We then carried out solution-phase XAS measurements to determine whether the results obtained from the SC-XRD analysis could be extended to the solvated states of 2a and 3a. A magnified view of the pre-edge and edge region of the Ni K-edge X-ray absorption near edge structure (XANES) is shown in Figure . In the case of 2a, a pre-edge peak corresponding to the electric dipole transition from the Ni 1s orbital to the Ni 4p(-3d) orbitals was observed at 8326 eV and no characteristic peak was detected at the absorption edge, which is typical for nickel complexes with tetrahedral geometry. Meanwhile, a remarkable peak appeared in the edge region (8331 eV) for 3a, along with the greater pre-edge peak intensity compared to 2a. We attribute the characteristic edge peak to the Ni 1s→4pz transition in 3a, given the presence of the non-bonding 4pz orbital (a2'' symmetry) (Figure ). Considering that such non-bonding 4pz orbitals are commonly found in trigonal-planar 16-electron complexes, the results of the solutionphase XAS experiments clearly rationalize the adoption of a trigonal-planar geometry by 3a, even in toluene, as observed in the crystal structure.