The metallic skeleton describes a [Mn III 3Na6] tricapped trigonal prism with the Na ions sitting on the vertices and the Mn ions capping the square faces. A disordered [CO3] 2-ion sits in the centre of the cage, bonding to all nine metal ions (Mn-O, ~2.14-2.21 Å; Na-O, 2.43-2.48 Å). The square pyramidal Mn ions sit in the phenolic TBC [4] pockets and thus have [MnO5] coordination geometries with a sixth, longer contact to a MeCN molecule of crystallisation that sits in the TBC [4] cavity (~4.1 Å). The Mn-O(carbonate) bond (~2.14-2.21 Å) is significantly longer than the four Mn-O (phenoxide) bonds (~1.92-1.93 Å). The TBC [4] ions are all in their maximal µ5-bridging mode, each O-arm bonded to a Mn ion and further bridging to a Na ion, thus directing the formation of square pyramidal [MnNa4(TBC [4])] building blocks (for example as shown by Mn2, Na2, Na3, Na2* and Na3* in Fig. ). The triangular [Na3] faces of the prism are capped by a disordered mixture of one Cl -ion (Na•••Cl, ~2.6-2.7 Å) and one dmso molecule (Na•••O, ~2.4-2.6 Å), both present at 50% occupancy. The latter is asymmetrically situated with one Na-O distance of ~2.58 Å and two Na-O distances in the range ~2.42-2.48 Å. The remaining site on each 5-coordinate, distorted square pyramidal Na ion is occupied by a dmso molecule. The Na ions in 1 originate from the NaOH employed to deprotonate the H4TBC [4] ligands, and the [CO3] 2-ion from the fixation of atmospheric CO2. Deliberate addition of carbonate in the form of Na2CO3 or NaHCO3 increases the yield of 1 approximately two-fold (see the experimental section for details). We note the structure of 1 is rather similar to the TBC [4]-supported tricapped trigonal prisms [Cu II 9(OH)3(TBC [4])3Cl2(dmso)5.5(EtOH)0.5][Cu I Cl2] and [Cu II 9(OH)3(TBC [4])3(NO3)2(dmso)6](NO3). However, the Cu II -based cages do not contain a [CO3] 2-ion and neighbouring vertex Cu II ions in the trigonal prism are connected to each other with µ-OH -ions. Alongside the larger anionic radius of Na, the result is that the dimensions of the prisms are rather different, with [Mn3Na6] being "taller and thinner" than the "shorter and wider" [Cu9] (Fig ). Comparison of these [Cu9] and [Mn3Na6] cluster motifs shows remarkable similarity despite the marked change in the anions present in the centre of the cores, 3 x µ-OH -or 1 x µ6-CO3 2- respectively. This warrants further investigation into the nature of the anions in this general tricapped trigonal prismatic cluster topology, results of which will be reported in due course.