Thermal Transition from a Disordered, 2D Network to a Regular, 1D

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Thermal Transition from a Disordered, 2D Network, to a Regular, 1D, Fe(II)-DCNQI Coordination Network Jonathan Rodriguez-Fernandez, Yang Wang, Manuel Alcami, Fernando Martin, Roberto Otero, José M. Gallego, and Rodolfo Miranda J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b04288 • Publication Date (Web): 07 Jul 2016 Downloaded from http://pubs.acs.org on July 13, 2016

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The Journal of Physical Chemistry

Thermal Transition from a Disordered, 2D Network, to a Regular, 1D, Fe(II)-DCNQI Coordination Network Jonathan Rodríguez-Fernández,1 Yang Wang,2,3 Manuel Alcamí,2,3 Fernando Martín,2,3,4 Roberto Otero,1,3 José M. Gallego,5,* and Rodolfo Miranda1,3

1 Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain 2 Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049-Madrid, Spain 3 Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049-Madrid, Spain 4 Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049-Madrid, Spain 5 Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049-Madrid, Spain * corresponding author: email: [email protected] tel: (34) 91 334 8987

Abstract We report the formation of an Fe-DCNQI (DCNQI = Dicyano-p-quinodiimine) coordination network on the Ag(111) surface, where the Fe atoms are four-fold coordinated in a square-planar geometry with the N atoms of the cyano groups. Depending on the formation temperature, the coordination network can be a two-dimensional arrangement of Fe atoms in a hexagonal lattice joined by DCNQI molecules in an apparent random way, or a set of 1D chains bound together by hydrogen bonds, but with the Fe atoms

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maintaining the same hexagonal lattice. The electronic structure of this network is studied by a combination of photoemission spectroscopy and theoretical calculations based on the density functional theory. In particular, we show that the oxidation state of the Fe atoms in this 1D arrangement is +2, which has been compared with the atomic charges values obtained from first-principles calculations.

Introduction Coordination chemistry has been studied intensively over the last years, because traditional bulk coordination compounds have very interesting properties, with many applications in gas storage and separation, catalysis and magnetism.1 More recently, surface coordination chemistry, i.e., the fabrication of two dimensional coordination networks on solid surfaces, has increased the variety of properties and extended the fields of applications, including the possibility of integrating these networks into solid-state devices or catalysing nature-inspired chemical reactions.2 In addition, surface coordination chemistry is becoming a very attractive tool for the design and fabrication of nanostructured surfaces.3-5 Coordination bonds share specificity and directionality with hydrogen bonds, but they are stronger than hydrogen bonds, thus leading to more robust networks. In addition, coordination bonds do not suffer from the irreversibility inherent to covalent networks, and thus offer the possibility of preparing large areas of well-ordered arrays of molecules.6 However, the presence of the surface makes these compounds inherently different from their bulk counterparts, since the molecule-surface and metal-surface interactions may compete with both moleculemolecule and metal-ligand interactions. Thus, while the structures of some 2D coordination compounds are very similar to certain crystallographic planes already present in well-known bulk systems, in other compounds the coordination numbers and geometries are completely new. In addition, the nature of the


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coordination bonds may differ from the bulk compounds due to the influence of the neighbouring surface. In particular, the oxidation state of the metal atom remains an open question. Usually “integer”

7-13

oxidation states have been assigned according to photoemission or absorption experiments, while theoretical calculations usually predict different amounts of charge transfer.8,

14-19

In general, the

formation of the coordination bond moves away the metal atoms from the surface, reducing their hybridization with the substrate.15 In this work, we carried out STM (Scanning Tunneling Microscopy) and XPS (X-Ray Photoelectron Spectroscopy) measurements, and DFT (Density Functional Theory) calculations to characterize the structural and electronic configuration of a coordination network formed by DCNQI (Dicyano-pquinodiimine) molecules with iron atoms on a Ag(111) substrate. DCNQI is a strong electron acceptor from the TCNQ family, and is known to form a number of coordination compounds with different monovalent metals, with the general formula M(DCNQI)2, and also with Cu, which seems to have a mixed valency.20-21 To our knowledge, there have been no reports of coordination networks with Fe so far. However, our STM and XPS measurements show that, after depositing Fe on a DCNQI-precovered Ag(111) surface and annealing, an Fe-DCNQI coordination network is formed. In addition, depending on the annealing temperature, two types of networks are formed. In both cases the Fe atoms form a perfect hexagonal lattice with the same lattice constant. At low annealing temperatures the DCNQI ligands join the Fe atoms to form a 2D extended but disordered network, in the sense that the resulting system is not at all periodic. At higher temperatures the molecular arrangement changes to give rise to a set 1D FeDCNQI chains held together by hydrogen bonds.

