Assembly of Porous Metal Hydrogen-Bonded Organic Frameworks from Diamine-Functionalized Kuratowski Complexes

In comparison to the vast field of porous materials, research into hydrogen-bonded organic frameworks (HOFs)and especially the subclass of metal hydrogen-bonded organic frameworks (M-HOFs), with only very few structures showing permanent porosity thus faris still in its infancy. Herein, Kuratowski coordination units, which are well-known from various complexes and metal–organic frameworks, were applied to advance this field of research with the synthesis and characterization of a novel series of M-HOFs. Synthesis of Kuratowski complexes with the 1<i>H</i>-benzotriazole-5,6-diamine (<b>H-btda</b>) ligand resulted in molecular building blocks, which initially assemble into <b>CFA-20-Cl</b> and <b>CFA-20-Br</b> M-HOFs ((2,6-lutidinium)⁺[Zn₅X₄(btda)₆X]⁻·<i>n</i>(DMF); X = Cl, Br; CFA-20 = Coordination Framework Augsburg University-20, DMF = <i>N</i>,<i>N</i>-dimethylformamide). Both frameworks are isostructurally stabilized via a unique hydrogen bond framework between 12 amine functional groups of six <b>btda</b> ligands and a central 12-fold hydrogen bonded halogen anion, which adapts the coordination of an irregular icosahedron. Postsynthetic ligand exchange at the Kuratowski complex of <b>CFA-20-Cl</b> performed with Tp and Tp* ligands resulted in permanently porous <b>CFA-20-Tp</b> and <b>CFA-20-Tp*</b> M-HOFs ([Zn₅Y₄(btda)₆]; Y = Tp (trispyrazolylborate), Tp* (tris­(3,5-dimethyl-1-pyrazolyl)­borate)), which, thus, constitute an important addition to the meager subclass of permanently porous M-HOFs. Crystallization of the soluble complex of <b>CFA-20-Tp*</b> from dimethylsulfoxide (DMSO) was additionally shown to result in a variant <b>CFA-20-Tp*-DMSO</b> M-HOF structure.