Polyhedron 24 (2005) 1175–1184
www.elsevier.com/locate/poly
Interaction of Na(I), Ni(II) and Cu(II) with 2-cyano2-(hydroxyimino)acetic acid: Spectroscopic and theoretical studies
Kamilla Malek a, Henryk Kozłowski b, Leonard M. Proniewicz
a,c,*
a
Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060 Krakow, Poland
Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroclaw, Poland
Regional Laboratory of Physicochemical Analysis and Structural Research, Jagiellonian University, R. Ingardena 3, 30-060 Krakow, Poland
b
c
Received 15 December 2004; accepted 4 April 2005
Available online 23 May 2005
Abstract
Sodium(I) salt as well as nickel(II) and copper(II) complexes of 2-cyano-2-(hydroxyimino)acetic acid (1a) have been prepared and
characterized by infrared, Raman and EPR spectra. Molecular structures of the compounds in the solid state are proposed. The
bidentate 1a ligand chelates the copper and nickel ions through the oxime nitrogen and the carboxyl oxygen atoms to form a trans
bis-complexes. However, two sodium ions are bonded to the deprotonated oximic as well as carboxylic groups. Equilibrium geometries, atomic charges, harmonic vibrational frequencies with potential energy distribution (PED), infrared and Raman intensities
are calculated for all compounds studied here by using the hybrid functional of DFT (B3LYP) with 6-311++G(d,p) and LanL2DZ
basis sets, for sodium and transition metal ions complexes, respectively. The computed properties are compared to the experimental
values.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Cyanoxime complexes; IR; Raman; DFT; PED; Atomic charges
1. Introduction
The coordination properties of cyanoximes have significant impact on their biological activity such as
growth regulatory, antimicrobial or fungicidal properties. For instance, this class of oximes belongs to the
family of Althiomycin antibiotics [1–3]. Also organoantimony(V) cyanoximes have been intensively studied as
potential use in chemotherapy agents with lower toxicity
than Pt(II) and Pd(II) anticancer drugs [4–6].
This group of ligands, with the general formula
HOAN@C(C„N)AR, is characterized by the high acidity that is due to the presence of the cyano group located
*
Corresponding author. Tel.: +48 12 663 2253/2064; fax: +48 12 634
0515.
E-mail address: [email protected] (L.M. Proniewicz).
0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.04.007
close to the oximic moiety. Deprotonation of the oximic
proton in solution causes formation of stable anions.
This acidity is almost 103–105 greater than the acidity
of oximes with aliphatic or ring substituents at the a-carbon. Thus, the deprotonated cyanoximes form various
coordination compounds with different metal ions. The
type of metal ion (s-, p- d-metals) bonded by a
cyanoxime forces firstly a particular complexation structure. Additionally, H-bonding, conjugation, stabilizations of certain ligand molecule conformation are
responsible for structures of cyanoximes and their metal
complexes in solution as well as solid state [4–8].
As the extension of our previous studies, we now
present a systematic investigation of molecular structures of sodium(I) salt as well as nickel(II) and
copper(II) complexes of 2-cyano-2-(hydroxyimino)acetic acid (1a, [H2L]). In this ligand, the carboxylic group
1176
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
is adjacent to the oximic a-carbon. Far now, this particular oxime and their complexes with copper(II) and
nickel(II) ions have been studied in solution (potentiometric, UV–Vis, EPR studies) only [8]. It is known that
this class of oximes predominantly coordinates to metals
via the nitrogen atom (mainly transition metal ions) or
via the oxygen atom (s-, p-metal ions). Additionally,
deprotonation of the 1a oximic group allows formation
of dimeric species where the nitrogen and oxygen atoms
act as metal donors [8–11].
In the present work, the focus is on elucidating
molecular structures of mentioned-above 1a complexes
in solid state based on molecular spectroscopy methods
(IR, RA and EPR). To give detailed assignment of
vibrational spectra and consequently to solve molecular
structures we applied quantum-mechanical calculations
at the DFT level of theory. Additionally, we performed
potential energy distribution calculations (PED) to show
a detailed description of vibrational modes and atomic
charge distribution to give an explanation of the 1a anionic nature (the APT population analysis).
2. Experimental
2.1. Preparation
2.1.1. Na–1a
The sodium salt of 2-cyano-2-(hydroxyimino)acetic
acid was synthesized by the reported procedure [7]. Elemental analysis (C, H, N) was conducted at the Faculty
of Pharmacy of Jagiellonian University according to
standard microanalytical procedures (Anal. Calc. for
Na2C3H0.7N2O3.35: C, 21.9; H, 0.4; N, 17.0. Found: C,
22.2; H, 0.7; N, 16.7%). In the microcrystalline sample,
the sodium-to-1a molar ratio (2:1) was confirmed by a
standard analytical procedure (AAS).
