Specificity of salicylaldehyde S-alkylisothiosemicarbazones coordination in palladium(II) complexes

Article abstract of DOI:10.1016/j.poly.2014.05.006

S-alkylated salicylaldehyde thiosemicarbazones (HL) form with palladium(II) the complexes 1-3 of the general formula [Pd(L)Cl], where L is monodeprotonated S-ethyl- for 1, S-heptyl- for 2, and S-isopropyl- for 3 derivatives of HL. 5-Bromosalicyladehyde S-

Full text of DOI:10.1016/j.poly.2014.05.006

Accepted Manuscript
Specificity of salicylaldehyde S-alkylisothiosemicarbazones coordination in
palladium(II) complexes
Mihail Revenco, Petru Bulmaga, Elena Jora, Oleg Palamarciuc, Victor
Kravtsov, Paulina Bourosh
PII:
S0277-5387(14)00302-7
DOI:
http://dx.doi.org/10.1016/j.poly.2014.05.006
POLY 10718
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
29 December 2013
3 May 2014
Please cite this article as: M. Revenco, P. Bulmaga, E. Jora, O. Palamarciuc, V. Kravtsov, P. Bourosh, Specificity
of salicylaldehyde S-alkylisothiosemicarbazones coordination in palladium(II) complexes, Polyhedron (2014), doi:
http://dx.doi.org/10.1016/j.poly.2014.05.006
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REVISED-II
Specificity of salicylaldehyde S-alkylisothiosemicarbazones coordination in palladium(II)
complexes
Mihail Revencoa, Petru Bulmagaa, Elena Joraa, Oleg Palamarciuca, Victor Kravtsovb, Paulina
Bouroshb
a Faculty of Chemistry and Chemical Technology, Department of Chemistry,
Moldova State University, 60 Mateevici Street, MD 2009, Chisinau, Republic of Moldova
bInstitute of Applied Physics, Academy of Sciences, 5 Academiei street, MD 2028, Chisinau,
Republic of Moldova
Abstract
S-alkylated salicylaldehyde thiosemicarbazones (HL) form with palladium(II) the
complexes 1-3 of the general formula [Pd(L)Cl], where L is monodeprotonated S-ethyl- for 1, S-
heptyl- for 2, and S-isopropyl- for 3 derivatives of HL. 5-Bromosalicyladehyde S-methyl-4-
phenylisothiosemicarbazone gets the complex 4 - [Pd(L)Cl]·DMF. According to the results of X-
ray investigations the 1-4 complexes reveal the square planar coordination of Pd(II). The
monodeprotonated tridentate organic ligand is bound to the metal via O,N,S set of donor atoms.
The fourth site is occupied by the chloride ion. This coordination mode does not allow the
organic ligand to lose the second proton, keeps it as a potentially monobasic acid, does not
depend on the length, topology or branching of the substituents and is a new tendency observed
only for the palladium complexes.
Keywords: salicylaldehyde S-alkylisothiosemicarbazone, palladium complex, crystal structure.
*Correspondence
author.
Tel:
+37 322
577404.
E-mail:
revenco@usm.md,
revencom@yahoo.com (M.Revenco)
Introduction
The chemistry of the coordination compounds of thiosemicarbazones with transition metals,
attracts attention due to their remarcable properties and potential applications as biologically
active agents, analytical reagents, catalysts etc. [1]. As a rule, the thiosemicarbazide moiety
N(1)–N(2)H–C(3)(=S)–N(4)H2, in these complexes is coordinated via N(1),S atoms, although
other binding modes have also been reported [2]. Thioalkylation of the thiosemicarbazide and its
derivatives introduces a new tendency in their coordination abilities [3, 4]. The configuration of
the uncoordinated salicylaldehyde S-alkylthiosemicarbazones (HL) [5] shows that HL is
topologically predisposed to coordinate as an O,N,S tridentate ligand.
R1
OH
HL
N
S
N
R2
R3
N
H

