Survey Of Long d10âd10 Metallophilic Contacts in Four-Membered

Article pubs.acs.org/JPCA

Survey Of Long d10−d10 Metallophilic Contacts in Four-Membered Rings of Ag(I) and Au(I) Supported by Carbene−Pyrazole Mixed Ligands Raul Guajardo Maturana, Miguel Ponce Vargas, and Alvaro Muñoz-Castro* Departamento de Ciencias Quimicas, Universidad Andres Bello, Republica 275, Santiago, Chile S Supporting Information *

ABSTRACT: The interesting case of long intramolecular d10−d10 contacts has been studied through [Ag4L2]2+ and [Au4L2]2+ (L = 3,5-bis((N-methylimidazolyl)methyl)pyrazole) systems, showing interesting features gained by analysis of the electronic structure and the overall shielding tensor in the molecular domain, in terms of its components. The long intramolecular closed-shell separations are attributed to the population of the bonding, nonbonding, and antibonding combinations of the ns atomic shells in the [M4]4+ core, contrasting with that observed in systems with shorter d10−d10 distances. This point allows to concludeb that separations shorter then the sum of the van der Waals radii (3.4 Å for Ag−Ag, and 3.2 Å for Au−Au) of the nucleus involved requires a net bonding population between ns and np atomic shells of the d10 closedshell centers. Moreover, [Au4L2]2+ exhibits an increased covalency observed for the enhanced charge-donation due to the stabilization of the ns and destabilization of the (n − 1)d driven by the relativistic effects. The magnetic response denotes a slight interaction between the closed-shell centers at distances in the range of their sum of van der Waals radii because the observed remote effect (or anisotropic effect) caused by each d10 nucleus does not influence considerably the neighbor center. The analysis of δ in terms of its components allows to conclude that the [Au4L2]2+ system exhibits an increased magnetic response due to the increase in the number of the inner-electrons in comparison to [Ag4L2]2+.

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INTRODUCTION Discrete metallic cluster complexes containing direct interaction between redox centers represents a crucial discipline in the field of inorganic chemistry and material science,1 exhibiting unique optical, magnetical, chemical, and catalytic properties, which are of interest because of the wide range of current and potential applications in several technological issues.2 In this concern, since the past few decades, functionalized Nheterocyclic carbenes (NHCs) constitute an emerging and efficient alternative as stabilizing ligands to retain multinuclear arrays, as has been witnessed by the continuous growth of their chemistry3 prompted by its ease of preparation and good sigma donor capabilities (σ-donor).4 Indeed, the NHCs form stronger bonds than that obtained with the ubiquitous phosphines5 leading to more active complexes in several catalytic reactions than the metal−phosphine counterparts.6 Specially, the chemistry of N-heterocyclic carbenes with coinage-metal has been successful in the obtention of multinuclear compounds, highlighting the silver−NHC compounds since the first report by Adurengo,7 driven by its potential uses as catalysts,8 antimicrobial and chemotherapeutic agents in medicine,9 luminescent probes,10 and as ligand transfer agents.11 In addition to their simple preparation via the Ag2O route,8 Ag(I)−NHC compounds are efficient precursors of other metal−NHCs in relative good yields, through transmetalation12 with the respective metal source. © 2012 American Chemical Society

Among various silver complexes, three- and four-membered cyclic cores stabilized by functionalized NHC ligands turned out to be very unique, due to their ability to retain closed-shell d10−d10 interactions between Ag(I) centers depicting lesser separation than the sum of their van der Waals radii (3.4 Å).8 Although, quite short Ag(I)−Ag(I) intramolecular distances (∼2.7 Å) have been achieved in trimetallic cores ([Ag3]3+) stabilized by pyridinylmethyl-functionalized NHC ligands.13 The aggregation of formally closed-shell d10 centers were unexpected since only weak van der Waals forces should be experienced.14 The terms, aurophilic bonding and aurophilicity introduced by Schmidbauer14c,d where coined in order to account for formally nonbonding 5d10−5d10 interactions observed in Au(I) structures, which were attributed to the enhanced relativistic and correlation effects in such heavy element.14 The related phenomena acting Ag(I) centers, argentophillic interaction, are expected to be to a lesser degree in comparison to Au(I)−Au(I) interactions, suggesting that, in the stabilization of the [Ag(I)]nn+ core, some bonding situations between the centers should be present additionally to the metallophilic phenomena. Recently, our group have shown that the population of a highly bonding [Ag3]3+ core orbital Received: May 21, 2012 Revised: August 10, 2012 Published: August 13, 2012 8737

