Synthesis of five new molybdenum(VI) thiosemicarbazonato complexes. Crystal structures of salicylaldehyde and 3-methoxy-salicylaldehyde 4-methylthiosemicarbazones and their molybdenum(VI) complexes

Article abstract of DOI:10.1016/j.poly.2005.05.002

Polynuclear [MoO₂{SalTSC-4-Me}]_n (I), [MoO ₂{VanTSC-4-Me}]_n (II) and mononuclear [MoO ₂{SalTSC-4-Me}(CH₃OH)] (1a), [MoO₂{VanTSC-4-Me} (CH₃OH)] (2a) and [MoO₂

Full text of DOI:10.1016/j.poly.2005.05.002

Polyhedron 24 (2005) 1717–1726
www.elsevier.com/locate/poly
Synthesis of five new molybdenum(VI)
thiosemicarbazonato complexes. Crystal structures of
salicylaldehyde and 3-methoxy-salicylaldehyde
4-methylthiosemicarbazones and their molybdenum(VI) complexes
a
a,
a
Visnja Vrdoljak , Marina Cindric , Dalibor Milic , Dubravka Matkovic-Calogovic ,
a
ˇ
*
ˇ
´
Predrag Novak , Boris Kamenar
´
´
´
b
a
a
Laboratory of General and Inorganic Chemistry, Chemistry Department, Faculty of Science, University of Zagreb, Ulica kralja Zvonimira 8,
10000 Zagreb, Croatia
b
Laboratory of Analytical Chemistry, Chemistry Department, Faculty of Science, University of Zagreb, Strossmyerov trg 14, 10000 Zagreb, Croatia
Received 24 February 2005; accepted 11 May 2005
Available online 20 June 2005
Abstract
Polynuclear [MoO2{SalTSC-4-Me}]n (I), [MoO2{VanTSC-4-Me}]n (II) and mononuclear [MoO2{SalTSC-4-Me}(CH3OH)] (1a),
[MoO2{VanTSC-4-Me}(CH3OH)] (2a) and [MoO2{VanTSC-4-Me}(H2O)] Æ CH3CN (2b) complexes have been prepared by the
reaction of the [MoO2(acac)2] (acetylacetonate ligand, acacÀ, C5H7O2À) with 1 (salicylaldehyde 4-methylthiosemicarbazone ligand,
C6H4(OH)CH:NNC(SH)NHCH3H2SalTSC-4-Me) or 2 (3-methoxy-salicylaldehyde 4-methylthiosemicarbazone, CH3OC6H3(OH)-
CH:NNC(SH)NHCH3, H2VanTSC-4-Me) in acetonitrile or in dry methanol. All complexes have been characterized by means of
chemical analyses, thermogravimetric analyses, IR spectroscopy and some of them by 1H, 13C NMR spectroscopy and X-ray crys-
tallography. In all mononuclear complexes molybdenum atom is coordinated by two terminal oxo-oxygen atoms, by ONS atoms
from the ligand molecule and by an oxygen atom from methanol (in 1a and 2a) or water (in 2b) molecules. Ligands 1 and 2 have
been characterized by means of 1H, 13C NMR spectroscopy and X-ray crystallography. Molecules of both ligands are found to be in
the thioketo tautomeric form.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Molybdenum(VI) complexes; Thiosemicarbazones; Mononuclear and polynuclear complexes; Tridentate ligands; Crystal structures
1. Introduction
Our interest in studies of molybdenum(VI) com-
plexes containing ligands with oxygen, nitrogen and
sulfur donor atoms arises from their significant anti-
fungal, antiprotozoal, antibacterial and anticancer
activity [1,2]. Similarly, the thiosemicarbazone ligands
and related metal complexes have experienced long
standing applications in biology and medicine [3,4] as
well as in the catalysis of chemical and petrochemical
processes [5,6]. The thiosemicarbazones and their com-
plexes showed lower antibacterial activity than thiose-
micarbazides [7]. This may be correlated with the
In this paper we present a study of five new molybde-
num(VI) complexes in which molybdenum atoms are
coordinated by salicylaldehyde and 3-methoxysalicylal-
dehyde 4-methylthiosemicarbazones as ONS ligands.
The structure of both ligands as well as of three com-
plexes have been characterized by X-ray crystallography.
*
Corresponding author. Tel.: +385 1 460 6653; fax: +385 1 461 1191.
´
E-mail address: marina@chem.pmf.hr (M. Cindric).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.05.002

1718
V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
trile (40 cm3) was refluxed for 6 h for I and 20 h for II,
S
C
respectively. The brown products I or II were deposited
during refluxing of the reaction mixture and filtered off.
The orange crystals 2b were obtained from the filtrate
when it was left at room temperature for two weeks.
(I) Yield: 0.23 g, 74.58%. Anal. Calc. for C9H9Mo-
N3O3S: C, 32.3; H, 2.7; Mo, 28.6; N, 12.5; S, 9.6. Found:
C, 32.0; H, 2.6; Mo, 28.4; N, 12.4; S, 9.8%.
IR (cmÀ1): 3428(s), 1606(s), 1595(m), 1560(s), 1541(s),
1498(s), 920(vs), 843(s), 806(vs), 765(vs).
(II) Yield: 0.20 g, 59.5%. Anal. Calc. for C10H11Mo-
N3O4S: C, 42.7; H, 2.7; Mo, 26.3; N, 11.5; S, 8.8. Found:
C, 42.6; H, 2.6; Mo, 26.4; N, 11.4; S, 8.6%.
