During the last five years a lot of new metallo-organic mesogens have been synthesized. The molecular architecture is more or less modified by the metallic atom and therefore the molecular organization in the columnar, smectic or nematic mesophases containing metals is specific of this new kind of mesogens. We present a comparative study of various series of metallo-organic complexes. In these complexes one (or two) metallic atoms link two (or more) identical mesogenic ligands; the structural features of the mesophases depend on the nature of the metal bridge, and of the length and the nature of the ligand. It is also possible to compare, in their respective mesophases, the organization of the complex to that of ligand alone. The global molecular shape is derived from usual X-ray diffraction experiments. Taking into account some features of the diffraction pattern related to the metal atoms ordering, it is possible to describe the molecular environment. The short-range ordering depends of the nature of the complex. Moreover, there are specific methods of investigation of the metal environment: the comparison of variable wavelength X-ray scattering experiments and neutron scattering experiments might give access to the metal-metal pairs correlation function. At last, by X-ray spectroscopic methods (EXAFS and XANES), it is possible to investigate the close neighbouring of the metallic atom.