectrometer. NMR spec-
tra (1H, 13C, COSY, 13C–1H correlated, 31P NMR) were acquired in
compound as yellow oil. IR data (cmꢀ1), 3384(b)
m
(N–H), 2557
(C–N), 1049
(C–S). NMR data (ppm), dH (400 MHz, DMSO-d6) showed
m(S–H), 1640, 1602 m(C@O), 1589 d(N–H), 1201 m
m
Scheme 2. Synthesis route of ligands.

M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
165
trans:cis-acetamide isomers in the ratio 87:13; trans isomer 87%;
0.9 (3H, t, JHH 7.6, C5–H); 1.6 (2H, m, C4–H); 2.7 (2H, dd, JHH
7.6 Hz, C3–H); 3.0 (1H, t, JHH 7.4 Hz, S–H); 3.5 (2H, t, JHH 7.6 Hz,
C1–H); 8.3 (1H, s, N–H); cis isomer 13%; 0.8 (C5–H); 1.6 (C4–H);
3.0 (C3–H); 3.4 (d, C1–H); 4.7 (N–H); dC (100.63 MHz, DMSO-d6):
trans isomer 87%; 11.5 (C5), 21.1 (C4), 40.2 (C3), 43.7 (C1), 172.2
(C@O, C2); cis isomer 13%; 11.9 (C5), 22.8 (C4), 41.0 (C3), 43.9
(C1), 168.5 (C@O, C2). The positive (EI) mass spectrum of W2
showed the parent ion peak at m/z 133.16 (14.70%) corresponding
to (M)+ and the following fragments; 100.75 (6.3%) (M–SH)+, 85.5
(100%) [M–(SH+CH3)]+, 38.4 (61.76%) [M–(SH+CH3+CH5NO)]+.
which was washed several times with hot methanol. Elemental
analysis data, colours, and yields for the complexes are given in
(Table 1).
NMR data (ppm): K[Zn(L1)]; the 1H and 31P{1H} NMR spectra of
the complex; dH (400 MHz, DMSO-d6): 7.6–7.3 (4H, d, 12 Hz,
0
0
0
0
0
C
4,4 ;8,8 –H); 7.2–6.9 (4H, dd, 12 Hz, C5,5 ;7,7 –H), 7.6 (2H, t, C6,6 –
0
H); 3.6 (4H, d, JPH 22.4 Hz, PCH2); 3.4 (4H, s, C1, 1 –H); dP
(109.3 MHz, DMSO-d6): 51.
K[Zn(L2)]; the 1H and 31P{1H} NMR spectra of the complex; dH
(400 MHz, DMSO-d6): 3.5 (4H, d, JPH 24.4 Hz, PCH2); 3.1 (4H, s,
0
0
0
C1, 1 –H); 1.5 (4H, m, C3, 3 –H); 1.2 (4H, m, C4, 4 –H); 0.8 (6H, m,
0
C
5, 5 –H); dP (109.3 MHz, DMSO-d6): 25.
