Magnetocaloric behavior of REE porphyrin-based paramagnets at room temperature

Article abstract of DOI:10.1142/S1088424619501220

REE complexes with cyclic aromatic ligands are ranked as the molecular materials with both electronic functionality and a single-molecule magnet behavior at temperatures lower 80 K. At the temperature close to room, they display a positive magnetocaloric effect (MCE) often comparable with one in ferromagnetics. We were determined MCE during the magnetization of both (5,10,15,20-tetra(4-tert-butylphenylporphinato))ytterbium(III)chloride, (Cl)YbTtBuPP and (5,10,15,20-tetraphenylporphinato)ytterbium(III)chloride, (Cl)YbTPP in their aqueous suspensions over the temperature range of 278-320 K and in magnetic fields from zero to 1 T by the direct microcalorimetric method. Specific heat capacity in the solid of (Cl)YbTtBuPP/(Cl)YbTPP has been directly determined in zero magnetic fields using differential scanning calorimetry. Thermodynamic parameters of ytterbium(III) complexes magnetization namely enthalpy/entropy change was determined. To improve understanding of the correlation between (Cl)YbTtBuPP/(Cl)YbTPP magnetic properties and its electronic structure, we have compared magnetic behavior of paramagnets studied with those for (Cl)MTPP where M = Gd, Eu, Tm.

Full text of DOI:10.1142/S1088424619501220

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 1110–1117
DOI: 10.1142/S1088424619501220
Published at http://www.worldscinet.com/jpp/
Magnetocaloric behavior of REE porphyrin-based
paramagnets at room temperature
◊
V. V. Korolev, T. N. Lomova* , A. G. Ramazanova, O. V. Balmasova
and E. G. Mozhzhukhina
G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, Akademicheskaya str., 1,
Ivanovo, 153045, Russia
Received 25 June 2019
Accepted 20 August 2019
ABSTRACT: REE complexes with cyclic aromatic ligands are ranked as the molecular materials with
both electronic functionality and a single­molecule magnet behavior at temperatures lower 80 K. At the
temperatureclosetoroom, theydisplayapositivemagnetocaloriceffect(MCE)oftencomparablewithone
in ferromagnetics. We were determined MCE during the magnetization of both (5,10,15,20­tetra(4­tert­
t
butylphenylporphinato))ytterbium(III)chloride, (Cl)YbT BuPP and (5,10,15,20­tetraphenylporphinato)
ytterbium(III)chloride, (Cl)YbTPP in their aqueous suspensions over the temperature range of
2
78–320 K and in magnetic fields from zero to 1 T by the direct microcalorimetric method. Specific
t
heat capacity in the solid of (Cl)YbT BuPP/(Cl)YbTPP has been directly determined in zero magnetic
fields using differential scanning calorimetry. Thermodynamic parameters of ytterbium(III) complexes
magnetization namely enthalpy/entropy change was determined. To improve understanding of the
t
correlation between (Cl)YbT BuPP/(Cl)YbTPP magnetic properties and its electronic structure, we have
compared magnetic behavior of paramagnets studied with those for (Cl)MTPP where M = Gd, Eu, Tm.
KEYWORDS: porphyrins, ytterbium(III) complexes, specific heat capacity, magnetocaloric effect,
magnetization thermodynamics, molecular structure effect.
structure creating [5], macrocycle substitution [6] or a
INTRODUCTION
building of the molecular structure with an additional
spin center [7] is very promising. Transition from REE
mononuclear 1: 1 complexes to double­, triple­ or qua­
druple­decker structures in the case of phthalocyanine/
tetraazaporphyrin/porphyrin complexes leads to the
improvement many applicable properties of these com­
pounds, namely a photochemical activity, a charge car­
rier concentration/mobility i.e. semiconductivity, photo
and chemical stability [5, 8–12].
