XAFS study of metal chelates of phenylazo derivatives of Schiff bases

Article abstract of DOI:10.1016/j.molstruc.2013.12.007

The Schiff base derived from o-tosylaminobenzaldehyde and p-aminoazobenzene and its metal chelates (Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) have been synthesized and investigated (IR, ¹H NMR, XANES, EXAFS spectro

Full text of DOI:10.1016/j.molstruc.2013.12.007

Accepted Manuscript
XAFS study of metal chelates of phenylazo derivatives of Schiff bases
Anatolii S. Burlov, Sergey A. Mashchenko, Valery G. Vlasenko, Yan V.
Zubavichus, Ali I. Uraev, Konstantin A. Lyssenko, Sergei I. Levchenkov, Igor
S. Vasilchenko, Dmitrii A. Garnovskii, Gennadii S. Borodkin
PII:
S0022-2860(13)01030-2
DOI:
http://dx.doi.org/10.1016/j.molstruc.2013.12.007
MOLSTR 20196
Reference:
Journal of Molecular Structure
To appear in:
Please cite this article as: A.S. Burlov, S.A. Mashchenko, V.G. Vlasenko, Y.V. Zubavichus, A.I. Uraev, K.A.
Lyssenko, S.I. Levchenkov, I.S. Vasilchenko, D.A. Garnovskii, G.S. Borodkin, XAFS study of metal chelates of
phenylazo derivatives of Schiff bases, Journal of Molecular Structure (2013), doi: http://dx.doi.org/10.1016/
j.molstruc.2013.12.007
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XAFS study of metal chelates of phenylazo derivatives of Schiff bases
Anatolii S. Burlov a, Sergey A. Mashchenko a, Valery G. Vlasenko b,
Yan V. Zubavichus c, Ali I. Uraev a, Konstantin A. Lyssenko d,
Sergei I. Levchenkov e, Igor S. Vasilchenko a, 1, Dmitrii A. Garnovskii a,e,
Gennadii S. Borodkin a
a Institute of Physical and Organic Chemistry of Southern Federal University, Stachki ave. 194/2, Rostov-on-Don,
344090 Russian Federation, e-mail: garn@ipoc.rsu.ru
b Institute of Physics of Southern Federal University, Stachki ave. 194, Rostov-on-Don, 344090 Russian
Federation
c National Research Centre “Kurchatov Institute”, Akademik Kurchatov sq. 1, Moscow, 123182 Russian
Federation
d A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova str. 28,
Moscow, 119991 Russian Federation
e Southern Scientific Center of Russian Academy of Sciences, Chekhova str. 41, 344006 Rostov-on-Don, Russian
Federation
A B S T R A C T
The Schiff base derived from o-tosylaminobenzaldehyde and p-aminoazobenzene
and its metal chelates (Co2+, Ni2+, Cu2+, and Zn2+) have been synthesized and
1
investigated (IR, H NMR, XANES, EXAFS spectroscopy, X-ray diffraction, magnetic
measurements). It was found that the azomethine exists in the amino-imine tautomeric
form both in solutions and solid state. XAFS investigations reveal that the complexes
1 Author to whom correspondence should be addressed
1

adopt either distorted tetrahedral or octahedral (due to additional coordination of oxygen
atoms of the tosylamino group) ligand environment.
Keywords: azophenyl Schiff bases; 3d-metals; mononuclear complexes; N,N-
coordination, XAFS, X-ray diffraction
1. Introduction
Schiff bases are among the most important ligands of the modern coordination
chemistry [1-12] since their complex-forming activity makes them attractive for the
design of novel multifunctional materials, e.g., molecular magnets [13-16],
luminophores [17, 18], and bioactive chelates [19, 20].
Coordination compounds of Schiff bases bearing an azo group are represented by
complexes of ligands containing an Ar-N=N- fragment in the aldehyde moiety, which
are essentially chelates of azomethines of arylazosalicylaldehyde 1 [8, 15, 21, 22-24].
Ts
H
Ts
N
N
N
N
M/2
O
N
N
M/2
Ar
N
R
N
N
N N
Ph
Ph
1
2: Ts = -SO2C6H4CH3-p
3: M = Co (a), Ni (b),
Cu (c), Zn (d)
Metallocomplexes of azomethines containing arylazo-group in the amine moiety
presented only by chelates on the base of ligands with N2O2 donor atoms set [25, 26].
2

