Copper(II)-phenylmalonate complexes with the bifunctional ligands nicotinamide and isonicotinamide

The use as coligands of the nicotinamide (nia) and isonicotinamide (inia) molecules in the complex formation between copper(II) and phenylmalonate [Phmal = dianion of phenylmalonic acid] yielded the compounds of formula [Cu(inia)(Phmal)(H2O)] (1) and [Cu(inia)(Phmal)(H2O)]n (2). Although single crystals of 1 of appropriate size were grown, their unresolved twinning and space group ambiguity prevented a satisfactory X-ray structure determination. The crystal structure 2 consists of corrugated layers of copper(II) ions with intralayer carboxylate–phenylmalonate bridges in the anti-syn (equatorial-apical) coordination mode. A water molecule and the isonicotinamide group are coordinated to the copper atom in trans position being located above and below each layer. The Phmal ligand adopts the bidentate/monodentate coordination mode with the bidentate coordination involving one equatorial and one apical bonds, a feature which is unprecedented for the copper(II) complexes with alkyl(aryl)substituted-malonate derivatives. Intra- and interlayer H-bonds together with intralayer π–π type interactions between the phenyl and inia aromatic groups contribute to the stabilization of the three-dimensional supramolecular structure. Magnetic susceptibility measurements of complexes 1 and 2 in the temperature range 1.9–300 K are quasi identical and they correspond to a very weak ferromagnetic interaction between the copper(II) ions [J = +0.091(2) cm−1 (1) and +0.097(2) cm−1 (2) through the spin Hamiltonian for an isotropic square grid of interacting spin doublets which is defined as H = −JΣiSi · Si+1]. The strong similarity in the magnetic properties of 1 and 2 allow us to conclude that although they are not isostructural species, their structures have to be very close.

Nicotinamide and isonicotinamide as hydrogen-bond pillars for ferromagnetic layers constructed with the phenylmalonate ligand (Phmal) in two novel compounds of formulae [Cu(inia)(Phmal)(H2O)] (1) and [Cu(inia)(Phmal)(H2O)]n (2) [nicotinamide (nia) isonicotinamide (inia)].Figure optionsDownload as PowerPoint slideHighlights
► Two copper(II) 2D coordination polymers based on phenylmalonate have been synthesized.
► Nicotinamide and isonicotinamide have been used to supramolecularly link the layers.
► Ferromagnetism occurs in these complexes, the carboxylate being the exchange pathway.