A close inspection of Ag(I) coordination to molecular baskets. A study of solvation and guest encapsulation in solution and the solid state

Four molecular baskets 1–4, each comprising a modular bowl-shaped platform and a set of distinctive aromatic gates, were synthesized. The gates were made to incorporate a nitrogen heteroatom at different positions, as in 2–4, or without a coordinating nitrogen, as in 1 (Fig. 1). For polydentate 3 and 4, the location of the nitrogen was revealed to have an effect on directing the basket's coordination to Ag(I) cation, and subsequent folding to enclose space. The folded geometries were shown to encompass a helical, Ag(I):3, or C3v/C2v symmetrical, Ag(I):4, dynamic arrangement of the gates (from density functional theory). For 2 and 1, however, the presence of Ag(I) caused the sole formation of oligomers and the absence of coordinating interactions, respectively. Variable temperature (VT) 1H and 19F NMR measurements of Ag(I):3 did not provide direct evidence for the solvation of its inner space and the encapsulation of the BF4− counterion. Moreover, CH3CN or CH3NC substrates were not found inside of Ag(I):3. The finding is in contrast with the behavior of Cu(I):3, which is known to encapsulate these guests. The intriguing guest selectivity was accounted for by small structural and electronic differences of Ag(I)/Cu(I) folded baskets. The X-ray solid-state structural studies of 2, 3, and 4 revealed the basket's capacity to fill its inner space with small compounds. Thus, 3 was found with an ordered molecule of chloroform, while 4 contained molecules of CH3OH and H2O. The basket selectivity for enclosing and positioning guests, in the solid state, was deduced to be guided by their size and weak host–guest and guest–guest noncovalent interactions.

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