Novel heteroditopic chelate for self-assembled gadolinium(iii) complex with high relaxivityElectronic Supplementary Information (ESI) available: synthesis and analytical data for tpy-DTTA4? and for the complexes. See http://www.rsc.org/suppdata/cc/b4/b400169a/

[Fe(tpy-DTTA)(2)Gd(2)] is a self-assembled trinuclear complex based on a novel ligand in which a terpyridine and a poly(amino carboxylate) moiety are connected; it has a well-defined topology with favourable features to attain high relaxivities, i.e. a rigid Fe(II)(tpy)(2) core, reduced flexibility at the periphery thanks to a short linker, and efficient separation of the two Gd(III) centres.