Donor abilities of heterocyclic neutral Lewis bases in a nickel(II) salicylaldehyde 4-phenylthiosemicarbazonato coordination environment

Article abstract of DOI:10.1002/ejic.201201050

Eight mononuclear [Ni(sal 4-Phtsc)·D] thiosemicarbazonato complexes [sal 4-Phtsc = salicylaldehyde 4-phenylthiosemicarbazonato ligand; D = imidazole (1), methylimidazole (2), pyridine (3), 4-aminopyridine (4), 4-methylpyridine (6), morpholine (7), thiomorpholine (8), 2-aminophenol (9)] and one dinuclear {[Ni(sal 4-Phtsc)]₂·D}·2DMSO [D = 4,4′-bipyridine (5)] complex have been prepared by adding the corresponding Lewis base to the methanol suspension of the parent complex [Ni(sal 4-Phtsc)(H₂sal 4-Phtsc)]·CH₃OH. The exchange of the neutral salicylaldehyde 4-phenylthiosemicarbazone (H₂sal 4-Phtsc) ligand in the parent complex for the appropriate Lewis base has been confirmed by IR spectroscopy and powder X-ray diffraction (PXRD) in the solid state. The single-crystal X-ray diffraction of seven complexes 1 and 3-8 confirmed the formation of the complexes with the Ni^II ion, coordinated through O,N,S-donor atoms from the dibasic salicylaldehyde 4-phenylthiosemicarbazonato ligand and endocyclic N-donor atom from the neutral ligand D in the form of a distorted square-planar coordination. NMR spectroscopy in DMF or DMSO and quantum mechanical calculations have been performed in order to explain and compare the stability of the complexes in solution, depending on the polarity of solvents in the context of donor properties and the nucleophilicity of the heterocyclic Lewis base. The single-crystal X-ray data enables a comparison with calculated standard Gibbs energies of binding in the context of crystal packing forces, leading to a general conclusion that the stability of the mononuclear complexes results in the formation of more stable hydrogen-bonded cyclic dimers as a crystal packing pattern. The mononuclear [Ni(sal 4-Phtsc)·D] thiosemicarbazonato complexes [sal 4-Phtsc = salicylaldehyde 4-phenylthiosemicarbazonato ligand; D = imidazole (1), methylimidazole (2), pyridine (3), 4-aminopyridine (4), 4-methylpyridine (6), morpholine (7), thiomorpholine (8), 2-aminophenol (9)] and dinuclear {[(Ni(sal 4-Phtsc)] ₂·D}·2DMSO [D = 4,4′-bipyridine (5)] complex have been prepared and characterized. Copyright

Full text of DOI:10.1002/ejic.201201050

FULL PAPER
DOI:10.1002/ejic.201201050
Donor Abilities of Heterocyclic Neutral Lewis Bases in a
Nickel(II) Salicylaldehyde 4-Phenylthiosemicarbazonato
Coordination Environment
Marina Cindric´,*[a] Gordana Pavlovic´,*[b] Tomica Hrenar,[a]
[a]
[c]
´
´
Marina Uzelac, and Manda Curic
Keywords: Nickel / S,N ligands / Lewis bases / Hydrogen bonds
Eight mononuclear [Ni(sal4-Phtsc)·D] thiosemicarbazonato
complexes [sal4-Phtsc = salicylaldehyde 4-phenylthiosemi-
carbazonato ligand; D = imidazole (1), methylimidazole (2),
pyridine (3), 4-aminopyridine (4), 4-methylpyridine (6),
morpholine (7), thiomorpholine (8), 2-aminophenol (9)] and
one dinuclear {[Ni(sal4-Phtsc)]2·D}·2DMSO [D = 4,4Ј-bipyr-
NiII ion, coordinated through O,N,S-donor atoms from the di-
basic salicylaldehyde 4-phenylthiosemicarbazonato ligand
and endocyclic N-donor atom from the neutral ligand D in
the form of a distorted square-planar coordination. NMR
spectroscopy in DMF or DMSO and quantum mechanical
calculations have been performed in order to explain and
idine (5)] complex have been prepared by adding the corre- compare the stability of the complexes in solution, depending
sponding Lewis base to the methanol suspension of the par-
ent complex [Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH. The ex-
change of the neutral salicylaldehyde 4-phenylthiosemicarb-
azone (H2sal4-Phtsc) ligand in the parent complex for the
appropriate Lewis base has been confirmed by IR spec-
troscopy and powder X-ray diffraction (PXRD) in the solid
state. The single-crystal X-ray diffraction of seven complexes
1 and 3–8 confirmed the formation of the complexes with the
on the polarity of solvents in the context of donor properties
and the nucleophilicity of the heterocyclic Lewis base. The
single-crystal X-ray data enables a comparison with calcu-
lated standard Gibbs energies of binding in the context of
crystal packing forces, leading to a general conclusion that
the stability of the mononuclear complexes results in the for-
mation of more stable hydrogen-bonded cyclic dimers as a
crystal packing pattern.
the different ligands enhance the catalysis of all the reac-
tions. In recent years investigations have been done on
structural and biological properties of thiosemicarbazones
and their complexes as a potential model system for redox
enzymes.[2–8] Thiosemicarbazones have received consider-
able attention because of their coordination chemistry[9–11]
and biological activities. Thiosemicarbazones derived from
2-hydroxy-aromatic aldehydes such as H2sal4-Phtsc can lig-
ate metal centres in a monodentate or chelate mode through
a S-donor atom or O,N,S-donor system. While free tsc li-
gands are dominated by the thione tautomeric form, both
thione and thiol tautomers can be presented in metal com-
plexes, sometimes in the same complex. Thiosemicarb-
azones derived from 2-hydroxy-aromatic aldehydes, which
coordinate metal ions monodentately or tridentately, are in
the thione and thiol form, respectively. Dibasic forms of
such tridentate ligands are generated by the deprotonation
of –OH and –SH groups.
