Trinuclear CoIILnIIICoII Complexes (Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb) with 2,6-Dipicolinoylbis(N, N-diethylthiourea): Synthesis, Structures, and Magnetism

Article abstract of DOI:10.1021/acs.inorgchem.9b02648

One-pot reactions of 2,6-dipicolinoylbis(N,N-diethylthiourea) (H₂L) with Co(CH₃COO)₂·4H₂O and LnCl₃, where Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb, in warm methanol in the presence of Et₃N,

Full text of DOI:10.1021/acs.inorgchem.9b02648

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Trinuclear CoIILnIIICoII Complexes (Ln = La, Ce, Nd, Sm, Gd, Dy, Er,
and Yb) with 2,6-Dipicolinoylbis(N,N‑diethylthiourea): Synthesis,
Structures, and Magnetism
Jecob J. Jesudas,† Chien Thang Pham,‡ Adelheid Hagenbach,† Ulrich Abram,*,†
and Hung Huy Nguyen*,‡
†
̈
Institute of Chemistry and Biochemistry, Freie Universitat Berlin, Fabeckstrasse 34/36, D-14195 Berlin, Germany
‡Department of Inorganic Chemistry, VNU University of Science, 19 Le Thanh Tong, Hanoi, Vietnam
S
* Supporting Information
ABSTRACT: One-pot reactions of 2,6-dipicolinoylbis(N,N-
diethylthiourea) (H2L) with Co(CH3COO)2·4H2O and
LnCl3, where Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb, in
warm methanol in the presence of Et3N, give stable trinuclear
complexes of the composition [LnCo2(L)2(μ1,3
-
OOCCH3)2X] (“CoLnCo” complexes), where X− = κ2-
CH3COO− or Cl−. X-ray structure determinations reveal
symmetric trinuclear complexes containing two organic
ligands (L2−), two terminal CoII ions, and one central LnIII
ion. The organic ligands coordinate equatorially to the two
CoII ions via two bidentate (O,S) N-acylthiourea moieties and
tridentate to the central Ln ion via the (O,N,O) 2,6-
dipicolinoyl moieties. Two acetate bridges established
between each of the terminal Co and central Ln ions complete the square-pyramidal coordination spheres of CoII. All
products possess an additional chlorido ligand axially coordinated to the lanthanide except the gadolinium(III) and
lanthanum(III) complexes, where bidentate acetato ligands are coordinated. Fitting the χmT versus T data of the “CoLaCo”
complex gives the axial and rhombic zero-field-splitting parameters D = 24.3(4) cm−1 and E = −1.0(2) cm−1, respectively, and
anisotropic Lande values gx,y = 2.81(1) and gz = 2.00 as well as weak antiferromagnetic interactions between two high-spin CoII
́
centers with J = −0.49(2) cm−1. The nature of the magnetic interactions between the LnIII ions and the CoII ions in the
“CoLnCo” complexes is deduced by comparing their χMT values to the sum of χMT values of the analogous “CoLaCo” and
related “ZnLnZn” complexes. The “CoDyCo” complex reveals an antiferromagnetic interaction, while the remaining “CoLnCo”
complexes show ferromagnetic interactions.
isophthaloylbis(thiourea) ligands (4′) are also synthesized and
structurally characterized (Chart 2).26,27 In all crystallo-
graphically characterized complexes of bipodal aroylthiourea
derivatives with divalent metal ions, square-planar coordination
spheres with cis arrangement of the donor atoms to the metal
centers are established.
