trans-Tetraiodidobis(tri-p-tolylphosphine oxide-κO)tin(IV)

The centrosymmetric title compound, [SnI4(C21H21OP)2], is a monomeric complex that displays a nearly octahedral coordination of tin(IV), with an Sn—O bond distance of 2.159 (2) Å and an average Sn—I bond distance of 2.79 (3) Å.


S1. Comment
Tin(IV) iodide may be readily prepared by oxidation of tin metal with iodine (Woollins, 2003). A relatively weak Lewis acid, SnI 4 nevertheless forms complexes with phosphines and phosphine oxides (Genge et al. 1999;Davis, Clarke et al. 2006;Caldwell & Tanski, 2008) et al. 1993;Tursina, Yatsenko et al. 1986). In the structure of the iodide, the triphenyl phosphine oxide ligands of cis-[Ph 3 PO] 2 SnI 4 are found to be cis (Tursina, Aslanov et al. 1986). As reported here, tri(p-tolyl) phosphine oxide results in an iodide complex wherein the phosphine oxide ligands are found to be trans.
Complex (I) exhibits a nearly octahedral coordination at tin, which resides on a crystallographic inversion center. The phosphine oxide ligands are mutually trans, with an Sn-O distance of 2.159 (2) Å, and Sn-I distances of 2.7674 (2) and 2.8158 (2) Å. Relevant bond lengths and angles can be found in Table 1. Despite the p-CH 3 substituent and trans orientation of the phosphine oxide ligands in (I), the Sn-O and Sn-I distances in (I) are very similar to those found in cis-[Ph 3 PO] 2 SnI 4 , wherein the Sn-O distances are 2.15 (2) and 2.11 (2) Å, and the Sn-I distances range from 2.781 (2) to 2.816 (2) Å (Tursina, Aslanov et al. 1986).

S2. Experimental
Complex (I) was prepared by treating a chloroform (ca 10 ml) solution of SnI 4 (626 mg, 1.00 mmol) with an excess of (p-CH 3 C 6 H 4 ) 3 P (647 mg, 2.13 mmol) in the presence of air. Suitable crystals for single-crystal X-ray analysis separated as orange plates within 2 weeks at room temperature.

S3. Refinement
H atoms on carbon atoms were included in calculated positions using a riding model at C-H distances 0.95 and 0.98 Å and U iso (H) = 1.2 and 1.5U eq (C) of the aryl and methyl C-atoms, respectively.

Refinement.
A suitable crystal was mounted in a nylon loop with Paratone-N cryoprotectant oil and data was collected on a Bruker APEX 2 CCD platform diffractometer. The structure was solved using direct methods and standard difference map techniques, and was refined by full-matrix least-squares procedures on F 2 with SHELXTL Version 6.14 (Sheldrick, 2008). All non-hydrogen atoms were refined anisotropically. Refinement of F 2 against ALL reflections. 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 Rfactors(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. EXTI refined to zero and was removed from the refinement.