IR (cmÀ1): 3409(s), 3342(m), 3309(m), 1568(s),
1545(s), 1273(vs), 923(s), 808(vs).
N
NH
keto (thione) form A
CH
OH
HR
N
SH
C
CH
OH
N
N
NHR
enol (thiol) form B
Scheme 1.
(2b) Yield: 0.01 g, 2.7%. Anal. Calc. for C12H16Mo-
N4O5S: C, 42.4; H, 3.6; Mo, 22.6; N, 13.2; S, 7.6. Found:
C, 42.1; H, 3.5; Mo, 22.8; N, 13.1; S, 7.6%.
decrease of negative charge at the substituted N hydra-
zinic atom [8].
The thiosemicarbazone ligands can act as tridentate
ligands (A form) being coordinated through the depro-
tonated phenolic O, imino N and thiocarbonyl S, or as
doubly negatively charged tridentate ligands by losing
another proton from the tautomeric mercapto group
(B form) (Scheme 1) [8].
The biological activity, particularly antitumour activ-
ity of this class of compounds is most probably associ-
ated with their structures [9–11] as it was found for
thiosemicarbazone copper(II) complexes.
IR (cmÀ1): 3376(s), 1593(s), 1565(s), 1525(s), 1412(s),
1259(s), 933(s), 891(vs).
The methanolic solution (15 cm3) of I (0.10 g) or II
(0.10 g) was refluxed for 4 h and was then evaporated
to one-third of its volume. Upon standing at room tem-
perature for few days the orange crystals of 1a (or 2a)
were obtained and filtered off.
(1a) Yield: 0.08 g, 23.7%. Anal. Calc. for C10H12Mo-
N3O4S: C, 32.7; H, 3.3; Mo, 26.1; N, 11.4; S, 8.7. Found:
C, 32.8; H, 3.5; Mo, 26.0; N, 11.2; S, 9.0%.
IR (cmÀ1): 3315(m), 1606(s), 1559(s), 1526(s), 1412(s),
1288(s), 1013(vs), 932(s), 890(vs), 758(vs).
2. Experimental
(2a) Yield: 0.05 g, 13.8%. Anal. Calc. for C11H15Mo-
N3O5S: C, 42.3; H, 3.6; Mo, 24.2; N, 10.6; S, 8.1. Found:
C, 42.5; H, 3.5; Mo, 24.5; N, 10.4; S, 8.4%.
The starting complex [MoO2(acac)2] [12], salicylalde-
hyde and 3-methoxysalicylaldehyde 4-methylthiosemic-
arbazone were prepared as described in the literature
[7]. Acetonitrile was of reagent grade and used as pur-
chased. Methanol was dried over magnesium ethoxide.
C, H and N analyses were provided by the Analytical
IR (cmÀ1): 3332(s), 1602(s), 1568(s), 1538(vs),
1467(s), 1438(s), 1293(s), 1258(vs), 934(vs), 889(vs).
2.2. X-ray crystallography
ˇ
´
Services Laboratory of Rudjer Boskovic Institute,
Zagreb. Molybdenum was determined according to the
already known method [13]. Infrared spectra were re-
corded in KBr with an FTIR 1600 Fourier transform
spectrophotometer in the 4500–450 cmÀ1 region. Ther-
mogravimetric analyses were measured on a Mettler
TG 50 thermobalance using aluminum crucibles under
Diffraction intensity data for 1, 1a, 2, 2a and 2b were
collected by x-scans on Oxford Diffraction Xcalibur
CCD diffractometer with graphite-monochromated Mo
˚
Ka radiation (k = 0.71073 A) and reduced using the
CRYSALIS software package [14]. Crystal data, experimen-
tal conditions and final refinement parameters are sum-
marized in Table 1. The structures were solved using
SHELXS97 [15]: the structures of ligands 1 and 2 by direct
methods, and the structures of complexes 1a, 2a and 2b
by the Patterson method. The refinement procedure by
the full-matrix least-squares method based on F2 against
all reflections included anisotropic displacement param-
eters for all non-hydrogen atoms. All hydrogen atoms
were located in the difference Fourier maps. Those with
poor geometry were then refined with restraints. Hydro-
gen atoms in 1 and 2 were refined isotropically except
the methyl H atoms in both structures for which only
the torsion angles and grouped isotropic temperature
oxygen atmosphere with a heating rate of 5 ꢁC minÀ1
.
For all experiments the temperature ranged from 25 to
600 ꢁC. The results were developed by applying the
Mettler STARe 6.1. programme.