INTRODUCTION
■
The coordination chemistry of transition metals with N,N-
dialkyl-N′-acylthioureas (1; Chart 1) has constantly been
studied in the last decades.1−19 Most of the structurally
characterized compounds with these ligands are mononuclear
complexes of nickel(II), palladium(II), platinum(II), or
copper(II) with a cis square-planar coordination mode (2;
Chart 1), in which the ligands commonly act as bidentate,
monoanionic chelators.10−16 Facial coordination of the ligands
is observed in mononuclear octahedral complexes with
technetium(III) or cobalt(III) (3; Chart 1).17−19
The coordination chemistry of bipodal aroylthiourea
derivatives with transition-metal ions is less explored. Sym-
metrical bipodal derivatives with two S,O chelating moieties
such as meta-substituted phthaloylbis(thiourea) ligands (4) are
able to form binuclear complexes, as demonstrated for divalent
metal ions such as Cu2+, Ni2+, Co2+, Pd2+, or Pt2+,20−23 as well
as trivalent metal ions such as In3+ or Fe3+.24,25 Trinuclear
complexes of nickel(II) and platinum(II) with para-substituted
In order to extend the coordination abilities of 4, the
introduction of an additional donor atom by replacing the
central m-phenylene ring by a 2,6-disubstituted pyridine ring
28
̈
was first reported by Schroder et al. The resulting 2,6-
dipicolinoylbis(N,N-alkylthiourea) (5) forms a polymeric
silver(I) complex.28 More interestingly, some series of
trinuclear heterometallic complexes (6) with this ligand have
been published recently.25,29 The central metal ions in such
complexes could be varied in a wide range, and products with
Received: September 3, 2019
© XXXX American Chemical Society
A
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Chart 1. N,N-Dialkyl-N′-acylthioureas and Their Coordination Modes
Chart 2. Bipodal Aroylthioureas and Their Metal Complexes
alkali, alkaline-earth-metal, or lanthanide ions have been
isolated and structurally characterized.
heteronuclear d−f complexes because of the presence of an
undefinable microscopic magnetic mechanism between the
metal centers. Until now, no specific theoretical calculations
have been available to have a clear view and a better
understanding of the magnetic interactions involved in 3d−
4f complexes. In many reports, Kahn’s empirical approach
based on a comparison of the magnetic susceptibilities of M−
Ln complexes to those of analogous M′−Ln and M−Ln′
complexes (where M′ and Ln′ are diamagnetic cores) is used
for evaluation of the nature of magnetic interactions between
the paramagnetic cores MII and LnIII.36−38,43,48
In the present work, the synthesis and structural and
magnetic studies of a series of new trinuclear CoIILnIIICoII
complexes (Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb) with the
2,6-dipicolinoylbis(N,N-alkylthiourea) ligand system are re-
ported.
The opportunities given with the tailor-made synthesis of
heteronuclear complexes, where the metal ions can be chosen
from a large variety with various chemical, structural, and
physical properties, make such systems interesting for many
applications. One potential field of interest is given with their
magnetic behavior. Analysis of the magnetic interactions
between dissimilar metal ions with defined (and tunable)
distances may contribute to a better understanding of such
interactions in molecular-based magnetic materials.30−35
Unfortunately, because of the weak d−f interactions and
large anisotropic effects of lanthanide ions, the magnetic
interactions involved in d−f systems are not easy to
understand. Because gadolinium(III) has no first-order orbital
angular momentum and a high-spin quantum number (S =
7/2), most of the 3d−4f systems are studied with gadolinium-
(III).36−38 Among the reported heteronuclear complexes
containing transition-metal (M) and lanthanide (Ln) ions, a
considerable number of trinuclear complexes of the composi-
tion MIILnIIIMII are published.39−56 Especially, the magnetic
interactions between M2+ (M = Cu or Ni) and Ln3+ ions in
linear trinuclear complexes with 2,6-di(acetoacetyl)pyridine
ligands have been studied in detail for an almost complete
series of Ln ions.43,48 In comparison with other 3f−4f
trinuclear bimetallic complexes, CoIILnIIICoII systems are
structurally as well as magnetically less explored. Such studies
of magnetic interactions between CoII and LnIII might be
complicated because of the high magnetic anisotropy of CoII
ions. However, ferromagnetic interactions between GdIII and
CoII in a linear trinuclear CoIIGdIIICoII system have previously
been reported.46,47
EXPERIMENTAL SECTION
■
Materials. All chemicals used in this study were reagent-grade and
were used without further purification. Solvents were dried and
distilled prior to use.