Rare earths in both elemental and ionic states are
important magnetic carriers in the construction of mole­
cular magnetic materials. REE organic complexes cause
great interest in finding new functionalities and applica­
tions. Tetrapyrrole lanthanide complexes were revealed
to exhibit typical single­molecule magnets (SMMs)
behavior with an effective energy barrier determined
by a ligand field around a lanthanide ion and a block­
ing temperature not exceeding 50 K [1–4]. Different
strategies are useful for enhancing the ligand field effect
on a lanthanide ion. Electron and spin density redistri­
bution within a molecule achieved by a double­decker
However, we recently established MCE in the mono­
phthalocyanine gadolinium(III) complex (Cl)GdPc to be
higher by almost an order of magnitude compared with
·
corresponding double­decker GdPc2 due to the preva­
lence intermolecular coupling of two radical spins over
the intramolecular oxidation­activated spin coupling it
contains [13]. The large and giant MCE at close to room
temperature were obtained in the REE complexes of por­
phyrins with a simple 1 : 1 composition [14, 15]. A gen­
eral strategy of variations in the temperature­dependent
◊
SPP full member in good standing.
*
Correspondence to: T.N. Lomova, G.A. Krestov Institute
of Solution Chemistry of the Russian Academy of Sciences,
Akademicheskaya str., 1, Ivanovo, 153045, Russia, tel.:
+
7(4932)336990, email tnl@isc­ras.ru.
Copyright © 2019 World Scientific Publishing Company

MAGNETOCALORIC BEHAVIOR OF REE PORPHYRIN-BASED PARAMAGNETS AT ROOM TEMPERATURE 1111
magnetic behavior through modification of the macro­
cyclic ligand and spin carrier was provided [16–18].
It was shown, using examples of Eu , Gd , and Tm
that the porphyrin/phthalocyanine REE complexes have
magnetothermal properties useful in the field of room­
temperature magnetic refrigeration and hyperthermia
development. The macrocycle modification is carried out
in order to change a ligand field­effect on the paramag­
netic carrier in the REE tetrapyrrole complexes which
determines the effective energy barrier against magnetic
EXPERIMENTAL
III
III
III
Materials
5
,10,15,20-(tetra-4-tert-butylphenyl)21H,23H-
t
porphinato)ytterbium(III) chloride, (Cl)YbT BuPP, was
synthesized by the reaction Yb(Cl) 6H O and 5,10,15,­
.
3
2
20­(tetra­4­tert­butylphenyl)21H,23H­porphyrin in
a
molar ratio of 1 : 5 in boiling imidazole for 30 min. The
reaction mixture was dissolved in chloroform and repeat­
edly washed from imidazole with distilled water in a
relaxation (U ) [2] and therefore the magnetic behavior
ef
t
of the paramagnets.
separating funnel. (Cl)YbT BuPP was isolated by column
The aim of the study in this article was to establish the
chromatography on Al O using chloroform, ethanol, and
2
3
3
+
first MCE value in paramagnetic Yb ions surrounded
by macroheterocycles with increased aromaticity and
to obtain the thermodynamic parameters of magnetiza­
tion in (5,10,15,20­tetra(4­tert­butylphenylporphinato))
finally the ethanol–1% AcOH mixture. After the column,
the ethanol solution was diluted with chloroform and
repeatedly washed from acid with distilled water. The
chloroform solution was evaporated to precipitate solid
t
t
ytterbium(III)chloride, (Cl)YbT BuPP vs. an unsubsti­
(
Cl)YbT BuPP. Then the spectral parameters of the com­
tuted analog, (5,10,15,20­tetraphenylporphinato)ytter­
