Synthesis and stereochemistry of cobalt(III) complexes containing 2-thiocytocine and derivatives

Abstract

Three series of mixed-ligand cobalt(III) complexes containing four-membered N,S chelates [CoL_n(en)_3–n]^(3–n)+[n= 1 or 2; HL = 2-thiocytocine (4-aminopyrimidine-2-thione, Hapymt), 4,6-diaminopyrimidine-2-thione (4,6-Hdapymt) or 2,4-diaminopyrimidine-6-thione (2,4-Hdapymt); en = ethane-1,2-diamine] have been prepared photochemically and/or thermally and characterized by elemental analysis, UV/VIS absorption, and ¹H and ¹³C NMR spectra. The crystal structure of [Co(apymt)(en)₂][ClO₄]₂ was determined from 1897 observed reflections to R= 0.048 (R′= 0.053): space group Pbca(orthorhombic) with a= 11.849(7), b= 27.551(8), c= 11.201(3)Å and Z= 8. The apymt ligand co-ordinates through the N¹ and S² donors and the complex adopts a remote linkage form where the C⁴ amino group is distant from the en chelate rings. A new type of intramolecular hydrogen bond between the co-ordinated sulfur atom of one dapymt ligand and one of the amino groups of the other dapymt ligand was found in trans-(S)-[Co(4,6-dapymt)(en)₂]⁺ and trans-(S)-[Co(2,4-dapymt)(en)₂]⁺, which is responsible for their relatively high formation yield.