2.1. Syntheses of molybdenum(VI) complexes: I, II, 1a,
2a, 2b
A mixture of [MoO2(C5H7O2)2] (0.30 g, 0.92 mmol)
and salicylaldehyde 4-methylthiosemicarbazone (0.19 g,
0.92 mmol) for I (or 3-methoxysalicylaldehyde 4-methyl-
thiosemicarbazone 0.22 g, 0.92 mmol for II) in acetoni-

Table 1
Crystallographic data for compounds 1, 1a, 2, 2a and 2b
Compound
1
1a
2
2a
2b
Chemical formula
Mr
C9H11N3OS
209.27
[MoO2(C9H9N3OS)(CH3OH)]
367.23
C10H13N3O2S
239.29
[MoO2(C10H11N3O2S)(CH3OH)]
397.26
[MoO2(C10H11N3O2S)(H2O)] Æ CH3CN
424.29
Crystal colour, habit
Crystal size (mm)
Crystal system
Space group
colourless, plate
0.12 · 0.77 · 0.84
triclinic
orange, needle
0.06 · 0.07 · 0.59
orthorhombic
Pna21
colourless, needle
0.05 · 0.09 · 0.34
monoclinic
P21/c
orange, needle
0.10 · 0.18 · 0.68
monoclinic
orange-red, prismatic
0.15 · 0.18 · 0.42
monoclinic
ꢀ
P1
P21/n
P21/c
Unit cell dimensions
˚
a (A)
˚
6.0270(10)
8.5276(11)
10.4743(13)
75.724(11)
75.802(13)
82.155(12)
504.12(13)
2
20.635(3)
7.1710(10)
11.699(2)
6.0149(10)
16.048(3)
90
21.2125(10)
6.9469(4)
7.4539(5)
16.4922(12)
b (A)
˚
c (A)
17.832(2)
90
21.2189(13)
90
13.2293(10)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
102.234(18)
90
108.105(5)
90
2972.0(3)
104.995(6)
90
1570.9(2)
3
˚
V (A )
2638.7(6)
8
295(2)
1103.6(3)
4
Z
T (K)
8
100(1)
4
100(1)
295(2)
1.379
0.291
100(1)
1.440
0.282
Dcalc (g cmÀ3
)
1.849
1.165
1.776
1.047
1.794
0.998
l(Mo Ka) (mmÀ1
Absorption correction
Tmin
)
multi-scan
0.778
0.966
analytical
0.685
none
analytical
0.622
analytical
0.739
Tmax
0.947
1472
0.899
1600
0.883
856
F(0 0 0)
Total data
220
6721
504
12946
27744
7029
49514
8632
13686
4326
Unique data
Rint
2775
0.0281
3217
0.0576
0.0422
0.0521
0.0219
0.0153
0.0157
0.0128
Rr
Observed data [I > 2r(I)]
hmax (ꢁ)
Ranges of h, k, l
0.0206
2455
0.0528
2250
5283
30.00
7862
30.00
4040
29.99
30.07
À5, 8; À12, 12; À14, 14
160
30.06
À16, 16; À7, 8; À22, 22
À29, 29; À9, 10; À25, 25
À29, 29; À8, 9; À29, 29
À10, 10; À23, 23; À18, 17
Number of parameters
Flackꢀs parameter x
348
175
393
227
0.48(3)
0.0371
0.0700
0.951
0.56
R1
wR2
S
0.0419
0.1203
1.053
0.26
0.0622
0.1688
1.009
0.68
0.0322
0.0741
1.158
1.51
0.0209
0.0527
1.087
0.51
À3
˚
Dqmax (e AÀ3
)
˚
Dqmin (e A
)
À0.38
À0.40
À0.38
À0.58
À0.63

1720
V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
factor were refined while the geometry was kept fixed. In
the structures of the complexes, only H atoms refined
isotropically were H atoms bound to the oxygen atoms
in 2a, and H atoms attached to C1 and to the heteroa-
toms in 2b, while the other H atoms were refined using
the riding model. The structure of 1a was refined as
twinned and consisted of two components with opposite
polarities. The final BASF coefficient (Flackꢀs parameter
x) for 1a was 0.48(3) [16,17]. Refinement was performed
using SHELXL97 [18], geometry calculations were done
using PLATON [19,20] and PARST [21,22], and the structure
drawings were prepared using ORTEP [23].
respectively. Digital resolution was 0.12 and 0.48 Hz
per point, respectively. The number of scans was 16
1
for H and 500–1000 for APT spectra.
The COSY spectra were recorded under the following
conditions: spectral width was 7700 Hz in both dimen-
sions, 2K data points were applied in time domain and
512 increments were collected for each data set with lin-
ear prediction and zero filling to 2K. 8 scans were applied
for each increment. Digital resolution was 6.50 Hz per
point in both dimensions. The gradient selected inverse
1H–13C correlation experiments, gHSQC and gHMBC
were recorded using the acquisition matrix of 1K · 256
with 16 and 32 scans, respectively, and processed with
2K · 1K transformed matrix. The spectral width was
6600 Hz in f2 dimension and 32 000 Hz in f1 dimension
for both experiments. Digital resolution was 3.25 Hz per
point and 30.70 Hz per point in f2 and f1, respectively.
HMBC spectra were recorded using a low-pass J-filter
(3.4 s) and a delay for long-range coupling of 65 ms.
2.3. NMR spectroscopy
All one- (1H and APT), and gradient-selected two-
dimensional (gCOSY, gHSQC and gHMBC) NMR
spectra were recorded at ambient temperature on a Bru-
ker Avance DRX500 and Bruker Avance DPX 300 spec-
trometers equipped with 5 mm inverse detection probe
and dual probe, respectively. Sample concentration in
DMSO-d6 was 20 mg mlÀ1. TMS was used as the inter-
nal standard.
3. Results and discussion
The typical spectral conditions for one-dimensional
1H and 13C (APT) spectra were as follows. The spectra
were recorded using 64K data points and spectral widths
of 7700 and 32 000 Hz for 1H and 13C experiments,
3.1. Synthesis of the complexes
As a part of our studies [24–26] on molybdenum
complexes with oxygen, sulfur and/or nitrogen donor
[MoO2{C6H4(O)CH:NNC(S)NHCH3}(CH3OH)]
(1a)
CH3OH
[MoO2{C6H4(O)CH:NNC(S)NHCH3}]n
(I)
(1)
CH3CN
[MoO2(C5H7O2)2]
CH3CN
(2)
[MoO2{CH3OC6H3(O)CH:NNC(S)NHCH3}]n
(II)
2 weeks
CH3OH
.
