Dication

A dication is any cation, of general formula X²⁺, formed by the removal of two electrons from a neutral species.

Diatomic dications corresponding to stable neutral species (e.g. H2+
2 formed by removal of two electrons from H₂) often decay quickly into two singly charged particles (H⁺), due to the loss of electrons in bonding molecular orbitals. Energy levels of diatomic dications can be studied with good resolution by measuring the yield of pairs of zero-kinetic-energy electrons from double photoionization of a molecule as a function of the photoionizing wavelength (threshold photoelectrons coincidence spectroscopy – TPEsCO). The He2+
2 dication is kinetically stable.

An example of a stable diatomic dication which is not formed by oxidation of a neutral diatomic molecule is the dimercury dication Hg2+
2. An example of a polyatomic dication is S2+
8, formed by oxidation of S₈ and unstable with respect to further oxidisation over time to form SO₂.

Many organic dications can be detected in mass spectrometry for example CH2+
4 (a CH2+
2·H
2 complex) and the acetylene dication C
2H2+
2.^[1] The adamantyl dication has been synthesized.

Divalent metals

Common element dications

Some metals are commonly found in the form of dications when in the form of salts, or dissolved in water. Examples include the alkaline earth metals, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ra²⁺, later transition metals V²⁺, Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and the heavy members of the carbon group Sn²⁺ and Pb²⁺.

References