Complexes of some transition metal ions with selected dichlorophenoxyacetic acid: Thermal, spectral and magnetic properties

Article abstract of DOI:10.1007/s10973-016-5321-1

This paper presents the interpretations of data obtained from the investigations of 2,4-dichlorophenoxyacetates of selected lanthanide(III) ions. The compounds of 2,4-dichlorophenoxyacetic acid ion with La(III), Pr(III)–Lu(III) with the formula Ln(C₈

Full text of DOI:10.1007/s10973-016-5321-1

J Therm Anal Calorim
DOI 10.1007/s10973-016-5321-1
Complexes of some transition metal ions with selected
dichlorophenoxyacetic acid
Thermal, spectral and magnetic properties
1
2
•
Wiesława Ferenc1 Beata Cristova˜o Jan Sarzynski Dariusz Osypiuk1
•
•
´
´
Received: 1 October 2015 / Accepted: 3 February 2016
´
´
Ó Akademiai Kiado, Budapest, Hungary 2016
Abstract This paper presents the interpretations of data
obtained from the investigations of 2,4-dichlorophenoxy-
acetates of selected lanthanide(III) ions. The compounds of
2,4-dichlorophenoxyacetic acid ion with La(III), Pr(III)–
Lu(III) with the formula Ln(C8H5O3Cl2)3ÁnH2O, where
Ln(III) = lanthanides, n = 2, 4 or 5 depending on Ln(III)
ions, were synthesized and characterized by elemental
analysis, FTIR spectroscopy, magnetic and thermogravi-
metric studies and also by X-ray powder diffraction (XRD)
measurements. The compounds crystallize in monoclinic or
triclinic systems. The carboxylate groups act as bidentate
chelating agents. On heating in air up to 1173 K, the
analysed compounds are decomposed in three steps: they
are dehydrated to anhydrous salts which next are decom-
posed to the oxides of respective metals with intermediate
formation of the oxychlorides. The enthalpy values of the
Introduction
2,4-Dichlorophenoxyacetic acid exhibits selective weed
killer properties. Therefore, it is used as active substance in
many herbicides applied for protection of wheat, rye, bar-
ley and oat. This xenobiotic is deliberately introduced by
man into the environment in order to increase crops and
improve their quality. However, if used unskilfully or
excessively, it can pose a threat to the environment. The
pesticides and the products of their decomposition pollute
the soil, ground and surface waters, agricultural and food
products [1–3].
The chlorophenoxyacetic acids and their derivatives as
widely used herbicides may form complexes with metal
ions present in soil. Those of their compounds being
slightly soluble in water may cause retention of metals in
soil or in underground parts of the plants and stop their
transport to the above-ground sections. This behaviour can
reduce the level of pesticides in food or water. The com-
pounds show also the antimicrobial activity [4–10].
The carboxylic group present in the acid molecule may
interact with metal ions effecting their properties and
biological activity. The lanthanide(III) ions show the
interesting biochemical properties; therefore, they may be
used in the metabolism investigations. Under temperature
changes, the lanthanide ions may migrate from their min-
erals to soil, water or organic materials and next they may
penetrate to plants, animals and also to human organism.
The biological activity of coordination compounds is
modulated by many such factors like the following: the
nature of group substituted to the basic ligand, type of
metal and environment around the central metal ion in
complex.
dehydration process changed from 44.00 to 91.34 kJ mol-1
.
The magnetic moments of compounds were determined in the
ranges of 76–303 K and for some of them at 4.2–303 K.
Keywords 2,4-dichlorophenoxyacetates Á Lanthanides Á
Magnetic properties Á Thermal stability
& Wiesława Ferenc
wetafer@hermes.umcs.lublin.pl;
wetafer@poczta.umcs.lublin.pl
1
Faculty of Chemistry, Maria Curie-Skłodowska University,
20-031 Lublin, Poland
2
2,4-Dichlorophenoxyacetic acid may form the com-
plexes with metals present in the soil. Therefore, the
Institute of Physics, Maria Curie-Skłodowska University,
20-031 Lublin, Poland
123

W. Ferenc et al.
studies of the structures, conditions of the formation and
physico-chemical properties of its compounds with various
metal ions seem interesting for practical application [1, 10].
As part of our research on carboxylate complexes, we
synthesized and investigated also the 2-(4-chlorophe-
noxy)acetates of lanthanides(III) [11]. These hydrated
compounds were characterized by elemental analysis,
FTIR spectroscopy, magnetic and thermogravimetric
studies and X-ray diffraction (XRD) analysis. In the com-
plex molecules, the carboxylate groups act as bidentate
chelating agents. On heating in air to 1273 K, they
decompose in three steps. At first, they dehydrate forming
at first anhydrous salts and next the oxides of respective
metals. The oxychlorides are their intermediate products of
thermal destruction. Over the ranges of 76–303 and
1.8–300 K, the magnetic susceptibility of 2-(4-chlorophe-
noxy)acetates of lanthanides(III) were measured and
magnetic moments calculated. The results revealed them to
be high-spin complexes with weak ligand fields.
