New complexes of 4-[(4-fluorophenyl)amino]-4-oxobut-2-enoic acid with selected transition metal ions: Synthesis, thermal, and magnetic properties

Article abstract of DOI:10.1134/S1070363217110305

Complexes of 4-[(4-fluorophenyl)amino]-4-oxobut-2-enoic acid, HL, with Mn(II), Co(II), Ni(II), Cu(II), Nd(III), Gd(III), and Er(III) were synthesized and characterized by various physico-chemical methods: elemental analysis, FT-IR, TG, DTG, DSC, TG/FT-IR, XRF, XRD, and magnetic measurements using the Gouy’s method and a SQUID-VSM magnetometer. The complexes were found to be hydrates (except Er(III) complex) containing 1 to 4 molecules of water. The carboxylate groups acted as bidentate ligands.

Full text of DOI:10.1134/S1070363217110305

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 11, pp. 2719–2727. © Pleiades Publishing, Ltd., 2017.
New Complexes
of 4-[(4-Fluorophenyl)amino]-4-oxobut-2-enoic Acid
with Selected Transition Metal Ions: Synthesis, Thermal,
and Magnetic Properties1
W. Ferenca*, P. Sadowskia, B. Tarasiuka, B. Cristóvãoa, D. Osypiuka, and J. Sarzyńskib
a Faculty of Chemistry, Department of General and Coordination Chemistry,
Maria Curie-Skłodowska University, Lublin, 20031 Poland
*e-mail: wetafer@poczta.umcs.lublin.pl
b Institute of Physics, Maria Curie-Skłodowska University, Lublin, 20031 Poland
Received October 5, 2017
Abstract―Complexes of 4-[(4-fluorophenyl)amino]-4-oxobut-2-enoic acid, HL, with Mn(II), Co(II), Ni(II),
Cu(II), Nd(III), Gd(III), and Er(III) were synthesized and characterized by various physico-chemical methods:
elemental analysis, FT-IR, TG, DTG, DSC, TG/FT-IR, XRF, XRD, and magnetic measurements using the
Gouy’s method and a SQUID-VSM magnetometer. The complexes were found to be hydrates (except Er(III)
complex) containing 1 to 4 molecules of water. The carboxylate groups acted as bidentate ligands.
Keywords: 4-[(4-fluorophenyl)amino]-4-oxobut-2-enoic acid, selected 3d- and 4f-metals, IR and X-ray
spectra, thermal stability, magnetic properties
DOI: 10.1134/S1070363217110305
Transition metals carboxylates demonstrate variable
stereochemistry depending upon the mechanism of
their formation. Their activity is modulated by the
nature of substituents at the basic ligand and kinds of
coordinated metal ions [1–3].
Cr(III), and Sb(III) were synthesized and studies as
well [12–15]. (Z)-4-Oxo-4-(phenylamino)but-2-enoic
acid and its compounds with La(III), Eu(III), Tb(III),
and Yb(III) were prepared and characterized by some
physicochemical methods [16].
Maleic acid is used in pharmacology for producing
corresponding maleates that make the drugs more
stable. In biochemistry maleate ion acts as an inhibitor
of transaminase reactions that catalyze transfer of the
amino group of an amino acid to a carbonyl com-
pound, commonly an α-keto acid. The maleinic acid
derivatives demonstrate cytotoxic activity towards
leukaemic cells and a strong antifungal activity [4].
Those may also act as inhibitors of aldose reductase [5].
Complexes of selected transition metal ions with 4-
oxo-4-{[3-(trifluoromethyl)phenyl]amino}but-2-enoic
acid anion have been studied [17].
The current study targeted synthesis of new Mn(II),
Co(II), Ni(II), Cu(II), Nd(III), Gd(III), and Er(III)
complexes with 4-[(4-fluorophenyl)amino]-4-oxobut-2-
enoic acid anion and elucidation of their molecular
structures. Because of poor crystallization of the
compounds in neutral solvents the molecular structures
of the complexes were not determined. Instead, their
diffractograms are presented. The particular attention
was directed towards determination of stoichiometry of
the complexes by elemental analysis, X-ray fluore-
scence spectroscopy (XRF) and thermogravimetric
methods. IR spectroscopy was used for determining
possible centers of coordination of HL anion. IR
spectroscopy and magnetic susceptibility data were
used for determining geometry around Mn(II), Co(II),
Ni(II), Cu(II), Nd(III), Gd(III), and Er(III) ions.
