Copper(II) and molybdenum(VI) complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone: Syntheses, characterizations and crystal structures

Article abstract of DOI:10.1080/00958972.2012.748191

A new tridentate Schiff base, 5-bromosalicylaldehyde S- allylisothiosemicarbazone hydrobromide (H₂L), and several new mononuclear complexes of copper(II) and molybdenum(VI) of this ligand with general formulas ([Cu(L)Im] (1)), ([Cu(L)NH₃].4H₂O (2)), and ([MoO₂(L)1-MeIm] (3), Imidazole: Im, 1-methylimidazole: 1-MeIm) were prepared and characterized by elemental analyses, IR, Proton Magnetic Resonance Spectroscopy and Ultraviolet-visible techniques. The physico-chemical results suggested that the H₂L coordinates in the dianionic tridentate form. Crystal structures of the Cu(II) complexes reveal a square planar configuration surrounded by the dianionic tridentate isothiosemicarbazone (ONN) and Im and NH₃ for 1 and 2, respectively. The L₂-, two oxo, and 1-methylimidazole are coordinated to molybdenum(VI) in a distorted octahedral geometry in 3. Formation of pure metal oxide residues was confirmed by thermal degradation of the complexes.

Full text of DOI:10.1080/00958972.2012.748191

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Copper(II) and molybdenum(VI)
complexes with 5-
bromosalicylaldehyde S-
allylisothiosemicarbazone: Syntheses,
characterizations and crystal structures
REZA TAKJOO a , ALIREZA HASHEMZADEH a , HADI AMIRI RUDBARI b
& FRANCESCO NICOLÒ b
a Department of Chemistry, School of Sciences, Ferdowsi
University of Mashhad, Mashhad, Iran
b Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica
Fisica Università di Messina, Contrada Papardo, Messina, Italy
Accepted author version posted online: 08 Nov 2012.
To cite this article: REZA TAKJOO , ALIREZA HASHEMZADEH , HADI AMIRI RUDBARI & FRANCESCO
NICOL (2013) Copper(II) and molybdenum(VI) complexes with 5-bromosalicylaldehyde S-
allylisothiosemicarbazone: Syntheses, characterizations and crystal structures, Journal of
Coordination Chemistry, 66:2, 345-357, DOI: 10.1080/00958972.2012.748191
To link to this article: http://dx.doi.org/10.1080/00958972.2012.748191
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Journal of Coordination Chemistry
Vol. 66, No. 2, 20 January 2013, 345–357
Copper(II) and molybdenum(VI) complexes with
5-bromosalicylaldehyde S-allylisothiosemicarbazone:
Syntheses, characterizations and crystal structures
REZA TAKJOO†*, ALIREZA HASHEMZADEH†, HADI AMIRI RUDBARI‡ and
FRANCESCO NICOLÒ†
†Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad,
‡
Mashhad, Iran; Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica
Università di Messina, Contrada Papardo, Messina, Italy
(Received 17 June 2012; in final form 20 September 2012)
A new tridentate Schiff base, 5-bromosalicylaldehyde S-allylisothiosemicarbazone hydrobromide
(H2L), and several new mononuclear complexes of copper(II) and molybdenum(VI) of this ligand
with general formulas ([Cu(L)Im] (1)), ([Cu(L)NH3]·4H2O (2)), and ([MoO2(L)1-MeIm] (3), Imid-
azole: Im, 1-methylimidazole: 1-MeIm) were prepared and characterized by elemental analyses, IR,
Proton Magnetic Resonance Spectroscopy and Ultraviolet-visible techniques. The physico-chemical
results suggested that the H2L coordinates in the dianionic tridentate form. Crystal structures of the
Cu(II) complexes reveal a square planar configuration surrounded by the dianionic tridentate isothi-
osemicarbazone (ONN) and Im and NH3 for 1 and 2, respectively. The L2-, two oxo, and 1-methyl-
imidazole are coordinated to molybdenum(VI) in a distorted octahedral geometry in 3. Formation
of pure metal oxide residues was confirmed by thermal degradation of the complexes.
Keywords: Schiff base; Isothiosemicarbazone; Copper and molybdenum complexes; TGA; Crystal
structure
1. Introduction
Complexes of palladium and nickel with thiosemicarbazide were synthesized by Jensen
et al. [1, 2]. Reaction of thiosemicarbazide with alkyl halides produces isothiosemicarbaz-
ides which can participate in condensation reactions with aldehydes and ketones, producing
isothiosemicarbazones [3–5]. Alkylation of sulfur makes the isothioamidic nitrogen a better
donor [6]. Tridentate isothiosemicarbazides are usually coordinated to the metal via isot-
hioamide nitrogen, azomethine nitrogen, and related heteroatoms of aldehydes or ketones
(XNN donor set, X = N or O). Numerous structures of tridentate isothiosemicarbazone com-
plexes were determined [1]. In general, isothiosemicarbazides or their derivatives in the
complexes show antimicrobial, antituberculosis [7, 8], antileukemia [9, 10], antibacterial,
and antifungal activities [11]. The kind of aldehydes or ketones used to prepare isothiose-
micarbazones or different metal centers such as molybdenum or copper will affect their
*Corresponding author. Email: r.takjoo@um.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.748191

