Reactions of thiosemicarbazones derived from β-keto amides and β-keto esters with Zn(II) and Cd(II) acetates: Influence of metal, substitution, reagent ratio and temperature on metal-induced cyclization

Article abstract of DOI:10.1039/b401674b

Zinc(II) and cadmium(II) acetates were reacted in methanol under various experimental conditions with thiosemicarbazones derived from β-keto amides or β-keto esters (HTSC). Some of these reactions afforded thiosemicarbazonate complexes [M(TSC)₂] with IR and NMR spectra compatible with N,S-coordination, but most gave complexes [ML₂], where HL is a substituted 2,5-dihydro-S-oxo-1H-pyrazole-1-carbothioamide resulting from cyclization of the HTSC. Some of these pyrazolonates and two of the HL ligands were studied by X-ray diffractometry, and their structures are discussed. Surprisingly, the reactions of zinc(II) acetate with HTSC in 1 : 1 mol ratio usually gave a third, previously unreported type of complex with a dideprotonated ligand, [Zn(L - H)], which was also formed when [ZnL₂] and Zn(OAc)₂ interacted at room temperature in 1 : 1 mol ratio. These L - H complexes are highly insoluble in all common solvents, which hinders their characterization but suggests that they are polymeric in nature.

Full text of DOI:10.1039/b401674b

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Reactions of thiosemicarbazones derived from ꢀ-keto amides and
ꢀ-keto esters with Zn(II) and Cd(II) acetates: influence of metal,
substitution, reagent ratio and temperature on metal-induced
cyclization†
José S. Casas,a María V. Castaño,*a María S. García-Tasende,*a
Enrique Rodríguez-Castellón,b Agustín Sánchez,a Luisa M. Sanjuána and José Sordoa
a Departamento de Química Inorgánica, Facultade de Farmacia,
Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain
b Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Málaga,
E-29071 Málaga, Spain
Received 4th February 2004, Accepted 22nd April 2004
First published as an Advance Article on the web 4th May 2004
Zinc() and cadmium() acetates were reacted in methanol under various experimental conditions with
thiosemicarbazones derived from β-keto amides or β-keto esters (HTSC). Some of these reactions afforded
thiosemicarbazonate complexes [M(TSC)2] with IR and NMR spectra compatible with N,S-coordination, but
most gave complexes [ML2], where HL is a substituted 2,5-dihydro-5-oxo-1H-pyrazole-1-carbothioamide resulting
from cyclization of the HTSC. Some of these pyrazolonates and two of the HL ligands were studied by X-ray
diffractometry, and their structures are discussed. Surprisingly, the reactions of zinc() acetate with HTSC in 1 : 1
mol ratio usually gave a third, previously unreported type of complex with a dideprotonated ligand, [Zn(L Ϫ H)],
which was also formed when [ZnL2] and Zn(OAc)2 interacted at room temperature in 1 : 1 mol ratio. These L Ϫ H
complexes are highly insoluble in all common solvents, which hinders their characterization but suggests that they
are polymeric in nature.
Introduction
Although examples of chain-ring tautomerization of thio-
semicarbazones have long been known,1 exploration of this
phenomenon among monothiosemicarbazones derived from
β-keto esters and β-keto amides (I in Scheme 1) is more recent.2
Cyclization of I in the presence of a metallic salt or organo-
metallic substrate such as Zn(OAc)2, Cd(OAc)2, [ReX(CO)5]
or [ReX(CO)3(MeCN)2] (X = Cl, Br) usually constitutes a mild
route to the corresponding pyrazolone, the free pyrazolones
easily being obtained from the resulting metal complex.
Pyrazolones are an interesting synthetic target because of their
potential as antiinflammatory drugs.
Previous studies2 suggest that these cyclizations probably
start with the complexation of I by the metal or organometallic
substrate inducing its deprotonation, and that cyclization of the
resulting thiosemicarbazonate complex II comes about through
nucleophilic attack by the deprotonated N(2) atom on the
C(O)R3 group (Scheme 1). The rearrangement of the resulting
ring to the final pyrazolonate is less well-elucidated, but
Ϫ
experiments with Re compounds2a suggest that loss of R3
Scheme 1
gives III, which evolves via the enol form IV to the final
of thiosemicarbazones HTSCn (Scheme 2) during reaction with
zinc() and cadmium() acetates. Our findings included the
discovery of a hitherto unreported kind of zinc complex with
a dideprotonated ligand, [Zn(Ln Ϫ H)].
complex V, losing a proton in the process.
In our earlier work we found that cyclization is faster with
Cd(OAc)2 than with Zn(OAc)2.2b In the work described here we
investigated the influence of the substituents R1, R2 and R3, of
the metal : I mol ratio and of the temperature on the cyclization
Experimental
† Electronic supplementary information (ESI) available: SM1: Analyti-
cal and spectroscopic data for the ligands. ST1: Complexes obtained
in the assayed experimental conditions. ST2: IR spectra of the new
Physical measurements
1
complexes. ST3: H NMR spectra of the new HTSCn and HLn com-
Elemental analyses were performed on a Fisons instruments
EA1108CHNS-O microanalyser or, for some [Zn(Ln Ϫ H)]
complexes, by Galbraith Laboratories Inc. (Knoxville, TN,
USA). Melting points (mp) were determined with a Büchi
apparatus. The EI mass spectra of the ligands were recorded on
a Hewlett-Packard model HT5988A spectrometer. The electro-
spray mass spectra of the complexes were measured on a
plexes. ST4: 13C and 113Cd NMR spectra of some new complexes. ST5:
Hydrogen bond lengths (Å) and angles (Њ) in ligands and complexes.
SF1: Intermolecular interactions in [CdL5 (DMSO)]ؒDMSO. SF2: (a)
2
1
1H NMR spectrum of [Cd(TSC4)2] at room temperature; (b) H NMR
spectrum of the same sample after 1 h heating at 90 ЊC. SF3: O1s core
level spectra for [ZnL4 ]ؒH2O and [Zn(L4 Ϫ H)]. See http://www.rsc.org/
2
suppdata/dt/b4/b401674b/
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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until a pH of ca. 8 was reached, and then stirring for 6 h; the
white solid formed was filtered out and dried under reduced
pressure. HL5 was obtained by bringing a solution of HTSC5 in
MeOH to pH 8 by addition of 0.1 M NaOH, and then adding
trifluoroacetic acid to an aqueous solution of the resulting
sodium salt (NaL5). Recrystallization of HL3 and HL5 from
MeOH solution gave crystals suitable for X-ray analysis.
Analytical data and spectroscopic properties of all the ligands
are included as ESI (SM1).†
Synthesis of complexes
The experimental conditions used for preparing the cyclized
and uncyclized complexes are described below. Analytical data,
physical properties and the main peaks in the mass spectra are
listed in Table 1.
Scheme 2
M(OAc)2/HTSC1 reaction. (a) M = Zn. 1 : 2 mol ratio, reflux.
