Fe-4(0+,1+)-(CH4)(n), n = 1-4, systems were studied with the BPW9l/6-311++G(2d,2p) method. In the 2S= 14 (S= total spin) Fe-4-CH4 ground state, (GS) two weak CH Fe bonds are formed and two C-H bonds are activated. For the higher 2S = 12 and 10 energy states, a weak Fe-C bonding also appears. The CH4. adsorption shows magnetic selectivity, because the GS have 2S = 14, 12, and 12 for n = 1, 2, and 3, respectively; n = 4 does not hold. Complete saturation was achieved for [Fe-4-(CH4)(n)]+, n = 1-4, which have 2S = 1'1 GSs and similar C-H activation. (C) 2007 Elsevier B.V. All rights reserved.