bium(III)chloride, (Cl)YbTPP (Formulas). For this, we
have performed direct determinations of MCE/the ther­
modynamic parameters of magnetization in aqueous
suspensions and the specific heat capacity of the solid
samples of the ytterbium(III) complexes. MCE and the
specific heat capacity were obtained by means of the
original microcalorimetric method [19] and differential
scanning calorimetry (DSC), respectively. The examined
compounds display positive room­temperature mag­
netocaloric effect when magnetic induction increases
from zero to 1.0 T in adiabatic conditions. Despite the
fact that magnetic characteristics of molecular magnetics
are more modest than those of nonorganic magnets, the
ytterbium(III) complexes MCE values are only an order
of magnitude smaller than those in some nanomagnets
plex were obtained. UV­vis spectrum in CHCl , (λmax, nm
3
(
logε)): 591 (3.88), 553 (4.34), 514 (3.68), 485 (3.52)
shoulder, 424 (5.64), 403 (4.63) shoulder. IR spectrum
­1
in KBr (n, cm ): 3122, 3026, 2962, 2904, 2868, 1910,
1
1
8
3
809, 1572, 1519, 1477, 1461, 1394, 1363, 1330, 1268,
242, 1203, 1109, 1080, 1026, 1005, 993, 908, 868, 852,
39, 810, 799, 724, 584, 561, 465, 435, 394, 383, 377,
1
72. (For the bands assignment see Table S1). H NMR
(
4
2
CDCl ), δ, ppm : 8.54 (m, 4H, H , 3H, H ); 7.99 (d,
3
o
m
H, H ); 2.63 (br. s, 6H, H ); 2.36 (br. s, 16H, H );
o b CH
3
.23 (d, 5H, H ); 1.64 (s, 20H, H ); 0.33 (s, 2H, Hb).
m
CH
3
(For the spectrum see Fig. S1 in the Supporting infor­
mation). MALDI­TOF MS: calc. for C H N YbCl —
6
0
60
4
+
1
[
045.54, found — 1009.26 [M–Cl] , found — 474.83
M­4C(CH ) ­Cl+2K+5H] . (For the spectrum see
+
+
3
3
Fig. S2).
[
20, 21]. Moreover, the magnetics based on the REE
5
,10,15,20-(tetra-phenyl)21H,23H-porphinato)
porphyrin/phthalocyanine complexes are often solution­
processable or easily sublimated; they can be conjugated
with inorganic coats, quantum dots and Ag nanoparticles
giving promising nonlinear optical and shift­reagent
properties [22].
ytterbium(III) chloride, (Cl)YbTPP, was synthesized by
.
the reaction Yb(Cl) 6H O and 5,10,15,20­(tetra­4­tert­
3
2
butylphenyl)21H,23H­porphyrin in a molar ratio of 1 : 2
in boiling imidazole for 30 min. The reaction mixture
was dissolved in chloroform and repeatedly washed from
Scheme 1. Paramagnets chemical structure
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 1111–1117

1
112 V. V. KOROLEV ET AL.
imidazole with distilled water in a separating funnel. (Cl)
YbT BuPP was isolated by column chromatography on
The UV­vis spectra were measured on Agilent 8453
UV­vis spectrophotometers; IR spectra were recorded
on a VERTEX 80v spectrometer; mass spectra was
performed on Shimadzu AXIMA Confidence mass
spectrometer and H NMR spectra were recorded on a
Bruker AVANCE­500 spectrometer.
t
Al O with the using chloroform, chloroform–ethanol
2
3
(
1:2 vol%), and finally the ethanol–1% AcOH mixture.
1
After the column, the ethanol solution was diluted with
chloroform and repeatedly washed from acid with dis­
tilled water. The chloroform solution was evaporated
to precipitate the solid (Cl)YbTPP. Then the spectral
parameters of the complex were obtained. UV­vis spec­
2.3. Calculation of thermodynamic parameters
The amount of heat QMCE (J/g), which was allocated
because of the magnetocaloric effect in a magnetic
material when magnetic field was switched on in the iso­
thermal conditions, was calculated by Equation 1.
