The synthesis and the crystal structure refinement for the superstructure of KNa2[NiO2] are reported (orthorhombic, Cmca, Z = 8, a = 6.261(3) Angstrom, b = 10.474(3) Angstrom, 12.472(7) Angstrom). It is compared with the subcell, described recently. EPR measurements of powder and single crystal samples of K-3[NiO2] and KNa2[NiO2] are presented, and confirm a (2) Sigma(g) ground state for the "Linear" [NiO2](3-) complexes in these compounds. Absorption spectra have been measured between 4500 and 20000 cm(-1) For the first time both d-d transitions of a "Linear" d(9)-system are resolved, and the energies of these have been analyzed using the angular overlap model. The near-infrared bands of K-3[NiO2] exhibit fine structure at low temperature, allowing comparison of the Ni-O symmetric stretching frequencies and bond lengths in the ground and excited states.