Synthesis of heteroleptic violurato complexes of coIII. Influence of the co-ordinated ligands on the protonation–deprotonation reactions of dihydrogenviolurate anion. Crystal structure of potassium dihydrogenviolurato(nitrilotriacetato)cobaltate(III) dihydrate, K[Co(H2vi)(nta)]·2H2O

Abstract

Six cobalt(III) heteroleptic violurato complexes of formula [Co(Hvi)(trien)]Cl·4H₂O, K[Co(H₂vi)(nta)]·2H₂O, [Co(Hvi)(phen)₂]NO₃·5H₂O, [Co(H₂vi)₂(phen)]NO₃·4.5H₂O, Na[Co(Hvi)₂(phen)]·8H₂O, and [Co(H₂vi)(salen)]·4H₂O [H₃vi, trien, nta, phen, and salen being violuric acid (1H, 3H-pyrimidine-2,4,5,6-tetrone 5-oxime, triethylenetetramine, nitrilotriacetate(3–), 1,10-phenanthroline, and N,N′-ethylenebis(salicylideneiminate)(2–)] have been synthesized. The protonation and deprotonation constants of the violurato ligand in these complexes have been determined by potentiometry and the influence on them of the different co-ordinated ligands has been analyzed. The crystal structure of K[Co(H₂vi)(nta)]·2H₂O was solved by direct methods. Crystals of K[Co(H₂vi)(nta)]·2H₂O are monoclinic with a= 21.705(5), b= 9.930(3), c= 7.451 (2)Å, β= 98.24(3)°, space group P2₁/n, and Z= 4. The structure consists of [Co(H₂vi)(nta)]^– anions, potassium cations, and water molecules of crystallization. The cobalt(III) ion is in a trans-N₂O₄ distorted octahedral environment. The H₂vi^– anion is co-ordinated to the metal ion as a bidentate ligand through the oxime nitrogen and one of the amide oxygens. The nitrilotriacetate anion is co-ordinated as a tetradentate ligand with the characteristic butterfly conformation.