Reactions of N-and S-substitutetl thiosemicarbazones with Cu(1) have been examined. No complexes are formed when the S atom is substituted and(or) when the N2 hydrogen atom is replaced by Me. 4,i-Dimethyl derivatives not only give the itsual 1:l conlplexes, but also 2:l complexes (2 thiosemicarbazoncs to 1 copper) in which copper has been oxidized t o Cu(I1). Reactions of thiosetuicarbazones with Cu(I1) give 1:1,2:1, and probably a mixture which corresponds to 2:s complexes. A discussion on the possible structures for the 1:1 complexes is given and they are best represented as polymers, the metal being borlded to the sulphur and to a nitrogen atom of the thiosemicarbazide portion of the ~nolecule. Infrared spectra of these c o m p o u~~d s have been examined, particularly in the 1100 cm-1 region where a strong to medium band disappears in going fro111 thiosemicarbazones to copper complexes. I t is suggested that this band is due to the C=S \vibration.Various metallic complexes of organic sulphur compounds are described in the literature (1-10). Many of these were prepared for phpsiological studies and their structures are not discussed fully (7, 10). I n earlier publications we have reported the preparation of Cu (I) complexes of tl~iosemicarbazones* (1 tsc :l Cu) (1 1) and their fungicidal action (12). This paper presents a discussion of the possible structures for these complexes based mainly on the reactions of several N-inethyl tl~ioseinicarbazones with copper ions in ammoniacal and neutral media.Thiosen~icarbazo~les have the structure (I) ( R = alkyl, aryl, or H).When Rg and R4 and(or) K j are hydrogen atoms, tautoineric thiols (11) and (IV) and thione (111) forms are possible, these being interconvertible through their common anions (V) and cations (VI). The dipolar structures (IIIal and (IIIb) may contribute to (111).