A series of calix[5]arene bismuth(III) and antimony(III) mono- and bimetallic complexes were synthesized and fully characterized by NMR, X-ray, IR, mp, UV-Vis and elemental analysis. Reaction of p-tert-butylcalix[5]arene (tBuC5(H)5) trianionic salts M'3.tBuC5(H)2 (M'=Li, Na, K) with MCl3 (M=Bi, Sb) yielded monometallic complexes [Bi{tBuC5(H)2}] 1 and [Sb{tBuC5(H)2}] 2, respectively. 1H NMR spectra of both complexes showed two remaining OH groups available for further reactivity. Alternatively, complexes 1 and 2 can be obtained by reacting tBuC5(H)5 in a 1:1 ratio with M(OtBu)3, but the yields are lower. When the tBuC5(H)5 lower rim monobenzyl ether [tBuC5(Bn)(H)4] is treated in a 1:1 ratio with Bi(OtBu)3, the monometallic complex [Bi{tBuC5(Bn)(H)}]2 3 is prepared. If, however, [tBuC5(Bn)(H)4] reacts with Sb(NMe2)3 or Sb(OtBu)3 in a 1:2 ratio the production of the bimetallic complex [Sb2O{tBuC5(Bn)}] 4 is observed. p-Benzylcalix[5]arene (BnC5(H)5) reacts with excess Bi(OtBu)3 to produce the bimetallic complex [Bi2O{BnC5(H)}]2 5. 1H NMR spectra of 5 display patterns characteristic for a cone conformer in solution. Treatment of calix[5]arene [HC5(H)5] with one equivalent of Bi[N(SiMe3)2]3 or with 0.75 equivalents of Sb(NMe2)3 yields bimetallic complexes [Bi2O{HC5(H)}] 6 and [Sb2O{HC5(H)}] 7, respectively. The reactivity of monometallic complexes 1 and 2 was tested in order to investigate the availability of their remaining OH groups. Treatment of 1 with Bi(OtBu)3 at ambient temperature yields bimetallic complex [Bi2O{tBuC5(H)}]2 8 while the reaction of complex 2 with Sb(OtBu)3 in a 1:1 ratio produces complex [Sb2O{tBuC5(H)}] 9. The crystal structures of the monometallic bismuth complexes 1 and 3 display dimeric units with the calixarene ligands in distorted cone and "paco-in" conformations, respectively. Complexes 4, 7 and 9 are all monomeric units, displaying [(RO)2Sb]2(micro-O) cores and the calixarene ligands in 1,2-alternate conformation. The dimeric units of bimetallic complexes 5 and 8 contain Bi4O2(OR)8 core structures that force the calixarene ligands to adopt a flattened cone conformation.