Synthesis and stereochemistry of cobalt(III) complexes containing purine-6-thione and related ligands

Abstract

Seven cobalt(III) complexes containing five purinethiones [Co(L-N,S)(en)₂]ⁿ⁺ and [H_nL = H₂put = 9H-purine-6(1H)-thione, H₂aput = 2-amino-9H-purine-6(1H)-thione, H₃tpuo = 3,6-dihydro-6-thioxo-9H-purine-2(1H)-one, H₃oput = 2,3-dihydro-2-thioxo-9H-purin-6(1H)-one and H₂pzpymt = 1H-pyrazolo[3,4-d]-pyrimidine-4(5H)-thione; en = ethane-1,2-diamine] were thermally or photochemically prepared and characterized by elemental analysis, UV/VIS absorption and ¹H and ¹³C NMR spectra. The crystal structure of [Co(put)(en)₂]Cl·2H₂O was determined. The put ligand co-ordinates through S⁶ and N⁷ forming a five-membered chelate ring. The other purine-6-thione ligands all adopt this mode rather than the four-membered one of N¹/S⁶. Carbon-13 NMR spectroscopy is very useful for the assignment of the above linkage isomers.