Supramolecular synthesis through dihydrogen bonds: Self-assembly of controlled architectures from NaBH₄·poly(2-hydroxyethyi)cyclen building blocks

A systematic investigation of molecular structures/supramolecular organization relationships in dihydrogen-bonded complexes comprising NaBH₄ and poly-2-hydroxyethyl-cyclen (poly-HEC) building blocks is reported. Like in the prototype compound 1, a (NaBH₄-poly-HEC)₂ dimeric arrangement has been found in the analogous structures 3 and 5, but not in compound 2, which lacks dihydrogen bonds. The exact connectivity of the dimers is determined by a complex interplay of noncovalent interactions such as OH···HB dihydrogen bonds, OH···O conventional hydrogen bonds, Na-O and Na-N coordinative bonds, and dispersion interactions. The persistent recurrence of this general supramolecular motif permits controlled assembly of extended networks with desired architectures, by the use of appropriate spacers for linking the dimers, as demonstrated by the solid-state structure of 7. Additionally, the intrinsic solid-state reactivity of these dihydrogen-bonded networks makes this approach a promising strategy for the rational construction of functional extended covalent solids.