Transmetalation in Surface-Confined Single-Layer Organometallic Networks with Alkynyl–Metal–Alkynyl Linkages

Transmetalation represents an appealing strategy toward fabricating and tuning functional metal–organic polymers and frameworks for diverse applications. In particular, building two-dimensional metal–organic and organometallic networks affords versatile nanoarchitectures of potential interest for nanodevices and quantum technology. The controlled replacement of embedded metal centers holds promise for exploring versatile material varieties by serial modification and different functionalization. Herein, we introduce a protocol for the modification of a single-layer carbon–metal-based organometallic network via transmetalation. By integrating external Cu atoms into the alkynyl–Ag organometallic network constructed with 1,3,5-triethynylbenzene precursors, we successfully realized in situ its highly regular alkynyl–Cu counterpart on the Ag(111) surface. While maintaining a similar lattice periodicity and pore morphology to the original alkynyl–Ag sheet, the Cu-based network exhibits increased thermal stability, guaranteeing improved robustness for practical implementation.

Firstly, the gas phase DFT optimization for unit cell representation of the alkynyl-Ag-alkynyl and alkynyl-Cu-alkynyl linkage reveals that the length of Ag-TEB is longer than the Cu-TEB linkage, as shown in Figure S2a and S2e.Secondly, we proposed and built calculated models as shown in Figure S2, with possible unit cells: hexagonal unit cells with vectors 4◊√3 in Figure S2b and S2f (hexagonal), rectangular unit cells with vectors 12◊√3 in Figure S2c and S2g (rectangular-12) and rectangular unit cells with vectors 13◊√3 in Figure S2d and S2h (rectangular-13), to simulate both networks adsorbed on the Ag(111) substrate by DFT.The rectangular-12 is in principle the same as the hexagonal one with two unit cells of the hexagonal cell inserted into the rectangular cell.The rectangular-13 has one more row of Ag substrate to be extended.Additionally, the formation energy for all network modes was calculated per two molecules and three metal atoms.The Ag atoms are coded in green and the Cu atoms are marked in orange.
In the case of the Cu-TEB OMN model, the hexagonal, rectangular-12 and rectangular-13 models are presented in Figure S2f-h, respectively.The corresponding Ebind(Cu/hexagonal) = -6.90eV, Ebind(Cu/rectangular-12) = -6.91 eV and Ebind(Cu/rectangular-13) = -6.68eV are found, which implies Figure S2f to be the most stable structure for Cu-TEB OMN.As we discussed before, hexagonal and rectangle-12 model are in principle similar, hence the formation energy for both are close, while also implies no distortions and nice matching between Cu-TEB OMN and Ag(111) substrate.The lattice constants for hexagonal one of Cu-TEB (Figure S2f-g Comparing the rectangular-13 structure of Ag-TEB with the hexagonal one and rectangular-12 ones of Cu-TEB OMN, all the Cu atoms can be located at the hollow position (we show the case of hcp hollow sites for hexagonal one in Figure S2f, but fcc hollow sites for rectangular-12 in Figure S2g).Moreover, the benzene ring centers also seat at hollow positions.This reveals an excellent matching between the Cu-TEB OMN and the Ag(111) substrate.However, in the case of the Ag-TEB OMN (cf. Figure S2g) one cannot place all metal atoms at the same substrate sites in an extended ordered hexagonal network.The simulated model thus gives proof of a mismatch between the Ag-TEB OMN and the Ag(111) substrate, which causes some distortion in the network, and leads to the rectangular unit cell rather than the rhombic counterpart of the hexagonal structure.Besides, the alkynyl-Ag-alkynyl structure is flexible as described in previous study [1][2][3] .Therefore, the Ag-TEB OMN may be distorted due to this mismatch, whereas the Cu-TEB tends remain hexagonal.
In the following, we proceed to explain the principle driving force inside of the transmetalation on the surface focusing formation energy for the alkynyl-M-alkynyl structures.The DFT calculated formation energy for Ag-TEB and Cu-TEB OMN was apparently different.Ebind(Ag/rectangular-13) = -3.88eV for Ag-TEB OMN, and Ebind(Cu/hexagonal) = -6.90eV for Cu-TEB OMN.Thus, one can clearly see that the formation energy for alkynyl-Cu-alkynyl is lower than for alkynyl-Ag-alkynyl by 3.0 eV, which emphasizes that alkynyl-Cu-alkynyl is significantly more stable than alkynyl-Ag-alkynyl linkage.Specifically, herein we propose a superstructure matrix ( 13 0 4 8 ) for the Ag-TEB OMN periodicity according to models' parameters from Figure S2, as shown in Figure S7a, whose reciprocal-space pattern was simulated via the LEEDpat simulator software 4 .The real-space structure encompasses three inequivalent symmetry domains and the resulting reciprocalspace pattern matches well the experimental LEED pattern of Ag-TEB OMN (Figure 2a and

