Crown ether mediated cadmium halide dimers and polymers

Abstract

The reactions of cadmium halides with the 15-membered macrocyclic crown ethers, 15-crown-5 and benzo-15-crown-5, have been carried out and six new complexes have been isolated and structurally characterized. Metal to ligand stoichiometries of 1:1, 2:1, 3:1 and 3:2 have been observed with a variety of different formulations. Examples of charge separated ion pairs ([(NH 4)(benzo-15-crown-5) 2] 2[Cd 2I 6]), halogen bridged monomers, dimers or polymers ([Cd(15-crown-5)(OHMe)(μ-Br)CdBr 3], [Cd(15-crown-5)(μ-Br) 2CdBr(μ-Br)] 2(isolated from the same reaction mixture) and [(CdCl 2) 2CdCl 2(15-crown-5)] n ), and hydrogen bonded finite chains or polymers ([(Cd(OH 2) 2(15-crown-5)][CdI 3(OH 2)] 2·2(15-crown-5)·2CH 3CN and [CdI 2(OH 2) 2(THF)]·benzo-15-crown-5) have been isolated. Three different types of 15-crown-5 coordination modes have been observed in these complexes. In-cavity coordination resulting in pentagonal bipyramidal geometries about Cd 2+ was observed in [(CdCl 2) 2CdCl 2(15-crown-5)] n , [Cd(15-crown-5)(OHMe)(μ-Br)CdBr 3], and [Cd(OH 2) 2(15-crown-5)][CdI 3(OH 2)] 2·2(15-crown-5)·2CH 3CN, [Cd(15-crown-5)(μ-Br) 2CdBr(μ-Br)] 2 displays out-of-cavity coordination with one etheric donor distorted into an axial position of a distorted pentagonal bipyramid. The third coordination mode is secondary sphere coordination via hydrogen bonding which is observed for [Cd(OH 2) 2(15-crown-5)][CdI 3(OH 2)] 2·2(15-crown-5)·2CH 3CN. The good fit of Cd 2+ within the cavity of 15-crown-5 results in shorter bonding contacts and a more narrow distribution in CdO values (2.273(7)-2.344(6) Å) than observed for cadmium halide complexes of 18-crown-6 ( Cd O = 2.69(1)–2.81(1) A ̊ ) .