Synthesis and characterization of mixed-ligand copper(II) saccharinate complexes containing tridentate NNS Schiff bases. X-ray crystallographic analysis of the free ligands and one complex

Article abstract of DOI:10.1007/s11243-013-9780-y

Four new Schiff bases containing N and S heteroatoms (HL1-HL4) have been prepared and characterized, including determination of the X-ray crystal structures of HL1 and HL3. Spectroscopic evidence indicates that these Schiff bases behave as uninegatively charged tridentate NNS ligands in complexes of general formula [Cu(Ln)sac] (Ln is the anionic form of NNS, and sac represents saccharinate anion). Crystals of both HL1 and [Cu(L4)sac)(H₂O)] ·Hsac crystallized in triclinic system with P 1 1 space group, while HL3 crystallized in monoclinic system with P 2₁/c space group. [Cu(L4)sac)(H₂O)]·Hsac has a distorted square-pyramidal structure with a non-bonded saccharin molecule present in the outer coordination sphere. The tridentate NNS ligands are coordinated to Cu through pyridine nitrogen, azomethine nitrogen and thiolate sulfur atoms, while the fourth and fifth coordination positions are occupied by the N-bonded saccharinate anion and a water ligand, respectively.

Full text of DOI:10.1007/s11243-013-9780-y

Transition Met Chem (2014) 39:119–126
DOI 10.1007/s11243-013-9780-y
Synthesis and characterization of mixed-ligand copper(II)
saccharinate complexes containing tridentate NNS Schiff bases.
X-ray crystallographic analysis of the free ligands and one
complex
•
Siti Aminah Omar Thahira B. S. A. Ravoof
•
•
M. Ibrahim M. Tahir K. A. Crouse
Received: 5 September 2013 / Accepted: 29 October 2013 / Published online: 14 November 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Four new Schiff bases containing N and S
heteroatoms (HL1–HL4) have been prepared and char-
acterized, including determination of the X-ray crystal
structures of HL1 and HL3. Spectroscopic evidence
indicates that these Schiff bases behave as uninegatively
charged tridentate NNS ligands in complexes of general
formula [Cu(Ln)sac] (Ln is the anionic form of NNS, and
sac represents saccharinate anion). Crystals of both HL1
and [Cu(L4)sac)(H2O)]ꢀHsac crystallized in triclinic sys-
chemistry remains of interest since the presence of three
different donor atoms, namely the imino N and the car-
bonyl and sulfonyl O atoms, makes saccharin a versatile,
polyfunctional ligand [3]. It may behave as a N- or O-
monodentate ligand or as a bidentate (N, O) chelating agent
[4]. There are also published reports on the free sacchari-
nate anion present in the complex cation [5] and as a
counter-ion outside the coordination sphere [6, 7]. A spe-
cial point of interest can be seen in the synthesis of pal-
ladium(II) and platinum(II) complexes of saccharin with
2,20-dipyridylamine (dpya) which yielded both neutral and
cationic complexes [8]. The neutral complexes contain two
N-coordinated saccharinate ligands and two nitrogen atoms
of dpya, while in the cationic complexes the metal ions are
coordinated by two dpya ligands to generate square-planar
cationic species with a saccharin counter-ion.
ꢀ
tem with P 1 space group, while HL3 crystallized in
monoclinic system with P 21/c space group. [Cu(L4)sa-
c)(H2O)]ꢀHsac has a distorted square-pyramidal structure
with a non-bonded saccharin molecule present in the outer
coordination sphere. The tridentate NNS ligands are
coordinated to Cu through pyridine nitrogen, azomethine
nitrogen and thiolate sulfur atoms, while the fourth and
fifth coordination positions are occupied by the N-bonded
saccharinate anion and a water ligand, respectively.
Dithiocarbazate and thiosemicarbazide are among the
most widely studied N, S donor ligands [9]. Interest in
these compounds is stimulated by their intriguing physi-
cochemical properties and biological activities [10–12],
which are usually enhanced upon coordination with metal
ions [13].
Introduction
The Schiff bases synthesized in this study are structurally
related to the well-known cytotoxic agent, pyridine-2-alde-
hydethiosemicarbazone [14]. The Cu(II) complex of pyr-
idine-2-aldehydethiosemicarbazone was found to be more
potent than the ligand itself toward Chinese hamster ovary
cells [15]. A Schiff base formed from 2-pyridinecarboxyal-
dehyde and S-benzyldithiocarbazate, S-benzyl-b-N-(2-pyr-
idyl)methylendithiocarbazate and its Cu(II) complex [16],
and the biological activities of this Schiff base and its Cu, Cd
and Zn complexes have also been evaluated [11].
