Hydrogen‐Bonded Polyrotaxane‐like Structure Containing Cyclic (H2O)4 in [Zn(OAc)2(μ‐bpe)]⋅2 H2O: X‐ray and Neutron Diffraction Studies

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Abstract
The reaction of 4,4′‐bipyridylethane (bpe) and 4,4′‐dipyridyl disulfide (dpds) with Zn(OAc)2⋅2 H2O has led to the formation of two coordination polymers, [Zn(OAc)2(μ‐bpe)]⋅2 H2O (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, R66(24)). One of the two bpe ligands associated with each ZnII 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 OH⋅⋅⋅O hydrogen bonds among four waters to form cyclic (H2O)4. This results in a one‐dimensional hydrogen‐bonded ribbon‐like polymer comprising fused alternating 24‐ and eight‐membered OH⋅⋅⋅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.