Nevertheless, these ligands generally bind to 3d-metals via O,N,N donor set and behave as a
monobasic acid coordinated in imino-form M(L) or as a twice deprotonated ligand in amino-
form M(L-H) [6].
R1
O
N
O
N
M
Pd
N
S
R3
R2
CH3
S
N
HN
N
H
Pd(L)
M(L)
H
The survey of transition metals complexes with salicylaldehyde S-alkylthiosemicarbazones
in Cambridge Structural database [7] reveals 36 complexes with O,N,N manner of coordination,
and only one complex, in which this ligand is bound to the palladium(II) ion using O,N,S donor
set [4] as it is shown on the scheme for Pd(L).
In order to clarify if the coordination of S-alkylthiosemicarbazones through sulphur atom
is an exceptional case or it is a new trend of coordination mode of HL which occurs in palladium
complexes, we have prepared and investigated the structure of four new compounds of the
formulas [Pd(L)Cl] (1–3) and solvate [Pd(L)Cl]·DMF (4) which differ by length, topology or
branching of the radicals in organic molecule. Complexes 1–3 differ only by R2 in the formula
HL (R2 = C2H5 in 1; C7H15 in 2, and iso-C3H7 in 3 ), while R1 = R3 = H. The compound 4 derives
from 5-bromosalicyladehyde S-methyl-4-phenylisothiosemicarbazone (R1= Br, R2 = CH3, and
R3 = C6H5).
2. Experimental
2.1. Materials
Salicylaldehyde, 5-bromosalicylaldehyde, thiosemicarbazide, 4-phenylthiosemicarbazide,
methyl iodide, ethyl iodide, iso-propyl iodide, heptyl iodide and PdCl2 were purchased from
Sigma-Aldrich and used as received.
2.2. Synthesis of the ligands and initial salts.
The hydroiodides of the S-alkylisothiosemicarbazides were prepared using the method
reported earlier for S-methylderivative [4], refluxing 20 mmol of thiosemicarbazide and 25
mmol of the suitable alkyl iodide in 50-75 mL of dry methanol. The salicylaldehyde S-

alkylisothiosemicarbazones of the general formula HL were synthesized by adding a methanol
solution (40 mL) of the aldehyde (10 mmol) to the warm methanol-water (1:1) solution (100 mL)
of appropriate S-alkylisothiosemicarbazides hydroiodides (10 mmol). The mixture was treated
with a warm water solution (10 mL) of NaHCO3 and pale yellow crystalline solids were
precipitated. The resulting products were filtered, washed with methanol, diethyl ether and dried
at room temperature. The purity of the products was determined by elemental C, H, and N
analysis.
The salt K2[PdCl4] was prepared according to [8].
2.3. Synthesis of the complexes 1–4.
The complexes 1–4 were synthesized using a general method. To 10 mL of warm (65°С)
water solution containing 0.326 g (1 mmol) of К2[PdCl4], 25 mL of methanol –
dimethylformamide (DMF) (1:1) solution containing 1 mmol of the respective salicylaldehyde S-
alkylisothiosemicarbazones HL were added drop-wise. The mixture was maintained at this
temperature during 5-7 min. Upon cooling, the obtained dark orange rhombus-shaped crystals
were filtered, washed with methanol, diethyl ether, and dried in air at room temperature. The
general formula of the compounds derived from salicylaldehyde S-alkylisothiosemicarbsazone is
[Pd(L)Cl] (1–3). For the 5-brom derivative the formation of a solvate [Pd(L)Cl]•DMF (4) has
been observed.
1: Orange solid, yield: 74%. Anal. Calc. for C10H12ClN3OPdS: C, 32.98; H, 3.32; N,
11.54; Pd, 29.22. Found: C, 32.73; H, 3.25; N, 11.39; Pd, 29.10.
2: Orange solid, yield: 78%. Anal. Calc. for C15H22ClN3OPdS: C, 41.48; H, 5.11; N, 9.67;
Pd, 24.50. Found: C, 41.25; H, 5.05; N, 9.49; Pd, 24.32.
3: Orange solid, yield: 71%. Anal. Calc. for C11H14ClN3OPdS: C, 34.93; H, 3.73; N,
11.11; Pd, 28.14. Found: C, 34.68; H, 3.56; N, 11.56; Pd, 28.02.
4: Orange solid, yield: 81 %. Anal. Calc. for C18H20BrClN4O2PdS: C, 37.39; H, 3.49; N,
9.69; Pd, 18.40. Found: C, 37.18; H, 3.37; N, 9.74; Pd, 18.26.
2.4. X-ray Crystallography
The X-ray intensity data for 1 and 3 were collected at a room temperature on a Xcalibur E
diffractometer, and for 2 at 150K and for 4 at 100K on a Bruker-AXS SMART 1K CCD
diffractometer both equipped with graphite monochromatized Mo-Kα radiation (λ = 0.71073 Å ).

