| Popis: |
Six tetraamine ligands, 2,5,8,11-tetraazadodecane, 2,5,9,12-tetraazatridecane, 3,7-dimethyl-3,7-diazanonane-l,9-diamine, 2,6,9,13-tetraazatetradecane, 4,7-dimethyl-4,7-diazadecane-l,10-diamine, 4-methy]-4,7-diazadecane-l,10-diamine, and their nickel(II) complexes have been synthesized. The equilibrium constants and thermodynamic parameters of the high-spin-low-spin conversion of these complexes at various temperatures in 0.10 M NaC1O4 have been investigated by spectrophotometric techniques. Influences of the enthalpies of these reactions are attributed to an endothermic contribution due to the breaking of the two Ni-OH2 bonds, an exothermic contribution due to the strengthening of the four in-plane Ni-N bonds, an exothermic contribution due to the different ligand field stabilization energies of the square-planar and the octahedral complexes, an endothermic contribution due to the steric repulsions between the N-methyl group(s) and methylene groups as well as that between the two N-methyl groups of the tetraamine, an exothermic contribution due to the steric repulsions between the N-methyl group(s) and the coordinated water molecules, and an exothermic contribution due to the inductive effect of the N-methyl group(s). The important factors influencing the values of the entropies of these reactions are a negative term due to the reduction of spin multiplicity and a large positive term due to the release or the mobilization of the two coordinated water molecules. |
Plný text