Iron–sulfur clusters are molecular ensembles of iron and sulfide. They are most often discussed in the context of the biological role for iron-sulfur proteins, which are pervasive.S. J. Lippard, J. M. Berg “Principles of Bioinorganic Chemistry” University Science Books: Mill Valley, CA; 1994. ISBN 0-935702-73-3. Many Fe-S clusters are known in the area of organometallic chemistry and as precursors to synthetic analogues of the biological clusters (see Figure).