So synthesis and investigation of the same complexes with N4 donor environment
is a matter of interest.
We have synthesized and investigated Schiff base 2 with an azo group within the
amine moiety and its metal complexes 3, and have studied of influence of the character
of such substituent on their structural and magnetic characteristics.
2. Experimental
2.1. Materials
All solvents, metal acetates and organic precursors were purchased from Aesar,
Lancaster.
2.2. Synthesis of the azoderivative 2
A hot solution of 1.97 g (0.01 mol) of 4-aminoazobenzene in 30 ml of methanol
was added to a hot solution of 2.75 g (0.01 mol) of 2-tosylaminobenzaldehyde in 20 ml
of the same solvent. Resulting mixture was refluxed for 1 h. Precipitate formed after
cooling to the room temperature was filterred off, washed with cool methanol, dried in
air and recrystallized from the chloroform-methanol mixture (1:2). Obtained crystals
were available for X-ray structural investigations. Red-orange crystals, m.p. 204-205
°C, yield 84 %. Found, %: C, 68.75; H, 4.95; N, 12.41. Calculated for C26H22N4O2S, %:
1
C, 68.71; H, 4.88; N, 12.32. NMR H (CDCl3), δ (ppm): 2.36 (3H, s, CH3), 7.11 (1H, t,
C-HAr), 7.21 (1H, d, C-HAr), 7.23 (1H, d, C-HAr), 7.36-7.57 (7H, m, C-HAr), 7.70 (1H, d,
C-HAr), 7.79 (1H, d, C-HAr), 7.80 (1H, d, C-HAr), 7.94 (1H, d, C-HAr), 7.96 (1H, d, C-
HAr), 8.01 (1H, d, C-HAr), 8.04 (1H, d, C-HAr), 8.56 (1H, s, HC=N), 12.75 (1H, s, NH).
3

IR spectrum, ν (cm-1): 2700-3100 (br, NH), 1617 (s, C=N), 1334 (vs, SO2, as), 1152 (vs,
SO2, sym).
2.3. Synthesis of the complexes 3a-d
All complexes have been obtained according to the below common method. A
hot solution of 0.001 mol of the acetate of the corresponding d-metal in 10 ml of
methanol was added to a hot solution of 0.91 g (001 mol) of azomethine 2 in 50 ml of
the same solvent. The resulting mixture was refluxed for 1 h and cooled for the room
temperature. Precipitates of complexes was filtered off, washed with hot methanol and
dried in vacuo.
3a. Red-brown powder, m.p. 241-242 °C, yield 98 %. Found, %: C, 64.68; H,
4.42; N, 11.58. Calculated for C52H42N8O4S2Co, %: C, 64.66; H, 4.38; N, 11.60. IR
spectrum, ν (cm-1): 1604 (s, C=N), 1258 (vs, SO2, as), 1134 (vs, SO2, sym). µeff = 4.29
BM (294 K).
3b. Brown powder, m.p. > 250 °C, yield 88 %. Found, %: C, 64.65; H, 4.40; N,
11.65. Calculated for C52H42N8O4S2Ni, %: C, 64.68; H, 4.38; N, 11.60. IR spectrum, ν
(cm-1): 1603 (s, C=N), 1257 (vs, SO2, as), 1125 (vs, SO2, sym). µeff = 3.89 BM (294 K).
3c. Dark-brown powder, m.p. > 250 °C, yield 85 %. Found, %: C, 64.42; H, 4.38;
N, 11.60. Calculated for C52H42N8O4S2Cu, %: C, 64.35; H, 4.36; N, 11.54. IR spectrum,
ν (cm-1): 1606 (s, C=N), 1261 (vs, SO2, as), 1130 (vs, SO2, sym). µeff = 1.74 BM (294
K).
3d. Orange powder, m.p. > 250 °C, yield 75 %. Found, %: C, 64.34; H, 4.30; N,
1
11.62. Calculated for C52H42N8O4S2Zn, %: C, 64.23; H, 4.35; N, 11.52. NMR H
(DMSO-d6), δ (ppm): 2.25 (6H, s, CH3), 6.70-7.87 (34H, m, C-HAr), 8.87 (1H, s,
HC=N). IR spectrum, ν (cm-1): 1607 (s, C=N), 1261 (vs, SO2, as), 1133 (vs, SO2, sym).
4

