Unusual coexistence of magnetic and nonmagnetic Mo6 octahedral clusters in a chalcohalide solid solution: Synthesis, X-ray diffraction, EPR, and DFT investigations of Cs3Mo6I6 iI2-xi_SexiI 6a

Kaplan Kirakci, Stéphane Cordier, Alex Shames, Bruno Fontaine, Olivier Hernandez, Eric Furet, Jean François Halet, Régis Gautier, Christiane Perrin

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Abstract

The C3Mo6I6iI 2-xiSexiI6a series has been obtained by a solidstate route. There is evidence for a solid solution between the compositions Cs3Mo6T6 iI0.8iSe1.2iI 6a and Cs2Mo6I6 iI0.4iSe1.6iI 6a (space group: R3̄c, Z = 6; a = 16.7065(4), c = 20.5523(4) Å, V = 4967.8(2) Å3 and a = 16.6354(3), c = 20.5444(4) Å. V = 4923.7(2) Å3, respectively). The structure of this new series is based on magnetic [Mo6I 6iSe2iI6 a]3- and diamagnetic [Mo6I7 iSeiI6a]3- units with 23 and 24 valence electrons per Mo6 cluster, respectively. For a particular x, the structure of Cs3Mo6I6 iI2-xiSexI6a is based on a mixture of (x-1)[Mo6I6iSe 2iI6a]3- with 2-x) [Mo6I7iSeiI6 a]3.This leads to an average [Mo6I 6iI2-xiSexI 6a]3- ionic unit deduced from single-crystal X-ray diffraction investigations. The two inner positions of the average face-capped [Mo6I8-xiI6 a]3 ionic units (located on the threefold axis of the unit) are randomly occupied by iodine and selenium, whereas the other ligand positions are fully occupied by iodine. Low-temperature electron paramagnetic resonance (EPR) studies reveal a signal split into two components with g ∥ > g ∏. The reciprocal double integration intensity of the EPR signal versus T graph reveals a typical Curie law behavior. A density functional theory (DFT) study indicates that occupation of the inner position on the threefold axis by selenium atoms is preferred energetically among the three possible distributions of selenium atoms. The comparison of experimental and theoretical g values confirms the crystallographic analysis and agrees with the axial elongation of the Mo6 cluster within the crystal structure.

Original languageEnglish
Pages (from-to)9608-9616
Number of pages9
JournalChemistry - A European Journal
Volume13
Issue number34
DOIs
StatePublished - 7 Dec 2007

Keywords

  • Cluster compounds
  • Halides
  • Magnetic properties
  • Molybdenum
  • Solid-state reactions

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