Introduction
Nickel is an essential trace element for living organisms
and nickel enzymes known to date are divided into two
groups: hydrolases and redox enzymes. Nickel(II) acts as
the Lewis acid in hydrolase enzymes, while the presence of
SH coordination of redox active enzymes is crucial for cata-
lytic cycles of nickel centres.[1–4] Although the discovery of
urease as the first biological system for which nickel is es-
sential for activity dates to 1975 and despite several thor-
ough studies on biochemical and physical properties of
nickel enzymes, we do not have all the answers as to how
[a] Faculty of Science, University of Zagreb,
Horvatovac 102a, Zagreb 10000, Croatia
Fax: +385-1-461-1191
E-mail: marina@chem.pmf.hr
Homepage: www.chem.pmf.hr
[b] Faculty of Textile Technology, Department of Applied
Chemistry, University of Zagreb,
Their biological properties and activities are often related
to their ability to form chelates with metal ions and to the
presence of a substituent at the peripheral nitrogen atom.[4]
Minor modifications in thiosemicarbazonato ligands, such
as the bulky substituent at the peripheral nitrogen atom,
can cause substantial changes in their biological and phar-
macological properties.[12] The biological activity of thio-
Prilaz baruna Filipovic´a 28a, Zagreb 10000, Croatia
Fax: +385-1-3712-599
E-mail: gpavlov2@ttf.hr
Homepage: www.unizg.ttf.hr
[c] Rudjer Bosˇkovic´ Institute,
P. O. Box 1016, Zagreb 10000, Croatia
Homepage: www.irb.hr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201050.
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semicarbazonato complexes differs from that of either of observed the decomposition of the [Ni(sal4-Phtsc)(H2sal4-
the ligands or the metal ions and is increased and/or de- Phtsc)]·CH3OH complex in the DMSO solution and the
creased, depending on lipophillicity, which controls the rate substitution of the S-bound H2sal4-Phtsc ligand by a
of entry of molecules or ions into the cell, and is modified DMSO molecule. This reaction inspired us to investigate
by coordination.[5] This is a very important process that the influence of various neutral Lewis bases on the nickel-
modulates electronic properties and activity of the metal (II) coordination sphere, according to their nucleophilicity
centre and is decisive for the activity of metalloenzymes, and stereochemistry. A number of square-planar NiII sal-
because it changes the coordination around the metal cen- icylaldehyde 4-phenylthiosemicarbazonato complexes are
tre by breaking and forming coordinative bonds with sub- known where monodentate ligands with N- or P-donor
strates or other molecules.
atoms occupy the fourth coordination site, but a study on
Because of their promising biological and catalytic activi- the influence of the nucleophilicity and stereochemistry of
ties, salicylaldehyde thiosemicarbazonato nickel(II) com- ligands providing N, O/N or N/S donor sets is absent.[17]
plexes with different substituents at the peripheral N3 atom The reactions of [Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH
have been studied extensively.[13–15] Recently, we have inves- with different Lewis bases such as imidazole (1), 2-methyl-
tigated new synthetic routes, such as mechanochemical and imidazole (2), pyridine (3), 4-aminopyridine (4), 4,4Ј-bipyr-
electrochemical ones, in the preparation of square-planar idine (5), 4-methylpyridine (6), morpholine (7), thiomorph-
and octahedral nickel(II) complexes with salicylaldehyde oline (8) and 2-aminophenol (9) yielded new crystalline
thiosemicarbazone ligands. The ligands were substituted at square-planar NiII complexes. (Figure 1). All the complexes
the peripheral N3 atom. We have compared these non-con- are red to orange in colour and soluble in most organic
ventional routes with the classical approach.[16] We have solvents. Superimposition of the experimental powder pat-
also studied the influence of synthetic conditions on the terns confirms the structural differences for complexes 1–9
coordination around NiII, since the control of geometry and mutually and in relation to the parent complex (Figure S2).
spin states of metal ions has a very important role in inor-
ganic and biological chemistry, especially in catalytic pro-
IR Spectroscopy
cesses. In a continuation of the investigations of salicylalde-
hyde thiosemicarbazonato NiII complexes we have prepared
eight mononuclear complexes and one dinuclear of the type
[Ni(sal4-Phtsc)·D] and {[Ni(sal4-Phtsc)]2·D}·2DMSO.
Square-planar NiII complexes are coordinated with the tri-
dentate salicylaldehyde 4-phenylthiosemicarbazonato li-
gand, while the fourth coordination site is occupied by a
heterocyclic Lewis base, D [D = imidazole (1), methylimid-
azole (2), pyridine (3), 4-aminopyridine (4), 4,4Ј-bipyridine
(5), 4-methylpyridine (6), morpholine (7), thiomorpholine
(8) and 2-aminophenol (9)]; see Figure 1, parts a–c, the
complexes 1 and 5 are chosen as representatives.
The complexes were characterized by NMR spectroscopy
in solution and IR spectroscopy, powder X-ray diffraction
(PXRD) and single-crystal X-ray diffraction (SCXRD) in
the solid state, in order to follow up the donor abilities of
various Lewis bases in a salicylaldehyde 4-phenylthiosem-
icarbazonato environment of NiII complexes, i.e. the com-
petition of provided donor atoms for the NiII coordination
Their IR spectra are in accordance with the literature
data for similar types of compounds (Figure S1).[18] In all
complexes, the bands observed over the range 3349 to
3127 cm–1 correspond to ν(O–H) and ν(N–H) stretching vi-
brations from the thiosemicarbazonato ligand. The strong
ν(C=N) bands between 1606 and 1581 cm–1 indicate the co-
ordination of the azomethine nitrogen to NiII. The thio-
amide bands, ν(C–S), lie in the range 820–860 cm–1, and
indicate the coordination of NiII to the sulfur atom. The
ligation of the Lewis bases, morpholine, 2-aminophenol and
thiomorpholine, takes place through a N-donor atom, and
the characteristic C–N bands appear in the spectra of 7, 8
and 9 at 1112, 1114 and 1212 cm–1.