Experimental Section and Computational Details Film growth and STM and XPS investigations were carried out in ultrahigh-vacuum (UHV) conditions, with a base pressure of ~2 × 10-10 torr. Atomically flat, crystalline Ag(111) surfaces were prepared by standard sputter/anneal procedures (sputter with 1 kV Ar+ ions for 15 min followed by annealing to 800 K



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for another 15 min), resulting in large terraces (~200 nm wide) separated by monoatomic steps. The molecules were deposited from a low-temperature Knudsen cell, heated at 340 K, onto the clean Ag(111) substrate, which was held at room temperature. Fe was sublimated from an iron rod using an electronbeam evaporator. The UHV vacuum chamber was equipped with a variable temperature “Aarhus” type STM purchased from SPECS. STM measurements were performed both at room temperature, with tunneling conditions chosen so as not to disturb individual molecules. From the STM chamber, the samples were transferred in-situ to the XPS chamber, where photoemission spectra were recorded using monochromatized Al Kα X-rays. To check for any possible influence of the radiation on the sample structure, STM images were taken both before and after the X-ray measurements. No damage or structural change was found in any case. Density functional theory calculations, with the Perdew, Burke, and Ernzerhof (PBE)22 functional, were carried out using the Vienna ab-initio simulation package (VASP).23-25 The projector-augmented wave (PAW) pseudopotentials26-27 were employed to describe the ionic cores. A Methfessel-Paxton smearing28 of 0.2 eV was used to calculate the occupation of electronic states. A 3×3×1 k-point mesh was generated by the Monkhorst-Pack scheme29 for the Brillouin-zone sampling. The cutoff energy was set to 450 eV for the plane wave expansion. The Ag(111) surface was modelled by a four atomic-layer thick slab in a 3D periodic unit cell, separated by 15 Å of vacuum in the surface normal direction. The atomic positions of the whole molecule and the two topmost surface layers were fully optimized using a conjugated-gradient algorithm until all forces on each ion were smaller than 0.02 eV Å-1. The total energy at each optimization step was corrected by the dispersion term following Grimme’s DFT-D2 scheme,30 as implemented in the VASP package. Atomic charges were computed based on a Bader’s analysis31-33 of the electron density (including the core charge) using the Bader analysis program for VASP.34

Results and Discussion


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Figures 1a,b show a set of increasing resolution STM images of the Ag(111) surface almost completely covered by DCNQI molecules deposited with the substrate held at room temperature. The molecules are ordered with an almost square unit cell, with sides length b1 = 16.1 ( 1.3) Å and b2 = 14.7 ( 0.9) Å, parallel, respectively, to the [110] and [112] directions of the silver surface. The clear Moiré fringes visible in Figure 1a seem to indicate that the overlayer is incommensurate in the compact [110] direction, while it is commensurate in the perpendicular direction, with b2 = 3a1 + 6a2 (a1 and a2 being the lattice vectors of the Ag(111) surface).

Figure 1. a,b) STM images taken after depositing almost one monolayer of DCNQI at room temperature on Ag(111). The images were taken also at room temperature. The black squares in b) and c) indicate the unit cell of the 2D assembly, with the proposed model superimposed in b). The white arrows in a) indicate the substrate directions. c) Result of DFT calculations for the minimum energy configuration of a DCNQI free-standing layer. The short blue lines represent hydrogen bonds between molecules. a) 138 Å

 172 Å, Vb = -0.65 V, It = 0.41 nA; b) 32 Å  40 Å, Vb = -0.65 V, It = 0.32 nA. Close-up STM images (Figures 1b) are consistent with the DCNQI molecules being flat on the surface, all of them in the syn conformation (see Figure S1 in the Supplementary Information). Figure 1c shows the minimum energy configuration obtained from DFT calculations for a 2D free-standing layer of synDCNQI molecules. The lattice parameters obtained from the calculations are b1 = 15.44 Å, b2 = 15.44 Å, in good agreement with the experimental values. In this arrangement each molecule forms eight hydrogen bonds with neighbouring molecules (red lines in Figure 1c). The binding energy per molecule (defined as



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Ebind = - (Enet – 4*Emol), where Enet is the total energy of the free-standing DCNQI layer and Emol is the total energy of a DCNQI molecule) amounts to 0.45 eV. After trying different geometries, this is the highest binding energy that can be obtained for a 2D free-standing layer of DCNQI molecules. A very similar arrangement is obtained when DCNQI is deposited onto the Cu(100) surface when the substrate is held at room temperature.35 After depositing ~ 0.1 ML of Fe at room temperature on this surface, a number of islands appear on the surface (Figure 2). Most of the islands are ~ 4.2 Å high with respect to the substrate (~ 3.0 Å with respect to the molecular layer). A closer look (see the island circled in blue in Figure 2.a) shows that some islands have two different levels: a rather unstructured one, with a height of 3.0 Å with respect to the substrate (probably a bilayer high iron island), and a second one, 1.2 Å higher, which appears to be composed of DCNQI molecules. On the other hand, the space between the islands is covered by the original hydrogen-bonded DCNQI layer, although somewhat distorted, especially close to the islands, as can be seen in Figure 2b. Apparently, the iron atoms have diffused over the silver surface without disturbing the DCNQI layer (probably by diffusing underneath the molecular layer),36 to form iron islands which are covered almost completely by DCNQI molecules. Notice that this situation is different from the case of Fe on clean Ag(111), where the growth is three dimensional, i.e., the Fe islands are several layers high. (It is, however, very similar to what happens when Fe is deposited on Ag(111) when the surface has been precovered with a monolayer of FeTPP (iron tetra-phenyl-porphyrin),37 or for the Fe/Cu(111) system when the surface has been precovered with lead).38-39 Thus, the DCNQI layer acts as a surfactant, preventing the growth of 3D islands.40


