Influence of the coligand in the magnetic properties of a series of copper(ii)–phenylmalonate complexes

Abstract

This work presents a series of layered systems based on phenylmalonate-containing copper(II) complexes and different coligands. Eight compounds [Cu(L)(Phmal)]_n where L = pyrimidine (pym, 1) pyrazine (pyz, 2), 3-cyanopyridine (3-CNpy, 3), 4-cyanopyridine (4-CNpy, 4), 3-fluoropyridine (3-Fpy, 5), 3-chloropyridine (3-Clpy, 6), 3-bromopyridine (3-Brpy, 7) and 3-iodopyridine (3-Ipy, 8), have been synthesized and magneto-structurally characterized. The coligands selected not only modify the coordination environment of the metal ion, blocking or extending the polymerization, but also interact with the phenyl ring of the phenylmalonate ligand and dramatically affect the crystal packing through weak interactions. The crystallographic analysis reveals that compounds 1–8 present a corrugated square grid of carboxylate bridged copper(II) atoms where the pyridine ligands are alternatively located above and below each layer and, at the same time, inversely to the position of the phenyl group of the Phmal ligand. It is important to note that the pym and pyz ligands in 1 and 2 do not act as bridges between two copper atoms, whereas weak interactions between the cyano groups are also present in the structures of the complexes 3 and 4. The increase of the Van der Waals radius of the halogen along the series 5–8 accounts for the increase of the interlayer separation. Variable-temperature magnetic susceptibility measurements show the occurrence of different magnetic behaviours. Weak interactions are expected for the anti–syn carboxylate bridge in the out-of-plane configuration, that can be either ferro- or antiferromagnetic. Therefore, in this manuscript we shed light on the influence of the magneto-structural relationship in these square grid layered Cu(II) complexes.