The data reduction included a correction for Lorentz and polarization effects and multi-scan
method of absorption correction [9a]. The crystal structure was solved and refined using the
SHELX97 [9b] program suite. The positions of all hydrogen atoms were calculated
geometrically and refined using a riding model with Uiso(H) =1.2Ueq(C, N) or 1.5Ueq(C(-CH3).
The X-ray data and the details of the refinement of the structures are summarized in Table 1, the
selected geometric parameters are given in Table 2, and hydrogen bonds geometry is given in
Table 3.
Table 1
Crystal data and structure refinement parameters for compounds 1–4.
Compound
1
2
3
4
Formula weight
Crystal system
364.14
triclinic
434.27
triclinic
378.16
triclinic
578.20
Monoclinic
Space group
P21/c, No.14
P1, No.2
P1, No.2
P1, No.2
a (Å)
b (Å)
c (Å)
α (°)
7.9960(7)
8.1829(4)
11.0640(8)
99.638(5)
90.222(6)
119.126(7)
620.39(8)
2
8.3345(6)
14.763(1)
15.565(1)
113.559(4)
98.894(4)
93.809(4)
1717.0(2)
4
7.5233(5)
7.7982(5)
12.9709(9)
72.564(6)
80.118(6)
66.312(6)
663.70(8)
2
11.1525(4)
10.8672(5)
17.4665(5)
90
102.668(3)
90
2065.35(13)
4
1.859
β (°)
γ (°)
V (Å3)
Z
Dcal (Mg/m3)
µ (mm-1)
F(000)
1.949
1.865
360
1.680
1.362
880
1.892
1.747
376
3.086
1144
Crystal size (mm)
θ range for data
collection (°)
Reflections
collected / unique
0.40x0.36x0.10
2.93 – 26.50
0.40x0.30x0.25 0.50x0.40x0.10
0.40x0.35x0.30
3.28 – 25.49
1.46 – 25.50
2.96 – 26.50
4615 / 2560
[R(int) = 0.0294] [R(int) =
11135 / 6366
4680 / 2746
6340 / 3811
[R(int) = 0.0314] [R(int) =
0.0799]
0.0329]
Reflections with
I>2σ(I)
Refinement method
Parameters
2195
3818
2482
3395
Full-matrix least-squares on F2
399
156
165
256
Completeness (%)
99.8 (θ=26.50°)
99.9 (θ=25.50°) 99.6 (θ=26.50°)
99.1 (θ=25.49°)
Goodness-of-fit on
F2
1.000
1.007
1.001
1.003
0.0344, 0.0550
0.0420, 0.0602
0.0561, 0.1351
0.1223, 0.1831 0.0359, 0.0751
0.0312, 0.0703
0.0284, 0.0747
0.0332, 0.0768
R1, wR2 [I>2σ(I)]
R1, wR2 (all data)
3. Results and discussion