2.4. Physical measurements
C, H, and N analyses were performed with a Carlo Erba Instruments TCM 480
analyzer. IR spectra of powder samples and as KBr pellets were recorded using a Varian
1
Еxcalibur-3100 FT-IR spectrophotometer. Н NMR spectra (in CDCl3 for organic
derivative and in DMSO-d6 for complexes) were measured with a Bruker Avance-600
1
spectrometer (600 МHz) with the signal of residual Н in solvent as the internal
standard.
2.5. X-ray diffraction
Orange-red crystals of N-(4-phenylazo)phenyl-(2-tosylamino)benzaldimine
C26H22N4O2S (2) are monoclinic: a = 11.7576(12) Å, b = 11.7288(12) Å, c =
16.7054(17) Å, α = 90°, β = 100.899(5)°, γ = 90°, V = 2262.2(4) Å3, M = 454.54, F(0 0
0) = 952, ρcalcd = 1.318 g cm-1, µ = 0.175 g cm-1, Z = 4, space group P 21/c, T = 120(2)
K.
Experimental data for 2 were obtained with an Bruker SMART 1000
diffractometer (λ Mo-Kα, graphite monochromator, θ/2θ-scanning, θmax = 28°).
Intensities of 874 reflections were measured.
The structure of this compound was determined by direct methods (SHELXS
PLUS) [27], refined by full-matrix least-squares on F2 in the anisotropic approximation
for all non-hydrogen atoms. Hydrogens were placed in the calculated positions and
refined according to the riding model with fixed Debye factors of UH = 0.08 Å2.
The final fitting parameters for 2 are: R1 = 0.0593, wR2 = 0.1311 on 874
reflections with Fo ≥_2σ(Fo), R1 = 0.1021, wR2 = 0.1565 on all reflections, 299 variable
parameters, index range: -15 ≤ h ≤ 15, -15 ≤ k ≤ 15, -22 ≤ l ≤ 22, goodness-of-fit =
1.004, residual electronic density ∆ρmin = -0.284, ∆ρmax = 0.460 e Å-3.
5

2.6. XAS measurements and analysis
Ni K-, Co K- and Cu K-edges EXAFS spectra for the complexes were obtained at
the Station К1.3b "Structural Materials Science" of the Kurchatov Center of
Synchrotron Radiation and Nanotechnology (KCSRNT, Moscow, Russia) [28]. The
storage ring with electron beam energy of 2.5 GeV and a current of 70–90 mA was used
as the source of radiation. All the spectra were recorded in the transmission mode using
a channel-cut Si(111) monochromator and two N2/Ar-filled ionization chambers as
detectors. EXAFS data (
) were analyzed using the IFEFFIT data analysis package
χexp (k)
[29]. EXAFS data reduction used standard procedures for the pre-edge subtraction and
spline background removal.
The radial pair distribution functions around the Ni, Co, and Cu ions were
obtained by the Fourier transformation of the k3-weighted EXAFS functions over the
ranges of photoelectron wave numbers 2.4–12.5 Å–1. The structural parameters,
including interatomic distances (R), coordination numbers (CN) and the distance mean-
square deviations also known as Debye–Waller factors (σ2), were found by the non-
linear fit of theoretical spectra to experimental ones. The experimental data were
simulated using the theoretical EXAFS amplitude and phase functions, which were
2
calculated using the program FEFF7 [30]. The amplitude reduction factor S0 , and the
threshold energy offset ∆E0 were calibrated by fitting EXAFS data for model
2
compounds. The amplitude reduction factor S0 was found equal to 0.9 in all cases.
The quality of fits was estimated from discrepancy factors between the
experimental and simulated functions (Q-factor).
2
[
kχexp (k) − kχth (k)
]
∑
Q(%) =
·100%
[
kχexp (k) 2
]
∑
6

