Copper(II)-assisted hydrolysis of 2,4,6-tris(2-pyridyl)-1,3,5-triazine. Part 3. Crystal structures of diaqua[bis(2-pyridylcarbonyl)amido]copper(II) nitrate dihydrate and aquabis(pyridine-2-carboxamide)copper(II) nitrate monohydrate
Abstract
Copper(II) has been found to promote the hydrolysis of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) to yield [bis(2-pyridylcarbonyl)amido]copper(II) and free pyridine-2-carboxamide, NC5H4CONH2. The compounds [Cu{(NC5H4CO)2N}(H2O)2]NO3·2H2O (1) and [Cu(NC5H4CONH2)2(H2O)][NO3]2·H2O (2), where (NC5H4CO)2N– is the bis(2-pyridylcarbonyl)amide anion (L), were grown from aqueous solutions of tptz and copper(II) nitrate. Crystals of (1) and (2) are triclinic, space group P and Z= 2, with a= 6.811(1), b= 10.211(1), c= 12.039(1)Å, α= 88.65(1), β= 82.32(1), and γ= 89.79(1)° for (1) and a= 11.622(3), b= 11.280(3), c= 8.007(3)Å, α= 90.33(2), β= 101.85(4), and γ= 115.28(3)° for (2). The copper(II) ion is five-co-ordinate in both structures and its co-ordination geometry is near square pyramidal. The three nitrogen atoms of the (NC5H4CO)2N– ligand and the oxygen atom of a water molecule form a distorted square plane around the copper ion in complex (1), whereas such a basal plane is built by the pyridine nitrogen and oxygen atoms of two carboxamides in (2). The axial position is filled by a water molecule in both cases. The proton association and acid dissociation constants of the complex [CuL(H2O)]+[equations (i) and (ii)] have been determined by potentiometry in aqueous solution: log K1=[CuL(H2O)]++ H+ [graphic omitted] [Cu(HL)(H2O)]2+(i), [CuL(H2O)]+ [graphic omitted] [CuL(OH)]+ H+(ii) 1.83(1) and log K2=–8.80(1)(25 °C, 0.1 mol dm–3 NaNO3). The co-ordination of L to copper(II) decreases the basicity of the imide nitrogen atom as shown by the low value of log K1. The value of the hydroxo stability constant falls within the range established for hydroxocopper(II) complexes with N-donor tridentate ligands. A discussion of the factors which determine the nature of the isolated products of this copper(II)-promoted hydrolysis is made in the light of the available structures.