Suboxide

Suboxides are a class of oxides wherein the electropositive element is in excess relative to the “normal” oxides. When the electropositive element is a metal, the compounds are sometimes referred to as “metal-rich”. Thus the normal oxide of caesium is Cs 2 O, which is described as a Cs + salt of O 2− . A suboxide of caesium is Cs 11 O 3 , where the charge on Cs is clearly less than 1+, but the oxide is still described as O 2− . Suboxides typically feature extensive bonding between the electropositive element, often leading to clusters. Examples of suboxides other than alkali metal derivatives: * Carbon suboxide, C 3 O 2 ; * Boron suboxide, B 6 O; * Phosphorus suboxide, PO; * Titanium suboxides, TiO, Ti 2 O 3 , Ti 3 O 5 , Ti 4 O 7 , and Ti 5 O 9 .

Suboxides are a class of oxides wherein the electropositive element is in excess relative to the “normal” oxides. When the electropositive element is a metal, the compounds are sometimes referred to as “metal-rich”. Thus the normal oxide of caesium is Cs 2 O, which is described as a Cs + salt of O 2− . A suboxide of caesium is Cs 11 O 3 , where the charge on Cs is clearly less than 1+, but the oxide is still described as O 2− . Suboxides typically feature extensive bonding between the electropositive element, often leading to clusters. Examples of suboxides other than alkali metal derivatives: Carbon suboxide, C 3 O 2 ; Boron suboxide, B 6 O; Phosphorus suboxide, PO; Titanium suboxides, TiO, Ti 2 O 3 , Ti 3 O 5 , Ti 4 O 7 , and Ti 5 O 9 . ==Metal-containing suboxides== Suboxides are intermediates along the pathway that forms the normal oxide. Suboxides are sometimes visible when certain metals are exposed to small amounts of O 2 : 22 Cs + 3 O 2 → 2 Cs 11 O 3 4 Cs 11 O 3 + 5 O 2 → 22 Cs 2 O Several suboxides of caesium and rubidium have been characterized by X-ray crystallography. As of 1997, the inventory includes the following Rb 9 O 2 , Rb 6 O, Cs 11 O 3 , Cs 4 O, Cs 7 O, Cs 11 O 3 Rb, Cs 11 O 3 Rb 2 , and Cs 11 O 3 Rb 3 . Suboxides are generally colored compounds indicating a degree of electron delocalisation. Cs 7 O has a unit cell containing a Cs 11 O 3 cluster and 10 Cs atoms. The cluster can be visualised as being composed of three face-sharing octahedra. In the picture below the caesium atoms are purple and the oxygen atoms are red. The Cs-Cs distance in the cluster is 376 pm, which is less than the Cs-Cs distance in the metal of 576 pm. Rb 9 O 2 and Rb 6 O both contain the Rb 9 O 2 cluster, which can be visualised as two face-sharing octahedra. Rb 6 O can be formulated as (Rb 9 O 2 )Rb 3 . The Rb-Rb distance in the cluster is 352 pm which is shorter than the Rb-Rb in the metal of 485 pm. It is suggested that caesium suboxides play a role in the Ag-O-Cs (S1) and multialkali Na-K-Sb-Cs photocathodes. ==Carbon suboxide== The suboxide of carbon adopts an unremarkable structure. As for related organic cumulenes (e.g. ketene), C 3 O 2 obeys the octet rule. ==Related compounds== Subnitrides are also known. For example, Na 16 Ba 6 N features a nitride-centered octahedral cluster of six barium atoms embedded in a matrix of sodium. ==References==

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