2.7. Magnetic susceptibility measurements
The magnetic susceptibility of the sample has been measured by the Faraday
method at 294 K. Hg[Co(NCS)4] was used as a reference sample for settings of the
equipment.
3. Results and discussion
3.1. Structure of the ligand 2
IR (ν NH 2700-3100 cm-1, ν C=N 1617 cm-1) and NMR 1H (δ HC=N 8.56 ppm, δ
NH 12.75 ppm) data reveal that the compound 2 favorable exists as amino-imine
tautomer 2a in solution and as a solids.
Ts
Ts
N
N
N
N
H
H
N N
N N
2a
2b
Ph
Ph
The same structure (Fig. 1) has been found for the imine 2 in crystal that is in
agreement with literatural data for other azomethine derivatives of 2-
7

tosylaminobenzaldehyde [31-34]. The broad peak at 2700-3100 cm-1 in the IR spectrum
of 2 may be attributed to the stretching of N-H group involved in the strong hydrogen
bond. Among other IR spectral data point the bands at 1152 and 1334 cm-1
corresponding to the sym and asym vibrations of SO2 group which are important fot the
discussion of the structure of coordination compounds [35-38].
Fig. 1. Structure of the azomethine 2. Selected bond distances (Å): S(1)-O(1)
1.4282(18), S(1)-O(2) 1.4349(18), S(1)-N(1) 1.630(2), S(1)-C(1) 1.759(2), N(1)-C(8)
1.412(3), N(1)-H(1)N 0.9121, N(2)-C(14) 1.279(3), N(2)-C(15) 1.413(3), N(3)-N(4)
1.261(3), N(3)-C(18) 1.422(3), N(4)-C(21) 1.425(3); and valence angles (°)
:O(1)S(1)O(2) 119.43(11), O(1)S(1)N(1) 109.91(11), O(2)S(1)N(1) 104.06(10),
O(1)S(1)C(1) 107.02(11), O(2)S(1)C(1) 109.19(12), N(1)S(1)C(1) 106.59(11),
C(8)N(1)S(1) 125.30(16), C(8)N(1)H(1)N 111.5, S(1)N(1)H(1)N 108.7,
C(14)N(2)C(15) 121.5(2), N(4)N(3)C(18) 114.2(2), N(3)N(4)C(21) 113.7(2).
Bond distances C(8)–N(1) (1.412(3) Å) and C(14)–N(2) (1.280(3) Å) correspond
to amino-imine form of compound 2 in the solid state [39]. This form stabilized in the
8

crystal by almost strong hydrogen bond N(1)–H(1N)…N(2) (Table 1) forming six-
membered cycle N(1)H(1N)N(3)C(14)C(13)C(8) (fragment II - see Fig. 1).
Table 1
Characteristics of hydrogen bonds in the crystal of compound 2.
D–H…A
D–
H…A,
D…A,
∠DHA,
H, Å
Å
Å
deg.
N(1)–H(1N)…N(2)
C(2)–H(2A)…O(1)
C(9)–H(9A)…O(1)
C(6)–H(6A)…O(1)i
C(25)–
0.91
0.95
0.95
0.95
0.95
1.88
2.49
2.51
2.35
2.47
2.656(3)
2.872(3)
3.164(3)
3.216(3)
3.234(3)
142
104
126
151
138
H(25A)…O(2)ii
Crystallographic sites: (i) 2–x, 1–y, 1–z; (ii) 1–x, ½+y, ½–z.
The X-ray structural data reveal that the central part of the molecule is almost
planar - dihedral angle between cycles C(8)C(9)C(10)C(11)C(12)C(13) (I) and II is
2.09° (Fig. 1). Hydrogen atom H(1N) deviates from N(1)C(8)C(14)C(13)N(2) plane on
0.140 Å. Cycle III is turned clockwise (looking from the cycle IV) relative cycle I on
31.37º, bond N(3)-N(4) forms angles with planes III and IV in 2.609(97) and
8.099(109)° respectively, so this moiety of the molecule has a helix-like form.
The planes of phenyl rings C(15)C(16)C(17)C(18)C(19)C(20) (III) and
C(21)C(22)C(23)C(24)C(25)C(26) (IV) linked by the azo group are partially non-
coplanar (dihedral angle between mean planes is equal to 19.51º).
9

