2D Cu-TCNQ Metal–Organic Networks Induced by Surface Alloying

Abstract

We have studied the self-assembly of 7,7,8,8-tetracyanoquinodimethane molecules on the (3√2 × √2)R45°reconstruction of the SnCu(001) surface alloy by means of X-ray photoemission spectroscopy, scanning tunneling microscopy, near-edge X-ray absorption fine structure spectroscopy, and density functional theory calculations. Our results show that surface alloying strongly attenuates the chemical interaction of the molecule with the surface, but it does not inhibit the charge transfer from the substrate to the molecules. The assembly mechanism of the molecules is completely modified with respect to the bare Cu(001) surface. We show that, on the SnCu(100) surface alloy, the strong CN−Cu interaction drives the formation of different coordination structures with native Cu adatoms. We found that the flexible coordination chemistry of Cu allows the formation of three different stable phases, each one with the Cu ions in a different coordination geometry (coordinations 4, 3, and 2). Moreover, we show that both the formation of lateral H bonds between adjacent molecules and the interaction of the Cu ion with the substrate play determinant roles in the stabilization of the structures.

Mn–Cu Transmetalation as a Strategy for the Assembly of Decoupled Metal–Organic Networks on Sn/Cu(001) Surface Alloys

“…When TCNQ molecules are deposited on the 3 2 -Sn/ Cu(001) substrate kept at 150 °C, followed by a cooling down step to RT, two coexisting coordination structures based on native Cu adatoms are observed forming large ribbon-type domains: the γ and β phases, where native Cu adatoms are bond to three and two nitrile groups, respectively (see Figure 1). 19 While the β-phase with a Cu:TCNQ ratio of 2:1 and a molecular coverage of 1/14 ML dominates at low coverages, the γ-phase with a Cu:TCNQ ratio of 1:1 and a molecular coverage of 1/12 ML dominates at coverages close to a saturated monolayer. A distinctive characteristic of the γ and β phases is the presence of TCNQ molecules azimuthally rotated with respect to the [100] crystallographic direction (see Figure 1).…”

“…34 In this particular case, the Sn-mediated coordination can be discarded since the Cu−nitrile coordination bonds are dominant over the Sn−nitrile bonds. 19,34 The rectangular Mn−TCNQ network, with a Mn:TCNQ ratio of 1:1 and each Mn atom coordinating four TCNQ molecules by their nitrile groups, seems to be the most reasonable candidate for the obtained structure. Although geometrically similar to the RT α phase of Cu−TCNQ, the structure of the Mn− TCNQ unit cell is predicted to be significantly different in terms of adsorption sites and molecular conformation, as will be shown hereafter.…”

“…16−19 In particular, we have shown in previous work that TCNQ molecules deposited on the 3 2 -Sn/Cu(001) substrate present a rich phase diagram where TCNQ forms different MOCNs with native Cu adatoms. 19 A possible route to the formation of novel metal−organic structures on surfaces is by means of transmetalation reactions. 20−24 Very recently, Hoẗger et al reported an interesting study of the Fe → Co transmetalation reaction taking place in Fe-porphyrins adsorbed on Au(111), where the reaction paths were theoretically analyzed with great detail.…”

Two-Dimensional Rare Earth–Gold Intermetallic Compounds on Au(111) by Surface Alloying

“…nanocluster or molecules. 8 Further, the periodical modulations in the coupling between the adlayer and the subsequent layer, e.g. substrate, might give rise to new exotic phenomena.…”

Remarkably stable metal–organic frameworks on an inert substrate: M-TCNQ on graphene (M = Ni, Fe, Mn)

“…Here, we present three well-defined and remarkably stable 2D MOFs supported on an inert graphene/Ir(111) substrate. As the organic linker we utilize a TCNQ molecule (7,7,8,8-tetracyanoquinodimethane), which is a strong electron acceptor and a popular choice for MOF synthesis both on-surface 7,9,[18][19][20][21][22] and in solution. 23,24 TCNQ-based 2D MOFs are also intensively studied computationally, [25][26][27][28][29][30][31] but the simulated free-standing systems are not directly comparable to metal-supported nor solution-based MOFs.…”