Studies of Proton-Ligand and Metal-Ligand Stability Constants of Cu(II) and Ni(II) Complexes of Substituted 1,3-Thiazines

Abstract

The interactions of Cu(II) and Ni(II) metal ions with (i) 4-(2-
hydroxy-5-methylphenyl)-5-benzoyl-6-(2'-furyl)-2-imino-6H-2,3-
dihydro-1,3-thiazine (L₁). (ii) 4-(2-Hydroxy-5-methylphenyl)-6-(4-
methoxyphenyl)-2-imino-6H-2,3-dihydro-1,3-thiazine (L₂) have
been studied at 0.1 M ionic strength. It is observed that and Cu(II)
and Ni(II) metal ions form 1 : 1 and 1 : 2 complexes with L₁ and
L₂. The substituted 1,3-thiazines show formation of stepwise complexes.
The order of proton-ligand stability constant is as
pK_L1 > pK_L2 . The data obtained for pK and log K are used (i) to
see the effect of substitutents, (ii) to check the validity of
log K = a pK + b. Here proton-ligand and metal-ligand stability
constants have been studied pH-metrically by Calvin-Bjerrum titration
technique.