Spectroscopic Properties and Molecular Structure of 1,3-Dimethyl-2-(Se,Se-dibromoseleno)-2(3H)-imidazolylidene

Oxidative addition of Br₂ to 1, 3-dimethyl-2(3H)-irnidazoleselone results in a compound that can be viewed as a Se(II) bromide complex with a stabilized imidazolylidene ring as verified by X-ray crystallography. The structure consists of dimeric pairs containing nearly linear Br-Se-Br units bonded through carbon to planar imidazolyidene rings at torsion angles of 91.4° for N1-C1-Se1-Br1 and 76.8° for N3-C6-Se2-Br4. Significant; intermolecular contacts between dimeric units are seen through short Se–Se [3.494(1) Å] and Se1–Br₄, bridging [3.509(1) Å]. Solution state Raman data show the characteristic peaks for a linear Br-Se-Br moiety with a strong polarized peak at 158 cm⁻¹ and a weak shoulder at 181 cm⁻¹ corresponding to the symmetric and asymmetric Br-Se-Br stretching modes respectively. In the absence of X-ray data, correlation of structure to vibrational data provides further support for structural speculations in other compounds with the linear SeBr₂ grouping. Crystal structure data for C₅H₈N₂Br₂Se. Cell parameters: space group P2₁/c, a = 7.999(2)Å, b = 14.624(3)Å, c = 16.697(3)Å, β = 95.41(2), Z = 8, V = 1945(1) ų, D_c = 2.288 g/cm³, unique reflections = 3783, R = 0.045.