Figure 2 Fraction of the structure of (I) with atomic labelling scheme in a projection approximately along the a-axis. The atoms are drawn as displacement ellipsoids at the 50% probability level. [Symmetry codes: (i) x, y + 1, z; (ii) -x + 1, -y + 1, -z - 1; (iii) -x + 1, -y, (iv) x, y - 1, z; -z - 1; (x) -x, -y, -z; (xii) x + 1, y, z; (xiii) x + 1, y + 1, z; (xiv) -x + 1, -y - 1, -z; (xv) x + 1, y - 1, z.]