A new tetrameric CuII cluster with square topology exhibiting ferro- and antiferromagnetic magnetic pathways : which is which?

[Cu(4)L(2)(bpy)(4)(H(2)O)(3)](ClO(4))(4).2.5H(2)O, 1, a new tetranuclear Cu(II) cluster showing square planar geometry, formed with aspartate bridging ligand (L) has been synthesized. The global magnetic coupling is ferromagnetic but theoretical DFT/B3LYP calculations are necessary to assign which Cu-L-Cu side is ferro or antiferromagnetically coupled.