Crystal Structure Description
The molecular structures of the six mononuclear com-
sphere. The X-ray structural analysis of the majority of the plexes, [Ni(sal4-Phtsc)·D] (1, 3, 4 and 6–8) and one dinu-
prepared complexes (1 and 3–8) enables us to follow the clear complex,{[Ni(sal4-Phtsc)]2·D}·2DMSO (5), were de-
placement of the Lewis base molecule in the coordination termined by single-crystal X-ray diffraction studies (Fig-
sphere of the NiII ion and its influence on the conformation ure 1 and Supporting Information, Figures S3–S7). Com-
and stability of the complex molecule in the solid state. plex 3 is the conformational polymorph of the previously
These effects are accompanied by quantum mechanical cal- published pyridine derivative,[13k] which contains two con-
culations of standard Gibbs energies of binding in vacuo formers of complex molecules within an asymmetric unit.
and in the solvents of differing polarity.
A comparison of the powder patterns calculated from the
single-crystal data along with overlaying of molecular struc-
tures confirms conformational differences between 3 and
the previously published polymorph (Figure S8 and S9,
respectively). The asymmetric unit of each molecular struc-
ture contains one complex molecule, except in the case of
Results and Discussion
General Considerations
During our investigations on the synthesis and charac- structure 8 with two crystallographically independent mole-
terization of the thiosemicarbazonato NiII complexes,[16] we cules per asymmetric unit. The two complex molecules dif-
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Figure 1. (a) Schematic overview of complexes 1–9 obtained from the reaction of complex [Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH with
the methanol suspension of the corresponding Lewis base. The Mercury rendered view of the ball and stick molecular structures of
complexes 1 and 3–8 are shown. The colour scheme applied is: Ni – purple, S – yellow, oxygen – red, nitrogen – blue, carbon – gray,
hydrogen – light gray. The almost identical molecular orientations can be seen. The dashed lines represent weak intramolecular C14–
H14–N2 hydrogen bonds in complexes 3–8. The probable structures of complexes 2 and 9 are outlined by chemical diagrams. Solvent
DMSO molecules in 5 are omitted. The asymmetric unit of complex 8 with two crystallographically independent complex molecules is
shown. (b) The Mercury POV-Ray view of the asymmetric unit of 1 with the atom-labelling scheme. The displacement ellipsoids are
drawn at the 50% probability level at 296(2) K. (c) The Mercury POV-Ray view of the asymmetric unit of 5 with the atom-labelling
scheme. The displacement ellipsoids are drawn at the 50% probability level at 296(2) K. DMSO molecules are omitted.
fer mainly in the N-phenyl ring conformation (Figure S10).
The nickel to sulfur bond lengths (which are always
The crystal structure of complex 5 contains two DMSO shorter for the thiol form than that of the thione due to the
molecules as the solvent of crystallization. The NiII ion is chelate effect, since the chelate rings have a pseudoaromatic
chelated in a square-planar deformed coordination by the character)[13] indicate a –C=N–N=C–SH thiol form of the
sal4-Phtsc tridentate dibasic ligand through the thioamide sal4-Phtsc ligand along with the other bond lengths of the
sulfur, azomethine nitrogen and phenolato oxygen atoms central ligand backbone, such as the nitrogen-to-carbon
and by the nitrogen atom from the heterocyclic neutral bond length in the –N=C–SH region, which has a signifi-
Lewis base trans to the azomethine nitrogen atom (Table 1). cant π character, and the carbon-to-sulfur bond length,
Such chelation results in the formation of two chelate rings: which is dominantly σ in character.
six-membered and five-membered ring with the azomethine
The sal4-Phtsc ligand consists of three structural frag-
nitrogen atom acting as a common atom, forming a bicyclic ments: the salicyl part, the central thiosemicarbazonyl moi-
system slightly folded along the nickel-to-imine nitrogen ety and the phenyl part. The salicyl-thiosemicarbazonyl
axis.
moiety is almost planar, while the lack of planarity of the
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Table 1. Nickel(II) coordination sphere geometry (bond lengths [Å] and angles [°]) for the 1 and 3–8 complexes. *The corresponding
values in 5 and 8 are: Ni1–S11, Ni1–O11, Ni1–N11, Ni1–N14, Ni2–S21, Ni2–O21, Ni2–N21 and Ni2–N24. **D: nitrogen atom from
the neutral Lewis base.