A suspension of HTSC1 (0.15 g, 0.54 mmol) and Zn(OAc)2ؒ
2H2O (0.06 g, 0.25 mmol) in methanol (25 ml) was refluxed for
6 h. The white solid formed, [Zn(TSC1)2], was filtered out and
dried under reduced pressure. 1 : 1 mol ratio, reflux. Similar
treatment of a suspension of 0.25 mmol of HTSC1 and 0.25
mmol of Zn(OAc)2ؒ2H2O in 25 ml of methanol afforded a
mixture of unidentified products. At room temperature,
reactions in 1 : 1 and 1 : 2 mol ratios both gave [Zn(TSC1)2]. (b)
M = Cd. 1 : 2 mol ratio, reflux. A suspension of HTSC1 (0.15 g,
0.54 mmol) and Cd(OAc)2ؒ2H2O (0.07 g, 0.27 mmol) in
methanol (25 ml) was refluxed for 6 h. Concentrating the
solution to half its initial volume and keeping it for 12 h at low
Hewlett-Packard model LC-MSD 1100 instrument (positive
ion mode, 98 : 2 MeOH–HCOOH as mobile phase, 30 to 100
V). The mass spectra of the [Zn(Ln Ϫ H)] complexes (see below)
were also explored by LDI or MALDI experiments using a
Voyager-DE PRO apparatus (Applied Biosystems) operating
in linear mode {5 mg mlϪ1 of DHB or trans-2-[(4-tert-butyl-
phenyl)-2-methyl-2-propenylidene]malononitrile in 50 : 50 of
water–acetonitrile with 0.1% trifluoroacetic acid, 337 nm
nitrogen laser, 25 keV}. The masses of the metallated peaks
were calculated for 114Cd or 64Zn. IR spectra were recorded
from KBr discs on a Bruker IFS66V FT-IR spectrometer and
1
are reported in cmϪ1. The H, 13C and 113Cd NMR spectra of
DMSO solutions were recorded on Bruker WM-250, AMX-300
or AMX-500 instruments; chemical shifts are expressed on the
δ scale (downfield shifts positive) relative to tetramethylsilane
(1H and 13C NMR spectra) or 0.1 M Cd(ClO4)2 (119Cd NMR).
X-Ray photoelectron spectra were recorded at the University of
Malaga using a Physical Electronics PHI 5700 spectrometer,
non–monochromatic Mg–Kα radiation (300 W, 15 kV, 1253.6
eV) and a multichannel detector for determination of the
photoelectronic signals of C1s, N1s, O1s, S2p and Zn2p. The
ZnLMN Auger line was also observed to calculate the Auger
parameter. Spectra of powdered samples were recorded with
constant pass energy values at 29.35 eV using a 720 µm diam-
eter analysis area. In processing the XPS spectra, binding
energy values were referred to the C1s peak (248.8 eV) of the
adventitious contamination layer. The PHI ACCESS ESCA–
V6.0 F software package was used for data acquisition and
analysis. A Shirley–type background was subtracted from
the signals. All recorded XPS spectra were fitted with Gauss–
Lorentz curves for more accurate determination of the binding
energies of the various element core levels. The error in BE was
estimated to be ca. 0.1 eV. All physical measurements except the
elemental analyses (performed by Galbraith), the XPS spectra
(performed at the University of Malaga) and the LDI and
MALDI MS spectra (see Acknowledgements) were carried
out in the RIAIDT services of the University of Santiago de
Compostela.
temperature allowed isolation of the complex [CdL1 ]ؒ3H2O,
2
which was dried under reduced pressure. The same compound
was obtained using 1 : 1 mol ratio and also at room temperature
(in both 1 : 2 and 1 : 1 mol ratio). [CdL1 ]ؒ3H2O has previously
2
been prepared by reacting cadmium acetate with methyl-
acetoacetate thiosemicarbazone.2c
M(OAc)2/HTSC2 reaction. (a) M = Zn. The 1 : 2 mol ratio
reaction, at room temperature or reflux, afforded, as pre-
viously,2b [ZnL2 (H2O)]. 1 : 1 mol ratio, reflux. A solution
2
of HTSC2 (0.15 g, 0.69 mmol) in methanol (25 ml) was added to
a solution of Zn(OAc)2ؒ2H2O (0.152 g, 0.69 mmol) in the same
solvent (10 ml). The mixture was refluxed for 2 h and the solid
formed, [Zn(L2 Ϫ H)], was filtered out and dried under reduced
pressure. The same compound was also obtained when this 1 : 1
mixture was stirred for one day at room temperature. (b) M =
Cd. 1 : 2 mol ratio, room temperature. A solution of Cd(OAc)2ؒ
2H2O (0.09 g, 0.34 mmol) in methanol (3 ml) was added
dropwise, with stirring, to a solution of HTSC2 (0.15 g, 0.69
mmol) in the same solvent (25 ml). After 4 days stirring at room
temperature, the white solid formed was filtered out, dried
under reduced pressure, and identified as [CdL2 ]. Single
2
crystals of [CdL2 (H2O)]ؒ2DMSO suitable for X-ray dif-
2
fractometry were obtained by recrystallization from DMSO.
Stirring the reagents in 1 : 1 mol ratio for 6 h, at room temper-
ature or under reflux, also gave [CdL2 ].
2
Materials
M(OAc)2/HTSC3 reaction. (a) M = Zn. 1 : 2 mol ratio. To a
solution of HTSC3 (0.11 g, 0.53 mmol) in methanol (25 ml) at
room temperature were added 0.06 g (0.27 mmol) of solid
Zn(OAc)2ؒ2H2O. After 6 h of stirring and further addition of
10 ml of water, the solution was cooled. The white solid formed,
Thiosemicarbazide (Merck), p-acetoacetanisidide (Aldrich),
methyl propionylacetate (Aldrich), ethyl benzoylacetate
(Aldrich), methyl 4-methoxyacetoacetate (Aldrich), ethyl
2-methylacetoacetate (Aldrich), zinc acetate (Aldrich) and
cadmium acetate (Probus) were used as received.
