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A dianion is an anion with a net charge of −2. While there exist many stable molecular dianions, such as BeF4 2− and MgF4 2−,[1] thus far no stable atomic dianion has been found: Electron shielding and other quantum mechanical effects tend to make the addition of another electron to an atomic anion unstable.[2]

The most heavily studied atomic dianion is H2−, usually as a short-lived resonance between an electron and a hydrogen ion.[2] In 1976, its half-life was experimentally measured to be 23 ± 4 nanoseconds.[3]

In the field of physiology, molecular dianions play an important roles, such as the monohydrogen phosphate ([HPO
), present at a concentration of around 1 mM in the blood and in cells, where it plays a role in pH buffering.[4]

See also[edit]


  1. ^ Middleton, Roy; Klein, Jeff (1999-11-01). "Experimental verification of the existence of the gas-phase dianions BeF42− and MgF42−". Physical Review A. 60 (5): 3515–3521. doi:10.1103/PhysRevA.60.3515.
  2. ^ a b Andersen, T. (2004-05-01). "Atomic negative ions: structure, dynamics and collisions". Physics Reports. 394 (4): 208–209. doi:10.1016/j.physrep.2004.01.001. ISSN 0370-1573.
  3. ^ "Double-negative hydrogen ion found". Chemical & Engineering News Archive. 54 (7): 8. 1976-02-16. doi:10.1021/cen-v054n007.p008. ISSN 0009-2347.
  4. ^ Wadsworth, Rl; Siddiqui, S (September 2016). "Phosphate homeostasis in critical care". BJA Education. 16 (9): 305–309. doi:10.1093/bjaed/mkw033.