Conformational Versatility of Open‐Chain Polyethers: Crystal and Molecular Structures of the Ba(SCN)₂ Complexes of Two Heptaethyleneglycol Diaryl Ethers

The crystal structures of the Ba(SCN)₂ complexes of two linear octaethers, heptaethyleneglycol diphenylether (HGPE; 1,20‐bis(phenyloxy)‐3,6,9,12,15,18‐hexaoxaicosane) and heptaethyleneglycol dinaphthylether (HGNE; 1,20‐bis(naphthyloxy)‐3,6,9,12,15,18‐hexaoxaicosane), are reported. In spite of their close similarity, the ligands adopt quite different conformations in their Ba(SCN)₂ complexes. HGPE wraps around the metal ion in a discontinuous helix providing seven of its eight ether oxygens for coordination. 10‐fold coordination of Ba²⁺ is completed by the nitrogens of the SCN⁻ ions and by a water molecule for which an occupancy of 0.37(5) was determined. In contrast, HGNE behaves as a hexadentate only. The barium ion is 9‐fold coordinated to six ether oxygens, to a water molecule, to one SCN⁻ ion via its nitrogen atom and to a symmetry‐related thiocyanate ion via its sulphur atom. The second SCN⁻ ion does not contact the metal ion but is hydrogen‐bonded to two symmetry‐generated water molecules. HGNE displays some unusual conformational features never found before for open‐chain polyethers.