The flexibility of molecular components as a suitable tool in designing extended magnetic systems

Abstract

In this work we show how the design of n-dimensional magnetic compounds (nD with n = 1–3) can strongly benefit from the use crystal engineering techniques, which can give rive to structures of different shapes with different properties. We focus on the networks built by assembling the malonato-bridged tetranuclear copper(II) units Cu₄(mal)₄ (mal²⁻ is the dianion of propanedioic acid, H₂mal) through the potentially bridging 2,4′-bipyridine (2,4′-bpy), 4,4′-bipyridine (4,4′-bpy) and pyrazine (pyz). The magneto-structural study of the complexes of formula [Cu₄(mal)₄(2,4′-bpy)₄(H₂O)₄]·8H₂O (1), [Cu₄(mal)₄(H₂O)₄(4,4′-bpy)₂] (2) (this compound was the subject of a previous report but it is included here for comparison) and [Cu₄(mal)₄(pyz)₂]·4H₂O (3) reveals that the ferromagnetically coupled Cu₄(mal)₄ unit which occurs in 1–3 is propagated into two- (2) and three-dimensions (3) by using 4,4′-bpy and pyz as linkers, respectively. Whereas in the case of complex 1, this tetranuclear unit is magnetically isolated, significant antiferromagnetic interactions between these units mediated by the bridges 4,4′-bpy and pyz occur in 2 and 3.