Synthetic Analogues of the Active Sites of Iron–Sulfur Proteins**Abbreviations used in this chapter: BM, Bohr magneton; Cys-S, coordinated cysteinate; DMF, N,N-dimethylformamide; DMSO, dimethyl sulfoxide; edt, (SCH2CH2S)2-; Fd, ferredoxin; HP, high-potential iron protein; mnt, S2C2(CN)2; Rd, rubredoxin; S*, sulfide; salen, bis(salicylaldehyde)ethylenediimine dianion; S2-o-xyl, o-xylyl-α,α′-dithiolate dianion; tfd, S2C2(CF3)2; X, amino acid residue; z, generalized charge on ionic species.