In contrast to former ligand held predictions, the standard energetic order of the metal 3d orbitals, delta< pi < sigma, is not reproduced here. Throughout, the 3d sigma molecular orbital (MO) level is found rather low lying because of sigma-donating ligand induced 3d-4s hybridization in these linear dicoordinated compounds, while the 3d pi is rather high due to the pronounced rr-donor character of the halogen ligands at the short distances of the digonal halides. This results in an unexpected electron distribution for the ground state and in an unusual order of electronic states. The calculations are in general consistent with recent experimental findings. The approach yields semiquantitatively correct geometric parameters and vibrational frequencies, and qualitatively correct trends for the dissociation energies. Those properties show a secondary periodicity, similar to the one known for octahedral high-spin complexes, though for different electronic reasons. Unknown structures, vibrational frequencies, and dissociation energies are predicted.