2.1.2. Cu–1a and Ni–1a
The complexes were prepared as described below
using 1:2 molar ratio of metal ions to 1a. An aqueous
solutions of Cu(NO3)2 Æ 2.5H2O and NiCl2 Æ 6H2O
(21.9 and 21.4 mg in 5 ml H2O, respectively) were added
to Na–1a (25 mg) dissolved in water (5 ml). In case of
the Cu–1a complex the clear dark green solution was
stirred (20 min) with heating (35 °C) and treated dropwise with 0.5 M HNO3 (to pH 2). The resulting green
solution was still heated and stirred (1 h) then filtered
and concentrated by evaporation at room temperature.
Dark green microcrystalline precipitate began to form
within a week. The procedure for the Ni–1a complex
was analogues. The NiCl2 Æ 6H2O–1a mixture was clear
straw-colored and after treating with 1 M KOH (to
pH 8) the solution became dark red. Finally, after a
few days dark red microcrystalline powder was obtained. Despite of co-precipitation of the synthesized
complexes with nitrate and chloride ions, respectively,
elemental analyses indicated clearly that the metal-to1a molar ratio is about (1:2).
2.2. Spectroscopy
For FT-Raman measurements, a few milligrams of
the compound was placed in capillary tube and measured directly; 512 and 3000 scans were collected (with
a resolution of 4 cm1) for the sodium and the transition
metal ions compounds, respectively. Fourier transform
mid-infrared (FT-MIR, 256 scans) and Fourier transform far-infrared (FT-FIR, 512 scans) spectra were
run in KBr and low molecular weight polyethylene discs,
respectively. Resolution was set at 4 cm1 (MIR) and
2 cm1 (FIR). Sodium–1a salt FT-Raman spectrum
was recorded on a Bio-Rad step-scan spectrometer
(FTS 6000) combined with a Bio-Rad Raman Accessory
(FTS 40). Excitation at 1064 nm was made by a SpectraPhysics Topaz T10-106c cw Nd:YAG laser. Raman
spectra of the copper and nickel complexes were collected on a Jobin Yvon spectrometer model T6400
equipped with an argon ion laser (excitation at
514.5 nm) and a CCD camera as a detector (Princeton
Instruments). FT-IR spectra were measured on Bruker
(IFS 48) and Bio-Rad (FTS 60V) spectrometers in the
mid and far IR regions, respectively. The accuracy of
the readings was ±1 cm1.
EPR spectrum of the Cu–1a complex (the microcrystalline powder sample) was recorded on a Bruker spectrometer ELEX SYS X500 [X-band (9.5 GHz)] at
298 K.
3. Computational details
B3LYP [12,13] calculations with 6-311++G(d,p) and
LanL2DZ [14,15] basis sets (for the sodium salt and the
transition metals complexes, respectively) were carried
out using the quantum-mechanical GAUSSIAN-98 set of
programs [16]. Optimum geometries and harmonic frequencies were determined by using SGI 2800 computer
in the Academic Computer Center ‘‘Cyfronet’’ in Krakow and on a Cray SV1ex-1-32 computer in Interdisciplinary Center for Mathematical and Computational
Modeling in Warsaw. No symmetry constraints were
imposed during the optimization process. At the
B3LYP/6-311++G(d,p) level a scaling factor of 0.983
was applied to the most harmonic frequencies [except
to m(OH) modes (0.953)] in order to yield the best fit
to the experimental data, as suggested by Michalska
and co-workers [17]. Raman intensities were determined
by RAINT program [18] using values of Raman scattering activities obtained from the Gaussian outputs. The
potential energy distributions (PED) were obtained
from the Veda program [19], while atomic charge
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
calculations were performed using APT population
analysis (GAPT, Generalized Atomic Polar Tensor)
[20]. For the latter, the optimized geometries at the
B3LYP/LanL2DZ level of theory were used.
4. Results and discussion
The 1a complexes can exist as variety of geometrical
isomers, where a metal ion is chelated by the ligand in
the bidentate mode via the carboxylic oxygen and oximic nitrogen atoms or in the monodentate fashion via
either the carboxylate ion or the oximato fragment
(Scheme 1). Potentiometric and UV–Vis studies have
suggested that the copper complex exists as [CuHL2]
species at pH 2, while the nickel complex is present in
the [NiL2]2 form at pH range of 6–10. In these complexes, two ligand molecules are located to each other
in the trans configuration. However, crystallographic
data of Cu(II) complex showed the dimeric structure
[8]. All discussed above molecular structures of 1a complexes are presented in Scheme 1.
In order to identify the molecular structures of the 1a
complexes obtained in this work we used theoretical
simulation of their vibrational spectra. It should be
emphasized that this method allows to predict a general
coordination pattern only but it is very valuable in the
case of the lack of crystallographic data. However, this
is more than enough to distinguish between cis and trans
conformation of the metallocomplex with information
whether coordinated ligands are protonated or not.