dx.doi.org/10.1021/jp304928k | J. Phys. Chem. A 2012, 116, 8737−8743

The Journal of Physical Chemistry A

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composed mainly by ns and np atomic shells, from the ligand sigma donation contribute to the stabilization of the d10 multimetallic array.15 A similar situation has been described for [Hg3]6+ compounds.16 The interest toward Au(I)−NHC compounds has surged by the well-known properties of closed-shell gold compounds, depicting a rich and intriguing structural diversity,14c,d,17,18 driving their tendency to aggregate in stable gold supramolecules by intermolecular interactions, exhibiting luminescence properties,18 and rising to potential applications in sensors19 and medical probing.20 In this respect, Chen and Zhou have reported the synthesis of closed-shell compounds supporting formally [Ag4]4+ and [Au4]4+ cores, afforded by the use of a rationally designed pyrazole-linked bis(NHC) ligand (L) offering four coordinating sites denoted as a tetradentade CNNC ligand.21 The obtention of [Ag4L2]2+ (1) was achieved via the Ag2O route, and the Au(I) counterpart, [Au4L2]2+ (2), as the product of the transmetalation of 1 with Au(SEt2)Cl in acetonitrile.21 These compounds are composed by four closed-shell centers, supporting d10−d10 separations in the range of the sum of their van der Waals radii (3.4 Å for Ag−Ag and 3.2 Å for Au−Au), which suggests a slight interaction between the centers depicting long intramolecular metallophilic interactions, contrasting with compounds showing shorter d10−d10 distances.13,14,17,18 In this work, we focus on the bonding and magnetical response properties of 1 and 2 in order to understand the behavior of rings displaying long closed-shell contacts by using relativistic density functional (DFT) methods. The increase of the atomic number (Z) of the involved coinage metal enhances the relativistic effects22 affecting both electronic and geometric structures as well as the magnetic behavior;22−24 therefore, relativistic effects have to be taken into account in order to obtain a reliable description of the geometric structures, bonding models, and various molecular properties.22,25,26

incorporating the scalar relativistic (OPBE/ZORA), and both scalar and spin−orbit effects (OPBE/ZORA+SO) through the ZORA Hamiltonian and STO-TZP as basis set.

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RESULTS AND DISCUSSION Molecular Structure. The calculated and experimental21 selected distances are given in Table 1, and a structural scheme Table 1. Selected Distances (Å) and Angles (deg) of the Systems 1 and 2 1 M−M′ M−M″ M−NPz M−CNHC CNHC−M−NPz a

2 a

calcd

exptl

3.376 3.281 2.058 2.120 174.9°

3.295 3.208 2.088b 2.063b 178.1°b

calcd

exptla

3.304 3.227 2.044 2.045 176.2°

3.292 3.276 2.037b 1.986b 177.9°b

From ref 21. bAveraged experimental values from ref 21.

Figure 1. Schematic representation of [Ag4L2]2+ (1) and [Au4L2]2+ (2), denoting the symmetry operation, which generates the C2h point group.

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showing atom labels is presented in Figure 1. Both compounds, 1 and 2, belong to the C2h point group denoting a slightly distorted M44+ square with different M−M′ and M−M″ distances composed by formally d10 (M(I)) centers. For 1, the Ag−Ag′ and Ag−Ag″ distances are of 3.376 Å and 3.281 Å, respectively, which decrease in 2, showing Au−Au′ and Au− Au″ distances of about 3.304 Å and 3.227 Å, respectively. These d10−d10 separations are in the range of the sum of their van der Waals radii (3.4 Å for Ag−Ag and 3.2 Å for Au−Au) suggesting a slight interaction between closed-shell redox centers depicting long intramolecular metallophilic interactions. The tetradentade ligand, 3,5-bis((N-methylimidazolyl)methyl)pyrazole (L),21 include two N-heterocyclic carbene (NHC) moieties bonded to a central pyrazolate (Pz) fragment displaying different coordinating sites, which promote the slight distortion of the square core. The M−NPz distance varies from 2.058 Å to 2.044 Å; similarly, the M−CNHC separation decreases from 2.120 Å to 2.045 Å suggesting an increased metal−ligand interaction in 2 due to the bond-length contraction reflecting the direct relativistic effect22,26 acting over the bond distances. The calculated structures are in good agreement with the experimental data (Table 1) denoting the performance of the level of theory here employed to optimize molecular geometries. Electronic Structure. In order to obtain an overall representation of the electronic structure denoting the contribution from the (n − 1)d, ns, and np subshells of the

