Experimental. Analysis of 3764 reflections having I/σ(I) > 12 and chosen fromthe full data set with CELL_NOW (Sheldrick, 2008) showedthe crystal to belong to the monoclinic system and to be twinnedby a 180° rotation about the c* axis. The raw data wereprocessed using the multi-component version of SAINT undercontrol of the two-component orientation file generated byCELL_NOW.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)are estimated using the full covariance matrix. The cell e.s.d.'s are takeninto account individually in the estimation of e.s.d.'s in distances, anglesand torsion angles; correlations between e.s.d.'s in cell parameters are onlyused when they are defined by crystal symmetry. An approximate (isotropic)treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR andgoodness of fit S are based on F2, conventional R-factors R are basedon F, with F set to zero for negative F2. The threshold expression ofF2 > σ(F2) is used only for calculating R-factors(gt) etc. and isnot relevant to the choice of reflections for refinement. R-factors basedon F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. H-atoms were placed incalculated positions (C—H = 0.95 - 0.98 Å) and included as ridingcontributions with isotropic displacement parameters 1.2 - 1.5 times thoseof the attached carbon atoms. The model was refined as a 2-component twin.