title: Carbon dichalcogenide
text: # Carbon dichalcogenide
  
  Carbon dichalcogenides are chemical compounds of carbon and chalcogen elements. They have the general chemical formula $CZ_2,$ where Z = O, S, Se, Te.
  
  This includes:
  
  * Carbon dioxide, $CO_2$
  * Carbon disulfide, $CS_2$
  * Carbon diselenide, $CSe_2$
  * Carbonyl sulfide, OCS
  * Carbonyl selenide, OCSe
  * Thiocarbonyl selenide, SCSe
  * Thiocarbonyl telluride, SCTe
  
  ## Stability
  
  Double bonds between carbon and chalcogen elements, C=Z, become weaker the heavier the chalcogen, Z. This trend means carbon dichalcogenide monomers are less stable and more susceptible to polymerisation as Z changes from O to Te. For example, $CO_2$ is stable, $CS_2$ polymerises under extreme conditions, $CSe_2$ tends to polymerise, CSeTe is unstable and $CTe_2$ does not exist. This trend is an example of the double bond rule.
  
  ## Bonding
  
  In carbon dichalcogenides, C=O bond lengths are around 1.16 Å, C=S around 1.56 Å, C=Se around 1.70 Å and C=Te around 1.90 Å.
  
  Carbon–chalcogen double bond lengths in carbon dichalcogenides, Z=C=Z′ :
  
  | Species | Formula | Z | Z′ | Bond | Bond in molecule | Bond length / Å | Method of determination |
  | - | - | - | - | - | - | - | - |
  | Carbon dioxide | $CO_2$ | O | O | C=O | O=C=O | 1.163 | infrared spectroscopy |
  | Carbonyl sulfide | OCS | O | S | C=O | S=C=O | 1.158 | microwave spectroscopy |
  | Carbonyl selenide | OCSe | O | Se | C=O | Se=C=O | 1.159 | microwave spectroscopy |
  | Carbonyl sulfide | OCS | O | S | C=S | O=C=S | 1.560 | microwave spectroscopy |
  | Carbon disulfide | $CS_2$ | S | S | C=S | S=C=S | 1.553 | infrared spectroscopy |
  | Thiocarbonyl selenide | SCSe | S | Se | C=S | Se=C=S | 1.553 | microwave spectroscopy |
  | Thiocarbonyl telluride | SCTe | S | Te | C=S | Te=C=S | 1.557 | microwave spectroscopy |
  | Carbonyl selenide | OCSe | O | Se | C=Se | O=C=Se | 1.709 | microwave spectroscopy |
  | Thiocarbonyl selenide | SCSe | S | Se | C=Se | S=C=Se | 1.693 | microwave spectroscopy |
  | Carbon diselenide | $CSe_2$ | Se | Se | C=Se | Se=C=Se | 1.689 | neutron diffraction |
  | Thiocarbonyl telluride | SCTe | S | Te | C=Te | S=C=Te | 1.904 | microwave spectroscopy |
  