Synthesis, spectroscopy, crystal structure and magnetism of tetrakis(2-aminopyrimidine)bis(μ-methoxo)bis(perchlorato)dicopper(II): a rare case of distortion isomerism

Abstract

The dinuclear compound [Cu(ampym) 2(μ-CH 3O)(ClO 4)] 2 (ampym=2-aminopyrimidine) has been synthesized and characterized by X-ray crystallography and infrared spectroscopy. In addition, EPR and magnetic measurements have been performed and related to the dinuclear structural details. The compound crystallizes in the monoclinic space group P2 1/ c, with a=8.0190(13), b=18.2500(11), c=10.955(2) Å, β=116.390(13)°, V=1436.2(4) Å 3 and Z=2. The coordination geometry around the Cu(II) ion is distorted square pyrimidal with the basal plane formed by two nitrogen atoms of two ampym molecules (Cu–N distances 2.002(3) and 2.031(3) Å) and two oxygen atoms of the bridging methoxo molecules (Cu–O distances of 1.936(2) and 1.937(3) Å). The apical position is occupied by a semi-coordinated oxygen of a perchlorate anion (Cu–O distance 2.442(2) Å). The H-bonds, formed by the amino group and the uncoordinated pyrimidine nitrogen atom of a neighbouring ampym molecule, give rise to an interesting Watson–Crick type pairwise aggregation of ampym ligands. In the far-IR, the Cu–N vibrations are observed at 443 and 265 cm −1, and the Cu–O are observed at 353 and 240 cm −1. At room temperature the compound gives an EPR silent behaviour and magnetic susceptibility measurements, down to 4 K, agree with a strong antiferromagnetic interaction having a very large singlet–triplet splitting ( J=−621 cm −1). The title compound appears to be a distortion isomer of a recently reported X-ray structure of identical stoichiometry.