Specific Features of Lanthanide Stereochemistry in Sulfides
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ICAL METHODS OF INVESTIGATION
Specific Features of Lanthanide Stereochemistry in Sulfides V. N. Serezhkina, *, M. Albakajajia, D. V. Pushkina, and L. B. Serezhkinaa a
Samara National Research University, Samara, 443011 Russia *е-mail: [email protected]
Received June 16, 2020; revised July 21, 2020; accepted July 27, 2020
Abstract—Crystallochemical analysis with the use of Voronoi–Dirichlet polyhedra (VDPs) has been performed for 711 sulfides, whose structures contain 1199 coordination polyhedra LnSn, where Ln is a lanthanide from La to Lu. It has been established that the sulfides incorporate Ln(II), Ln(III), and Ce(IV) atoms bonding from 6 to 10 sulfur atoms, which exist in the form of S2– or S– ions. The VDP parameters provide the possibility to determine the valence state of Ln atoms in the structures of sulfides and distinguish S2– or S– ions. The VDPs of 2913 sulfur atoms have been characterized to establish the dependence between the multiplicity of S–S bonds and their length. A quantitative estimate of lanthanide contraction in LnIIIXn polyhedra is given depending on the nature of chalcogen Х (O, S, Se, or Te). Keywords: Voronoi–Dirichlet polyhedra, stereochemistry, lanthanides, sulfides, chalcogenides, lanthanide contraction DOI: 10.1134/S0036023620120153
INTRODUCTION The compounds whose crystal structures contain coordination polyhedra LnSn (Ln is a lanthanide) have been actively studied during recent decades. The interest in such compounds (hereinafter, for convenience, sulfides) is provoked by some practically important features of their optical, thermoelectrical, magnetic, and a number of other physicochemical properties [1– 7]. At the same time, the Ln sulfides also are of significant theoretical interest as providing the possibility to assess the crystallostructural role of homoatomic S–S interactions, which represent an important feature of sulfur stereochemistry. Thus, the Ln sulfides have S– S interatomic contacts, whose length exceeds the sum of the covalent radii of sulfur atoms (2.08 Å [8]) but is smaller than the sum of their van der Waals radii (3.6 Å [9]). For this reason, in compliance with the recently adopted IUPAC recommendations [10], such contacts may be considered as a particular case of chalcogen bonds. The presence of S–S contacts with various lengths in the structures of sulfides complicates the estimation of formal atomic charges, especially if the compounds contain the atoms of elements able to exist in different valence states. A real example may be CsCuCeS3 {156245}, whose two possible formal valence distribution variants Cs+Cu+Ce4+(S2–)3 or Cs+Cu2+Ce3+(S2–)3 were complemented by the authors [11] with the third variant Cs+Cu+Ce3+(S2–)2(S–) taking into account the magnetic susceptibility estimation results. Hereinafter, the curly brackets enclose the
code of a compound in the databases (digital in [12] or literal in [13]). When performing the crystallochemical analysis of compounds containing more than 4800 crystallochemically different coordination polyhedra (CPs) LnХn, whe
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