3.3. Preparation of H3L1
4. Results and discussion
A mixture of phosphinic acid (0.52 g, 8.00 mmol) and 2-mercap-
tophenylacetamide (3.5 g, 16 mmol) in (1 mL HCl 37%, 40 mL
EtOH) was heated under reflux, then paraformaldehyde (0.5 g,
16 mmol) was added dropwise over 20 min. The reaction was al-
lowed to reflux for 3–4 h. The solution was concentrated under re-
The compounds, 2-mercaptophenylacetamide W1 and 2-mer-
captopropylacetamide W2 were obtained in high yield from the
reaction of 2-mercaptoacetic acid with aniline and N-propylamine,
respectively. The compounds were characterised by elemental
analysis, IR, 1H, 13C NMR and mass spectra. IR and NMR spectral
data revealed the exists of two isomers (the cis form I and the trans
form II) in the solid state and in solutions (Scheme 3). The Mannich
duced pressure and
a white solid was formed. This was
recrystallised from methanol/diethylether, and the white solid
formed was collected and dried under vacuum. Yield (5.3 g, 63%),
mp 188–189 °C. NMR data (ppm), dH (400 MHz, DMSO-d6): 2.5
bases,
bis((2-mercapto-N-phenylacetamido)methyl)phosphinic
0
(2H, m, S–H), 3.3 (4H, d, JPH 18.4 Hz, PCH2), 4.1 (4H, C1,1 –H), 6.7
acid H3L1 and bis((2-mercapto-N-propylacetamido)methyl)phos-
phinic acid H3L2 were obtained in good yields from condensation
of phosphinic acid and paraformaldehyde with 2-mercaptopheny-
lacetamide and 2-mercaptopropylacetamide, respectively (Scheme
2). Monomeric complexes of the two ligands with CrIII, MnII, FeII,
CoII, NiII, CuII, ZnII CdII and HgII were synthesised by heating
1 mmole of each ligand with 1 mmole of metal chloride, using
methanolic potassium hydroxide as a base. No reaction occurred
with the ligands in the absence of a base and only an intractable
mixture was recovered by using 2 equivalents of base (potassium
hydroxide). The choice of base was also important, and no pure
complexes could be isolated using sodium acetate- or triethyl-
amine–methanol mixture. Complexes of general formulae
0
0
0
0
0
(2H, m, C6,6 –H), 7.0 (4H, m, C5,5 ;7,7 –H), 7.2 (4H, m, C4,4 ;8,8 –H),
10.30 (1H, s, POH); dC (100.63 MHz, DMSO-d6): 32.2 (C1), 54.8 (d,
0
0
0
0
0
JPH 40 Hz, PCH2), 113.4 (C4,4 ;8,8 ), 128.9 (C5,5 ;7,7 ), 133.4 (C6,6 ),
0
145 (C3,3 ), 170.0 (C@O, 2C); dP (109.3 MHz, DMSO-d6): 26.5. The
positive (EI) mass spectrum of H3L1 showed the parent ion peak
at m/z 424.02 (20.68%) corresponding to (M)+ and the following
fragments: 396 (48.37%) (MꢀCH2CH2)+, 340 (36%) [Mꢀ{(CH2CH2)+
(O@CCH2CH2)}]+, 250 (80%) [Mꢀ{(CH2CH2)+(O@CCH2CH2)+
(NPh)}]+, 221.9 (100%) [Mꢀ{(CH2CH2)+(O@CCH2CH2)+(NPh)+
(C@O)}]+, 158 (22%) [Mꢀ{(CH2CH2)+(O@CCH2CH2)+(NPh)+(C@O)+
(HOP@O)}]+.
3.4. Preparation of H3L2
II
K2[CrIII(Ln)Cl2], K3[M0 (Ln)Cl2] and K[M(Ln)] (M0 = Mn(II) or Fe(II);
M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) were
obtained (Scheme 4). The complexes are solids, stable in air and
soluble in DMF and DMSO (but not other common organic sol-
vents). The analytical data (Table 1) agree well with the suggested
formulae. The molar conductivities indicate that the Cr(III) com-
plexes are a 2:1 electrolyte, while the Mn(II) and Fe(II) complexes
are 3:1 electrolytes and the rest are 1:1 electrolytes (Table 1) [24].
H3L2 was prepared in the same manner as H3L1, but 2-merca-
ptopropylacetamide (3.0 g, 22.0 mmol) was used instead of 2-mer-
captophenylacetamid. The quantities of other reagents used were
adjusted accordingly. An identical work-up procedure was
employed for purification and recrystallisation of the product to
give (5.8 g, 73%) of H3L2 as a pale yellow solid, mp 156–158 °C.
