Designed Topology and Site‐Selective Metal Composition in Tetranuclear [MM′⋅⋅⋅M′M] Linear Complexes

The ligand 1,3‐bis[3‐oxo‐3‐(2‐hydroxyphenyl)propionyl]benzene (H 4 L), designed to align transition metals into tetranuclear linear molecules, reacts with M II salts (M=Ni, Co, Cu) to yield complexes with the expected [MM⋅⋅⋅MM] topology. The novel complexes [Co 4 L 2 (py) 6 ] ( 2 ; py=pyridine) and [Na(py) 2 ][Cu 4 L 2 (py) 4 ](ClO 4 ) ( 3 ) have been crystallographically characterised. The metal sites in complexes 2 and 3 , together with previously characterised [Ni 4 L 2 (py) 6 ] ( 1 ), favour different coordination geometries. These have been exploited for the deliberate synthesis of the heterometallic complex [Cu 2 Ni 2 L 2 (py) 6 ] ( 4 ). Complexes 1 , 2 , 3 and 4 exhibit antiferromagnetic interactions between pairs of metals within each cluster, leading to S =0 spin ground states, except for the latter cluster, which features two quasi‐independent S =1/2 moieties within the molecule. Complex 4 gathers the structural and physical conditions, thus allowing it to be considered as prototype of a two‐qbit quantum gate.