Thus, for the purpose of this work, we considered as
models bis-chelate square planar molecules with different conformation of the ligand (cis [MHL2] and trans
1177
with the protonated [MH2L2] as well as deprotonated
oximic group [ML2]2). However, for the sodium complex we assumed that sodium ions can be coordinated
to either oximate or carboxylate moieties [MHL] or to
both of them simultaneously [M2L] (see Scheme 1).
In case of the nickel–1a complex, frequency calculations at equilibrium geometries yield only real values;
hence all models correspond to local minima. The comparison of theoretical and experimental IR spectra in the
range of 1000–1800 cm1 showed (Fig. 1) that [NiL2]2
model reproduces the best obtained experimental data,
where Ni(II) coordinates to deprotonated 1a ligands in
trans configuration (Fig. 2). The deprotonation of both
ligand molecules is confirmed by the detailed analysis of
the oximic vibrations as it is discussed below. It is clear
that there has to be a counter cation for the dianionic
form of 2-cyano-2-(hydroxyimino)acetic acid in this
structure. It is known, from our previous works
[22,24], that the type as well as the binding site of a
counterion do not effect significantly experimental and
theoretical vibrational spectra. Hence, in our models
the presence of the counterion is neglected.
(d)
(c)
O
NC
O
O
O
C
O
C
M
M
C
MO
C
NC
O
N
N
N
OH
O-
O
OH
C
M
C
O
C
O
N
O
O
N
(a)
M
M
C
O
CN
C
O
O
N
C
(b)
cis bidendate mode
monodendate mode
NC
CN
N
O
CN
OH
NC
trans bidendate mode
Scheme 1.
dimeric mode
O
Fig. 1. Comparison of theoretical and experimental IR spectra (1000–
1800 cm1) of the 1a nickel complex: (a) cis [NiHL2], (b) trans
[NiH2L2], (c) trans [NiL2]2 and (d) experimental spectrum.
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K. Malek et al. / Polyhedron 24 (2005) 1175–1184
Fig. 2. Model structures of 1a complexes with the atom numbering used in calculations.
The same procedure was applied to determinate the
structure of the 1a complex with Cu(II) ions. The dimeric species can be ruled out based on the EPR spectrum typical for a complex with orthorhombic
symmetry (g1 = 2.249, g2 = 2.188 and g3 = 2.051; cf.
Fig. 3). Frequency analysis of trans [CuL2]2 showed
one imaginary value what indicated this model to be a
transition state and excluded it finally from further studies. Moreover, the differences in experimental IR and
Raman spectra of the nickel and copper complexes evidently indicates that these compounds are not isostructural. Additionally, the comparison of the calculated
vibrational spectra of the other copper complex models
with experimental IR and Raman clearly indicates that
trans [CuH2L2] form exists in solid state (see Figs. 2
and 4). Also, the presence of the protonated oximic
groups has been established by their positions in the
vibrational spectra (Section 4.3).
In case of the sodium–1a, several structures with different binding of this metal ion to the carboxylic and/
or oximic groups were taken into consideration. As mention in Section 2 two sodium atoms are present in this
complex of 1a. Furthermore, despite of the elemental
analysis results (water-to-Na–1a molar ratio is 1:3),
two water molecules were added to the model structure
to mimic H-bond presented in experimental IR spectrum
(see Fig. 5). Finally, the comparison of experimental and
simulated vibrational spectra showed that both NOH
and COOH have to be deprotonated to allow coordination of two sodium ions ([Na2L] Æ 2H2O; cf. Fig. 2).
(c)
(b)
(a)
Fig. 3. Microcrystalline EPR spectra of the 1a copper complex at the
X band frequency at 298 K.
Fig. 4. Comparison of theoretical and experimental IR spectra (900–
1800 cm1) of the 1a copper complex: (a) cis [CuHL2], (b) trans
[CuH2L2] and (c) experimental spectrum.
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
Geometrical parameters, charge distribution and
vibrational spectra for assigned molecular structures of
1a complexes are discussed below.
