Study of thermochemical properties of lanthanides pentafluorophenolates with coordination ligands

Article abstract of DOI:10.1134/S1070363216060165

Saturated vapor pressure of lithium pentafluorophenolate and the lanthanide complexes as a function of temperature has been determined by the Knudsen effusion method. Processing of the pressure data allowed the calculation of thermodynamic parameters of t

Full text of DOI:10.1134/S1070363216060165

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 6, pp. 1319–1321. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © B.I. Petrov, N.M. Lazarev, A.A. Maleev, A.A. Fagin, M.N. Bochkarev, 2016, published in Zhurnal Obshchei Khimii, 2016, Vol. 86,
No. 6, pp. 989–991.
Study of Thermochemical Properties of Lanthanides
Pentafluorophenolates with Coordination Ligands
B. I. Petrov, N. M. Lazarev, A. A. Maleev, A. A. Fagin, and M. N. Bochkarev
Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
ul. Tropinina 49, Nizhny Novgorod, 603950 Russia
е-mail: bip@iomc.ras.ru
Received November 12, 2015
Abstract—Saturated vapor pressure of lithium pentafluorophenolate and the lanthanide complexes as a
function of temperature has been determined by the Knudsen effusion method. Processing of the pressure data
allowed the calculation of thermodynamic parameters of the compounds sublimation. Mass spectra and
differential scanning calorimetry data are presented.
Keywords: rare-earth element, pentafluorophenolate complex, Knudsen method, pressure, sublimation
enthalpy
DOI: 10.1134/S1070363216060165
Lanthanides perfluorophenolates are sufficiently
stable compounds exhibiting high volatility; their
ability to be sublimated in a vacuum without
decomposition is important in view of their practical
application [1]. The absence of the С–Н bonds (well
known luminescence quenchers) can enhance the
intensity of the complexes emission. In view of the
special features of the pentafluorophenolate ligand,
organic light-emitting diode (OLED) devices have
been manufactured via evaporation–condensation of
these compounds in a vacuum, and their electro-
luminescent properties have been studied [1].
ligand and diethyl ether (В) (in the dysprosium
complex).
Pentafluorophenolate complexes of lanthanides
Ln(OC6F5)3(Phen)x [Ln = Pr, x = 1 (1); Eu, x = 1 (2);
Er, x = 3 (2)], Tb(OC6F5)3(bpy)2 (5) were prepared via
the interaction of amides Ln[N(SiMe3)2]3 with penta-
fluorophenol in benzene or toluene medium in the
presence of 1,10-phenanthroline or 2,2'-bipyridyl, in
the absence of air and moisture. Lithium pentafluoro-
phenolate LiOC6F5 (6) was prepared similarly, but no
phenanthroline or bipyridyl was added. The Dy(OC6F5)3·
(Phen)(Et2O)2 complex (4) was prepared via the
interaction of amide Dy[N(SiMe3)2]3 with penta-
fluorophenol and 1,10-phenanthroline in the presence
of diethyl ether. The preparation methods have been
described in detail elsewhere [1, 2].
In order to develop the methods of preparation of
emission layers via the vapor phase deposition, the
quantitative data on the volatility and thermal stability
of the complexes are required. However, thermo-
chemical properties of the said compounds have not
been studied so far.
The composition and structure of the prepared com-
pounds were confirmed by the data of elemental
analysis, IR spectroscopy, and X-ray diffraction (XRD)
analysis.
Here we present the results of the study of the
saturated vapor pressure as a function of temperature,
the gas phase composition, and thermodynamic
parameters of melting and sublimation for mono-
dentate lithium pentafluorophenolate LiOC6F5 and
Ln(OC6F5)3(A)х(В)у (Ln = Pr, Eu, Tb, Er, Dy) com-
plexes containing neutral (А) phenanthroline (Phen)
(in the praseodymium, europium, and erbium com-
plexes) or bipyridyl (bpy) (in the terbium complex)
Prior to further studies, the prepared compounds
were purified via sublimation in a vacuum (10–3 Торр
at 437 K).
Phase transitions of compounds 1–6 were studied
by means of differential scanning calorimetry at 30–
350°С. The studied compounds were single-phase,
1319