0
NMR data (ppm), dH (400 MHz, DMSO-d6): 1.1 (6H, t, C5, 5 –H),
0
1.5 (4H, m, C4, 4 –H), 2.6 (2H, t, JHH 8.1 Hz, S–H), 3.3 (4H, m, C3,
0
0
3 –H), 3.5 (4H, d, JPH 20.1 Hz, PCH2), 4.4 (4H, d, C1, 1 –H), 7.5 (1H,
4.1. IR spectra
0
0
s, POH); dC (100.63 MHz, DMSO-d6): 11.0 (C5,5 ), 20.1 (C4,4 ), 31.3
0
0
0
(C1,1 ), 49.8 (d, JPC 38.3 Hz, C2,2 ), 49.8 (C3,3 ), 169.8 (C@O, 2C); dP
(109.3 MHz, DMSO-d6): 0.52. The positive (EI) mass spectrum of
H3L2 shows the parent ion peak at m/z 356.41 (13.43%) corre-
sponds to (M)+ and the following fragments: 302.5 (13%)
(MꢀNCHCO)+, 301.5 (33%) [Mꢀ(NCHCO+CH2)]+, 287.3 (19%)
[Mꢀ{(NCHCO+CH2)+(OPOH)}]+, 221 (10%) [Mꢀ{(NCHCO+CH2)+
(OPOH)+(HSCH2CO)}]+, 159 (16%) [Mꢀ{(NCHCO+CH2)+(OPOH)+
(HSCH2CO)+(CH3CH2SH)}]+, 128.2 (100%) [Mꢀ{(NCHCO+CH2)
+(OPOH)+(HSCH2CO)+(CH3CH2SH)+ (CH3OH)}]+.
The IR spectra of the W1 and W2 show characteristic bands due
to the
groups. The IR spectra show bands originating from the amide
groups were split. The amide stretching band (C@O) for W1 and
m(N–H), m(S–H), d(N–H), m(C@O), and m(C–N) functional
m
W2 appear as a doublet of almost equally intense bands at 1659,
1620 and 1640, 1602 cmꢀ1, respectively. This may be due to the
fact that the vibration mode is strongly affected by the presence
of intermolecular hydrogen bonds (Scheme 5), the bands at 1659
and 1640 cmꢀ1 was assigned to relatively free carbonyl groups
and the peaks at 1620 and 1602 cmꢀ1 to the hydrogen bonded ones
[25], and/or resulted from the exists of two isomers in the solid
state; the cis form I and the trans form II, (Scheme 3). The IR spectra
of the free Mannich bases show characteristic bands at 2440,
3.5. General synthesis of the complexes with H3L1 and H3L2 ligands
A solution of the appropriate Mannich base (1 mmol) and potas-
sium hydroxide (3.3 mmol) in methanol (20 mL) was stirred for
10 min. A methanolic solution (15 mL) of the metal salt (1 mmol)
(metal salts are hydrated chlorides except zinc as the anhydrous
chloride) was then added dropwise. The resulting mixture was
refluxed under N2 for 2 h, resulting in the formation of a solid mass
1645–1660 and 1029–1035 cmꢀ1 due to the
and (C–S) functional groups, respectively. The distinct frequency
at ca. 1410 cmꢀ1 assigned for
(P–C) band confirms formation of
the Mannich bases [26–28]. While the frequency around
2545–2619 cmꢀ1 assigned for
(S–H) band confirms presence of
m(P–OH), m(C@O)
m
m
m

166
M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
Table 1
Colours, yields, elemental analyses, and molar conductance values.
Compound
Colour
Yield (%, g)
mp (°C)
Found (Calcd.) (%)
KM (cm2 ꢀ1 molꢀ1
X )
M
–
C
H
N
Cl
Wl
Pale yellow
White
80, 0.63
93–94
57.3
(57.5)
51.2
5.1
(5.3)