According to the literature survey, the complexes of
maleic acid with Tl(I), Sn(IV), Mo(IV), and Co(II)
ions and its various amido derivatives with Cu(II) ion
were prepared and characterized [6–10]. The thermo-
dynamic functions of compounds of 4-nitro- and
4-methoxymaleanilic acids with Mn(II), Co(II), Ni(II),
Cu(II), and Zn(II) were determined [11]. The new
complexes of maleanilic and phtalanilic acids with
1 The text was submitted by the authors in English.
2719

2720
FERENC et al.
Scheme 1. synthesis of 4-[(4-fluorophenyl)amino]-4-oxobut-2-enoic acid.
O
O
NH2
NaOAc, Ac2O
N
O
+
F
F
O
O
O
NH−C−CH=CH−C
NaOH, EtOH−H2O; HCl
OH
O
F
EXPERIMENTAL
with the palladium rod sample. In the case of the
Gouy’s method the mass changes were determined on
a Cahn RM-2 electrobalance. The calibrate employed
was Hg[Co(SCN)4] for which the magnetic suscepti-
bility was assumed to be 1.644×10–5 cm3/g. The
measurements were made at a magnetic field strength
of 0.99 T. Corrections for diamagnetism of the con-
stituent atoms were calculated using the Pascal’s
constants [18, 19]. Effective magnetic moment values
were calculated by the equation:
Chemicals and solvents used in the synthesis were
commercially available, reagent grade and used
without purification. CHN analysis was carried out on
a CHN 2400 Perkin-Elmer analyzer. The amounts of
Ln(III) and M(II) metals and fluorine were determined
by X-ray fluorescence XRF method using an energy
dispersion spectrophotometer XRF-1510 (Canberra-
Packard). FT-IR spectra (KBr discs) were recorded
over the range of 4000–400 cm–1 on a M–80 Perkin–
Elmer spectrophotometer. 1H NMR spectrum for HL in
DMSO-d6 was measured on a Bruker Avance 300 MHz
NMR spectrometer at 298.1 K.
µeff = 2.83 (χmcorrT)1/2,
where µeff is an effective magnetic moment, χmcorr is a
magnetic susceptibility per molecule, and T ia sn
absolute temperature.
X-Ray diffraction patterns of compounds and the
products of their decomposition were determined on a
HZG–4 (Carl Zeiss, Jena) diffractometer using Ni
filtered CuKα radiation. The measurements were made
within the range of 2θ = 4º–80º by means of the Bragg-
Brentano method. For interpretation of diffractograms
the Dicvol 06 programme was used. Thermal stability
and decomposition processes of complexes were
studied using a Setsys 16/18 (Setaram), TG, DTG and
DSC instrument. The experiments were carried out
under the air flow in the temperature range of 293–
1173 K at a heating rate of 5 K/min. The initial masses
of complexes samples changed from 3.69 to 4.74 mg.
The compounds were heated in Al2O3 crucibles.
Synthesis. HL was prepared by the two-steps
process (Scheme 1). At first N-(4-fluorophenyl)
maleimide was obtained in the following way. A
mixture of 11.1 g (0.1 mol) of 4-fluoroaniline with
10.0 g (0.105 mol) of maleic anhydride, 8.2 g sodium
acetate, and 50 mL acetic acid was stirred over 1 h at
room temperature. Then the mixture was heated at 80–
85ºC for 5 h. Upon following cooling down the flask
content was poured onto ice. The colourless precipitate
was filtered off and washed with water. Yield 18.3 g
(95.5%), mp 147.5ºC [20].