trum in CHCl , (λmax, nm (logε)): 588 (3.73), 551 (4.35),
3
5
11 (3.66), 483 (3.46), 421 (5.64), 401 (4.64). IR spec­
­
1
trum in KBr (n, cm ): 371, 378, 409, 426, 442, 462, 522,
5
9
1
1
3
79, 622, 636, 660, 701, 723, 753, 799, 832, 848, 881,
90, 1007, 1034, 1070, 1156, 1177, 1202, 1233, 1275,
290, 1331, 1440, 1478, 1518, 1539, 1575, 1596, 1705,
811, 1890, 1951, 2529, 2614, 2855, 2925, 2962, 3021,
QMCE = Q (DT/DT ),
(1)
J
J
Here Q (J/g) is the Joule heat, injected in the calo­
J
rimetric experiment, DT and DT are the values of the
J
054, 3076, 3101, 3432. (For the bands assignment see
1
absolute temperature change of the calorimetric system
resulting from injecting the Joule heat and the magnetic
field change, respectively. The numerical MCE values,
DTMCE (K) were calculated by using the heat balance
Equation (2) [24].
ESM, Table S2). H NMR (CDCl ), δ, ppm 11.66 (br. s,
6
4
3
H, H ); 9.67 (br. s, 2H, H ); 8.57 (d 4H, H ); 8.00 (d,
m m o
H, H ); 5.96 (br. s, 3H, H ); 4.19 (d, H, H ); ­0.39 (br.
o
p
p
s, 8H, H ). (For the spectrum see Fig. S3). MALDI­TOF
b
MS: calc. for C H N YbCl — 821.15, found — 786.93
4
4
28
4
+
++
[
M–Cl+H] , found 474.81 [M–Cl+2K+3H] . (For the
spectrum see Fig. S4).
All reagents were of analytical grade. Yb(Cl) 6H O,
QMCE = m(M) Cp(M) DTMCE
(2)
.
Here, DTMCE is the temperature change that is MCE,
m(M) (g) and Cp(M) (J/g K) are the mass and specific heat
capacity of the magnetic material. The enthalpy change,
DH (J/mol), in the magnetic material resulting from the
changes in the magnetic field was determined from the
3
2
chloroform, imidazole, ethanol, AcOH, and 5,10,15,20­
tetra­phenyl)21H,23H­porphyrin were purchased from
Sigma–Aldrich. 5,10,15,20(Tetra­4­tert­butylphenyl)­
(
2
1H,23H­porphyrin were synthesized by Gruzdev [23].
Crystalline samples of (Cl)YbT BuPP and (Cl)YbTPP
t
experimental values of QMCE
.
The heat capacity of the samples in magnetic fields
was experimentally determined using the same apparatus
following known methods [25]. It was established that
the heat capacity values of samples in zero field and in
magnetic fields up to 1 T are close to or lie within the
limits of experimental error. Therefore, the heat capacity
of samples was measured in zero magnetic fields by the
DSC method.
were used for the 1.7 weight percentage water suspen­
sions. There were no changes in the chemical composi­
tion of the solids during a microcalorimetric and DSC
experiments, which was confirmed by spectrophotometry.
Equipment
Magnetocaloric effects of paramagnetics were studied
in the temperature range from 278 to 340 K and at the
magnetic inductions of 0.2, 0.4, 0.6, 0.8, and 1.0 T using
the special calorimetric device, the isothermal­shell
microcalorimeter, the shape and construction of which
are detailed in the work [19]. The microcalorimetric cell
full of ytterbium complex suspension together with the
isothermal shell was placed in the gap of the electro­
magnet. Adiabatic conditions for magnetization process
were achieved by rapid magnetic field changes. The tem­
perature fluctuation of 0.0002°C in the thermostatically
controlled calorimetric cell space during the calorimetric
The values of changes in the entropy of the studied
molecular magnetics in magnetic field, DS (J/g K) were
calculated by Equation 3
DS = –Cp(M) DTMCE/T
(3)
Here, Cp(M) is the specific heat capacity, DTMCE is the
magnetocaloric effect; T is the absolute temperature.
RESULTS AND DISCUSSIONS
­5
experiment and the setup sensitivity of 2 × 10 K were
maintained. The error in MCE measurements, which
were repeated five times, did not exceed 2%.
