Figure 1 A fragment of the structure of the title compound with atom labelling scheme and 50% probability displacement ellipsoids. Symmetry code: (i) x + 1, y, z; (ii) -x + 1, y + [{1\over 2}], -z + 2; (iii) -x + 1, y - [{1\over 2}], -z + 2; (iv) -x + 1, y - [{1\over 2}], -z + 1; (v) -x, y - [{1\over 2}], -z + 1.  [article HTML]