The dinuclear compound [Cu(ampym) 2 (μ-CH 3 O)(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) A, β=116.390(13) o , V=1436.2(4) A 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) A) and two oxygen atoms of the bridging methoxo molecules (Cu-O distances of 1.936(2) and 1.937(3) A). The apical position is occupied by a semi-coordinated oxygen of a perchlorate anion (Cu-O distance 2.442(2) A). 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.