Chemical structure of ytterbium complexes
t­
The molecular structure of synthesized (Cl)YbT
Heat capacities with an error of about 2% were mea­
sured in zero fields by means of a 204 F1 Phoenix DSC
calorimeter (NETZSCH, Germany). Heat capacities
in magnetic fields were obtained by microcalorimetric
experiment performed as described above.
BuPP/(Cl)YbTPP strictly corresponds to the formulas
(Scheme 1), which follow from the spectral UV­vis, IR,
and MALDI­TOF MS data (see Experimental section,
Figs 1 and 2 and Supporting information). UV­vis spec­
tra of complexes conforming the ytterbium +3 oxidation
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 1112–1117

MAGNETOCALORIC BEHAVIOR OF REE PORPHYRIN-BASED PARAMAGNETS AT ROOM TEMPERATURE 1113
Fig. 3. Temperature dependencies of the specific heat capac­
ity of the samples in a zero magnetic field. Sample 1 — (Cl)
t
YbT BuPP, Sample 2 — (Cl)YbTPP. (DSC data, with the
experimental uncertainty 1.5%)
t
Fig. 1. UV­vis spectra of (Cl)YbT BuPP (1–4) and (Cl)YbTPP
­
6
­6
­5
(
5) in CHCl . C
(Cl)YbT BuPP
t
(1) 5.88⋅10 , (2) 5.19⋅10 , (3) 2.3 10 ,
and (4) 1.73⋅10 mol/L. 1, 3 — initial, 2, 4 — after microcalo­
3
­
5
rimetric experiment
mass spectrum assigned to a single and doubly charged
molecular ion (see Experimental section). The invariabil­
ity of the samples after microcalorimetric experiments is
confirmed by the data in Fig. 1 and Fig. S5. The work of
extracting a sample from a sealed capsule after a DSC
experiment is very laborious. In this case, it was not exe­
cuted. However, it has been performed for many other
samples, always showing immutability [28].
Specific heat capacity in solid
The temperature dependences of the specific heat
capacity of the samples of the studied paramagnetics in
zero magnetic fields are represented in Fig. 3.
The gradual increase in the (Cl)YbTPP C –T depen­
p
dence is consistent with the corresponding MCE decrease
(
see below). A more complex view of this dependence in
t
the case of (Cl)YbT BuPP is not reflected in the corre­
sponding MCE–T dependence of the same type on (Cl)
YbTPP (Figs 4 and 5 below). Therefore not high (Cl)
t
YbT BuPP curve maximum should be interpreted as a
result of structure improvement in the solid with the tem­
perature growth [29]. This may be due to the removal of
voids and the associated increase in the regularity of the
crystal structure of the ytterbium(III) complex. Unsubsti­
tuted (Cl)YbTPP does not display such behavior. Notice
that the C values of both paramagnets differ little.
p
Magnetocaloric effect in paramagnetics studied
t
Fig. 2. IR spectra of (Cl)YbT BuPP (top) and (Cl)YbTPP
(
down) in KBr
The field and temperature dependences of MCE in
the studied molecular paramagnetics are shown in Figs 4
and 5 (for the MCE magnitude in (Cl)YbTPP as a func­
tion of both the magnetic field induction and the tempera­
ture see Fig. S6). Generally, the temperature dependence
degree are “normal type” [26] and are consistent with data
in the literature [9]. The IR spectra clearly corresponds to
the manifestation of the signals of ytterbium(III) com­
plexes bonds and fragments including Yb­Cl and Yb­N.
The studied complexes display H NMR spectra typical of
paramagnetic metal porphyrins [27]. Finally, the chemi­
cal structure is also confirmed by two signals in each
t
of MCE in (Cl)YbT BuPP does not repeat straight­line
temperature dependence of specific heat QMCE shown
in Figs 6 and 7 below. These data show the presence of
lattice contribution that was mentioned in the previous
section in MCE (see Fig. 5 and Eq. 2).
1
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 1113–1117

1
114 V. V. KOROLEV ET AL.
t
Fig. 4. Magnitudes of the magnetocaloric effects in (Cl)Yb BuTPP as functions of magnetic induction (a) and temperature (b). The
experimental uncertainty of the MCE measurements was 2%
on metallic surfaces and magnetic nanoparticles (MNPs)
comprising magnetite.