1
3
4
5*
6
7
8*
Bond lengths
Ni1–S1
2.138(1)
1.862(2)
1.851(3)
1.911(2)
2.153(2)
1.873(5)
1.862(6)
1.928(5)
2.156(1)
1.879(2)
1.852(2)
1.908(2)
2.140(3)
2.140(2)
1.856(6)
1.856(5)
1.858(5)
1.854(5)
1.925(5)
1.920(5)
2.1586(7)
1.862(2)
1.854(2)
1.914(2)
2.151(4)
1.843(8)
1.856(9)
1.953(8)
2.143(2)
2.144(1)
1.858(3)
1.851(3)
1.871(4)
1.862(4)
1.960(4)
1.958(4)
Ni1–O1
Ni1–N1
Ni1–D**
Bond angles
N1–Ni1–O1
94.8(1)
174.3(1)
87.8(1)
87.1(1)
172.6(1)
91.1(1)
95.4(2)
177.4(3)
86.4(2)
87.4(2)
176.5(2)
90.9(2)
95.29(7)
175.92(8)
86.88(7)
87.15(6)
176.05(5)
90.87(5)
95.4(3)
95.6(2)
178.2(3)
177.3(3)
86.4(3)
86.1(2)
87.8(2)
87.6(2)
176.8(2)
175.9(2)
90.4(2)
90.8(2)
95.61(8)
177.83(8)
86.00(7)
87.09(6)
176.95(5)
91.34(6)
95.3(4)
178.0(4)
84.0(4)
87.1(4)
177.0(3)
93.6(3)
95.3(2)
95.3(2)
179.2(2)
179.5(2)
84.5(2)
84.5(2)
87.1(1)
87.2(1)
177.3(1)
177.5(1)
93.2(1)
93.1(1)
N1–Ni1–D
O1–Ni1–D
N1–Ni1–S1
O1–Ni1–S1
D–Ni1–S1
ligand as a whole is described by dihedral angles calculated
between the two peripheral phenyl rings of the sal4-Phtsc
ligand in 1 and 3–8 (Table S4). The significant discrepancy
in the dihedral angle value among all complexes is observed
only for structure 1 [Table S4; 80.6(2)°]. The configuration
of the sal4-Phtsc ligand reveals that the sulfur atom is ori-
ented at the same side as the –NH group in the complexes
3–8, but not in the imidazole derivative 1. This is evidenced
by the twisting of the phenyl ring in the –NHPh moiety
around the C8–N3 single bond trans to the sulfur atom
(Figure 2 and Table S5). Many structures of uncomplexed
and unprotonated thiosemicarbazones reveal the trans con-
figuration of the sulfur atom to the azomethine nitrogen
and the cis configuration of the –NH group and azomethine
nitrogen atom.[19]
The complexation of the sal4-Phtsc ligand requires a cis
configuration of the sulfur atom to the azomethine nitro-
gen, which is afforded in complexes 1 and 3–8, but not the
unavoidable cis configuration of the –NH group and azo-
methine nitrogen atom. The latter configuration of sal4-
Phtsc ligand is achieved in complexes 3–8, while the trans
configuration of the –NH group and azomethine nitrogen
atom is achieved in the imidazole derivative 1.
Figure 2. The Mercury rendered view of the overlapping diagram
for compounds 1 and 3–8. The applied colour scheme is: gray – 1,
yellow – 3, green – 4, cyano – 5, purple – 6, blue – 7 and red – 8
(molecule 1). The diagrams were constructed by overlapping the
molecules through nickel and donor atoms O,N,S. The main con-
formational misalignment is perceived in the spatial orientation of
the Lewis base heterocyclic rings in relation to the salicyl thiosemi-
carbazone moiety and in the different orientation of the phenyl
ring in the –NHPh moiety in the imidazole derivative 1 (in gray)
compared with the other structures 3–8 (Table S5).
The formation of the intramolecular C14–H14···N2 hy-
drogen bond found in other complexes, is precluded in 1
(Figure 3, a). Both cis and trans ligand configurations of N1 nitrogen atoms; see Table S3 and part a in Figure 3. In
the –NH and azomethine nitrogen atom can be stabilized complexes 3, 4 and 6 the –NH group participates in the N–
by different intermolecular hydrogen bonds, consequently H···S intermolecular hydrogen-bond formation (Figure 3,
accomplishing similar crystal architectures of the complexes b–d). Therefore, the crystal packing patterns are basically
(Figure 3). The sal4-Phtsc ligand configuration in 1 is as- characterized by the formation of the centrosymmetric
sisted by the formation of the N–H···N type of intermo- R22(8) rings (in a “carboxylic acid manner”) through either
lecular hydrogen bond between the –NH and azomethine the weak N–H···N intermolecular hydrogen bond in 1 (Fig-
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ure 3, a) or the N–H···S intermolecular hydrogen bond in
complexes 3, 4 and 6, see parts b–d in Figure 3. The cyclic
dimers in 1 are further propagated through the N–H···O
hydrogen bonds with the imidazole –NH group as a bridge
into the 3D hydrogen-bonded network (Figure 3, a). The
rings in 3 are stacked along the b axis through π···π interac-
tions. Such molecular piles are arranged in a herringbone
fashion along the c axis [Table S3 and Figure S11(a)]. On
the contrary, hydrogen-bonded dimers in 4 and 6 are ad-
ditionally connected through N–H···O (in 4) or C–H···O (in
6) hydrogen bonds as the result of the presence of NH2 or
CH3 groups on the pyridine ring at position 4 in complexes
4 and 6, respectively. Therefore, the new centrosymmetric
ring assigned by a graph-set analysis as R22(16) forms a
chain of rings alternating with R22(8) rings in 4 and 6 (Fig-
ure 3, b–d). The hydrogen-bonded chains are spread along
the a axis in 4 and 6. The chains are assembled in a herring-
bone fashion along the c axis; see Table S3 and Fig-
ure S11(b) and S11(c). The presence of two DMSO mole-
cules per complex molecule in 5 and acceptor capabilities
of the oxygen atom in morpholine (7) or the sulfur atom in
thiomorpholine (8) derivatives prevents the cyclic dimeriza-
tion found in complexes 1, 3, 4 and 6 and enables other
crystal packing patterns achieved by the –NH group of
the –NHPh structural fragment as a proton donor (Fig-
ures S12, S13 and S14).
Theoretical Calculations and Correlation with NMR
Spectroscopy
The calculated standard Gibbs energies of binding are
in accordance with the experimentally observed trends and
linear correlation model between the experimentally mea-
sured distances and the calculated standard Gibbs energies
of binding for all ligands presented in Table 2 (except for
bipyridine). They give an R2 value of 0.97, confirming the
validity of the theoretical methods.