Table 1
Selected computed bond lengths [Å] for 1a and its complexes with
Na(I), Ni(II) and Cu(II) ions
Bond
H2L 6-311
++G(d,p)
[Na2L] Æ 2H2O
6-311++G(d,p)
[NiL2]2
LanL2DZ
[CuH2L2]
LanL2DZ
C@O
CAO
C@N
NAO
C„N
Cox–Ccar
Cox–Ccya
MAO
1.199
1.347
1.287
1.359
1.154
1.506
1.433
1.254
1.298
1.316
1.292
1.157
1.481
1.427
2.256a
2.197b
2.439b
2.236
1.263
1.339
1.357
1.300
1.189
1.496
1.423
1.883b
1.236
1.342
1.305
1.393
1.181
1.559
1.428
1.920b
1.935
1.962
4.1. Geometry
Computed bond lengths obtained for structures of
E-isomer [H2L] of 1a and its complexes with metal ions
present here are shown in Table 1. The comparison between bond length values in all studied complexes with
the uncoordinated protonated 1a molecule shows differences mainly in ‘‘functional’’ groups coordinating to the
metal ions. The carbonyl bonds in the complexes
lengthen considerably (0.04–0.06 Å) after the coordination, whereas the CAO bond involved in metal ion binding shorten slightly in the transition metal complexes
(0.01 Å) and over 0.05 Å in the sodium salt. This results probably from the bidentate coordination of the
sodium ion by carboxylate group. The observed trend
of changes in bond lengths for this group is typical
for many oxocarboxylic acid oximic complexes
[3,7,21,23,24].
The oximic NO and CN bonds in the sodium and
nickel compounds are close to those reported for the
N-coordinated deprotonated oxime group [3–5,23]. This
(c)
(b)
(a)
Fig. 5. Mid-IR spectra (400–4000 cm1) of (a) the 1a sodium complex,
(b) the 1a copper complex and (c) the 1a nickel complex.
1179
MAN
Functional groups are denoted as: ox – oximic, car – carboxylic, cya –
cyano groups and M as metal ion. Upper symbols are denoted as:
[H2L] – the fully protonated ligand; [CuH2L2], [Na2L] Æ 2H2O, [NiL2]2
– applied models of complexes.
a
The oximic oxygen atom.
b
The carboxylic oxygens.
indicates that the CNO moiety exists in the nitrosoform (CAN@O). The lengths of the oximic bonds in
the protonated copper complex are longer than those
in the 1a molecule, contrary to the deprotonated complexes, where the C@N bond is elongated and the
NAO bond is shortened upon coordination. The latter
effect was observed for the cis complex of 2-hydroxyiminopropanoic acid [H3CAC(COOH)@NOH, hpa] with
Cu(II) ion regardless of the ligand protonation state
[22]. Besides, in the 1a copper complex the elongation
of the oximic bonds supports the trans configuration
of the investigated compound like it was found for the
trans nickel hpa complex.
Regarding the cyano group, its bond lengthens upon
the complexation with all metal ions studied here. Interestingly, coordination of the alkali ion causes a slight
change of the C„N length (0.003 Å), whereas for transition metal ions the elongation is rather significant
(0.03 Å). Besides, the deprotonation of the oximic
group causes the decrease of the electron density of
the cyano bond, and consequently, its lengthening.
The B3LYP/LanL2DZ method predicted this bond to
be too long (cf. Table 1), but it is still close enough to
those observed in related cyanoxime complexes (1.13–
1.15 Å) [3–5,7].
The metal–ligand bond distances were calculated in
the range comparable to other complexes. For sodium
salt of 1a, the distances between sodium and carboxylic
oxygen atoms were calculated at 2.20 and 2.44 Å. These
values are consistent with the range of 2.01–2.59 Å
found for other oximic complexes with alkali metal ions.
Similarly, the Na–Noximic bond length is 2.24 Å, while its
typical value is observed in the 2.22–2.54 Å range
[21,25,26]. However, the comparison of calculated
1180
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
metal–ligand bond lengths for proposed structures (trans
[NiL2]2 and [CuH2L2]) indicates the stronger binding of
Ni(II) than Cu(II) ion to 1a. It seems that the transition
metal ion rather than the deprotonation state of the
oximic group is responsible for this effect. As calculated
for trans [NiH2L2] isomer, the metal–nitrogen bond
lengths (NiAN = 1.855 Å, NiAO = 1.851 Å) are still
shorter than respective bonds in [CuH2L2]. All calculated
metal–ligand bond lengths are in the range of the oximic
complexes studied so far [3–5,7,22–26].
4.2. Atomic charges
The atomic charges at all atoms in 1a at the different
protonation stages and its complexes studied here are given in Table 2. The effective charges at the metal ions are
reduced up on binding ligand and are +1.06 [(Cu(II)],
+0.91 and +0.86 [Na(I), for the ion bonded to the carboxylate and oximato groups, respectively], +0.72 a.u.
[Ni(II)]. The smallest change of the charge value in the
sodium ion is consistent with the weakest metal–ligand
interaction.
As expected, the electron density on the oxygen
atoms in the deprotonated carboxylic group of 1a (denoted in Table 2 as [HL]) is almost equal on both oxygens. The further deprotonation of the oximic group
(see data for [L]2) causes only a charge increase at
the carboxylic oxygens by 0.1 a.u. Upon coordination of the copper ion, the withdrawal of electronic
charge towards O-atom bonded to the metal ion is expected and observed. The similar distribution of the
electron density on the carboxylic group is found for
the sodium salt. The difference between charges on the
O-atoms for the sodium compound is lower than for
[CuH2L2]. It results from the fact that Na(I) ion coordinates to both oxygen atoms. Interestingly, a reverse
trend is observed for the nickel complex. It appears that
the deprotonation of the oximic group reduces the elec-
tron density at the carboxylic O-atom and shifts it towards the Ni-atom.
