The period 1951–1954 was a golden one for structural chemistry; proteins, DNA, Ferrocene (1952) and the one I discuss here, a bonding model for Zeise’s salt ( 3 ). In “A review of π Complex Theory”, Bull. Soc. Chim. Fr. , 1951 , 1 8 , C79 (it is not online) M. J. S. Dewar sets out his theory of the role of π-complexes in (mostly) organic chemistry.