In the second step thus obtained N-(4-fluorophenyl)
maleimide was hydrolyzed in a solution of NaOH. N-
(4-fluorophenyl)maleimide (9.6 g, 0.05 mol) were
mixed with 100 mL of ethanol, 60 mL of water, and 2 g
(0.05 mol) of NaOH. The mixture was boiled for 1.5 h,
then it was cooled down and acidified with 10% HCl
(pH = 1). The obtained crystalline solid was filtered
off and purified by crystallization from methanol–
water solution. Yield 8.3 g (79%), mp 211–212ºC [21].
1H NMR spectrum (CDCl3), δ, ppm: 6.36 s (2H,
Magnetic susceptibility of samples was studied at
the temperature ranges of 76–303 and 2–300 K. The
measurements were carried out using the Gouy’s
method and with the use of a Quantum Design SQUID-
VSM magnetometer. A superconducting magnet was
generally operated at a field strength ranging from 0 to
7 T. Measurements of samples were made at magnetic
field 0.1 T. A SQUID magnetometer was calibrated
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NEW COMPLEXES OF 4-[(4-FLUOROPHENYL)AMINO]-4-OXOBUT-2-ENOIC ACID
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CH=CH), 7.17–7.63 m (4H, Ar-H), 10.43 s (1H, NH,),
12.86 s (1H, COOH). Found, %: C 57.51; H 3.90; N
6.71. C10H8FNO3 Calculated, %: C 57.42; H 3.85; N
6.70. M 209.17.
1612 [νas(COO–)], 1508 [ν(CAr=CAr)], 1408 (νC=C),
1352 [νs(COO–)], 1224 (ωCH), 1098 (νC–F), 832 (ωCH),
640 (δN–H), 488 (νNi–O). Found, %: C 48.09; H 3.60; N
5.58; F 7.68; Ni 11.60. Calculated, %: C 48.72; H
3.68; N 5.68; F 7.71; Ni 11.90.
CuL2·4H2O. Green crystals. IR spectrum, ν, cm–1:
3412 (νN–H), 3132 (νOH), 1676 (νC=O), 1632 (νC=C),
1612 [νas(COO–)], 1492 [ν(CAr=CAr)], 1408 (νC=C),
1364 [νs(COO–)], 1224 (ωCH), 1100 (νC–F), 836 (ωCH),
640 (δN–H), 486 (νCu–O). Found, %: C 43.43; H 4.27; N
5.00; F 6.80; Cu 11.42. Calculated, %: C 43.52; H
4.37; N 5.08; F 6.89; Cu 11.52.
Ammonium salt of HL (pH~5) of 0.1 mol/L
concentration was prepared by adding NH3aq solution
(25% pure, Polish Chemical Reagents in Gliwice,
Poland) to water solution of HL. For obtaining the 4f
element(III) chlorides the samples of 0.8 g of those
elements oxides (99.9% pure, Aldrich Chemical
Company) were digested in the equivalent amount of
concentrated HCl (35–36% pure, Polish Chemical
Reagents in Gliwice–Poland). The formed chlorides
were dried, dissolved in water giving the solutions of
corresponding chlorides, concentration 0.1 mol/L, pH ca 5.
NdL3·2H2O. Light-green crystals. IR spectrum, ν,
cm–1: 3372 (νN–H), 3300 (νOH), 1664 (νC=O), 1632
(νC=C), 1600 [νas(COO–)], 1508 [ν(CAr=CAr)], 1408
(νC=C), 1352 [νs(COO–)], 1232 (ωCH), 1100 (νC–F), 836
(ωCH), 632 (δN–H), 488 (νNd–O). Found, %: C 44.36; H
3.46; N 5.20; F 7.06; Nd 17.82. Calculated, %: C
44.70; H 3.50; N 5.22; F 7.08; Nd 17.92.
GdL3·3H2O. Creamy crystals. IR spectrum, ν, cm–1:
3364 (νN–H), 3292 (νOH), 1664 (νC=O), 1632 (νC=C),
1612 [νas(COO–)], 1508 [ν(CAr=CAr)], 1408 (νC=C),
1356 [νs(COO–)], 1232 (ωCH), 1100 (νC–F), 832 (ωCH),
628 (δN–H), 480 (νGd–O). Found, %: C 43.33; H 3.51; N
5.00; F 6.68; Gd 18.62. Calculated, %: C 43.11; H
3.61; N 5.03; F 6.82; Gd 18.82.
