Abstract
The solid-state structure of di-μ-iodido-bis-{[(1,2,5,6-η)-cyclo-octa-1,4-diene]rhodium(I)}, [Rh2I2(C8H12)2] or [Rh(μ-I)(COD)]2, was determined from two crystals with different morphologies, which were found to correspond to two polymorphs containing Rh dimers with significantly different mol-ecular structures. Both polymorphs are monoclinic and the [Rh(μ-I)(COD)]2 mol-ecules in each case possess C2 v symmetry. However, the core geometry of the butterfly-shaped Rh2I2 core differs substanti-ally. In the C2/c polymorph, the core geometry of [Rh(μ-I)(COD)]2 B is bent, with a hinge angle of 96.13 (8)° and a Rh⋯Rh distance of 2.9612 (11) Å. The P21/c polymorph features a more planar [Rh(μ-I)(COD)]2 P core geometry, with a hinge angle of 145.69 (9)° and a Rh⋯Rh distance of 3.7646 (5) Å.
Highlights
A previous theoretical study found relatively small energetic differences (< 10 kcal molÀ1) between planar and bent [Rh(-X)(L)2]2 geometries (Aullon et al, 1998)
The structural differences between the dimers in the two polymorphs of [Rh(-I)(COD)]2 are attributed to differences
The bent and planar geometries are likely similar in energy
Summary
Crystallization of [Rh(-I)(COD)]2 in toluene at 236 K produced two types of crystals with different colors and morphologies, namely dark-orange and yellow–orange blocks. [Rh(-I)(COD)]2B exhibits a geometry significantly different from that of [Rh(-Cl)(COD)]2 and [Rh(Br)(COD)]2, which both exhibit more planar Rh2X2 cores with hinge angles of 169.08 (6) and 148.74 (7) and RhÁ Á ÁRh distances of 3.5169 (6) and 3.5648 (14) A , respectively (De. Ridder & Imhoff, 1994; Pettinari et al, 2002). The Rh2I2 core geometry of [Rh(I)(COD)]2P is more planar, with a hinge angle of 145.69 (9) and a RhÁ Á ÁRh distance of 3.7646 (5) A (Fig. 2). The average Rh—C distance in the bent and planar structures are similar to the average Rh—C distances reported for the [Rh(-Cl)(COD)]2 and [Rh(-Br)(COD)]2 analogues (De Ridder & Imhoff, 1994; Pettinari et al, 2002), with all four compounds having an average Rh—C distance of 2.12 A. As expected based on the inherent differences in covalent radii, the average Rh—I distances in [Rh(I)(COD)]2B and [Rh(-I)(COD)]2P (2.70 and 2.69 A , respectively) are considerably longer than the average Rh—Br and Rh—Cl distances in [Rh(-Br)(COD)]2 and [Rh(Cl)(COD)]2 (2.54 and 2.38 A , respectively)
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