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Figure 2. STM images taken after depositing 0.1 ML of Fe on 1 ML of DCNQI/Ag(111) at room temperature. a) 277 Å  364 Å, Vb = 1.53 V, It = 0.18 nA; b) 184 Å  229 Å, Vb = 1.13 V, It = 0.22 nA. When annealing to 320 K the 2D assembly between the islands changes appreciably and, along with areas showing the structure of the DCNQI layer, there have emerged new areas with a different, apparently disordered, structure (Figure 3a). However, a closer look (Figure 3b) reveals that this arrangement is composed of flat-lying DCNQI molecules, also in the syn conformation, that are connecting in an irregular way a number of smaller round structures, that we attribute to Fe atoms, separated ~11.5 Å and that form themselves an almost perfect hexagonal network. Thus, at 320 K the step edge iron atoms are able to detach from the Fe islands and coordinate with the DCNQI molecules, which, at this temperature, are already mobile enough to allow this bonding. (Although, to our knowledge, there are no reported values for atom detachment from iron islands, the values reported for silver islands, which has a larger bond dissociation energy than iron,41 is 0.71 eV).42 The disordered appearance of the FeDCNQI coordination network comes from the fact that, although almost every Fe atom is connected to four DCNQI molecules, these are arranged in an apparent random way, and the resulting system is not at all periodic (a model for the STM image in Figure 3b is shown in Figure 3c). Although other 2D “disordered” coordination networks have been reported before,43-44 this new structure is unique in the sense that it is the first one reported where the metal centers form a perfect hexagonal network, and the disorder is present only in the arrangement of the molecular ligands.



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Figure 3. a) STM images taken after annealing the Fe/DCNQI/Ag(111) system to 320 K. The measurements were made at room temperature. b) A close-up image of the area between the islands, with some molecular modeld superimposed. c) Proposed structural model of the Fe-DCNQI coordination network imaged in (b). The white circles in (a) and (b) are drawn as reference points. a) 138 Å  172 Å, Vb = -0.52 V, It = -0.26 nA; b) 47 Å  51 Å, Vb = 0.14 V, It = 0.36 nA.

When increasing the annealing temperature to 380 K, a different ordered structure appears embedded within the DCNQI layer (Figure 4a). A closer look (Figure 4b) reveals that this new structure seems to be composed of Fe atoms forming the same hexagonal lattice as before, but now the connecting DCNQI molecules are arranged in a regular form, in such a way that two Fe atoms are connected by two DCNQI molecules (every Fe atom is connected to 4 DCNQI molecules) forming a set of parallel 1D chains. A model for the STM image in Figure 4b is shown in Figure 4c. The lattice parameter of this hexagonal lattice is also ~11.5 Å, and it can exist in three different orientations. One of them has its lattice vectors aligned with the high symmetry directions of the silver surface, and can be described by the epitaxial relationship

4 0

0 . The other two, that are probably incommensurate, are rotated ±12º with respect to 4

these directions.


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Figure 4. a) STM images taken after annealing the Fe/DCNQI/Ag(111) system to 380 K. The measurements were made at room temperature. b) Zoom of the area enclosed by the white rectangle in (a) with some molecular models superimposed. c) Proposed structural model of the Fe-DCNQI coordination network. a) 102 Å  120 Å, Vb = 1.13 V, It = 0.43 nA; b) 40 Å  49 Å, Vb = 1.13 V, It = 0.43 nA. As mentioned above, although DCNQI-Me salts have been reported,45-49 to our knowledge there are no bulk DCNQI-Fe coordination compounds. Also, the reported DCNQI salts, where the molecule is always in the trans conformation, crystallize in the group I41/a 20-21, 45 (or at least in the sub-groups C2/c or P4/n). In these compounds the metal ions are arranged forming a 1D chain, and each metal ion is surrounded by four DCNQI ligands. That is, they share stoichiometry and metal-coordination with the 2D Fe-DCNQI complex, although in the DCNQI salts the metal atoms form a square 2D lattice, while here the coordination network is strictly 1D. The formation of an extended hexagonal lattice of Fe atoms is due to the hydrogen-bond interaction between the chains (see below) and the epitaxy with the hexagonallysymmetric Ag(111) surface. In order to shed some light on the nature of the electronic structure of this Fe-DCNQI layer, XPS spectra have been measured during the different stages of growth. Figure 5 shows the N1s, Fe2p and C1s core levels a) of the clean Ag(111) surface; b) after depositing a submonolayer amount of DCNQI; c) after depositing Fe on this molecular layer; and d) after annealing to 380 K. The two peaks appearing at ~398.5 and 393.0 eV in the N1s spectra of the clean Ag surface are due to bulk plasmon losses.50 After



depositing DCNQI a small new feature appears at ~398.5 eV, which is similar to the N1s binding energy measured after depositing DMe-DCNQI on Ag(110),51 but lower than the one measured for a DMeDCNQI multilayer on Ag(111),52 possibly indicating a charge transfer from the substrate to the molecule.51 Similar results, i.e., a shift to lower binding energy of the N1s core level when compared to the bulk compound, have been reported for the closely related TCNQ molecule when deposited on copper or silver substrates.16, 53-55 After Fe deposition and annealing, the position of this peak does not change appreciably, indicating that the molecule remains approximately in the same charged state after coordination. The C 1s core level is composed of two contributions at 284.7 and 286.1 eV, with an area ratio of ~3:1, which would correspond to the C atoms of the C ring and the C atoms of the cyano groups, respectively.52 Once again, this peak does not change appreciably after Fe deposition and annealing. The Fe peak, on the other hand, does change noticeably. On the freshly deposited sample, the main Fe 2p peak appears at ~707 eV, which is characteristic of metallic iron, Fe0.56-57 After annealing, the peak appears just as a broad feature centered around 710.0 eV, i.e., close to the position reported for Fe2+.56-57 This seems to be in agreement with the oxidation state of iron in other molecular systems with similar squareplanar geometry and coordination (see below), like iron (II) phthalocyanines and porphyrins.