346
R. Takjoo et al.
biological activities [12], although sometimes similarities could be found [13, 14]. N-donor
ligands such as imidazole and its derivatives can improve the bioactivities of mixed ligand
complexes [15]. Compounds containing amine groups such as NH3 and imidazole deriva-
tives can make supramolecular structures and are used in crystal engineering architectures
[16]. In addition, imidazole derivatives in complexes have enzyme properties [17].
Some copper sites have antibacterial, antifungal, and anticancer properties [18]. Mixed
ligand copper(II) complexes with N-donors such as imidazole have been considered as
‘model compounds’ [19, 20]. Also, the active site of some metalloenzymes contain copper
(II) [21].
Mo complexes which can change their metal oxidation number can have some oxido-
reductases, hydrogenase, xanthine oxidase, DMSO reductase, and other oxo-transferase
properties [22]. Moreover, molybdenum complexes [cis-MoO2(L)D], D can be a solvent,
are useful due to easy replacement of the solvent. Molybdenum(VI) complexes participate
in sulfite oxidase, DMSO reductase, aldehyde oxidoreductase, and nitrate reductase
reactions [23–25].
Here, we report 5-bromosalicylaldehyde S-allylisothiosemicarbazone hydrobromide
(H2L) (Scheme 1) and its [Cu(NH3)L]·4H2O (1), [Cu(Im)L] (2) and [MoO2(1-MeIm)L] (3)
(Im: imidazole, 1-MeIm: 1-methylimidazole) complexes. All compounds were thoroughly
characterized by elemental analyses, IR, Proton Magnetic Resonance Spectroscopy (1H
NMR), and Ultraviolet-visible (UV-Vis) methods; in the case of the complexes, X-ray
crystallography and thermogravimetric analysis were done as well.
2. Experimental
2.1. Reagents and physical measurements
All compounds were purchased from commercial sources and used without purification.
Elemental analyses (C, H, N, and S) were performed on a Thermo Finnigan Flash Elemen-
tal Analyzer 1112EA. IR spectra from 400 to 4000 cm-1 were recorded in KBr pellets on a
1
Buck 500 Scientific spectrometer. H NMR spectra of DMSO-d6 solutions were recorded
on a Bruker BRX 100 AVANCE with the signal of the free DMSO at 2.49 ppm as a refer-
ence. Electronic spectra were measured with a SHIMADZU model 2550 UV–Vis spectro-
photometer (250-1100 nm) in DMF. The TGA diagrams were recorded in a TGA-50
SHIMADZU instrument at a heating rate of 10 °C/min under air from 20 to 950 °C.
2.2. 5-Bromo S-allylisothiosemicarbazone hydrobromide (H2L)
Allyl bromide (1.1 g, 9.0 mmol) was added to an ethanolic solution (5 mL) of thiosemicar-
bazide (0.82 g, 9.0 mmol) and refluxed for 10 min on a water bath at ca. 90 °C. 5-Bromo-
salicylaldehyde (1.8 g, 9.0 mmol) was then mixed to the resulting solution and the reflux
Scheme 1. Synthesis of 5-bromosalicylaldehyde S-allylisothiosemicarbazone hydrobromide (H2L).

Complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone
347
was continued for an additional 30 min. A yellow precipitate was separated by filtration,
washed with ethanol, and dried in air. Yellow. Yield: 2.8 g, 78.7%. m.p.: 216 °C. Anal.
Calcd for C11H13Br2N3OS (392.76 g mol-1): C, 33.44; H, 3.32; N, 10.63; S, 8.12. Found:
C, 32.80; H, 3.31; N, 10.41; S, 8.02%. IR (KBr) cm-1: ν(OH) 3336, ν(NH) 3268 m, 3173s,
ν(C=N) 1542 m, 1623s, ν(C=C) 1474 m, ν(C–O) 1235 m, ν(N–N) 1097 m. UV/Vis (DMF)
1
λ
max, nm (logɛ, L mol-1 cm-1): 266 (4.38), 304 (4.62), 314 (4.62), 346 (4.74). H NMR
(100 MHz, DMSO-d6): δ = 11.4, 10.8 (s, 1H, OH), 9.8 (s, 2H, N3H), 8.7 (s, 1H, C5H), 8.2
(d, 1H, C11H), 7.5 (dd, 1H, C9H), 6.9 (d, 1H, C8H), 5.7-6.1 (m, 1H, C2H), 5.3 (t, 2H,
C1H), 4.1 (d, 2H, C3H).
2.3. Synthesis of complexes
2.3.1. [Allyl[(5-bromo-2-hydroxyphenyl)methylene]hydrazincarboximidothioato(-2)-N,
N2,O2]ammonia-copper, tetrahydrate (1). A mixture of H2L (0.034 g, 0.1 mmol) and a
molar excess of ammonia 25% (0.1 mL, 5.7 mmol) were dissolved in ethanol (5 mL).
CuCl2·2H2O (0.017 g, 0.1 mmol) was added to the solution. The reaction mixture was stir-
red and refluxed for 1 h. After standing at room temperature for one week, crystals were
formed from the resulting clear green solution. The crystalline product was collected,
washed with cold ethanol, and dried in air. [Cu(NH3)L]·4H2O (1): irregular, green. Yield:
0.023 g, 59.0%. m.p.: 163 °C. Anal. Calcd for C11H13BrCuN4OS·4H2O (464.82 g mol-1):
C, 27.42; H, 4.55; N, 12.05; S, 6.90. Found: C, 27.51; H, 4.59; N, 12.13; S, 6.93%. IR
(KBr) cm-1: ν(OH) 3419 m, ν(NH) 3149s, ν(C=N) 1605 m, ν(C=C) 1507 m, ν(C–O)
1090 m, ν(N-N) 1024 m. UV/Vis (DMF) λmax, nm (logɛ, L mol-1 cm-1): 326 (4.11)sh, 336
(4.12), 348 (3.27).
2.3.2. [Allyl[(5-bromo-2-hydroxyphenyl)methylene]hydrazincarboximidothioato(-2)-N,
N2,O2]imidazole-copper (2). Cu(CH3COO)2·H2O (0.20 g, 1 mmol) was added to a
mixture of H2L (0.034 g, 0.1 mmol) and imidazole (0.20 g, 3 mmol) in EtOH (5 mL). The
mixture was heated under reflux for 45 min, then cooled, and allowed to stand in air for
several days. Red crystals were collected, washed (EtOH), and dried in air. [Cu(Im)L] (2):
irregular, green. Yield: 0.026 g, 59.1%. m.p.: 184 °C. Anal. Calcd for C14H14BrCuN5OS
(443.81 g mol-1): C, 37.89; H, 3.18; N, 15.78; S, 7.22. Found: C, 38.03; H, 3.11; N, 15.99;
S, 7.27%. IR (KBr) cm-1: ν(NH) 3411s, ν(C=N) 1579 m, ν(C=C) 1491 m, 1437w, ν(C=N)
1535s, ν(Im) 1249w, ν(C–O) 1172 m, ν(N–N) 1056 m. UV/Vis (DMF) λmax, nm (log
ɛ L mol-1 cm-1): 336 (4.00)sh, 350 (4.08), 400 (4.32), 584 (2.02)sh.
2.3.3. [Allyl[(5-bromo-2-hydroxyphenyl)methylene]hydrazincarboximidothioato(-2)-N,
N2,O2]dioxido(1-methylimidazole)-molybdenum (3). To a boiling ethanol solution
(6 mL) of the H2L (0.034 g, 0.1 mmol) and 1-methylimidazole (0.25 g, 3 mmol), a 5 mL
ethanolic solution of MoO2 (acac)2 (0.33 g, 1mmol) was added to a boiling ethanolic solu-
tion (6 mL) of the H2L (0.034 g, 0.1 mmol) and 1-methylimidazole (0.25 g, 3mmol). This
solution was refluxed for 1 h. The deep red solution was allowed to stand in air for one
week. The crystalline red complex was separated, washed with ethanol, and dried in air.
[MoO2(1-MeIm)L] (3): Irregular, red. Yield: 0.037 g, 72.6%. m.p.: 207 °C. Anal. Calcd for
C15H16BrMoN5O3S (522.25 g mol-1): C, 34.50; H, 3.09; N, 13.41; S, 6.14. Found: C, 34.68;