In order to obtain the rare earth element(III) chlorides,
LnCl3ÁnH2O, the samples of 0.8 g of lanthanide(III) oxides
(99.9 % pure, Aldrich Chemical Company) were digested
in the equivalent amounts of concentrated HCl [35–38 %
pure, Polish Chemical Reagents in Gliwice (Poland)]. The
solutions were constantly heated. The lanthanide(III)
chlorides were practically evaporated to dryness. The
residue was dissolved in water forming the solutions of
lanthanide(III) chlorides, the concentration of which was
equal to 0.1 mol L-1 and pH 5.
Synthesis
The complexes of lanthanides(III) with 2,4-dichlorophe-
noxyacetic acid anion were prepared by adding the equiva-
lent quantities of 0.1 mol L-1 ammonium salt of 2,4-
dichlorophenoxyacetic acid (pH 5) to a warm solutions of
lanthanide(III) chlorides and crystallizing at 293 K. For the
reaching equilibrium state, the solids were constantly stirred
for 1 h. Next they were filtered off, washed with warm water
to remove ammonium and chloride ions and dried at 303 K to
a constant mass. The sodium salt of 2,4-dichlorophenoxy-
acetic acid was prepared by the addition of equivalent
amount of 0.1 mol L-1 ammonium salt of that acid to NaOH
solution containing 0.1 g NaOH [analytically pure, Polish
Chemical Reagents in Gliwice (Poland)] and crystallizing.
From the review of the available literature on the 2,4-
dichlorophenoxyacetates of metal ions, it appears that there
are papers on the mixed ligand complexes of 2,4-
dichlorophenoxyacetates with Cu(II) and 2,20- bipyridine
and 4,40- bipyridine [12–14]. Metal(II) compounds of 2,4-
dichlorophenoxyacetic acid with N-bases, a-aminoacids
and bovine serum albumin are described in the articles [13–19].
There are also publications concerning the investigations of
2,4-dichlorophenoxyacetic acid anion with Ag(I), Zn(II),
Cu(II), Co(II), Mn(II) and Ni(II) which were characterized
by IR and X-ray spectra, TG/DTA and conductometric
methods [20–32].
Methods and apparatus applied
The contents of carbon and hydrogen were determined by
elemental analysis using a CHN 2400 Perkin-Elmer anal-
yser. The amounts of Cl and Ln(III) metals were estab-
lished by X-ray fluorescence XRF method with the use of
spectrophotometer of X-ray fluorescence with energy dis-
persion EDXRF-1510 (Canberra-Packard).
The aim of this paper was to synthesize the complexes of
the selected lanthanides(III) such as: La, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb and Lu with 2,4-dichlorophenoxy-
acetic acid and to examine their properties such as thermal
stability in air at 293–1173 K, magnetic properties in the
ranges of 77–303 and 4.2–303 K and to record their FTIR
and X-ray spectra. Next our investigations on these com-
pounds will be devoted to examine their biological activity.
The FTIR spectra of complexes and the products of the
final complex decompositions were recorded over the
range of 4000–400 cm-1 using an M-80 Perkin-Elmer
spectrometer. The samples were prepared as KBr discs.
The X-ray diffraction patterns of compounds and the
products of decomposition process were taken on a HZG-4
(Carl-Zeiss. Jena) diffractometer with Ni filtered CuKa
radiation. The measurements were made within the range
of 2h = 4°–80° by means of Bragg–Brentano method.
The thermal stabilities and decompositions of the com-
plexes were studied in air using a Setsys 16/18 (Setaram)
TG, DTG and DSC instrument. The experiments were
carried out under air flow rate of 1 L h-1 in the tempera-
Experimental
Materials
All chemicals and solvents used for the synthesis were of
commercially available reagent grade and were used
without further purification.
2,4-Dichlorophenoxyacetate of ammonium (pH 5) of
0.1 mol L-1 concentration was prepared by the addition of
NH3 (aq) solution [25 % pure, Polish Chemical Reagents
in Gliwice (Poland)] to 2,4-dichlorophenoxyacetic acid in
water solution (99 % pure, Aldrich Chemical Company).
ture range of 297–1173 K at a heating rate of 5 K min-1
.
The initial mass of samples of 2,4-dichlorophenoxyacetates
of lanthanides(III) used for measurements changed from
5.41 to 4.30 mg. Samples of these compounds were heated
in Al2O3 crucibles.