[MoO2{CH3OC6H3(O)CH:NNC(S)NHCH3}(H2O)] CH3CN
(2b)
[MoO2{CH3OC6H3(O)CH:NNC(S)NHCH3}(CH3OH)]
(2a)
(1)
(2)
C6H4(OH)CH:NNC(SH)NHCH3
H2SalTSC-4-Me
CH3OC6H3(OH)CH:NNC(SH)NHCH3 H2VanTSC-4-Me
Scheme 2.

V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
1721
ligands we describe here the syntheses and structures
of molybdenum(VI) complexes coordinated by salicyl-
aldehyde or by 3-methoxysalicylaldehyde 4-methylthi-
osemicarbazone ligand (Scheme 2). The brown
polymeric complexes [MoO2{SalTSC-4-Me}]n (I) and
[MoO2{VanTSC-4-Me}]n (II) were obtained by the
reaction of [MoO2(C5H7O2)2] with a stoichiometric
amount of corresponding thiosemicarbazone ligand
in acetonitrile.
The monomeric complex [MoO2{VanTSC-4-Me}-
(H2O)] Æ CH3CN (2b) was obtained when the filtrate of
II was left at room temperature for two weeks. In 2b,
the molybdenum atom is additionally coordinated by a
water molecule most probably from the atmospheric
moisture and stabilized by the solvated acetonitrile mole-
cule. Also, it should be mentioned that such a product was
obtained only when the ligand was 3-methoxysalicylalde-
hyde 4-methylthiosemicarbazone. All attempts to isolate
Table 2
Selected bond distances (A), angles (ꢁ) and torsion angles (ꢁ) for 1, 1a, 2, 2a and 2b
˚
Compound
1
1a
A
2
2a
A
2b
B
B
Bond distances
O3–C6
C6–11
1.3604(17)
1.3997(18)
1.4501(18)
1.2861(16)
1.3763(16)
1.3501(16)
1.6833(13)
1.3236(17)
1.4484(18)
1.336(5)
1.410(6)
1.440(5)
1.298(5)
1.399(4)
1.319(6)
1.757(4)
1.332(5)
1.441(6)
1.686(3)
1.706(3)
1.927(3)
2.265(3)
2.4120(13)
2.399(3)
1.340(5)
1.407(6)
1.453(5)
1.292(5)
1.419(4)
1.305(5)
1.766(4)
1.335(5)
1.442(6)
1.686(3)
1.712(3)
1.934(3)
2.236(3)
2.4047(13)
2.400(3)
1.363(3)
1.395(3)
1.461(3)
1.287(3)
1.370(3)
1.363(3)
1.695(2)
1.326(3)
1.457(3)
1.341(3)
1.400(3)
1.342(3)
1.407(3)
1.3418(17)
1.4035(19)
1.4441(19)
1.2999(18)
1.3963(16)
1.3137(18)
1.7506(13)
1.3430(17)
1.4537(18)
1.6998(12)
1.7172(10)
1.9359(10)
2.2733(12)
2.4504(4)
C11–C1
C1–N1
N1–N2
1.449(3)
1.294(3)
1.449(3)
1.292(3)
1.409(2)
1.317(3)
1.410(2)
1.317(3)
N2–C3
C3–S1
1.763(2)
1.333(3)
1.453(3)
1.763(2)
1.335(3)
1.456(3)
C3–N4
N4–C5
Mo1–O1
Mo1–O2
Mo1–O3
Mo1–N1
Mo1–S1
Mo1–O4
1.7000(14)
1.7206(16)
1.9322(14)
2.2558(18)
2.4226(5)
2.3594(15)
1.7002(15)
1.7188(14)
1.9332(16)
2.2554(16)
2.4206(5)
2.3792(15)
2.3081(12)
Bond angles
N1–C1–C11
N2–N1–C1
N1–N2–C3
N2–C3–N4
S1–C3–N2
122.60(11)
114.94(11)
121.89(11)
117.46(12)
118.54(10)
124.00(10)
123.87(12)
126.2(3)
115.0(3)
124.8(3)
113.8(3)
120.8(2)
125.0(2)
125.38(19)
114.03(16)
111.99(16)
120.65(19)
124.16(16)
115.16(16)
122.67(18)
96.45(6)
126.79(12)
112.95(11)
114.24(11)
118.86(12)
125.37(10)
115.78(10)
122.85(12)
96.19(4)
115.07(19)
120.36(19)
116.1(2)
113.88(17)
112.34(17)
120.5(2)
111.8(3)
120.5(4)
111.4(3)
121.3(4)
124.6(3)
114.8(4)
124.4(4)
124.3(3)
114.4(3)
124.1(4)
119.29(17)
124.65(18)
124.0(2)
124.18(16)
115.29(16)
123.22(19)
96.26(6)
S1–C3–N4
C3–N4–C5
S1–Mo1–O1
S1–Mo1–O2
S1–Mo1–O3
S1–Mo1–O4
S1–Mo1–N1
O1–Mo1–O2
O1–Mo1–O3
O1–Mo1–O4
O1–Mo1–N1
O2–Mo1–O3
O2–Mo1–O4
O2–Mo1–N1
O3–Mo1–O4
O3–Mo1–N1
O4–Mo1–N1
96.54(11)
90.33(12)
153.37(9)
83.54(8)
96.68(11)
90.02(12)