4.7
8.1
(8.4)
6.5
–
–
–
H3L1
63, 5.3
163–165
273–275⁄
311–317⁄
255–258⁄
244–246
266–269⁄
219–223⁄
288–295⁄
203–208⁄
253–257⁄
–
–
(50.9)
35.1
(34.7)
31.9
(32.5)
32.7
(32.4)
41.4
(41.6)
41.9
(41.6)
41.1
(41.2)
40.9
(41.1)
38.0.9
(37.7)
32.9
(4.9)
2.7
(2.9)
2.8
(2.7)
3.1
(2.7)
3.1
(3.4)
4.1
(3.5)
3.4
(3.4)
4.1
(3.4)
3.0
(6.6)
4.6
(4.5)
4.1
(4.2)
4.3
(4.2)
5.8
(5.4)
5.5
(5.4)
5.7
(5.3)
5.1
(5.3)
5.3
K2[CrIII(L1)Cl2]
K3[MnII(L1)Cl2]
K3[FeII(L1)Cl2]
K[CoII(L1)]
K[NiII(L1)]
K[CuII(L1)]
K[ZnII(L1)]
K[CdII(L1)]
K[HgII(L1)]
Blue
68, 0.41
8.1
(8.3)
8.5
(8.3)
8.2
11.1
(11.4)
11.1
(10.7)
10.5
(10.6)
–
155.4
237.9
221.1
105
Brown
Dark red
Red-brown
Green
77.3, 0.5
76.5, 0.5
79.4, 0.4
59.7, 0.31
81.1, 0.42
66.2, 0.34
68.3, 0.38
73.2, 0.47
(8.4)
11.3
(11.3)
11.1
(11.3)
11.8
(12.1)
12.2
(12.4)
20.1
(19.6)
30.8
(30.3)
–
–
–
–
–
107.2
110.1
115.4
116.2
106.8
Green
White
White
(3.1)
2.7
(2.7)
(4.9)
4.3
(4.2)
White
(32.7)
W2
Pale yellow
Yellow
Blue
84, 0.61
73, 5.8
Oily
–
45.6
(45.1)
40.3
(40.4)
26.3
(26.0)
23.8
(24.1)
24.21
(24.1)
31.6
(31.9)
31.7
(31.9)
31.9
(31.6)
30.9
8.4
(8.3)
7.5
(7.1)
4.4
(4.0)
4.3
(3.7)
4.2
(3.7)
5.1
(4.9)
5.2
(4.9)
4.4
(4.8)
5.2
(4.8)
5.0
(4.6)
4.0
(3.7)
10.2
(10.5)
7.7
(7.8)
4.8
(5.0)
5.1
(4.7)
4.3
(4.7)
6.1
(6.2)
6.1
(6.2)
5.8
(6.1)
5.9
–
–
–
–
H3L2
156–158
277–279
281–286⁄
210–213
>320
–
–
K2[CrIII(L2)Cl2]
K3[MnII(L2)Cl2]
K3[FeII(L2)Cl2]
K[CoII(L2)]
K[NiII(L2)]
K[CuII(L2)]
K[ZnII(L2)]
K[CdII(L2)]
K[HgII(L2)]
73, 0.39
82, 0.48
58, 0.29
64, 0.28
81, 0.35
66, 0.29
60, 0.26
63, 0.31
70.2, 0.40
9.2
(9.4)
9.4
(9.2)
9.2
13.1
(12.8)
11.6
(11.9)
12.4
(11.9)
–
149.1
247.9
210.5
98.6
118.2
100.1
105.4
106.2
116
Red-brown
Red
(9.3)
13.3
(13.0)
13.1
(13.0)
13.6
(13.9)
14.4
(14.3)
21.7
(22.2)
33.1
(33.8)
Brown
Green
180–183
257–260⁄
201–204⁄
181–187⁄
300–303⁄
–
–
–
–
–
Green
White
(31.4)
27.9
(28.5)
24.9
(6.1)
5.3
(5.5)
5.1
Pale yellow
White
(24.3)
(4.7)
(⁄) = Decomposed.
round 1029–1035 cmꢀ1 in the the H3L1 and H3L2 is shifted to
higher frequency and observed around 1040–1060 and
1036–1081 cmꢀ1 for H3L1 and H3L2 complexes, respectively indi-
cating coordination of sulfur atom of the C–S moiety to the metal
atoms [32]. At lower frequency the complexes exhibited bands
around 453–583 and 366–398 cmꢀ1 which are assigned to the
m
(M–N) and m(M–S) vibration modes, respectively [32,33]. The IR
II
spectra of the complexes K2[CrIII(Ln)Cl2] and K3[M0 (Ln)Cl2]
(M0 = Mn(II) or Fe(II); n = 1 or 2) exhibit far-IR active bands around
Scheme 3. The cis I and trans II forms of precursors exist in the solid state and in
283–301 cmꢀ1 which are assigned to the
m(M–Cl) vibrations. These
solution.
vibrations are characteristic of terminally coordinated chloride
[32,34,35].