Valence angles at the atoms N(1) and S(1) correspond to their sp3 hybridization.
Atom O(1) forms two short contacts which may be assigned to intramolecular C–
H…O hydrogen bonds [40]. Atoms O(1) and O(2) participate in the intermolecular C–
H…O hydrogen bonds (Table 1). Any π-stacking interactions in the crystal are not
found.
Fig. 2. View of crystal packing of 2 along b crystallographic axis.
3.2. Characterization of the complexes
Formation of the bis-chelates 3a-d as result of the coupling ligating Schiff base 2
with acetates of bivalent d-metals (method of direct interaction [2]) is supported by the
1
results of element analysis (composition ML2, where LH – compound 2) and IR, H
NMR, XAFS spectroscopy and magnetochemical (for chelates 3a-c) measurements.
10

3.2.1. IR and 1H NMR spectra
IR spectra of the complexes 3a-d demonstrate disappearing of the broad band of
the NH stretching (2700-3100 cm-1) as compared with the spectrum of the compound 2
that may be relevant to the substitution of the proton by the metal ion. Low frequency
shifts of the C=N stretching band in the IR spectra of the complexes 3a-d (by 10-13 cm-
1
as compared with the spectrum of the azomethine 2) may point [13, 35] to the
coordination of the nitrogen atom of this group to the metal and formation of the chelate
structure. Analogous behaviour of the stretching bands SO2(as) (by the 73-76 cm-1) and
SO2(sym) (by the 19-27 cm-1) may be coused by coordination interactions of metal with
1
oxygen atoms of the above group [41]. NMR H data zinc for complex confirm above
conclusion – disappearing the proton signal of the NH group (12.75 ppm), upfield shift
of the proton signal of HC=N group (8.87 ppm in the spectrum of compound 3d vis 8.56
ppm in the spectrum of 2).
3.2.2. Magnetochemical investigation
Magnetic susceptibility measurements results in the temperature range of 77-294
K show that the magnitudes of µeff (4.29 – 3a, 3.89 – 3b, 1.74 – 3c) are practically
independently on the temperature. These values may be relevant to the tetrahedral or
distorted-octahedral (due to the coordination of the oxygen atoms of SO2 groups to the
metal) coordination geometry.
3.2.3. XAS spectroscopy
11

X-ray absorption spectroscopy (XAS) was used to investigate the structure of
metal complexes 3. While extended X-ray absorption fine structure (EXAFS) analysis
provides information on the types of coordinated atoms and very accurate first-shell
metal-ligand distances, it determines the coordination numbers with a lower accuracy
and generally gives little or no information on the coordination site 3D geometry.
However, complementary information can be obtained from the near-edge region of
XAS spectra, i.e., XANES.
K-edge XAS spectra of first-row transition metals typically have a weak pre-edge
features at an energy 10 eV below the absorption edge. This feature is traditionally
assigned to a 1s→3d transition [42, 43]. For complexes in a centrosymmetric
environment, the 1s→3d transition is strictly forbidden by electric dipole selection rules
due to parity considerations. However, a very weak pre-edge feature is still
experimentally observed for such complexes due to the electric quadrupole contribution.
Since the electric quadrupole-coupled mechanism is so much weaker than the electric
dipole-coupled mechanism, only a few percent of 4p mixing into the 3d orbitals can
make a significant effect on the intensity of the 1s → 3d pre-edge feature [44].
Complexes in a noncentrosymmetric environment are expected to exhibit a more intense
pre-edge feature than centrosymmetric complexes. This increase in intensity has been
attributed to the 4p-3d metal orbital mixing, which provides some electric-dipole-
allowed 1s → 4p character to the transition. Thereby, the energy, intensity, and splitting
of the 1s → 3d pre-edge feature are extremely sensitive to the chemical and structural
local environment of the metal site in complexes.
The XAS edge spectra for Cu, Ni, and Co metal complexes 3 are shown in
Figures 3-5. An expanded view of the 1s → 3d pre-edge region and the first derivative
of the K-edge of these metal complexes 3 are shown as insets in Figures 3-5. All three
complexes have relatively intense pre-edge features. Such an intensity of the pre-edge
features of the complexes are due to 1s →3d electronic transitions originated from both
the electric quadrupole and 3d-4p mixing (electric dipole) mechanisms, and thus is an
indication of a noncentrosymmetric environment around the metal ions in these
complexes.
12