123

Complexes of some transition metal ions with selected dichlorophenoxyacetic acid
Table 1 Elemental analysis data (%) for the lanthanide(III) 2,4-dichlorophenoxyacetates
Complex
C/%
H/%
Cl/%
Cald.
M/%
Cald.
L = C8H5O3Cl-2
Cald.
Found
Cald.
Found.
Found
Found
LaL3Á4H2O
PrL3Á2H2O
NdL3Á2H2O
SmL3Á2H2O
EuL3Á2H2O
GdL3Á2H2O
TbL3Á5H2O
DyL3Á2H2O
HoL3Á2H2O
ErL3Á2H2O
TmL3Á2H2O
YbL3Á5H2O
LuL3Á2H2O
33.06
34.41
34.29
34.02
33.96
33.76
31.71
33.54
33.45
33.37
34.00
31.20
33.06
33.20
34.60
34.55
34.72
34.49
33.70
31.28
34.49
34.10
34.17
34.00
32.00
33.04
2.64
2.27
2.26
2.24
2.24
2.23
2.75
2.21
2.20
2.20
2.19
2.70
2.18
2.33
1.90
2.16
1.68
1.93
1.99
2.66
1.85
1.68
1.60
1.90
2.67
2.01
24.45
25.45
25.36
25.16
25.11
24.97
23.45
24.81
24.76
24.68
24.65
23.07
24.45
24.30
25.25
25.34
25.10
25.10
25.00
23.20
24.93
24.50
24.60
24.48
23.00
24.40
15.94
16.83
17.14
17.76
17.92
18.41
17.50
18.92
19.06
19.35
19.55
18.74
20.08
15.84
16.50
17.10
17.40
18.20
18.39
18.20
18.50
18.90
18.90
19.40
18.60
20.00
Magnetic susceptibility of polycrystalline samples of
2,4-dichlorophenoxyacetates of lanthanides(III) was
investigated at 76–303 K and some of them at 4.2–303 K.
The measurements in the range of 76–303 K were carried
out using the Gouy’s method. Mass changes were obtained
from Cahn RM-2 electrobalance. The calibrant employed
was Hg[Co(SCN)4] for which the magnetic susceptibility
was assumed to be 1.644 9 10-5 cm3 g-1. The measure-
ments were made at a magnetic field strength of 9.9 khe.
Correction for diamagnetism of the constituent atoms was
calculated by the use of Pascal’s constants [33].
depends on the Ln(III) ions. The data of the elemental
analysis are presented in Table 1.
Infrared spectra
Comparing the IR spectra of lanthanide complexes with
that of 2,4-dichlorophenoxyacetic acid, the characteristic
band of stretching vibrations of free carboxylic acid at
1730 cm-1 disappears and splits into two peaks of asym-
metric and symmetric vibrations of COO- group at
1628–1556 and 1394–1331 cm-1, respectively (Table 2).
The magnitudes of separations, DmOCO, between the fre-
quencies due to masOCO and msOCO in the spectra of analysed
compounds indicate that carboxylate groups act as biden-
tate chelating ligands [34–37]. The analysis of band fre-
quency values of OCO group allowed to determine the
separation of masOCO - msOCO = Dm, value of which is used
as a criterion of the carboxylate bonding with metal ions.
Taking into account the spectroscopic criteria, especially
the Nakamoto criterion [11, 35, 36], the carboxylate ions in
the analysed complexes seem to be bidentate chelating.
The carboxylate group is bidentate chelating when the
DmOCO value of studied complex ꢀ than the DmOCO value
of the sodium salt [11, 35, 36]. A bidentate bridging
structure exists when the DmOCO value of the analysed
complex &DmOCO of that of the sodium salt [11, 36]. For
monodentate geometry of carboxylate group the DmOCO
value of the studied complex is considerably larger than the
DmOCO of the sodium salt. The values of DmOCO for anal-
ysed 2,4-dichlorophenoxyacetates of Ln(III) are smaller
(DmOCO = 246–210 cm-1) than that for 2,4-dichlorophe-
noxyacetate of Na(I) (DmOCO = 284 cm-1). The different
The effective magnetic moment values were calculated
from the Eq. 1:
1=2
leff ¼ 2:83 ðvm Á TÞ
ð1Þ
where leff—effective magnetic moment, vm—magnetic
susceptibility per molecule and T—absolute temperature
The measurements in the range of 1.8–303 K were
carried out with the use of Quantum Design SQUID-VSM
magnetometer. The superconducting agent was generally
operated at a field strength ranging from 0 to 7 T. Mea-
surements of samples were made at magnetic field 0–1 T.
The SQUID magnetometer was calibrated with the palla-
dium rod sample.