1320
PETROV et al.
Temperature, °С
log p
103/Т, K
Plots of saturated vapor pressure of compounds 1–6. (1) Pr(OC6F5)3(Phen); (2) Eu(OC6F5)3(Phen); (3) Er(OC6F5)3(Phen);
(4) Dy(OC6F5)3(Phen)3(Et2O)2; (5) Tb(OC6F5)3(bру)2; and (6) Li (OC6F5).
within the experimental accuracy limits. Compounds
1–6 underwent the phase transition (melting) in the
specified temperature range.
[ErL3]+, 893.5 (28) [ErL3Phen]+; 4, 542.6 (9) [DyL2OH]+,
709.2 (16) [DyL3]+, 889.5 (12) [DyL3Phen]+; 6, 197.1
(99) [LiL]+ (L = OC6F5).
The composition of the gas phase had to be
determined in order to find the saturated vapor
pressure of crystalline compounds 1–6. To do so, we
performed mass spectroscopy experiments over the
50–450°С temperature range. The first stage of the
compounds ionization consisted in the elimination of
phenanthroline (complexes 1–4) or bipyridyl (complex
5) ion. Further fragmentation of the studied com-
pounds under the electron impact conditions was
similar. Molecular ions of the complexes decomposed
with the elimination of the pentafluorophenolate
ligand. The strongest peaks in the mass spectra of
compounds 1–4 and 6 were those of the molecular and
metal-containing ions, m/z (Irel, %): 1, 522.6 (18)
[PrL2OH]+, 686.5 (52) [PrL3]+, 866.5 (15) [PrL3Phen]+;
2, 537.1 (5) [EuL2OH]+, 695.5 (5) [EuL3]+, 878 (4)
[EuL3Phen]+; 3, 546.7 (17) [ErL2OH]+, 713.5 (31)
The appearance of the [ML2OH]+ peaks was likely
owing to the background water present in the mass
analyzer trap (i.e. the feature of the mass spectrometer
construction). The processes of hydrolysis and ion-
molecular reaction involving the formed ions have
been discussed in detail in [4].
Analysis of mass spectra of compounds 1–4 and 6
revealed the absence of other ions (including those
heavier than the molecular ones) in the saturated
vapor. Hence, it was concluded that the gas phase
contained exclusively the corresponding monomeric
molecular forms.
Thermodynamic parameters of vaporization and
sublimation to the monomeric vapor were calculated
basing on the mass spectrometry data of the studied
compounds in the vapor phase.
Coefficients of the vapor pressure equation log p = A – B/T and sublimation enthalpies of the studied compounds
Compound
Li OC6F5
Pr(OC6F5)3Phen
М
ΔТ, K
А
В
R2a
ΔsHT, kJ/mol
41.08
190
305.9–353.4
333.4–372.7
351.4–385.7
359.9–380.6
384.6–411.7
412.1–447.5
2.1513
2.7724
3.2102
3.7986
4.1319
3.5243
4.9467
6.4457
7.3079
8.0277
8.3391
8.1102
0.997
0.996
0.998
0.995
0.998
0.998
867.3
867.3
977.7
1034
1254
53.08
60.56
72.71
79.08
Eu(OC6F5)3Phen
Dy(OC6F5)3(Phen)(Et2O)2
Tb(OC6F5)3(bру)2
Er(OC6F5)3(Phen)3
83.02
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 6 2016

STUDY OF THERMOCHEMICAL PROPERTIES OF LANTHANIDES PENTAFLUOROPHENOLATES
1321
(1)
K = 1/[1 + 0.5(l/r)].
The saturated vapor pressure of the sublimated
complexes as a function of temperature (30–180°С)
was measured using the effusion Knudsen method (see
the Figure). The obtained data were described by the
log p = A – B/T equation (р being the vapor pressure in
Pa) with the correlation coefficient R above 0.995.
Parameters А and В (see the table) were found using
the least-squares method, the accuracy being of at least
±5%. The obtained data were then used to calculate
thermodynamic parameters of sublimation.
Temperature range of the vaporization was chosen
according to DSC data.
Hence, the product of K and the effusion hole area
was of 8.14 × 10–4 cm2.
ACKNOWLEDGMENTS
This work was financially supported by the
Presidium of Academy of Sciences (Program no. 17)
and Russian Foundation for Basic Research (project
no. 13-03-00097).
REFERENCES
The table shows the values of the sublimation
enthalpies at the midpoint of the temperature range.
The volatility of the studied compounds was decreased
in the series of the corresponding metals (lithium to
erbium). Molecular mass of the compounds made the
major contribution to their volatility, the heat of
sublimation growing with the increase in the
compound molecular mass.
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Saturated vapor pressure was measured using a
stainless steel effusion chamber with the evaporation
area to the effusion hole (l = 0.050 mm, d = 0.35 mm)
area ratio of 660. The experimental conditions have
been described elsewhere [7, 8]. The Klausing coef-
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 6 2016