the thiolate group [29]. The IR spectra of the complexes exhibited
H3L1 and H3L2 bands with the appropriate shifts due to complex
4.2. NMR spectra
formation (Table 2). The absence of
a
peak around
2545–2619 cmꢀ1 in all the complexes indicates the deprotonation
The 1H and 13C NMR spectra of W1, W2 and the Mannich bases
H3L1 and H3L2 displayed signals corresponding to the various pro-
ton and carbon nuclei consistent with the proposed structural for-
mula (Section 3). In solution, as in solid state, W1, W2 can exist in
two conformation forms; the cis form I and the trans form II
(Scheme 3). In the NMR spectra (DMSO-d6 solution), for both
of (S–H) group upon complex formation. The m(C@O) amide vibra-
tion at 1660–1645 cmꢀ1 in the free ligands is shifted and observed
around 1600–1650 and 1597–1640 cmꢀ1 for the H3L1 and H3L2
complexes, respectively indicating coordination of the nitrogen of
the amide group to the metal atoms [30,31]. The m(C–S) stretching

M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
167
Scheme 4. Proposed structures of the complexes.
it was found that the P–OH signal, appeared in the spectra of
H3L1 and H3L2 ligands at 10.30 and 7.5 ppm, respectively is com-
pletely disappeared in the spectra of their Zn(II) complexes indicat-
ing that the POH proton is removed and replaced by the potassium
ion. This has been supported by the chemical analysis and the
molar conductivity measurements of the complexes, indicating
the ligands behave as a tribasic molecule upon complex formation.
Upon Zn(II) coordination, the protons PCH2N are shifted downfield,
indicating the coordination of the nitrogen atoms to the metal cen-
Scheme 5. Intermolecular hydrogen bonding interaction formed in the solid state.
tre, because the deshielding effect of the metal centre. The protons
1
assigned due to the C4,4 ;8,8 –H and C3,3 –H in the H3L and H3L2,
respectively were found at around d7.2 and 3.3 ppm in the spectra
of the free ligands. These protons undergo downfield shift in the
zinc complexes indicating participation of the nitrogen atoms
attached to these groups in coordination with the metal ions. Thus
the 1H NMR results support the modes of coordination suggested
by IR data. Upon complexation, the 31P{1H} signal is shifted down-
field by ca. 24 ppm because the deshielding effect of the metal
centre.
0
0
0
precursors, we observed the presence of double signals for the pro-
tons, as well as double signals for carbons of both compounds. Sig-
nals at 148.4 (C2, C@O; cis isomer), 166.7 (C2, C@O; trans isomer)
and 168.5 (C2, C@O; cis isomer), 172.2 (C2, C@O; trans isomer) were
observed for W1 and W2, respectively. This is perhaps due to the
fact that the rotational isomers of thioacetamide were sufficiently
slow on the NMR time scale to allow the detection of the trans and
cis isomers by NMR spectroscopy [36]. The NMR spectra for
K[Zn(L1)] and K[Zn(L2)] complexes in DMSO-d6 are examined in
comparison with those of the parent Mannich bases H3L1 and
H3L2. In the 1H NMR spectra of complexes, a signal assignable to
thiol group protons at ca. 2.6 ppm in the free ligands was absent,
indicating that deprotonation of thiol group occurred and that
coordination through this group took place. Upon complexation
4.3. Mass spectra
The mass spectra of the ligands and precursors were also con-
sistent with the proposed structural formulae (see Section 2). The
Table 2
IR frequencies (cmꢀ1) of the compounds.
