Structural and magnetic analysis of retrosynthetically designed architectures built from a triply bridged heterometallic (CuL)₂Co node and benzenedicarboxylates

Abstract

The flexible trinuclear metallatecton {(CuL)₂Co}²⁺ [H₂L = N,N′-bis(salicylidene)-1,3-propanediamine] has been used as a building block and its coordinative interaction with ortho-, meta-, and para-benzenedicarboxylates (BDCs) has been investigated to evaluate the positional isomeric effect of these carboxylate ligands on the resulting compounds. Structural characterization reveals that o-H₂BDC produces a discrete trinuclear complex, namely [(CuL)₂Co(o-HBDC)₂]•H₂O (1). As expected from the retrosynthetic design, one-dimensional (1D) coordination polymers, i.e. [{(CuL)₂Co(m-BDC)}•CH₃OH]_∞ (2) and [{(CuL)₂Co(p-BDC)}•2CH₃OH]_∞ (3), are obtained with m-BDC and p-BDC linkers, respectively. In all three complexes, the triply bridged bimetallic trinuclear coordination clusters are linear and solely a syn-syn bridging mode is observed for the carboxylates. In 2, the nodes are connected sidewise and are inclined toward each other to be accommodated by the 120°-angular m-BDC units, whereas in 3, the linear p-BDC linkers connect the parallel nodes diagonally. These differences in connectivity give rise to one-dimensional “great wall”-like chains for 2 and to quasi-linear coordination chains for 3. These distinct one-dimensional propagations induced by the different BDC isomers influence the three-dimensional columnar packing of 2 and 3. Magnetic susceptibility measurements and fitting of the results confirm that these three compounds are made by analogous magnetic building blocks, with very similar antiferromagnetic intramolecular magnetic exchange (with J in the –16.96 to –11.80 cm^–1 range, using the –2JS₁S₂ convention). The structural homogeneity of the magnetic fragment within this family of compounds has allowed magnetostructural correlations to be explored, which has not previously been attempted.