X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection

The structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)- 9,10-dihydro-10,10-dimethylanthracene-9-ol, C24H30O6.H2O (1), code name P32 6, the parent compound for a series of derivatives, has been determined by both X-ray diffraction at room temperature and neutron diffraction at very low temperature. The unit cells are very similar at both temperatures and i n both cases the crystals exhibit P2(1) symmetry with Z = 4 (two molecules, A and B, respectively, per asymmetric unit) and pseudosymmetry P2(1)/c. Th e higher symmetry is broken mainly by the two independent water molecules i n the unit cell, some reflections which would be absent in P2(1)/c having s trong intensities in both the X-ray and neutron data. In both molecules A a nd B hydrogen bonds involving the water molecule stabilize the macrocyclic ring structure, one involving the macrocyclic O(9) as a donor. Close contac ts between the water and macrocyclic O atoms in each molecule also suggest the presence of two bifurcated hydrogen bonds, involving water HW2 to both O(16) and O(18), and water HW1 to both O(18) and O(20), respectively, with considerable variation in the geometry being present. Both molecules A and B exhibit very close pseudosymmetry across a plane perpendicular to the mol ecular plane and through atoms C(9) and O(18), and in addition are predomin antly planar structures. The X-ray analysis failed to reveal one H atom per water molecule, each being subsequently included after location and refine ment in the neutron analysis.