Rare antimony(iii) imidazole selone complexes: steric controlled structural and bonding aspects

Abstract

Novel antimony(III) imidazole selone complexes in a super crowded environment are reported for the first time. The super bulky selone antimony complexes, [{IPr*Se}(SbCl₃)₂] (1) and [{IPr*Se}(SbBr₃)₂] (2), were isolated from the reactions between IPr*Se (IPr*Se = [1,3-bis(2,6-diphenylmethylphenyl)imidazole selone]) and suitable antimony(III) halides. 1 and 2 are dinuclear complexes with a Sb : Se ratio of 1 : 0.5 with an unusual coordination mode of selone. The molecules 1 and 2 consist of both Menshutkin-type Sb⋯π_aryl interactions and a Sb–Se coordination bond. However, the reaction between antimony(III) halides and [(IPaul)Se] ([(IPaul)Se] = [1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole selone]) with a spatially defined steric impact gave the dinuclear complex [{(IPaul)Se}(SbCl₃)]₂ (3) and the mononuclear complex [{(IPaul)Se}(SbBr₃)] (4) without Menshutkin-type interactions. The Sb : Se ratio in 3 and 4 is 1 : 1. Interestingly, the Menshutkin-type interaction was absent in 3 and 4 due to the efficient coordinating ability of the ligand [(IPaul)Se] with the Sb(III) center compared to that of the super bulky ligand IPr*Se. The thermal property of these antimony selone complexes was also investigated. Density functional theory (DFT) calculations were carried out on the model systems [L(SbCl₃)₂] (1A), [L(SbCl₃)] (1B), [L′(SbCl₃)₂] (1C), and [L′(SbCl₃)] (1D), where L = [1,3-bis(2,6-diisopropyl-4-methyl phenyl)imidazole selone] and L′ = [1,3-bis(phenyl)imidazole selone], to understand the nature of orbitals and bonding situations. The computed metrical parameters of 1A are in good agreement with the experimental values. Natural population analysis of the model system reveals that the natural charge and total population of antimony(III) are comparable. The unequal interaction between selenium and antimony obtained using Wiberg bond indices (WBIs) is fully consistent with the findings of the single-crystal X-ray studies.