[ZnL3 ], was filtered out and dried under reduced pressure. The
2
same product formed when the 1 : 2 mol ratio reaction was
carried out under reflux for 6 h. 1 : 1 mol ratio. A solution of
Zn(OAc)2ؒ2H2O (0.20 g, 0.90 mmol) in methanol (5 ml) was
added to a solution of HTSC3 (0.18 g, 0.90 mmol) in the same
solvent (25 ml). After 48 h of stirring under reflux, the white
solid formed, [Zn(L3 Ϫ H)], was filtered out and dried under
reduced pressure. The same complex was obtained when the
Synthesis of ligands
The thiosemicarbazone ligands were prepared by a published
method.3 Physical and analytical properties of HTSC,2 HL1 and
HL2 have been reported elsewhere.2b HL3 and HL4 were
obtained by adding a 0.1 M aqueous solution of NaOH to a
solution of HTSC3 or HTSC4 (0.68 mmol) in MeOH (25 ml)
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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Table 1 Elemental analyses (%), melting points (ЊC), colour and mass spectra (m/z) of the new complexes
Compound
C
H
N
S
Zn
Mp
210
Colour
White
MS (%)
[Zn(TSC1)2]
44.4
4.7
17.3
10.6
623 (100.0) [M ϩ H]
(C24H34N8O4S2Zn)
(46.2)
(4.8)
(18.0)
(10.3)
500 (24.6) [M Ϫ NHPh(OCH3)]
343 (45.0) [Zn(TSC1)]
[Zn(L2 Ϫ H]
(C6H7N3OSZn)
[CdL2 ]
29.8
(30.7)
31.0
3.3
(3.0)
3.2
17.4
(17.9)
18.3
13.8
(13.7)
15.1
28.0
(27.9)
>300
220
White
White
455 (16.7) [M ϩ H]
(C12H126N6O2S2Cd)
(31.8)
(3.6)
(18.6)
(14.2)
394 (22.6) [M Ϫ C(S)NH2]
284 (13.7) [CdL2]
[ZnL3 ]
35.1
(35.5)
4.0
(4.0)
20.5
(20.7)
16.3
(16.1)
130
White
405 (55.8) [M ϩ H]
(C12H216N6O2S2Zn)
346 (33.0) [M Ϫ 2Et]
315 (12.7) [M Ϫ C(S)NH2 Ϫ Et]
234 (7.6) [ZnL3]
[Zn(L3 Ϫ H)]
31.1
(30.7)
29.8
3.6
(3.0)
3.7
18.1
(17.9)
17.0
235
190
White
White
(C6H7N3OSZn)
[CdL3 ]ؒH2O
13.7
(13.6)
455 (100.0) [(M Ϫ H2O) ϩ H]
394 (11.3) [M Ϫ H2O Ϫ C(S)NH2]
284 (5.0) [CdL3]
(C12H128N6O3S2Cd)
(30.6)
(3.8)
(17.8)
[Zn(TSC4)2]
33.6
(33.5)
32.1
(32.9)
28.2
(28.8)
29.5
4.7
(4.8)
3.8
(3.7)
2.8
(2.8)
4.4
16.8
(16.8)
18.2
(19.2)
16.2
(16.8)
14.6
12.4
(12.8)
14.0
(14.6)
12.9
(12.8)
12.0
145
130
White
White
White
White
501 (100.0) [M ϩ H]
C14H24N6O6S2Zn
469 (49.0) [M Ϫ (OCH3)]
437 (38.4) [M ϩ H]
[ZnL4 ]
C12H126N6O4S2Zn
[Zn(L4 Ϫ H)]
(C6H7N3O2SZn)
[Cd(TSC4)2]
250 (100.0) [ZnL4].
24.7
(26.1)
>300
170
551 (100.0) [M ϩ H]
C14H24N6O6S2Cd
(30.6)
(4.4)
(15.3)
(11.7)
519 (38.6) [M Ϫ (OCH3)]
332 (17.2) [Cd(TSC4)]
[CdL4 ]ؒH2O
28.0
(28.7)
3.9
(3.6)
16.0
(16.7)
12.1
(12.7)
185
White
487 (33.0) [(M Ϫ H2O) ϩ H]
426 (22.4) [M Ϫ H2O Ϫ C(S)NH2]
300 (60.0) [CdL4]
2
C12H18N6O5S2Cd
[ZnL5 ]ؒMeOH
C21H220N6O3S2Zn
[CdL5 ]ؒMeOH
(C21H220N6O3S2Cd)
45.5
(47.2)
41.7
3.0
(3.8)
4.0
15.9
(15.7)
14.1
12.5
(12.0)
10.4
190
180
White
White
501 (78.0) [(M ϩ H]
440 (9.5) [M Ϫ C(S)NH2]
551 (5.4) [(M Ϫ MeOH) ϩ H]
490 (6.3) [M Ϫ MeOH Ϫ C(S)NH2]
473 (100.0) [M Ϫ MeOH Ϫ Ph]
332 (22.4) [CdL5]
(43.4)
(3.5)
(14.5)
(11.0)
1 : 1 mol ratio reaction was carried out at room temperature.
(b) M = Cd. 1 : 1 mol ratio. A solution of HTSC3 (0.15 g,
0.74 mmol) in methanol (25 ml) was added to a solution
of Cd(OAc)2ؒ2H2O (0.20 g, 0.74 mmol) in the same solvent
(10 ml). After 6 h stirring at room temperature, the white solid
M(OAc)2/HTSC5 reaction. (a) M = Zn. 1 : 2 mol ratio. A
solution of HTSC5 (0.15 g, 0.57 mmol) in methanol (25 ml) was
added to a solution of Zn(OAc)2ؒ2H2O (0.06 g, 0.28 mmol) in
the same solvent (10 ml). The white solid [ZnL5 ]ؒMeOH,
2
formed after 6 h of stirring at room temperature, was filtered out
and dried under reduced pressure. The same complex was also
obtained when this 1 : 2 mixture was refluxed. In 1 : 1 mol ratio,
however, the result depended on the temperature: refluxing for
6 h gave first a white solid that has not yet been completely
formed, [CdL3 ]ؒH2O, was filtered out and dried under reduced
2
pressure. The same compound was obtained when this 1 : 1
mixture was refluxed for 6 h or when the 1 : 2 mol ratio reaction
was carried out at room temperature or under reflux.
identified, and the mother-liquor then gave [ZnL5 ]ؒMeOH;
2
while at room temperature the 1 : 1 mixture gave only unidenti-
fied products. (b) M = Cd. 1 : 2 mol ratio. A solution of
Cd(OAc)2ؒ2H2O (0.07 g, 0.27 mmol) in methanol (5 ml) was
added to a solution of HTSC5 (0.15 g, 0.57 mmol) in the same
M(OAc)2/HTSC4 reaction. (a) M = Zn. 1 : 2 mol ratio, room
temperature. A solution of HTSC4 (0.15 g, 0.68 mmol) in
methanol (20 ml) was added to a solution of Zn(OAc)2ؒ2H2O
(0.07 g, 0.34 mmol) in the same solvent (10 ml). The mixture
was stirred for 10 min, and after partial evaporation of the
solvent the solid formed, [Zn(TSC4)2] was filtered out and dried
under reduced pressure. Refluxing the 1 : 2 mol ratio mixture for
solvent (25 ml). The white solid [CdL5 ]ؒMeOH was formed
2
after 3 h of stirring at room temperature and was filtered out
and dried under reduced pressure. The same product was
obtained under reflux and also when the 1 : 1 mol ratio was
used at room temperature or under reflux. Recrystallization
6 h, followed by partial evaporation of the solvent, gave [ZnL4 ]
2
which was filtered out and dried under reduced pressure. The
from DMSO gave single crystals of [CdL5 (DMSO)]ؒ2DMSO
mother-liquor afforded single crystals of [ZnL4 ]ؒ0.5H2O suit-
2
2
suitable for X-ray study.