COMPUTATIONAL DETAILS Relativistic density functional theory22 calculations were done by using the ADF 2010.02 code,27 incorporating both scalar and spin−orbit corrections via the two-component ZORA Hamiltonian.22,28 Triple-ξ Slater basis set plus two polarization functions (STO-TZ2P) for valence electrons were employed within the generalized gradient approximation (GGA) according to the Perdew−Burke−Ernzerhof (PBE) exchangecorrelation functional,29 due to its improved performance on long-range interactions.30 Frozen core approximation was applied to the [1s2−4f14] core for Au, [1s2−3d10] for Ag, and [1s2] for C, leaving the remaining electrons explicitly treated variationally. Geometry optimizations were done without any symmetry restrain, via the analytical energy gradient method implemented by Verluis and Ziegler,31 where the energy minima for the optimized geometries were confirmed by calculation of vibrational frequencies. Population analysis were carried out on the basis of the natural population analysis (NPA) scheme by using the NBO5 stand alone suite.32 Energy decomposition analysis (EDA) was carried out according to the Morokuma−Ziegler (M−-Z) scheme.33 The molecular shielding tensor34,35 at several points of the molecular domain,36 were calculated within the GIAO formalism, employing the GGA exchange expression proposed by Handy and Cohen37 and the correlation expression proposed by Perdew, Burke, and Ernzerhof29 (OPBE), 8738



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Table 2. Natural Population Analysis on Fragments [M4]4+ and [L]2− and Natural Valence Population for Ag(I) and Au(I)

metallic center, the density of states (DOS) and projected DOS (pDOS) are given in Figure 2. Compounds 1 and 2 can be

[Ag4(L)2]2+ M(I) fragment [M4]4+ [L]2− ns combinationsa bg (ab)b au (nb)b bu (nb)b ag (b)b EDAc (kcal/mol) ΔEorbd ΔEelstatd ΔEpauli ΔEint

9.79

4d

0.64

5s

0.01

5p

[Au4(L)2]2+ 5d9.616s0.976p0.01

+2.24 −0.24

+1.66 +0.34

0.27 0.42 0.34 0.56

0.22 0.58 0.58 0.66

−572.9 (40.4%) −843.8 (59.6%) 673.9 −742.8

−909.2 (45.6%) −1082.6(54.4%) 1198.5 −793.2

a Combination of the four ns shells of the [Ag4]4+ and [Au4]4+ core, respectively. bb, bonding; nb, nonbonding; ab, antibonding. cEnergy decomposition analysis of the [M4]4+−[L2]2+ interaction, where ΔEint = ΔEorb + ΔEelstat + ΔEpauli. dPercent of the stabilizing terms to the nonrepulsive part of the decomposition, where %ΔEorb = ΔEorb/ (ΔEorb+ ΔEelstat) and %ΔEelstat = ΔEelstat/(ΔEorb+ ΔEelstat) .

Figure 2. Density of states (DOS) and partial DOS for (n − 1)d, ns, and np of the [M4]4+ in 1 and 2.

