rac-{[2-(Diphenylthiophosphanyl)ferrocenyl]methyl}trimethylammonium iodide chloroform monosolvate

The title compound, [Fe(C5H5)(C21H24NPS)]I·CHCl3, is built up from a (ferrocenylmethyl)trimethylammonium cation, a iodine anion and a chloroform solvent molecule, all residing in general positions. The N atom of the ammonium group is displaced by 1.182 (2) Å from the plane of the substituted cyclopentadienyl (Cp) ring towards the Fe atom, whereas the C atom attached to the same Cp ring is slightly below this plane by −0.128 (2) Å. These deviations might result from weak agostic interactions between the two H atoms of the CH2 group and the Fe atom.

The asymmetric unit is built up from the (ferrocenylmethyl)trimethylammonium cation, the iodine anion and a chloroform molecule as solvate (Fig. 1). Except for the occurrence of the chloroform solvate, the structure is closely related to the one reported by Ferguson et al. (1994). However, in their case, the iodine was in weak interaction with one of the H atom of the bridging CH 2 group whereas in our case the shortest interactions with the iodine involved one of the methyl of the ammonium and the H atom of the chloroform ( Table 1). The phosphorus, P1 atom, is roughly in the plane of the Cp ring to which it is attached deviating only by -0.013 (1) Å whereas the sulfur, S1, is endo located -0.887 (1) Å below the Cp ring.
In the Cambridge Structural Database (CSD version 5.33, 2011;Allen, 2002), there are, to the best of our knowledge, 34 hits corresponding to structures involving the (ferrocenylmethyl)trimethylammonium cation with different counter ions. A comparison of selected distances and angles within the Cp-C-NMe 3 framework is reported in supplementary materials. Surprisingly, there is no real influence of the counter ion on the geometry of this framework. In all compounds the bridging C sp 3 atom is always endo with respect to the Cp ring to which it is attached with values ranging from -0.07 to -0.426 Å, whereas the ammonium N atom is always exo with values ranging from 0.999 to 1.914 Å. Surprisingly, these two extreme values are related to compound containing a very large anion, the (µ 12 -phosphato)-tetracosakis(µ 2 -oxo)dodecaoxo-molybdenum(v)-undeca-molybdenum(vi) . However, it is worthwhile to note that the asymmetric unit in this polyoxomolybdate anions contains four molecules of which two of them have distance of the N from the Cp ring within the usual range: 1.248 and 1.152 Å. Moreover there are other compounds containing polyoxomolybdate anions Li et al. 2009) for which the values are within the normal range. So, these two extreme values might be the consequence of crystal packing which should accommodate four molecules within the asymetric unit.

Experimental
(2-diphenylthiophosphanylferrocenyl) trimethylammonium iodide was synthesized by a published procedure (Mateus et al., 2006). Single crystals suitable for X-ray diffraction analysis were grown from a chloroform solution by slow evaporation of the solvent.

Figure 1
Molecular view of compound I with the atom labeling scheme. Ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.

Special details
Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. CrysAlisPro (Agilent Technologies, 2012) Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq