Templated Growth of Metal–Organic Coordination Chains at Surfaces

Abstract

Metal-organic coordination networks (MOCNs) formed by coordination bonding between metallic centers and organic ligands can be efficiently engineered to exhibit specific magnetic, electronic, or catalytic properties [1]. Instead of depositing prefabricated MOCNs onto surfaces, it has been recently shown that two-dimensional (2D) MOCNs can be directly grown at metal surfaces under ultrahigh vacuum (UHV), thus creating highly regular 2D networks of metal atoms [2]. We show here [3] that this approach allows to predefine the geometry of the MOCN by using the substrate as a template to direct the formation of novel 1D metal-organic coordination chains (MOCCs).The templating role of substrates is well known in the field of surface epitaxial growth. Among the highly anisotropic substrates, the Cu(110) surface is one of the most commonly used. To demonstrate its strong 1D templating effect on organic molecules, a ligand with a triangular symmetry was selected, namely 1,3,5-benzenetri-carboxylic acid (trimesic acid, TMA). The three-fold rotation symmetry of TMA supports the formation of hexagonal 2D and 3D architectures, therefore strongly disfavoring the linear geometry.The deposition of TMA on Cu(110) under UHV at 300 K results in the formation of 1D chains along the <1bar10> direction, as observed by scanning tunneling microscopy (STM). This deposition temperature is high enough to provide mobile Cu adatoms through evaporation from kinks and steps onto the terraces. Analysis of similar systems by X-ray photoelectron spectroscopy showed that these adatoms catalyze the deprotonation of molecular carboxylate groups and are necessary for the formation of copper carboxylate complexes. The chains formed at 300 K typically show irregular kinks and poor long-range order. These inhomogeneities are removed by postannealing to 380-410 K to yield straight and highly periodic chains, referred to as MOCC-I hereafter.

Two-Dimensional Nanotemplates as Surface Cues for the Controlled Assembly of Organic Molecules

“…The system TMA/Cu was also used to prepare in situ 1D metal-organic coordination chains on the anisotropic Cu(110) surface [92]. TMA was deposited on Cu(110) at 300 K, a temperature high enough to ensure the presence of mobile Cu adatoms that catalyse the deprotonation of carboxylate groups.…”

Hydrogen and Coordination Bonding Supramolecular Structures of Trimesic Acid on Cu(110)

“…19,44 The creation of MOCNs directly at surfaces is considered to be relevant for similar technological applications including information storage and processing 5,40,45 and also constitutes a model system to study low-dimensional magnetism at surfaces. 34,35 A typical linker molecule used for surface MOCNs is trimesic acid (TMA) comprised of three carboxylic acid groups ordered in a planar triangular arrangement around the central phenyl ring, Figure 1. TMA has been investigated in its acidic form in solids 46,47 as a three-dimensional MOCN coordinated to Cu ions 23, 48 and on low reactivity surfaces, 12,14,[49][50][51][52][53][54][55] where mostly hexagonal honeycomb networks are found, which are formed by intermolecular hydrogen bonding.…”

“…However, in its deprotonated form, the carboxylate groups may combine with metal atoms to form extended metal-organic coordination networks in three dimensions in the solid state 48,56,47 and on surfaces in two [24][25][26]28 and one dimensions. 34 We have used a combination of complementary experimental techniques to achieve complete insight into these surface networks. RAIRS is particularly useful for establishing the chemical identity, the local coordination modes, and the orientation of the surface acid/carboxylate groups.…”

Rhodizonic Acid on Noble Metals: Surface Reactivity and Coordination Chemistry

“…We note that although our calculations showed only minimal energetic differences of less than 0.05 eV/molecule between both adsorption sites in the closer-packed network, the linker Cu atoms, by contrast, always reside in the hollow sites on the surface, and this has been identified to be energetically favorable in earlier publications. 14,15,[33][34][35] When Cu atoms were manually lifted off the surface above the organic layer, they were always found to migrate back upon geometry optimization.…”