Table ST1 (ESI†) summarizes the syntheses described above.
able for X-ray study. [ZnL4 ] was also formed after 6 h stirring
2
of the 1 : 2 mol ratio mixture at room temperature. The reaction
in 1 : 1 mol ratio, at room temperature or under reflux always
afforded the very insoluble compound [Zn(L4 Ϫ H)], which was
filtered out and dried under reduced pressure. (b) M = Cd. 1 : 2
mol ratio. A solution of HTSC4 (0.15 g, 0.68 mmol) in methanol
(25 ml) was added to a solution of Cd(OAc)2ؒ2H2O (0.09 g, 0.34
mmol) in the same solvent (5 ml) and the mixture was stirred for
6 h at room temperature. The white solid formed, [Cd(TSC4)2],
was filtered out and dried under reduced pressure. The 1 : 1 mol
ratio reaction at room temperature gave the same compound.
When refluxed for 6 h, the 1 : 2 and 1 : 1 mixtures both gave
X-Ray crystallography
Crystal data were collected at room temperature on Enraf-
Nonius CAD-4 or Bruker SMART diffractometers. Structures
were solved using direct methods for the ligands and the
Patterson method for the complexes, followed by normal differ-
ence Fourier techniques. Hydrogen atoms were included at ideal
geometrical positions, except that of the water molecule in
[CdL2 (H2O)]ؒ2DMSO, which was located. In this complex, one
2
of the DMSO molecules is disordered. In [ZnL4 ]ؒ0.5H2O the
2
[CdL4 ]ؒH2O, which was filtered out and dried under reduced
occupancy of the water oxygen was fixed at 0.5 because its
2
pressure.
temperature factor was very high; and the hydrogen on this
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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Table 2 Selected crystallographic data for ligands and complexes
HL3
HL5
[ZnL4 ]ؒ0.5H2O
[CdL2 (H2O)]ؒ2DMSO
[CdL5 (DMSO)]ؒDMSO
2
2
2
Empirical formula
M
C6H9N3OS
171.22
C10H9N3OS
219.26
C12H17N6O4·5S2Zn
446.81
C16H30N6O5S4Cd
627.10
C24H28N6O4S4Cd
705.16
λ/Å
0.71073
0.95 × 0.53 × 0.44
Monoclinic
C2/m (no. 12)
18.825(4)
6.9385(14)
6.1461(12)
–
1.54180
0.71073
0.34 × 0.31 × 0.25
Tetragonal
P41212 (no. 92)
9.3579(15)
–
22.554(5)
–
0.71073
0.71073
Crystal size/mm
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
0.24 × 0.16 × 0.04
Triclinic
0.66 × 0.65 × 0.63
Monoclinic
C2/m (no. 12)
15.665(3)
20.270(4)
8.1761(17)
–
100.030(3)
–
4
0.57 × 0.31 × 0.09
Monoclinic
P21/c (no. 14)
10.636(3)
13.317(3)
20.713(5)
–
91.174(5)
–
4
¯
P1 (no. 2)
6.0107(3)
7.8604(13)
11.2049(9)
94.399(12)
100.733(7)
95.417(11)
2
90.087(3)
–
4
–
–
4
γ/Њ
Z
Refl. collec./uniq.
Rint
R1 [I > 2σ(I )]
Rw [I > 2σ(I )]
2519/890
0.0338
0.0578
2270/2065
0.0354
0.0438
11298/2052
0.0372
0.0327
0.0920
5924/2696
0.0158
0.0261
14594/5964
0.0432
0.0448
0.1661
0.1242
0.0718
0.1041
Table 3 Selected bond lengths (Å) and angles (Њ) in ligands and complexes
HL3
HL5
[ZnL4 ]ؒ0.5H2Oa
[CdL2 (H2O)]ؒ2DMSOb
[CdL5 (DMSO)]ؒDMSOc
2
2
2
M(1)–S(1)
Cd(1)–S(11)
M(1)–N(3)
Cd(1)–N(13)
Cd(1)–O(1D)
Cd(1)–O(1W)
Cd(1)–O(1)i
S(1)–C(1)
N(1)–C(1)
C(1)–N(2)
N(2)–N(3)
N(3)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–O(1)
C(4)–N(2)
2.3731(10)
1.971(3)
2.5733(7)
2.5908(15)
2.5910(15)
2.392(4)
2.355(4)
2.499(4)
2.2342(18)
2.319(3)
2.374(4)
1.687(5)
1.312(6)
1.385(6)
1.405(5)
1.342(6)
1.390(7)
1.381(7)
1.266(6)
1.421(6)
1.659(3)
1.329(3)
1.379(3)
1.379(3)
1.323(3)
1.372(4)
1.403(4)
1.248(3)
1.410(3)
1.663(2)
1.326(3)
1.388(3)
1.392(2)
1.358(3)
1.369(3)
1.409(3)
1.251(2)
1.412(2)
1.703(3)
1.315(5)
1.359(4)
1.387(4)
1.316(4)
1.413(5)
1.384(5)
1.244(4)
1.448(4)
1.705(2)
1.308(3)
1.370(3)
1.391(3)
1.327(3)
1.391(3)
1.390(3)
1.266(3)
1.436(3)
C(1)–N(2)–N(3)
N(2)–N(3)–C(2)
N(3)–C(2)–C(3)
C(2)–C(3)–C(4)
S(1)–Cd(1)–S(11)
S(1)–M(1)–S(1)i
S(1)–M(1)–N(3)
S(1)–M(1)–N(3)i
S(1)–Cd(1)–O(1)i
S(11)–Cd(1)–O(1D)
N(3)–Cd(1)–N(13)
N(3)–M(1)–N(3)i
N(3)–Cd(1)–O(1W)
S(1)–Cd(1)–O(1W)
121.9(2)
108.8(2)
110.0(2)
107.9(2)
121.14(15)
107.09(15)
110.27(17)
108.24(18)
120.2(3)
106.4(3)
111.9(3)
107.5(3)
120.88(17)
105.23(17)
113.1(2)
120.3(4)
103.3(4)
113.5(4)
107.1(5)
152.61(5)
106.90(19)
106.83(6)
84.93(8)
126.43(9)
122.18(4)
77.38(5)
104.75(5)
74.24(10)
85.57(9)
76.53(10)
84.37(14)
129.82(16)
175.71(10)
87.85(5)
118.910(19)
a i = Ϫy ϩ 1, Ϫx ϩ 1, Ϫz ϩ 3/2. b i = Ϫx, y, Ϫz. c i = Ϫx, y Ϫ 1/2, Ϫz ϩ 1/2.
atom was not included. The program used was SHELX97.4
Molecular graphics were obtained with ORTEP-3.5 Crystal and
refinement data are listed in Table 2, and selected bond lengths
and angles are included in Table 3. Bond lengths and angles in
hydrogen bonds in ligands and complexes are included as ESI†
in Table ST5.
