Encyclopedia of Geochemistry

2018 Edition
| Editors: William M. White


  • Jay R. BlackEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-39312-4_60


Aqueous species; Coordination complex; Ion pair


Complexes are compounds that form in solutions due to interactions between ions or neutral molecules forming coordinating bonds between them. Coordination complexes commonly form between positively charged cations (e.g., Ca2+, Mg2+, Na+ and Cu2+), which act as a central atom and are bound to negatively charged anion species (e.g., Cl, SO42−, HCO3 and F) or neutral species (e.g., H2O and NH3), also referred to as ligands. The types of bonds that form may be ionic due to Coulombic forces or covalent due to sharing of electrons between atoms or other types of interactions such as dipole-dipole interactions (See entries  “Chemical Bonds” and  “Van der Waals Force”). Ligands that form more than one bond with a central metal atom, thus occupying more than one coordination site, are called chelates (See entry  “Chelation”). Many organic ligands act as chelates forming multiple bonds with a metal, such as porphyrin a ring...

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© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.School of Earth SciencesThe University of MelbourneMelbourneAustralia