Formation and crystal structures of novel seven-coordinate 15-crown-5 complexes of manganese(II), iron(II) and cobalt(II)

Abstract

The reactions of Mn(CO)₅Br, Fe(CO)₅ and Co₂(CO)₈ with HCl(g) in the presence of 15-crown-5 and H₂O in toluene have been explored. These reactions were promoted with the use of UV radiation and formed liquid clathrates almost immediately upon reaction. For each metal species, oxidation of the metal center from either [+1] (for Mn) or [0] (for Fe, Co) to [+2] occurred. For manganese, the MnII species [MnII(H₂O)₂·15-crown-5][Br⁻Cl⁻] (1) was obtained from the liquid clathrate layer in the reaction mixture. For iron the FeII species [FeIICl(H₂O)·15-crown-5][H₅O₂+][FeIICl₄²⁻] (2) rapidly formed, and for cobalt the CoII species [CoII(H₂O)·15-crown-5][H₉O₄⁺][CoII·15-crown-5][H₉O₄⁺][CoII(H₂O)·15-crown-5][CoIICl₄²⁻]₄ (3) was deposited from the liquid clathrate layer. It was established by X-ray crystallography that each species contains a seven-coordinate metal center with pentagonal bipyramidal stereochemistry. Complex 1 is a hydrogen-bonded single-stranded polymer through bridging halide atoms. Complex 2 has a H₅O2+ oxonium ion hydrogen-bonded to the cations and complex 3 has a remarkable H₂O–Co²⁺–H₉O₄⁺–Co₂⁺–H₉O₄⁺–Co₂⁺–H₂O cationic chain.