The electronic and magnetic properties of a series of one-dimensional carbon-free sandwich polymers [(Ge 5 )TM] N (TM ¼ Ti, V, Cr, Mn, Fe) are examined, based on first principles calculations. Our results show that all of the five polymers are metallic and magnetic. The polymers [(Ge 5 )V] N , [(Ge 5 )Cr] N and [(Ge 5 ) Mn] N exhibit antiferromagnetic behavior, and the other two polymers [(Ge 5 )Ti] N and [(Ge 5 )Fe] N display ferromagnetic spin ordering. It is found that the magnetic moments are mainly contributed by the TM 3d orbitals. It is predicted that the magnetic properties of [(Ge 5 )TM] N polymers can be manipulated by the use of different combinations of TM atoms. This system is one of the few carbon-free sandwich polymers which can be used in spintronics. These results may pave the way for further experimental studies on molecular spintronics.