CCDC reference numbers 230381–230385.
See http://www.rsc.org/suppdata/dt/b4/b401674b/ for crystal-
lographic data in CIF or other electronic format.
HL5 were also studied by X-ray diffractometry. All except
HTSC4, which is ochre in colour, are white solids, and all melt
without decomposition at temperatures between 80 and 198 ЊC.
Fig. 1(a) and (b) show the molecular structures of HL3 and
HL5 together with the atomic numbering schemes used.
Selected bond lengths and angles are listed in Table 3. In both
ligands, the bond lengths and angles are similar to those found
in the two pyrazolone ligands previously studied by X-ray
diffraction,2c,6 the major difference being that HL3 has a sig-
nificantly shorter C(2)–N(3) bond. Both ligands adopt the
keto-thione form. In the HL3 molecule all the atoms, with
the exception of hydrogens on C5 and C6, are in the same
plane. In HL5 the plane containing the pyrazolone ring and the
carbothioamide group (rms = 0.03) forms an angle of 21Њ with
the phenyl ring. Both ligands have an N(1)H ؒ ؒ ؒ O(1) intra-
molecular hydrogen bond [N(1) ؒ ؒ ؒ O(1) = 2.634(4) Å in HL3
and 2.664(3) Å in HL5] and two intermolecular hydrogen bonds
Results and discussion
Synthesis and identification of the ligands
All the thiosemicarbazones HTSCn and pyrazolones HLn were
characterized by elemental analysis, mass spectrometry, and IR
and 1H and 13C NMR spectroscopy (ESI,† SM1), and HL3 and
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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derived from β-keto amides and β-keto esters that have been
isolated so far (two in this work and three previously2b), the
least prone to cyclization are the three derived from β-keto
amides. Their higher stability may be due to nucleophilic attack
by N(2) on C(4)᎐O (see Scheme 1) being slowed down or
᎐
prevented by the involvement of the N(2) lone pair in an
N(4)–H ؒ ؒ ؒ N(2) intramolecular hydrogen bond, the presence
of which has been shown by X-ray crystallography in the
case of [Zn(TSC)2]ؒDMSO (HTSC = o-acetoacetanisidide
thiosemicarbazone).2b
Complexes [MLn ] were obtained, normally without heating,
2
in all the Cd(OAc)2/HTSCn reactions except those of HTSC4 at
room temperature, which afforded [Cd(TSC4)2]. The reactions
of zinc acetate with HTSCn in 1 : 2 mol ratio also gave [MLn2]
complexes for n = 2–5 (Table ST1 in ESI†).
The reactions of Zn(OAc)2 with HTSCn in 1 : 1 mol ratio
(n = 2, 3 and 4) afforded a third, previously unreported type
of complex, [Zn(Ln Ϫ H)] (ST1 in ESI†). No reaction of cad-
mium() acetate gave a [Cd(Ln Ϫ H)] complex. It was found
that the [Zn(Ln Ϫ H)] derivatives can also be prepared by
stirring [ZnLn2] for 48 h with zinc acetate in 1 : 1 mol ratio at
room temperature, but not by refluxing [ZnLn ] in the absence
2
Fig. 1 Molecular structures and numbering scheme of ligands (a) HL3
of Zn(OAc)2; this suggests that 1 : 1 metal : ligand mol ratio
is essential for preparation of the complexes containing
dideprotonated pyrazolones. The fact that the [Zn(Ln Ϫ H)]
compounds are insoluble in water and in the common organic
solvents, which prevents their crystallization, suggests that
they are polymeric in nature. They are nevertheless soluble in
trifluoroacetic acid, in which they react releasing the free
pyrazolone ligand.
and (b) HL5.
(see Table ST5 in ESI†). One of the latter links the N(3)–H
group and the carbonyl oxygen atom of a neighbouring
molecule [N(3) ؒ ؒ ؒ O(1)ii = 2.746(3) Å in HL3 (ii = x, y, z Ϫ 1),
2.924(2) Å in HL5 (ii = x Ϫ 1, y, z)] and gives rise to a polymeric
chain parallel to the z axis in HL3 and the x axis in HL5. The
other intermolecular hydrogen bond, between the N(1)–H(1B)
group and the Si atom [N(1) ؒ ؒ ؒ Si = 3.413(4) Å in HL3 (i = Ϫx,
y, Ϫz ϩ 2), 3.404(2) Å in HL5 (i = Ϫx, Ϫy, Ϫz ϩ 1)], links the
chains in pairs. The distance between molecules in the same
chain is somewhat longer in HL5, probably because of steric
hindrance by the phenyl group.
Structures of the complexes
(a) [M(TSCn)2]. The main change in the IR spectra of HTSC1
and HTSC4 upon coordination to the metal in the complexes
[Zn(TSC1)2], [Zn(TSC4)2] and [Cd(TSC4)2] is that one of the
ν(C᎐S) absorptions vanishes or shifts to lower wavenumbers,
᎐
Synthesis of the complexes
suggesting coordination through the S atom (see Table ST2
in ESI†). Comparison of these spectra with those of similar
compounds studied by X-ray diffractometry2b,c also suggests
coordination via the lone pair of N(3), since in these
Depending on the metal, the ligand and the reaction conditions,
the reactions of Cd() and Zn() acetates with the selected thio-
semicarbazones (Scheme 2) led to three types of complex: thio-
semicarbazonates [M(TSCn)2] (II in Scheme 1), pyrazolonates
with monodeprotonated ligands [MLn2] (V in Scheme 1), and
pyrazolonates with dideprotonated pyrazolones, [Zn(Ln Ϫ H)].
Thiosemicarbazonate complexes were only obtained in
reactions with HTSC1 and HTSC4 (Table ST1 in ESI†).
[Zn(TSC1)2] was isolated when zinc() acetate was reacted with
HTSC1 in 1 : 2 mol ratio at room temperature or under reflux,
or in 1 : 1 mol ratio at room temperature. The reaction of
zinc() acetate with HTSC4 gave the thiosemicarbazonate only
when carried out in 1 : 2 mol ratio and interrupted after 10 min,
with the solid formed being filtered off immediately.
[Cd(TSC4)2] was easily formed at room temperature from
Cd(OAc)2 and HTSC4 in both 1 : 1 and 1 : 2 mol ratio, but was
not obtained when the reaction mixture was refluxed. In keep-
ing with earlier work,2b,c these results suggest that stabilization
of the thiosemicarbazonate complexes is probably easier with
Zn() than with Cd(). In fact, [Cd(TSC4)2] is the first Cd()
complex of this type to have been isolated, and its readiness to
undergo cyclization is shown by the fact that heating it for 1 h at
90 ЊC in DMSO-d6 led to its 1H NMR spectrum showing
signals for both thiosemicarbazonate and pyrazolonate com-
plexes (Fig. SF2 in ESI†); in the same conditions, [Zn(TSC1)2]
underwent no such evolution. The stabilization of [M(TSCn)2]
seems also to depend on the leaving group R3 (vide infra), the
identity of R1 (possibly because its inductive effect influences
the deprotonation of N(3)H), and the temperature. It seems
plausible that all the HTSCn ligands would have been cyclized
by both metals given a long enough reaction time.
compounds the ν(C᎐N) absorptions suffer small but significant
᎐
changes in its position respect to the free ligands.
