Jw. Steed et al., HYDROGEN-BONDED POLYMERS AND OLIGOMERS FROM METAL-SALTS AND 18-CROWN-6, Journal of the Chemical Society. Dalton transactions (Print), (20), 1998, pp. 3417-3423
Reaction of hydrated metal salts M(ClO4)(2) with 18-crown-6 in water r
esults 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 prefe
rence 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 comp
lexes of type 1. With a 3. 1 electrolyte, hydrogen bonded dimers of [A
l(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 co
mplexes 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.