348
R. Takjoo et al.
H, 3.11; N, 13.47; S, 6.18%. IR (KBr) cm-1: ν(NH) 3421s, ν(C=N) 1564 m, 1632 m, ν(C=C)
1488 m, ν(C=N) 1535s, ν(1-MeIm) 1257w, ν(C–O) 1185w, ν(N–N) 1036 m. UV/Vis (DMF)
1
λ
max, nm (log ɛ L mol-1 cm-1): 304 (4.34), 340 (4.08)sh, 438 (3.59). H NMR (100 MHz,
DMSO-d6): δ = 9.4 (s, 1H, N3H), 8.5 (s, 1H, C5H), 7.8 (s, 1H, C14H), 7.6 (d, 1H, C11H), 7.5
(d, 1H, C12H), 7.1 (s, 1H, C9H), 6.9 (d,1H, C8H), 6.75 (d,1H, C13H), 5.8-6.1 (m, 1H, C2H),
5.2 (t, 2H, C1H), 3.8 (d, 2H, C3H), 3.65 (s, 3H, C15H3).
2.4. Structure determination
Data were collected at room temperature with a Bruker APEX II CCD area-detector
diffractometer using MoKα radiation (λ = 0.71073 Å). Data collection, cell refinement, data
reduction, and absorption correction were performed using multiscan methods with Bruker
software [26]. The structures were solved by direct methods using SIR2004 [27]. The non-
hydrogen atoms were refined anisotropically by the full matrix least squares method on F2
using SHELXL [28]. All hydrogens were placed at calculated positions and constrained to
ride on their parent. The details concerning collection and analysis are presented in table 1.
3. Results and discussion
The physical and analytical data for all compounds are listed in the Experimental section.
Table 2 shows a comparison of spectral characterizations between the compounds.
H2L, 5-bromosalicylaldehyde S-allylisothiosemicarbazone hydrobromide, was synthe-
sized by S-alkylation of thiosemicarbazide with allyl bromide and then condensation of the
resulting S-allylisothiosemicarbazone hydrobromide with 5-bromosalicylaldehyde to
produce the product in good yield (scheme 1).
The complexes were formed by direct reaction of H2L, a dianionic tridentate NNO
donor, with imidazole solution (ammonia or 1-methylimidazole) and finally the corre-
sponding metal salts. The materials are stable in air. The physical and analytical results are
compatible with the empirical formulas.
3.1. Spectral studies
In order to elucidate H2L coordination to metal ions, the important bands in the IR spectra
of the ligand and its complexes are compared with each other.
In the ligand, the band at 3336 cmÀ1 can be assigned to ν(OH) [29, 30]. After complex-
ation, this band disappears, confirming that coordination takes place via phenolic oxygen
[31]. In the ligand spectrum, strong and weak peaks at 3268 and 3173 cm-1 [32] are
assigned to asymmetric and symmetric vibrations of N4H2, respectively. These peaks shift
to lower frequencies after coordination [33, 17]. A new band in the IR spectrum of the
complexes is seen at 3411 cm-1 for v(NH).
The azomethine and isothioamide combined absorption of the free ligand, ascribed to
δ(NH2) and v(N2=C4), appear at 1623 and 1542 cm-1, respectively [34].
A shoulder at 1593 cm-1 can be attributed to the aryl-C5=N1-N2- stretching vibration in
H2L [35].
The aromatic and allylic C=C absorptions generally appear at 1450–1600 cm-1 [17].
After coordination, the phenolic O–H deformation band at 1408 cm-1 is not present and the

Complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone
Table 1. Crystal, collection, and refinement data for 1-3.
349
1
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C22H26Br2Cu2N8O2S2·4H2O
C28H28Br2Cu2N10O2S2
887.62
C15H16BrMoN5O3S
522.24
856.58
293(2)
0.71073
Monoclinic
P2(1)/n
296(2)
0.71073
Monoclinic
P2(1)/n
296(2)
0.71073
Monoclinic
P2(1)/n
Space group
Unit cell dimensions
a = 10.5875(6) Å
b = 19.8013(11) Å
c = 16.7014(10) Å
β = 106.593(2)°
3355.6(3)
a = 12.1513(3) Å
b = 8.2481(2) Å
c = 17.3218(4) Å
β = 103.6770(10)°
1686.85(7)
a = 8.7847(2) Å
b = 22.4449(5) Å
c = 9.8363(2) Å
β = 102.8790(10)°
1890.65(7)
4, 1.835
Volume (Å3)
Z, Calculated
density (Mg/m3)
Abs. coeff. (mm-1)
F(000)
4, 1.696
2, 1.748
3.820
1716
3.797
884
2.943
1032
Crystal size (mm)
Theta range for data
collection
0.26 Â 0.14 Â 0.10
0.22 Â 0.12 Â 0.07
0.23 Â 0.08 Â 0.05
1.64 to 25.00°
2.33 to 27.53°
2.81 to 27.00°
Limiting indices
À9<=h<=12,
À23<=k<=23,À19<=l<=19
25,505 / 5896 [R(int) =
0.0446]
À15<=h<=15,
À10<=k<=10,À22<=l<=22
21,508 / 3881 [R(int) =
0.0337]
À11<=h<=11,
À28<=k<=28,À10<=l<=12
44,309 / 4125 [R(int) =
0.0452]
Reflections
collected/unique
Comp. to
99.8%
99.8%
99.9%
theta = 27.53
Refinement method
Full-matrix least-squares on Full-matrix least-squares on Full-matrix least-squares on
F2
F2
F2
Data/restraints/
parameters
5896/2/413
3881/1/212
4125/1/240
Goodness-of-fit on
1.019
1.062
1.042
F2
Final R indices
[I > 2sigma(I)]
R indices (all data)
R1 = 0.0453, wR2 = 0.1142
R1 = 0.0785, wR2 = 0.1333
R1 = 0.0304, wR2 = 0.0762
R1 = 0.0436, wR2 = 0.0849
R1 = 0.0292, wR2 = 0.0641
R1 = 0.0461, wR2 = 0.0704
phenolic C-O band at 1235 cm-1 in the free ligand shifts to lower frequency in the metal-
ion complexes [35]. These are strong evidence for ligand coordination to the metal ions
via phenolic oxygen. The v(N–N) vibration at 1097 cm-1 in the ligand spectrum is shifted
to higher and lower frequency in Cu- and Mo-complexes, respectively.
1H NMR spectra of the ligand and Mo-complex in DMSO-d6 show narrow signals. The
ligand can show syn/anti and cis/trans isomers, resulting from different arrangements of
1
various groups around the C=N double bond [36]. H NMR spectra can be used to investi-
gate and identify the intermolecular interactions in isothiosemicarbazones including O–
H∙∙∙N1 and N1∙∙∙N4–H, syn/anti isomer around C=N1 bond and cis/trans isomer around
N2=C [37,38].
The ligand spectrum shows singlets at δ 11.4 and 10.8 ppm, attributed to OH. The exis-
tence of these two different signals confirms the presence of syn/anti isomers in solution
[37,39]. The ratio of 26 : 74 in the 1H NMR data demonstrates the ratio of syn/anti
isomers. The more downfield OH signals may be due to hydrogen bonding interactions
and loss of electron density. The OH bands disappear in the Mo-complex spectrum indicat-
ing that ligand deprotonation resulted from metal chelation.
H2L shows a sharp singlet with an integration of two at δ 9.8 ppm, which is ascribed to
the isothioamidic NH2 protons [37]. This singlet shows cis and trans tautomers in solution
[40]. This proton is shifted to upfield after H2L coordination by 0.4 ppm revealing that the