rationalized in terms of two main fragments considering their initial formal charges, namely, the d10 metallic core [M4]4+ and the ligands [L2]2−; in this sense, the charge transfer toward the metallic core reflects the covalent character in the formation of [M4L2]2+, denoting the formation of bonding interactions between such constituent fragments as consequence of the mixing of their wave functions.15,33 For 1, the 4d shell of the [M4]+4 core mainly remains as a nonbonding region at about −12 eV, showing additionally a 4d/5s mixing (s−d hybridization) located between ∼−11 to −10 eV in a region of ligand character denoting the charge donation toward the initially unoccupied atomic shells of the Ag(I) center in the formation of 1. The natural valence population analysis indicates a 4d9.795s0.645p0.01 configuration (Table 2) for the formal Ag(I) center quantifying the acceptor character of the Ag4 core, which leads to a charge transfer of 1.76 e−, resulting in a net charge of [Ag4]2.24+ and [L2]0.24− for the core and the ligands fragments, respectively. For the gold counterpart (2), the pDOS exhibits a larger mixing between the d and s shells (s−d hybridization) of the metallic core in the region located between ∼−12 to −10 eV denoting, resulting in a larger donation from the 5d toward the 6s shell, which, in conjunction to the ligand-to-metal charge transfer, leads to a total valence population of 5d9.616s0.976p0.01 for each metallic center. The charge transfer from the ligands toward the of 2.36 e− indicates a net charge of [Au4]1.66+ and [L2]0.34+ for the different fragments. The latter results exhibit the increased acceptor character of the gold-based system as consequence of the relativistic effects as has been described in the literature.22,26 In order to gain more insight into the interaction energy between the metallic core and the ligands, we perform an energy decomposition analysis within the Morokuma−Ziegler scheme.33 From Table 2, it can be observed that the ΔEorb term contributes up to 40.4% to the stabilizing terms (ΔEorb and ΔEelstat) in 1, whereas for 2, it rises up to 45.6% depicting a more favorable mixing between the metallic-core and ligand orbitals in the latter reflecting the more charge transfer as observed from the net charge of such fragments, which account

for a larger covalent character of the interaction.33 Thus, [Au4L2]2+ exhibits an increased covalency observed for the enhanced ligand-to-metal charge-donation due to the stabilization of the ns and destabilization of the (n − 1)d driven by the relativistic effects.22,26 Further analysis on the bonding scheme in terms of two constituent fragments, namely, [M4]4+ and [L2]2−, reveals that the main metal−ligand stabilization of the pseudo square core results from the net charge donation toward the different combination of the ns shell at each vertex. The four ns shells give rise to a bonding combination of ag symmetry into the C2h point-group, two nonbonding combinations of bu and au, and the corresponding antibonding counterpart bg (Supporting Information). Each ligand depicts different coordinating sites of σ-donor character showing two NHC and one Pz moieties, resulting in several σ-donor combinations at similar energies allowing the charge transfer toward the four combinations of the ns shell (Table 2), hence populating the bonding, nonbonding, and antibonding levels (Supporting Information), decreasing the overall bonding in the pseudo square core resulting in the observed relatively long M(I)−M(I) (d10−d10) contacts.21 The total σ-donation from the lone-pairs of the NHC fragments (σ-NHC) results in a charge transfer of 0.85 e− and 1.05 e− toward the core in 1 and 2, respectively, whereas the Pz moiety (σ-Pz) leads to a charge transfer of 0.67 e− and 0.89 e−, respectively, describing the NHC as the main interacting coordinating site of the Carbene−Pyrazole mixed ligand. In addition, the π-Pz levels contribute 0.07 e− and 0.10 e− to the ns-based core levels. Moreover, it is important to note that the possible backdonation toward NHC and Pz fragments of the ligand38 are negligible in the studied systems due to the nonoccupancy of the initially unoccupied ligand π orbitals in 1 and 2. A similar behavior has been observed in the description of the electronic structure of [Ag3((pyCH2)2im)3]3+ and [Ag3((pyCH2)2bzim)3]3+ (py = pyridine, im = imidazol, and bzim = benzimidazol).15 8739



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properties are influenced by the relativistic effects denoted by σ22−24 and therefore affect the evaluation of δ as is described through the vicinal heavy-atom effect on light atoms (HALA effect) and by the effects on the shielding of the heavy atom itself (HAHA effect).40,41 Hence, our calculation includes both scalar and spin−orbit effects with the aim to take into account the relativistic effects.22 For the description of the tensor quantities derived from a nucleus-independent point in the molecular space, we define our frame of reference in relation to a molecule-fixed Cartesian coordinate system (x, y, z) where the z-axis is perpendicular to the plane defined by the pseudo square core Ag4 or Au4 . In order to account for the local and remote effects,34 at the nucleus and the neighbor anisotropic contributions to the magnetic response, respectively, by producing the observed shielding, we consider the fast tumbling of the molecule in solution, which average the components of δij leading to the isotropic component, δiso = 1/3(δxx + δyy + δzz) (Figure 3).34−36

