Polycatenane systems from Co(II) and trans-1,2-bis(4-pyridyl)ethene (bpe).Synthesis and structure of Co(bpe)(2)(NCS)(2)center dot CH3OH, [Co(bpe)(2)(H2O)(2)](ClO4)(2)center dot 2CH(3)OH and [Co(bpe)(2)(H2O)(2)(CH3OH)(2)](ClO4)(2)center dot bpe center dot H2O

Three new compounds of formulae Co(bpe)(2)(NCS)(2). CH3OH, 1, [Co(bpe)(2)(H 2O)(2)](ClO4)(2). 2CH(3)OH, 2 and [Co(bpe)(2)(H2O)(2)(CH3OH)(2)](ClO4)(2). bpe .H2O, 3, [bpe = trans-1,2-bis(4-pyridyl)ethene] have been synthesised a nd characterised by single crystal X-ray diffraction. The metal environment in 1-3 is distorted octahedral. Compound 1 is a polycatenane. Its structur e consists of parallel layers containing Co2+ ions linked by bpe ligands, t he Co . . . Co distance through the bpe bridge being 13.65(3) Angstrom. Eac h metal ion, in a layer, defines the edges of a rhombus. Two thiocyanate gr oups trans-coordinated to the metal atoms are perpendicular to the sheets. Each sheet has an infinite number of perpendicular sheets concatenated with it in such a way that a polycatenane structure results. The structure of 2 also contains parallel sheets composed of cobalt atoms and bpe molecules, but concatenation is absent and the thiocyanate groups are replaced by wate r molecules. In this case, the metal atoms define the edges of a square and the Co . . . Co distance through the bpe bridge is 13.78(3) Angstrom. Unco ordinated perchlorate anions and methanol molecules are linked by means of hydrogen bonds to the water molecules and they connect alternate parallel l ayers, occupying the middle of the intermediate layers. The structure of 3 exhibits an almost planar arrangement of Co2+ ions forming rectangular ring s through hydrogen bonds involving both coordinated and free bpe groups and coordinated water and methanol molecules. The Co . . . Co distances throug h the coordinated and uncoordinated bpe bridges are 14.6(1) and 16.8(1) Ang strom, respectively. No concatenation of rings from different layers occurs in 3.