Synthesis, crystal structure, and physical properties of KNa2[NiO2] and K-3[NiO2] containing linear [NiO2](3-) anions

The synthesis and the crystal structure refinement for the superstructure of KNa 2[NiO 2] are reported (orthorhombic, Cmca, Z = 8, a = 6.261(3) Å, b = 10.474(3) Å, c = 12.472(7) Å). It is compared with the subcell, described recently. EPR measurements of powder and single crystal samples of K 3[NiO 2] and KNa 2[NiO 2] are presented, and confirm a 2Σ g ground state for the "linear" [NiO 2] 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[NiO 2] exhibit fine structure at low temperature, allowing comparison of the Ni-O symmetric stretching frequencies and bond lengths in the ground and excited states. © 1995 American Chemical Society.