Physical Measurements. IR spectra were measured as KBr
pellets on a Shimadzu Fourier transform infrared spectrometer
between 400 and 4000 cm−1. Electrospray ionization mass
spectrometry (ESI-MS) spectra were measured with an Agilent
6210 ESI-TOF spectrometer (Agilent Technologies). All MS results
are given in the following form: m/z, assignment. Elemental analyses
of carbon, hydrogen, nitrogen, and sulfur were determined using a
Heraeus Vario EL elemental analyzer.
Magnetic Measurements. The magnetic susceptibility measure-
ments were carried out on powdered samples with a Quantum Design
MPMS 7XL SQUID magnetometer in the temperature ranges of 2−
300 K for the CoLaCo complex and 8−300 K for the other CoLnCo
complexes, under an external magnetic field of 0.5 T. The obtained
data were analyzed with the simulation software PHI.57 Diamagnetic
Details of the magnetic interactions between d and f metal
ions are only poorly understood in most of the reported
B
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Scheme 1. Synthesis of the Complexes
corrections were applied using Pascal’s constants. Effective magnetic
evaporation of a CHCl3/n-hexane (1:1) solution for the CoLaCo
complex and CH2Cl2/MeOH (1:1) solutions for the other complexes.
moment values were determined by the equation μeff = (8χMT)1/2
.
X-ray Crystallography. The intensities for the X-ray determi-
nations were collected on a STOE IPDS 2T instrument or a Bruker
D8 QUEST CMOS diffractometer with Mo Kα radiation (λ =
0.71073 Å). Standard procedures were applied for data reduction and
absorption correction. Structure solution and refinement were
performed with SHELXS and SHELXL.58,59 H-atom positions were
calculated for idealized positions and treated with the “riding model”
option of SHELXL. To finish the structure calculations of CoLaCo, a
highly disordered solvent was treated by the SQUEEZE option in
PLATON, and a remarkably large potential solvent volume of 571 Å3
for the unit cell volume was identified. The electron count in this
solvent-accessible volume is 133 electrons, which fits a disordered n-
hexane molecule per asymmetric unit. The use of PLATON/
SQUEEZE resulted in an improvement of the R1 values of about
4.9%. More details on data collections and structure calculations are
contained in the Supporting Information. Additional information on
the structure determinations has been deposited with the Cambridge
Crystallographic Data Centre.
RESULTS AND DISCUSSION
■
Mixtures of 2 equiv of H2L, 2 equiv of Co(CH3COO)2·4H2O,
and 1 equiv of LnCl3, where Ln = La, Ce, Nd, Sm, Gd, Dy, Er,
and Yb, in warm MeOH rapidly change their color after the
addition of a weak base such as triethylamine and form dark-
green (Ln = Ce, Nd, Sm, and Gd) or dark-red (Ln = Dy, Er,
and Yb) solutions (Scheme 1).61 Green solids precipitate in
high yields from the reaction mixtures after approximately 30
min in the cases of Ln = Ce, Nd, Sm, and Gd. They are readily
soluble in CH2Cl2 and can be crystallized by the slow
evaporation of CH2Cl2/MeOH (1:1) mixtures. In the cases of
Dy, Er, and Yb, single crystals are formed in high yields directly
from slow evaporation of the reaction mixtures. The general
composition of [LnCo2(L)2(CH3COO)2Cl] for Ln = Ce, Nd,
Sm, Dy, Er, and Yb and [LnCo2(L)2(CH3COO)2(CH3COO)]
for Ln = La and Gd are strongly suggested from elemental
analysis.
