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Self-Assembling Synthesis of Cyclic Tri- and Tetranuclear Cobalt(III) Complexes Bridged by Purine-6-thione and Their Characterization by Electrospray Mass Spectrometry and X-ray Crystal Analysis

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posted on 26.09.1998, 00:00 by Kazuaki Yamanari, Ito Fukuda, Tatsuya Kawamoto, Yoshihiko Kushi, Akira Fuyuhiro, Naoko Kubota, Tsuyoshi Fukuo, Ryuichi Arakawa
The cyclic multinuclear complexes [Con(L-N,S,N‘)n(tacn)n]n+ (L = purine-6-thiones; tacn = 1,4,7-triazacyclononane) were synthesized through self-assembly of the mononuclear complex [Co(HL-N,S)Cl(tacn)]+ based on the multidentate bridging ability of purine-6-thione. Three kinds of purine-6-thione ligands were used:  9H-purine-6(1H)-thione (H2put), 2-amino-9H-purine-6(1H)-thione (H2aput), and 3,6-dihydro-6-thioxo-9H-purin-2(1H)-one (H3tpuo). The complexes [Con(L-N,S,N‘)n(tacn)n]n+, n = 3 and 4 for put and n = 4 for aput and Htpuo, were characterized by NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and X-ray crystal structure analysis. ESI-MS proved to be a very powerful tool for determining the nuclearity (n value) unambiguously. X-ray crystal structure analyses of [Co4(put)4(tacn)4](CF3SO3)4·12H2O [triclinic, P1̄ (No. 2)] and [Co4(aput)4(tacn)4]Cl4·16H2O [monoclinic, C2/c (No. 15)] reveal that all purinethione ligands act as tridentate ligands via S6/N(7) chelation and the N(9) bridge and both tetranuclear complexes adopt the cyclic S4 structure which is stabilized by four intramolecular hydrogen bonds between N(3) and H−N(tacn). The trinuclear complex [Co3(put)3(tacn)3]3+ having the C1 structure was optically resolved. Stereochemistry for the cyclic molecular boxes containing chiral octahedral ions is developed.