The M(I)−M(I) distances in 1 and 2, describe long intramolecular metallophilic interactions suggesting a slight bonding interaction between the redox center (see above). This fact contrasts with the Ag(I)−Ag(I) distance in other similar compounds exhibiting distances ranging from 2.72 Å to 2.97 Å,8,13,14 where the population of the bonding combination (totally symmetric irreducible representation) of the initially unoccupied ns and np atomic shells favor the short d10−d10 contact,15,16 suggesting that the bonding situation from the population of such combination is mandatory in the formally nonbonding d10−d10 metallophilic interaction.14 It is useful, in order to gain more insight into the two different d10−d10 scenarios, to compare the long d10−d10 distance in the studied systems with a similar compound exhibiting short d10−d10 contacts. In this sense, we focus on the comparison between [Ag4L2]2+ (1) and [Ag4(Mes)4] (Mes = 2,4,6-Me3C6H2),13c which depicts an experimental averaged Ag−Ag distance of about 3.25 Å and 2.74 Å (calculated at 3.304 Å and 2.812 Å), where weak and strong metallophilic interactions can be assumed, respectively. In the latter compound ([Ag4(Mes)4]), through a similar analysis of the bonding, we have described the importance of the ns and np shells into the stabilization of the coinage-metal ring,15,16 which are similar to those obtained for the triangular [Ag3((pyCH2)2im)3]3+ and [Hg3(C6X4)3] (X = H, F)15,16 where the population of a highly symmetric bonding combination composed by (n − 1)d, ns, and np contribute to the metal−metal and metal−ligand stabilization. In the case of the studied systems [Ag4L2]2+ and [Au4L2]2+, this stabilization decrease is due to the additional population of the nonbonding and antibonding combination as has been discussed above. Magnetic Response. The magnetic response provides a uniquely sensitive and powerful tool for studying the chemical environment of the individual nucleus produced by its neighbors and the nucleus itself.34−36,39 The response of the molecule can be conveniently generalized through the space, allowing to account for short- and long-range magnetic behavior driven by the presence of induced currents. In this context, with the aim to study the magnetic behavior of the long d10−d10 intramolecular interaction in systems 1 and 2, we describe the molecular response to a uniform external magnetic field (Bext), which gives rise to a nonuniform induced magnetic field (Bind) in terms of the second-ranked magnetic shielding tensor (σij)34,35 for a given point in the space, as follows:

Figure 3. Map representation of the shielding tensor denoting its isotropic (δiso) and zz-components (δzz) for [Ag4L2]2+ (1) and [Au4L2]2+ (2).

From the isotropic representation magnetic response, it can be observed that the slight interaction between the closed-shell centers due that the remote effect (or anisotropic effect) caused by each nucleus does not influence considerably the neighbor center showing values of −2.46 ppm and −1.22 ppm at the middle point between the farthest Ag−Ag and Au−Au nucleus, denoting a slightly increase between the closest centers showing values of −4.81 ppm and −3.64 ppm, for 1 and 2 respectively. A deeper understanding of the magnetic response can be achieved through the analysis of certain components of the chemical shift tensor.35 The δzz component depicted in Figure 2 accounts for the magnetic response to an external field perpendicular to the plane defined by the [M4]4+ core revealing strong differences between 1 and 2, showing an enhanced response in [Au4L2]2+ due to the increase in the number of inner-electrons.24 At the center of the [M(I)4]4+ core, the δzz component denotes values of 4.32 ppm (1) and 12.75 ppm (2), which increase toward the region defined by the M−M contact where δzz for the farther centers at the middle point of the distance are about 10.13 ppm and 16.30 ppm, increasing for the closest centers up to 11.34 ppm and 19.55 ppm for 1 and 2, respectively. These values quantify the enhanced magnetic response for [Au4L2]2+ in comparison to [Ag4L2]2+ similarly to the observed behavior in the series denoted by [Cu5(Mes)5], [Ag4(Mes)4], and [Au5(Mes)5].42 In addition, this component has been extensively used to characterize theoretically the presence of diatropic or paratropic induced ring currents43 leading to shielding or deshielding regions, respectively, which can be directly related to the ring