In the oximic group, the electron density is systematically shifted toward the oxygen atom. The deprotonation of the carboxylic proton causes an increase of
negative charge at the NOH moiety (see data for
[HL] form of 1a). After coordination of Cu(II), the
negative charge density is accumulated on the N-atom
and partially moved towards the metal ion. Upon the removal of the oximic proton the distribution of electron
density changes significantly. The C and O atoms become strongly negative, whereas positive charge is accumulated on the N atom. This affects the C@N and NAO
bond lengths as discussed above. These changes of the
charge distribution follow the coordination of the sodium and nickel ions to the fully deprotonated ligand.
Again, the largest withdrawal of the electronic charge
from the N-atom towards the metal ion is observed in
[NiL2]2.
It is worth to look at the charge distribution of the cyano group. Upon the deprotonation of the carboxylic
proton, the negative charge of the N-atom increases by
0.18 a.u. whereas a charge at the C-atom decreases by
0.13 a.u., due to the withdrawing electron character of
C„N. After coordination of Cu(II), the electron density
flows from the N-atom through the cyano carbon towards the remaining fragment of the ligand. However,
the deprotonation of the oximic proton causes more ionic character of the cyano bond than in the [HL] form.
This group behaves as an electron donating substituent
in coordination of sodium and nickel ions. Regardless
the coordination mode and the type of a metal ion,
the same effective charge (0.08 a.u.) is shifted from
C„N towards the adjacent oximic C-atom. Furthermore, the difference between the effective charges at
the carbon and nitrogen atoms in C„N follows the
trend: [CuH2L2] (0.03 a.u.), [Na2L] Æ 2H2O (0.55 a.u.)
and [NiL2]2 (0.99 a.u.). It worth to note that this differ-
Table 2
Computed atomic charges [APT population analysis (GAPT)] of 1a forms and its complexes with metal ions [M@Na(I), Ni(II) and Cu(II)]a
Atom
[H2L]
[HL]
[CuH2L2]
[L]2
[Na2L] Æ 2H2O
[NiL2]2
Ocarboxylic
Ccarboxylic
Ocarbonyl
Hcarboxylic
Coximic
Noximic
Ooximic
Hoximic
Ccyano
Ncyano
M
0.726
+1.195
0.678
+0.349
0.008
+0.251
0.543
+0.333
0.003
0.185
0.873
+1.199
0.887
1.010
+1.266
0.750
0.968
+1.206
0.979
1.229
+1.433
1.052
0.871
+1.264
0.925
0.007
+0.163
0.610
+0.254
+0.131
0.370
+0.210
+0.079
0.521
+0.415
0.125
0.094
+1.059
0.518
+0.332
0.779
0.413
+0.376
0.792
0.535
+0.611
0.694
+0.405
0.699
+0.169
0.381
+0.911
+0.858
+0.388
0.599
+0.724
Upper symbols are denoted as: [HL] – ligand with the deprotonated carboxylic group; [L]2 – the fully deprotonated ligand.
a
Geometry by B3LYP/LanL2DZ for all models.
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
1181
ence for models [CuL2]2 and [NiH2L2] are 0.97 and
0.01 a.u., respectively. It clearly indicates that polarization of the cyano group strongly depends on the deprotonation of the oximic group only. That can be traced in
vibrational properties of this group as will be shown
below.
4.3. Vibrational spectra
The calculated and experimental vibrational frequencies and assignments of the characteristic modes for all
investigated complexes are summarized in Table 3 (full
description of the internal coordinates and vibrational
spectra are given in the Supplementary Material, Tables
I–VI). Experimental (IR and Raman) spectra of the
complexes are shown in Figs. 5–7. It should be emphasized that the simulated spectra refer to the isolated molecule at 0 K, whereas the assignments are made for the
vibrational spectra of the solid state. Thus, some differences in the calculated versus experimental frequencies
or intensities are most probably caused by intermolecular interactions (crystal packing) or by anharmonicity of
vibrations. Vibrational modes which are of great importance in the determination of discussed molecular structures are shown below.
4.3.1. m(OH) and d(OH)
The IR spectra of all compounds exhibit broad
absorption bands with maxima at 3456 and 3234 [Na–
1a], 3450 [Cu–1a] and 3430 cm1 [Ni–1a] (cf. Fig. 5).