The interaction of the potassium tetrachloropalladate with HL in mixed methanol-
dimethylformamide solutions results in the formation of the complexes 1–4. The ratio
palladium:organic ligand in the final products is 1:1 and remains the same when the initial ratio
was 1:2 or when the mixing order has been changed. Although the tridentate coordination of HL,
the composition of the complexes and their square-planar structure may be anticipated, the
manner of these ligands coordination to palladium ion remains unresolved, because, as we
previously have shown [3, 4], the S-methyl derivative may act both as tridentate O,N,N or O,N,S
ligand.
The X-ray single crystal investigation showed that crystals 1–4 comprise neutral
[Pd(L)Cl] complexes (Fig. 1a–1d). The organic ligand in all complexes is coordinated to the
palladium ion as tridentate ONS monoanion and forms with Pd(II) six-membered PdONC3 and
five membered PdN2CS chelate rings. Thus, the alkylated sulfur atom is involved in
coordination. It should be noted that during the formation of complexes, the ligand keeps the
same configuration as in the structures of uncoordinated agent [5]. Coordination surrounding of
the palladium is completed up to square-planar by the chloride anion. The distances Pd–Cl, Pd–
S, Pd–N и Pd–O in 1–4 are in the range 2.3060(8) – 2.342(2) Å, 2.2232(4) – 2.234(3) Å,
1.969(8) – 1.979(2) Å and 2.000(9) – 2.021(6) Å, respectively, (Table 2) and close to the
corresponding distances 2.311(2), 2.226(3), 1.967(7) and 1.978(6) Å in the Pd(II) complex
described in [4]. The metal-ligand distances in 1–4 are also close to those found in the complex
chloro(N-ethylsalicylidene-thisemicarbazonato)palladium(II) monohydrate [1h]. In the square
planar core of all reported here complexes, the deviations of the donor atoms from their mean
plane are less than 0.10 Å and Pd(II) displacement from this plane is less than 0.04 Å. The sum
of bond angles at S(1) atom equals 305.1° in 1, 302.1° in 2A, 307.0° in 2B, 305.9° in 3 and
308.2° in 4. The interatomic distances in the thiosemicarbazide fragment indicate a localization
of double C(8)–N(2) bond (Table 2), which is typical for the uncoordinated alkylated
thiosemicarbazones molecules [5], for the coordinated twice deprotonated forms with O,N,N
donor atoms [3a, 10], and tetradentate derivatives [3a, 3b, 11]. In the solvate 4 the dihedral
angles between the mean planes of five-membered chelate ring and phenyl moiety attached to
N(3) atom equals 8.6º. The almost coplanar mutual arrangement of these moieties is stabilized by
intramolecular C(11)–H⋅⋅⋅N(2) H-bond (Table 3) [1k].
In the crystal of 1 hydrogen bonds N(3)–H⋅⋅⋅O(1) and С(4)–H⋅⋅⋅N(2) (Table 3) join
complexes in the chains along [110] direction (Fig. 2a). Two metallocycles and aromatic moiety
are coplanar and deviation of corresponding non-hydrogen atoms from the common plan is less
then 0.04 Å. The infinite stacking interaction between this flat part of center symmetry related
complexes involving aromatic moieties and both metallocycles unite chains in layers parallel to

(ab) crystallographic plan (Fig. 2a). The interplanar separation between the plans of parallel
overlapped fragments equal 3.389 and 3.399 Å. The alkyl substituents on sulphur atoms are
pointed outside such layers and provide hydrophobic interactions along c axis.
b
A
C
d
Fig. 1. ORTEP drawings for 1 (a), 2 (b), 3 (c) and 4 (d) display the formula units with atom
numbering scheme. Thermal ellipsoids are shown at 50% probability level.
Table 2
Selected bond distances (Å) and angles (°) for compounds 1 – 4
1
2
2
3
4
A
B
Pd(1)–O(1)
Pd(1)–N(1)
Pd(1)–S(1)
Pd(1)–Cl(1)
2.002(2)
1.974(3)
2.2232(10) 2.234(3)
2.3163(10) 2.342(2)
2.021(6)
1.969(8)
2.013(6)
1.977(7)
2.227(3)
2.333(2)
2.008(2)
1.979(2)
2.2294(9)
2.3150(9)
2.000(2)
1.971(2)
2.2259(7)
2.3060(8)
1
3
4
A
B
O(1)–Pd(1)–N(1)
O(1)–Pd(1)–S(1)
93.8(1)
178.38(7)
94.1(3)
179.0(2)
94.0(3)
178.9(2)
93.63(10)
177.15(6)
94.08(9)
174.70(6)