Results
2,4-Dichlorophenoxyacetates of lanthanides(III) were
obtained as crystalline products of general formula:
Ln(C8H5O3Cl2)3ÁnH2O, where Ln(III) = La, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, n = 2, 4 or 5—
123

W. Ferenc et al.
Table 2 Wavenumbers cm-1 of OCO, M–O, C–Cl and O–H in the FTIR spectra of 2,4-dichlorophenoxyacetates of lanthanides(III)
Complex L = C8H5O3Cl2-
mOH
mas(OCO)
ms(OCO)
Dm(OCO)
mC–Cl
mM–O
LaL3Á4H2O
PrL3Á2H2O
NdL3Á2H2O
SmL3Á2H2O
EuL3Á2H2O
GdL3Á2H2O
TbL3Á5H2O
DyL3Á2H2O
HoL3Á2H2O
ErL3Á2H2O
TmL3Á2H2O
YbL3Á5H2O
LuL3Á2H2O
3428
3412
3410
3400
3319
3320
3384
3577
3380
3336
3566
3404
3040
1568
1580
1628
1584
1556
1624
1584
1556
1584
1584
1585
1584
1604
1332
1348
1392
1340
1340
1382
1348
1331
1342
1338
1341
1360
1394
236
232
236
244
216
242
236
225
242
246
244
224
210
724
764
796
796
768
752
769
769
796
796
769
722
720
472
472
472
468
467
467
468
440
458
468
440
442
440
values of DmOCO for complexes may suggest that car-
boxylate groups have various symmetry connected with the
delocalization of 4f electrons in the lanthanide series.
determination applying the Dicvol 06 programme (Table 3).
From the obtained results, it follows that all analysed com-
plexes form low symmetry compounds. 2,4-Dichlorophe-
noxyacetates of La(III) and Nd(III) crystallized in triclinic
system, while those of the rest of them in monoclinic one.
The values of a, b and c for La(III) complex unit cell are
The bands with the maximum at 3577–3040 cm-1
,
characteristic for m(OH) vibrations, confirmed the presence
of crystallization of water molecules in the complexes. The
bands of C-H were observed at 2930–2919 cm-1 and those
of the ring vibrations at 1624, 1476 and 1104 cm-1. The
C–Cl vibration bands occurred at 796–720 cm-1, while
those of the asymmetric and symmetric m(C–O–C) vibra-
˚
equal to 11.5951, 12.1635 and 15.0942 A, respectively, and
for Nd(III) compound they are 5.6537, 12.5261 and
˚
15.0375 A.
The values of their angles are following: a = 67.2300°,
b = 71.984°, c = 76.432° for 2,4-dichlorophenoxyacetate
of La(III) and a = 83.082°, b = 87.349° and c = 86.900°
for that of Nd(III).
tions are at 1288–1260 cm-1 and 1048–1044 cm-1
,
respectively. The bands at 472–440 cm-1 indicate the ionic
metal–oxygen stretching bond vibrations [38, 39]. The
separations of the masOCO and msOCO modes (DmOCO
=
In the case of monoclinic system of complexes, the values
˚
of unit cells change from 7.9670 A [Gd(III) complex] to
masOCO - msOCO) may also serve as the criterion for the
evaluation of the metal–oxygen nature bond. For analysed
complexes, these values are smaller (DmOCO = 246–210
cm-1) than that of the sodium salt (DmOCO = 1620–
1336 = 284 cm-1). Therefore, it indicates the smaller
degree of ionic M–O bond in 2,4-dichlorophenoxyacetates
compared to that of the sodium salt.
˚
21.9371 A [for Yb(III) complex] for a, from 4.8430 A
˚
˚
[Lu(III) complex] to 20.0728 A [Sm(III) compound] for
˚
˚
b and from 10.1840 A [Gd(III)] to 25.2047 A [Pr(III)] for
c parameters.
In the series of monoclinic complexes, the values of b
angles change from 94.8850° for Sm(III) compound to
112.3490° for Lu(III) one (Table 3).
X-ray powder diffraction
Generally, the values of the volumes of elementary unit
cells are greater for 2,4-dichlorophenoxyacetates of heavy
lanthanides than those for light ones, which is probably
connected with the greater values of ionic potentials for
heavy lanthanides compared to those of light ones (the
dependence of V vs. Z may show the ‘‘gadolinium break’’).
The greater ionic potentials, the greater polarization and
greater covalent bonds may be expected between central
ion and ligands. The values of unit cell volumes for com-
plexes of Tb(III) and Yb(III) are similar being equal to
From the X-ray powder diffraction of 2,4-dichlorophe-
noxyacetates of lanthanides(III), it follows that they are
crystalline compounds (as an example Fig. 1). The struc-
tures of analysed complexes were not determined since
suitable single crystals were not obtained. The trials to
obtain them by the recrystallization process from various
solvents (H2O, alcohols, DMSO and DMF) and addition-
ally with various metals/ligand ratios were undertaken, but
they did not give the expecting results.