350
R. Takjoo et al.

Complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone
351
Table 3. Selected bond lengths (Å) and angles (°) for 1-3 with esd’s in parentheses.
Distances (Å)
Angles (°)
1
Cu1-N1
Cu1-N3
Cu1-N4
Cu1-O1
C7-N1
N1-N2
N2-C4
C4-N3
C4-S2
2
1.948(5)
1.935(4)
1.998(5)
1.922(3)
1.280(8)
1.382(5)
1.322(8)
1.292(7)
1.776(5)
N1-Cu1-N3
N3-Cu1-N4
N4-Cu1-O1
O1-Cu1-N1
C5-N1-N2
N1-N2-C4
N2-C4-S1
N2-C4-N3
S1-C4-N3
80.0(2)
95.3(2)
91.4(2)
93.3(2)
117.8(5)
108.9(5)
110.8(4)
123.5(5)
125.5(4)
Cu1-N1
Cu1-N3
Cu1-N4
Cu1-O1
C5-N1
N1-N2
N2-C4
C4-N3
C4-S1
3
1.954(2)
1.951(2)
1.975(2)
1.913(2)
1.280(3)
1.392(3)
1.315(3)
1.322(3)
1.770(2)
N1-Cu1-N3
N3-Cu1-N4
N4-Cu1-O1
O1-Cu1-N1
C5-N1-N2
N1-N2-C4
N2-C4-S1
N2-C4-N3
S1-C4-N3
80.50(8)
97.63(9)
90.48(8)
91.40(8)
117.1(2)
109.6(2)
111.0(2)
123.5(2)
125.5(2)
Mo1-N4
Mo1-O2
Mo1-O3
Mo1-O1
Mo1-N1
Mo1-N3
C5-N1
N1-N2
N2-C4
C4-N3
C4-S1
2.391(3)
1.712(2)
1.697(2)
1.943(2)
2.254(2)
2.030(3)
1.280(4)
1.399(4)
1.301(4)
1.345(4)
1.753(3)
O3-Mo1-N4
N1-Mo1-N4
N3-Mo1-N4
O2-Mo1-N4
O1-Mo1-N4
O1-Mo1-N3
N1-Mo1-O2
O3-Mo1-O1
O3-Mo1-N1
O3-Mo1-N3
O3-Mo1-O2
167.1(1)
77.92(9)
81.1(1)
86.5(1)
77.20(9)
148.3(1)
160.3(1)
96.6(1)
90.2(1)
99.7(1)
106.2(1)
Figure 1. ORTEP drawing with atom numbering of one of the two crystallographically independent units of 1.
Displacement ellipsoids are drawn at 30% probability level and hydrogens are shown as small spheres of arbitrary
radii. The water molecules are not shown for clarity.

352
R. Takjoo et al.
Figure 2. ORTEP drawing of 2 with atom numbering. Displacement ellipsoids are drawn at 50% probability
level and hydrogens are shown as small spheres of arbitrary radii.
ligand binds to the metal ion via the isothioamidic nitrogen. Signals at δ 8.7 and 8.5 ppm
are attributed to the azomethine in the ligand and Mo(VI)-complex spectra, respectively.
The upfield shift from δ 8.7 ppm to 8.5 ppm confirms coordination through the azomethine
nitrogen [41]. The protons of the phenyl ring are not chemically and magnetically equiva-
lent, and have three different signals at δ 6.9, 7.5, and 8.2 ppm, corresponding to C8H,
C9H, and C11H, respectively [42]. The C1H proton is found at δ 5.3 and 5.2 ppm as a trip-
let in the ligand and complex, respectively. In H2L and the molybdenum complex, the sig-
nals at δ 5.7–6.1 and 3.8–4.1 ppm are assigned to C2H and C3H protons, respectively [34].
The electronic spectrum of H2L in DMF indicates four bands at 260–380 nm. The first
two bands at 266 and 304 nm are attributed to π→π⁄ transitions of the aromatic rings, and
azomethinic and isothioamidic moieties, respectively [43]. The two other bands at 314 and
346 nm have been assigned to n→π⁄ transitions of azomethinic and isothioamidic moieties,
respectively [44, 45]. After H2L coordination, a blue shift occurred for the π→π⁄ transi-
tions; however, it could not be detected in DMF solution due to a shift to lower wave-
lengths. On the other hand, the n→π⁄ transitions are shifted to lower energy. The reason
for these changes is related to electron density variation after coordination. In other words,
despite n orbitals, the π orbitals are more stable after complexation.
Spectra of the complexes show LMCT charge transfer bands at 348–438 nm. Three tran-
2
2
2
sitions as B1g→2B2g, B1g→2A1g, and B1g→2Eg are expected for a square planar geome-
try of copper complexes [30]. However, due to extension of charge transfer transition to
low-energy visible region, only one transition can be seen at 584 nm for 2. The lack of
electrons in the 4d electronic configuration of Mo(VI) leads to absence of d–d transitions
in the visible region.
3.2. Thermal studies
The TGA curve of the powder of 1 in air shows four steps on the DrTGA curve at 20–
270 °C, 280–550 °C, 550–690 °C, and 660–700 °C. In the first stage, waters are eliminated
with a weight loss of 15.4% (Calcd 15.5%). The second stage of thermal decomposition is

Complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone
353
attributed to removal of ammonia with a weight loss of 3.7% (Calcd 3.66%). The complex
loses 45.74% (Calcd 45.62%) of weight with the removal of the remaining organic part in
the third step. Finally, the CuO remains after 79.89% (Calcd 80.14%) weight loss of the
initial material.
For 2, three stages are detected at 160–230 °C, 260–385 °C, and 495–685 °C. The first
peak in the thermogram, having a maximum at 200 °C, shows a weight loss of 18.10%
(Calcd 18.0%) due to loss of Br. In the second step, allyl is removed with weight loss of
9.30% (Calcd 9.25%). The major mass decrease occurs at 520–569 °C which is related to
decomposition of 2 to CuO with a weight loss of 18.11% (Calcd 17.91%).
The TG/DTG curve of 3 exhibits four decomposition steps at 160–230 °C, 310–390 °C,
435–565 °C, and 670–760 °C. At 160–230 °C (maximum 212 °C), the elimination of Br
occurs with a 14.82% (Calcd 15.32%) weight loss. The allyl fragment is removed in the
second step (8.0% weight loss (Calcd 7.86%)). In the third step, the residue shows about
56.11% (Calcd 58.46%) weight loss due to decomposition of the remaining organic part;
and finally, the conversion to MoO2 at 520–695 °C is confirmed by the last TGA peak.
The decomposition products of 2 and 3 are similar – Br, allyl moiety, and finally metal
oxide. However, for 1, water, ammonia, and CuO are products of the thermal degradation
process.
3.3. Structure of the complexes
Data summary of crystallographic parameters are given in table 1. Relevant bond lengths
and angles are given in table 3. The thermal ellipsoid ORTEP images of the complexes
with their atom numbers are shown in figures 1–3.
The ligand is a tridentate dianionic ONN donor, using a phenolic oxygen, azomethine
nitrogen, and deprotonated isothioamide nitrogen, coordinated to metal by forming stable
five- and six-membered rings. As ONN donors are situated on the same side, the ligand
Figure 3. ORTEP drawing of 3 with atom numbering. Displacement ellipsoids are drawn at 50% probability
level and hydrogens are shown as small spheres of arbitrary radii.

354
R. Takjoo et al.
shows syn and trans configuration about C4–N2 and C5–N1, respectively. Decrease in the
thioamide C4=N3 bond length in the complexes compared to free isothiosemicarbazone
shows that deprotonation occurs through H2L coordination via the isothioamide nitrogen.
In the complexes, azomethine C5=N1 bonds are equal and C4=N3 and N1–N2 bond
lengths increase. The C–S and N–N bond distances are similar to and smaller than those
of their analogous isothiosemicarbazone complexes, respectively [3].
Complexes 1 and 2 adopt distorted square-planar geometries surrounded by an N-donor
ligand and the dianionic tridentate L2- which coordinates through its [ONN] donor set; for
the molybdenum bis-oxo complex (3), L2À, two oxo, and 1-methylimidazole are coordinated
in a distorted octahedron. Deviation of the copper(II) complexes from square planar (the
N1N3N4O1 plane) is negligible. In 1, the asymmetric unit contains two neutral complexes
and four waters. There are four hydrogen bonds, N2∙∙∙Hw3–Ow2 (2.769(6) Å), N2A∙∙∙Hw2–
Ow3 (2.833(7) Å), O1∙∙∙Hw4–Ow2 (2.720(6) Å), and O1A∙∙∙Hw1–Ow3 (2.839(6) Å), for
Figure 4. The N5–H…N2 (2.799(3) Å) hydrogen bonding expands the network along the bisector angle of bc
plane as 1-D in 2.
Figure 5. A view of the dimer of 3 with R22(8) graph-set motifs. Note: Hydrogen bonds are shown as dashed
lines.

Complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone
Table 4. Details of hydrogen bonding.
355
Compounds
d(D–H)
d(D...A)
D–H...A
\(DHA)
1
OW2–HW3...N1
OW2–HW3...N2
OW3–HW2...N2A
OW3–HW2...N1A
C9–H9B...OW1
N3–H3...OW1
N4–H4A...OW1
N4A–H4A2...S2
C7–H6...OW
OW2–HW4...O1
OW3–HW1...O1A
C7A–H20...OW
N4A–H4A1...Br1A
N5–H...N1
N5–H...N2
C3–H3B...O1
C11–H11...O3
C9–H9...O3
C15–H15B...N2
N3–H...O2
0.870(.064)
0.870(.064)
0.882(.033)
0.882(.033)
0.970(.009)
0.860(.005)
0.890(.005)
0.890(.005)
0.930(.005)
1.024(.076)
0.889(.087)
0.930(.006)
0.890(.005)
0.860(.002)
0.860(.002)
0.970(.003)
0.930(.003)
0.930(.003)
0.960(.004)
0.866(.027)
3.764(.006)
2.769(.006)
2.834(.007)
3.796(.006)
3.665(.020)
3.125(.019)
3.325(.019)
3.611(.005)
3.729(.008)
2.720(.006)
2.839(.006)
3.710(.009)
3.838(.005)
3.778(.003)
2.799(.003)
3.485(.004)
3.708(.004)
3.713(.004)
3.759(.005)
2.951(.003)
2.948(.062)
1.906(.065)
1.957(.031)
2.988(.028)
2.779(.017)
2.328(.019)
2.493(.019)
2.759(.002)
2.803(.006)
1.752(.075)
1.977(.092)
2.875(.007)
2.998(.001)
2.940(.002)
1.950(.002)
2.531(.002)
2.803(.003)
2.857(.003)
2.856(.002)
2.093(.028)
157.01(5.83)
171.25(6.52)
172.69(2.58)
153.21(2.22)
152.16(0.64)
154.32(0.46)
155.87(0.51)
160.72(0.29)
174.44(0.35)
156.21(6.49)
163.05(8.60)
150.17(0.37)
158.08(0.31)
165.19(0.14)
168.88(0.15)
167.70(0.18)
164.74(0.19)
153.49(0.20)
157.23(0.24)
170.41(2.66)
2
3
two molecules in the asymmetric unit, playing an important role in lattice expansion. In 2,
the asymmetric unit contains a neutral molecule. The N5–H…N2 (2.799(3) Å) hydrogen
bond expands the network along the bisector angle of the bc plane in 1-D (figure 4).
A Schiff base (NNO donor), two oxo, and a 1-methylimidazole occupy six sites of
metal coordination in 3. The angles and distances of cis-MoO2 unit are 106.2(1)°, 1.697
(2) Å, and 1.712(2) Å, respectively, which fall within the range of other complexes
[46–48]. The N3 proton of coordinated isothioamide participates in a hydrogen bond
2
(2.951(4) Å) and forms a dimer with R2 (8) graph set (figure 5). Hydrogen bond distances
and angles for all complexes are given in table 4.
4. Conclusion
We synthesized 5-bromo-2-hydroxybenzaldehyde S-allylisothiosemicarbazone hydrobro-
mide (H2L) as a tridentate NNO chelating agent. Neutral CuLIm, CuLNH3·4H2O, and
MoO2L(1-MeIm) complexes were obtained by ligand reactions with an appropriate metal
salt and imidazole (Im), NH3 or 1-methylimidazole (1-MeIm). The compounds were fully
1
characterized by elemental analyses, FT-IR, H NMR, UV-Vis, TGA, and X-ray diffraction
methods. The results show distorted square planar and octahedral geometry for copper and
molybdenum complexes, respectively. H2L is coordinated via phenolic hydroxyl, azome-
thine nitrogen, and nitrogen of isothioamide, forming six- and five-membered metallocy-
cles. The thermogravimetric analyses showed that the complexes decompose via partial
loss of the organic moiety, and finally the relevant metal oxides remained.
Supplementary material
Crystallographic data for the structures reported in this article have been deposited with
the Cambridge Crystallographic Data Center as supplementary publication Nos. CCDC

356
R. Takjoo et al.
1
871107-871109 for 1-3. TGA thermogram, FT-IR, H NMR, and UV-Vis spectra of the
compounds are presented in supplementary materials.
Acknowledgements
Reza Takjoo would like to thank the Ferdowsi University of Mashhad for supporting this
work. We thank the Università di Messina (Italy) for the provision of a diffractometer.
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