The IR spectra of the complexes show strong νC=O
absorptions between 1585 and 1593 cm−1, which are
bathochromically shifted by about 100 cm−1 compared to
the νC=O stretch in the uncoordinated ligand and can be
regarded as a strong indication for the formation of an
extended π system in the chelate rings. The absence of NH
bands in the spectra of the complexes, which are observed at
3267 cm−1 in the spectrum of H2L, confirms deprotonation of
the ligand.62,63
The recording of instructive NMR spectra was not possible
because of the paramagnetism of the complexes, but their ESI+-
MS spectra give evidence for the formation of trinuclear
“CoLnCo” compounds. The appearance of intense peaks with
the composition of [LnCo2(L)2(CH3COO)2]+, where Ln = La,
Ce, Nd, Sm, Gd, Dy, Er, and Yb, confirms the presence of
three metal ions with two doubly deprotonated ligands and
two acetate moieties. The additional Cl− or CH3COO− ligands
are obviously abstracted during the ionization process.
The molecular structures of the products were studied by
single-crystal X-ray diffraction. All complexes crystallize
monoclinic in the space group C2/c with only half of the
molecules in the asymmetric units. The complete molecules
are generated by a rotation axis through the central Ln ions
and their Cl− or C−C bond of κ2-acetato ligands. Figure 1
shows the molecular structure of [NdCo2(L)2(μ1,3-OAc)2Cl]
as a representative of the complexes with central Ce3+, Nd3+,
Dy3+, Er3+, and Yb3+ ions in two different projections. The
Synthetic Procedures. N,N-Diethylthiourea (Et2tu). The syn-
thesis of Et2tu was performed by the procedure of Hartmann and
Reuther.60
2,6-Dipicolinoylbis(N,N-diethylthiourea) (H2L). A solution of
pyridine-2,6-dicarboxylic acid dichloride (0.76 g, 3.72 mmol) in 10
mL of tetrahydrofuran (THF) was dropwise added to a mixture of
N,N-diethylthiourea (1.00 g, 7.56 mmol) and triethylamine (0.76 g,
7.51 mmol) in 10 mL of THF at 40 °C. After stirring for 1 h, the
mixture was allowed to cool to room temperature and filtered. The
filtrate was evaporated to dryness, and the residue was recrystallized
from a CH2Cl2/ethanol (2:1) mixture. Yield: 1.3 g (78%). Mp: 173−
175 °C. Anal. Calcd for C17H25N5O2S2: C, 51.62; H, 6.37; N, 17.71;
S, 16.21. Found: C, 51.64; H, 6.05; N, 17.76; S, 16.34. IR (KBr,
cm−1): 3267 (m), 2974 (w), 2935 (w), 2874 (w), 1686 (vs), 1524
1
(vs), 1423 (vs), 1277 (m), 1223 (vs), 1134 (m), 752 (m). H NMR
(400 MHz, CDCl3): δ 1.32 (bs, 12H, CH3), 3.65 (m, 4H, CH2), 4.02
(m, 4H, CH2), 8.07 (t, 1H, J = 8.0 Hz, Py), 8.37 (d, 2H, J = 8.0 Hz,
Py), 9.91 (s, 2H, NH). ESI+-MS: m/z 418.13 [(M + Na)+], 434.10
[(M + K)+], 813.27 [(2M + Na)+].
[LnCo2(L)2(CH3COO)2(X)] (X− = CH3OO− or Cl−) Complexes. A
solution of Co(CH3COO)2·4H2O (50 mg, 0.2 mmol) in methanol
(MeOH; 3 mL) was added to a solution of LnCl3 (0.1 mmol) and
H2L (79.1 mg, 0.2 mmol) in MeOH (3 mL). A total of 2 drops of
triethylamine was added, and the mixture was stirred at 40 °C for 30
min. In the cases of Ln = La, Ce, Nd, Sm, and Gd, the formed
precipitates were filtered, washed with MeOH, and dried under
vacuum. In the cases of Ln = Dy, Er, and Yb, no immediate
precipitation was observed, but crystalline solids deposited overnight,
which were collected, washed twice with MeOH, and dried under
vacuum. The analytical and spectroscopic data of the individual
complexes are summarized in the Supporting Information. Single
crystals suitable for X-ray diffraction studies were obtained by slow
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Figure 2. Molecular structures of [GdCo2(L)2(μ1,3-OOCCH3)2(κ2-
CH3COO)].