3
˚
2865.29 and 2825.46 A , respectively, which is probably
In order to estimate the unit cell parameters, the X-ray
powder diffraction of analysed compounds were used for their
connected with the contents of 5 water molecules in
complex molecule.
123

Complexes of some transition metal ions with selected dichlorophenoxyacetic acid
100
80
La(III) complex
60
40
20
0
10
30
50
70
θ
2 /°
100
80
60
40
20
0
Er(III) complex
10
30
50
70
θ
2 /°
Fig. 1 X-ray diffraction patterns of 2,4-dichlorophenoxyacetates of
La(III) and Er(III)
Thermal analysis
The thermal stability of the lanthanide(III) 2,4-
dichlorophenoxyacetates was studied in air in the range of
293–1173 K (as an example Fig. 2; Table 4). The TG,
DTG and DSC curves were recorded using the DSC/TG
technique. All the complexes are hydrated. They lose water
molecules between 305 and 451 K. The dehydration pro-
cess of the compounds is connected with endothermic
effects (DSC curves). The complexes dehydrate in one step
losing two, four or five molecules of water and form
anhydrous compounds. The mass losses calculated from
TG curves being equal to 3.53 and 9.90 % correspond to
the loss of 2, 4 and 5 molecules of water (theoretical values
change from 4.04 to 9.91 %).
From the initial decomposition temperature data, it
appears that Sm(III) and Eu(III) complexes with their
highest values are the most thermally stable compounds
whereas those of Pr(III), Nd(III) and Yb(III) are the least
ones in the group of analysed 2,4-dichlorophenoxyacetates
of lanthanides(III). The energetic effects accompanying the
hydration processes were also determined. The enthalpy
values, DH, change from 44.00 to 91.34 and from 16.79 to
32.00 kJ mol-1 per one molecule of water. Its different
123

W. Ferenc et al.
La(III) complex
Dichlorophenoxyacetate of Lu(III) shows the highest value
while that of Yb(III) the least one. The anhydrous com-
plexes of lanthanides(III) in their second step of decom-
position form oxychlorides being intermediate products
releasing gradually one by one the parts of ligands in the
range of 438–1023 K with the strong exothermic effects
(DSC curves).
Exo
TG
0
20
40
60
80
DTG
DSC
The mass losses calculated from TG curves indicate the
oxychloride formations. In the third stage of decomposi-
tion, the intermediate products, LnOCl, are decomposed to
the oxides of appropriate metals: Ln2O3 for La, Nd, Sm,
Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu and Pr6O11 and Tb4O7.
The found masses change from 13.40 to 19.50 % (theo-
retical values from 13.83 to 21.22 %). The final tempera-
ture values of their formation are in the range of
923–1173 K.
0
373
473
573
673
773
873
973 1073
T/K
Gd(III) complex
TG
DTG
Exo
0
20
40
60
80
The final mass losses determined from TG curves
change from 80.50 to 86.60 % (theoretical values are 78.78
and 86.17 %). The residue obtained as the oxide metals
was verified by comparing their FTIR spectra and
diffractograms with those of the pure oxides.
DSC
The results indicate that the thermal decompositions of
2,4-dichlorophenoxyacetates of lanthanides(III) in air pro-
ceed in the following ways (Schemas 2 and 3):
0
373
473
573
673
773
873
973 1073
T/K
LnL3 Á nH2O ! LnL3 ! LnOCl
Fig. 2 TG, DTG and DSC curves of La(III) and Gd(III) complexes in
air atmosphere
! Ln2O3; ðLnðIIIÞ = La, Nd À Gd; DyÀLuÞ
ð2Þ
PrðTbÞL3 Á nH2O ! PrðTbÞL3 ! PrðTbÞOCl
values may suggest that the water molecules are coordi-
nated with different strengths depending on their various
positions in the complex coordination spheres. 2,4-
! Pr6O11ðTb4O7Þ
n = 2, 4, 5 depends on the kind of central ions.
ð3Þ
Table 4 Temperature ranges of thermal mass losses of lanthanide(III) 2,4-dichlorophenoxyacetates in air at 293–1173 K
Complex
DT1/K
Mass loss/%
n
DT2/K
Mass loss/%
Residue mass/% TK/K DH/kJ mol-1 DH°/kJ mol-1
L = C8H5O3Cl-2
Cald. Found
Cald. Found Cald.
