Hydrogen‐Bonded Polyrotaxane‐like Structure Containing Cyclic (H 2 O) 4 in [Zn(OAc) 2 (μ‐bpe)]⋅2 H 2 O: X‐ray and Neutron Diffraction Studies

The reaction of 4,4′‐bipyridylethane (bpe) and 4,4′‐dipyridyl disulfide (dpds) with Zn(OAc) 2 ⋅2 H 2 O has led to the formation of two coordination polymers, [Zn(OAc) 2 (μ‐bpe)]⋅2 H 2 O ( 1 ) and [Zn(OAc) 2 (μ‐dpds)] ( 2 ). Both the compounds have zigzag coordination polymeric structures as revealed by X‐ray crystallography. However, the presence of two lattice water molecules in 1 results in an interesting difference between the crystal structures. In 1 , the carboxylate carbonyl oxygen atoms of the Zn(OAc) 2 groups from two different adjacent zigzag polymers and four lattice water molecules form 24‐membered hydrogen‐bonded rings (graph set notation, R 6 6 (24) ). One of the two bpe ligands associated with each Zn II center passes through the center of this ring to form a two‐dimensional hydrogen‐bonded coordination polymeric structure. In the solid state, the adjacent 24‐membered hydrogen‐bonded rings further fuse together through OH⋅⋅⋅O hydrogen bonds among four waters to form cyclic (H 2 O) 4 . This results in a one‐dimensional hydrogen‐bonded ribbon‐like polymer comprising fused alternating 24‐ and eight‐membered OH⋅⋅⋅O hydrogen‐bonded rings. One of the bpe ligands passes through the center of the larger ring to produce an unexpected single self‐penetrating three‐dimensional hydrogen‐bonded network with polyrotaxane‐like association. A neutron diffraction study provides a detailed description of the hydrogen bonds involved.