Saccharin (also known as o-sulphobenzoimide or 1,2-
benzisothiazoline-3-(2H)one 1,1-dioxide) has been widely
used as a non-caloric artificial sweetening agent since 1885
[1]. Saccharin has attracted much attention mainly because
of its suspected carcinogenicity, which has since been
shown to be unfounded [2]. However, its coordination
S. A. Omar ꢀ T. B. S. A. Ravoof (&) ꢀ
M. I. M. Tahir ꢀ K. A. Crouse
Department of Chemistry, Faculty of Science, Universiti Putra
Malaysia, 43400 UPM Serdang, Selangor, Malaysia
e-mail: thahira.begum@science.upm.edu.my;
thahira@upm.edu.my
As part of the structure–activity relationship study of
compounds derived from dithiocarbazate and thiosemicar-
bazide, we report herein the synthesis and characterization
123

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Transition Met Chem (2014) 39:119–126
of some new tridentate NNS Schiff bases and their mixed-
ligand copper(II) complexes containing saccharin together
with the single crystal X-ray structural analyses for HL1,
HL3 and [Cu(L4)sac)(H2O)]ꢀHsac.
Preparation of S-4-methylbenzyldithiocarbazate
(S4MBDTC)
The compound was synthesized by adopting the procedure
to synthesize SBDTC by replacing benzyl chloride with
4-methylbenzyl chloride (0.2 mol, 26.5 ml) (S4MBDTC
Yield 85 %, m.p 86–89 °C).
Experimental
All chemicals and solvents were of analytical grade and
were used as received. Chemicals: benzyl chloride
(ACROS), 4-methylbenzylchloride (ACROS), potassium
hydroxide (BDH), hydrazinium hydroxide (Panreac Sinte-
sis), carbon disulfide (Merck), 2-acetyl-4-methylpyridine
(Aldrich), 2-acetyl-5-methylpyridine (AB Chem, Inc.),
4-methyl-3-thiosemi-carbazide (Alfa Aesar), copper(II)
acetate (Analar), nitric acid (65 %, R & M).
Synthesis of the Schiff bases
A solution of dithiocarbazate or thiosemicarbazide was
combined with a solution containing an equimolar
amount of ketone to prepare all the Schiff bases. The
Schiff bases precipitated from the resulting mixture after
heating to reduce the volume by half or until crystals
started forming.
Solvents: absolute ethanol (99.8 %, Systerm), ethanol
(95 %, Systerm), dimethylsulfoxide (Systerm), acetonitrile
(Baker).
The analyses for C, H, N and S were carried out using
a LECO CHNS-932 instrument. The IR spectra (UATR)
were recorded on a Perkin-Elmer 100 spectrophotometer
(4,000–400 cm-1). Copper determinations were carried
out using a Perkin-Elmer Plasma 1,000 Emission Spec-
trometer. Molar conductivities of 10-3 M solutions of the
metal complexes in DMSO were measured at 29 °C using
a Jenway 4310 conductivity meter and a dip-type cell with
a platinized electrode. Magnetic susceptibilities were
measured at room temperature using a Sherwood Scien-
tific MSB-AUTO magnetic susceptibility balance. The
UV–Vis spectra were run on a Shimadzu UV–Vis 1601
recording spectrophotometer (1,000–200 nm) in DMSO
solution.
S-Benzyl-b-N-(2-acetylpyridin-4-
ylmethylene)hydrazinecarbodithioate, HL1
SBDTC (0.39 g, 2 mmol, absolute ethanol 50 ml) was
reacted with 2-acetyl-4-methylpyridine (absolute ethanol
25 ml). Upon standing overnight, beautiful yellow crystals
suitable for single crystal X-ray diffraction analysis formed.
1
Yield 74 %, m.p 128–131 °C. H-NMR: (DMSO-d6, ppm,
12.54 (s, 1H, NH), 7.22–8.42 (multiplet, 8H, Ar–H), 4.48
(s, 2H, –SCH2), 2.28, 2.40 (s, 6H, –CH3). 13C–NMR:
(DMSO-d6, ppm), 199.21 (C=S), 154.57 (C=N),
121.32–153.34 (Ar–C), 38.19 (S–CH2), 13.80, 21.27 (CH3).
Mass data m/z(%): [M]? 315(0.22), [C9H11N3S2]?
223(4.12), [C9H10N3S]? 191(48.61), [C7H8S]? 124(37.61),
[C7H7]? 91(100).
Preparation of S-benzyldithiocarbazate (SBDTC)
The ligand was prepared according to the published
method [16]. Potassium hydroxide (0.2 mol, 11.4 g) was
dissolved in absolute ethanol (70 ml). Hydrazine hydrate
(0.2 mol, 10 g) was added, and the mixture was then
cooled in an ice-salt bath to 0 °C. Carbon disulfide
(0.2 mol, 15.2 g) was added dropwise while stirring over a
period of 1 h. The resulting two layers were then separated
using a separating funnel. The brown organic lower layer
was dissolved in 40 % ethanol. Benzyl chloride (0.2 mol,
25 ml) was added dropwise with vigorous stirring. After
the complete addition of benzyl chloride, the white product
(SBDTC) was filtered off, washed with cold ethanol and
dried in a desiccator over anhydrous silica gel. It was then
recrystallized using absolute ethanol (Yield 75 %, m.p
124–126 °C, lit. m.p 125 °C).