Found
LaL3Á4H2O
PrL3Á2H2O
NdL3Á2H2O
SmL3Á2H2O
EuL3Á2H2O
GdL3Á2H2O
TbL3Á5H2O
DyL3Á2H2O
HoL3Á2H2O
ErL3Á2H2O
TmL3Á2H2O
YbL3Á5H2O
LuL3Á2H2O
316–362 8.23
305–408 4.30
305–383 4.28
401–428 4.23
402–444 4.24
323–428 4.22
324–373 9.91
398–451 4.19
390–451 4.18
390–430 4.17
390–420 4.16
305–351 9.75
310–360 4.04
8.58
5.06
4.30
4.13
4.51
4.18
9.84
3.82
4.53
3.53
3.67
9.90
4.12
4
2
2
2
2
2
5
2
2
2
2
5
2
523–801
523–873
523–618
491–827
462–840
438–718
523–873
523–923
473–873
81.50 81.55
83.64 83.90
80.10 80.90
83.50 82.91
86.17 86.60
78.78 80.50
83.60 83.29
83.70 84.20
85.80 86.60
18.50
16.36
20.02
16.50
13.83
21.22
16.40
16.30
14.20
16.59
16.73
16.00
16.35
18.45
16.10
19.01
17.09
13.40
19.50
16.70
15.80
13.40
17.50
16.98
15.30
16.40
973 85.53
923 57.31
923 57.11
923 48.57
923 50.32
1173 60.57
973 91.34
1023 63.26
923 53.26
1023 44.00
973 48.14
923 83.99
933 64.00
21.38
28.65
28.56
24.28
25.16
30.28
18.26
31.63
26.63
22.00
24.07
16.79
32.00
573–1023 83.41 82.50
554–873
473–790
480–800
83.27 83.02
84.00 84.70
83.65 83.60
DT1, temperature range of dehydration process; n, number of water molecules lost in one step; DT2, temperature range of anhydrous complex
decomposition; TK, final temperature of decomposition process; DH°, enthalpy value for one molecule of water
123

Complexes of some transition metal ions with selected dichlorophenoxyacetic acid
From the obtained results it follows that the water
molecules may be lattice or coordinated water despite of
their loss at a low temperature [40–43]. All dihydrated
complexes contain probably two coordinated water mole-
cules in the inner sphere yielding coordination number 8.
The coordination number of lanthanide ions may change
from 6 to 12 or to higher value depending on lan-
thanide(III) ions and the ligand sizes [35].
2,4-dichlorophenoxyacetates at 76 and 303 K are given in
Table 5. In the lanthanide(III) 2,4-dichlorophenoxyac-
etates, the paramagnetic central ions remain practically
unaffected by the diamagnetic ligands around them. The
4f electrons are well (although not totally) shielded from
external fields by the overlying 5s2 and 5p6 shells. There-
fore, the states arising from the various 4fn configurations
tend to remain nearly invariant for a given ion. The spin-
orbit coupling constants are quite large (order of
1000 cm-1). The states of the 4fn configurations are
approximated by a Russell–Saunders coupling [48]. The
lanthanide ions have ground state with a single well-de-
fined value of the total angular momentum, J, with the next
lowest J state at energies many times kT (at ordinary
temperatures equal to *200 cm-1) above, hence virtually
unpopulated. Therefore, the susceptibilities and magnetic
moments should be given straightforwardly by formulas
considering only this one well-defined J state, and indeed
such calculations give results that are with only two
exceptions, in good agreement with experimental values.
From Sm(III) and Eu(III) ions, it appears that the first
excited J state is sufficiently close to the ground state for
this state (and in the case of Eu(III) even the second and
third excited states) to be appreciably populated at ordinary
temperatures. Since these excited states have higher J val-
ues than the ground state, the actual magnetic moments are
higher than those calculated by considering the ground
The initial dehydration temperature values for all com-
plexes indicate that the water molecules may be outer
sphere water because they are released below 423 K
(305–402 K) [41, 43], but in fact they may be also coor-
dinated water being bounded with different strength in the
inner complex coordination yielding the small value of
initial dehydration temperature [40, 41, 43].
In the case of complexes of Dy(III), Er(III) and Tm(III),
the peaks observed at 483, 480 and 473 K on the DSC
curves, respectively, indicate the melting or polymorphic
changes.
The data obtained from the determination of the com-
plete structure of these complexes can give fair information
on the position of water molecules in the compounds, but
their monocrystals have not been yet determined. However,
attempts to prepare them have still been done.