Figure 1. Molecular structures of [NdCo2(L)2(μ1,3-OOCCH3)2Cl].
structures of the other compounds of this family are virtually
identical and, thus, are only depicted in separate figures in the
Supporting Information. The CoII ions equatorially coordinate
to each of the two bidentate N-acylthiourea sites via the S- and
O-donor atoms. All structures reveal two acetato bridges
between each terminal Co ion and central Ln ion. The O-
donor atoms of these ligands bind to the axial coordination
sites of the CoII ions and, thus, complete their square-
pyramidal coordination spheres. The Ln ions coordinate with
the tridentate 2,6-dipicolinoyl moiety of both organic ligands
via the N-donor atom of the pyridine ring and the O-donor
atoms of both carbonyl groups, the two bridging acetato
ligands, and an additional chlorido ligand. This gives an overall
coordination number of 9, and the coordination polyhedra of
the [LnCo2(L)2(μ1,3-OAc)2Cl] complexes can roughly be
described as distorted tricapped trigonal prisms. A more
detailed estimation of the coordination environments of the
Ln3+ ions in the [LnCo2(L)2(μ1,3-OAc)2Cl] complexes can be
done with the program SHAPE.64 It delivers a so-called “hula-
hoop” (C2v) geometry with the symmetry designator HH-9 for
complexes with Ln = Ce, Nd, and Sm and a “muffin” (Cs)
geometry (MFF-9) for those with Ln = Dy, Er, and Yb (for
details, see also Table S4).
2.401(2) Å and the Co−O bonds are between 2.020(1) and
2.155(1) Å. This is the range in which the corresponding
bonds are also observed in the previously reported binuclear
cobalt(II) complexes with isophthaloylbis(thioureas) (4).22
Similar to the situation of the cobalt(II) complexes with ligand
4, the chelate skeleton formed by the {Co2Ln(L2)} units is also
essentially planar in the lanthanide-centered compounds
(Figure 3c). Slight deviations are due to the different sizes of
the embedded Ln3+ ions within the isostructural Ce−Nd−
Sm−Dy−Er−Yb series and the increased coordination number
in the lanthanum and gadolinium compounds (see the
Supporting Information). This results in the equatorial Ln−
O5 and Ln−O15 bonds in the ranges of 2.359(3)−2.570(1)
and 2.514(2)−2.615(1) Å, respectively. The equatorial Ln−
N46 bond is 2.705(2) Å for the lanthanum-centered
compound and stepwise decreases with the ionic radii of the
Ln3+ ions to a value 2.541(3) Å for the ytterbium complex.
This effect is independent of the observed coordination
number of the lanthanide. Similar Ln−O and Ln−N bond
lengths are observed in chelating systems of trinuclear
CuIILnIIICuII and NiIILnIIINiII complexes with 2,6-bis-
(acetoacetyl)pyridine, where the central Ln3+ ions coordinate
similarly with a 2,6-dipicolinoyl site.43,48 The Ln−O63-
(acetate) bonds are in the range between 2.286(3) and
2.537(1) Å and the Ln−Cl bonds are between 2.599(2) and
2.759(2) Å. More selected bond lengths and angles of the
individual complexes are summarized in the Supporting
Information.
The structures with central LaIII and GdIII ions differ from
those described above in a way that the chlorido ligands on the
LnIII ions are replaced by unbridged bidentate acetato ligands.