Compound
m(C@O)
m(P@O)
m
(C–S)
m
(P–C)
m(M–N)
m(M–S)
m(M–Cl)
H3L1
1660
1620
1610
1645
1617
1605
1600
1608
1621
1650
1645
1599
1601
1616
1607
1597
1611
1621
1626
1640
1178
1140
1160
1133
1140
1120
1140
1160
1159
1175
1180
1139
1165
1110
1155
1130
1154
1155
1158
1170
1029
1045
1040
1042
1044
1060
1039
1055
1045
1040
1035
1036
1081
1080
1058
1068
1039
1038
1041
1037
1442
1330
1327
1350
1333
1350
1373
1370
1326
1380
1440
1400
1388
1400
1391
1388
1397
1396
1390
1401
K2[CrIII(L1)Cl2]
K3[MnII(L1)Cl2]
K3[FeII(L1) Cl2]
K[CoII(L1)]
K[NiII(L1)]
583
563
466
453
459
516
505
510
560
–
385
388
376
389
366
390
388
391
398
–
287
291
301
–
–
–
K[CuII(L1)]
K[ZnII(L1)]
K[CdII(L1)]
K[HgII(L1)]
H3L2
–
–
–
K2[CrIII(L2)Cl2]
K3[MnII(L2)Cl2]
K3[FeII(L2) Cl2]
K[CoII(L2)]
K[NiII(L2)]
550
530
466
453
459
516
495
511
542
385
388
376
389
366
390
385
391
389
283
288
299
–
–
–
K[CuII(L2)]
K[ZnII(L2)]
K[CdII(L2)]
K[HgII(L2)]
–
–

168
M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
Table 3
Magnetic moment and UV–Vis spectral data in DMF solutions.
Compound
leff (BM) (per atom)
Band position (k, nm)
Extinction coefficient emax (dm3 molꢀ1 cmꢀ1
)
Assignments
K2[CrIII(L1)Cl2]
3.81
317
370
425
675
820
320
465
690
319
469
670
307
368
540
672
342
370
404
585
333
353
671
815
314
334
320
366
282
351
299
370
440
746
310
440
560
302
360
590
288
313
409
603
275
348
404
633
319
580
815
304
374
295
366
299
356
573
203
300
40
p ?
p⁄
CT
4A2g(F)
4A2g(F)
?
?
4T1g(F)
4T2g(F)
(
(
m2)
m1) (10Dq)
18
(4A2g ? 2T1g, 2Eg(G)
)
K3[MnII(L1)Cl2]
K[FeII(L1)]
5.38
4.25
3.88
830
130
88
p ?
p⁄
6A1g ? 4T2g(G)
6A1g ? 4T1g(G)
890
205
100
527
850
105
110
780
1100
148
47
p ?
p⁄
5A2g ? T2g
5T2g ? 5Eg
K[CoII(L1)]
p ?
p⁄
CT
4A2g(F)
4A2g(F)
?
?
4T2g(F)
4T1g(F)
K[NiII(L1)]
K[CuII(L1)]
Diamagnetic
1.82
p ?
p⁄
CT
1A1g ? 1B1g
1A1g ? 1A2g
1050
810
95
p ?
p⁄
CT
2B1g ? 2B2g
2B1g ? 2A2g
75
K[ZnII(L1)]
Diamagnetic
Diamagnetic
Diamagnetic
3.83
1000
570
1500
300
1920
400
850
750
250
20
690
110
33
1010
615
90
527
344
87
110
551
228
148
47
p
CT
p
CT
p
CT
p
?
p⁄
p⁄
p⁄
p⁄
K[CdII(L1)]
K[HgII(L1)]
K3[CrIII(L2)Cl2]
?
?
?
CT
4A2g(F)
4A2g(F)
?
?
4T1g(F)
4T2g(F)
(
(
m2)
m1) (10Dq)
K2[MnII(L2)Cl2]
K[FeII(L2)]
5.36
4.25
3.81
p ?
p⁄
6A1g ? 4T2g(G)
6A1g ? 4T1g(G)
p ?
p⁄
CT
5T2g ? 5Eg
K[CoII(L2)]
p ?
p⁄
CT
4A2g(F)
4A2g(F)
?
?
4T2g(F)
4T1g(F)
K[NiII(L2)]
K[CuII(L2)]
Diamagnetic
1.80
p ?
p⁄
CT
1A1g ? 1B1g
1A1g ? 1A2g
415
58
15
720
385
790
310
790
300
p ?
p⁄
2B1g ? 2B2g
2B1g ? 2A2g
K[ZnII(L2)]
K[CdII(L2)]
K[HgII(L2)]
Diamagnetic
Diamagnetic
Diamagnetic
p
?
p⁄
CT
p
?
p ⁄
p⁄
CT
p
?
CT
positive ion FAB mass spectra for K3[Fe(L1)Cl2], K[Ni(L1)],
K3[Fe(L2)Cl2], K[Zn(L2)] and K[Hg(L2)] complexes were reported.
