Project Details Preferred IUPAC Names (PINs) for Inorganic Compounds

Project No.:
Start Date:
01 January 2007
End Date:
Division Name:
Chemical Nomenclature and Structure Representation
Division No.:


To develop rules for choosing the Preferred IUPAC Names (PIN) forinorganic compounds, including coordination compounds, organometalliccompounds, and compounds that either do not contain carbon, or docontain at least one element from groups 1-12. These rules shouldresult in names that are suitable for use in legal and regulatorydocumentation.


The PIN concept has been developed in response to the difficulties that users of nomenclature strike when there is more that one systematic way of naming a compound. This issue is particularly problematic in legal and regulatory applications, where confusion over names could have major health and safety, legal, or financial implications.
Rules for choosing PINs for organic molecules have been developed as a major goal of the project for the revision of the Blue Book (project 2001-043-1-800). That project is nearing completion, and the resulting manuscript is in the IUPAC review process. It is obvious that PINs must also be available for inorganic compounds, but the methods that are typically used to name such compounds are different from those used for organic compounds, and consequently new rules will have to be developed.

A number of critical issues will have to be addressed; these include:

  • choice of central atom(s), particularly in polynuclear species;
  • clear definition of grammatical rules for the placement of k/h symbols in complicated ligand names;
  • selection of retained names, particularly for oxo-acids.

Once these issues have been addressed, the proposals that are developed will be submitted to the IUPAC review process. Further documents will then be prepared that provide detailed guidance for selecting PINs for particular classes of compounds (coordination compounds, organometallic compounds, main group compounds).


Jan 2012 update: A draft document has been prepared that expands and better delineates the grammar required for use of the kappa convention for describing coordination. The implications for more complicated systems are currently being discussed before the document is sent out for review.

After considerable discussion, the task group has a clearer idea of the extent of coverage of this project, particularly regarding the division of responsibility between this project and that on revision of the Blue Book (project 2001-043-1-800). Significant progress has been made on choice of central atoms.


Jan 2017 update: The kappa convention has been identified as vital to providing complete and unambiguous names for coordination compounds using additive nomenclature. It has not been well delineated in past documents and the grammar of the convention is being extended to cope with a number of structural situations that could not previously be described. Numerous ways have been considered for dealing with these situations, and possible new approaches have been developed as successive drafts of the kappa convention document have been prepared. It has taken considerable time to fully develop these ideas and then assess and compare the resulting nomenclature.

A separate document on making choices of central atoms within additive nomenclature is being considered, but the difficulties that have been revealed by the more detailed work in both of these areas have led us to question whether the aim of producing PINs for all inorganic compounds is practical or possible.


Jul 2018 update: Through 2017, work continued on developing the detail of the kappa convention. Numerous attempts were made to find ways in which names could be shortened, but ultimately this led to the resulting names being very challenging to interpret/decipher.
In addition, it became apparent that the kappa convention would need to be able to be applied to systems other than coordination compounds, notably boron compounds. Furthermore, some of the challenges overlapped with other conventions for representing chemical structures (e.g. isotopic substitution, stereodescriptors). The breadth of these new concerns formed a central aspect of a new “alignment project” within IUPAC (see project 2017-033-1-800). The kappa document is now being completely re-written in response to this work.


page last update 3 July 2018