The work described in this thesis deals with the co-ordination chemistry of the macrocyclic ligands [9]aneS₃ (1,4,7-trithiacyclononane), [12]aneS₄ (1,4,7,10-tetrathiacyclododecane), [14]aneS₄ (1,5,8,12-tetrathiacyclotetradecane), [16]aneS₄ (1,5,9,13-tetrathiahexadecane), [15]aneS₅ (1,4,7,10,13-pentathiacyclopentadecane), [18]aneS₆ (1,4,7,10,13,16-hexathiacyclooctadecane), [24]aneS₈ (1,4,7,10,13,16,19,22-octathiacyclotetraeicosane), [15]aneS₂O₃ (1,4,7-trioxa-10,13-dithiacyclopentadecane), [18]aneS₂O₄ (1,4,7,10-tetraoxa-13,16-dithiacyclooctadecane), benzo[18]aneS₂O₄ (4,7,10,13-tetraoxa-1,16-dithial[16]-o-cyclophane), [21]aneS₂O₅ (1,4,7,10,13-pentaoxa-16,19-dithiacycloheneicosane), [18]aneS₃O₃ (1,4,7-trioxa-10,13,16-trithiacyclooctadecane) and [20]ane₃O₃ (1,4,7-trioxa-10,14,18-trithiacycloeicosane). The synthesis of [18]aneS₂O₄, [18]aneS₃O₃ benzo[18]aneS₂O₄ and [20]aneS₃O_3, the single crystal X-ray structures of [15]aneS₂O₃, [18]aneS₂O₄ and ([21]aneS₂O₅)1.1/2H₂O, and molecular mechanics calculations on [18]aneS₂O₄ are described. ([21]aneS₂O₅). 11/2H₂O is the first example of a neutral molecule binding to a mixed O/S-donor ionophore with H-bonding to the hard polyether binding site. Studies of Ru(II) and Pd(II) complexes with these ligands were initiate in order to establish the fundamental co-ordination chemistry between mixed O/S-donor ionophores and to establish the potential of these complexes to be used in the development of a metal mixed O/S-donor macrocyclic host guest chemistry. [RuC1₂PPh₃([15]aneS₂O₃)] and [RuCI(PPh₃)([15]aneS₂O₃)₂]PF₆ were prepared by the reaction of [15]aneS₂O₃ with [RuCI₂(PPh₃)₃]. The role of [RuCI₂PPh₃([15]aneS₂O₃)] as a potential intermediate in the formation of the two isomers of [RuCI(PPh₃)([15]aneS₂O₃)₂]PF₆ is discussed. The reaction of [18]ane₂O₄ with [RuC1₂(PPh₃)₃] afforded [RuCI(PPh₃)([18]aneS₂O₄)₂]PF₆. [Ru([18]aneS₂O₄)₃](PF₆)₂ was prepared by the reaction of [18]aneS₂O₄ and 'RuCI₃.xH₂O' in the presence of K₂(C₂O₄) as a reducing agent. Reactions of [18]aneS₂O₄ with [Ru₂CI₄(η⁶-C₆H₆)₂] and [RuCI(PPh₃)₂(η⁵-C₅H₅)] afforded the organometallic species [RuCI(η⁶-C₆H₆)([18]aneS₂O₄)]PF₆, [RuCI(η⁶-C₆H₆)([18]aneS₂O₄)]BPh₄ and [Ru(η⁵-C₅H₅)(PPh₃)([18]aneS₂O₄)]PF₆. The single crystal X-ray structures of all compounds prepared are described. In all cases the macrocyclic ligands co-ordinate to the RU(II) ion in an exo bidentate manner.