The mass spectrum of K3[Fe(L1)Cl2] showed several peaks corre-
sponding to successive fragmentation of the molecule. The first
peak observed at m/z 665.63 (7.57%) represents the molecular
ion peak of the complex. Other distinct peaks were observed in
the mass spectrum at m/z 627.5, 118 and 56 can be assigned to
the (MꢀK)+, (CH3FeCH2SH)+, fragments and the final metal residue
(Fe). The spectrum of K[Ni(L1)] showed several peaks in the mass
spectrum at m/z 481.3, 156 and 58 assigned to the (MꢀK)+,
(HOP(O)NiSH)+ fragments of the complex and the metal residue,
respectively. These results are similar to those of analogous com-
plexes reported earlier by others [32,33]. The mass spectrum of
K3[Fe(L2)Cl2] showed the molecular ion peaks at m/z 449. Other
peaks at m/z 367, 296 and 56 assigned to [Mꢀ{(K)+(H2C@CH–
CH3)}]+, [Mꢀ{(K)+(H2C@CH–CH3)+(HNCOCH2)}]+ and (Fe) residue,
respectively. The mass spectrum of K[Zn(L2)] showed peaks at m/
z 418.03, 87 and 65 assigned to (MꢀK)+, ZnS and metal residue,
respectively. The mass spectrum of K[Hg(L2)] showed peaks at m/
z
555.19, 504.38, 312.81 and 243 assigned to [Mꢀ(K+H)]+,
[Mꢀ(K+CH2SH)]+, [Mꢀ{(K+CH2SH)+(HOPOHg)}]+ and HgS,
respectively.
4.4. Electronic spectra and magnetic moments measurements
The UV–Vis spectrum of H3L1 exhibits an intense absorption
peak at 299 nm, assigned to
p ?
p⁄. A very low intensity peak at
320 nm in H3L1 spectrum was attributed to the n ? p⁄ transition.

M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
169
Table 4
electronic spectrum of the Co(II) complex is consistent with tetra-
hedral assignment [41]. The observed room temperature magnetic
moment value is 3.88 BM, which supports a high-spin tetrahedral
structure for the Co(II) ion with the 4A2 ground state. The slightly
lower magnetic moment might be due the slight deviation from
the regular tetrahedral geometry. The electronic spectrum of the
Ni(II) complex displayed two d–d transitions at 404 and 585 nm.
L:M mole ratio of some metal complexes at kmax nm in DMF solutions.
Complexes
kmax (nm)
L:M ratio
K2[CrIII(L1)Cl2]
K3[FeII(L1)Cl2]
K[ZnII(L1)]
425
469
334
351
440
404
374
1:1
1:1
1:1
1:1
1:1
1:1
1:1
K[HgII(L1)]
K2[CrIII(L2)Cl2]
K[NiII(L2)]
The molar conductance value, in DMF at 107.2 cm2
X
ꢀ1 molꢀ1 indi-
K[ZnII(L2)]
cated that the complex is a 1:1 electrolyte, and other analytical
data supported the formation of four coordinate Ni-complex. Based
on the diamagnetic behaviour of the Ni(II) complex the four coor-
dinate Ni(II) complex is consistent with a square planar geometry
[42]. The magnetic moment value of the green Cu(II) complex, as
well as the other analytical data, are in agreement with square pla-
nar structures [37,43–45]. The Cu(II) complex gave brown colour in
DMF solution indicating further coordination to solvent molecules.
Thus, the spectrum of the Cu(II) complex in DMF exhibited two low
intensity bands which are characteristic of distorted octahedral
Cu(II) complexes. The spectra of the Zn(II), Cd(II) and Hg(II) com-
The spectrum of H3L2 exhibits a similar intense absorption at
312 nm, and the expected n ? p⁄ transition is hidden by this band.
The electronic spectra of the complexes of H3L1 exhibited various
extents of bathochromic shift of the bands related to the intra-
ligand
p ?
p⁄ transition, except for that of the Hg(II) complex
which showed a hypsochromic shift (see Table 3). Bands related
to the (CT) transitions were observed in the spectra of the com-
plexes, (Table 3). The electronic spectrum of the Cr(III) complex
displayed three additional bands, which could be attributed to
plexes exhibited bands assigned to ligand
p ?
p⁄ and L ? M
the spin allowed d–d transitions 4A2g(F) ? 4T1g(F)
(m
2),
charge transfer [37]. These complexes are diamagnetic as expected.