This increases the coordination number of the Ln ions from 9
to 10. The structure of the gadolinium(III) compound is
shown in two projections in Figure 2 (for that of the
lanthanum complex, see the Supporting Information). The
Some fundamental features of all structurally characterized
complexes of this study are compared in Table 1. The ionic
radii of Ln ions steadily decrease from LaIII to YbIII, which is
known as lanthanide contraction. In the case of isostructural 9-
coordinate [LnCo2(L)2(μ1,3-OAc)2Cl] complexes, the stepwise
decrease of the separation between the Ln and Co ions from
Ln = Ce to Yb can readily be explained by the changes of the
radii of the central Ln ions. There is no systematic change of
the Co1−Ln−Co1# angles. Expectedly, the 10-coordinate
coordination polyhedra of the [LnCo2(L)2(μ1,3
-
OOCCH3)2(κ2-CH3COO)] complexes can best be approxi-
mated as a bicapped square antiprism with the symmetry
designator J-17 (Ln = Gd; Figure 3b) and a tetradecahedron
(Ln = La; TD-10). More details are contained in Table S5.
Independent of the bonding situation around the Ln ion, the
equatorial Co−S bonds are in the range from 2.290(2) to
D
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Figure 3. Coordination patterns and polyhedra of [LnCo2(L)2(μ1,3-OOCCH3)2Cl] (a) and [LnCo2(L)2(μ1,3-CH3COO)2(κ2-CH3COO)] (b) and
a top view to the central chelating unit in the [LnCo2(L)2(μ1,3-CH3COO)2(X)] complexes (c).
Table 1. Ionic Radii,65 Ln−Co1 and Co1−Co2 Separations,
and Co1−Ln−Co2 Angles of the Complexes
program with the spin Hamiltonian applied for two equivalent
high-spin CoII ions (eq 1)57
k
Ln−Co1
q
q
̂
̂
Bk ΘkOk + 2μB·S·g·B
ionic radius of
Ln3+ (Å)
separation
(Å)
Co1−Co2
Co1−Ln−Co1#
H = −2S·J·S + 2
∑ ∑
Ln
separation (Å)
angle (deg)
k=2,4,6 q=−k
(1)
Coordination Number 9
Ce
Nd
Sm
Dy
Er
1.010
0.983
0.958
0.912
0.890
0.868
3.678
3.667
3.664
3.656
3.643
3.647
7.304
7.281
7.278
7.265
7.239
7.247
166.36
166.39
166.60
167.10
166.99
167.11
where S is the spin vector operator, Bqk are the crystal-field
parameters in Steven’s notation, Θk are the operator equivalent
factors, Ok are the operator equivalents, and B and μB are the
q
̂
magnetic field vector and Bohr magneton, respectively. The
three components in eq 1 represent the exchange coupling, the
crystal-field interaction, and the Zeeman effect, respectively. It
should be noted that the relationships between the axial (D)
and rhombic (E) zero-field splitting (ZFS) and crystal-field
parameters are described by the equations D = 3B02Θ2 and E =
3B22Θ2. During the fitting, gz was fixed at 2.00, while gx and gy
were equally constrained.67 The best fits gave J = −0.49(2)
cm−1, D = 24.3(4) cm−1, E = −1.0(2) cm−1, and gx,y = 2.81(1).
The positive sign of the D parameter arises from interaction
between the ground and excited electronic states coupled
through spin−orbit coupling.67 The simulated (solid line) and
measured data of the temperature dependence of χM and χMT
(inset) for the CoLaCo complexes are compared in Figure 4.
The discrepancy factors R(χM) and R(χMT) defined by eq 2
are 1.13 × 10−2 and 3.61 × 10−3, respectively, showing good
agreement between the simulated and observed data. The
small negative J value clearly shows very weak antiferromag-
netic interactions between the two CoII ions, which is
consistent with the long distances between them (7.304 Å).
Magnetization measurements of the “CoLaCo” complex were
carried out at 2.0 K in the range 0−5 T. The Mmol versus H
plot (Figure S8) shows a linear behavior of Mmol in the region
H = 0−4.5 T, followed by a gradual increase toward the 5.04
Nβ value at 5 T.
