SYNTHESIS AND STEREOCHEMISTRY OF COBALT(III) COMPLEXES CONTAINING PURINE-6-THIONE AND RELATED LIGANDS

Seven cobalt(III) complexes containing five purinethiones [Co(L-N,S)(e n)(2)](n+) and [H(n)L - H(2)put = 9H-purine-6(1H) -thione, H(2)aput = 2-amino-9H-purine-6(1H)-thione, H(3)tpuo = 3,6-dihydro-6-thioxo-9H-pur ine-2(1H)-one, H(3)oput = 2,3-dihydro-2-thioxo-9H-purin-6(1H)-one and H(2)pzpymt = 1H-pyrazolo[3,4-d]-pyrimidine-4(5H)-thione; en = ethane-1 ,2-diamine] were thermally or photochemically prepared and characteriz ed by elemental analysis, UV/VIS absorption and H-1 and C-13 NMR spect ra. The crystal structure of [Co(put)(en)(2)]Cl . 2H(2)O was determine d. The put ligand co-ordinates through S-6 and N-7 forming a five-memb ered chelate ring. The other purine-6-thione ligands all adopt this mo de rather than the four-membered one of N-1/S-6. Carbon-13 NMR spectro scopy is very useful for the assignment of the above linkage isomers.