The FTIR spectra recorded for the gaseous products
released during complex decompositions revealed them to
be molecules of H2O, CO2, CO, CH4, hydrocarbons and
hydrogen chloride. For all the analysed complex decom-
positions, the bands at 4000–3500 and 1700–1500 cm-1
(348–481 K) confirmed the presence of H2O molecules in
the products. At higher temperatures, the bands at
2250–2500 and 600–760 cm-1 result from CO2 vibrations,
while the bands observed at 2000–2220 cm-1 are charac-
teristic for CO. The absorbance peak of methane (CH4)
appears around 3000 cm-1 and HCl in the range of
3060–2650 cm-1 [44, 45].
140000
Er(III) complex
22000
120000
18000
100000
14000
10000
6000
80000
60000
40000
Magnetic properties
50
100
150
200
250
300
T/K
For estimating the character of metal–ligand bonding in the
complexes and to find the reasons why their colours are
typical for Ln(III) ions, the magnetic susceptibilities of the
2,4-dichlorophenoxyacetates were determined over the
range of 76–303 K. The magnetic susceptibilities of the
complexes were also investigated between 1.8 and 303 K
in order to know whether the nature of atomic magnetic
interactions changed at low temperatures.
200000
160000
120000
16000
12000
8000
Pr(III) complex
80000
40000
The complexes obey the Curie–Weiss law (Fig. 3) [46, 47].
For all of them, the Weiss constant values, hm, had a
negative sign, which may result from the antiferromagnetic
spin interaction or from a crystal field splitting of the
paramagnetic spin state [46–52]. The experimentally
determined effective magnetic moment, leff, values for the
4000
50
100
150
200
250
300
T/K
Fig. 3 Relationship of vm and v-g 1 versus T for 2,4-dichlorophe-
noxyacetates of Er(III) and Pr(III)
123

W. Ferenc et al.
Table 5 Effective magnetic moment leff/lB, values for the Ln(III) 2,4-dichlorophenoxyacetates at 76 and 303 K
Trivalent ion
T = 76 K
T = 303 K
Trivalent ion
T = 76 K
T = 303 K
Pr
3.04
2.84
0.89
2.57
8.26
3.29
3.09
1.29
3.59
8.12
Tb
Dy
Ho
Er
9.67
10.39
8.96
8.90
6.95
2.00
9.97
10.87
9.88
9.66
7.54
3.54
Nd
Sm
Eu
Gd
Tm
Yb
Table 6 Magnetic moment values leff of lanthanide(III) ions calculated by Hund and Van Vleck [47, 49, 53] and those obtained experimentally
for Ln(III) 2,4-dichlorophenoxyacetates at room temperature
Trivalention
Configuration
leff/lB
Calculated by Hund
Calculated by Van Vleck
Experimental
Pr
f2
f3
f5
f6
f7
f8
f9
f10
f11
f12
f13
3.58
3.62
0.84
0.00
7.94
9.70
10.60
10.60
9.60
7.60
4.50
3.62
3.29
3.09
1.29
3.59
8.12
9.97
10.87
9.88
9.66
7.54
3.54
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
3.68
1.55–1.65
3.40–3.51
7.94
9.70
10.60
10.60
9.60
Tm
Yb
7.60
4.50
states only. Calculations taking into account the population
of excited state afford results in good agreement with
experiment [48].
lanthanide ions. Therefore, the colours of these complexes
determined by rare earth (III) ions remain the same as those
in the free lanthanides [11, 52]. The metal–ligand bonding
in these analysed lanthanide(III) compounds is mainly
electrostatic in nature [11, 52].
Because the 4f orbitals are so well shielded from the
surroundings of the ions, the various states arising from the
4fn configurations are split by external fields only to the
extent *100 cm-1. Thus, when electronic transition, called
f–f transitions, occurs from one J state of an fn configuration
to another J state of this configuration, the absorption bands
are extremely sharp. They are similar to those for free atoms
and are quite unlike the broadbands for d–d transitions. As
the colours are due to the f–f transition, they are virtually
independent of the environment of the ions [48].
The magnetic properties of Ho(III) were also studied over
the temperature range of 1.8–303 K. Plots of magnetic sus-
ceptibility v-m1 and of the product vmT versus T are shown in
Fig. 4. The thermal dependence of v-m1 obeys the Curie–
Weiss law over the whole temperature range. From the shape
of the dependence of the vmT versus T curve, it follows that it
decreases on cooling in the range of 303–1.8 K. Between 303
and 48 K, the decrease is very slow showing the saturation
paramagnetic state, while it is drastic between 48 and 1.8 K.
The value of vmT for Ho(III) 2,4-dichlorophenoxyacetate at
room temperature was 11.30 cm3 mol-1 K, which is similar
to that calculated theoretically for the free Ho(III) ion,
11.60 cm3 mol-1 K [47, 53, 54]. At 1.8 K, the vmT value was
6.16 cm3 mol-1 K. The decrease in the vmT versus T curve in
the range of 48–1.8 K indicates a negative h value, which may
confirm the antiferromagnetic intermolecular interactions.