153.13(9)
83.25(8)
91.05(5)
91.40(6)
91.33(4)
153.82(5)
84.16(4)
74.90(5)
153.33(4)
84.04(4)
74.69(5)
154.71(3)
81.38(3)
75.84(3)
74.71(8)
74.78(9)
105.43(16)
98.95(13)
172.34(13)
95.51(13)
106.12(14)
82.23(14)
155.60(14)
78.27(11)
82.32(11)
77.09(10)
105.73(16)
99.18(14)
170.78(13)
94.13(13)
106.23(14)
83.48(14)
156.36(14)
77.68(11)
82.54(12)
76.92(10)
104.92(7)
97.99(7)
105.04(7)
98.45(7)
105.27(5)
98.66(5)
172.31(7)
94.79(7)
172.70(6)
95.40(7)
169.91(4)
92.66(5)
106.24(7)
82.74(6)
105.81(7)
82.21(6)
104.25(4)
84.62(5)
157.02(7)
78.87(6)
82.11(6)
156.52(7)
78.46(6)
81.98(6)
159.08(5)
80.43(4)
83.11(4)
77.88(7)
77.67(7)
77.25(4)
Torsion angles
O3–C6–C11–C1
C6–C11–C1–N1
C11–C1–N1–N2
C1–N1–N2–C3
N1–N2–C3–S1
S1–C3–N4–C5
À2.53(19)
0.6(6)
À11.4(6)
176.1(3)
160.1(3)
À3.6(4)
2.3(6)
À1.2(3)
À0.4(3)
12.7(3)
0.7(3)
1.5(2)
À5.2(2)
1.4(2)
À11.2(7)
173.8(4)
158.3(4)
À3.7(5)
À177.3(2)
176.2(2)
174.3(2)
175.18(16)
1.7(3)
À12.9(3)
176.6(2)
158.0(2)
À176.74(11)
175.50(12)
À170.08(9)
2.20(19)
À176.5(2)
À159.8(2)
2.3(3)
175.53(13)
171.93(12)
4.69(18)
À2.1(3)
À176.8(3)
À176.7(3)
178.09(16)
À177.67(16)
À172.64(11)
In 1a and 2a two crystallographically independent complex molecules are labelled A and B.

1722
V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
the mononuclear molybdenum(VI) complex coordinated
by a water molecule after isolation of complex I were
unsuccessful even if some water was added to the solution.
We believe that the electronic effect of the methoxy group
attached to the phenolic ring 3-methoxysalicylaldehyde is
responsible for the formation of this aqua complex.
We were also able to isolate monomeric orange crys-
tals of [MoO2{SalTSC-4-Me}(CH3OH)] (1a) and
[MoO2{VanTSC-4-Me}(CH3OH)] (2a) from the meth-
anolic solution of I and II.
(1) loss of coordinated methanol, water or acetonitrile
within the range 92–141 ꢁC in 1a, 30–92 ꢁC in 2a;
loss of coordinated water and acetonitrile in one step
30–95 ꢁC in 2b,
(2) complex decomposition occurring within the
range 170–507 ꢁC for I, 221–514 ꢁC for II and
210–530 ꢁC for 2b.
3.2. Structural studies
The IR data for thiosemicarbazone ligands are in
accordance with the literature data [27]. The IR spectra
of the complexes I and II showed characteristic strong
vibrations at 806 and 808 cmÀ1, respectively, assigned
to the bridging Mo–OÁ Á ÁMo group which were absent
in the case of mononuclear 1a, 2a and 2b complexes.
Also I and II showed single stretching frequencies at
920 and 923 cmÀ1, respectively, assigned to m(Mo@O),
while the IR spectra of all three mononuclear complexes
with the cis-MoO2 core showed usual doublet at 933 and
891 cmÀ1 in 1a, 934 and 889 cmÀ1 in 2a and 932 and 892
cmÀ1 in 2b.
The thermal analysis data of complexes 1a and 2a
showed that their ligands decomposed in the range
224–554 ꢁC and 222–512 ꢁC, respectively, while those
of complexes 1a, 2a and 2b revealed two main
processes:
Comparison of the selected bond distances, bond an-
gles and torsion angles of the free ligands 1 and 2 and of
their complexes 1a, 2a and 2b is given in Table 2. Hydro-
gen bonding parameters are listed in Table 3.
