Conservation of Nickel Ion Single‐Active Site Character in a Bottom‐Up Constructed π‐Conjugated Molecular Network

Abstract

On-surface chemistry holds the potential for ultimate miniaturization of functional devices. Porphyrins are promising building-blocks in exploring advanced nanoarchitecture concepts. More stable molecular materials of practical interest with improved charge transfer properties can be achieved by covalently interconnecting molecular units. On-surface synthesis allows to construct extended covalent nanostructures at interfaces not conventionally available. Here, we address the synthesis and properties of covalent molecular network composed of interconnected constituents derived from halogenated nickel tetraphenylporphyrin on Au(111). We report that the π-extended two-dimensional material exhibits dispersive electronic features. Concomitantly, the functional Ni cores retain the same single-active site character of their single-molecule counterparts. This opens new pathways when exploiting the high robustness of transition metal cores provided by bottom-up constructed covalent nanomeshes.

Tuning Transition Metal‐Containing Molecular Magnets by On‐Surface Polymerization

“…This is characteristic of the formation of a 𝜋-extended covalent nanostructure with flat phenyl substituents, which are closely parallel to the surface plane due to cyclo-dehydrogenation side reactions. [8,31] A better understanding of the interaction of the macrocycle with the surface can be obtained from the N K-edge spectra. The resonances observed in the N K-edge spectra of metalloporphyrins can be classified into pure macrocycle (index m) states and states arising from the mixing of metal 3d and N ligand 2p states (index Ni).…”

“…[32] We further remark on the broadening of the pure macrocycle 𝜋*-resonance, which reflects the formation of a covalent nanomesh with an extended degree of 𝜋-conjugation. [8,31] NiTPP units within polymerized nanomeshes are known to be dehydrogenated on Au(111). [8,31] Even though the intermolecular coupling occurred at the predefined connection points defined by the Br positions in the NiTBrPP precursor, a control on the different dehydrogenation pathways was not observed.…”

“…[6,7] It was further demonstrated that the single ion configuration is uniform across covalently extended porphyrin structures. [8] For extended one-dimensional metalloporphyrin chains, it was shown that the magnetic anisotropy can be manipulated by cyclodehydrogenation without any differences between the functional centers stabilized within the polymerized structure and those of their single-molecule counterparts. [9] However, it remains largely unexplored how the magnetic properties of the central metal ion are influenced within 2D nanostructures as a consequence of the polymerization of the molecular constituents and the formation of a 𝜋-extended molecular backbone.…”

Extended π-conjugation: a key to magnetic anisotropy preservation in highly reactive porphyrins

“…9–11 Furthermore, on-surface synthesis allows the modification of the chemical structure and the formation of extended covalent nanostructures, which further strengthens porphyrin-based architectures. 12…”

“…[9][10][11] Furthermore, onsurface synthesis allows the modification of the chemical structure and the formation of extended covalent nanostructures, which further strengthens porphyrin-based architectures. 12 In this regard, a well-known surface-assisted ring-closure reaction in the case of tetraphenylporphyrin (TPP) results in the formation of a planarized porphyrin molecule with an extended p-conjugated macrocycle ring. 13,14 Recently, the on-surface planarization reaction has also been suggested as an effective way to alter the magnetic properties, as evidenced by the increase of the effective spin moment in iron(II)-tetrabenzoporphyrin.…”