DINUCLEAR 5-COORDINATED MIXED-LIGAND COMPLEXES .1. INTERACTION OF NICKEL(II) COMPLEXES WITH NONAQUEOUS SOLVENTS

The dinuclear 5-coordinate Ni(II) complex [Ni-2(taet)(pmdt)(2)](2+), w here taet = 1,1,2,2-tetraacetylethanate and pmdt = N,N,N',N'',N''-pent amethyldiethylenetriamine, has been prepared and characterized by vibr ational and electron spectroscopy and by magnetic measurements. In non -coordinating solvents such as DCE or NM and with non- or weakly coord inating anions like ClO4- or B phi(4)(-) these complexes occur as bis- five-coordinate species. In solvents with stronger donor properties (F a or DMF) and with more strongly coordinating anions, mono- or bis-oct ahedral species are formed. Spectrophotometric titration was used to e valuate equilibrium constants and associated reaction enthalpies and e ntropies for the stepwise coordination of donor solvents in DCE. Free energy changes are found to be entropy controlled.