Dinuclear helicate and tetranuclear cage assembly using appropriately designed ditopic triazole-azine ligands

Four new, symmetrical, bis-bidentate ditopic Rdpt-type, Rat (R azine-triazole), ligands have been prepared, Lnpym-meta/para (n = 2 or 4), which contain bidentate n-pyrimidine/triazole binding pockets connected through an appropriate aromatic spacer, meta/para-phenyl, to enable assembly into dinuclear helicates or tetranuclear tetrahedral cages, respectively. The 3:2 self assembly reactions of each Lnpym-meta/para ligand with iron(ii) tetrafluoroborate gave the desired complexes, as shown by X-ray crystal structure determinations of the pair of helicates [FeII2(Lnpym-meta)(3)(BF4)(4)]6CH(3)CN, with n = 2 (16CH(3)CN) or 4 (26CH(3)CN), and the pair of Td cages [FeII4(Lnpym-para)(6)(BF4)(8)]xsolvent, with n = 2 (3xsolvent) or 4 (4xsolvent). Reversible Fe-II/III processes at E-m = 0.95 +/- 0.05 V vs. 0.01 M AgNO3/Ag in MeCN are a feature of 1-4, with little variation in the redox potential as a function of nuclearity, architecture or choice of n-pyrimidine isomer. In all four complexes the iron(ii) centres are low spin, despite having employed the weakest field diazines, the 2- and 4-pyrimidines, in these ditopic Rat ligands. Nevertheless this is an exciting proof of principle that Rdpt-type ligands (previously used to generate about 50 spin crossover-active complexes) can be extended into ditopic forms that are suitable for supramolecular assembly of helicates and cages.