These are assigned to the stretch vibration of the oximic
OH (in the copper complex) as well as free or weakly Hbonded hydrated water molecules in the other complexes. Calculations for the applied models predict the
presence of those vibrations at 3720, 3719, 3265 and
2983 cm1 [mðOHÞH2 O ] for the sodium salt (cf. Fig. 2)
and at 3496 and 3499 cm1 [m(OH)ox] for the copper
complex. Additionally, calculations of vibrational spectra for Ni and Cu complexes with hydrated waters
showed that mðOHÞH2 O should appear in the mentioned-above experimental range (data not shown).
Moreover, bands at 1620 cm1 are characterized by
significant values of FWHM resulting from the presence
of bending modes of H2O [d(OH)]. Hence, we can conclude that water molecules are not directly coordinated
to the complex structures. Furthermore, the absence of
IR absorptions characteristic for water molecules located in the first coordination sphere of a complex confirms this assumption (at 900 and 770 cm1, the
rocking and the wagging vibrations of the OH group,
respectively).
4.3.2. m(C„N)
The stretches modes of cyano bond in the IR and Raman spectra of the 1a complexes (cf. Table 3) definitely
indicate the shortening of this bond in the following or-
(c)
(b)
(a)
Fig. 6. Far-IR spectra (50–400 cm1) of (a) the 1a sodium complex,
(b) the 1a copper complex and (c) the 1a nickel complex.
der: Na–1a, Ni–1a and Cu–1a. The mode frequencies of
the sodium and nickel compounds are typical for their
coordination motifs [3,5]. However, a participation of
the C„N group in the metal binding may be suggested
by the high-shift of the C„N stretch (2242 cm1, Raman spectrum, see Fig. 7(b)) for the cooper complex
comparing to the latter. Surprisingly, IR and Raman
intensities for this complex are very low, in the contrary
to the other complexes. That is due to the electron density distribution. As showed above, the smallest polarization of the cyano bond is observed for [CuH2L2].
4.3.3. mas(COO) and ms(COO)
A characteristic features of the vibrational spectra of
the 1a complexes is the lowering of frequencies of the
asymmetric carboxylate stretching [mas(COO)] down to
1610 cm1. Thus, the change in these mode frequencies can be attributed to the deprotonation of the carboxylic group as well as the ability to bind the metal
centers. The position of this band in the sodium complex
is typical for the alkali complexes of hpa [21]. That
clearly indicates the absence of a significant influence
of the withdrawing electron cyano group on the coordination fashion by the carboxylate anion. Furthermore, a
2281 [86]b
1695 [83]b
1143 [60]b
1678 [66]b
1038 [56]b
156 [53]b
290 [41]b
1674 [48]a
1048 [53]a
344 [41]a
376 [39]a
2281 [86]
1691 [64]a
1154 [56]a
Raman
[CuH2L2] (calc.)
IR
a
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
(c)
1650
1045
316 [18]b
427 [48]a
363
1649
1050
330
1423 [74]b
1275 [45]b
202 [12]b
c
d
a
b
In-counter-phase.
In-phase.
The oximic oxygen atom.
The carboxylic oxygens.
162d
330c
m(C@N)
m(NO)
m(M–N)
m(M–O)
m(C„N)
mas(COO)
ms(COO)
2275
1538
1359
1136
1454
1260
294
337
294
165
[90]
[81]
[36]
[30]
[69]
[70]
[32]
[46]c
[23]d
[19]d
2208
1611
1381
1144
1444
1211
2209
1613
1383
1140
1440
1214
307
330c
307d
161d
408
1489
1252
357
356
1496
1263
1431 [73]a
1269 [42]a
373 [46]a
2242
1668
1165
1649
1110
2212 [62]
1614 [81]b
1130 [36]b
2229
1645
1160
2210 [63]
1605 [84]a
1126 [22]a
b
a
Raman
Cu–1a (exp.)
Ni(1a)2 (calc.)
IR/Raman
Raman
IR
2226
1619
1152
Fig. 7. Raman spectra (50–2500 cm1) of (a) the 1a sodium complex,
(b) the 1a copper complex, (c) the 1a nickel complex.
[Na2L] Æ 2H2O (calc.)
IR
(a)
Na–1a (exp.)
[NiL2]2 (exp.)
Raman
IR
Raman
IR
(b)
Mode
Table 3
Computed [with potential energy distribution (PED, %)] and experimental IR and Raman frequencies (in cm1) of the selected stretching modes for sodium, nickel and copper complexes of 1a
1182
smaller low-frequency shifts of this vibration for 3-d metal ions complexes support bidentate coordination of the
2-cyano-2-(hydroxyimino)acetate anion to metal center.
Similar behavior has been found previously for other
transition metals oximates [22]. Additionally, the vibrational spectra of those complexes exhibit the splitting of
the COO stretching vibration. The in-counter-phase
modes are observed in IR whereas the in-phase counterparts are present in the Raman spectrum. That is consistent with the proposed model where two ligands in trans
configuration coordinate to the metal ion (see Table 3).
