First principles studies on the geometry, electronic structure and magnetic properties of neutral, cationic, and anionic Fe2Sin (1 <= n <= 12) have been performed to better understand magnetic dopants in silicon. The doubly- Fe doped clusters in the size range 1 <= n <= 12 are marked by finite spin moments at the Fe sites, and Fe2Si3, Fe2Si4, and Fe2Si7 are found to exhibit antiferromagnetic coupling. Fe2Si3 and Fe2Si12 are relatively stable. We find that short Fe-Fe bond distances correlate with ferromagnetic coupling due to the destabilization of antibonding orbitals between the iron sites, while longer Fe-Fe bond distances lead to nonbonding atomic orbitals that favor antiferromagnetic coupling. (C) 2018 Elsevier B.V. All rights reserved.