Fe 2p

intensity (arb. units)

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N 1s

C 1s

d) + Fe + annealing d) + annealing d) + Fe + annealing b) + DCNQI

a) Ag(111) b) Ag(111) + DCNQI

c) Ag(111) + DCNQI + Fe 720

715

710

705

700

400

395

390

binding energy (eV)


290

285

280

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Figure 5. Fe2p (after background substraction), N1s and C1s region of the XPS spectra taken a) on a clean Ag(111) surface; b) after DCNQI deposition; c) after Fe deposition on the DCNQI layer; and d) after annealing to 380 K the Fe-DCNQI/Ag(111) system. Based on the model proposed in Figure 4c, we have carried out DFT calculations of the optimized structure of a free-standing monolayer of this Fe-DCNQI coordination network. The results are shown in Figure 6a,b. The lattice parameters of the rhombohedral unit cell are a1 = 11.63 Å and a2 = 11.48 Å (along the chains), which are very close to the experimental results. The Fe atoms are four-fold coordinated, in a square planar geometry, with the N atoms, all of them in the same plane, forming N-FeN angles of ~ 90º. The calculated bond energy is 2.66 eV per Fe-N bond. The distance between the Fe atoms and the N atoms is 1.88 Å (to be compared to 1.99 Å in (2,5-DM-DCNQI)2Cu 45 or 2.31 Å in (2,5DM-DCNQI)2Ag.58 To avoid the electrostatic repulsion between the inner H atoms of the phenyl rings in the same chain these are rotated by ±11.6º with respect to the plane containing the Fe atoms (see Figure 6b). An electron density isosurface (0.2 e/Å3) colour-coded according to the electrostactic potential on every point of the isosurface is shown in Figure 6c. Notice that two different types of interaction contribute to this particular arrangement: one is the Fe-DCNQI coordination bond that drives the formation of 1D chains; the other is the interaction between chains, mainly through the formation of N…H-C hydrogen bonds, i.e, one nitrogen belonging to the imine group of one molecule in one chain is connected to the hydrogen of the carbon ring in the other chain. (The average distance between the H atom and the N atoms in the hydrogen bonds is 2.52 Å). The formation of a hexagonal lattice of Fe atoms is just a coincidence due to the particular length and shape of the DCNQI molecule. A Bader analysis of the charge density in the 2D Fe-DCNQI coordination network gives a local charge for the Fe atoms of +1.36 |e-| (that is, each DCNQI molecule donates 0.68 |e-| to the Fe atom), while the magnetic moment of the Fe atom is calculated to be 2.05 B.



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Figure 6. Results of the DFT calculations showing the a) top and b) side views of a free-standing FeDCNQI layer. c) Charge density isosurface coloured according to the electrostatic potential on every point of the surface (blue: more positive; red: more negative).

DCNQI/Ag(111) DCNQI

Fe/Ag(111)

Fe-DCNQI/Ag(111)

Fe-DCNQI

-1.14

-0.68

+1.20

+1.36

0.18

0.09

1.74

2.05

-1.03

q (|e-|) Fe

+0.37

DCNQI m (B) Fe

3.49

Table 1. Charge (q) and magnetic moment (m) of the Fe atom and the DCNQI molecule in the different environments mentioned in the text, according to the Bader analysis of the results of the DFT calculations. To study the effect of the silver surface on the geometrical and electronic properties of the coordination network, we have carried out DFT calculations of the complete Fe-DCNQI/Ag(111) system, which we modelled using a commensurate unit cell

4 0

0 with b1 = b2 = 11.74 Å and = 120º . The 4

optimized structure is shown in Figure 7a,b. Since the lattice parameters are very close to the ideal freestanding layer, the in-plane geometric structure is also very similar. The main effect of the surface is, due


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to the van der Waals interaction, to decrease the angles that the phenyl rings are rotated with respect to the Fe plane, which now become 9.9º and 3.1º. The conformation of the DCNQI molecule, with all the atoms almost coplanar, is very different from the conformation when the molecule is isolated on the silver surface. Figures 7c,d shows the DFT optimized geometry of a single DCNQI molecule, in the syn conformation, on the Ag(111) surface. In this case there is a strong molecular distortion: the molecule is no longer planar, with the N atoms closer to the surface than to the C ring. This distortion is facilitated by the charge transfer from the metal to the molecule (~1.0 e-), which makes the central C ring almost aromatic and the bond between the C ring and the imine nitrogen single bond-like.53 On the contrary, in the Fe-DCNQI/Ag(111) system the C atoms are almost coplanar with the N atoms and the Fe atoms, which are 2.61 Å above the average surface plane. This is much larger than the height of an isolated Fe atom above the topmost surface plane, which is 2.01 Å (Figure 7e). Thus, the formation of the coordination network lifts the Fe atoms away from the surface and flattens the DCNQI molecule, decreasing the electronic influence of the substrate with respect to the isolated constituents. Note that the square-planar coordination geometry of the Fe atoms with the four N atoms in the free-standing layer is maintained on the silver substrate. It is probably the combination of the hydrogen bonds formation between chains and this square-planar geometry, more stable due to steric and electronic reasons than the distorted shape formed at 320 K,59 what stabilizes the set of parallel 1D chains with respect to the disordered 2D network.



