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Abstract <p>Magnesium bis-(dipivaloylmethanato)(N,N,N′,N′-tetramethylethylenediamine) [Mg(tmeda)(thd)<sub>2</sub>] is one of the most demanded volatile fluorine-free precursors to deposit MgO films. By means of single crystal and powder X-ray diffraction we have found for the first time that during recrystallization and vacuum sublimation different polymorphs of this complex are formed: space groups <i>P</i>2<sub>1</sub>/<i>n</i> <b>I</b> (previously unknown) and <i>C</i>2/<i>c</i> <b>II</b> (new) respectively. The new modification is also stable upon storage but does not exhibit a low-temperature phase transition with crystal splitting and symmetry lowering to <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$P\bar{1}$</EquationSource> </InlineEquation> <b>III </b>due to the ordering of <i>tert</i>-butyl groups. The thermal behavior of the new polymorph is analyzed by DSC and tensimetry (flow method), which enabled us to determine the thermodynamic parameters of transformations in the condensed phase and sublimation processes. It is determined that although molecules of the complex are packed closer in the <i>P</i>2<sub>1</sub>/<i>n</i> crystals, it does not substantially affect the vapor pressure and thermal properties at temperatures used in deposition processes. By the density functional theory with periodic boundary conditions (Quantum Espresso 7.4, PBEsol-D3(BJ)/SSSP Precision) it is shown that differences in the crystal lattice energies of three polymorphs <b>I–III</b> studied do not exceed 2.4&#xa0;kJ/mol.</p>

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Structure and Thermal Properties of New Polymorphs of Magnesium Bis-(dipivaloylmethanato)(N,N,N′,N′-tetramethylethylenediamine)

  • 期刊论文

  • 发表日期：

    2025年11月1日

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  • G. S. Evseev,
  • A. S. Sukhikh,
  • K. V. Zherikova,
  • A. M. Makarenko,
  • I. V. Korolkov,
  • D. P. Pishchur,
  • N. B. Morozova,
  • E. S. Vikulova

摘要

Abstract

Magnesium bis-(dipivaloylmethanato)(N,N,N′,N′-tetramethylethylenediamine) [Mg(tmeda)(thd)2] is one of the most demanded volatile fluorine-free precursors to deposit MgO films. By means of single crystal and powder X-ray diffraction we have found for the first time that during recrystallization and vacuum sublimation different polymorphs of this complex are formed: space groups P21/n I (previously unknown) and C2/c II (new) respectively. The new modification is also stable upon storage but does not exhibit a low-temperature phase transition with crystal splitting and symmetry lowering to $P\bar{1}$ III due to the ordering of tert-butyl groups. The thermal behavior of the new polymorph is analyzed by DSC and tensimetry (flow method), which enabled us to determine the thermodynamic parameters of transformations in the condensed phase and sublimation processes. It is determined that although molecules of the complex are packed closer in the P21/n crystals, it does not substantially affect the vapor pressure and thermal properties at temperatures used in deposition processes. By the density functional theory with periodic boundary conditions (Quantum Espresso 7.4, PBEsol-D3(BJ)/SSSP Precision) it is shown that differences in the crystal lattice energies of three polymorphs I–III studied do not exceed 2.4 kJ/mol.