The 1H and 13C NMR spectra of these complexes show
signals for only one conformer (Tables ST3 and ST4 in ESI†).
Deprotonation of the ligand was confirmed by the absence of
N(2)H signals. In the 13C NMR spectra the major changes upon
coordination are the shielding of C(1) and C(3) (in the former
case due to thione-to-thiol evolution), and the deshielding of
C(2) [due to N(3)-coordination]. In the cadmium complex, the
main 113Cd NMR signal appears at lower field (448 ppm) than
in thiosemicarbazonate complexes with [N4S2]-coordination
(420 ppm),7 in keeping with the [N2S2]-coordination proposed
for [Cd(TSC4)2]. Nevertheless, the presence of two weak signals
at higher field (439 and 371 ppm) suggests the presence of
minor species, possibly involving DMSO molecules. These
species are presumably uncyclized, since the signal of the
cyclized complex appears at 280 ppm (vide infra).
(b) [MLn ]. The structures of [ZnL4 ]ؒ0.5H2O, [CdL2 (H2O)]ؒ
2
2
2
2DMSO and [CdL5 (DMSO)]ؒDMSO were established by
2
X-ray diffractometry.
Fig. 2(a) shows the solid-state molecular structure of [ZnL4 ]ؒ
2
0.5H2O and the atomic numbering scheme used in this paper.
Selected bond lengths and angles are listed in Table 3. In the
crystal structure the Zn and O1W atoms lie on a two-fold axis.
Two S,N-bidentate ligands chelate the zinc atom, giving rise
to a distorted tetrahedral coordination polyhedron with an
S(1)–Zn(1)–N(3) angle of only 85Њ. The O(2) and O(2)i atoms
(i = Ϫy ϩ 1, Ϫx ϩ 1, Ϫz ϩ 3/2), are located 2.74 Å from the zinc
It is noteworthy that of the five zinc thiosemicarbazonates
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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N(1)H ؒ ؒ ؒ O(1) hydrogen bond of the free ligand persists in
the complex, but is weaker [N(1) ؒ ؒ ؒ O(1), 2.711(3) Å]. An
intermolecular hydrogen bond between the water molecule and
O(1)ii [O(1w) ؒ ؒ ؒ O(1)ii 2.807(2) Å, ii = Ϫx ϩ 1/2, Ϫy ϩ 1/2, Ϫz]
gives rise to polymeric chains. The two DMSO molecules bridge
between chains through hydrogen bonds with the NH2 groups,
making a three-dimensional network [N(1) ؒ ؒ ؒ O(1D) 2.961(3)
Å; N(1) ؒ ؒ ؒ O(2D) 2.902(3) Å]. This compound is isostructural
with the complex of Zn() with the same ligand.2b
Fig. 2(c) shows the molecular structure of [CdL5 (DMSO)]ؒ
2
DMSO and the atomic numbering scheme (for clarity, the
DMSO molecule that is not coordinated to the cadmium is not
represented). Selected bond lengths and angles are listed
in Table 3. The metal atom has coordination number six, a
trigonal prismatic coordination geometry being created by the
two N,S-bidentate thiosemicarbazone ligands, a DMSO oxygen
(O1D), and a carbonyl oxygen belonging to a neighbouring
molecule [O(1)i, i = Ϫx, y Ϫ 1/2, Ϫz ϩ 1/2]. This Cd(1)–O(1)i
bond links the molecules in chains along the y axis (Fig. SF1 in
ESI†). Each NH2 group is involved in one intra- and one inter-
molecular hydrogen bond (Table ST5 in ESI†), the former with
the oxygen of a carbonyl group [N(1)–O(1) 2.617(6) Å;
N(11) ؒ ؒ ؒ O(11) 2.646(6) Å] and the latter with either a DMSO
molecule [N(11) ؒ ؒ ؒ O(2D) 2.749(7) Å] or a carbonyl oxygen
atom belonging to a neighbouring molecule [N(1) ؒ ؒ ؒ O(11)ii
(ii = x Ϫ 1, y, z) 2.770(5) Å]. These N(1) ؒ ؒ ؒ O(11)ii bonds link
the above-mentioned chains along the x axis. The major
modifications in bond lengths with respect to the free ligand are
the lengthening of S(1)–C(1) from 1.663(2) to 1.687(5) Å and of
C(2)–C(3) from 1.369(3) to 1.390(7) Å, and the shortening of
C(3)–C(4) from 1.409(3) to 1.381(7) Å due to the new charge
distribution in the anion. In each ligand the plane containing
the pyrazolone ring and the thioamide group [rms = 0.015,
S(1)N(1)C(1)N(2)N(3)C(2)C(3)C(4)O(1)] makes
a dihedral
angle of 22Њ with the plane of the phenyl group. The two pyra-
zolone planes form an angle of about 20Њ.
Fig. 2 Molecular structures of complexes: (a) [ZnL4 ]ؒ0.5H2O; (b)
The above structures show that in [MLn ] complexes the four
2
[CdL2 (H2O)]ؒ2DMSO; (c) [CdL5 (DMSO)]ؒDMSO
2
2
2
bonds with the two pyrazolone ligands can be increased to five
or six by incorporation of additional donor molecules when the
R substituents on the pyrazolone ring do not block access to
the metal centre as they do in [Zn(L4)2]ؒ0.5H2O. This suggests
that in some of the complexes formulated in Table 1 as hydrates
or solvates the water or organic solvent molecule may in fact
occupy a position in the inner coordination sphere of the metal.
In the IR spectra of most of the [MLn2] compounds, the
atom, a distance that is less than the sum of the van der Waals
radii (2.90 Å8) and suggests the existence of a very weak
interaction with the metal centre. Be that as it may, the
positions of O(2) and O(2)i are probably responsible for
keeping the water molecule outside the coordination sphere and
so preventing a coordination number higher than four. Except
for the O(2) and C(6) atoms, the pyrazolone ligands are almost
planar [rms = 0.0185 for S(1)C(1)N(1)N(2)N(3)C(2)C(3)C(4)-
C(5)O(1); O(2) and C(6) lie about 0.27 and 0.29 Å, respectively,
from this plane], and their planes form a dihedral angle of 78Њ.
The N(1) atom is involved in two hydrogen bonds with O(1)
atoms (see Table ST5 in ESI†), one of them being intra-
molecular [N(1) ؒ ؒ ؒ O(1), 2.696(4) Å] and one intermolecular
[N(1) ؒ ؒ ؒ O(1)ii (ii = Ϫx ϩ 5/2, y Ϫ 1/2, Ϫz ϩ 5/4), 2.804(4) Å].