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Figure 7. Results of the DFT calculations showing a) top and b) side views of the Fe-DCNQI coordination network on the Ag(111) surface; c) top and d) side views of an isolated DCNQI molecule on Ag(111); e) side view of an isolated Fe atom on Ag(111). Figure 8a shows a profile of the charge density difference of the Fe-DCNQI/Ag(111) system (with respect to the free-standing layer) along the line drawn in Figure 8b (electron depletion and accumulation are indicated in blue and red, respectively). The most obvious features are a partial electron accumulation on the molecule, an electron depletion just above the metal surface, and an electron redistribution around the Fe atoms, which decreases slightly their positive charge. Thus, the Bader analysis of the electronic density shows that the partial charge on the DCNQI molecules, -1.14 |e-|, is larger than in the freestanding layer, -0.68 |e-|, (and close to the value for the isolated molecule, -1.03 |e-|), while the positive charge on the Fe atoms (+1.20 |e-|) is slightly smaller than for the free standing layer (+1.36 |e-|). As can be seen in Figure 9, that shows the density of stated projected on the d-orbitals for both the free-standing layer and the Fe-DCNQI/Ag(111) system, the decrease of the positive charge is the result of the partial filling of the dz2 orbitals.


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A word concerning the difference between the oxidation state of the Fe atom as measured by XPS, and the local charge coming from the DFT calculations: These show that the charge on the Fe atoms is, approximately, +1.2 |e-|. However, the XPS data indicate that the oxidation state is +2. As it has been previously shown,60-66 the difference relies on the fact that, due to the deformation of the electron shell of the ligand and the electron density transfer from it to the interatomic space of the coordinating bond, the Bader charge usually gives smaller values than nominal oxidation states. This discrepancy between the nominal oxidation state and the atomic charge has been reported for a number of transition metal complexes,60-65, 67 and is not limited to the Bader analysis of the charge density,66-67 but it is general to all charge decomposition methods and the relationship of the calculated effective charge with the concept of “oxidation state”.61, 68



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Figure 8. a) Profile of the charge density difference of the Fe-DCNQI/Ag(111) system calculated with respect to the Fe-DCNQI free-standing layer. b) 3D plot of an isosurface (0.027 e/Å3) of the electron density. In both plots red colour represents electron enrichment, while blue colour represents electron loss. The calculated magnetic moment of the Fe atoms is 1.74 μB, which is just slightly smaller than in the free-standing layer. Using a 2x2 supercell containing four Fe atoms we have calculated the total energies for different spin alignments of the Fe atoms. It turns out that the ferromagnetic, the antiferromagnetic and the two ferrimagnetic phases are energetically degenerate, as a result of the weak interaction among the Fe atoms in the network due to the relatively long Fe⋯Fe distance (> 11.5 Å). This seems unfortunate, because it would interesting to study the effects of a geometry like that shown in Figure 3b on the magnetic properties of the system.


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PDOS (arb. units)

PDOS (arb. units)

PDOS (arb. units)

PDOS (arb. units)

(a)

PDOS (arb. units)

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(b)

1.0

1.0

0.5

0.5

dxy

0.0

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Figure 9. Density of states projected on the d-orbitals for a) the free-standing Fe-DCNQI layer; b) the FeDCNQI / Ag(111) system.

Conclusions In summary, we have studied the geometry and electronic structure of an Fe-DCNQI coordination network on Ag(111) after the successive deposition of DCNQI and Fe. Depending on the annealing temperature, two types of networks are formed, but in both of them the Fe atoms share the same



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hexagonal arrangement. At low temperatures (320 K), the network is truly 2D, but the DCNQI molecules connect the Fe atoms in an irregular way, forming a non-periodic structure. At higher temperatures (380 K), the coordination network is strictly 1D, with the different chains bound together by hydrogen bonds. The structure electronic of this network has been studied by XPS and DFT, which seem to indicate that the Fe atoms are in a +2 oxidation state.

Acknowledgments Our own work has been supported by the MICINN of Spain (FIS2010-18847, FIS2013-42002-R, FIS2013-40667-P

and

CTQ2013-43698-P),

Comunidad

de

Madrid

(NANOFRONTMAG-CM

S2013/MIT-2850), and European Union (SMALL PITN-GA-2009-23884, COST Action CM1204 XLIC). We also acknowledge the Centro de Computación Científica of the Universidad Autónoma de Madrid and the Barcelona Supercomputing Center (BSC) for allocation of computer time.

