Polycation

Polycation of tellurium

Polycations are particles made up of several atoms of the same element that have gathered together and, as a group, have a positive charge. The number of known polycationic compounds of main group elements is far fewer than that of polyanionic compounds. Examples are the cations of the chalcogens such as S ₄ ²⁺ , S ₈ ²⁺ , Se ₁₀ ²⁺ or Te ₆ ²⁺ , which are formed when the elements react with Lewis acids under oxidizing conditions . The terms polyanion and polycation were coined by Eduard Zintl around 1930 .

presentation

Oxidizing agents such as B. Peroxodisulfuryldifluorid S ₂ O ₆ F ₂ in fluorosulfuric acid HSO ₃ F or sulfur trioxide SO ₃ in sulfuric acid lead selenium (Se) or tellurium (Te) into cations. In addition, the cations are formed by comproportionation or disproportionation of Se, Te in AlCl ₃ -containing SO ₂ solutions. The tendency of selenium and tellurium to form cations is overall greater than that of the more electronegative sulfur , and the acidity of the Se and Te cations is smaller than that of the sulfur cations.

The red Te ₄ ²⁺ - cation ( Tetratellur dication ), for example from elemental tellurium by oxidation in hot concentrated sulfuric acid (H ₂ SO ₄ are shown). Part of the sulfuric acid is reduced to sulfuric acid (H ₂ SO ₃ ) during the reaction , which, due to the high temperatures, breaks down into water (H ₂ O) and its anhydride sulfur dioxide (SO ₂ ), which escapes as a gas:

${\displaystyle \mathrm {4\ Te\ +\ 3\ H_{2}SO_{4}\longrightarrow \ Te_{4}^{2+}\ +\ 2\ H_{2}O+\ SO_{2}\uparrow \ +\ 2\ HSO_{4}^{-}} }$

This reaction serves as a qualitative proof of tellurium in an analysis mixture.

Structures

Structures of different polycations of the chalcogens:

• 

  Se ₁₀ ²⁺

• 

  Te ₆ ²⁺

• 

  Te ₆ ⁴⁺

• 

  Te ₈ ²⁺

• 

  Te ₈ ²⁺

• 

  Te ₈ ⁴⁺

• 

  (Te ₄ ²⁺ ) _x

• 

  (Te ₇ ²⁺ ) _x

• 

  (Te ₁₀ ²⁺ ) _x

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• Ulrich Müller: Inorganic Structural Chemistry . Vieweg + Teubner, Wiesbaden 2008, ISBN 978-3-8348-0626-0 , p. 204 f .
• AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 622.
• University of Giessen: Investigations on the reactivity of chalcogen polycations hexachlorozirconates and hafnates (PDF; 3.7 MB)
• Uni-Bonn: Cluster
• Uni-Bonn: Gallery

See also

• Polyelectrolytes