ErL3. Creamy crystals. IR spectrum, ν, cm–1: 3368
(νN–H), 1664 (νC=O), 1632 (νC=C), 1616 [νas(COO–)],
1508 [ν(CAr=CAr)], 1408 (νC=C), 1356 [νs(COO–)], 1228
(ωCH), 1100 (νC–F), 828 (ωCH), 624 (δN–H), 482 (νEr–O).
Found, %: C 45.40; H 3.05; N 5.30; F 7.18; Er 21.03.
Calculated, %: C 45.50; H 3.06; N 5.31; F 7.20; Er 21.13.
The complexes of 3d- and 4f-electron metal ions
with HL were prepared by adding the equivalent
amounts of 0.1 mol/L ammonium salt of HL (pH ca 5)
to warm solutions of the corresponding element
chlorides and crystallized at 293 K. Certain volumes of
solutions, 39, 84, 84, 116, 142, 132, and 125 cm3, of
0.1 M ammonium 4-[(4-fluorophenyl)amino]-4-oxobut-
2-enoate were added to the certain chloride solutions
of Mn(II), Co(II), Ni(II), Cu(II), Nd(III), Gd(III), and
Er(III). For reaching equilibrium state the solids were
constantly stirred for 1 h, then filtered off, washed with
warm water to remove ammonium chloride and dried
at 303 K until reaching the constant mass.
Sodium salt of HL acid was synthesized by the
reaction of the equivalent amount of 0.1 mol/L ammo-
nium salt of HL acid with the solution containing 0.1 g
of NaOH (analytically pure, Polish Chemical Reagents
in Gliwice–Poland) and crystallized.
MnL2·2H2O. Grey solid. IR spectrum, ν, cm–1:
3436 (νN–H), 3228 (νOH), 1672 (νC=O), 1636 (νC=C),
1612 [νas(COO–)], 1508 [ν(CAr=CAr)], 1408 (νC=C),
1356 [νs(COO–)], 1228 (ωCH), 1096 (νC–F), 828 (ωCH),
620 (δN–H), 488 (νMn–O). Found, %: C 46.46; H 4.02; N
5.45; F 7.38; Mn 10.60. Calculated, %: C 46.89; H
3.93; N 5.47; F 7.42; Mn 10.73.
RESULTS AND DISCUSSION
IR spectra of HL, its complexes and sodium salt
were recorded for monitorring the complexation process
and identifying the atoms of ligand carboxylate
coordinated to the appropriate cations. For parent
carboxylic ligand, HL, broad bands with the maxima at
3408 and 2940 cm–1 indicated the N–H and –CH2
stretching bonds vibrations, respectively [22–27]. In its
complex spectra the bands at 3328–3128 cm–1
indicated the presence of water molecules (except of
Er(III)) in the compounds and those at 3464–3359 cm–1
originated from the N–H bond vibrations. The band at
1700 cm–1 was attributed to stretching vibrations of the
COOH group of HL. Upon deprotonation two strong
bands at 1616–1600 and 1364–1352 cm–1 were
CoL2·H2O. Light-brown crystals. IR spectrum, ν,
cm–1: 3460 (νN–H), 3328 (νOH), 1684 (νC=O), 1636
(νC=C), 1612 [νas(COO–)], 1512 [ν(CAr=CAr)], 1408
(νC=C), 1356 [νs(COO–)], 1224 (ωCH), 1100 (νC–F), 836
(ωCH), 620 (δN–H), 492 (νCo–O). Found, %: C 48.55; H
3.58; N 5.58; F 7.60; Co 11.55. Calculated, %: C
48.70; H 3.68; N 5.68; F 7.70; Co 11.95.
NiL2·H2O. Light-green crystals. IR spectrum, ν, cm–1:
3359 (νN–H), 3228 (νOH), 1672 (νC=O), 1632 (νC=C),
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

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FERENC et al.
