E.S.R. studies of the solute-solute interactions between copper(II) and nickel(II) thiosemicarbazone chelates in non-aqueous solutions

The X-band e.s.r. spectra due to the copper(II) chelates of the thiosemicarbazones salicylaldehyde thiosemicarbazone (stsc), salicylaldehyde 4-methyl(thiosemicarbazone) (smtc), salicylaldehyde 4- ethyl-(thiosemicarbazone) (setc), salicylaldehyde 4- phenyl(thiosemicarbazone) (sptc), 2-hydroxyacetophen- one 4- ethyl(thiosemicarbazone) (aetc) and 2-hydroxypropiophenone 4- ethyl(thiosemicarbazone) (petc) dissolved in various organic solvents have been studied at room temperature and down to 77 K. The e.s.r. spectra show evidence of hyperfine structure due to the 14N nucleus of the ligand. Addition of the nickel(II) chelate of the thiosemicarbazone ligands to organic solvent solutions of the corresponding copper(II) chelate brings about a profound change in the e.s.r. spectrum of the copper(II) chelate in frozen solution. These changes are interpreted as arising from a change in the ground state of the copper(II) ion from essentially dx2-y2 to d3z2-r2, which arises as a result of specific solute- solute interactions between the copper(II) and nickel(II) chelates.