[en] In low valency niobium and tantalum halides, interunit linkages are observed between the (Me₆X₁₂)X₆ units. They are insulators and interesting magnetic properties are observed, due to the intrinsic potential magnetism of the Me₆ cluster and depending on the inserted cations, for instance rare earths in MM'Nb₆Cl₁₈ (M = monovalent cation, M' = rare earth). Of special interest are the niobium iodides which exhibit (Me₆X₈)X₆ units, an exception in the niobium chemistry; interesting properties have been reported for some of these iodides