Conformational Versatility of Open-Chain Polyethers: Crystal and Molecular Structures of the Ba(SCN)₂Complexes 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.