Table 1. The unit cell parameters for polycrystalline series of 4-[(4-fluorophenyl)amino]-4-oxobut-2-enoic acid with Mn(II),
Co(II), Ni(II), Cu(II), Nd(III), Gd(III), and Er(III)
Complex
Crystal system
Triclinic
a, Å
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
L– = C10H7O3FN
MnL2·2H2O
CoL2·H2O
NiL2·H2O
7.7901
13.8315
9.2713
17.1655
7.9569
20.2041
19.2611
19.2483
16.6121
15.0070
15.1010
14.3824
70.583
90.000
92.494
90.000
73.430
93.485
99.815
86.964
97.486
98.150
92.968
73.091
108.712
97.626
81.139
90.000
101.609
90.000
68.679
109.349
90.128
2517.64
2101.72
2419.60
2904.30
1746.10
1665.84
1406.86
Monoclinic
Triclinic
14.0216
12.7944
12.9079
12.8367
12.1803
CuL2·4H2O
NdL3·2H2O
GdL3·3H2O
ErL3
Monoclinic
Triclinic
13.6829
10.3250
9.7889
Triclinic
Triclinic
8.2255
attributed to COO– asymmetric and symmetric
stretching vibrations, respectively. The bands of C=C
valency vibrations were recorded at 1636–1632 cm–1.
The –C=C– stretching ring vibrations, νC=C, were
recorded at 1512–1452 cm–1. The C–F stretching
vibrations, νC–F, were recorded at 1100–1096 cm–1. The
bands characteristic for –N-H deformation vibrations,
parameters the X–ray powder diffractions data were
calculated by applying the Dicvol06 program [30]
(Table 1).
Thermogravimetric studies of analyzed transition
metal complexes were carried out in the air in the
range of 293–1273 K (Table 2, Fig. 1). TG, DTG, and
DSC curves were recorded using the DSC/TG
technique. Upon heating to 1273 K the compounds
decomposed in three steps. They were stable up 310–
410 K. In the range of 310–439 K they dehydrated in
one step with endothermic effects (DSC curves) losing
molecules of water and forming anhydrous com-
pounds. The mass losses calculated from TG curves
were equal to 4.25–13.00% corresponding to the loss
of two and four molecules of water (calculated 3.65–
13.05%).
δ
N–H, appeared at 640–620 cm–1 and those at 836–
828 cm–1 were attributed to C–H valency vibrations in
the 1 : 4 substituted ring. The bands at 492–480 cm–1
confirmed the presence of the ionic metal–oxygen
bond [22–27]. In the spectra of complexes the bands of
νas(OCO–) and νs(OCO–) were shifted to lower frequen-
cies compared to those of sodium salt [νas(OCO–) =
1672 cm–1, νs(OCO–) = 1332 cm–1] [27]. With
reference to Nakamoto criterion, the carboxylate ion
acted as a bidentate chelating group [1, 3, 27]. The
values of ∆νOCO for the analyzed compounds were
smaller (∆νOCO = 260–248 cm–1) than those for sodium
salt (∆νOCO = 340 cm–1).
Energy effects accompanying the dehydration
processes were also determined. Enthalpy values, ∆H,
changed from 9.65 to 185.9 kJ/mol and from 2.41 to
93.98 kJ/mol per one molecule of water. The values
demonstrated that water molecules were bounded in
these compounds with different strengths depending
on their positions in the complexes coordination
spheres and nature of the central ions.
Position of the C–F stretching vibrations in the
complexes spectra (1100 cm–1) was practically in the
same position as that in the parent ligand spectrum
(1096 cm–1), which suggested that F atom did not
coordinate with the metal center. The fingerprint
regions have been also compared. Several bands
Upon heating the anhydrous complexes of 3d- and
4f-electrons metals ions formed intermediates,
oxyfluorides (427–785 K), that ultimately yielded the
oxides of the appropriate metals. Mass losses cal-
culated from TG curves were in the range of 30.09–
76.19% indicating formation of oxyfluorides (cal-
culated values changed from 29.13 to 77.87%). The
intermediate compounds decomposed into the oxides
of respective metals MO and Ln2O3, where M(II) =
Mn, Co, Ni, Cu and Ln(III) = Nd, Gd, Er. Temperature
present in the HL spectrum (for example, νN–H or δN–H
)
were observed in different positions compared to those
in its metal complexes IR spectra due to interactions of
these groups vibrations with neighbouring atoms or
ions in the molecules.
