Crystal structures of rac- and meso-o-Phenylenebis(iodomethylarsine), the latter as its lattice complex with the methiodide of 1,3-Dimethyl-1,3-dihydro-2,1,3-benzoxadiarsole

The crystal structures of the title compounds, o-C₆H₄(AsMeI)₂ (1), and o-C₆H₄(AsMeI)₂₋ [o-C₆H₄(AsMe)(As⁺Me₂)O] I⁻ (2), have been determined at 295 K by single-crystal X-ray diffraction and refined by least squares to residuals of 0.037 and 0.067 for 2095 and 2913 reflections respectively. Crystals of (1) are triclinic, Pī, a 9.865(5), b 9.837(7), c 7.765(4) Å, α 98.89(5), β 96.71(4), γ 60.72(4)°, Z 2. <As-I> is 2.58₅ Å and <As-C> 1.97 Å. The angles about the arsenic differ only trivially, the mean being 98.4°. Crystals of (2) are monoclinic, P2₁/n, a 15.315(4), b 21.511(8), c 7.952(2) Å, β 98.19(2)°, Z 4. In the cation As-O distances are unequal [1.75(1) (quaternary As), 1.86(2) Å]; As-O-As is very small being 115.8(8)°. Charge-transfer interactions between iodine species are present in both derivatives; in (2), there is an interaction between the tertiary arsenics of the meso molecule and the iodide anion, As… I being 3.307(3), 3.551(3) Å, with the geometry of the arsenics approaching that of a tetrahedral disposition. Within the cation, the geometry about the quaternary arsenic is typical of arsenic(v), the bond lengths being shorter than those about the ternary arsenic.