3.2.1. Structures of ligands
Figs. 1 and 2 show ORTEP plots of the structures of the
free ligand molecules 1 and 2. Both molecules are found to
be in the thioketo tautomeric form with the distances C3–
S1 [1.6833(13) in 1 and 1.695(2) in 2] and N2–C3
[1.3501(16) in 1 and 1.363(3) in 2] similar to those found
in the analogous thiosemicarbazone compounds [8,28–
34]. The bond distances (Table 2) suggest electron delocal-
ization throughout the thiosemicarbazone chain. The
ligand molecules consist of two nearly planar moieties
connected by a single N1–N2 bond: N-methylthioureide
Table 3
Hydrogen bonding geometry in structures 1, 1a, 2, 2a and 2b
˚
d(D–H) (A)
˚
˚
D–HÁ Á ÁA
d(HÁ Á ÁA) (A)
d(DÁ Á ÁA) (A)
\(D–HÁ Á ÁA) (ꢁ)
Compound 1
N2–H2Á Á ÁO3i
O3–H3Á Á ÁN1
N4–H4Á Á ÁN1
0.83(2)
0.84(3)
0.85(2)
2.50(3)
1.92(3)
2.33(2)
3.1285(18)
2.6846(17)
2.6961(16)
133(2)
150(2)
106.5(18)
Compound 1a
N4A–H4AÁ Á ÁO2Bii
N4B–H4BÁ Á ÁO2Aiii
O4A–H41AÁ Á ÁN2B
O4B–H41BÁ Á ÁN2Aiv
0.86
0.86
0.93
0.93
2.40
2.15
1.93
2.01
3.243(5)
2.996(5)
2.819(4)
2.911(4)
166
169
159
162
Compound 2
N2–H2Á Á ÁO3v
O3–H3Á Á ÁO5
O3–H3Á Á ÁS1v
N4–H4Á Á ÁN1
0.90(4)
0.82(4)
0.82(4)
0.81(3)
2.13(3)
2.17(3)
2.50(4)
2.31(3)
2.935(3)
2.631(3)
3.1861(19)
2.639(3)
148(3)
115(3)
141(3)
105(3)
Compound 2a
N4A–H4AÁ Á ÁO2B
N4B–H4BÁ Á ÁO2Avi
O4A–H41AÁ Á ÁN2Avii
O4B–H41BÁ Á ÁN2Bviii
0.88
0.88
2.09
2.08
2.892(2)
2.924(2)
2.827(3)
2.851(2)
151
160
0.75(4)
0.76(3)
2.10(4)
2.09(3)
165(3)
174(3)
Compound 2b
N4–H4Á Á ÁO2ix
O4–H41Á Á ÁN2x
O4–H42Á Á ÁN3
0.80(2)
0.81(3)
0.80(3)
2.20(2)
1.97(3)
2.09(2)
2.9287(16)
2.7761(16)
2.8742(18)
151.2(18)
173(3)
168(2)
Symmetry codes: i = 1 + x, y, z; ii = 1Àx, 1Ày, À1/2 + z; iii = 3/2Àx, 1/2 + y, 1/2 + z; iv = x, 1 + y, z; v = 2Àx, 1Ày, 1Àz; vi = 1/2 + x, 3/2Ày, 1/2 + z;
vii = 1/2Àx, À1/2 + y, 1/2Àz; viii = 1/2Àx, À1/2 + y, 3/2Àz; ix = x, 3/2Ày, À1/2 + z; x = 1Àx, 1Ày, Àz.

V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
1723
In the crystal structure of 1 molecules are intercon-
nected by the N2–H2Á Á ÁO3 (1 + x, y, z) hydrogen bonds
thus forming chains parallel to the crystallographic a
axis. In 2 a pair of molecules related by a centre of sym-
metry dimerize by forming the N2–H2Á Á ÁO3 (2 À x,
1 À y, 1 À z) and O3–H3Á Á ÁS1 (2 À x, 1 À y, 1 À z)
hydrogen bonds. In both ligand structures there is an
intramolecular hydrogen-bond-like contact N4–
H4Á Á ÁN1.
O3
C5
C7
C6
C8
C9
N4
C3
N2
C1
N1
C11
S1
C10
3.2.2. Structures of complexes
Fig. 1. ORTEP plot of the ligand molecule 1 with the atom labelling
scheme. Ellipsoids are drawn at the 50% probability level. The O3–
H3Á Á ÁN1 hydrogen bond is denoted by dashed line.
Complex molecules found in the crystal structures of
1a and 2a are shown in Figs. 3 and 4, respectively. The
asymmetric unit of structures 1a and 2a consists of two
crystallographically independent complex molecules de-
noted as A and B. In 2b the complex molecules cocrys-
tallize with molecules of acetonitrile (Fig. 5).
The complex molecules consist of the cis-[MoO2]2+
core to which the doubly deprotonated tridentate ligand
(1 in 1a; 2 in 2a and 2b) is meridionally bonded through
the S1, N1 and O3 atoms. The sixth site of the distorted
octahedral coordination around Mo is occupied either
by methanol (in 1a and 2a) or water molecules (in 2b).
C9
C5
C8
C10
N4
S1
C7
C3
C12
C1
O5
N2
C11
N1
C6
O3
Fig. 2. ORTEP plot of the ligand molecule 2 with the atom labelling
scheme. Ellipsoids are drawn at the 50% probability level.
C5
C10
N2
C9
C7
C1
C11
O3
N4
N1
C3
fragment comprising N2, C3, S1, N4 and C5 [mean plane
C8
˚
deviation of 0.007(6) A in 1 and 0.0070(1) A in 2] and sal-
˚
O1
C6
icylaldimine fragment comprising N1, C1, C6–C11 and
˚
O3 [mean plane deviation of 0.0154(1) A in 1 and
˚
0.0160(1) A in 2]. Dihedral angles between these two
Mo1
S1
O4
planes are 12.54(3)ꢁ and 12.27(1)ꢁ for 1 and 2, respec-
tively. The atoms O5 and C12 from the methoxy group
in 2, although rather coplanar with others from the sali-
cylaldimine fragment [mean plane deviation of 0.0237(1)
O2
C13
˚
A], were excluded from the planarity calculations for
the sake of comparability.
Fig. 3. ORTEP plot of the complex molecule 1aA with the atom
labelling scheme. Ellipsoids are drawn at the 50% probability level.
The striking difference between the molecular struc-
tures of the two ligands is the orientation of the phenyl
ring moiety. In 1 the syn conformation of the C6 atom in
respect to the N1 atom [torsion angle C6–C11–C1–
N1 = 1.4(2)ꢁ] is stabilized by the intramolecular reso-
nance-assisted O3–H3Á Á ÁN1 hydrogen bond, while in 2
the atoms C6 and N1 are anti to each other [torsion an-
gle C6–C11–C1–N1 = –177.3(2)ꢁ] and O3–H3Á Á ÁO5 and
O3–H3Á Á ÁS1 (2 À x, 1 À y, 1 À z) hydrogen bonds are
formed (Table 3). This seems to confirm an already gi-
ven observation for the structures of the salicylaldehyde
thiosemicarbazone derivates [31]: the intramolecular
hydrogen bond between the hydroxyl group and the
azomethine N atom would not be formed if another po-
tential hydrogen bond acceptor for the hydroxyl H atom
is present.