S-Benzyl-b-N-(2-acetylpyridin-5-
ylmethylene)hydrazinecarbodithioate, HL2
SBDTC (1.98 g, 0.01 mol, absolute ethanol 50 ml) was
reacted with 2-acetyl-5-methylpyridine (ethanol 25 ml).
Overnight standing yielded a yellow precipitate which was
filtered off and recrystallized from acetonitrile. Yield
70 %, m.p 139 °C. 1H-NMR: (DMSO-d6, ppm, 12.53
(s, 1H, NH), 7.22–8.39 (multiplet, 8H, Ar–H), 4.44 (s, 2H,
–SCH2), 2.26, 2.40 (s, 6H, –CH3). 13C–NMR:(DMSO-d6,
ppm), 199.05 (C=S), 153 (C=N), 120.42–152.15 (Ar–C),
38.37 (S–CH2), 13.55–18.38 (CH3). Mass data m/z(%):
[M]? 315(0.08), [C9H11N3S2]? 223(1.93), [C9H10N3S]?
191(35.32), [C7H8S]? 124(23.55), [C7H7]? 91(100).
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Transition Met Chem (2014) 39:119–126
121
4-Methylbenzyl-2-(2-acetylpyridin-4-
ylmethylene)hydrazinecarbodithioate, HL3
(40 ml), and the resulting mixture was heated on a water
bath for 30 min [18]. On standing overnight, the mixtures
yielded crystalline complexes which were filtered off,
washed with ethanol and dried in a desiccator over anhy-
drous silica gel. Yields: ca 75 %. Crystals of [Cu(L4)sa-
c)(H2O)]ꢀHsac suitable for X-ray diffraction analysis were
obtained. Analytical, physical and spectral data are given in
Tables 1 and 2.
S4MBDTC (0.85 g, 4 mmol, hot acetonitrile 100 ml) was
reacted with 2-acetyl-4-methyl pyridine (absolute ethanol
25 ml). Recrystallization yielded beautiful brown crystals
suitable for X-ray diffraction analysis from acetonitrile.
Yield 13 %, m.p 154–156 °C. 1H-NMR: (DMSO-d6, ppm,
12.50 (s, 1H, NH), 7.10–8.42 (multiplet, 7H, Ar–H),
4.45 (s, 2H, –SCH2), 2.23, 2.28, 2.40 (s, 9H, –CH3),
13C–NMR: (DMSO-d6, ppm,), 199.31 (C=S), 154.86
(C=N), 121.31–153.26 (Ar–C), 38.15 (S–CH2), 13.78,
21.22, 21.27 (CH3). Mass data m/z(%): [M]? 329(0.02),
[C9H10N3S]? 191(38.49), [C8H10S]? 138(45.36), [C8H9]?
105(100), [C7H8]? 92(45.18).
X-ray crystallography
Single crystals were mounted on a fiber loop using per-
fluoropolyether oil and cooled rapidly to 100 K in a stream
of cold N2 using an Oxford Cryosystems Cobra unit. Dif-
fraction data were measured using an Oxford Diffraction
Gemini E CCD Diffractometer. Intensity data were pro-
cessed with the CrysAlis Pro software suite [32]. The
structures were solved using the direct methods program
SIR92 [20] which located all non-hydrogen atoms. Sub-
sequent full-matrix least-squares refinement was carried
out using the CRYSTALS Program Suite [21]. Coordinates
and anisotropic thermal parameters of all non-hydrogen
atoms were refined. All H atoms were located in a differ-
ence map. Those attached to carbon atoms were reposi-
tioned geometrically. The H atoms were initially refined
with soft restraints on the bond lengths and angles to reg-
ularize their geometry, after which the positions were
refined with riding constraints. A summary of the crystal
data, experimental details and refinement results is given in
Table 3. Crystallographic data for the structure reported in
this paper have been deposited with the Cambridge Crys-
tallographic Data Center. CCDC numbers 935312, 935305
and 935315 contain the supplementary crystallographic
data for HL1, HL3 and [Cu(L4)sac)(H2O)]ꢀHsac. These
data can be obtained free of charge from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge,
CG2IEZ, UK: Fax: (?44) 1223-336-033; or email:
deposit@ccdc.cam.ac.uk or at http://www.ccdc.cam.ac.uk/
conts/retrieving.html.
