Hydrogen bonded polymers and oligomers from metal salts and 18-crown-6

Reaction of hydrated metal salts M(ClO4)(2) with 18-crown-6 in water results in the isolation of [M(H2O)(6)][ClO4](2). (18-crown-6) (M = Ni, 1a; Co, 1b; Zn, 1c) which adopt an infinite hydrogen bonded sandwich type structure. Reaction of Cu(ClO4)(2) with 18-crown-6 under similar conditions leads to a mixture of the analogous [Cu(H2O)(6)][ClO4](2). (18-crown-6) 1d and a new complex [Cu(H2O)(3)(18-crown-6)](2)[ClO4](4).(18-crown-6) 2, containing both complexed and free crown ether rings as a discrete unit. This difference in behaviour arises from the preference of Cu(lr) to adopt a Jahn-Teller distorted geometry. Reaction of NiBr2 results in the formation of the striking complex [Ni(H2O)(6)](3)[NiBr2(H2O)(4)]Br-6. 4(18-crown-6). 2H(2)O 3, closely related to complexes of type 1. With a 3. 1 electrolyte, hydrogen bonded dimers of [Al(H2O)(6)][NO3](3).(18-crown-6)4 are formed, unrelated to complexes 1. Removal of equatorial aqua ligands as in the complex [Cu-2(O2CCH3)(4)(H2O)(2)] gives [Cu-2(O2CCH3)(4)(H2O)(2)].(18-crown-6). 2H(2)O 5 which consists of a very different linear, hydrogen bonded chain. Analogous reactions with eight-coordinate complexes led to [M(CF3CO2)(2)(H2O)(6)][CF3CO2].(18-crown-6) (M = Eu, 6a; Y, 6b) which somewhat resemble complexes 1. In general, it is found that the stability of the structure as a whole, and not one dominant set of interactions, governs crystal packing, and even molecular stoichiometry within these equilibrating systems.