Quantum chemical calculations at the gradient corrected DFT level using the exchange correlation functionals BP86 and B3LYP of the geometries of the title compounds are reported. The theoretically predicted bond lengths and angles of the model compounds are in excellent agreement with experiment. The nature of the metal-ligand interactions is quantitatively analyzed with an energy decomposition method. The analysis of the electronic structure of the neutral metal germylyne complexes 1a-1d and the metallogermylenes 11a-11d shows that the former compounds have about the same degree of electrostatic and covalent bonding, while the relative strength of the covalent contributions in the latter molecules is lower (41-42%) than the electrostatic attraction (58-59%). The a"(pi) bonding contribution in the group-6 germylyne complexes 1a-1c is rather high (42% of the orbital interactions). In the iron complex 1d, it is even higher (53.8%) than the a bonding. The or bonding contributions to the covalent bonding become much less (18-20%) in the metallogermylenes 11a-11d.