Cobalt(III) complexes of monodentate N(9)-bound adeninate (ade -), [Co(ade-κ N9)Cl(en)2]+ (en = 1,2-diaminoethane): Syntheses, crystal structures, and protonation behaviors of the geometrical isomers

Takayoshi Suzuki, Yoko Hirai, Hideaki Monjushiro, Sumio Kaizaki

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In acidic aqueous solution, a cobalt(III) complex containing monodentate N(9)-bound adeninate (ade-), cis-[Co-(ade-κ N 9)Cl(en)2]Cl (cis-[1]Cl), underwent protonation to the adeninate moiety without geometrical isomerization or decomposition of the CoIII coordination sphere, and complexes of cis-[CoCl(Hade)(en) 2]Cl2 (cis-[2]Cl2) and cis-[Co-(H 2ade)Cl(en)2]Cl3 (cis-[3]Cl3) could be isolated. The pKa values of the Hade and H2ade + complexes are 6.03(1) and 2.53(12), respectively, at 20 °C in 0.1 M aqueous NaCl. The single-crystal X-ray analyses of cis-[2]Cl 2·0.5H2O and cis-[3]Cl2(BF 4)·H2O revealed that protonation took place first at the adeninate N(7) and then at the N(1) atoms to form adenine tautomer (7H-Hade-κ N9) and cationic adeninium (1H,7H-H 2ade+-κ N9) complexes, respectively. On the other hand, addition of NaOH to an aqueous solution of cis-[1]Cl afforded a mixture of geometrical isomers of the hydroxo-adeninato complex, cis- and trans-[Co(ade-κ N9)(OH)(en)2]+. The trans-isomer of chloro-adeninato complex trans-[Co(ade-κ N 9)Cl(en)2]BF4 (trans-[1]BF4) was synthesized by a reaction of cis-[2](BF4)2 and sodium methoxide in methanol. This isomer in acidic aqueous solution was also stable toward isomerization, affording the corresponding adenine tautomer and adeninium complexes (pKa = 5.21(1) and 2.48(9), respectively, at 20 °C in 0.1 M aqueous NaCl). The protonated product of trans-[Co(7H-Hade-κ N 9)Cl(en)2](BF4)2·H 2O (trans-[2](BF4)2·H2O) could also be characterized by X-ray analysis. Furthermore, the hydrogen-bonding interactions of the adeninate/adenine tautomer complexes cis-[1]BF4, cis-[2](BF4)2, and trans-[2](BF4)2 with 1-cyclohexyluracil in acetonitrile-d3 were investigated by 1H NMR spectroscopy. The crystal structure of trans-[Co(ade)(H 2O)(en)2]HPO4·3H2O, which was obtained by a reaction of trans-[Co(ade)(OH)(en)2]BF4 and NaH2PO4, was also determined.

Original languageEnglish
Pages (from-to)6435-6444
Number of pages10
JournalInorganic Chemistry
Issue number20
Publication statusPublished - Oct 4 2004
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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