(E)-N-Methyl-2-(1-(5-methylpyridin-2-
yl)ethylidene)hydrazinecarbothioamide, HL4
Thiosemicarbazide (1.05 g, 0.01 mol) dissolved in abso-
lute ethanol (50 ml) was reacted with 2-acetyl-5-methyl-
pyridine in absolute ethanol (25 ml). The yellowish
precipitate obtained was filtered off, washed with ethanol
and dried in a desiccator over anhydrous silica gel. Yield
1
53 %, m.p 136–138 °C. H-NMR: DMSO-d6, ppm, 10.19
(s, 1H, NH), 8.56 (s, 1H, NH), 7.60–8.36 (multiplet, 3H,
Ar–H), 3.10 (s, 1H, –CH3), 2.30, 2.27 (s, 6H, –CH3)),
13C–NMR: (DMSO-d6, ppm,), 179.05 (C=S), 152.65
(C=N), 120.80–149.10 (Ar–C), 31.66 (N–CH3), 18.28,
12.612 (CH3). Mass data m/z(%): [M]? 222(0.06),
[C9H10N3S]?
[CH3N2S]? 74(100).
191(0.03),
[C6H5N2]?
105(87.75),
Preparation of Cu(II) saccharinate salt,
[Cu(sac)2(H2O)4]ꢀ2H2O
The synthesis was done as outlined by Ravoof et al. [18].
Sodium saccharinate monohydrate in water was mixed
with Cu(II) acetate solution (boiling water) in 2:1 mol
ratio. The mixture was heated to reduce the volume to half.
Overnight standing yielded blue crystals of [Cu(sa-
c)2(H2O)4]ꢀ2H2O which were filtered off, washed with cold
ethanol and dried in a desiccator over anhydrous silica gel.
Yield: ca. 90 %.
Results and discussion
Syntheses and characterization
Structures, physical and analytical data are shown in Fig. 1
and Table 1. Elemental analyses data are in agreement with
the proposed formulae. The complexes are soluble in organic
solvents and are air stable. The Cu(II) complexes exhibit room
temperature magnetic moments ranging from 1.77 to 1.97
B.M, respectively, as expected for 3d9 metal ions (Table 1).
The molar conductance values of the complexes in DMSO
Synthesis of mixed-ligand Cu(II) complexes
[Cu(sac)2(H2O)4]ꢀ2H2O (0.536 g, 0.001 mol) dissolved in
boiling water (25 ml) was mixed with a solution of the
appropriate Schiff base (0.001 mol) in ethanol/acetonitrile
123

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Transition Met Chem (2014) 39:119–126
Table 1 Analytical data and physical properties of the Schiff bases and their metal complexes
Complexa
Color
m.p (°C) Kb
lc (B.M) Analytical data (%) found (calc)
C
H
N
Cu
–
HL1 (C16H17N3S2)
Yellow
130
–
–
61.3(60.9) 5.4(5.4) 13.3(13.3)
50.0(49.3) 3.7(3.6)
61.1(60.9) 5.9(5.4) 14.5(13.3)
48.6(49.3) 3.4(3.6) 9.6(10.0) 11.1(11.3)
61.9(61.9) 5.6(5.8) 12.7(12.7)
49.9(50.2) 3.9(3.8) 9.6(9.7)
54.3(54.0) 6.1(6.3) 24.7(25.2)
[Cu-HL1(sac)] (C23H20CuN4O3S3)
HL2 (C16H17N3S2)
Dark green 205
Yellow 139
Dark green 192
Brown 155
Dark green 196
Yellow 131
11.08 1.77
9.9(10.0) 10.8(11.3)
–
–
–
[Cu-HL2(sac)] (C23H20CuN4O3S3)
HL3 (C17H19N3S2)
5.48
–
1.97
–
–
[Cu-HL3(sac)] (C24H22CuN4O3S3)
HL4 (C10H14N4S)
10.51 1.87
10.9(11.0)
–
–
–
[Cu(L4)sac)(H2O)]ꢀHsac (C24H24CuN6O7S3) Dark green 215
HL1 = S-benzyl-b-N-(2-acetylpyridin-4-ylmethylene)hydrazinecarbodithioate, HL2 = S-benzyl-b-N-(2-acetylpyridin-5-ylmethylene)hydra-
zinecarbodithioate, HL3 = 4-methylbenzyl-2-(2-acetylpyridin-4-ylmethylene)hydrazinecarbodithioate, HL4 = (E)-N-methyl-2-(1-(5-methyl-
pyridin-2-yl)ethylidene)hydrazinecarbothioamide
27.65 1.85
44.3(43.1) 3.6(3.6) 13.2(12.5) 10.4(9.5)
a
b
Molar conductance (X-1 cm2 mol-1) of ca. 10-3 M solutions in DMSO
c
Magnetic moments at 298 K; sac = saccharinate anion
Table 2 Selected IR bands and electronic spectral data for the Schiff bases and their metal complexes
Compound
IR bands (cm-1 a
)
Electronic spectra kmax (log e)b
vNH
vCN
vNN
vCSS
vsSO2
vasSO2
vCO
HL1
3,160
1,588
1,591
1,582
1,593
1,587
1,597
1,613
1,629
1,058
1,067
1,059
1,029
1,056
1,033
1,052
1,057
829
835
828
834
881
888
912
949
–
–
–
337(4.39)
[Cu-HL1(sac)]
–
1,150
–
1,281
–
1,656
–
650(2.57), 397(3.98), 330(4.35)
337(4.63)
HL2
2,956
[Cu-HL2(sac)]
–
1,145
–
1,290
–
1,661
–
706(2.0), 406(3.28), 326(3.65)
385(4.25), 319(4.40)
616(3.0), 429(3.47), 332(4.50)
320(4.66)
HL3
3,163
[Cu-HL3(sac)]
–
1,141
–
1,290
–
1,670
–
HL4
3,197, 3,278
2,934
[Cu(L4)sac) (H2O)]ꢀHsac
1,145
1,290
1,677
627(2.32), 408(4.25), 295(4.35)
a
Wavenumbers are in units of cm-1
b
Units of kmax are in nm and units of log e are in L mol-1 cm-1
(Table 1) fall in the range 5.48–27.65 X-1 cm2 mol-1, indi-
cating that they are essentially non-electrolytes in DMSO [22]
(Fig. 2).