The X–ray powder diffraction patterns of com-
plexes indicated the crystalline nature of those
[28, 29]. In order to determine their unit cell
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NEW COMPLEXES OF 4-[(4-FLUOROPHENYL)AMINO]-4-OXOBUT-2-ENOIC ACID
(a) (b)
2723
Weight loss, %
Weight loss, %
Heat flow, mW
Heat flow, mW
T, K
T, K
Fig. 1. (1) TG, (2) DTG, and (3) DSC curves for (a) Mn(II) and (b) Nd(III) complexes.
LnL3·nH2O → LnL3 → LnOF → Ln2O3,
of their formation was in the range of 706–1273 K.
The masses of residues determined from TG curves
were in the range of 9.47–23.10% (theoretical values
changed from 9.02 to 24.14%). Those were obtained as
metal oxides and verified by comparing their FT-IR
spectra and powder diffractograms with those of pure
oxides. The results indicated that thermal decomposi-
tion of analyzed complexes in the air proceeded along
the following pathways:
Ln(III) = Nd, Gd, Er; n = 2 for Nd; n = 3 for Gd;
n = 0 for Er.
The accumulated data demonstrated that the coor-
dination numbers of central ions were probably equal
to 6, 8 or 9 for trivalent ions. In the case of Nd(III) and
Gd(III) the water molecules seemed to be aqua ligands
[31, 32]. For Mn(II), Co(II), Ni(II), and Cu(II) com-
plexes the coordination numbers could be equal to 5, 6
or 8 depending on nature of the central ion.
ML2·nH2O → ML2 → M2OF2 → MO,
Data accumulated for the complete structures of the
complexes could give fair information about positions
M(II) = Mn, Co, Ni, Cu; n = 1 for Co, Ni;
n = 2 for Mn; n = 4 for Cu;
Table 2. Temperature ranges for thermal stability in the air at 293–1273 K and enthalpy values of dehydration processes for
the studied complexesa
Weight loss, %
Weight loss, %
Residue, %
Complex
Tk,
K
∆H,
kJ/mol kJ/mol
∆H0,
∆T1, K
nH2O ∆T2, K
L– = C10H7O3FN
calculated found
calculated found calculated found
MnL2·2H2O 331–352
7.10
3.85
3.65
7.90
4.25
4.35
13.00
4.84
6.34
–
2
1
1
4
2
3
–
431–473
431–493
427–514
493–680
693–773
452–773
535–785
29.13
33.07
48.23
46.18
77.87
77.01
74.59
30.09
34.00
49.76
46.02
76.19
73.21
74.60
10.63
11.28
9.02
10.52 773 185.9 92.95
11.37 752 93.98 93.98
9.47 752 87.74 87.74
CoL2·H2O
NiL2·H2O
CuL2·4H2O
NdL3·2H2O
GdL3·3H2O
ErL3
327–360
310–373
310–423 13.05
14.50
20.89
22.22
24.14
15.01 706 9.65
2.41
385–439
410–439
–
4.47
6.46
–
21.95 1073 91.98 45.99
21.65 1273 112.72 37.57
23.10 1273
–
–
a
(∆T1) temperature range of dehydration; (n) number of water molecules; (∆T2) temperature range of anhydrous complex decomposition;
(Tk) final temperature of decomposition, (∆H) enthalpy value for dehydration process, (∆H0) enthalpy value per one water molecule.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

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FERENC et al.
(a)
(b)
T, K
T, K
Fig. 2. Relashionships between (1) χmcorr and (2) (χmcorr –1
)
values, and T for (a) Ni(II) and (b) Er(III) complexes.
