Flexible Building Blocks of N,N‘-Bis(picolinoyl)hydrazine for Hydrogen-Bonding Directed Cocrystallization: Structural Diversity, Concomitant Polymorphs, and Synthon Prediction

Two new flexible dipyridyl building blocks, N, N ‘ -bis(4-picolinoyl)hydrazine (4-bph) and its N -orientation isomer N, N ‘ -bis(3-picolinoyl)hydrazine (3-bph), have been synthesized as versatile cocrystallizing agents and introduced into the reactions with pyromellitic acid (H 4 BTA) and fumaric acid (H 2 Fa). Hydrogen-bonded directed assemblies of two hydrates of bphs and four binary cocrystals were validated by single-crystal X-ray diffraction analysis. With the presence of the reliable hydrogen-bonding donor/acceptor(s) of bph, the crystalline lattices of [4-bph]·2H 2 O ( 1 ) and [3-bph]·2H 2 O ( 4 ) are managed by N−H···O water and O−H···O carbonyl to afford one-dimensional (1D) arrays, which are further extended to distinct three-dimensional (3D) (for 1 ) and two-dimensional (2D) (for 4 ) networks via O−H···N pyridyl interactions. While for the concomitant polymorphs [(H 2 BTA)·(H 2 -4-bph)] ( 2 and 3 ), charge-assistant bifurcated N−H···O bonds do favor 1D acid−base hydrogen-bonding tapes, which are interlinked to result in a 2D layer in 2 and a 3D network in 3 through the competition of O−H···O carboxyl and O−H···O carbonyl forces. [(H 3 BTA) 2 ·(H 2 -3-bph)]·4H 2 O ( 5 ) is also a charge-transfer organic salt with a 2D bilayered array. Proton transfer from weak H 2 Fa to 3-bph is not observed, and this leads to the formation of a binary neutral cocrystal [(H 2 Fa)·(3-bph)] ( 6 ), in which the 2D undulating herringbone pattern is constructed via the expected carboxylpyridyl heterosynthon and amide−amide homosynthon.