A novel extended covalent tripod for assembling triple-helical nine-co-ordinated lanthanide(iii) podates: the rational design of a single conformerElectronic supplementary information (ESI) available: tables of molecular peaks obtained by ESI-MS (Table S1), elemental analyses (Table S2), structural data for the lanthanide co-ordination sphere in [Eu(L13)](ClO4)3 (19, Table S3) and paramagnetic 1H NMR shifts (Table S4). Figures showing views of [Eu(L13)]3+ along (Fig. S1) and perpendicular to (Fig. S2) the 3-fold axis. See http://www.rsc.org/suppdata/dt/b3/b303404f/