An unusual dimerization of 6-amino-2-thiouracilate in a cobalt(III) complex

Abstract

Thermal reaction between trans-[CoCl₂(en)₂]Cl (en = ethane-1,2-diamine), H₂atuc (6-amino-2-thiouracil) and NaOH in the presence of activated charcoal produced two red complexes 1 and 2. The crystal structures of complexes 1 and 2 were determined from 5090 and 4567 reflections to R= 0.048 (R′= 0.052) and 0.055 (0.068), respectively. Complex 1 has the composition [Co(atuc)(en)₂]⁺ where atuc co-ordinates through atoms 2-S and 3-N. Complex 2 has an unusual composition [Co(HL)(en)₂]⁺{H₃L = 6-amino-5-[6-amino-4-oxo-(1H)-pyrimidin-2-yl]thio-2,3-dihydro-2-thioxo-(1H)-pyrimidin-4-one}: a new bond is formed between the 5-carbon atom of the co-ordinated atuc and the 2-sulfur atom of an unco-ordinated atuc, that is the atuc is dimerized. This complex has self-associated double intermolecular hydrogen bonds in the crystals in addition to an intermolecular hydrogen bond.