4,4′‐Methylenediphenol–4,4′‐bipyridine (2/3): decarboxylation of 5,5′‐methylenedisalicylic acid under hydrothermal conditions

Reaction of 5,5′‐methylenedisalicylic acid (5,5′‐H₄mdsa) with 4,4′‐bipyridine (4,4′‐bipy) and manganese(II) acetate under hydrothermal conditions led to the unexpected 2:3 binary cocrystal 4,4′‐methylenediphenol–4,4′‐bipyridine (2/3), C₁₃H₁₂O₂·1.5C₁₀H₈N₂ or (4,4′‐H₂dhdp)(4,4′‐bipy)_1.5, which is formed with a concomitant decarboxylation. The asymmetric unit contains one and a half 4,4′‐bipy molecules, one of which straddles a centre of inversion, and one 4,4′‐H₂dhdp molecule. O—H...N interactions between the hydroxy and pyridyl groups lead to a discrete ribbon motif with an unusual 2:3 stoichiometric ratio of strong hydrogen‐bonding donors and acceptors. One of the pyridyl N‐atom donors is not involved in hydrogen‐bond formation. Additional weak C—H...O interactions between 4,4′‐bipy and 4,4′‐H₂dhdp molecules complete a two‐dimensional bilayer supramolecular structure.