Effect of a metal ion on intramolecular spin exchange in spin-labeled complexes

The characteristic features of intramolecular spin exchange in 14 complexes of Ag-I, Hg-II, Ni-II, Pd-II, Pt-II, Au-III, and Pt-IV with spin-labeled l igands were studied by ESR spectroscopy. The measured values of the exchang e integral \J\ and the differences between the enthalpies of the efficient conformations (Delta H) were compared with the electronic polarization (ref raction) R-f of the Ni-II, Pd-II, and Pt-II ions and Klopman's rigidity par ameters sigma(K), which characterize the total polarazibility of the ions a nd the degree of covalence of the bond between the metal atom and the donor atom of the ligand, respectively. Delocalization of the electron spin dens ity and the efficiency of spin exchange are determined by the relative cont ributions of the s, p, and d orbitals. which produce the overlap integral o f wave functions, \J\, and by the geometric features of the coordination po lyhedron, which affect the mutual orientation of the N-O fragments.