Yb
Coordination Number 10
La
Gd
1.032
0.935
3.652
3.621
7.116
7.164
153.99
163.15
complexes [LnCo2(L)2(μ1,3-OOCCH3)2(κ2-CH3COO)] (Ln
= La and Gd) do not follow the trends observed for the 9-
coordinate compounds. In particular, the Co1−La−Co1# and
Co1−Gd−Co1# angles are significantly smaller with values of
153.99(1) and 163.15(1)°, respectively. The Co−Co distances
are in the range of 7.116−7.164 Å. The previously observed
value for the binuclear cobalt(II) complex with
isopththaloylbis(thiourea) is 7.249 Å,22 which is in the range
of the values observed in the present study.
At room temperature, the χMT product of the CoLaCo
complex is 6.00 cm3 mol−1 K, which is clearly larger than the
spin-only value of 3.75 cm3 mol−1 K for two isolated high-spin
CoII ions (S = /2), indicating the significant orbital angular
3
momentum of CoII ions.47,66 The χMT versus T plot of the
complex is almost unchanged in the temperature range from
300 to 100 K but slightly decreases in the lower-temperature
region and then dramatically decreases in the range below 15
K. At 2 K, χMT reaches a value of 1.34 cm3 mol−1 K. The sharp
decrease of the χMT curve in the low-temperature region is
commonly explained by the intrinsic magnetic anisotropy of
CoII ions.47,66
∑ [χM(calculated) − χM(observed)]2
R χ
=
∑ χM(observed)2
M
(2)
To evaluate the magnetic anisotropy of the CoLaCo
complex, the magnetic susceptibility data in the temperature
range 2−300 K were simulated and fitted using the PHI
The χMT versus T plots of the other trinuclear complexes
CoLnCo in the temperature range of 8−300 K (Figure 5) are
classified into three groups. The first group consists of plots of
E
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Figure 4. χM versus T and χMT versus T (inset) plots of the “CoLaCo” complexes. The solid lines are the simulated curves.
Figure 5. χMT versus T plots of the CoLnCo complexes in the temperature range of 8−300 K.
the cerium, neodymium, samarium, and erbium complexes.
Such compounds possess room temperature χMT products of
7.46, 8.71, 7.21, and 19.59 cm3 mol−1 K, respectively, which
slowly increase and reach maxima of 8.20, 9.21, 8.54, and 22.30
cm3 mol−1 K at about 50 K before decreasing to 7.64, 8.14,
7.75, and 19.51 cm3 mol−1 K at 8 K. The second type is the
χMT plot of the gadolinium complex showing a slow increase of
the χMT value from 14.33 cm3 mol−1 K at room temperature to
15.68 cm3 mol−1 K at 20 K before a dramatic rise to 16.99 cm3
mol−1 K at 8 K. The increasing χMT products in the range 50−
300 K of the first two groups of complexes may suggest
ferromagnetic interactions between CoII and the corresponding
LnIII centers. The third group includes of plots of the
dysprosium(III) and ytterbium(III) complexes, which present
a continuous decrease of the χMT values from 20.67 and 8.10
cm3 mol−1 K at room temperature to 16.27 and 5.93 cm3 mol−1
F
DOI: 10.1021/acs.inorgchem.9b02648
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Article
Figure 6. ΔχMT versus T plots of the CoLnCo complexes in the T range 8−300 K.
Table 2. Number of f Electrons and Unpaired Electrons, S, L, J, and gJ Values of the Ln3+ Ions, and μeff Values of the
CoIILnIIICoII Complexes
Ln
f electrons in Ln3+
unpaired electrons in Ln3+
S
L
J
gJ
μeff(calculated)/μB
μeff(observed) at 300 K/μB
5
9
5
7
Ce
Nd
Sm
Gd
Dy
Er
1
3
1
3
5
7
5
3
1
+1/2
+3/2
+5/2
+7/2
+5/2
+3/2
+1/2
+3
+6
+5
0
/
0.86
0.73
0.29
2
7.48
7.91
7.73
8.35
2
2
2
/
/
/
5
7.09
7.60
7
10.61
12.74
11.89
8.36
10.71
12.86
12.52
8.05
2
15
15
7
9
+5
+6
+3
/
1.33
1.20
1.14
2
11
13
/
2
Yb
/
2
K at 8 K, respectively. The described patterns reveal probable
antiferromagnetic interactions in the complexes.
