Self-assembly by co-ordination and strong hydrogen bonding. X-ray crystal structures of a dimeric trisodium complex of a new acidic complexing ligand and its dihydrate

Abstract

The new acidic complexing ligand triethanolamine-O,O,O-triacetic acid, 3, is synthesized by reaction of triethanolamine with chloroacetic acid in the presence of sodium tert-butoxide. The resulting Na complex, 4, and its dihydrate, 5, contain two ligand molecules, both with one Na⁺ ion interaction and both co-ordinated to a third, central, Na⁺ ion. In addition the acidic ligands are hydrogen bonded to each other, like carboxylic acids, and in 4, by three crystallographically symmetric hydrogen bonds, while in 5, due to the breakdown of symmetry, two normal and one crystallographically symmetrical hydrogen bond. Inside this extraordinary dimeric assembly (a pseudo-cryptate) are the three sodium ions encapsulated, like in cryptates, with a Na⁺…Na⁺ distance of 3.357(3) Å (4) and 3.325(2) Å (5). Crystal data, 4: a = 12.198(1) Å, c = 40.926(5) Å, V = 5274(3) Å, trigonal, space group = R-3c (no. 157), d _calc = 1.346 g cm^?3, Z = 6, obs. refl. [I > σI] = 396, R = 0.045; 5: a = 25.045(5) Å, b = 11.373(2) Å, c = 14.301(2) Å, β = 122.38(1)°, V = 3440(1) ų, monoclinic, space group = C2/c, d _calc = 1.446 g cm^?3, Z = 4, obs. refl. [I > 2σI] = 1362, R = 0.041.