4A2g(F) ? 4T2g(F) 1)(10 Dq) and 4A2g ? 2T1g, 2Eg(G) [37–39]. The
(m
Based on molar conductance values of the complexes in DMF
band related to the m3 may be located at higher wave number
and hidden by the (CT) or ligand band [26]. The magnetic behav-
iour of octahedral Cr(III) is independent of the field strength of
the ligand. It is expected that the magnetic moment for Cr(III) com-
plexes should be approximately equal to the calculated spin value
only. The Cr(III) complex under consideration has the value of 3.81
BM, which matches. Thus, the ligand field bands, magnetic mo-
ment value, molar conductance as well as the other analytical data
support an octahedral geometry [32,40]. The electronic spectra of
the Mn(II) complex presents a signal in the UV region at 320 nm
assigned to ligand field and/or a transfer of electric load, according
with the theory data for a d5 ion. Mn-complex shows two spin for-
bidden transition bands at 465 and 690 nm, which may be
assigned to 6A1g ? 4T2g(G) and 6A1g ? 4T1g(G) respectively, indicat-
ing a distorted octahedral geometry for the complex. The magnetic
moment of this complex is typical for a high spin octahedral struc-
106–115 cm2
X
ꢀ1 molꢀ1 as well as the other analytical data, we
proposed tetrahedral coordination for these three complexes. This
assignment is in analogy with those described for Zn(II), Cd(II) and
Hg(II) complexes containing N2S2 system [32,31]. The electronic
spectra of the complexes of H3L2 exhibited bands related to the
intra-ligand
p ?
p⁄ and the (CT) transitions (see Table 3). The spec-
tra of the Cr(III), Mn(II), Fe(II) and Cu(II) complexes of H3L2 showed
similar behaviour to those of H3L1 suggesting octahedral geome-
tries for the complexes in solutions. As for K[Co(L1)] the spectrum
of Co(II) complex of H3L2 together with the leff values (Table 3)
suggests tetrahedral geometry [32,37,41]. The spectrum of the
Ni(II) complex displayed bands characteristic of square planar
geometry [37,42]. The magnetic moment value was consistent
with the square planar structure. The spectra of Zn(II), Cd(II) and
Hg(II) complexes of H3L2 showed similar behaviour to those of
H3L1 suggesting tetrahedral geometries [37].
ture. The Fe(II) complex showed the
p ?
p⁄ and d–d bands which
could be attributed to spin forbidden transition in a distorted octa-
hedral geometry [37,39,40]. The observed magnetic moment of
4.25 BM is consistent with a high spin octahedral structure. For
the Co(II) complex, there are 2 orbital forbidden absorptions bands
at 603 and 408 nm are observed. These were assigned to
4A2g(F) ? 4T2g(F) and 4A2g(F) ? 4T1g(F) transitions, respectively. The
5. Molar ratio
Complex formation by molar ratio of ligand to metal ion was
also studied in DMF solution. A series of solutions containing con-
stant concentration of metal ion (1 ꢁ 10ꢀ3 M) were treated with
Fig. 1. Plot represents mole ratio; absorbance of solution at kmax vs. [L]/[M] for some complexes.

170
M.J. Al-Jeboori et al. / Inorganica Chimica Acta 379 (2011) 163–170
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In this paper, we have explored the synthesis and coordination
chemistry of some monomeric complexes obtained from the reac-
tion of the polydentate N2S2 Mannich base ligands H3L1 and H3L2
with some metal ions. The mode of bonding and overall structure
of the complexes were determined through physico-chemical
and spectroscopic methods. Upon complex formation, the ligands
provide the appropriate arrangement around metal centre allow-
ing the metal to achieve its preferred geometry. The metals follow
similar patterns, adding chlorides when a preference of octahedral
geometries is required. Complex formation study via molar ratio
has been investigated and results were consistent to those found
in the solid complexes with a ratio of (M:L) as (1:1).
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