Figure S9. LEED patterns for (a) Ag-TEB OMN and (b) Cu-TEB OMN after annealing at 450 K, both taken with the same primary electron energy of 35 eV.
The LEED pattern for Ag-TEB at 450 K is shown in Figure S9a, which maintains the same pattern as Ag-TEB at 375 K (cf. Figure 2a and Figure S8a).The ordered LEED pattern for Ag-TEB could not be obtained at 500 K, since the network decomposed at such temperature.However, the LEED pattern for Cu deposition on Ag-TEB followed by annealing at 450 K is compared in Figure S9b, which shows the same lattice periodicity as Cu-TEB OMN at 500 K (cf. Figure 3b and Figure S8b).The disappearance of triple dot motifs indicating Ag-TEB to Cu-TEB transmetalation can still be recognized clearly.For further study and to complement the transmetalation protocol, we also monitored the preparation of the Cu-TEB OMN under conditions in the initial formation of Ag-TEB OMN was prevented.Pristine TEB molecules self-assembled on Ag(111) were exposed to O2 gas at an amount of 600 L at 200 K, forming deprotonated TEB.Subsequently, an appropriate amount of Cu atoms was dispersed onto the deprotonated TEB self-assembly at 200 K, followed by stepwise annealing up to a final temperature of 450 K.In the real-space STM images of Figure S11        We also tried Bi to replace Ag in the Ag-TEB system by LEED.As shown in Figure S19a, b and c, the addition of Bi still maintains rotational domains leading to some dot triplets reminiscent of the Ag-TEB OMN pattern, but new features indicative of a weaker, new ordered periodic structure appeared, suggesting that Bi may modify the Ag-TEB network.However, the LEED pattern turned into much weaker after annealing at 350 K, proving lower as well as weaker structural order than the Ag-TEB OMN.Therefore, it is unlikely that Bi simply replaces Ag in the networks.Additionally, in the system of Ni combined with the Ext-TEB molecule (which also has terminal alkynyl groups) 2 , LEED measurements did not support the successful replacement of Ag with Ni atoms.Figure S19d-f shows the LEED pattern of the Ext-TEB network and its structure worsening upon Ni deposition. in particular, the long-range order is totally disrupted following followed annealing at 400 K (cf. Figure S19f).Thus, these metals could not demonstrate their ability to replace Ag in the pre-existing organometallic system, but instead the observed findings suggest that there may be deeper factors deserving further investigation.
Other used materials: 1,3,5-Tris (4-ethynylphenyl) benzene (Ext-TEB) molecules were synthesized by Svetlana Klyatskaya and Mario Ruben according to a procedure described in Ref 5 .Ni, a highly pure metal foil of 0.2 mm thickness purchased from GoodFellow GmbH, was cut into a ribbon with dimensions of 15 × 20 mm 2 and clamped in between two copper rods.Metallic Bi is typically supplied in the form of flakes and grains from GoodFellow GmbH.

Figure S3 .
Figure S3.Detailed STM images and single pores of Ag-TEB and Cu-TEB OMN.

Figure S5 .
Figure S5.LEED patterns of Ag-TEB OMN acquired at 90 K with different primary electron energy.

Figure S6 .
Figure S6.LEED patterns of Cu-TEB OMN acquired at 90 K with different primary electron energy.

Figure S7 .
Figure S7.Simulated LEED patterns for Ag-TEB and Cu-TEB OMN and corresponding STM images.

Figure S8 .
Figure S8.Original LEED pattern of Ag-TEB OMN and Cu-TEB OMN with primary electron energy of 30 eV.

Figure
Figure S9.LEED patterns for Ag-TEB and Cu-TEB OMN after annealing at 450 K.

Figure S10 .
Figure S10.Peak fit of Cu 2p3/2 XP spectrum for Cu-TEB OMN and Cu 2p3/2 XPS measurements of Cu on pristine Ag(111) annealed to different temperatures.

Figure S11 .
Figure S11.STM images of deprotonated TEB self-assembly and Cu addition on deprotonated TEB self-assembly at 200 K, then annealing at 450 K.

Figure S13 .
Figure S13.Constant height STM images, theory LDOS maps and STS line spectra for Ag-TEB and Cu-TEB OMN.

Figure S19 .
Figure S19.LEED patterns for Bi deposition onto Ag-TEB OMN and Ni onto Ext-TEB OMN.Other used materials.

Figure S1 .
Figure S1.Large-area STM images of Ag-TEB OMN with 0.2 μm-size (a) and 50 nm-size (b); the inset presents the 2D-FFT of the 50 nm × 50 nm area shown in panel (b).Panel (c) emphasizes the glide symmetry of neighboring distorted hexagons.In panel (d) we outline a rhombic unit cell (in yellow) similar to the Cu-TEB network of Figure 1c, as a comparison to the rectangle unit cell assumed in Figure 1a.The tunneling parameters are Vb = -500 mV, It = 100 pA (a); Vb = 400 mV, It = 1 nA (b); and Vb = 350 mV, It = 300 pA (c) and (d).

