Molecular receptors. Synthesis and X-ray crystal structure of an 18-crown ether phenol complex of 1,2-diaminoethane

Abstract

Treatment of 18-crown-5 p-nitrophenol (1) with 1,2-diaminoethane produces a 1:2 cage-like complex (2) in which proton transfer has occurred to both amino groups. The crystal structure of (2) has been determined. Crystals of (2)·2EtOH are monoclinic, space group P2₁/n with two formula units in a cell of dimensions a= 11.903(2), b= 14.361(3), c= 13.014(2)Å, β= 95.98(2)°. The structure was solved by direct methods and refined by full-matrix least-squares calculations; R= 0.058 for 961 reflections with I > 2σ(I). The diammonium cation lies about a crystallographic inversion centre and the asymmetric crystal unit contains half a dication, one crown-ether phenolate, and one ethanol. Reception of the NH₃ moiety by the corwn-ether phenolate after proton transfer involves N–H ⋯ O hydrogen bonding to three ethereal oxygen atoms [N⋯· O 2.952(8), 2.789(8), and 2.899(8)Å]; the phenolate oxygen atom does not participate in receptor binding via hydrogen bonding, but instead is linked to ethanol of solvation via an O–H ⋯ O hydrogen bond [O ⋯ O 2.820(8)Å]. The structure is thus unlike that of the monoammonium salt of (1) in that the N–H moieties hydrogen bond to the macrocycle only and in an endo rather than an exo fashion.