Table 2. The calculated standard Gibbs energies of binding at
298.15 K and 101.325 kPa for complexes of Ni2+ with salicylalde-
hyde 4-phenylthiosemicarbazone and various Lewis bases with the
binding atom indicated in parenthesis where necessary. The B3LYP/
6-311++g(d,p) level of theory; solvent effects were incorporated
using the IEFPCM method.
Complex
ΔrG°binding [kcalmol–1
in vacuo in CH3OH in DMF
(ε = 32.613) (ε = 37.219) (ε = 46.826)
]
in DMSO
1
–612.16
–606.96
–171.28
–165.69
–169.43
–163.86
–167.89
–161.29
Figure 3. The Mercury POV-Ray rendered view of the different as-
sembly architectures found in the crystal structures of 1(a), 3(b),
4(c) and 6(d) as a result of the presence of different potential pro-
ton donors. The hydrogen bonds are denoted by dashed lines in
orange and green. All four packing patterns are basically charac-
terized by the formation of the centrosymmetric R22(8) rings by
means of weak N–H···N (in 1) and N–H···S (3, 4 and 6) intermo-
lecular hydrogen bonds between the N3 atom of the –NHPh moiety
and the donor S1 atom. In the crystal structures of 4 and 6 [3(c)
and 3(d), respectively] the R22(16) rings are formed by the N–
H···O(metal bound) (4) or C–H···O(metal bound) (6) hydrogen
bonds, while in 1 the R22(8) rings are further linked by N(imid-
azole)–H···O(metal bound) hydrogen bonds (in green) and in 3 by
the π···π interactions (see Supporting Information for further crys-
tal structure descriptions).
2 (N)
3
4
6
–609.49
–614.58
–611.53
–604.55
–598.10
–604.11
–602.19
–607.14
–607.86
–169.61
–173.05
–168.90
–165.70
–158.81
–165.62
–161.92
–163.45
–163.83
–167.83
–171.50
–167.09
–163.92
–157.01
–163.83
–160.12
–161.64
–162.01
–165.33
–168.60
–164.51
–161.41
–154.47
–161.34
–157.57
–159.11
–159.44
7 (N)
morpholine (O)
8 (N)
thiomorpholine (S)
dmf (O)
dmso (O)
1H NMR spectroscopic study of complexes 1–9 in [D6]-
DMSO (or [D7]DMF) solution showed that the structures
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of complexes 1, 5, 7 and 8 in the solution are consistent thus demonstrating that the morpholine and thiomorph-
with those observed in the solid state (Table S1). The parent oline are not locked rigidly into the chair conformation in
complex [Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH and its de- solution as in the solid state and that their conformation
rivatives 2, 3, 4 and 6 decompose very fast in [D6]DMSO changes are not fast on the NMR timescale. This is sup-
producing the [Ni(sal4-Phtsc)(DMSO)] complex and a free ported by variable-temperature 1H NMR experiments in
ancillary ligand, since DMSO replaces S-bound neutral sal- [D6]DMSO (and [D7]DMF) since the spectra recorded in
icylaldehyde 4-phenylthiosemicarbazone in the parent com- [D6]DMSO at 90 °C contain only two broad signals. One is
plex, 2-methylimidazole in 2, pyridine in 3, 4-aminopyridine the signal of proton H-7, which interacts with oxygen of
in 4 and 4-methylpyridine in 6.
the six-membered chelate ring.[22] The other signals of the
In contrast to these ligands, imidazole in 1, 4,4Ј-bipyr- thiosemicarbazone ligand in the spectrum of complex 9 re-
idine in 5, morpholine in 7 and thiomorpholine in 8, which corded in [D6]DMSO (or [D7]DMF) at ambient tempera-
also act as monodentate ligands (bridging in the case of 4, ture are sharp and their integration is in good agreement
4Ј-bipyridine), are more nucleophilic than DMSO and can- with the number of protons (Figure S15). However, the sig-
not be replaced. Among all the theoretical investigations of nals corresponding to the 2-aminophenol are rather broad
the
[Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH,
[Ni(sal4- and their integration is in disagreement with the number of
Phtsc)D] and {[Ni(sal4-Phtsc)]2D}·2DMSO complexes protons, thus indicating that the [D6]DMSO (or [D7]DMF)
with different N-donor Lewis bases, the inclusion of 4- molecule replacement is fast on the NMR timescale with
aminopyridine in 4 and imidazole in 1 produced the most the 2-aminophenol bound to NiII in complex 9 through ni-
stable complexes with the lowest standard Gibbs energies trogen of the amino group as suggested by quantum chemi-
of binding. For complexes 3 and 6, with pyridine and 4- cal calculations. Similar values for Gibbs energies (Table 2)
methylpyridine, respectively, standard Gibbs energies of of binding for complex 9 and DMSO (or DMF) suggested
binding were similar, whereas the introduction of the amino the possibility of ligand interchange with the solvent mole-
group in the position 4 of the pyridine molecule (in complex cule, which is observable from the low temperature NMR
4) resulted in the significant stabilization of the complex spectra (Figure S15). Hence, in a [D6]DMSO or [D7]DMF
(ca. 4 kcalmol–1). Spectroscopic investigation showed a solution of complex 9 we assumed a coexistence of complex
very fast decomposition of 4 in [D6]DMSO yielding a [Ni- 9, complex [Ni(sal4-Phtsc)(DMSO)] or [Ni(sal4-Phtsc)-
(sal4-Phtsc)(DMSO)] complex. This is in agreement with (DMF)] and free 2-aminophenol, which is supported by
the literature data on the influence of nucleophilicity on the variable-temperature 1H NMR experiments in [D7]DMF
complex stability. The oxygen centre in DMSO acts as a (Figure S15). The spectra recorded in [D7]DMF at –25 and
nucleophile toward the hard electrophile, such as NiII, that –50 °C contain very well resolved signals of the 2-
prefers the oxygen donor site, whereas the nitrogen atom in aminophenol ligand as well as a H-7 signal of thiosemicarb-
4-aminopyridine acts as a soft nucleophile.[20] The inter- azone, whose integration is in good agreement with the
change of 4-aminopyridine with DMSO is mostly con- number of protons, thus demonstrating that in [D7]DMF
trolled by the kinetics.[21] These facts could explain the ob- at –25 and –50 °C complex 9 is predominant, since at low
servation from the temperature-dependent NMR spectra temperatures the exchange between solvent molecules and
that does not follow the trend in the calculated standard 2-aminophenol is much slower. The coordination of the NiII
Gibbs energies where complex 4 with the 4-aminopyridine by nitrogen of 2-aminophenol in complex 9 results in large
derivative appears to be thermodynamically more stable. In downfield shifted signals of NH2 and OH protons relative
the complexes 7 and 8, morpholine and thiomorpholine, to the free ligand signals (Table S1 and Figure S15). A large
respectively, are bound to nickel through nitrogen rather downfield shift of the OH signal could be a consequence of
than through oxygen or sulfur, as confirmed by single-crys- an intramolecular hydrogen bond between this proton and
tal X-ray diffraction studies. The calculated standard Gibbs oxygen of the six-membered chelate ring.[22] Finally, the cal-
energies of the binding of 8 (with thiomorpholine) through culated Gibbs energies revealed that the stability of all com-
a nitrogen or sulfur atom are similar (Table 2). Since this plexes is lower with the increase of the solvent dielectric
difference is relatively small (ca. 1.9 kcalmol–1 in vacuo, giv- constant (Table 2).
