1. Where a term is introduced or defined in the text it is given in italics.
2. Throughout this paper the term “atom” is used regardless of cationic or anionic character. When necessary, the terms “cationic atoms” and “anionic atoms” are used instead of “cations” and “anions”.
3. IUPAC Compendium of Chemical Terminology, Electronic version, http://goldbook.iupac.org.
4. Ueber eine neue Reihe organischer Körper, welche Metalle enthalten