This latter hydrogen bond gives rise to a three-dimensional
network. The water molecule seems not to interact with other
components of the lattice, OW1 lying 3.235 Å from the closest
atom [O(1)iii, iii = x Ϫ 1, y, z].
ν(C᎐O) absorption has shifted to significantly lower wave-
᎐
numbers than in the spectrum of the free ligand (SM1 and
Table ST2 in ESI†), presumably either because of coordination
of the carbonyl group to the metal atom (as in [CdL5 (DMSO)]ؒ
2
DMSO) or because the oxygen atom is involved in stronger
hydrogen bonds than in the free ligand. The possible exceptions
are [ZnL4 ] and [ZnL5 ]ؒMeOH, which have spectra in which
2
2
very broad absorptions hinder interpretation. The ν(C–N)
absorption, located at 1340–1300 cmϪ1 in the ligand spectra
shifts to wavenumbers 30–90 cmϪ1 higher in the spectra of all
the complexes due to the redistribution of the π charge upon
coordination. The ligand absorptions associated with the
The solid-state molecular structure of [CdL2 (H2O)]ؒ2DMSO
ν(C᎐S) mode, one near 1100 cmϪ1 and the other near 900–850
᎐
2
is shown in Fig. 2(b) together with the atomic numbering
scheme, and selected bond lengths and angles are listed in Table
3. In the crystal structure the Cd and O1W atoms lie on a
two-fold axis. Cd() is pentacoordinated by two N(3),S-biden-
tate ligands and a water molecule, which create a distorted
trigonal bipyramidal coordination geometry (τ = 0.899) with
the N atoms apical [N(3)ϪCdϪN(3)i 175.71Њ]. The pyrazol-
onate rings are planar [rms = 0.056 Å] and the dihedral angle
between the planes is about 55.9Њ. Deprotonation and co-
ordination promote a thione-to-thiol transition (the C(1)–S(1)
bond is longer than in the free pyrazolone6) and also cause
delocalization of π-charge in the ring. The intramolecular
cmϪ1, either shift to lower wavenumbers in the spectra of the
complexes or, in the case of the higher-energy absorption,
disappear. [CdL3 ]ؒH2O is an exception to this rule because in
2
this case the absorption at higher wavenumber disappears upon
complexation and the lower-energy absorption shifts to higher
wavenumber and becomes weaker.
As expected, the 1H NMR spectra of [MLn2] show no N(3)H
signal, due to deprotonation. In the 13C NMR spectra almost
all the signals lie downfield of their positions in the free ligands,
the only exception being that C(3) is shielded (see SM1 and ST4
in ESI†). The 113Cd NMR spectra all show a single signal at ca.
280 ppm, a chemical shift almost identical to that previously
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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Table 4 Solid-state 13C NMR data
Compound
δ[C(1)]
δ[C(2)]
δ[C(3)]
δ[C(4)]
δ[R1]
[ZnL4 ]
175.5
176.6
157.8
153.5
85.1
89.8, 87.5
165.6
163.6
67.2 [C(5)], 57.9 [C(6)]
68.4 [C(5)], 60.2 [C(6)]
[Zn(L24 Ϫ H)]
Table 5 Theoretical and experimental atomic ratios for [ZnL4 ]ؒ0.5H2O and [Zn(L4 Ϫ H)]
2
Theoretical atomic ratios
Surface atomic ratio (XPS)
Sample
O/Zn
S/Zn
N/Zn
C/Zn
O/Zn
S/Zn
N/Zn
C/Zn
[ZnL4 ]ؒ0.5H2O
[Zn(L24 Ϫ H)]
4.50
2.00
2.00
1.00
6.00
3.00
12.00
6.00
4.32
2.17
2.01
1.31
5.83
3.04
13.58
7.93
Table 6 Binding energies, in eV, of Zn2p3/2, ZnLMN, S2p, N1s and O1s, and the Auger parameter α, for [ZnL4 ]ؒ0.5H2O and [Zn(L4 Ϫ H)]
2
Complex
Zn2p3/2
ZnLMN
265.4
α
S2p
N1s
O1s
[ZnL4 ]ؒ0.5H2O
1022.3
2010.5
162.6
398.8
399.8
400.9
398.5
399.7
400.9
530.9
532.6
2
[Zn(L4 Ϫ H)]
1022.3
265.4
2010.5
162.8
531.5
532.9
found for [CdL1 ]ؒ3H2O (281 ppm).2c As in this latter case,
13C NMR spectrum (Table 4), the carbonyl carbon [C(4)]
is shielded by 2 ppm when the second deprotonation of the
pyrazolone occurs, which is also compatible with O–Zn()
interaction.
2
δ(113Cd) is larger than expected for an [N2S2] kernel;10 this may
be due to an increase in coordination number due to the
coordination of solvent molecules (as seen in the solid state for
[CdL2 ] and [CdL5 ]).
In view of the probable polymeric nature of these [Zn(Ln Ϫ
H)] complexes and the deprotonation of their amine group, and
assuming that the carbonyl oxygen atom does coordinate to the
zinc() atom, we hypothesize that they may have the structure
shown in Scheme 3.
2
2
(c) [Zn(Ln ؊ H)]. The very poor solubility of these com-
plexes, which suggests a polymeric structure, severely hindered
their characterization. Although the presence of the metal is
guaranteed by the elemental analyses (see Experimental
section), the LDI and MALDI MS experiments only produced
signals for small organic fragments, which might reflect either
the desorption of polymers that then break up under the laser
radiation, or the existence of a polymeric structure from which
polymeric fragments are not desorbed. Other MS methods
(ESI) gave no additional clues. The results of the solid-state 13
C
NMR experiments (Table 4) suggest that the organic moiety has
a cyclic structure similar to that of (Ln)Ϫ, the signals of all the
pyrazolone ring carbons of the monodeprotonated ligands
having counterparts within 4 ppm in the [Zn(Ln Ϫ H)] spectra.
Furthermore, all the [Zn(Ln Ϫ H)] complexes afforded the free
pyrazolone when treated with trifluoroacetic acid.
Scheme 3
To support this assumption, samples of [ZnL4 ]ؒ0.5H2O and
2
[Zn(L4 Ϫ H)] were studied by XPS. Table 5 shows the theoret-
ical and the experimental atomic ratios. There is very good
agreement between the theoretical and experimental surface
compositions, confirming that the surfaces of both samples
have chemical compositions similar to the bulk. The higher
observed C/Zn atomic ratios can be attributed to adventitious
carbon. To determine the redox state of Zn, the Auger
parameter α was calculated from the equation
The pyrazolonate ligand (Ln)Ϫ can only lose an additional
proton from the –NH2 group. Although the acidity of the
amine group is very low, it is well documented that in certain
Zn() complexes with similar coordination to the present
compounds the metal cation is bound to a deprotonated –NH2
group.11,12 It is nevertheless interesting that whereas in the
synthesis of these latter complexes the deprotonation of –NH2
had been induced by a basic reagent (hydride ion) or a basic
solvent (DMF), the presence of the metal ion and the acetate
group seems to suffice in the formation of [Zn(Ln Ϫ H)].