(a)
(b)
T, K
T, K
Fig. 3. Relashionships between (1) (χmcorr –1
)
and (2) χmcorrT values, and T for (a) Ni(II) and (b) Cu(II) complexes.
of water molecules in the compounds but their single
crystals have not been isolated so far from various
solvents (H2O, alcohols, DMSO, DMF) and using
different metal:ligand ratios.
moment values experimentally determined in the range
of 76–303 K changed from: 2.1 µB to 1.77 µB for
Cu(II); 3.40 to 3.70 µB for Co(II); 2.31 to 2.35 µB for
Ni(II); 4.45 to 4.55 µB for Mn(II); 3.08 to 3.49 µB for
Nd(III); 5.85 to 5.83 µB for Gd(III), and from 8.34 to
8.70 µB for Er(III) complexes.
The initial dehydration temperature values for
complexes indicated that the water molecules could be
also lattice water because it was released below 423 K
[33].
In Nd(III), Gd(III) and Er(III) complexes the para-
magnetic central ions remained practically unaffected
by diamagnetic ligands. The 4f orbitals were effect-
tively shielded by 5s2 and 5p6 orbitals. They were not
involved in the bonds between Ln(III) ions and their
close neighbours. Accordingly the metal–ligand
bonding in Ln(III) compounds appeared to be pre-
dominantly electrostatic [39–41] as it was deduced
from IR spectra.
Magnetic measurements. For estimation of metal
ligand bonding nature in analyzed complexes and
determining the reason for their colour to be typical for
4f-electron metal(III) ions and for studying of the sur-
rounding of coordination ions the magnetic suscepti-
bility of compounds was measured over the ranges of
76–303 K [34–40], and of 2–300 K for determining
whether the nature of atomic magnetic interaction
changed at low temperatures (Figs. 2, 3).
Due to the fact that the 4f orbitals were well
shielded by the surroundings of the ions, various states
arising from 4fn configurations were split by external
fields only to ca 100 cm–1. Therefore the electronic f–f
The accumulated data indicated that the complexes
obeyed the Curie–Weiss law. The effective magnetic
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NEW COMPLEXES OF 4-[(4-FLUOROPHENYL)AMINO]-4-OXOBUT-2-ENOIC ACID
2725
transitions caused the absorption bands to be very
sharp being similar to those of free atoms. As the
colours were determined by the f–f transitions, they did
not depend upon the environment of the ions [41]. The
magnetic properties could be considered as those of the
ground state alone. Therefore 4f-electron meatal(III)
ions in the compounds acted the same way as free ions.
The values of µeff determined for the studied com-
plexes of 4f metals(III) were close to those calculated
by the Hund and Van Vleck [2, 34] for Ln(III) ions.
lowering the χmT and the magnetic moment values
decreased to 0.8729 cm3 K mol–1 (µeff = 2.64 µB) at
2 K, which indicated the weak antiferromagnetic order
between Co(II) centers or the intermolecular hydrogen
bonds in the compound crystal lattice.
For Ni(II) ion complex the magnetic moments
changed from 1.9 (at 2.029 K) to 2.03 µB (at 300 K).
At 300 K the χmT value was equal to 0.5126 cm3 K mol–1,
which increased to 0.6129 cm3 K mol–1 at 47.40 K at
lower temperature. This could be due to weak
ferromagnetic order between Ni(II) centres of crystal
lattice. In the range of 47.4–2.029 K the magnetic
moments changed from 2.22 to 1.9 µB. These values
were lower than those of calculated theoretically,
which could indicate the antiferromagnetic interaction
among Ni(II) ions (θ negative). The reason for this
could be the second order spin–coupling splitting the
3A2g ground state of Ni(II) ion, or perhaps it was
combined with an antiferromagnetic super–exchange
interaction [44]. The higher values in the range of 48–
300 K probably resulted from the ferromagnetic
effects. The lower values of magnetic moments than
theoretically calculated could also originate from the
alignment of the vectors L and S caused by the strong
field of the heavy atom in opposite directions. It
diminished the resultant magnetic moment. The
analyzed Ni(II) complex was expected to be high–spin
with the weak ligand field [1, 37, 40] and tetrahedral
environment of central ion with its sp3 hybridization
[40].