The highest room­temperature MCE values, 0.0046
t
and 0.028 K for (Cl)YbT BuPP and (Cl)YbTPP, respec­
tively, are obtained at the magnetic induction of 1.0 T
and at the lowest temperature taken. The corresponding
MCE values of 0.623, 0.449, and 0.281 K were earlier
3
+
3+
3+
obtained respectively for Eu , Gd , and Tm complexes
of similar composition, (Cl)LnTPP (Ln is lanthanide
ion) [15]. As it is known [42], elemental gadolinium and
thulium are ferromagnetic, unlike paramagnetic euro­
pium and ytterbium. The picture changes in the case of
their tetrapyrrolic complexes. The decrease of MCE in
Fig. 5. Temperature dependencies of DTMCE in the samples at
changed magnetic field for B = 0.2; 1.0 T. Sample 1 — (Cl)
(Cl)YbTPP by an order of magnitude is logical but the
t
YbT BuPP, Sample 2 — (Cl)YbTPP. The experimental uncer­
higher MCE in (Cl)EuTPP within (Cl)LnTPP studied
should be explained by regularities of its valence electron
tainty of the MCE measurements was 2%
6
2
6
3+
shell, 4f 5s 5p forcing conditions of Ln — macrocycle
3
+
3+
dianion π interactions. Eu and Yb in the (Cl)LnTPP
structure are similar to each other in the desire to com­
The experimental fact of positive room­temperature
MCE in the samples of ytterbium(III) complexes shows
7
14
plement their f­shell to stable 4f and 4f , respectively
due to a dative π bonding with the aromatic system of
the macrocycle. This property was confirmed in many
experimental facts united as “gadolinium fractures” on
the dependence “composition–property” graphs. We
have obtained [10, 43, 44] similar fractures examining
the dependence of the kinetic stability constants for tetra­
pyrrole complexes on the serial number of the f element
in the periodic table (for graphic representation of k – Z
dependence see Fig. S7). However, a different situation
of Eu andYb in the lanthanide series leads to the opposite
consequences of the mentioned π bonding in the mag­
netic behavior of their porphyrin complexes. The contri­
bution to the (Cl)YbTPP spin state from the dative Yb­N
π bonds is negative, unlike in the case of (Cl)EuTPP in
which the spin improviement is achieved. Notice that
such interaction does not appear in lanthanide non­cyclic
ligand complexes whose magnetic behavior is deter­
mined by magnetic properties of one isolated Ln(III) ion
and antiferromagnetic exchange couplings between the
neighboring Ln(III) ions in the crystalline samples [45].
Thus, the use of the REE tetrapyrrole complexes is one of
3
+
that the paramagnetic nature of theYb ion is preserved
in its tetrapyrrole complexes. They are also manifested
t
in the typical NMR spectrum. The (Cl)YbT BuPP
MCE value is not high enough to be very promising
in magnetic cooling practice but the paramagnetics we
deal with have a set of other useful properties, namely,
effective UV­vis absorption (see Experimental section)
and nuclear magnetic resonance shift reagent properties
t
1
[
30, 31] reflected also in the (Cl)YbT BuPP H NMR
spectrum in the downfield shift of tert­butyl group sig­
nals (see Experimental section). These are located at
t
1
.62 ppm in the spectrum of uncoordinated H T BuPP
2
[
31] but at 2.86 and 2.17 ppm in the spectra of paramag­
II
t
III
t
netic Co T BuPP and (AcO)Mn TAP(4­ BuPh) (TAP
8
is tetraazaporphin dianion), respectively [23, 32]. Sim­
ple 1 : 1 REE porphyrin complexes can be selected as
half­sandwich precursors for countless homoleptic/het­
eroleptic bis/tris­complexes with both a single­molecule
magnetism [33–38] and an optical activity [39]. Finally,
REE porphyrins being solution­processed can be
coated like the porphyrin d­metal complexes [40, 41]
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 1114–1117

MAGNETOCALORIC BEHAVIOR OF REE PORPHYRIN-BASED PARAMAGNETS AT ROOM TEMPERATURE 1115
t
Fig. 6. The (Cl)YbT BuPP specific heat temperature dependen­
Fig. 8. Temperature dependences of enthalpy change in (Cl)
YbT BuPP due to MCE in different magnetic fields
t
cies at different magnetic fields showed in Fig.
