Tailoring Large Pores of Porphyrin Networks on Ag(111) by Metal–Organic Coordination

Abstract

The engineering of nanoarchitectures to achieve tailored properties relevant for macroscopic devices is a key motivation of organometallic surface science. To this end, understanding the role of molecular functionalities in structure formation and adatom coordination is of great importance. In this study, the differences in formation of Cu-mediated metal-organic coordination networks based on two pyridyl- and cyano-bearing free-base porphyrins on Ag(111) are elucidated by use of low-temperature scanning tunneling microscopy (STM). Distinct coordination networks evolve via different pathways upon codeposition of Cu adatoms. The cyano-terminated module directly forms 2D porous networks featuring fourfold-coordinated Cu nodes. By contrast, the pyridyl species engage in twofold coordination with Cu and a fully reticulated 2D network featuring a pore size exceeding 3 nm only evolves via an intermediate structure based on 1D coordination chains. The STM data and complementary Monte Carlo simulations reveal that these distinct network architectures originate from spatial constraints at the coordination centers. Cu adatoms are also shown to form two- and fourfold monoatomic coordination nodes with monotopic nitrogen-terminated linkers on the very same metal substrate-a versatility that is not achieved by other 3d transition metal centers but consistent with 3D coordination chemistry. This study discloses how specific molecular functionalities can be applied to tailor coordination architectures and highlights the potential of Cu as coordination center in such low-dimensional structures on surfaces.

BN‐Patterning of Metallic Substrates through Metal Coordination of Decoupled Borazines

“…Interestingly, this network does not reflect the three‐fold symmetry of BNPPy , but bases on interconnected chains where only one of the three pyridyl‐substituents seems to engage in Cu coordination. Even if we cannot exclude the presence of some coordinative interactions along the chains, our data suggest the simultaneous expression of metal‐organic and organic bonding motifs . The measured center‐to‐center distance between BNPPy units along the coordinated substituents, that is, perpendicular to the chain direction, is (32.2±0.6) Å.…”

“…Interestingly,t his network does not reflect the three-fold symmetry of BNPPy,b ut bases on interconnected chainsw here only one of the three pyridyl-substituents seems to engage in Cu coordination.E ven if we cannot exclude the presence of some coordinative interactions along the chains, our data suggest the simultaneous expression of metal-organic and organic bondingm otifs. [27,28] Them easured center-to-center distance between BNPPy units alongt he coordinated substituents, that is, perpendicular to the chain direction, is (32.2 AE 0.6) .W ith ap yridyl-substituent length of 14.4 ,e xtracted from the structural model (after geometry optimization with the semi-empirical AM1 method in Hyper-Chem) [29] ,t his results in ap rojected pyridyl-Cu-pyridyl bond length of 3.4 ,s lightly reduced comparedt ot he 3.6 reported in the literature. [20,23,24,30] This can be rationalized by the inplane bending of the substituents.A ccordingly,t he projected NÀCu bond length corresponds to 1.7 .…”

On‐Surface Metalation and 2D Self‐Assembly of Pyrphyrin Molecules Into Metal‐Coordinated Networks on Cu(111)

“…About 10% of the surface is covered by molecular chains (framed in blue). Such chain morphology has been also observed for molecules with two cyano groups attached at opposite sides of the same molecule . At a higher coverage, the chain motif has been replaced by the denser honeycomb motif .…”

“…In solution, CoPyr derived complexes have been shown to catalyze the reduction of water under illumination with light . Cyano‐functionalized molecules in general may also act as ligands for surface adatoms . Such coordination at radial or terminal functional groups leads often to the formation of highly ordered 2D metal‐organic coordination networks …”

Conformational adaptation and manipulation of manganese tetra(4-pyridyl)porphyrin molecules on Cu(111)

“…Porphyrins and metalloporphyrins are versatile species for constructing supramolecular architectures on metal surfaces via non-covalent intermolecular interactions [1][2][3][4][5] or metalcoordination bonds. [4][5][6][7][8][9][10][11] In these assemblies, the molecules can take different conformations as a result of an adaptation to the substrate lattice periodicity as well as an optimization of the bonding energy to lateral neighbors (atoms or molecules). [12][13][14][15] These interactions can be steered by the design of the molecular endgroups.…”