Hetero‐Epitaxial Approach by Using Labile Coordination Sites to Prepare Catenated Metal–Organic Frameworks with High Surface Areas

Abstract

A solid-state approach that takes advantage of the ordered 3D arrangement of active secondary building units allows the preparation of new interlocked MOFs that grow hetero-epitaxially on the crystal faces of a precursor phase that acts as a "topological blueprint". The synthetic strategy is exemplified by using rigid acetylene-based ligands to produce highly augmented Cu(II) acetate-based MOFs.

Ultra-large supramolecular coordination cages composed of endohedral Archimedean and Platonic bodies

“…The SBUs of the coordination cages are dinuclear {Cu 2 } ‘paddlewheel' complexes in which O-donor atoms of syn, syn -bidentate carboxylate groups of the deprotonated, organic ligands provide the basal plane of the square pyramidal coordination polyhedra; O-donor atoms of coordinating H 2 O and DMF molecules bind in the apical positions. The observed structural characteristics of the {Cu 2 } units closely compare to those observed in other MOPs or MOFs1026424344. The Cu–O bond lengths of the outer located {Cu 2 } units in SK-1 involving the carboxylate functionalities vary between 1.939(5) and 1.985(6) Å while Cu–O bond distances of the coordinating solvent molecules range between 2.106(5) and 2.166(7) Å.…”

“…The analysis is further substantiated by Infra-Red (IR) spectra of as-prepared crystals of SK-1 and surface-deposited molecules from SK-1/PPP/CHCl 3 solutions. The resulting IR spectra of SK-1 are characterized by vibrational signals at 1,594 and 1,430 cm −1 corresponding to the asymmetric and symmetric carboxylate stretches; their positions (Δν=ν a −ν s =164 cm −1 ) agree with the observed syn-syn bidentate bridging mode of the benzoate functionalities of the m -BTEB ligands in dinuclear SBUs42. Depositions that result from the evaporation of SK-1/PPP/CHCl 3 solutions give rise to IR spectra that confirm the presence of PPP molecules and spectral signatures that closely match those of the parent bulk, crystalline material of SK-1 (Supplementary Fig.…”

“…At initial stages of the presented work we were particularly interested in the rotational flexibility associated with the acetylene moiety of the m -BTEB ligand, which was expected to produce a number of isomeric coordination compounds42. This rotational freedom is a feature of extended ligands that incorporate acetylene moieties and distinguishes these linker-types from less-extended stericially restrained derivatives.…”

“…Particularly, symmetric structures with linearly arranged {Cu 2 } SBUs can provide ‘molecular traps' for suitably sized molecules whose donor atoms facilitate the bridging between the two active coordination sites of adjacent SBUs262742. In this context, the observed symmetric arrangement of the six {Cu 2 } units whose labile solvent molecules locate linearly opposite to each other and whose molecular axes point towards a single focal point is expected to be ideal to facilitate guest binding.…”

“…Further binding sites are provided by {Cu 2 } units of the outer shell whose labile solvent sites point to the inside of the molecular entities. Noteworthy are the ‘super-paddlewheel' units in SK-1A which have previously been employed to trap suitably sized guests (for example, CO 2 gas molecules, pyrazine or pyridine derivatives) between opposite located {Cu 2 } units262742. The observed Cu–Cu distances in these sub-units in SK-1A vary between ca.…”