Cocrystals of 1,3,5-cyclohexanetricarboxylic acid with 4,4'-bipyridine homologues: acid···pyridine hydrogen bonding in neutral and ionic complexes

Abstract

cis,cis-1,3,5-Cyclohexanetricarboxylic acid (H₃CTA) is crystallized with bipyridine bases 1,2-bis(4-pyridyl)ethane (bipy-eta), 1,4-bis(4-pyridyl-2-ethyl)benzene (bipy-etabz), 1,2-bis(4-pyridyl)ethylene (bipy-ete), and 1,4-bis(2-(4-pyridyl)ethenyl)benzene (bipy-etebz) to afford molecular complexes (H₃CTA)·(bipy-eta)_1.5 1, (H₃CTA)·(bipy-etabz) 2, (H₂CTA-)·(bipy-ete2H⁺)_0.5 3, and (H₂CTA-)·(bipy-etebz2H⁺)_0.5 4. Cocrystal 1 has a super honeycomb hydrogen bond network stabilized by carboxylic acid-bipyridine O-H···N synthon Va. The hexagonal cavity of 34.1 × 36.7 Å is filled by parallel triple interpenetration of independent networks. 2 has zigzag chains of synthon Va connected via O-H···O hydrogen bonds. Carboxylic acid to pyridine proton transfer occurs in 3 and 4. These structures have undulated and flat 2D layers of O-H···O- and O-H···O hydrogen bonds that are connected to bipyridinium via N⁺-H···O- hydrogen bond Vb. H₂CTA- anions in 4 form a porous parquet grid of 14.5 × 7.5 Å with the channels accommodating two molecules of bipy-etebz2H⁺. Supramolecular organization and 3D architecture in H₃CTA crystal structures is compared with bipyridine adducts of trimesic acid.