Synthesis and characterization of monomeric diorganotellurium dihalides: crystal and molecular structures of diphenacyltellurium dibromide and -diiodide

Tellurium, but not selenium, reacts with phenacyl bromide (ω-bromoacetophenone) to give diphenacyltellurium dibromide (PhCOCH2)2TeBr2 (1), which represents the first example of a functionally substituted organotellurium halide to have been prepared directly from elemental tellurium and an organic halide. Metathesis of 1 with KI affords the crystalline diiodide, (PhCOCH2)2TeI2 (2), but halide–pseudohalide exchange does not proceed with KSCN or AgN3. Compounds 1 and 2 have been characterized by elemental analyses, IR, 1H- and 13C-NMR and mass spectrometry. Coordinative interaction of both the carbonyl groups in 1 and 2, in solid state as well as in solution, is indicated by IR spectra. Crystal and molecular structures of the dihalides were determined by X-ray diffraction method. Compounds 1 and 2 are isostructural and crystallize in the monoclinic system with space group P21/n. The primary geometry about the central Te atom in both the compounds is Ψ-trigonal-bipyramidal with axial halogens. Stereochemically active lone pair of electrons occupies the equatorial plane along with methylene C atoms of the organic ligands. The Te⋯O intramolecular attractive interactions, though weak [Te⋯O(1), Te⋯O(2): 2.938, 2.912 Å in 1 and 2.877, 2.818 Å in 2] appear to saturate tellurium(IV) atom coordinatively so as to prevent intermolecular Te⋯Br/I interactions. However, there is evidence of weak intermolecular TeBr⋯H(methylene) secondary interactions in compound 1, leading to the formation of supramolecular assemblies.