Figure S2 .
Figure S2.Gas phase optimized structure for unit cell representation of Ag-TEB (a).DFT simulated models of Ag-TEB OMN with possible hexagonal, rectangular-12 and rectangular-13 unit cells (b) (c) (d) on the Ag(111) surface.Gas phase optimized structure for unit cell representation of Cu-TEB (e), and DFT simulated models of Cu-TEB OMN with possible hexagonal, rectangular-12 and rectangular-13 unit cells (f) (g) (h) on the Ag(111) surface.In ) are a = b ≈ 20.0 Å, which are close to the average experimental results (a = 20.1 ± 0.2 Å, b = 20.3 ± 0.2 Å).

Figure S3 .
Figure S3.High-resolution STM images of (a) Ag-TEB and (b) Cu-TEB OMN with constant current scanning mode.Scanning parameter for (a) and (b): Vb = -10 mV, It = 1 nA.Zoom-in STM images of a single pore of Ag-TEB (c) and Cu-TEB OMN (d) recorded at constant height scanning mode at Vb = 10 mV.

Figure S5 )
FigureS5) with characteristic triplet motifs.Additionally, this matrix is consistent with the rectangle unit cell in Figure1aand FigureS7cwith a = 37.6 ± 0.2 Å, b = 20.7 Å ± 0.2 Å,   90.2 ± 1°.The agreements emphasize the reasonability of the Ag-TEB OMN model shown in Figure S2.Conversely, the LEED pattern of Cu-TEB OMN shown in Figure S7b can be assigned to the superstructure matrix ( 8 −4 −4 8 ), corresponding to a well-defined (4√3 × 4√3)R30° periodicity relative to the underlying substrate.This assignment is in excellent agreement with the rhombus primitive cell of Figure S7d for Cu-TEB OMN with lattice parameters a = 20.1 ± 0.2 Å, b = 20.3 ± 0.2 Å,   59.2º ± 1.0º, and is corroborated by the absence of spot splitting in the LEED patterns of the Cu-TEB OMN at different primary electron energies (cf. Figure S6).

Figure S8 .
Figure S8.As-recorded LEED patterns extracted from Figure 2 of the main manuscript without any overlapping drawing.(a) Ag-TEB OMN and (b) Cu-TEB OMN with the same primary electron energy of 30 eV.The disappearance of the triple (split) diffraction spots going from a to b is evident.

Figure S10 .
Figure S10.(a) Peak fit for the XP spectrum of the Cu 2p3/2 core level of the Cu-TEB OMN after annealing at 500 K.(b) Cu 2p3/2 XP spectra and fitting analysis for Cu deposited onto the pristine Ag(111) surface after annealing at 300 K (bottom), 450 K (middle) and 500 K (top), respectively.
the three subsequent stages of this preparation protocol used to form a Cu-TEB OMN are shown.The final structure of panel c matches the Cu-TEB OMN obtained through transmetalation.However, the OMN domains are generally not as large as those by transmetalation, suggesting a more straightforward and effective modification of the Ag-TEB OMN into Cu-TEB OMN.

Figure S12 .
Figure S12.Long-range dI/dV spectra from -1.0 V to 1.5 V of the Ag-TEB (blue curve) and Cu-TEB (red curve) OMN at the pore centers.

Figure S13 .S10Figure S14 .
Figure S13.Constant-height STM images of (a) Ag-TEB OMN at the bias Vb = 360 mV and (b) Cu-TEB OMN at the bias Vb = 380 mV, corresponding to Figure 4b and 4c of the main manuscript, respectively.Theory LDOS map for Ag-TEB at 660 mV (c), and for Cu-TEB OMN at 680 mV (d).Panel (e) and (g) depict STS line spectra across the pore centers of Ag-TEB and Cu-TEB OMN along the white dash line marked in Figure4b and c.Then simulated LDOS line spectra for Ag-TEB and Cu-TEB OMN are presented in panel (f) and (h), respectively.

Figure S16 .
Figure S16.(a) STM images for the structure of Ag-TEB OMN emerging after annealing at 500 K and for (b) Cu-TEB OMN after annealing at 600 K. Tunneling parameters are Vb = -100 mV, It = 500 pA in (a) and Vb = -100 mV, It = 200 pA in (b).

Figure S17 .
Figure S17.STM images of Cu-TEB OMN (a) after annealing at 500 K for 1h and (b) at 600 K for 10 mins.(c) Large-area and (d) zoom-in STM images of Cu-TEB OMN containing alkynylalkynyl coupling linkages.(a) (c) and (d) were scanned at Vb = 380 mV and It = 300 pA, (b) was scanned at Vb = 370 mV and It = 200 pA,

Figure S19 .
Figure S19.Top line: LEED patterns for Ag-TEB OMN (a), Bi on Ag-TEB OMN at 300 K (b) and followed by annealing at 350 K (c), acquired at 90 K with primary electron energy of 30 eV.Bottom line: LEED patterns for Ext-TEB OMN (d), Ni deposition on Ext-TEB OMN at 300K (e) and followed by annealing at 400 K (f), acquired at 90 K with primary electron energy of 15 eV.