ΔχMT values of the gadolinium and erbium complexes change
from 0.91 and 2.12 cm3 mol−1 K (at 300 K) to 5.47 and 11.30
cm3 mol−1 K (at 8 K), respectively. These strong increases of
the ΔχMT values, especially in the low-temperature region,
reveal strong ferromagnetic interactions in the complexes. The
room temperature ΔχMT value of the dysprosium complex is
close to zero (0.070 cm3·mol−1K) and gradually decreases to
reach −1.85 cm3 mol−1 K at 8 K, which apparently reflects
antiferromagnetic interactions in this complex. Because the
ZnTbZn analogous complex does not exist, the magnetic
interactions in the “CoTbCo” complex could not be estimated.
However, an antiferromagnetic interaction is expected for this
system because its χMT products continuously decrease with a
lowering of the temperature (Figure 5).
The temperature dependence of the magnetic susceptibility
of the other CoLnCo (except CoLaCo) complexes could not
be fitted to any reliable model. This is mainly due to their
intrinsic complicated magnetic properties and has been
experienced before with other trinuclear CoIILnCoII com-
plexes.47 The magnetic interactions between the CoII and LnIII
ions, however, can be empirically evaluated by a comparison of
the χMT values of the “CoLnCo” compounds with the sum of
the χMT values of the similar “CoLaCo” and “ZnLnZn”
complexes. It is noteworthy that the structures of the
“ZnLnZn” analogues well resemble those of the “CoLaCo”
and “CoGdCo” complexes.68 In this context, the magnetic
interactions between the two CoII centers may be neglected
compared to those between the CoII and LnIII ions. Thus,
positive ΔχMT = χMTCoLnCo − (χMTCoLaCo + χMTZnLnZn) values
reflect ferromagnetic interactions, and negative values suggest
antiferromagnetic interactions between the CoII and LnIII ions.
The plots of ΔχMT versus T for the complexes in the
temperature range 8−300 K are visualized in Figure 6. At room
temperature, the ΔχMT values of the cerium, neodymium, and
samarium complexes are in the range between 0.79 and 1.29
cm3 mol−1 K. These values are slowly increased to 3.4−3.9 cm3
mol−1 K at 8 K, indicating ferromagnetic interactions. The
The room temperature magnetic moments of trinuclear
“CoLnCo” complexes, with the assumption that two CoII ions
and one LnIII ion are magnetically isolated, can be roughly
estimated by eq 3
2
μ (calculated) = 2gCo SCo(SCo + 1) + g 2J(J + 1) μ
eff
B
J
(3)
́
where the Lande gCo factor is assumed to be equal to the giso
value of the CoLaCo complex, which can be calculated from
anisotropic g values by the expression giso2 = (gx2 + gy2 + gz2)/3.
G
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Article
SCo is the spin quantum number of CoII and has the value of
Foundation for Science and Technology Development)
through Project 104.03-2015.32.
3
́
/2, and gJ is the Lande g factor of the ground J level of each
S(S + 1) − L(L + 1)
2J(J + 1)
3
Ln3+ ion and is expressed as gJ =
+
with S,
2
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.9b02648.
■
S
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Analytical and spectroscopic data and tables containing
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AUTHOR INFORMATION
Corresponding Authors
*Email: ulrich.abram@fu-berlin.de (U.A.).
*Email: hunghuy78@yahoo.com (H.H.N.).
■
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́
́
Jimenez-Sanchez, A.; Manzano, J. L.; Monte, E.; Rodríguez-
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Ulrich Abram: 0000-0002-1747-7927
Notes
The authors declare no competing financial interest.
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of copper(II), nickel(II) and cobalt(II) complexes with novel thiourea
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gratefully acknowledges grants from the Center of Supra-
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DOI: 10.1021/acs.inorgchem.9b02648
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