[n + n]-Heterometallomacrocyclic complexes (n < or = 2) prepared from platinum(II)-centred ditopic 2,2':6',2''-terpyridine ligands: dimensional cataloguing by pulsed-field gradient spin-echo NMR spectroscopy

The reaction of 4`-(2-propyn-1-oxy)-2,2`:6`,2``-terpyridine (HC equivalent to CCH(2)Oterpy) with trans-[PtI2(PR3)(2)] (R = Et, Bu-n, Ph) results in the regioselective formation of the metalloditopic ligands trans-[Pt(C equivalent to CCH(2)Oterpy)(2)(PR3)(2)], crystallographic data for which are presented. Each ditopic ligand reacts with FeCl2 center dot 4H(2)O to give heterometallomacrocycles, the smallest of which is a [2 + 2] macrocycle, confirmed structurally for R = Et. The NMR spectroscopic data confirm the formation of symmetrical species, i.e. macrocyclic and not polymeric species. The distribution of products has been investigated using pulsed-field gradient spin-echo (PGSE) diffusion NMR spectroscopy, and indicates that the kinetic products from the reactions of 1, 2 or 3 (L) with iron(II) are [FenLn](2n+) with n = 2, 3 or 4. For L = 1 and 2, these mixtures of products convert in solution to the thermodynamically favoured [Fe2L2](4+).