ing a 96:4 ratio) both binding modes can be observed,
whereas for 8 (with morpholine) this difference is more pro-
Conclusions
nounced ca. 6.4 kcalmol–1 in vacuo) favouring only one
mode of binding (O over the N atom).
The
square-planar
[Ni(sal4-Phtsc)(H2sal4-Phtsc)]·
Coordination of the metal atom by nitrogen in these CH3OH complex[16] served as the parent complex in our
complexes causes a downfield shift of the NH signal by 1.2 study on the influence of heterocyclic Lewis bases as mono-
and 0.90 ppm, respectively, relative to the signals of free dentate ligands (or bridging in the case of complex 5) to
ligands (Scheme S1). In the spectra of the free ligands, the nickel(II) coordination sphere, depending on their nu-
morpholine and thiomorpholine, the rings show two re- cleophilicity and stereochemistry. Our previous investi-
solved triplets resulting from the fast conformational gations on the above-mentioned complex confirmed the la-
changes. However, these protons in the spectra of the com- bile bonding of the neutral salicylaldehyde 4-phenylthiose-
plexes show three or four broad signals at ambient tempera- micarbazonato ligand to the NiII ion through a S-donor
ture with intensity ratios of 4:2:2 or 2:2:2:2, respectively, atom and provided an opportunity to substitute it easily
Eur. J. Inorg. Chem. 2013, 563–571
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FULL PAPER
picoline, 2-aminophenol), N/O (morpholine) or N/S ligand (thio-
morpholine) (2.5 mol) was added to the suspension of [Ni(sal4-
Phtsc)(H2sal4-Phtsc)]·CH3OH (1 mol) and heated until the clear
reddish solution (without precipitate) was obtained. After a few
days, the crystals of 1–4 and 6–9 were filtered off, washed with a
small amount of cold alcohol and dried. In the case of 5, the reac-
tion was instantaneous and the precipitate was present at all times.
The crystals of 5 were obtained by recrystallization from the mix-
ture of DMSO and acetone.
with different Lewis bases with another –N, –N/O or –N/S
donor set introduced by using various heterocyclic Lewis
bases. Eight mononuclear complexes of the general formula
[Ni(sal4-Phtsc)·D] and one dinuclear {[Ni(sal4-Phtsc)]2·
D}·2DMSO complex were synthesized.
The structures of complexes where D is an imidazole (1),
4,4Ј-bipyridine (5), morpholine (7) and thiomorpholine (8)
are the same in the solid state and in [D6]DMSO, while
complexes 2 (2-methylimidazole), 3 (pyridine), 4 (4-amino-
pyridine), 6 (4-methylpyridine) and 9 (2-aminophenol) de-
compose very fast, producing a [Ni(sal-4-phtsc)(DMSO)]
complex. All these results are in accordance with theoretical
calculations of the standard Gibbs energies of binding, ex-
cept in the case of complex 4 where interchange of 4-amino-
pyridine with DMSO is mostly controlled by kinetics.[21]
The experimental structural and spectroscopic data are in
good agreement with the calculated standard Gibbs ener-
gies of binding. A linear correlation model between the ex-
perimentally measured distances and the calculated stan-
dard Gibbs energies of binding for all ligands (except for
4,4Ј-bypyridine) gives the R2 value of 0.97 confirming the
validity of the theoretical methods. All the results showed
the preferred binding affinity toward the N-donor atom
compared to the O- or S-donor atoms and could explain
the easy substitution of the S-bonded H2sal4-Phtsc in the
parent [Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH complex.
The stability of complexes is strongly connected with nu-
cleophilicity of the N-donor atom, but also with the po-
larity of the solvents since stability of all complexes is lower
with the increase of the solvent dielectric constant. A com-
parison of the calculated standard Gibbs energies of bind-
ing with the single-crystal X-ray data leads to the conclu-
sion that complexes 1, 3, 4 and 6 are thermodynamically
more stable than the others and that the cyclic dimerization
obtained either by N–H···N (in 1) or by the N–H···S (3, 4
and 6) intermolecular hydrogen bonds contributes to the
additional stabilization in the context of the crystal packing
framework. The results of the presented structural data and
the spectroscopic and quantum mechanical analysis show
these types of complexes as possible models for the explana-
tion of catalytic and biological activity of NiII because of
the labile fourth coordination site with the S-, O- or N-
donor ligand.
