Solid-state structure and solution behaviour of hypervalent organoantimony halides containing 2-(Me2NCH2)C6H4– moieties

Abstract

Hypervalent antimony(III) halides of the type R₂SbX [X = Cl (1), Br (2), I (3)] and RSbX₂ [X = Cl (4), Br (5), I (6)] [R = 2-(Me₂NCH₂)C₆H₄] have been prepared. Their dynamic solution behavior was investigated by ¹H and ¹³C NMR spectroscopy. The structures of compounds 2–6 were determined by single-crystal X-ray diffraction and the observed trends in the degree of intramolecular coordination of the N atom of the pending CH₂NMe₂ arm are discussed. Compounds 2 and 3 are monomeric and exhibit distorted square-pyramidal (C,N)₂SbX cores. The molecular structure of the adduct R₂SbI·HI (3·HI) indicates the strong coordination of one of the N atoms to antimony. The second pendant arm is twisted away from the metal center, its N atom being protonated and thus converted into an ammonium group. The molecules of 4–6 contain a pseudo-trigonal bipyramidal geometry around the antimony atom, with the N atom strongly coordinated trans to a halogen atom. Different degrees of association through asymmetric Sb–X⋯Sb bridges [overall distorted square-pyramidal (C,N)SbX₃ cores] were found in the crystal of the dichloride 4 (polymeric chains) and dibromide 5 and diiodide 6 (centrosymmetric dimers), respectively. In an attempt to obtain [R₃SbI]I₃ by addition of I₂ to R₃Sb in 2 ∶ 1 molar ratio, deep red-brown crystals of the new ionic species [R₃SbOH]⁺[I₃]⁻ (7) have been isolated. Crystals of 7 are built up from [R₃SbOH]⁺ cations and linear non-symmetric [I₃]⁻ anions.