Stability of the three tetracoordinated dianions Ni(CN)42-, Cr(SCN)42-, and Cu(N3)42-

Using quantum chemistry calculations, we have explored the physical properties of three tetracoordinate dianions, Ni(CN)42-, Cr(SCN)42-, and Cu(N3)42-, and find that the electronic and geometrical stabilities are in qualitative accordance with previous experimental findings. Density functional theory reproduces results for Ni(CN)42- obtained by more elaborate coupled cluster calculations. At the B3LYP/6-311++G(3d,2p)//B3LYP/6-31+G(d,p) level of theory, the adiabatic electron binding energies are 1.43 eV, −0.11 eV, and 0.16 eV for Ni(CN)42-, Cr(SCN)42-, and Cu(N3)42-, respectively, and the reaction energies for loss of a negatively charged ligand are 1.43 eV, −0.56 eV, and −1.57 eV.