1: Yield 100.2 mg (63.27%). C17H15N5NiOS (396.09): calcd. C
51.55, H 3.82, N 17.68, Ni 14.82, S 8.09; found C 51.12,
H 3.65, N 17.30, Ni 14.41, S 7.80. IR (KBr): ν = 3179 ν(NH); 3127
˜
ν(NHimidazole)
; 1601, 1583 ν(C=N); 1556 ν(C=Nimidazole); 1152
ν(COphen); 658 ν(CS) cm–1.
2: Yield 127.2 mg (77.79%). C18H18N5NiOS (410.11): calcd. C
52.71, H 4.18, N 17.07, Ni 14.31, S 7.82; found C 52.38, H 3.82,
N 16.58, Ni 14.19, S 7.55. IR (KBr): ν = 3324 ν(NH),ν(OH); 1603,
˜
1587 ν(C=N); 1555 ν(C=Nimidazole); 1148 ν(COphen); 689 ν(CS) cm–1.
3: Yield 127.2 mg (77.79%). C19H16N4NiOS (407.05): calcd. C
56.05, H 3.96, N 13.76, Ni 14.42, S 7.87; found C 55.87, H 3.56,
N 13.31, Ni 14.21, S 7.53. IR (KBr): ν = 3249 ν(OH),ν(NH); 1606,
˜
1587 ν(C=N); 1555 ν(C=Npy); 1143 ν(COphen); 668 ν(CS) cm–1.
4: Yield 132.6 mg (78.21%). C19H17N5NiOS (422.13): calcd. C
54.06, H 4.06, N 16.59, Ni 13.90, S 7.59; found C 53.70, H 3.63,
N 16.32, Ni 13.73, S 7.09. IR (KBr): ν = 3348 ν(OH),ν(NH); 3300,
˜
3179 ν(NHpy); 1600, 1593 ν(C=N); 1554 ν(C=Npy); 1162 ν(COphen); 668
ν(CS) cm–1.
5: Yield 139.4 mg (85.41%). C42H42N8Ni2O4S4 (968.50): calcd. C
52.09, H 4.37, N 11.56, Ni 12.12, S 13.24; found C 52.22, H 4.38,
N 11.65, Ni 12.01, S 13.31. IR (KBr): ν = 3346 ν(OH),ν(NH); 1601,
˜
1581 ν(C=N); 1559 ν(C=Nbpy); 1148 ν(COphen); 668 ν(CS) cm–1.
6: Yield 134.3 mg (79.39%). C20H18N4NiOS (421.14): calcd. C
57.04, H 4.31, N 13.30, Ni 13.94, S 7.61; found C 56.87, H 4.08,
N 12.95, Ni 13.70, S 7.10. IR (KBr): ν = 3349 ν(OH),ν(NH); 1606,
˜
1587 ν(C=N); 1554 ν(C=Npic); 1150 ν(COphen); 668 ν(CS) cm–1.
7: Yield 146.37 mg (87.75%). C18H20N4NiO2S (415.13): calcd. C
52.08, H 4.85, N 13.50, Ni 14.14, S 7.72; found C 51.55, H 4.48,
N 12.89, Ni 14.05, S 7.61. IR (KBr): ν = 3332 ν(OH),ν(NH); 3214
˜
ν(NHmorph.); 1602, 1586 ν(C=N); 1112 ν(C–Nmorph.); 1148 ν(COphen); 692
ν(CS) cm–1.
8: Yield 146.06 mg (84.30%). C18H20N4NiOS2 (431.20): calcd. C
50.14, H 4.67, N 12.99, Ni 13.61, S 14.87; found C 49.92, H 4.19,
N 12.46, Ni 13.43, S 14.67. IR (KBr): ν = 3392 ν(OH),ν(NH); 3180
˜
ν(NHthiomorph.)
; 1600, 1584 ν(C=N); 1114 ν(C–Nthiomorph.); 1150
ν(COphen); 688 ν(CS) cm–1.
Experimental Section
9: Yield 127.2 mg (77.79%). C20H18N4NiO2S (437.14): calcd. C
54.95, H 4.15, N 12.82, Ni 13.43, S 7.33; found C 54.78, H 3.83,
Materials: Salicylaldehyde, 4-phenylthiosemicarbazide, Ni(OAc)2·
4H2O, imidazole, 2-methylimidazole, pyridine, 4-aminopyridine,
4,4Ј-bipyridine, γ-picoline, morpholine, thiomorpholine and 2-
aminophenol were commercially available and used as received.
The ligand H2L (salicylaldehyde 4-phenylthiosemicarbazone) and
complex [Ni(sal4-Phtsc)(H2sal4-Phtsc)]·CH3OH were prepared ac-
cording to the literature procedure.[16] The methanol was of reagent
grade and used as received. IR spectra for the parent complex and
complexes 1–9 can be found in the Supporting Information [Fig-
ure S1(a)–Figure S1(j)].
N 12.36, Ni 13.32, S 7.18. IR (KBr): ν = 3316 ν(OH),ν(NH); 1604,
˜
1586 ν(C=N); 1212 ν(C–Naminophenol); 1150 ν(COphen); 690 ν(CS) cm–1.
Methods: Elemental analyses were carried out with a Perkin–Elmer
Series II 2400 CHNS/O analyser. Infrared spectra were recorded
with a Perkin–Elmer Spectrum RXI FTIR spectrometer from sam-
ples dispersed in KBr pellets (4000–400 cm–1 range).
