STUDIES ON MIXED CHELATES .19. 5-COORDINATE NICKEL(II) COMPLEXES WITH N,N,N',N'',N''-PENTAMETHYLDIETHYLENETRIAMINE AND BETA-DIKETONATES

Mixed Ni(II) chelates with N,N,N',N'',N''-pentamethyldiethylenetriamine (pmdt) and a beta-diketonate (dike) such as acetylacetonate(acac), dipivaloylmethanate(dipm), pivaloyltrifluoroacetonate(pfac), trifluoroacetylacetonate(tfac) or hexafluoroacetylacetonate(hfac) were prepared, and their structure and properties were studied. X-Ray crystal analysis confirmed that [Ni(acac)(pmdt)]ClO4 is a distorted square pyramidal complex, and the solid reflection spectra of the remaining chelates indicated that most of them are also essentially square pyramidal. This structure is retained in a nonpolar solvent like 1,2-dichloroethane, but in strong donor solvents like DMSO or DMF it is converted into a 6-coordinated structure, [Ni(dike)(pmdt)(Solvent)]+, containing a solvent molecule. The formation of this species is favored by increasing donor number(DN) of the solvent, and in the following order of dike:dipm<acac<<tfac, pfac<<hfac, which is almost opposite to the order of their pK(a) values.