Design of complex molecular architectures starting from constituent subunits is a central theme in inorganic chemistry. [1] Among such species, those containing magnetic ions are of particular interest because their magnetic properties directly stem from the geometrical arrangement of the constituent subunits. [2] The main challenge in this field is the synthesis of single-molecule magnets whose ground states have high spin and considerable negative axial anisotropy. [3] Pathways to such complex molecular entities are based on two orthogonal synthetic schemes: self-assembly methods [4] and step-by-step strategies. [5] In the former, the nature of the final products cannot be determined a priori. In contrast, the latter provide an efficient means to control both nuclearity and dimensionality of the polymetallic edifice.
Following a step-by-step approach, we prepared the new ligand N,N',N''-1,3,5-benzenetris(oxamate) (1). Being incapable of hexadentate ligation to a single metal center, this ligand rather self-assembles with Cu II ions in a 2/3 ligand/metal ratio to give the trinuclear complex Na 6 [Cu II 3 (1) 2 ]•11.5 H 2 O (Na 6 -2•11.5 H 2 O). In the [Cu II 3 (1) 2 ] 6À core 2, each ligand adopts a tris(N,O-bidentate) coordination mode (vide infra). Thus, the three bis(oxamate)copper(ii) spin-bearing residues are bridged by two 1,3,5-benzenetriyl moieties, which have already proved to be efficient ferromagnetic spin-coupling units in p-conjugated organic polyradicals [6] and metal complexes. [7][8][9][10] Additionally, 2 is a potential hexakis-bidentate ligand that can coordinate six other metal ions through its external oxygen atoms. Using this "complex-as-ligand strategy" with ancillary ligands on the additional metal ions to avoid polymerization, we obtained the novel homometallic enneanuclear complex [{Cu II 3 (1) 2 }{Cu II (pmdien)} 6 ]-(ClO 4 ) 6 •12 H 2 O (3-(ClO 4 ) 6 •12 H 2 O; pmdien = N,N,N',N'',N''pentamethyldiethylenetriamine).