O(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–S(1)
N(1)–Pd(1)–Cl(1)
S(1)–Co(1)–Cl(1)
91.40(7)
85.24(9)
174.79(9)
89.55(4)
91.7(2)
85.0(2)
172.8(2)
91.8(2)
85.1(2)
174.1(2)
89.13(8)
90.10(7)
85.06(8)
175.93(8)
91.14(3)
90.04(6)
84.94(7)
173.34(7)
91.43(3)
89.26(9)
1
2
3
4
A
B
1.35(1)
1.29(1)
1.404(10)
1.30(1)
1.32(1)
-
O(1)–C(3)
N(1)–C(1)
N(1)–N(2)
N(2)–C(8)
N(3)–C(8)
N(3)–C(10)
C(1)–C(2)
C(2)–C(3)
S(1)–C(8)
S(1)–C(9)
1.324(4)
1.297(4)
1.408(4)
1.280(4)
1.340(4)
1.32(1)
1.29(1)
1.383(10)
1.29(1)
1.37(1)
1.317(4)
1.291(4)
1.405(3)
1.281(4)
1.336(4)
-
1.424(5)
1.425(4)
1.806(3)
1.865(3)
1.318(4)
1.303(4)
1.404(3)
1.284(4)
1.353(4)
1.409(4)
1.429(4)
1.420(4)
1.820(3)
1.813(3)
-
-
1.330(5)
1.411(5)
1.802(4) 1.823(10)
1.42(1)
1.42(1)
1.43(1)
1.43(1)
1.810(9)
1.814(10)
1.814(4)
1.828(9)
1
2
3
4
A
B
C(9)–S(1)–Pd(1)
C(8)–S(1)–Pd(1)
C(3)–O(1)–Pd(1)
C(1)–N(1)–Pd(1)
N(2)–N(1)–Pd(1)
C(1)–N(1)–N(2)
N(1)–N(2)–C(8)
N(1)–C(1)–C(2)
C(1)–C(2)–C(3)
O(1)–C(3)–C(2)
N(2)–C(8)–N(3)
N(2)–C(8)–S(1)
N(3)–C(8)–S(1)
C(8)–S(1)–C(9)
108.1(1) 107.1(3)
96.5(1) 96.2(3)
124.3(2) 124.3(6)
124.7(3) 123.6(7)
120.9(2) 121.9(6)
108.5(3)
97.0(3)
111.0(1)
96.3(1)
110.63(10)
96.28(9)
124.3(2)
124.8(2)
121.8(1)
113.4(2)
114.8(2)
126.3(3)
124.9(3)
125.4(3)
124.8(3)
121.4(2)
113.7(2)
101.3(1)
124.3(6)
123.7(6)
121.3(6)
114.9(7)
121.3(6)
128.9(8)
124.1(8)
123.9(9)
123.4(8)
120.9(7)
115.7(7)
101.5(4)
124.7(2)
124.6(3)
121.0(2)
114.2(3)
115.2(3)
127.1(3)
124.8(3)
124.8(3)
124.0(3)
122.1(2)
113.9(3)
98.6(2)
114.3(3)
115.2(3)
127.0(3)
124.4(4)
125.7(3)
122.7(3)
122.0(3)
115.3(3)
100.5(2)
114.4(8)
115.9(8)
128.6(9)
124.1(9)
125.2(9)
122.2(9)
120.9(7)
116.9(8)
98.8(4)
The same hydrogen bonded chains, running along a axis were found in the structure of 2
for both symmetry independent complexes A and B (Table 3, Fig. 2b). Two neighboring
inversion center related chains of complexes A are stacked in the tapes due to overlapping of
parallel flat fragments each involving aromatic moiety and both metallocycles. The interplanar
separation of overlapping fragments equals 3.247 Å and the non-hydrogen atoms, which
constitute this fragment, deviate from the common plane within 0.03 Å. The complex B does
not reveal stacking interactions. The packing of tapes of complexes A and chains of complexes B
creates the channel along a axis filled with cross interpenetrated bulk aryl substituents. The
crystal structure of 3 is similar to 1. The H-bounded chains run along [-110] of the unit cell (Fig.
2c, Table 3). The interplanar separation between the planes of overlapped fragments in the
infinite stack equals 3.349 and 3.514 Å. In the crystal structure of 4 the molecules of DMF unite