X-ray crystallographic analyses of HL1, HL3
and [Cu(L4)sac)(H2O)]ꢀHsac
The Schiff bases exhibit the following absorption bands:
intra-ligand n ? p* at 385 nm and p ? p* band at
319–337 nm [23]. In addition to these, they displayed a
d–d band in the region 616–670 nm, while an S ? Cu(II)
charge transfer band was observed at 406–409 nm, giving a
positive indication of coordination of the Schiff bases to
Cu(II) via the thiolate sulfur atom [9, 24].
ORTEP diagrams for HL1, HL3 and [Cu(L4)sa-
c)(H2O)]ꢀHsac are given in Figs. 3, 4 and 5. Selected bond
lengths and angles are given in Tables 3, 4 and 5. Crystals of
both HL1 and [Cu(L4)sac)(H2O)]ꢀHsac crystallized in a
ꢀ
triclinic system with P 1 space group, while HL3 crystallized
in monoclinic system with P 21/c space group. Both Schiff
bases HL1 and HL3 are in their thione form with the C=S
˚
bond length of 1.6613(15) and 1.6582(15) A, respectively.
The IR spectra of the Schiff bases (Table 2) exhibit
v(C=N), v(N–N) and v(CS) which shift in the complexes as
a result of coordination to the azomethine nitrogen and the
thiolate sulfur atoms. The v(NH) is absent in the spectrum
of the metal complexes derived from dithiocarbazate,
indicating deprotonation of the Schiff base during coordi-
nation. Saccharinate bands, vs(SO2), vas(SO2) and v(CO)
confirm the presence of saccharin in the complexes.
These values are intermediate between a single and double
bond [25]. The C–S single bond length is shorter than
˚
expected (1.81 A) [26]. This can be explained by extensive
conjugation over the C=N–N–C chain and other intermo-
lecular interactions [27]. This characteristic has also been
observed in related dithiocarbazate Schiff bases such as
6-methyl-2-pyridinecarboxyaldehyde Schiff base of S-3-
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Transition Met Chem (2014) 39:119–126
123
Table 3 Crystallographic data and structure refinement details for HL1, HL3 and [Cu(L4)sac)(H2O)]ꢀHsac
Compound
HL1
HL3
[Cu(L4)sac)(H2O)]ꢀHsac
Empirical formula
Formula weight
Temperature
C16 H17N3S2
315.46
C17 H19N3S2
329.49
C24H24CuN6O7S3
668.23
100 K
100 K
100 K
˚
1.54184 A
˚
1.54180 A
˚
0.71073 A
Wavelength
Crystal system
Space group
Triclinic
Monoclinic
Triclinic
ꢀ
P 1
ꢀ
P 1
P 21/c
˚
a = 5.6934(3) A
˚
a = 5.7700(2) A
˚
a = 7.9981(5) A
Unit cell dimensions
˚
b = 12.6314(8) A
˚
b = 28.1486(10) A
˚
b = 9.3416(5) A
˚
c = 12.6415(7) A
˚
c = 10.2041(4) A
˚
c = 19.4346(10) A
a = 116.513(6)°
b = 92.160(5)°
c = 102.669(5)°
784.07
a = 90°
a = 91.140(4)°
b = 96.019(4)°
c = 113.464(5)°
1,321.62
b = 91.336(3)°
c = 90°
1,656.87(10)
Volume
Z
2
4
2
Absorption coefficient
F(000)
3.04 mm-1
2.897 mm-1
696
1.12 mm-1
332
686
Crystal size
0.34 9 0.16 9 0.14 mm
4°–71°
0.10 9 0.20 9 0.30 mm
3°–72°
0.21 9 0.11 9 0.09 mm
2.4°–28.9°
Theta range for data collection
Limiting indices
-16 B h C 6
-15 B k C 5
-15 B l C 5
15,531/3,017
(Rint = 0.023)
0.62, 0.65
-6 B h C 7
-34 B k B 34
-12 B l C 9
12,415/3,254
(Rint = 0.025)
0.61, 0.75
-10 B h C 10
-12 B k B 12
-25 B l C 25
17,192/6,144
(Rint = 0.037)
0.80, 0.90
Reflections collected/unique
Maximum and minimum transmission
Data/restraints/parameters
Goodness of fit on F2
3,004/0/190
0.99
3,243/0/203
0.99
6,126/0/370
0.96
Final R indices [I [ 2r(I)]