References

1. Metal-Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1201-1508 (Eds.: J. Long, O. M. Yaghi) 2. Gutzler, R.; Stepanow, S.; Grumelli, D.; Lingenfelder, M.; Kern, K., Mimicking Enzymatic Active Sites on Surfaces for Energy Conversion Chemistry. Acc. Chem. Res. 2015, 48, 2132-2139. 3. Stepanow, S.; Lin, N.; Barth, J. V., Modular Assembly of Low-Dimensional Coordination Architectures on Metal Surfaces. Journal of Physics-Condensed Matter 2008, 20, 184002. 4. Barth, J. V., Fresh Perspectives for Surface Coordination Chemistry. Surf. Sci. 2009, 603, 1533-1541. 5. Lin, N.; Stepanow, S.; Ruben, M.; Barth, J. V., Surface-Confined Supramolecular Coordination Chemistry. Top. Curr. Chem. 2009, 287, 1-44. 6. Kley, C. S.; Cechal, J.; Kumagai, T.; Schramm, F.; Ruben, M.; Stepanow, S.; Kern, K., Highly Adaptable TwoDimensional Metal-Organic Coordination Networks on Metal Surfaces. J. Am. Chem. Soc. 2012, 134, 6072-6075. 7. Tait, S. L.; Wang, Y.; Costantini, G.; Lin, N.; Baraldi, A.; Esch, F.; Petaccia, L.; Lizzit, S.; Kern, K., Metal-Organic Coordination Interactions in Fe-Terephthalic Acid Networks on Cu(100). J. Am. Chem. Soc. 2008, 130, 2108-2113. 8. Gambardella, P., et al., Supramolecular Control of the Magnetic Anisotropy in Two-Dimensional High-Spin Fe Arrays at a Metal Interface. Nature Materials 2009, 8, 189-193. 9. Li, Y.; Xiao, J.; Shubina, T. E.; Chen, M.; Shi, Z.; Schmid, M.; Steinrück, H.-P.; Gottfried, J. M.; Lin, N., Coordination and Metalation Bifunctionality of Cu with 5,10,15,20-Tetra(4-Pyridyl)Porphyrin: Toward a Mixed-Valence Two-Dimensional Coordination Network. J. Am. Chem. Soc. 2012, 134, 6401-6408. 10. Skomski, D.; Tempas, C. D.; Smith, K. A.; Tait, S. L., Redox-Active on-Surface Assembly of Metal–Organic Chains with Single-Site Pt(II). J. Am. Chem. Soc. 2014, 136, 9862-9865. 11. Skomski, D.; Tempas, C. D.; Cook, B. J.; Polezhaev, A. V.; Smith, K. A.; Caulton, K. G.; Tait, S. L., Two- and ThreeElectron Oxidation of Single-Site Vanadium Centers at Surfaces by Ligand Design. J. Am. Chem. Soc. 2015, 137, 7898-7902. 12. Umbach, T. R.; Bernien, M.; Hermanns, C. F.; Krüger, A.; Sessi, V.; Fernandez-Torrente, I.; Stoll, P.; Pascual, J. I.; Franke, K. J.; Kuch, W., Ferromagnetic Coupling of Mononuclear Fe Centers in a Self-Assembled Metal-Organic Network on Au(111). Phys. Rev. Lett. 2012, 109, 267207. 13. Giovanelli, L., et al., Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-Based Metal–Organic Networks. The Journal of Physical Chemistry C 2014, 118, 11738-11744.