C5
C10
N2
O1
C9
C1
C11
O3
N4
N1
C3
C8
C6
C7
Mo1
O5
S1
C12
O4
C13
O2
Fig. 4. ORTEP plot of the complex molecule 2aB with the atom
labelling scheme. Ellipsoids are drawn at the 50% probability level.

1724
V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
1a and 2aA], while the conformation of the 6-mem-
C5
bered ring is nearly a screw-boat with the Mo1 and
O3 atoms at the opposite sides of the mean plane of
the ring [/2 amounting to À154.0(4)ꢁ in 2aB and
24.1(4)–27.1(8)ꢁ in 1a and 2aA; h amounting to
À113.1(4)ꢁ in 2aB and 65.8(8)–66.6(8)ꢁ in 1a and
2aA] [41,42]. The 5-membered chelate ring in 2b is
C10
N2
C9
C8
C11
N4
N1
C3
C1
O1
C7
C6
S1
˚
nearly planar [mean deviation of 0.0131(9) A], but with
Mo1
O4
conformation closer to twisted than to the envelope
[/2 = 61(2)ꢁ] with C3 and S1 at the opposite sides of
the mean plane. The 6-membered chelate ring confor-
mation is almost an envelope with Mo1 being the atom
most out of the mean plane of the ring [/2 = 7.7(3)ꢁ
and h = 59.2(3)ꢁ] [41,42].
O3
O5
C12
O2
N3
Mean plane deviations for the N-methylthioureide
˚
[0.015(3) A and 0.015(4) A in 1a; 0.010(2) and
˚
C13
˚
0.012(2) A in 2a; 0.032(1) A in 2b] and the salicylaldi-
˚
˚
mine [0.026(4) A and 0.024(4) A in 1a; 0.034(2) A and
˚
˚
˚
˚
C14
0.030(2) A in 2a; 0.018(1) A in 2b] fragments (defined
above for the structures of the ligands) show that in
the molecules of the complexes these two fragments re-
tain their planarity. But, in 1a and 2a dihedral angles
between calculated RMS planes through the fragments
[34.00(10)ꢁ and 36.64(9)ꢁ in 1a; 35.05(4)ꢁ and 36.40(4)ꢁ
in 2a] are significantly different from those found in the
free ligands. Also, torsion angles C1–N1–N2–C3 differ
(Table 2), indicating rotation around the N1–N2 bond
upon ligand binding. This is accompanied by the N1–
Fig. 5. ORTEP plot of the asymmetric unit of 2b with the atom
labelling scheme. Ellipsoids are drawn at the 50% probability level. The
O4–H42Á Á ÁN3 hydrogen bond is represented by dashed line.
In all of the complex compounds, the Mo@O bond
˚
lengths [1.686(3)–1.7206(16) A] and the O@Mo@O
bond angles [104.92(7)–105.7(2)ꢁ] have values which
are usual for cis-dioxomolybenum(VI) complexes. Also,
˚
the bond distances of Mo1–S1 [2.4047(13)–2.4504(4) A],
˚
Mo1–N1 [2.236(3)–2.2733(12) A] and Mo1–O3
˚
[1.927(3)–1.9359(10) A] are similar to those found in
˚
N2 bond lengthening of ꢀ0.02–0.04 A. In 2b the dihe-
dral angle between the two fragments [10.74(4)ꢁ] and
the C1–N1–N2–C3 torsion angle are both similar to
those in 2, but the N1–N2 bond lengthening of ꢀ0.03
˚
other thiosemicarbazonato molybdenum(VI) complexes
[35–40]. The bond distances Mo1–O4 [2.359(2)–2.400(3)
A still occurs upon ligand binding.
In the crystal structure of 1a two crystallographi-
cally independent molecules are bonded into dimers
˚
˚
A in 1a and 2a; 2.308(1) A in 2b] are significantly larger
compared to the Mo1–O3.
As indicated by the bond distances N2–C3
7
8
˚
[1.305(5)–1.319(6) A] and C3–S1 [1.751(1)–1.766(4)
˚
A], the ligands in the complexes are bonded in their
9
OH
N
enthiol form, i.e., in the tautomeric form different from
that found in the structures of the free ligands (cf. in
Table 2). In both bonded ligands, the C5 atom from
the N-methyl group is trans relative to the S1 atom,
while in the free ligands it is in the cis conformation.
In order for ligands 1 and 2 to chelate the [MoO2]2+
moiety through the ONS donor set, as in the studied
complexes, rotation of ꢀ180ꢁ around the N2–C3 bond
is necessary. Additionally for 2, the phenyl ring moiety
has to flip around the C11–C1 bond (Table 2). The
5- and 6-membered chelate rings thus formed (Mo1–
N1–N2–C3–S1 and Mo1–O3–C6–C11–C1–N1) are
not planar, but are rather puckered. In 1a and 2a the
5-membered chelate ring is close to the envelope con-
formation with Mo1 being the atom most out of the
mean plane of the ring [/2 amounting to À3.5(2)ꢁ in
the complex molecule 2aB and 175.4(4)–176.8(2)ꢁ in
6
1
10
11
S
1
5
CH3
N
H
2
3
N
H
4
12
OMe
8
7
OH
9
6
2
10
11
S
N
1
N
H
2
5
CH3
3
N
H
4
Scheme 3.

