Antimony(III)-selenium complexes with synergetic effect between Sb-Se bond and Sb center dot center dot center dot pi interactions

Abstract

The imidazole-selone antimony(III) complexes have been described with unique bonding situations around the antimony center. The mononuclear complexes, (L-1)SbCl3 (1) and (L-2)SbCl3 (2) were isolated from the reaction between SbCl3 and corresponding symmetrically crowded, 1,3-bis(2,6-diisopropyl phenyl) imidazole selone (L-1) and unsymmetrically crowded, 2,(2,6-benzhydryl-4-methyl phenyl) imidazole pyridine selone (L-2), respectively. The bonding nature of 1 and 2 differ remarkably due to the unique steric hindrance around the antimony center. Besides, the lone-pair-pi-hole interaction was observed in 1 and 2. The extent of Se -{\textgreater} Sb bonding and (aryl)C -{\textgreater} Sb bonding were further investigated by density functional theory (DFT), including natural bond orbital (NBO), natural population analysis (NPA), and electron density difference (EDD) methods. The theoretical predictions are nearly convincing with a single crystal X-ray analysis. The increasing steric bulk of the imidazole-selone from symmetric to unsymmetrical nature was found to greatly influence the donor-acceptor magnitude of Se -{\textgreater} Sb bonding and (aryl)C -{\textgreater} Sb bonding and lone-pair-pi-hole interactions. The L-2 in 2 acts as a good sigma-donor and pi-donor to Sb(III) compare to L-1 in 1