Largest difference peak and hole
R = 0.034, Rw = 0.087
-3
R = 0.036, Rw = 0.0954
-3
R = 0.034, Rw = 0.082
-3
˚
0.34 and -0.27 eA
˚
0.51 and -0.25 eA
˚
0.56 and -0.62 eA
H
N
H
S
S
N
N
N
S
N
S
N
HL1
HL2
N
H
N
HN
N
S
NH
N
S
N
S
HL3
HL4
Fig. 1 Schiff bases HL1, HL2, HL3, and HL4
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Transition Met Chem (2014) 39:119–126
Fig. 2 E and Z isomers HL1
(R1=H, R2=CH3) and HL3
(R1=CH3, R2=CH3)
N
S
N
R2
N
S
S
R2
N
S
(E)
H
HN
N
(Z)
R1
R1
O31
C39
C10
C38
C13
C9
C37
C40
S30
C11
C41
O17
C36
C14
C34
O32
N8
N33
C12
N1
C2
O35
N4
N5
C7
C6
C15
C6
C12
C7
S3
C11
N5
N8
O20
C14
Cu1
C9
S1
C10
O21
S19
N4
C15
N18
C24
C13
C21
C20
C16
C2
C17
C22
C18
C29
C19
O25
C23
S3
C28
Fig. 3 ORTEP diagram of HL1 at 50 % probability (H atoms are
removed for clarity)
C26
C27
Fig. 5 ORTEP diagram of [Cu(L4)sac)(H2O)]ꢀHsac at 50 % proba-
C10
C13
bility (H atoms are removed for clarity)
C9
C11
˚
1.286(2) and 1.347(2) A, respectively, similar to com-
pounds reported by Ravoof et al. [28]. The N–N bond dis-
˚
tance is 1.3709(18) and 1.3712(18) A for HL1 and for HL3,
N8
C12
C7
C6
respectively. That these are shorter than a single bond sug-
gests significant p-charge delocalization along the C(S)NNS
chain [28], while the short N–N distance is probably due to
attachment of the pyridyl groups to the imino nitrogen [27].
Cis–trans (E–Z) isomerism was exhibited by the Schiff
bases since they possess the C=N moiety (Fig. 2). Both of
the Schiff bases adopt E geometry about the C(6)–N(5)
bond, which is similar to observations on the related
compounds derived from dithiocarbazate [9, 30]. The thi-
one sulfur is trans to the azomethine nitrogen atom with
respect to the C(2)–N(4). Using this conformation, it can-
not act as an NNS tridentate ligand due to steric hindrance.
Hence, the rotation of the S(1)–C(2)–S(3) fragment by
180° about the C(2)–N(4) bond and a simultaneous rotation
of the pyridine ring by 180° about the C(7)–C(6) bond can
place the N(5) atom, the S(3) atom and the pyridine N(8)
atom all on the same side, thus enabling the ligand to
function as an NNS tridentate chelating agent, as found for
N5
N4
C22
C18
C21
C14
S1
C17
C16
C19
C20
C2
C15
S3
Fig. 4 ORTEP diagram of HL3 at 50 % probability (H atoms are
removed for clarity)
methylbenzyldithiocarbazate with C=S and C–S bond
˚
lengths of 1.656 and 1.753 A [28], and 6-methyl-2-pyr-
idinecarboxyaldehyde Schiff base of S-methylbenzyl-
dithiocarbazate with C=S and C–S bond lengths of 1.655 and
˚
1.736 A [9]. The C=N and C–N bond lengths are 1.288(2)
˚
and 1.345(2) A for HL1, while for HL3 the values are
123

Transition Met Chem (2014) 39:119–126
125
˚
Table 4 Selected bond lengths (A) and bond angles (°) for HL1 and HL3
Bond lengths
HL1
HL3
Bond angles
HL1
HL3
S1–C2
S1–C15
C2–S3
C2–N4
N5–C6
N4–N5
C7–N8
1.7625(15)
1.8118(16)
1.6613(15)
1.345(2)
1.7624(15)
1.8173(16)
1.6582(15)
1.347(2)
S1–C2–S3
C2–N4–N5
S1–C15–C16
N4–N5–C6
C6–C7–N8
S1–C2–N4
S3–C2–N4
125.13(9)
124.96(9)
117.77(13)
116.09(11)
118.61(13)
116.12(14)
113.06(11)
121.80(11)
118.36(13)
110.40(11)
118.41(13)
115.84(14)
113.31(11)
121.73(12)
1.288(2)
1.286(2)
1.3709(18)
1.345(2)
1.3712(18)
1.343(2)
observed in analogous five-coordinate Cu(II) complexes
[17, 19, 29].