Fig. 9. Temperature dependences of DH in the samples at the
magnetic field of 1.0 T. Sample 1 — (Cl)YbT BuPP, Sample
Fig. 7. The specific heat temperature dependencies of samples
for B = 0.2; 1.0 T. Sample 1 — (Cl)YbT BuPP, Sample 2 — (Cl)
YbTPP
t
t
2
— (Cl)YbTPP
the ways of the deriving molecular paramagnets with the
controlled magnetic properties.
Thermodynamic parameters of ytterbium(III)
complexes magnetization
Figures 6 and 7 represent the experimental tempera­
ture dependences of specific heat, QMCE, released by
ytterbium(III) complexes due to MCE (for the tempera­
ture dependences of specific heat released by (Cl)YbTPP
at different magnetic fields see Fig. S8).
The QMCE values grow with an increase in magnetic
induction and decrease with a temperature rise. Higher
QMCE values in (Cl)YbTPP compared with these in the
tert­butyl­substituted analog correspond to the peculiari­
ties in the MCE values (see Eq. 2).
Fig. 10. Temperature dependences of DS in the samples at the
magnetic field of 1.0 T. Sample 1 — (Cl)YbT BuPP, Sample
2 — (Cl)YbTPP
t
The temperature dependences of the calculated
enthalpy changes, DH (J/mol), under magnetization are
shown in Figs 8 and 9. These values are the direct param­
eters for estimating the cooling capacity of magnets.
Comparative examination of temperature dependences
of the specific heat, specific heat capacity and MCE in
two ytterbium(III) complexes have shown the lattice
and electronic contributions in MCE value due to the
improvement of the crystalline structure when tempera­
ture grows and ytterbium–macrocycle spin density redis­
tribution, respectively. To confirm these conclusions, we
have explored the values of changes in the entropy of the
studied molecular paramagnetics in the magnetic field,
DS at different magnetic inductions and temperatures
(Fig. 10).
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 1115–1117

1
116 V. V. KOROLEV ET AL.
The straight lines represent temperature dependences
of DS, as one would expect. These confirm the compensa­
tion effect from the lattice negative contributions decreas­
ing with the temperature growth on a negative electronic
contribution in MCE. The uncompensated electronic
contribution in (Cl)YbTPP MCE being less than the one
2. Magnani N. Int. J. Quantum Chem. 2014; 114:
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— Eur. J. (2013); 19: 2266–2270.
t
in (Cl)YbT BuPP due to the tert­butyl groups absence is
reflected in the DTMCE–T/QMCE–T dependences which are
5. Kratochvílová I, Šebera J, Paruzel B, Pfleger J,
Toman P, Marešová , Havlová Š, Hubík P, Buryi
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a concave curve (Figs 5 and 7).
CONCLUSIONS
6
. Biswas S, Bejoymohandas KS, Das S, Kalita P,
Reddy MLP, Oyarzabal I, Colacio E and Chan­
drasekhar V. Inorg. Chem. 2017; 56: 7985–7997.
. Korolev VV, Lomova TN, Maslennikova AN,
Korolev DV, Shpakovsky DB, Zhang J and Milaeva
ER. J. Magn. Magn. Mater. 2016; 401: 86–90.
. J. Jiang (Ed.) Functional Phthalocyanine Molecu-
lar Materials. Springer: Berlin Heidelberg, 2018.
. Lomova TN, Axially coordinated metal porphyrins
in Science and Application. URSS, 2018.
