Convenient, high-yield routes have been developed to [Fe-10(OMe)(20)(O2CR)(10)] (1) "ferric wheels" involving the alcoholysis of [Fe3O(O2CR)(6)(H2O)(3)](+) salts in MeOH in the presence of NEt3. Reactivity studies have established [Fe-10(OMe)(20)(O2CMe)(10)] (1a) to undergo clean carboxylate substitution with a variety of other RCO2H groups to the corresponding [Fe-10(OMe)(20)(O2CR)(10)] product. In contrast, the reaction with phenol causes a nuclearity change to give a smaller [Fe-8(OH)(4)(OPh)(8)(O2CR)(12)] (2) wheel. Similarly, reactions of [Fe-10(OMe)(20)(O2CR)(10)] with the bidentate chelate ethylenediamine (en) cause a structural change to give either [Fe8O5(O2CMe)(8)(en)(8)](ClO4)(6) (3) or [Fe2O(O2But)(en)(4)](NO3)(3) (4), depending on conditions. Complex 3 possesses a "Christmas-star' Fe-8 topology comprising a central planar [Fe-4(mu(4) -O)](10+) square subunit edge-fused to four oxide-centered [Fe-3(mu(3)-O)](7+) triangular units. Variable-temperature, solid-state dc and ac magnetization studies on complexes 1a-4 in the 5.0-300 K range established that all the complexes possess an S = 0 ground state. The magnetic susceptibility data for 4 were fit to the theoretical chi(M) versus T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed an antiferromagnetic exchange parameter with a value of J = -107.7(5),cm(-1). This value is consistent with that predicted by a previously published magnetostructural relationship. Theoretically computed values of the exchange constants in 3 were obtained with the ZILSH method, and the pattern of spin frustration within its core and the origin of its S = 0 ground state have been analyzed in detail.