Complexes of copper(II) formate with 2-(phenylamino)pyridine and 2-(methylamino)pyridine: New copper formato paddle-wheel compounds

The derivatives of Cu(HCOO)2 · 4H2O with 2-(phenylamino)pyridine and 2-(methylamino)pyridine, [Cu2(μ-HCOO)4(PhNHpy)2] (1), [Cu2(μ-HCOO)4(MeNHpy)2] (2) and Cu(HCOO)2(MeNHpy)2 (3), have been synthesized and characterized. Compounds 1 and 2 show the paddle-wheel structure of [Cu2(μ-HCOO)4L2], with four syn–syn bridging formato groups and two molecules of PhNHpy or MeNHpy coordinated to the axial positions, respectively. Intramolecular hydrogen bonds are formed in both cases: two in each dimer of 1 and four in the dimer of compound 2. The dimer units are oriented in two different directions. Dimers with the same orientation form rows along the “c” and the “a” axis in compounds 1 and 2, respectively, with a π–π stacking of the pyridine rings. In compound 1, an intercalation of the phenyl rings of contiguous rows of dimers gives rise to a succession of phenyl rings at a distance of 4.38 Å and an angle of 30.44° between alternate rings. They are antiferromagnetic. Signals of the triplet state are observed in their EPR spectra and the zero-field splitting parameter has been determined. Compound 3 obeys the Curie–Weiss law and the magnetic results indicate the absence of magnetic interaction between Cu(II) atoms.