The structure of the complex Mn(N,N'-butylenebisimidazole)3(BF4)2 comprises two equivalent, mutually interpenetrating three-dimensional networks of 44-membered rings.A particularly interesting subset of the rapidly developing field of self-assembling framework materials is the class of compounds which form interpenetrating networks. These can involve two-or three-dimensional arrays, and doubly or triply interpenetrating lattices with a range of types of network 'building blocks'.' In the case of interpenetrating metal complexes, as distinct from purely organic compounds such as trimesic acid,2 building blocks based on essentially rigid cyanide or bi-or tri-pyridyl ligand bridges have been frequently used.l.3 Whereas this rigidity can assist in the design of predimensioned networks, it frequently limits their ability to accommodate ionic or non-ionic guest species. To this end we have been exploring the use of conformationally flexible bridging ligands to generate large-ring frameworks which have the ability to 'breathe' and thereby generate more adaptable receptor array^.^ One of the consequences, however, of the formation of largering structures is that, in the absence of appropriate guest species, such macrocycles tend to collapse in on themselves so as to be self-filling. A way of preserving an open network is for the voids that would inevitably be present to be occupied by a process of mutual interpenetration so as to form polycatenane array^.^ The majority of these are two-dimensional and examples of three-dimensional interpenetrating networks comprising flexible bridging ligands are comparatively rare.' We now report that the flexible, extended-reach ligand N,N'butylenebisimidazole (I, bbi) can be used to form not only large

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Reaction of 1 -(4-picolyl)pyrrolidin-2-one (ppo) with hydrated copper(I1) chloride or bromide in methanol affords the compounds [Cu(ppo),X,] (X = C1 or Br). A single-crystal X-ray diffraction study of [Cu(ppo),Br,] 1 shows that the ppo molecule acts as a bridging ligand with the formation of all trans-CuBr,N,O, units linked to produce sheets of contiguous 36-membered rings. The EPR spectra of 1 and its chloride analogue give well resolved rhombic-type spectra. The EPR and electronic spectra of [Cu(ppo),X2] (X = C1 or Br) are analysed in terms of angular-overlap bonding parameters. X-Ray studies show that the compound [cu4ocl6(ppo)4] comprises a cu4(&$-o)cl6 core with an N-bonded ppo ligand co-ordinated to each Cu atom.