The Cu, Ni, and Co K-edge XANES spectra and their first derivatives for metal
complexes 3 and model compounds are shown in Figures 3-5. XANES is generated by
the photoelectron transition from inner orbitals to upper unoccupied ones of absorbing
atoms 1s →4s and 1s →4p [45-47]. A spectral feature of XANES region depends upon
oxidation state of absorbing atoms, site symmetry, surrounding ligands and nature of
bonding.
The theoretical simulation of XANES spectra at the Cu, Ni and Co K-edges for
metal complexes 3 was performed using the self-consistent full multiple-scattering
approach as implemented in the FEFF8.2 code [48, 49]. Phase shifts of the
photoelectron were calculated in the framework of the self-consistent crystal muffin-tin
(MT) potential scheme with a 15% overlap of the MT spheres. The Hedin-Lundqvist
exchange-correlation potential neglecting the presence of a core hole gave the best
results. We performed a search for structural models with coordination site geometries
similar to those in each of metal complexes 3 in the Cambridge Structural Database
(CSD). More than twenty models were simulated for each complex, and the theoretical
curves along with their first derivatives were compared to the experimental ones.
It is clearly seen that the main peculiarities of the experimental XANES spectra
and their first derivatives are reproduced in detail in the simulated spectra. Some
disagreement is observed only in the pre-edge region, where absorption peaks are
shifted by several eV towards higher energies, as it can be seen from Fig. 3-5. As it has
been suggested in [50], the reason for the disagreement lies within the drawbacks of
muffin-tin approximation as regards of the exchange potentials employed in FEFF8
code. This approximation is sufficiently precise for solid state (most inorganic crystals),
but may result in significant deviations of theoretical and experimental spectra of
molecular crystals of metal complexes characterized by the presence of large cavities,
which are not treated adequately within the muffin-tin approximation.
The interligand tilt angle is one of the key quantitative characteristics of
coordination site geometry in metal complexes 3. This tilt angle ∆ is defined as an angle
between the planes going through the M-N1-N2 and M-N3-N4 atoms. Values of the tilt
angles for possible coordination environments are listed in Table 2. This angle ∆
13

characterizes the transformation from tetrahedral to planar coordination, when it
changes from to 90° or 0°. It is seen from Table 2 that the lowest value of the tilt angle
is obtained for 3b, which shows that the coordination in this compound is planar-like. It
should be noted that in this case the possible additional coordination of oxygen atoms of
tosylamine fragments was not taken into account. In this case the resulting symmetry of
the coordination site may be described as a more-or-less tetragonally distorted
octahedron, for example.
CuK-edge
1,2
0,10
0,8
0,08
0,12
0,06
0,04
0,02
0,06
0,00
0,4
8970
8975
8980
8985
E,eV
0,00
8950
9000
9050
9100
E, eV
0,0
8970
9000
9030
9060
9090
E, eV
Fig. 3. The experimental Cu K-edge XAS spectrum (solid line) of 3c complex
and calculated CuK-edge (dashed line) XAS spectrum of the model complex [51]. The
insets show expanded views of the 1s→3d pre-edge region and first derivatives of the
experimental (solid line) and the calculated (dotted line) data.
14

NiK-edge
1,0
0,5
0,0
0,24
0,20
0,16
0,12
0,08
0,04
0,10
0,05
0,00
7700
7705
E,eV
7710
8320
8340
8360
8380
E, eV
8400
8420
8340
8400
8460
E, eV
Fig. 4. The experimental Ni K-edge XAS spectrum (solid line) of 3b(Ni) complex
and calculated NiK-edge XAS spectrum (dashed line) of model complex [52]. The
insets show expanded views of the 1s→3d pre-edge region and first derivatives of the
experimental (solid line) and the calculated (dotted line) data.
15

