Very strong centrosymmetric [O...H...O]+ and asymmetric [O-H...O]+ hydrogen bonds in a new POM-Based hybrid material

A specific assembly process, driven by coexisting X-H...O hydrogen bonding and X...O short intermolecular contacts (X = C, N, O) is described, in which the pseudo-Keggin polyoxoanion and two types of molecule...cation pairs (with C1 and C_i symmetries) were assembled to the programmed supramolecular architecture. Cooperation of the positive-charge, resonance effect and the O=C...O_terminal intermolecular contact led to the short and strong symmetrical [O...H...O]⁺ hydrogen bond (O...O = 2.449(13) Å) in one of the molecule...cation pairs [C₄H₉NO...H...ONC₄H₉]⁺ with the H-bonded proton in the center of inversion. The other [C₄H₉NOH...ONC₄H₉]+ molecule...cation pair (non-centrosymmetric) was formed through a very strong asymmetric [O.H.O]+ hydrogen bond of 2.431(13) Å in length which was created via the synergistic effect between the minor N-H...O secondary interaction, +CAHB (positive-charge-assisted hydrogen bond) and RAHB (resonance assisted hydrogen bond) mechanisms.