By performing first-principles calculations, the intriguing electronic and magnetic properties of the semidecorated sheets of group-IV and III-V binary compounds are investigated. Our results indicate that the semifluorinated and semihydrogenated ab (ab = SiC, GeC, SnC, BN, AlN, and GaN) sheets exhibit diverse electronic and magnetic properties. Accordingly, the electronic and magnetic properties of the semidecorated sheets can be precisely modulated by controlling the adsorbed atoms on the a sites. Further, the preference of ferromagnetic or antiferromagnetic coupling can be attributed to the combined effects of both through-bond spin polarization and p-p direct interaction for the semidecorated ab sheets. (C) 2011 Elsevier B. V. All rights reserved.