CoK-edge
1,2
0,8
0,4
0,0
0,24
0,20
0,16
0,12
0,08
0,04
0,18
0,09
0,00
7700
7705
E,eV
7710
7700
7720
7740
7760
E, eV
7780
7800
7700
7750
7800
E, eV
Fig. 5. The experimental Co K-edge XAS spectrum (solid line) of 3a(Co)
complex and calculated CoK-edge XAS spectrum (dashed line) of model complex [53].
The insets show expanded views of the 1s→3d pre-edge region and first derivatives of
the experimental (solid line) and the calculated (dotted line) data.
3.2.4. EXAFS measurements
The EXAFS provides direct, local structural information about the atomic
surrounding of the metal being probed. The magnitude of Fourier transforms (MFT) of
k3-weighted experimental and simulated EXAFS data of the Cu, Ni, and Co K-edges for
3(a,b,c) complexes are presented in Fig. 6. A comparison of these MFT reveals that
they are almost identical, suggesting strong similarities in the geometry around the
metal ions. There is an intense major peak at r = 1.52-1.56 Å and several minor peaks at
longer distances. The first peak of MFT is associated to the nearest-neighbor scattering
from the coordinated nitrogen atoms of the azomethine ligands. The longer-distance
16

backscattering peaks arise partly from the more distant carbon atoms of the azomethine
ligands as well as sulfur atoms and coordinated oxygen atoms of the tosylamine
fragments. The suggestion that the oxygen atoms of the tosylamine fragments are
coordinated in the metal complexes can be derived from of analysis of similar structures
[51-53] retrieved from CSD.
Curve-fitting for the three spectra was performed on filtered first-shell and more
distant shells contributions of S and O atoms of the tosylamine fragments. Fitting results
(bond distances R, coordination numbers N, and Debye-Waller factors σ2) for the metal
nearest neighbor environment are listed in Table 2. All three complexes have a nitrogen
nearest neighbor shell at average distances from 1.96 Å for 3c to 2.01 Å for 3b and
intermediate value 2.00 Å for 3a. The use of two non-equivalent M-N distances for 3b
greatly improved the fit. In all cases the coordination number for the first shell was
equal to four, indicating the tetrahedral donor environment of central metal atoms. The
relatively large Debye-Waller factor for first shell in 3c indicates the disorder in the
metal-ligand bond lengths in this complex.
The outer-shells for all complexes 3(a,b,c) were modeled with sulfur and oxygen
atoms of the tosylamine fragments. The best-fit model for these complexes was built
using only one oxygen atom and one sulfur atom from both tosylamine groups. The
M…O(Ts) distances in complexes 3(a,b,c) are significantly different and they depend on
the metal type forming a series Cu…O(Ts) < Ni…O(Ts) < Co…O(Ts) (see Table 2).
17

20
16
12
8
4N
2S+2O (Toz)
3a
3c
4
3b
0
0
1
2
3
4
5
6
r/Å
Fig. 6. Magnitudes of Fourier transforms of k3-weighted EXAFS of the Cu, Ni, and Co K-edges for
3(a,b,c) complexes. The open cycles show the best fits.
Table 2
Curve fitting results for EXAFS of the 3(a,b,c) complexes (R is the metal–
scatterer distance, N- the number of scatterers, σ2 is a mean–square displacement in R,
Q- the goodness-of-fit parameter, ∆ is an interligand tilt angle).
Compound
N
R,
σ2, Å 2
∆,
degree
Scattering
atom
Q,
Å
%
4
2.00
0.0037
N
18