˚
Table 5 Selected bond lengths (A) and bond angles (°) for
[Cu(L4)sac)(H2O)]ꢀHsac
Bond lengths
Bond angles
Cu1–N5
Cu1–N8
Cu1–N18
Cu1–O17
Cu1–S3
C2–S3
1.9671(17)
2.0100(17)
1.9673(17)
2.3610(16)
2.2739(6)
1.710(3)
S3–Cu1–O17
S3–Cu1–N8
97.09(4)
162.53(5)
85.21(5)
97.00(5)
98.43(6)
91.07(6)
88.64(6)
172.25(7)
Discussion
S3–Cu1–N5
Schiff bases derived from S-alkyl/aryl esters of dithio-
carbazic acid are structurally related to thiosemicarba-
zones. The difference between the two lies in the terminal
non-coordinating functional group attached to the thiocar-
bonyl moiety [26]. Condensation reactions with various
ketones and aldehydes give Schiff bases which show
potential biological activities depending on the molecular
structures, although the structures may differ slightly from
one another [12, 16].
S3–Cu1–N18
O17–Cu1–N18
N8–Cu1–O17
N5–Cu1–O17
N5–Cu1–N18
other tridentate Schiff bases derived from dithiocarbazate
[9, 13].
S-Benzyl-b-N-(2-pyridyl)methylendithiocarbazate, which
is formed from the condensation reaction between 2-pyri-
dinecarboxyaldehyde and S-benzyldithiocarbazate as men-
tioned in the introduction, showed no significant activity
against bacteria and fungi, but it was found to be active
against leukemic and colon cancer cells, with its Cu and Cd
complexes showing higher activity than the Schiff base itself.
A related Schiff bases, 3-methylbenzyl 2-(6-methylpyridin-2-
ylmethylene) hydrazine carbodithioate formed by the con-
densation of 6-methylpyridine-2-aldehyde with S-3-methyl-
benzyldithiocarbazate was found to be highly active against
MCF-7 and MDA-MB-231 cell lines, while its Cu(II), Ni(II)
and Zn(II) complexes showed selective activity against both
cancer cell lines [28].
[Cu(L4)sac)(H2O)]ꢀHsac crystallized as a monomeric
species. The copper(II) complex has a distorted five-coor-
dinate geometry with a non-bonded saccharin present in the
outer coordination sphere. Coordination around the central
Cu(II) atom is almost square pyramidal with bond angles
ranging from 79.5° to 97.0°. The Schiff base donor atoms are
pyridine nitrogen, azomethine nitrogen and mercapto-sul-
fur. The fourth and fifth positions are occupied by saccha-
rinate nitrogen and oxygen from the water ligand. The Schiff
base is in its protonated (thione) form as evident from a short
C(2)–S(3) bond. This is a normal finding for thiosemicar-
bazone as thiosemicarbazone ligands have been found to
coordinate to metal ions in both protonated and deprotonated
˚
forms [30, 31]. The C(2)–S(3) bond length [1.710(2) A],
˚
which is intermediate between a C–S single bond [1.82 A]
˚
and C=S double bond [1.62 A] meaning it retains its partial
A Cu(II) complex containing saccharin and a tridentate
Schiff base derived from pyridine-2-carboxaldehyde Schiff
base of S-methyldithiocarbazate, S-methyl-b-N-(2-pyri-
dyl)methylendithiocarbazate has a distorted square-planar
structure, with the central Cu(II) ion bonded to the sacchari-
nate ion and deprotonated NNS donor ligand [17]. In the same
study, the Cu(II) saccharinate complex of 6-methyl-2-pyr-
idinecarbaldehydethiosemicarbazone formed as a dimeric
complex, with the sac anion behaving as a bridging bidentate
ligand, providing the imino nitrogen donor atom to one of the
copper(II) ions and the carbonyl oxygen as a weakly coor-
dinated axial ligand atom to the other Cu(II) ion.
