The IR and electronic excitation spectra of a series of new nickel(II) chelates containing N,N′-diphenylethylenediamine (dianilinoethane, ΦenΦ) and the anion of a 1,3-diketone (β-dione) were obtained in the solid state and in solution. The spectra suggest, in conjunction with other physicochemical measurements, bidentate coordination of the ligands. The composition and the overall structure of the new chelates depend on ligand concentration, on the substituents within the resonance-stabilized β-dionato moiety and the counter-ion present. The IR spectra disclose that the 1,2-diamine adopts the guache conformation and that the energy separation of the bands due to the perturbed ▪ and conjugated ▪ bonds of the β-dionato moiety is unaffected by the change in the coordination number of nickel(II). The ligand-field excitation spectra disclose that in the NiN 2O 2 chromophore the diamine nitrogens are coplanar with the resonance stabilized β-dionato ring, while an octahedral arrangement pertains in the NiH 4O 2 and the NiN 2O 4 chromophores. Solvatochromic shifts indicate that the NiN 2O 2 chromophore interacts with coordinating anions as well as with basic solvents and converts the square-planar structure to octahedral.