2
2
2
2
2
2
4
2
2
2.90
3.08
2.01
1.96
2.76
2.93
1.96
2.56
2.88
0.0040
0.0055
0.0038
0.0038
0.0050
0.0060
0.0053
0.0045
0.0045
51
16
O(Ts)
S(Ts)
N
4.3
5.6
3a
N
O(Ts)
S(Ts)
N
3b
3c
56
O(Ts)
S(Ts)
4.7
4. Conclusions
The four metal chelates (Co2+, Ni2+, Cu2+, and Zn2+) on the base of azomethine of
o-tosylaminobenzaldehyde and p-aminoazobenzene (2) was synthesized and
1
investigated by IR, H NMR spectroscopy, XAFS, and magnetic measurements. X-ray
data for ligand 2 showed that the azomethine exists in the amino-imine tautomeric form
both in solutions and solid state. XAFS investigations revealed that the complexes adopt
either distorted tetrahedral or octahedral donor environment that was in accordance with
magnetochemical data.
Acknowledgments
19

This investigation was performed with the financial support of the grant of
Russian Found for Basic Researches (grants 11-03-00475, 12-03-00462 and 13-03-
00171) and Ministry of Education and Science of Russian Federation (grant NS-
927.2012.3).
20

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24

Fig. 1. Structure of the azomethine 2. Selected bond distances (Å): S(1)-O(1)
1.4282(18), S(1)-O(2) 1.4349(18), S(1)-N(1) 1.630(2), S(1)-C(1) 1.759(2), N(1)-C(8)
1.412(3), N(1)-H(1)N 0.9121, N(2)-C(14) 1.279(3), N(2)-C(15) 1.413(3), N(3)-N(4)
1.261(3), N(3)-C(18) 1.422(3), N(4)-C(21) 1.425(3); and valence angles (°)
:O(1)S(1)O(2) 119.43(11), O(1)S(1)N(1) 109.91(11), O(2)S(1)N(1) 104.06(10),
O(1)S(1)C(1) 107.02(11), O(2)S(1)C(1) 109.19(12), N(1)S(1)C(1) 106.59(11),
C(8)N(1)S(1) 125.30(16), C(8)N(1)H(1)N 111.5, S(1)N(1)H(1)N 108.7,
C(14)N(2)C(15) 121.5(2), N(4)N(3)C(18) 114.2(2), N(3)N(4)C(21) 113.7(2).
25

Fig. 2. View of crystal packing of 2 along b crystallographic axis.
1,2
0,8
0,4
0,0
Cu K-edge
0,08
0,04
0,00
0,10
0,05
0,00
µ
8976
8979
8982
E/eV
8940
8970
9000
9030
9060
9090
E/eV
8960
9000
9040
9080
E/eV
26

Fig. 3. The experimental Cu K-edge XAS spectrum (solid line) of 3c complex
and calculated CuK-edge (dashed line) XAS spectrum of the model complex [51]. The
insets show expanded views of the 1s→3d pre-edge region and first derivatives of the
experimental (solid line) and the calculated (dotted line) data.
Ni K-edge
1,0
0,24
0,20
0,16
0,10
0,12
0,5
µ
0,08
0,05
µ
0,04
7700
7705
E,eV
7710
0,00
8320
8340
8360
8380
E/eV
8400
8420
0,0
8320
8360
8400
8440
E/eV
Fig. 4. The experimental Ni K-edge XAS spectrum (solid line) of 3b(Ni) complex
and calculated NiK-edge XAS spectrum (dashed line) of model complex [52]. The
insets show expanded views of the 1s→3d pre-edge region and first derivatives of the
experimental (solid line) and the calculated (dotted line) data.
27

Co K-edge
1,2
0,8
0,4
0,0
0,24
0,20
0,16
0,12
0,08
0,04
0,18
0,09
0,00
µ
7700
7705
E,eV
7710
7700
7720
7740
7760
7780
7800
E/eV
7680
7710
7740
7770
7800
E/eV
Fig. 5. The experimental Co K-edge XAS spectrum (solid line) of 3a(Co)
complex and calculated CoK-edge XAS spectrum (dashed line) of model complex [53].
The insets show expanded views of the 1s→3d pre-edge region and first derivatives of
the experimental (solid line) and the calculated (dotted line) data.
28

20
16
12
8
4N
2S+2O (Toz)
3a
3c
4
3b
0
0
1
2
3
4
5
6
r/Å
Fig. 6. Magnitudes of Fourier transforms of k3-weighted EXAFS of the Cu, Ni, and Co K-edges for
3(a,b,c) complexes. The open cycles show the best fits.
29