Page 19 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


14. Classen, T.; Fratesi, G.; Costantini, G.; Fabris, S.; Stadler, F. L.; Kim, C.; de Gironcoli, S.; Baroni, S.; Kern, K., Templated Growth of Metal-Organic Coordination Chains at Surfaces. Angew. Chem.Int.Ed. 2005, 44, 6142-6145. 15. Seitsonen, A. P.; Lingenfelder, M.; Spillmann, H.; Dmitriev, A.; Stepanow, S.; Lin, N.; Kern, K.; Barth, J. V., Density Functional Theory Analysis of Carboxylate-Bridged Diiron Units in Two-Dimensional Metal-Organic Grids. J. Am. Chem. Soc. 2006, 128, 5634-5635. 16. Tseng, T.-C., et al., Two-Dimensional Metal-Organic Coordination Networks of Mn-7,7,8,8-Tetracyanoquinodimethane Assembled on Cu(100): Structural, Electronic, and Magnetic Properties. Phys. Rev.B 2009, 80. 17. Abdurakhmanova, N.; Floris, A.; Tseng, T.-C.; Comisso, A.; Stepanow, S.; De Vita, A.; Kern, K., Stereoselectivity and Electrostatics in Charge-Transfer Mn- and Cs-TCNQ4 Networks on Ag(100). Nat. Commun. 2012, 3, 940. 18. Faraggi, M. N.; Jiang, N.; Gonzalez-Lakunza, N.; Langner, A.; Stepanow, S.; Kern, K.; Arnau, A., Bonding and Charge Transfer in Metal–Organic Coordination Networks on Au(111) with Strong Acceptor Molecules. J. Phys. Chem. C 2012, 116, 24558-24565. 19. Faraggi, M. N.; Golovach, V. N.; Stepanow, S.; Tseng, T.-C.; Abdurakhmanova, N.; Kley, C. S.; Langner, A.; Sessi, V.; Kern, K.; Arnau, A., Modeling Ferro- and Antiferromagnetic Interactions in Metal–Organic Coordination Networks. J. Phys. Chem.C 2014, 119, 547-555. 20. Hunig, S.; Erk, P., Dcnqis - New Electron-Acceptors for Charge-Transfer Complexes and Highly Conducting RadicalAnion Salts. Adv. Mater. 1991, 3, 225-236. 21. Hunig, S.; Herberth, E., N,N '-Dicyanoquinone Diimines (DCNQIs): Versatile Acceptors for Organic Conductors. Chem. Rev. 2004, 104, 5535-5563. 22. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. 23. Kresse, G.; Hafner, J., Ab Initio Molecular-Dynamics Simulation of the Liquid-Metal-Amorphous-Semiconductor Transition in Germanium. Phys.Rev. B 1994, 49, 14251-14269. 24. Kresse, G.; Furthmüller, J., Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15-50. 25. Kresse, G.; Furthmüller, J., Efficient Iterative Schemes for Ab-Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev.B 1996, 54, 11169-11186. 26. Blöchl, P. E., Projector Augmented-Wave Method. Phys. Rev.B 1994, 50, 17953-17979. 27. Kresse, G.; Joubert, D., From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev.B 1999, 59, 1758-1775. 28. Methfessel, M.; Paxton, A. T., High-Precision Sampling for Brillouin-Zone Integration in Metals. Phys. Rev.B 1989, 40, 3616-3621. 29. Monkhorst, H. J.; Pack, J. D., Special Points for Brillouin-Zone Integrations. Phys. Rev.B 1976, 13, 5188-5192. 30. Grimme, S., Semiempirical Gga-Type Density Functional Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. 31. Bader, R. F. W., Atoms in Molecules. Acc. Chem. Res. 1985, 18, 9-15. 32. Bader, R. F. W., A Quantum Theory of Molecular Structure and Its Applications. Chem. Rev. 1991, 91, 893-928. 33. Bader, R. F. W., Atoms in Molecules : A Quantum Theory; Oxford : Clarendon, 1990 (1994 printing), 1994. 34. Arnaldsson, A.; Tang, W.; Chill, S.; Henkelman, G., Code: Bader Charge Analysis, 028a. 2012. 35. Urban, C.; Wang, Y.; Rodríguez-Fernández, J.; Herranz, M. Á.; Alcamí, M.; Martín, N.; Martín, F.; Gallego, J. M.; Otero, R.; Miranda, R., Charge-Transfer-Induced Isomerization of DCNQI on Cu(100). J. Phys. Chem. C 2014, 118, 27388-27392. 36. Camarero, J.; Ferron, J.; Cros, V.; Gomez, L.; de Parga, A. L. V.; Gallego, J. M.; Prieto, J. E.; de Miguel, J. J.; Miranda, R., Atomistic Mechanism of Surfactant-Assisted Epitaxial Growth. Phys. Rev. Lett. 1998, 81, 850-853. 37. Buchner, F.; Kellner, I.; Steinrueck, H.-P.; Marbach, H., Modification of the Growth of Iron on Ag(111) by Predeposited Organic Monolayers. Z. Phys.Chem. 2009, 223, 131-144. 38. Passeggi, M. C. G.; Prieto, J. E.; Miranda, R.; Gallego, J. M., A Scanning Tunnelling Microscopy View of the SurfactantAssisted Growth of Iron on Cu(111). Surf. Sci. 2000, 462, 45-54. 39. Passeggi, M. C. G.; Prieto, J. E.; Miranda, R.; Gallego, J. M., Surfactant Effect of Pb in the Growth of Fe on Cu(111): A Kinetic Effect. Phys. Rev. B 2002, 65, 035409/1-5. 40. Ferron, J.; Gomez, L.; Gallego, J. M.; Camarero, J.; Prieto, J. E.; Cros, V.; de Parga, A. L. V.; de Miguel, J. J.; Miranda, R., Influence of Surfactants on Atomic Diffusion. Surf. Sci. 2000, 459, 135-148. 41. Lide, D. R., CRC Handbook of Chemistry and Physics, 84th Edition; Taylor & Francis, 2003. 42. Morgenstern, K.; Rosenfeld, G.; Lægsgaard, E.; Besenbacher, F.; Comsa, G., Measurement of Energies Controlling Ripening and Annealing on Metal Surfaces. Phys. Rev. Lett. 1998, 80, 556-559. 43. Ecija, D.; Vijayaraghavan, S.; Auwaerter, W.; Joshi, S.; Seufert, K.; Aurisicchio, C.; Bonifazi, D.; Barth, J. V., TwoDimensional Short-Range Disordered Crystalline Networks from Flexible Molecular Modules. ACS Nano 2012, 6, 4258-4265. 44. Urgel, J. I.; Ecija, D.; Auwärter, W.; Papageorgiou, A. C.; Seitsonen, A. P.; Vijayaraghavan, S.; Joshi, S.; Fischer, S.; Reichert, J.; Barth, J. V., Five-Vertex Lanthanide Coordination on Surfaces: A Route to Sophisticated Nanoarchitectures and Tessellations. J. Phys. Chem. C 2014, 118, 12908-12915. 45. Aumüller, A.; Erk, P.; Klebe, G.; Hünig, S.; von Schütz, J. U.; Werner, H.-P., A Radical Anion Salt of 2,5-DimethylN,N′-Dicyanoquinonediimine with Extremely High Electrical Conductivity. Angew. Chem. Int. Ed. 1986, 25, 740-741.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