Therefore, the magnetic moment value of the Ho(III)
The magnetic properties may be taken as those of the
ground state alone, and the lanthanide(III) ions in the
complexes act in the same manners as free ions. The values
of leff determined for all 2,4-dichlorophenoxyacetates
(except Eu) (Table 5) were similar to those calculated for
Ln(III) ions by Hund and Van Vleck (Table 6) [11, 49].
The values of magnetic moments determined for the
complexes indicate that the energies of 4f electrons in the
central ions are not changed compared to those in the free
123

Complexes of some transition metal ions with selected dichlorophenoxyacetic acid
From the IR spectra analysis [11], it follows that the
11
10
9
bands of masymOCO and msymOCO appear at a lower
wavenumber values for 4-chlorophenoxyacetates of Ln(III)
compared to those in the IR spectra of Ln(III) 2,4-
dichlorophenoxyacetates. Also the C–Cl vibration bands
have higher values for 2,4-dichlorophenoxyacetates than
those in 4-chlorophenoxyacetate IR spectra. This differ-
ence is connected with the various inductive and meso-
meric effects of the substituents on the electron density of
the system. The influence of the substituents on the reac-
tions of aromatic compounds is described by Hammett’s
constant d whose value depends on the substituent char-
acter and its position on the aromatic ring. The greater its
value, the stronger electrons are attracted by the given
25
20
15
10
5
8
7
0
0
0
50
100
150
T/K
200
250
300
Fig. 4 Relationship of vmT and v-m1 versus T for 2,4-dichlorophe-
noxyacetate of Ho(III)
substituent. The
d values for Cl substituent are
dm = ?0.373 and dp = ?0.227. In 2-(4-chlorophe-
noxy)acetates, the presence of the Cl in the para position
stabilizes the aromatic ring since the inductive effect of the
Cl substituent decreases the electron density in benzene
ring. In the case of 2,4-dichlorophenoxyacetates of Ln(III),
the presence of Cl in ortho position does not stabilize the
system because of the steric effect [55–59].
complex was equal to 7.00 (1.8 K) and 8.96 lB (283 K).
Next, this value increases to 9.88 lB (303 K) which is con-
nected with the change in the unpaired electron order. This
value is similar to that of the free Ho(III) ion value (10.60 lB)
[47, 53].
The 2-(4-chlorophenoxy)acetates of Ln(III) contain less
water molecules compared to those of 2,4-dichlorophe-
noxyacetates of those elements.
Conclusions
The thermal stabilities of Ln(III) 2-(4-chlorophe-
noxy)acetates are higher than those for 2,4-dichlorophe-
noxyacetates. Also the values of DH per one molecule of
From the obtained results, it follows that the lanthanide(III)
2,4-dichlorophenoxyacetates were prepared as di-, four and
pentahydrates with colours typical for respective Ln(III)
ions, having their origin in the lowest energy f–f electronic
transitions of the central ions. The Lu–O bonds are elec-
trostatic in nature. The compounds are crystalline com-
plexes. They crystallized in monoclinic or triclinic systems.
On heating in air to 1173 K they decompose in three steps.
At first, they dehydrate to form anhydrous complexes,
which further decompose to the oxides of the correspond-
ing metal(III) with the intermediate formation of LnOCl.
The values of leff experimentally determined for all anal-
ysed 2,4-dichlorophenoxyacetates of Ln(III) are close to
those theoretically calculated by Van Vleck but in the case
of Hund also for most of them however with the exception
of Sm(III) and Eu(III) complexes. The enthalpy values of
dehydration processes were in the range of 44.00–91.34
and 16.79–32.00 kJ mol-1 per one molecule of water.
As a continuation of our studies on lanthanide com-
plexes with chlorophenoxyacetic acids and taking into
account the presence and positions of one or two Cl sub-
stituents in benzene ring, the properties of 2-(4-
chlorophenoxy)acetates and 2,4-dichlorophenoxyacetates
of lanthanide elements were compared for investigating the
influence of the substituent positions in benzene ring on
their physico-chemical characterization.
water
are
greater
for
4-chlorophenoxyacetates
(60.20–21.43 kJ mol-1) in comparison with those for 2,4-
dichlorophenoxyacetates (32.00–16.79 kJ mol-1).
The magnetic moment values measured in the range of
77–303 K for 2-(4-chlorophenoxy)acetates and 2,4-
dichlorophenoxyacetates of Ln(III) are higher for 2-(4-
chlorophenoxy)acetates than those for 2,4-dichlorophe-
noxyacetates, which depends on the kind of ligands form-
ing the complex molecules.
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