Structural study on the organoantimony(III) NCN – Chelated compounds [2,6-(Me2NCH2)2C6H3]SbX2 – Influence of the polar group X

The reactions of organoantimony chloride LSbCl2 (1) (L = [2,6-(Me2NCH2)2C6H3]−) with the silver salts of selected carboxylic acids (1:2 molar ratio) resulted to the corresponding organoantimony carboxylates LSbX2, where X = CH3COO for (2); CF3COO for (3). Similar reactions of 1 with the silver salt of the low nucleophilic CB11H12- anion (1:0.5 and 1:1 molar ratio) gave the ionic compounds [LSb(Cl)--Cl–Sb(Cl)L]+[CB11H12]− (4), and [LSbCl]+[CB11H12]− (5). All compounds were characterized by the help of the elemental analysis, ESI-MS, 1H, 11B, 13C NMR spectroscopy and IR spectroscopy. The solid state structure investigation using single crystal X-ray diffraction technique (3–5) revealed the presence of the strong Sb–N intramolecular dative connections in all cases and also significant differences in the shapes of the coordination polyhedra around the central antimony atoms was observed, i.e. a tetragonal pyramidal environment in 3 (CF3COO groups are placed mutually in trans positions), an unusual chlorine bridged dinuclear cation consisting of one apex (Cl atom) sharing square pyramids in 4, and finally a vacant ψ-trigonal bipyramid around the central antimony atom in 5. Even more, crystallization of 5 from THF provided the single crystals of a THF aduct of 5 [LSbCl(THF)]+[CB11H12]−5a, where the central antimony atom is located in a tetragonal pyramidal environment. The solid state structures of 3–5 are retained in solution. Solution structure of the compound 2 was determined by the help of VT-1H NMR spectroscopy and IR spectroscopy showing, that both carboxylates (CH3COO) are unidentate and are placed mutually in cis positions in the coordination polyhedron around the central antimony atom. The whole coordination polyhedron in 2 might be best described as a biccaped – trigonal pyramid, due to the additional Sb–N intramolecular interactions.

It was demonstrated that the behaviour of polar group X in the compounds of the type [2,6-(Me2NCH2)2C6H3]SbX2 has a crucial effect on the geometry around the central antimony atom. The shapes of coordination polyhedron range from a bicapped – trigonal pyramid (X = CH3COO), and a distorted tetragonal pyramid (X = CF3COO) to a ψ-trigonal bipyramid (X = Cl, CB11H12). Even more, an unusual dinuclear ionic complex was prepared and characterized and in this case the structure of the organometallic cation can be described as one apex sharing distorted tetragonal pyramids.Figure optionsDownload as PowerPoint slide