ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2017, Vol. 62, No. 6, pp. 818–821. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © I.P. Malkerova, A.M. Makarevich, A.S. Alikhanyan, N.P. Kuz’mina, 2017, published in Zhurnal Neorganicheskoi Khimii, 2017, Vol. 62, No. 6, pp. 838–841.
PHYSICAL METHODS
OF INVESTIGATION
Volatility and Thermal Stability of Vanadyl β-Diketonate Complexes
a,
b
a
b
I. P. Malkerova *, A. M. Makarevich , A. S. Alikhanyan , and N. P. Kuz’mina
a
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
b
Moscow State University, Moscow, 119991 Russia
*
e-mail: IMalkerova@gmail.com
Received April 21, 2016
Abstract―Thermal behavior and thermodynamic characteristics of vanadyl β-diketonates—acetylacetonate
VO(acac) , dipivaloylmethanate VO(thd) , and tris-hexafluoroacetylacetonate VO(hfa) (Hacac, 2,4-pen-
2
2
2
tanedione; Hthd, 2,2,6,6-tetramethyl-3,5-heptanedione; Hhfa, 1,1,1,5,5,5-hexafluoro-2,4-pentanedi-
one)—have been studied by thermal analysis and the Knudsen effusion mass spectrometry study of gas phase
composition. The compounds have been shown to undergo congruent sublimation. Saturated vapor over the
complexes has been shown to comprise monomeric VOL molecules. Absolute values of partial pressures and
2
sublimation enthalpies of these compounds have been determined.
DOI: 10.1134/S0036023617060134
Vanadium dioxide attracts particular attention dium dioxide films preparation by decomposition of
among numerous oxide materials showing metal– vanadyl β-diketonates, the volatility and thermal sta-
dielectric (MD) transition. In spite of simple cationic bility of the complexes are not studied.
composition, VO shows a number of interesting fea-
2
The aim of this work is to study gas phase compo-
tures: MD transition proceeds instantly (τ < 1 ps) at sition by mass spectrometry, determine thermody-
temperatures close to ambient temperature (68°C for namic characteristics of evaporation processes, and to
bulk samples) and with giant change in conductivity compare volatility of vanadyl β-diketonates of general
5
(
~10 times for single crystals [1]). Electronic transi- formula VOL [L = acac (Hacac, 2,4-pentanedione);
2
tion in vanadium dioxide is accompanied by change in thd (Hthd, 2,2,6,6-tetramethyl-3,5-heptanedione);
magnetic and optical (in the IR region) properties. It hfa (Hhfa, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione).
can be caused not only by thermal impact but also
under the action of other physical factors (exposure to
EXPERIMENTAL
electric or magnetic field [2], laser radiation [3]). The
set of such unique properties makes vanadium dioxide
promising key component for a number of new micro
devices: electronic switches [4], thermal, optical, and
magnetic sensors, metamaterials, memory devices [5–
Synthesis of VO(acac) . An aqueous solution (300 mL)
2
of VOSO · 3H O (12.3 g) was added dropwise with
4
2
stirring to an aqueous solution (200 mL) of a mixture
of Hacac (15.09 g) and NaOH (6.04 g). The resultant
turquoise precipitate was washed with water, dried in
air, and sublimed at 190°C and 0.01 mmHg. The iden-
tity of the prepared product (265 g/mol) to composi-
tion VC H O was confirmed by the data of elemen-
7
]. Vanadium dioxide films are obtained by high-vac-
uum gas-phase methods with different methods of
ceramic or metallic target evaporation (laser, ion, or
electron beam) [8, 9]. However, expensive high-vac-
uum equipment makes these methods suitable for pre-
paring laboratory samples only.
10
14
5
tal analysis and IR spectroscopy.
Found (%): C, 45.43; H, 5.39. Calculated (%): C,
In recent time, vanadium dioxide films are pre-
pared by MOCVD method, which is widely used in
industry and free from many drawbacks described
above. Different modifications of this method are
developed (under low [10] and atmospheric pressure
4
5.30; H, 5.32.
–1
Characteristic bands in IR spectrum (ν, cm ): 993
ν(V=O); 685 ν(V–O); 1547 ν(C=O); 1520 ν(C=С);
2
900–3025 ν(C–H).
[
11], with liquid sputtering [12]). Special attention is
Synthesis of VO(thd) . The synthesis was con-
2
attracted by the variation of chemical gas-phase depo- ducted in aqueous alcohol medium (1 : 1). A solution
sition using as precursors vanadyl β-diketonates of of VOSO ⋅ 3H O (8.66 g, 99%) in 100 mL of H O was
4
2
2
general formula VOL , where L is thd [13], acac [14, added dropwise to 400 mL of solution of a mixture of
2
1
5], and hfa [16, 17]. However, in spite of growing 3.05 g NaOH (99%) and 14.03 g of Hthd (Dalchim,
popularity of chemical gas-phase methods for vana- 98%) with constant stirring. After 5 h, the resultant
818