The magnetic moments experimentally determined
at 76–303 and 2–299 K for Mn(II), Co(II), Ni(II), and
Cu(II) complexes seemed close to spin only values for
the respective ions calculated from the equation µeff
=
[4s(s + 1)]1/2 (s = n/2) in the absence of the magnetic
interactions for present spin-system. The theoretical
values calculated at room temperature for Mn(II),
Co(II), Ni(II), and Cu(II) ions were equal to 5.9, 3.88,
2.83, and 1.73 µB, respectively.
The magnetic moments determined at 2–300 K for
complexes changed from 3.57 to 4.56 µB for Mn(II),
2.64 to 3.81 µB for Co(II); 1.9 to 2.03 µB for Ni(II),
3.51 to 1.69 µB for Cu(II), 2.31 to 3.32 µB for Nd(III),
8.81 to 8.09 µB for Gd(III), and from 6.46 to 8.80 µB
for Er(III).
The magnetic moments for Mn(II) ion complex
were lower than the spin–only value, which could be
due to the fact that the vectors L and S were aligned by
the strong field of the heavy atom in opposite
directions and this diminished the resulting magnetic
moment. The experimental data demonstrated that
Mn(II) compound seemed to be the high–spin complex
with octahedral symmetry around the central ion and
the weak ligand field [1, 37, 40, 42, 43]. At 300 K the
The magnetic interpretation of data for Cu(II)
complex is presented in Fig. 3. At 300 K χmT values
were equal to 0.3564 cm3 K mol–1 (µeff = 1.69 µB),
being typical for non–coupled S=1/2 Cu(II) centres.
Upon temperature lowering the χmT value and the
magnetic moment increased to χmT = 1.8861 cm3 K mol–1
(µeff = 3.88 µB) at 3.43 K. It suggested a weak
ferromagnetic interaction between Cu(II) ions [45] or
intermolecular hydrogen bonds in molecular crystal
lattice [46]. The study of magnetostructural data
indicated that weak ferromagnetic or antiferromagnetic
coupling between adjacent copper ions depended on
the nature of magnetic orbitals (built up from d orbitals
of the metal ions and the symmetry adapted linear
contribution of the orbitals of the ligands) on Cu
neighboring ions [1, 47]. The complex could have a
distorted tetragonal pyramid geometry. According to
IR spectra, the carboxylate group was bidentate with
an equatorial position at one copper ion and a pseudo
equatorial position at the other. This feature could
χmT value was equal to 2.5977 cm3 K mol–1 (µeff
=
4.56 µB). Upon lowering of temperature the χmT value
and the magnetic moment decreased to 1.5956 cm3 K
mol–1 (µeff = 3.57 µB) at 2.02 K, which suggested an
antiferromagnetic interaction between Mn(II) centres
[44] or weak intermolecular hydrogen bonds in the
compound lattice. Around the central ion there were
probably four oxygen atoms from two carboxylate
bidentate groups and two atoms of water molecules.
In the case of Co(II) complex the values of magnetic
moments changed from 2.64 (at 2.03 K) to 3.81 µB (at
299 K). The experimental data indicated the Co(II)
complex to be high–spin compound with the weak
ligand field. At 300 K the χmT value was equal to
1.8113 cm3 K mol–1 (µeff = 3.81 µB). Upon temperature
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

2726
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CONCLUSIONS
Complexes of Mn(II), Co(II), Ni(II), Cu(II),
Nd(III), Gd(III), and Er(III) ions with 4-[(4-fluoro-
phenyl)amino]-4-oxobut-2-enoic acid anion form
hydrated or anhydrous crystalline compounds that
crystallize in a monoclinic or triclinic system. The
carboxylate groups act as bidentate ligands.
Thermal stability of analysed compounds was
studied in the air at 293–1273 K. The complexes
decomposed in three steps. At first they dehydrated
and formed anhydrous salts, which was followed by
decomposition with formation of the oxides of ap-
propriate metals via intermediate formation of oxy-
fluorides. Enthalpy values of dehydration processes
were determined. The magnetic susceptibility of
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76–303 K and 2–300 K. All of those obeyed the Curie–
Weiss law, demonstrating the paramagnetic properties.
In the molecular centres the ferromagnetic interactions
took place.
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