α = KE(ZnLMN) ϩ BE(Zn2p3/2
)
where KE (ZnLMN) is the kinetic energy of the ZnLMN Auger
electron [KE(ZnLMN) = 1253.6 Ϫ BE(ZnLMN), 1253.6 being the
energy of the Mg-Kα X-ray source, in eV] and BE(Zn2p3/2) is
the binding energy of the Zn2p3/2 photoelectron. Both
complexes have the same Auger parameter, 2010.5 eV, a value
that is intermediate between the 2009.8 eV of ZnO and
the 2011.3 eV of ZnS,13 and a Wagner plot (not shown here)
indicates that in both cases Zn is present as Zn().
The IR spectra of [Zn(L3 Ϫ H)] and [Zn(L4 Ϫ H)], the former
especially, are quite similar to those of [ZnL3 ] and [ZnL4 ]
2
2
everywhere except in the region corresponding to ν(N–H)
absorptions, as is to be expected if the only significant
structural change is deprotonation of the –NH2 group. The IR
spectrum of [Zn(L2
Ϫ H)] also differs from that of
[ZnL2 (H2O)]2b in this region, although in this case the absorp-
Table 6 lists the binding energies of the elements studied by
2
tions due to the water molecule of the latter complex hinder
XPS. The S2p signal appears at 162.6 and 162.8 eV for [ZnL4 ]ؒ
2
direct comparison. Except in the case of the HL3 derivatives,
0.5H2O and [Zn(L4 Ϫ H)], respectively, indicating that only
S(Ϫ) is present in these complexes. The N1s signal is very
broad for both compounds, and can be decomposed into three
contributions at 398.8, 399.8 and 400.9 eV (FWHM = 2.76 eV)
the ν(C᎐O) absorption shifts to lower wavenumbers, suggesting
᎐
coordination of the oxygen atom to the metal, although once
more an alternative explanation might be a strengthening of
hydrogen bonds involving the oxygen atom. In the solid state
for [ZnL4 ]ؒ0.5H2O and 398.5, 399.7 and 400.9 eV (FWHM =
2
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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3.45 eV) for [Zn(L4 Ϫ H)]. These contributions are assigned to
the three types of nitrogen atom of the ligand, and the greater
breadth of the [Zn(L4 Ϫ H)] signal is attributed to the co-
References
1 G. J. Karabatsos, F. M. Vane, R. A. Taller and N. His, J. Am. Chem.
Soc., 1964, 86, 3351.
ordination of the amine group to Zn(). [ZnL4 ]ؒ0.5H2O has
2
2 (a) R. Carballo, J. S. Casas, E. García-Martínez, G. Pereiras-Gabián,
A. Sánchez, J. Sordo and E. M. Vázquez-López, Inorg. Chem., 2003,
42, 6395; (b) J. S. Casas, M. V. Castaño, E. E. Castellano, J. Ellena,
M. S. García-Tasende, A. Gato, A. Sánchez, L. M. Sanjuán and
J. Sordo, Inorg. Chem., 2002, 41, 1550; (c) J. S. Casas, M. V. Castaño,
E. E. Castellano, M. S. García-Tasende, A. Sánchez, L. M. Sanjuán
and J. Sordo, Eur. J. Inorg. Chem., 2000, 83.
3 S. Jayasree and K. K. Aravindakshan, Polyhedron, 1993, 12,
1187.
4 G. M. Sheldrick, SHELX-97, An integrated system for solving and
refining crystal structures from diffraction data, University of
Göttingen, Göttingen, Germany, 1997.
three types of oxygen atom, two belonging to the ligand and the
third to the water molecule. However, [Zn(L4 Ϫ H)] has only
two types of oxygen atom according to the proposed structure.
The O1s spectrum for [ZnL4 ]ؒ0.5H2O shows a broad signal
2
centred at 532.3 eV (FWHM = 3.45 eV) that can be
decomposed into two signals at 530.9 and 532.6 eV (Fig. SF3 in
ESI†). The former is assigned to the oxygen of the carbonyl
group and the latter, more intense signal, to the oxygen of the
methoxy group (there may also be a contribution from the
oxygen of the water molecule). In the case of [Zn(L4 Ϫ H)], the
O1s signal is narrower (FWMH = 2.85 eV) and can be
decomposed into two signals of similar intensity at 531.5 and
532.9 eV (Figure SF3 in ESI†). The O1s binding energy of the
oxygen of the carbonyl group is shifted from 530.9 to 531.5 eV
as a consequence of its binding to zinc, which reduces the
partial negative charge of the oxygen atom. The XPS data,
therefore, seem to support the proposed structure for solid
[Zn(L4 Ϫ H)].
5 L. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
6 R. Carballo, J. S. Casas, E. García-Martínez, G. Pereiras-Gabián,
A. Sánchez, J. Sordo and E. M. Vázquez-López, Acta Crystallogr.,
Sect. E, 2002, 52, o787.
7 J. S. Casas, M. V. Castaño, M. S. García-Tasende, I. Martínez-
Santamarta, J. Sordo, E. E. Castellano and J. Zukerman-Schpector,
J. Chem. Res. (S), 1992, 234.
8 J. E. Huheey, E. A. Keiter and R. L. Keiter, Inorganic Chemistry,
HarperCollins, New York, 4th edn., 1993, p. A-30.
9 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and
G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349.
10 R. A. Santos, E. S. Gruff, S. A. Koch and G. S. Harbison, J. Am.
Chem. Soc., 1990, 112, 9257.
11 J. T. Ahlemann, H. W. Roesky, R. Murugavel, E. Parisini,
M. Noltemeyer, H. G. Schmidt, O. Müller, R. Herbst-Irmer,
L. N. Markovskii and Y. G. Shermolovich, Chem. Ber./Recueil, 1997,
130, 1113.
The smaller size of Zn(), its tendency to tetracoordination
and its “hard” acid character probably explain why this kind of
polymerization is induced by Zn() but not by Cd().
Acknowledgements
12 F. Hueso-Ureña, A. L. Peñas-Chamorro, M. N. Moreno-Carretero,
M. Quirós-Olazábal and J. M. Salas-Peregrin, Polyhedron, 1998, 18,
351.
13 C. D. Wagner, in Practical Surface Analysis, ed. D. Briggs and
M. P. Seah, Wiley, 1995, vol. 1, pp. 595–634.
We thank Dr Susanna Vogliardi, CNR, Padua (Italy) for
performing the MALDI and LDI MS experiments, and the
Xunta de Galicia (Spain) for financial support under Project
PGIDT00PX-120301PR.
D a l t o n T r a n s . , 2 0 0 4 , 2 0 1 9 – 2 0 2 6
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