46. Kobayashi, A.; Kato, R.; Kobayashi, H.; Mori, T.; Inokuchi, H., The Organic Π-Electron Metal System with Interaction through Mixed-Valence Metal Cation: Electronic and Structural Properties of Radical Salts of Dicyano-Quinodiimine, (DMeDCNQI)2Cu and (MeCl-DCNQI)2Cu. Solid State Commun. 1987, 64, 45-51. 47. Hünig, S., et al., Synthesis and Structure of New Anion Radical Salts from DCNQIs. Synth. Met. 1988, 27, 181-188. 48. Kato, R.; Kobayashi, H.; Kobayashi, A.; Mori, T.; Inokuchi, H., Preparation and Structure of Highly Conductive Anion Radical Salts, M(2,5-R1,R2-DCNQI2) ( DCNQI=N,N′-Dicyanoquinonediimine; R1,R2 = Me, Meo, Halogen; M = Ag, Li, Na, K, Nh4). Synth. Met. 1988, 27, 263-268. 49. Kato, R.; Kobayashi, H.; Kobayashi, A., Crystal and Electronic Structures of Conductive Anion-Radical Salts, (2,5-R1r2DCNQI)2Cu (DCNQI = N,N'-Dicyanoquinonediimine; R1, R2 = Ch3, Ch3o, Cl, Br). J. Am. Chem. Soc. 1989, 111, 5224-5232. 50. Leiro, J.; Minni, E.; Suoninen, E., Study of Plasmon Structure in Xps Spectra of Silver and Gold. J. Phys. F-Metal Phys. 1983, 13, 215-221. 51. Seidel, C.; Kopf, H.; Fuchs, H., Growth Process and Compressed Phase of DM-DCNQI on Ag(110) in the Monolayer Regime Observed by LEED, XPS, and STM. Phys. Rev.B 1999, 60, 14341-14347. 52. Baessler, M.; Fink, R.; Heske, C.; Mueller, J.; Vaeterlein, P.; Von Schuetz, J. U.; Umbach, E., Nexafs Investigations of Highly-Ordered Ultrathin Films of DMe-DCNQI on Ag(111). Thin Solid Films 1996, 284-285, 234-7. 53. Tseng, T. C., et al., Charge-Transfer-Induced Structural Rearrangements at Both Sides of Organic/Metal Interfaces. Nature Chemistry 2010, 2, 374-379. 54. Rodríguez-Fernández, J.; Lauwaet, K.; Herranz, M. Á.; Martín, N.; Gallego, J. M.; Miranda, R.; Otero, R., TemperatureControlled Metal/Ligand Stoichiometric Ratio in Ag-Tcne Coordination Networks. J. Chem. Phys. 2015, 142, 101930. 55. Urban, C., et al., Charge Transfer-Assisted Self-Limited Decyanation Reaction of TCNQ-Type Electron Acceptors on Cu(100). Chem. Commun. 2014, 50, 833-835. 56. McIntyre, N. S.; Zetaruk, D. G., X-Ray Photoelectron Spectroscopic Studies of Iron Oxides. Anal. Chem. 1977, 49, 15211529. 57. Wandelt, K., Photoemission Studies of Adsorbed Oxygen and Oxide Layers. Surf. Sci. Rep. 1982, 2, 1-121. 58. Kato, R.; Kobayashi, H.; Kobayashi, A.; Mori, T.; Inokuchi, H., Crystal Structures of M(DCNQIs)2 (DCNQIs=N,N'Dicyanoquinonediimines; M=Li, Na, K, Nh4, Cu, Ag). Chem. Lett. 1987, 16, 1579-1582. 59. Lawrance, G. A., Introduction to Coordination Chemistry; Wiley: Chichester, U.K., 2010, p xiii, 290 p. 60. Raebiger, H.; Lany, S.; Zunger, A., Charge Self-Regulation Upon Changing the Oxidation State of Transition Metals in Insulators. Nature 2008, 453, 763-766. 61. Sit, P. H. L.; Car, R.; Cohen, M. H.; Selloni, A., Simple, Unambiguous Theoretical Approach to Oxidation State Determination Via First-Principles Calculations. Inorg. Chem. 2011, 50, 10259-10267. 62. Baryshnikov, G. V.; Minaev, B. F.; Minaeva, V. A.; Podgornaya, A. T.; Ågren, H., Application of Bader’s Atoms in Molecules Theory to the Description of Coordination Bonds in the Complex Compounds of Ca2+ and Mg2+ with Methylidene Rhodanine and Its Anion. Russ. J. Gen. Chem. 2012, 82, 1254-1262. 63. Wang, Y.; Lee, S. H.; Zhang, L. A.; Shang, S. L.; Chen, L. Q.; Derecskei-Kovacs, A.; Liu, Z. K., Quantifying Charge Ordering by Density Functional Theory: Fe3O4 and CaFeO3. Chem. Phys. Lett. 2014, 607, 81-84. 64. Quan, Y.; Pickett, W. E., Analysis of Charge States in the Mixed-Valent Ionic Insulator Ago. Phys. Rev. B 2015, 91, 035121. 65. Otgonbaatar, U.; Ma, W.; Youssef, M.; Yildiz, B., Effect of Niobium on the Defect Chemistry and Oxidation Kinetics of Tetragonal ZrO2. J. Phys. Chem. C 2014, 118, 20122-20131. 66. Reeves, K. G.; Kanai, Y., Theoretical Oxidation State Analysis of Ru-(Bpy)3: Influence of Water Solvation and Hubbard Correction in First-Principles Calculations. J. Chem. Phys. 2014, 141, 024305. 67. Aullón, G.; Alvarez, S., Oxidation States, Atomic Charges and Orbital Populations in Transition Metal Complexes. Theor. Chem. Acc. 2009, 123, 67-73. 68. Jansen, M.; Wedig, U., A Piece of the Picture—Misunderstanding of Chemical Concepts. Angew. Chem. Int. Ed. 2008, 47, 10026-10029.

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