The 1H NMR spectra were recorded at 25 °C (and at 90 °C for
complexes 8 and 9) in [D6]DMSO with a Bruker AV-600 spectrome-
ter operating at 600.13 MHz. Variable-temperature 1H NMR ex-
periments were carried out at 25, 0, –25 and –50 °C in [D7]DMF
on the same instruments. The signal assignment (Table S1) was
based on the chemical shifts and spin-spin couplings, two dimen-
Synthesis of the Complexes
General Method: The methanol solution of the N-donor (imidazole,
2-methylimidazole, pyridine, 4-aminopyridine, 4,4-bipyridine, γ-
Eur. J. Inorg. Chem. 2013, 563–571
569
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FULL PAPER
sional experiments and quantum chemical calculations of the
Quantum Chemical Calculations: Quantum chemical calculations
were performed using the Gaussian 09 program package.[29] The
geometry optimization for the ground and the transition states were
performed at the B3LYP/6-311++G(d,p) level of theory.[30,31] For
all optimized structures the harmonic frequencies were calculated
to insure that obtained geometries correspond to the local mini-
mum (or maximum) on the potential energy surface. The Gibbs
energies were calculated at T = 298.15 K and p = 101.325 kPa and
the data are given in Table 2. The solvation effects were incorpo-
rated in the calculations using the reformulation of the polarizable
continuum model (PCM),[32,33] known as integral equation formal-
ism (IEFPCM) of Tomasi and coworkers.[34–37]
1
chemical shifts. The H-1H COSY spectra were obtained at 25 °C
in the magnitude mode with 2048 points in the F2 dimension and
512 increments in the F1 dimension.
X-ray Diffraction Experiments: The selected crystallographic and
refinement data for the structures 1 and 3–8 (Figure 1) obtained by
the single-crystal X-ray diffraction experiments are summarized in
Table S2. The selected geometries including valence bonds and
angles, hydrogen bonds and interaction geometries are given in
Table 1 and Table S3. The data collection has been performed by
applying the CrysAlis Software system,[23] Versions 1.171.33.66 or
1.171.34.40 on the Oxford Xcalibur diffractometer supplied by
CCD detector and graphite-monocromated Mo-Kα radiation (λ =
0.71703 Å) (structures 1 and 4), Oxford Xcalibur Nova dif-
fractometer and with graphite-monocromated Cu-Kα radiation (λ
= 1.54184 Å) (structures 3, 5, 6) and Oxford Xcalibur Gemini dif-
fractometer equipped with Sapphire CCD detector and graphite-
monocromated Cu-Kα radiation (λ = 1.5418 Å) (structures 7 and 8).
The data were collected at 296(2) K (structures 3, 5–8) or 120(2) K
(structure 4) all by using ω-scan. Programs CrysAlis CCD and Cry-
sAlis RED[23] were employed for cell refinement and data reduction
in all cases. The Lorentz-polarization effect was corrected and the
diffraction data have been scaled for the absorption effects by the
multi-scanning method. The structures were solved by direct meth-
ods and refined on F2 by weighted full-matrix least-squares. Pro-
grams SHELXS97 and SHELXL97[24] integrated in the WinGX[25]
v. 1.80.05 software system were used to solve and refine structures.
All non-hydrogen atoms were refined with the anisotropic displace-
ment parameters. The hydrogen atoms belonging to the stereo-
chemically different carbon atoms were placed in geometrically ide-
alized positions with assigned isotropic displacement parameters
and they were constrained to ride on their parent atoms by using
the appropriate SHELXL97 HFIX instructions. The hydrogen
atoms belonging to the nitrogen atom of the –NHPh fragment in
all structures were found as a small electron density in the differ-
ence Fourier map and the N–H distance has been restrained to the
target value of 0.86(2) Å by a SHELXL97 DFIX instruction (the
DFIX instruction was not applied for 1 and 4, already freely re-
fined) (or by constrained instruction HFIX 43 for the N23 atom
in complex 8) with assigned isotropic displacement parameters con-
strained to 1.2 times the equivalent isotropic displacement param-
eters of the nitrogen atom that the hydrogen binds to. The hydrogen
atoms of the amino group at the N5 atom in 4 were refined without
DFIX restraint. The target N–H bond length value of 0.91 Å for
the morpholine ligand in 7 has been generated by the HFIX 13
instruction with Uiso(H) = –1.2Ueq(N) and thiomorpholine in 8 has
been restrained to 0.89(2) Å with Uiso(H) = –1.2Ueq(N) at N14 and
N24.
Supporting Information (see footnote on the first page of this arti-
cle): The supplementary materials contain: IR spectra for the par-
ent complex and complexes 1–9, superimposition of the experimen-
tal XRPD patterns for complexes 1–9, the Mercury Pov-Ray over-
views with full atom-labelling scheme for complexes 3, 4 and 6–8,
superimposition of complex 3 and a previously published poly-
morph as well as overlaying of their calculated powder patterns
from the single-crystal X-ray data, the overlaying diagram of the
two crystallographically independent molecules in 8, the extended
1
packing diagrams for the complexes 3, 4, 5, 6, 7 and 8, H NMR
spectra of complex 9, 1H NMR spectroscopic data in DMSO solu-
tion for the complexes 1–9 with corresponding atom numbering of
the ligands used in the assignment of NMR resonances
(Scheme S1), the table of crystallographic data for complexes 1 and
3–8, the table of hydrogen bonding and contact geometries, the
table of the selected calculated dihedral angles for the thiosemicar-
bazonato ligand and the table of the selected torsion angles for the
thiosemicarbazonato ligand.
CCDC-887907 (for 1), -887908 (for 3), -887909 (for 4),
-887910 (for 5), -887911 (for 6), -887912 (for 7), -887913 (for 8)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Acknowledgments
This research was supported by the Ministry of Science, Education
and Sports of the Republic of Croatia (grant numbers 119-1191342-
1082, 119-1191342-2959 and 098-0982915-2950).
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Received: September 11, 2012
Published Online: December 10, 2012
Eur. J. Inorg. Chem. 2013, 563–571
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