(
5,10,15,20­tetra(4­tert­butylphenylporphinato)) and
(
5,10,15,20­tetraphenylporphinato)ytterbium(III) chlo­
7
rides have been synthesized using porphyrin base
coordination with ytterbium(III) chloride to investigate
the presence of a room­temperature magnetocaloric
effect and to observe practically useful thermodynamic
parameters of their magnetization. Direct determina­
tion of MCE/magnetization thermodynamic parameters
in aqueous suspensions and specific heat capacity in a
solid for the ytterbium(III) complexes in comparison
8
9
1
1
1
0. Lomova TN, Andrianova LG and Berezin BD. Zh.
Fiz. Khim [in Russian] 1987; 61: 2921–2928.
1. Lomova TN and Andrianova LG, Russ. J. Coord.
Chem. 2004; 30: 660–664.
2. Lomova TN, Sokolova TN, Morozov VV and Ber­
ezin BD. Koord. Khim. 1994; 20: 637–640.
13. Korolev VV, Lomova TN, Ramazanova AG,
Korolev DV and Mozhzhukhina EG. J. Organomet.
Chem. 2016; 819: 209–215.
III
III
III
with the Eu , Gd and Tm analogs was performed by
the microcalorimetric and DSC methods, respectively.
tert­Butyl­substituted and unsubstituted tetraphenyl­
porphyrin complexes display positive MCE of 0.0046
and 0.028 K at 278 K and magnetic induction of 1.0 T
III
associated with the Yb spin state and redistribution of
spin density between the spin carrier and the macrocycle
π electron system. Lanthanide ion/macrocyclic periph­
eral substitution in the lanthanide porphyrins is useful as
a way of improving magnetocaloric properties of molec­
ular paramagnets of this class.
1
4. KorolevVV, Korolev DV, Lomova TN, Mozhzhukh­
ina EG and Zakharov AG. Rus. J. Phys. Chem.
(Russian) 2012; 86: 504–508; (Engl. Transl.) 2012;
8
6: 578–582.
1
5. Lomova TN, Korolev VV and Zakharov AG. Mater.
Sci. Eng. B 2014; 186: 54–63.
Acknowledgments
This work was carried out under partial financial sup­
port from the Russian Foundation for Basic Research
16. Korolev VV, Lomova TN, Ramazanova AG and
Mozhzhukhina EG. Synth. Metals 2016; 220:
502–507.
17. Korolev VV, Lomova TN, Ramazanova AG and
Mozhzhukhina EG. Mendeleev Commun. 2016; 26:
301–303.
18. Korolev VV, Lomova TN, Korolev DV, Ramaza­
nova AG, Mozhzhukhina EG and Ovchenkova EN.
In Advanced Environmental Analysis: Applications
of Nanomaterials, Vol. 2. RSC Detection Science
Series, Hussain CM and Kharisov CM. (Eds.) 2017,
RSC Publishing: Cambridge, pp. 14–47.
(
Project No. 16­03­00578­a and 18­43­370022­r­a) and
from the Program of the State Academies of Sciences
Subject No. 0092­2014­0002 and 0092­2014­0003).
(
This work was carried out with the help from the Centre
for Joint Use of Scientific Equipment, The Upper Volga
Region Center of Physicochemical Research, and from
the PhD I. A. Khodov.
Supporting information
Figures S1–S8 and Tables S1 and S2 are given in the
supplementary material. This material is available free of
charge via the Internet at http://www.worldscinet.com/
jpp/jpp.shtml.
1
9. Korolev VV, Korolev DV and Ramazanova AG.
J. Therm. Anal. Calorim. 2018; 136: 937–941.
0. Anikin MS, Tarasov EN, Kudrevatykh NV, Osad­
chenko VH and Zinin AV. Acta Phys. Pol., A 2015;
2
1
27: 635–637.
2
1. Piskorsky P, Korolev DV, Valeev RA, Morgunov
RB, Kunitsyna EI. Physics and Engineering of
Permanent Magnets. Td. E.N. Kablov. Moskow:
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