Two-dimensional delocalized states in organometallic bis-acetylide networks on Ag(111)

Abstract

The electronic structure of surface-supported organometallic networks with Ag-bis-acetylide bonds that are intermediate products in the bottom-up synthesis of graphdiyne and graphdiyne-like networks were studied. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal a frontier, unoccupied electronic state that is delocalized along the entire organometallic network and proves the covalent nature of the Ag-bis-acetylide bonds. Density-functional theory (DFT) calculations corroborate the spatial distribution of the observed delocalized state and attribute it to band mixing of carbon and silver atoms combined with n-doping of the metal surface. The metal-bis-acetylide bonds are typical metal-organic bonds with mixed character containing covalent and strong ionic contributions. Moreover, the organometallic networks exhibit a characteristic graphene-like band structure with linear band dispersion at each K point.

On‐Surface Assembly of Hydrogen‐ and Halogen‐Bonded Supramolecular Graphyne‐Like Networks

“…The corresponding calculated STM images from optimized gas-phase structures for À0.35 Vand 4.85 V are shown as an inset. The shift towards negative energies in the experimentcompared to DFT in gas phase originates from acharge transfer from the surface to the H-TET-networks, which is consistent with the one previously reported for triethynyltriazine derivatives on Ag(111) [13]. f,g) DFT-optimizedH-TET hcp structure (g) on Ag(111) and (f)free-standing.…”

“…Chemical Synthesis. Thes ynthesis of 2,4,6-tris(bromoethynyl)-1,3,5-triazine (Br-TET) is described in Yang et al [13] 1,3,5-Tris(bromoethynyl)benzene (Br-TEB) was synthesizedf rom known 1,3,5triethynylbenzene [24] (H-TEB) and 2,4,6-tris[(trimethylsilyl)ethynyl]-1,3,5-triazine [10] through brominationwith N-bromosuccinimide.…”

“…TheB r À C(sp) bonds cleave on Ag(111) and Au(111) surfaces already below room temperature. [13] Therefore,B r-TET was deposited on Au(111) at 90 K, which forms small self-assembled islands at submonolayer coverage (Figure 3b,c). Three bright protrusions per molecule with as eparation of a = 1.00 AE 0.05 nm are visible at low bias voltages (see the yellow triangle in Figure 3d), which correspond to the Br groups and confirm that Br-TET adsorbs intact on Au(111) at these conditions.The hcp structure of the Br-TET self-assembly is qualitatively the same as for H-TET but formed by N triazine ···BrÀC(sp) halogen-bonded instead of hydrogen-bonded molecules.T he unit cell with dimensions of a = b = 1.00 AE 0.05 nm and q = 120 AE 38 8 is slightly larger than for H-TET because of the larger van der Waals radius of the Br moieties compared to H. TheB r···N triazine distance measures about 3 ,which is typical for ahalogen-bonded Nheterocycle with Br.…”

“…[12] In contrast, on the surface,t he reorientation of the Br-TET upon debromination results in the honeycomb Ag-bis(acetylide) networks reported previously. [13]…”

On‐Surface Assembly of Hydrogen‐ and Halogen‐Bonded Supramolecular Graphyne‐Like Networks

“…It is important to note, however, that the noncovalently ordered hcp structures do not directly convert into covalently linked N‐containing graphdiyne upon reaction, as demonstrated at the gas/liquid and liquid/liquid interface for several layered 2D materials . In contrast, on the surface, the reorientation of the Br‐TET upon debromination results in the honeycomb Ag‐bis(acetylide) networks reported previously …”