Moreover, the deprotonation of the oximic group but
not a metal ion [Cu(II) versus Ni(II)] seems to
be responsible for the lower shift-frequency of the
mas(COO) in the nickel complex. The IR frequency of
the latter is almost the same as for the sodium salt with
the deprotonated C@NO.
According to the DFT results, the symmetric stretching mode [ms(COO)] appears mainly in the range of
1165–1110 cm1 with its relatively small contribution
in the normal mode (22–60% PED). Merely, the spectra
of Na–1a exhibit additional bands in the typical
frequency range for ms(COO), at 1381 cm1 with 36%
participation of this vibration.
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
4.3.4. m(C@N) and m(NAO)
The positions of the m(C@N) and m(NO) vibrations in
IR and Raman spectra are dependent to a great extend
on the oxime or nitroso character of this group in a particular compound and are reflected by the coordination
mode. The vibrational spectra of the sodium and nickel
complexes exhibit a significant shift of m(C@N) to lower
frequencies, at 1440 and 1490 cm1, for Na–1a and
Ni–1a, respectively. That clearly indicates that 1a appears in these complexes as a nitroso-containing anion.
The lower shift of the band of the sodium salt results primarily from a participation in coordination of the oximic oxygen atom. DFT fully confirms this assignment
(1454 cm1, 69% PED). The m(C@N) of the nickel complex is found in our experiment in the similar range as
for the Ir(III) and Ru(II) complexes of other a-hydroxyiminocarboxylic acids with the deprotonated oximic
group (1515–1495 cm1) [23]. On the other hand, the
C@N stretch vibration of the copper complex is assigned
to the band at 1650 cm1 in the Raman spectrum
[1678 cm1 (66% PED) calculated]. This frequency indicates that oximic not nitroso group takes part in Cu(II)
coordination.
The high-frequency shift of the m(NO) modes in the
vibrational spectra of Na(I) and Ni(II) compounds
confirms additionally that these metal ions are bonded
to the ligand by the nitrogen atom of the nitroso group
(cf. Table 3). B3LYP predicts positions of this mode
very well, with an error less than 4.0%. Additionally,
the simulated spectra of the nickel complex exhibit
the different position of the mode in IR (1269 cm1)
and Raman (1275 cm1) spectra, respectively. The
same has been observed in the experimental spectra
and results from the trans ligand conformation. The
difference is equal to 9 cm1. The most pronounced
feature of vibrational spectra of the copper complex
is in their very low frequencies of the m(NO) vibrations
(1050 and 1045 cm1 in IR and Raman, respectively)
comparing to Na–1a and Ni–1a. Thus, the positions
of these bands are consistent with the protonated trans
structure.
4.3.5. Metal–ligand vibrations
The frequency region below 500 cm1 provides
information on the metal–ligand stretch vibrations.
The far IR and Raman spectra of the complexes present here in this particular range are shown in Figs. 6
and 7. The IR absorptions at 307, 330 and 357 cm1
are assigned to the metal–nitrogen stretching vibration
of Na, Cu(II) and Ni(II) complexes, respectively. The
contribution of this vibration to the normal modes is
less than 50%, as predicted by calculated PEDs (cf.
Table 3). As expected, the coordination by the oximic
nitrogen atom of the s-type metal ions is considerably
weaker. Similar observation has been found for the
metal-carboxylic oxygen stretch modes. Moreover,
1183
the comparison of frequencies of Na–Ooximic with
Na–Ocarboxylic indicates the stronger coordination this
alkali ion by the nitroso moiety than by the carboxylate anion.
5. Conclusions
The experimental IR and Raman spectra of solid
state supported by the DFT calculations have shown
that the transition metal complexes of 2-cyano-2(hydroxyimino)acetic acid have trans bidendate squareplanar geometry with the different protonation state of
the oximic group. This is similar to their structures in
solution determined previously by our potentiometric
and spectroscopic studies [8]. However, two sodium ions
are bonded to the carboxylate as well as oximate moieties. Vibrational analysis has clearly indicated the binding nature of the oximic and carboxylic oxygen atoms
and the oximic nitrogen atom. It also shows the presence
of the nitroso form of the oximic group in Ni–1a and
Na–1a. Furthermore, the latter effects the coordination
strength in all complexes presented. Namely, this causes
the increase of the stability of the nickel complex comparing to the copper one and the binding ability of the
oximic group comparing to the carboxylic one in Na–
1a. The magnitude of all stretch vibrations has been
shown to be well correlated with the atomic charge distribution. The calculations of atomic charges have suggested that the deprotonation of the carboxylic group
does not change significantly the electronic distribution
in the 1a molecule, whereas the removal of the oximic
proton causes the accumulation of the positive charge
on the oximic nitrogen. Moreover, the electron density
is shifted from the metal ion towards the carboxylic oxygens in the copper and sodium complexes in reverse to
Ni–1a. And in the oximic group, the N-atom is an electron donor for metal ions.