the couple of complexes in dimer via hydrogen bounds N(3)–H⋅⋅⋅O(2) and C(1)–H⋅⋅⋅O2 (Fig. 2d,
Table 3). The crystal packing in 4 does not reveal any other specific intermolecular interactions.
a
b
c
d

Fig. 2. Hydrogen bonded chain and packing motif in the structures 1 (a), 2 (b), 3 (c), and H-
bonded dimmers and packing diagram in 4 (d).
Table 3
Selected hydrogen bond distances (Å) and angles (°) for compound 1–4
Symmetry transformation for
acceptor
D–H⋅⋅⋅A
D(H⋅⋅⋅A) D(D⋅⋅⋅A)
∠(D–
H⋅⋅⋅A)
1
2.21
2.67
2.943(4)
3.486
143
147
x–1, y–1, z
x+1, y+1, z
N(3)–H⋅⋅⋅O(1)
C(4)–H⋅⋅⋅N(2)
2
2.08
2.61
2.08
2.59
2.89(1)
3.527
2.918(10) 165
157
168
x+1, y, z
x–1, y, z
x–1, y, z
x+1, y, z
N(3A)–H⋅⋅⋅O(1A)
C(4A)–H⋅⋅⋅N(2A)
N(3B)–H⋅⋅⋅O(1B)
C(4B)–H⋅⋅⋅N(2B)
3.500
165
3
2.16
2.69
2.68
2.973(3)
3.221(3)
3.539
152
122
154
x+1, y–1, z
x+1, y–1, z
x–1, y+1, z
N(3)–H⋅⋅⋅O(1)
N(3)–H⋅⋅⋅Cl(1)
C(4)–H⋅⋅⋅N(2)
4
2.06
2.70
2.28
2.865(3)
3.440
2.892
154
137
123
x, y, z
x+2, –y, –z
x, y, z
N(3)–H⋅⋅⋅O(2)
C(1)–H⋅⋅⋅O(2)
C(11)–H⋅⋅⋅N(2)
4. Conclusions
Our study shows, that the treatment of the potassium tetrachloropalladate with
salicylaldehyde S-alkylisothiosemicarbazones affords the square planar complexes in which
monoanionic organic ligands are coordinated to Pd(II) through O,N,S donor’s atom set.
Regardless of the length and branching of the alkyl substituent the sulfur atom is always
coordinated to Pd(II). The introduction of the substitutents in the position 5 of the salicyldehyde
and 4 of thiosemicarbazide moiety influences only on the complex packing in the crystal.
Thus, we extended the knowledge about possible manner of coordination of
salicylaldehyde S-alkylisothiosemicarbazones to Pd(II) from one exclusive example [4] to well
defined set of complexes. Such behaviour could be treated from the positions of Pearson theory
of “hard” and “soft” acids and bases [12]. Being “hard” or “intermediate” acids, the 3d-metal
ions adopt the coordination of a versatile ligand as a “soft” O,N,N base, while in the case of
palladium, as “soft” acid the coordination of the ligand with “hard” ONS donor is more
preferable.

Acknowledgments
M.R., P.B., E.J. and O.P. gratefully acknowledge the financial support of the Supreme Council
for Science and Technological Development of the Moldova Government.
Appendix A. Supplementary data
CCDC 978040 (1), 978041 (2) 978042 (3), and 978039 (4) contain the supplementary
crystallographic data for compounds 1-4. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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