The second example, [V V 2(p-tolylN)2(H2TBC [8])] (2), reported in 2001, was made from the reaction of [V(Ntolyl-p)(O t Bu)3] with H8TBC [8] in toluene (Fig. ). Its structure is similar to 1, but with an organoimido (NR 2-) ligand occupying the sixth coordination site on each metal. In this case the calixarene is hexadeprotonated and the complex is neutral. Four other [V dimers are known (Fig. [8])] (6). All are structurally similar to 1 and 2. In each case the sixth coordination site on each V centre is occupied by a terminally bonded O 2-/NR 2-ion, with the calix [8]arene being hepta-deprotonated and charge balance maintained through the presence of a single cation. Compound 5 is made via the reaction of H8TBC [8] with [NaVO(O t Bu)4], the latter being formed in-situ from VOCl3. Increasing the ratio of [NaVO(O t Bu)4] in the reaction leads to the formation of [Na(MeCN)6][V V 8Na7O16(TBC [8])2(MeCN)6] (7). The anionic cluster (Fig. ) sits on an inversion centre, with each half containing four VO2 moieties bonded to four Na ions, one of which is at half-occupancy. Each of the V ions is four coordinate and in tetrahedral {VO4} geometry. The fully deprotonated TBC [8] ligand adopts a pleated-loop conformation, bonded to the four V ions in the asymmetric unit (ASU). Two neighbouring O(Ph) groups possess µ-bridging O-atoms that serve to link the two halves of the molecule together, bonding to a single V ion in one half and to two Na ions on the other half. Charge balance is maintained through the presence of two half-occupancy [Na(MeCN)6] + cations. The same reaction but employing [KVO(O t Bu)4] results in the formation of the alkali-metal-free complex [V V 4O6(TBC [8])] (8; Fig. ). The metal-oxygen core of 8 describes a near planar [(VO)4O2] butterfly, each V ion being five coordinate and in square pyramidal {VO5} geometry. The fully deprotonated TBC [8] ligand adopts a double-cone conformation, lying "above" the [V4] plane (as drawn in Fig. ). Two of the eight O(Ph) atoms are µ-bridging across the body-wing edge of the butterfly, while the remaining six are terminally bonded. Employing LiO t Bu in a reaction with VOCl3 and H8TBC [8] in THF/Et2O leads to the isolation of the heterometallic complex [V V 4Li6O8(TBC [8])(O t Bu)2(THF)2(Et2O)2] (9; Fig. ). [8])(MeCN)2] (11; Fig. ), the hexamer [V V 3V IV 1Nb V 2O9(O n Pr)3(TBC [8])(MeCN)2] (12; Fig. ) and the monomer [HNEt3]2[V V O2(H5TBC [8])] (13; Fig. ). Complexes 10 and 11 result from the reaction of H8TBC [8] with [VO(O i Pr)3] and [Nb(OEt)5] or [Ta(OEt)5] in toluene, followed by crystallisation from MeCN. The central core of each complex contains a (bent) V-O-Nb/Ta-O-Nb/Ta-O-V chain. The fully deprotonated TBC [8] ligand is in the pleated-loop conformation, with each neighbouring pair of O(Ph) atoms chelating to either a V or Nb/Ta ion. The V ions are four coordinate and in {VO4} geometries, the fourth site being occupied by a terminally bonded O 2-ion. The Nb/Ta ions are six coordinate and in octahedral {Nb/TaO5N1} geometries, with their fifth and sixth sites being occupied by MeCN and O i Pr molecules.