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

Abstract

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 (H4BTA) and fumaric acid (H2Fa). 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]·2H2O (1) and [3-bph]·2H2O (4) are managed by N−H···Owater and O−H···Ocarbonyl 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···Npyridyl interactions. While for the concomitant polymorphs [(H2BTA)·(H2-4-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···Ocarboxyl and O−H···Ocarbonyl forces. [(H3BTA)2·(H2-3-bph)]·4H2O (5) is also a charge-transfer organic salt with a 2D bilayered array. Proton transfer from weak H2Fa to 3-bph is not observed, and this leads to the formation of a binary neutral cocrystal [(H2Fa)·(3-bph)] (6), in which the 2D undulating herringbone pattern is constructed via the expected carboxylpyridyl heterosynthon and amide−amide homosynthon.