The spin-polarized transport characteristics of homocatenated clusters of group 14 elements have been studied using the non-equilibrium Green's function formalism. Compared with the carbon cluster, silicon and germanium clusters with extended sigma-conjugation had a high tunnel magnetoresistance (TMR) ratio at a low bias voltage. This phenomenon was caused by the low energy level of the LUMO from s-conjugation extended throughout the whole molecule and by the spin polarization of the sulfur located between the sigma-conjugated system and the ferromagnetic electrode. (C) 2017 Elsevier B.V. All rights reserved.