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

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Oxidative addn. of Br to 1,3-dimethyl-2(3H)-imidazoleselone results in a compd. that can be viewed as a Se(II) bromide complex with a stabilized imidazolylidene ring as verified by x-ray crystallog. The structure consists of dimeric pairs contg. nearly linear Br-Se-Br units bonded through C to planar imidazolylidene rings at torsion angles of 91.4° for N1-C1-Se1-Br1 and 76.8° for N3-C6-Se2-Br4. Significant intermol. contacts between dimeric units are seen through short Se-Se [3.494(1) Å] and Se1-Br4 bridging [3.509(1) Å]. Soln. 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 sym. and asym. Br-Se-Br stretching modes resp. In the absence of x-ray data, correlation of structure to vibrational data provides further support for structural speculations in other compds. with the linear SeBr2 grouping. . Crystal structure data for C5H8N2Br2Se are: cell parameters: space group P21/c, a 7.999(2), b 14.624(3), c 16.697(3) Å, β=95.41(2), Z = 8, dc = 2.288 g/cm3, unique reflections = 3783, R = 0.045.