Acknowledgments
The authors thank Academic Computer Centre
CYFRONET of the University of Science and Technology in Krakow (grant no. KBN/SPP/UJ/027/1999) and
Interdisciplinary Center for Mathematical and Computational Modeling of Warsaw University in Warsaw
(grant no. G25-8) for the possibility to perform necessary calculations.
Appendix A. Supplementary data
Supplementary data associated with this article can
be found, in the online version at doi:10.1016/
j.poly.2005.04.007.
1184
K. Malek et al. / Polyhedron 24 (2005) 1175–1184
References
[1] H.A. Kirst, E.F. Szymanski, D.E. Doman, J.L. Occolowitz, N.D.
Jones, M.O. Chaney, R.L. Hamill, M.M. Hoehn, J. Antibiot. 28
(1975) 286.
[2] H. Nakamura, Y. Iitaka, H. Sakakibara, H. Umezawa, J.
Antibiot. 27 (1974) 894.
[3] V.V. Ponomareva, N.K. Halley, X. Kou, N.N. Gerasimchuk,
K.V. Domasevich, J. Chem. Soc. Dalton Trans. (1996) 2351.
[4] A.A. Mokhir, K.V. Domasevich, N.K. Dalley, X. Kou, N.N.
Gerasimchuk, O.A. Gerasimchuk, Inorg. Chim. Acta 284 (1999) 85.
[5] K.V. Domasevich, N.N. Gerasimchuk, A.A. Mokhir, Inorg.
Chem. 39 (2000) 1227.
[6] A. Gupta, R.K. Sharma, R. Bohra, V.K. Jain, J.E. Drake, M.B.
Hursthouse, M.E. Light, J. Organomet. Chem. 645 (2002) 118.
[7] T.Y. Sliva, A.M. Duda, T. Glowiak, I.O. Fritsky, V.M. Amirkhanov, A.A. Mokhir, H. Kozlowski, J. Chem. Soc. Dalton
Trans. (1997) 273.
[8] T.Y. Sliva, A. Dobosz, L. Jerzykiewicz, A. Karaczyn, A.M.
Moreeuw, J. Świaßtek-Kozłowska, T. Głowiak, H. Kozłowski, J.
Chem. Soc. Dalton Trans. (1998) 1863.
[9] Ch.O. Onindo, T.Y. Sliva, T. Kowalik-Jankowska, I.O. Fritsky,
P. Buglyo, L.D. Pettit, H. Kozlowski, T. Kiss, J. Chem. Soc.
Dalton Trans. (1995) 3911.
[10] A.A. Mokhir, E. Gumienna-Kontecka, J. Świaßtek-Kozłowska,
E.G. Petkova, I.O. Fritsky, L. Jerzykiewicz, A.A. Kapshuk,
T.Y. Sliva, Inorg. Chim. Acta 329 (2002) 113.
[11] T.Y. Sliva, T. Kowalik-Jankowska, V.M. Amirkhanov, T.
Głowiak, Ch.O. Onindo, I.O. Fritsky, H. Kozlowski, J. Inorg.
Biochem. 65 (1997) 287.
[12] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[13] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[14] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.
[15] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270.
[16] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A.
Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery,
R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D.
Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q.
Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, B.B. Stefanov, G.
Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A.
Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W. Gill, B.
Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M.
Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98 (Revision
A.6), Gaussian Inc., Pittsburgh, PA, 1998.
[17] D. Michalska, W. Zierkiewicz, D.C. Bienko, W. Wojciechowski,
Th. Zeegers-Huyskens, J. Phys. Chem. A105 (2001) 8734.
[18] D. Michalska, R. Wysokinski, Chem. Phys. Lett. 403 (2005) 211.
[19] M.H. Jamroz, Vibrational Energy Distribution Analysis: Veda 3.0
Program, Drug Institute, Warsaw, Poland, 2000.
[20] J. Cioslowski, J. Am. Chem. Soc. 111 (1989) 8333.
[21] A.W. Apblett, G.D. Georgieva, J.T. Mague, Inorg. Chem. 36
(1997) 2656.
[22] K. Malek, PhD dissertation, Jagiellonian University, Krakow,
2003.
[23] R. Bergs, R. Lampeka, C. Robl, W. Beck, Z. Naturforsch. b 49
(1994) 483.
[24] K. Malek, M. Vala, J. Swiatek-Kozlowska, L.M. Proniewicz,
New. J. Chem. 28 (2004) 477.
[25] T. Adatia, J. Chakrabarti, O. Carugo, C.B. Castellani, Polyhedron 15 (1996) 1331.
[26] G.P. Voutsas, K.G. Keramidas, M. Lalia-Kantouri, Polyhedron
15 (1996) 147.