A strategy to modulate the in‐plane structural arrangement in preferentially oriented crystalline metal–organic framework (MOF) nanosheets assembled by a two‐dimensional interfacial reaction between porphyrin units and metal ion linkers is reported. Starting with a tetratopic porphyrin MOF nanofilm, NAFS‐2, the framework size and shape are modified by employing specially designed building units, a trans‐ditopic and an expanded tetratopic porphyrin, and Cu2+ linkers. Reducing the number of binding parts affords a MOF nanosheet, NAFS‐31, with a distorted in‐plane structure. Extension of the peripheral substituents, while maintaining the tetratopic porphyrin geometry, results in marked unit cell size enlargement in an undistorted square grid in the MOF nanofilm, NAFS‐41. The exquisite geometric control that these structural modifications entail is valuable to allow switching of chemical/physical properties of the nanosheets and lead to realization of their use in nanotechnological applications.

Single crystals of a layer-structured coordination polymer, BNAS-11 [ZnTCPP(H 2 O)Zn 2 (H 2 O) 2 ] (ZnTCPP: 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinatozinc(II)), were obtained. Tetratopic ZnTCPP molecules are connected through dimer zinc paddle-wheel secondary building units and form a two-dimensional (2D) network with square grids. The layers are stacked electrostatically without the need of binding pillar ligands.Two-dimensional (2D) nanomaterials with monomolecular thickness are of considerable interest because they exhibit unique properties due to their dimensionality and can be utilized as extremely small components in nanodevices.1 Coordination compounds, including metalorganic frameworks (MOFs) or porous coordination polymers (PCPs), are attractive for assembling 2D nanosheets as their structures can be rationally designed from inorganic and organic building units and are endowed with various functionalities.2,3 We have synthesized 2D MOF nanosheets (NAFS) by a bottom-up approach utilizing reactions at the airliquid interface.4 Molecular building units with peripheral coordinative parts are spread on the surface of an aqueous solution of metal-ion linkers. This initiates a coordinative reaction at the interface and results in the formation of 2D MOF nanosheets. 4 The synthetic protocol is not restricted to MOFs and can be used for the creation of various 2D coordination compounds 5 as the reactants are strictly restricted to the direction parallel to the surface. Another way to obtain 2D nanosheets of various materials (e.g., graphite, 1c metal oxides, 1d transitionmetal chalcogenides, 1e and organic polymers 1f ) is by exfoliating the bulk crystals with layered structures; the starting components are strongly connected laterally, while the 2D layers are weakly stacked, allowing peeling by physical and chemical treatments.(Metallo)porphyrins are stable macrocyclic ligands with square-planar geometry 3c,3d,6 and are excellent candidates for constructing 2D nanonetworks through a suitable choice of peripheral coordinative substituents and metal-ion linkers. However, it is difficult to exfoliate MOF crystals as removal of the counter ions needed for charge balance destabilizes the peeled layers 3e3g or the individual layers are rigidly connected vertically by bidentate pillars.3h,3i On the other hand, porphyrinbased MOF crystalline materials without any pillars, reminiscent of the interlayer stacking mode of the NAFS nanofilms, 4 grown by the LangmuirBlodgett layer-by-layer (LB-LbL) methodology are rare. 3j,3kHere we report the isolation of a new bulk analogue of crystalline NAFS thin films [ZnTCPP(H 2 O)Zn 2 (H 2 O) 2 ] (designated BNAS-11). It is a polymorph of the PPF-1 MOF, 3k retaining the same ZnTCPPZn sheet structure but adopting a different stacking sequence perpendicular to the layers. The existence of such multiple polymorphs with differing sheet stacking patterns reflects the weak interlayer interactions and provides opportunities for facile exfoliation of the crystals to obtain 2D nanosh...