Chemistry Reference
In-Depth Information
Appendix A
Nomenclature
From very early times, alchemists gave names to substances, although these names gave
little if any indication of the actual composition and or structure, which is the aim of a
true nomenclature. This was eventually addressed in the early days of 'modern' chemistry
in the late eighteenth century, and modern nomenclature evolved from that early work.
Since nomenclature evolved along with chemistry, it was far from systematic even up to
the beginning of the twentieth century. In large part, our current approach in coordination
chemistry derived from nomenclature concepts introduced by Werner to represent the range
of new complexes that he and contemporaries were developing, providing both composition
and structural information. His system of leading with the names of ligands followed by the
metal name, as well as also employing structural 'locators', is still with us today. Although
an international 'language' for organic molecules commenced from a meeting in 1892,
it was some time later that a systematic international inorganic nomenclature developed,
and it was as late as 1940 that a full systematic nomenclature was assembled. Constant
development in the field has demanded evolution of nomenclature, and the international
rules were revised or supplemented in 1959, 1970, 1977, 1990 and again early in the
twentyfirst century; like all languages, chemical language continues to evolve.
In describing chemical substances, we are dealing with a need for effective commu-
nication using an appropriate language. In a sense, chemical nomenclature is as much a
language as is Greek or Mandarin, albeit a restricted one with a very specific purpose;
it has an organized structure, 'rules of grammar', conventions, and undergoes continuous
evolution. One advantage is that it is a universal language, governed by rules set in place
by the International Union of Pure and Applied Chemists (IUPAC). This body produces
'dictionaries' for chemical nomenclature that serve in much the same way as a conventional
dictionary, thesaurus or grammar rule topic, and which are updated regularly. The object of
the nomenclature adopted is to provide information on the full stoichiometric formula and
shape of a compound in a systematic manner. For coordination chemistry, we need to deal
with a number of aspects - the ligands (of which there may be more than one type), the cen-
tral metal (or metals, in some cases), metal oxidation state(s), ligand distributions around the
metal(s) and counter-ions (if the compound is ionic). Collectively, these place a great deal
of demand on the nomenclature system, to the point where it has become both sophisticated
and difficult to use. We shall try and provide just a basic and introductory nomenclature here,
even neglecting some more advanced aspects of naming for the sake of brevity and clarity.
Molecules can be described in terms of a structural drawing, a written name or a formula.
These are in a fashion all representations of the same thing - a desire to express the character
of a chemical compound in a manner that will be understandable to others. Let's examine
these options for two very simple examples (Figure A.1):