double bond character, indicating extensive delocalization
over the C(S)NNS chain [19]. The C–S bond length in the
present complex is close to those reported for [Cu(pys-
me)(sac)(MeOH)]
(pysme = S-methyl-b-N-(pyridine-2-
yl)methylenedithiocarbazate) [17] and [Cu(NNS0)(sac)]
(NNS0 = S-benzyl-b-N-(2-acetylpyrid-2-yl)meth-
ylenedithiocarbazate) [19]. Other bond lengths, Cu–S
˚
[2.2739(6) A], Cu–N (azomethine) [1.9671(17) A] and
˚
˚
Cu–N (py) [2.0100(17) A], are in accordance with those
123

126
Transition Met Chem (2014) 39:119–126
8. Emel G, Yilmaz VT, Abdurrahman S, Orhan B (2010) Inorg
Chim Acta 363:438
9. Akbar Ali M, Mirza AH, Fereday RJ, Butcher RJ, Fuller JM,
Drew SC, Gahan LR, Hanson GR, Boujemaa M, Murray KS
(2005) Inorg Chim Acta 358:3937
10. Hossain ME, Begum J, Alam MN, Nazimuddin M, Akbar Ali M
(1993) Transition Met Chem 18:4975
11. Tarafder MTH, Kasbollah A, Crouse KA, Ali AM, Yamin BM,
Fun HK (2001) Polyhedron 20:2363
Our group has previously reported the synthesis, char-
acterization and biological activity of mixed-ligand Cu(II)
saccharinate complexes containing dithiocarbazate Schiff
bases [18, 19]. Most of the Cu(II) complexes tested were
found to be very active against the leukemic HL-60 cell
lines. Biological activities of the complexes reported in this
work are currently ongoing and will be reported in a future
communication.
12. Hossain ME, Alam MN, Akbar Ali M, Nazimuddin M, Smith FE,
Hynes RC (1996) Polyhedron 15:973
13. Tarafder MTH, Khoo TJ, Crouse KA, Ali AM, Yamin BM, Fun
HK (2002) Polyhedron 21:2691
14. Rapheal PF, Manoj E, Prathapachandra Kurup MR (2007)
Polyhedron 26:818
Conclusion
15. Antholine WE, Gunn P, Hopwood LE (1981) Int J Radiat Oncol
Biol Phys 7:491
16. Akbar Ali M, Tarafder MTH (1977) J Inorg Nucl Chem 39:1785
17. Akbar Ali M, Mirza AH, Ravoof TBSA, Bernhardt PV (2004)
Polyhedron 23:2031
18. Ravoof TBSA, Crouse KA, Tahir MIM, Cowley A, Ali MA
(2004) Polyhedron 23:2491
19. Ravoof TBSA, Crouse KA, Tahir MIM, Cowley A, Ali MA
(2007) Polyhedron 26:1159
20. Altomare A, Cascarano G, Giacovazzo C, Guagliardi A, Burla
MC, Polidori G, Camalli M (1994) J Appl Cryst 27:435
21. Betteridge PW, Carruthers JR, Cooper RI, Prout K, Watkin DJ
(2003) CRYSTALS version 12: software for guided crystal
structure analysis
The reaction of S-benzyldithiocarbazate, S-4-methylbenzyl-
dithiocarbazate and thiosemicarbazide with ketones,
2-acetyl-4-methylpyridine and 2-acetyl-5-methylpyridine,
yielded Schiff bases which complexed with Cu(II) sacchari-
nate to form the mixed-ligand Cu(II) saccharinate complexes.
These Schiff bases chelated to Cu(II) as uninegatively
charged tridentate NNS ligands, via their pyridine nitrogen,
azomethine nitrogen and thiolate sulfur atoms. Interestingly,
crystal analysis of [Cu(L4)sac)(H2O)]ꢀHsac showed a dis-
torted square-pyramidal structure with a non-bonded sac-
charin outside the coordination sphere.
22. Tarafder MTH, Akbar Ali M, Wee DJ, Azahari K, Silong S,
Crouse KA (2000) Transition Met Chem 25:456
23. Akbar Ali M, Ibrahim NEH, Butcher RJ, Jasinski JP, Jasinski JM,
Bryan JC (1998) Polyhedron 17(11–12):1803
24. Akbar Ali M, Butcher RJ, Bryan JC (1999) Inorg Chim Acta
287:8–13
Acknowledgments The research was funded by Universiti Putra
Malaysia (UPM) under research University Grant Schemes (RUGS
No. 05–01–11–1243RU) and the Malaysian Fundamental Research
Grant Scheme (FRGS No. 01–03–11–986FR). S.A.O. wishes to thank
the UPM for the award of a Graduate Research Fellowship.
25. Sanderson RT (1967) Inorganic chemistry, 1st edn. Reinhold,
New York
26. Akbar Ali M, Mirza AH, Butcher RJ, Bernhardt PV, Karim MR
(2011) Polyhedron 30:1478
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