Treatment of the heterobimetallic iron(II) alkoxides [(THF)MFe(OtBu)(3)](2) with p-tert-butylcalix[4]areneH(4) (L(1)H(4)) affords the oxo-bridged diiron(III) complexes {Fe[M(NCMe)(x)](2)L(1)}(2)(mu-O), M = Na, x = 2 1 x 8(CH(3)CN), M = K, x = 3 2 x 3.5(CH(3)CN); similar use of p-tert-butylcalix[6]areneH(6) (L(2)H(6)) afforded [{Fe(2)(mu-O)Na(2)(OH(2))(NCMe)(2)L(2)}(2)][{Fe(2)(mu-O)Na(OH(2))(NCMe)(6)L(2)}(2)](2-)[Na(NCMe)(5)](2)(2+) 3 x 9.46(CH(3)CN) and [{Fe(2)(mu-O)L(2)(K(NCMe)(2))(2)}(2)] 4 x 10.8(MeCN), respectively. In the case of 4, a minor product {(L(2)(2)Fe(8)O(8))[K(NCMe)(1.5)K(H(2)O)(NCMe)(2.5)](2)} 5 x 6(CH(3)CN), which is comprised of chains of (L(2)(2)Fe(8)O(8)) clusters bridged by K/MeCN fragments, is also isolated. Use of p-tert-butylcalix[8]areneH(8) (L(3)H(8)) and two equivalents of [(THF)KFe(OtBu)(3)](2) affords [(K(2)(mu-NCCH(3))(4)(mu-OH(2)))(2)(Fe(2)(mu-O)L(3)H(2))(2)(CH(3)CN)(2)] 6 x 9(CH(3)CN). In the case of p-tert-butyltetrahomodioxacalix[6]areneH(6) (L(4)H(6)), reaction with [(THF)MFe(OtBu)(3)](2) (two equivalents) leads to isolation of the pseudoisomorphic complexes [M(2)(CH(3)CN)(4)L(4)Fe(2)(mu-O)] x 4 CH(3)CN M = Na 7 x 4(CH(3)CN), M = K 8 x 2(CH(3)CN); similar use of p-tert-butylhexahomotrioxacalix[3]areneH(3) (L(5)H(3)) led to [Na(2)Fe(2)(mu-OH)(2)(L(5))(2)(CH(3)CN)(4)] 9 x 2(CH(2)Cl(2)). The complex [L(4)(ZnEt)(4)Zn(2)(CH(3)CN)(4)(mu-OEt)(2)], 10 x 2(CH(3)CN), isolated from the reaction of L(4)H(6) and ZnEt(2) is also reported. Complexes 1-10 are structurally characterized (partially in the case of 4) and screened (not 5) as catalysts for the ring opening polymerization of epsilon-caprolactone.