V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
1725
Table 4
1H and 13C chemical shifts (ppm) of the ligands 1 and 2 and their molybdenum(VI) complexes I and II
Comp. atom
1
I
2
II
1H
13C
1H
13C
1H
13C
1H
13C
1
8.37
11.47
139.09
8.57
152.10
8.39
11.43
138.93
8.54
152.37
166.24
2
3
177.68
177.67
4
8.42
3.01
7.46
2.81
8.41
3.00
7.46
2.80
5
30.96
156.46
116.16
131.09
119.32
126.72
120.62
31.32
159.09
118.44
133.74
121.26
133.95
121.61
30.95
146.01
148.06
112.83
119.03
118.17
121.05
56.02
31.62
149.19
149.43
116.21
121.37
125.48
122.19
56.59
6
7
6.87
7.22
6.83
7.95
6.82
7.41
6.98
7.60
8
6.96
6.78
7.55
7.10
6.92
7.18
9
10
11
12
OH
3.81
9.17
3.77
9.87
by the O4A–H41AÁ Á ÁN2B hydrogen bond. Such dimers
are further connected in the infinite chain parallel to b
axis by the O4B–H41BÁ Á ÁN2A (x, 1 + y, z) hydrogen
bonds. Different chains are interlinked together by
the hydrogen bonds formed between the amino
N4–H4 and terminal oxygen O2 of the neighbouring
molecule (Table 3).
Two molecules in the asymmetric unit of 2a are con-
nected by the N4A–H4AÁ Á ÁO2B hydrogen bond. Simi-
larly to 1a, in the crystal structure of 2a, there are also
intermolecular hydrogen bonds between the amino
N4–H4 and terminal oxygen O2 of the neighbouring
molecule and between the methanol O4–H41 and the
imine N2 from the symmetry equivalent molecule.
One hydrogen atom from the coordinated water mol-
ecule in the structure of 2b participates in the hydrogen
bonding with the cocrystallized acetonitrile molecule
(Fig. 5), while the other hydrogen atom is part of the
hydrogen bond with the imine N2 atom from the mole-
cule related by an inversion centre. The centrosymmetri-
cal dimers formed in this way are further connected by
the intermolecular hydrogen bonds between the amino
N4–H4 and the terminal oxygen O2 (also observed in
1a and 2a).
OH signal was observed at 9–10 ppm indicating a partic-
ipation of this hydroxyl proton in an intramolecular
O–HÁ Á ÁN1 hydrogen bonds in DMSO, which is in line
with our previous results. Carbon chemical shifts and
HMBC correlation peaks have confirmed that both
ligands exist in the thioketo form in solution, as also
found in the solid state. The absence of OH and N2H
protons in the proton spectra of 1a and 2a corroborates
a formation of the complexes with molybdenum. An up-
field shift of N4H protons of about 1 ppm (Table 4) is in
accordance with this. Slight coordination induced down-
field shifts have also been observed for H1 protons. The
largest changes in carbon chemical shifts in 1a and 2a
have been found for carbons at the two interacting sites,
C-1 and C-3. The down-field shifts of up to 13.4 ppm for
the former and up-field shifts of approximately 11.0
ppm for the latter were observed. The shielding effects
at C-3 arised from two contributions, i.e. from a coordi-
nation induced-shift and from the formation of an imine
C@N bond in the complex instead of a thiocarbonyl
C@S bond in the ligand. The carbon atoms at the third
interacting site, e.g., C-6 exhibited only moderate chem-
ical shift changes, as already found for the related
molybdenum complexes with thiosemicarbazone
donors.
3.3. NMR spectroscopy
The complete 1H and 13C atom assignments in
DMSO-d6 were made on the basis of the combined use
of several one- (1H and APT sequences) and two-dimen-
sional homo- and heteronuclear experiments (COSY,
HSQC and HMBC sequences). The proton and carbon
chemical shifts of the ligands 1 and 2 (Scheme 3) and
complexes 1a and 2a are given in Table 4.
The observed chemical shift values are similar to
those reported previously for the related thiosemicarba-
zone ligands and their molybdenum(VI) complexes [40].
In the proton NMR spectra of the free ligands a broad
4. Supplementary material
CCDC nos. 260969, 260970, 260971, 260972 and
260973 contain the supplementary crystallographic
data for compounds 1, 1a, 2, 2a and 2b, respectively.
These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, UK, fax: +44 1223
336033.

1726
V. Vrdoljak et al. / Polyhedron 24 (2005) 1717–1726
[21] M. Nardelli, Comput. Chem. 7 (1983) 95.
Acknowledgements
[22] M. Nardelli, J. Appl. Crystallogr. 28 (1995) 659.
[23] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
´
ˇ
[24] M. Cindric, N. Strukan, T. Kajfez, G. Giester, B. Kamenar, Z.
This research was supported by the Ministry of Sci-
ence and Technology of the Republic of Croatia Grants
no. 0119631, 0119632 and 119641.
Anorg. Allg. Chem. 627 (2001) 2604.
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[25] M. Cindric, N. Strukan, V. Vrdoljak, B. Kamenar, Z. Anorg.
Allg. Chem. 630 (2004) 585.
[26] M. Cindric´, N. Strukan, T. Kajfezˇ, B. Kamenar, Struct. Chem. 13
(2002) 361.
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