Bi ind = −σijBj ext With the aim to rationalize this through-the-space quantity in terms of the more familiar chemical shift tensors (δ) in connection to the usual shielding or deshielding shift in the NMR spectra,35g we consider the relationship between each component of the magnetic shielding (σij) and chemical shift (δij) tensors, given by δ = (σref − σ)/(1 − σ) ≈ σref − σ,35 where σref is equal to zero for a given nucleus-independent point in the space, leading to the following relationship for each component of such tensor:35 δij = −σij

The representation of δij into the space allows to obtain a visualization of the shielding (negative values of δij) and deshielding regions (positive values of δij),36 which, in turn, denotes the presence of diatropic or paratropic induced currents in the space.35 It is well-known that the magnetic 8740



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As a final remark, the [Ag4L2]2+ and [Au4L2]2+ systems can be considered to support weak or mild metallophilic interactions in comparison to other systems denoting shorter d10−d10 separation. This leads to a reduced magnetic response at the center of the pseudo square, denoting the small interaction between the involved centers.

current effect44 according to the magnetic criteria.43 Consequently, the systems 1 and 2 can be considered as antiaromatic metallic rings because of a rise ing the deshielding response under a perpendicular applied field. The analysis of the δzz, δxx, and δyy components (Figures 3 and 4) denote the strong axis-dependent (orientation-depend-

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SUMMARY [Ag4L2]2+ and [Au4L2]2+ represents interesting cases of long intramolecular closed-shell interactions showing quite different behavior in relation to systems with shorter d 10 −d 10 separations. The analysis of the bonding scheme acting in the studied systems is based on the ligand-to-metal σ-donation from two N-heterocyclic carbenes and one pyrazolate moiety per ligand, affording a net charge donation toward the [M4]4+ core of 1.76 e− and 2.34 e− for 1 and 2, respectively. The Nheterocyclic carbenes play the main stabilizing role donating about 0.85 e− and 1.05 e− toward the core, respectively. Moreover, [Au4L2]2+ exhibits an increased covalency observed for the enhanced charge-donation due to the stabilization of the ns and destabilization of the (n − 1)d driven by the relativistic effects. The long intramolecular closedshell separations are attributed to the population of the bonding, nonbonding, and antibonding combination of the ns atomic shells in the [M4]4+ core, contrasting with that observed in closed-shell systems with shorter d10−d10 distances, this observation allows to conclude that separations shorter then the sum of the van der Waals radii (3.4 Å for Ag−Ag and 3.2 Å for Au−Au) of the nucleus involved requires a net bonding population of the ns and np atomic shells of the closed-shell redox centers. The magnetic response serve as a useful tool to gain a deeper understanding of the differences of both isoelectronic compounds, driven by the presence of the Ag or Au basedcore. The averaged response to the applied field shows a similar behavior between the studied systems, denoting a slight interaction between the closed-shell centers given that the remote effect (or anisotropic effect) caused by each nucleus, does not influence considerably the neighbor center at distances within the range of the sum of the van der Waals radii. The analysis of δ in terms of its components allows to observe that the [Au4L2]2+ system exhibits an increased magnetic response due to the increase in the number of the inner-electrons in comparison to [Ag4L2]2+.

Figure 4. Map representation of the shielding tensor denoting its xx(δxx) and yy-components (δyy) for [Ag4L2]2+ (1) and [Au4L2]2+ (2).

ent) behavior of the magnetical response exposing the complexity of the response in the two-dimensional d10 core of the studied systems. From the δxx and δyy components, both systems exhibits similar behavior under the axis of the applied field denoting enhanced values for 2, as discussed above. The long intramolecular d10−d10 distances of 1 and 2 within the range of the sum of their van der Waals radii suggests a weak interaction between the redox centers in comparison to other closed-shell metallacycles (see above). In order to increase the understanding into the differences between long and short d10−d10 scenarios, we compare the magnetic response through the δiso and δzz components of [Ag4L2]2+ and [Ag4(Mes)4] (Figure 5), which denotes that, in the latter compound, the remote effects affect the neighbor centers, thus obtaining an additive interaction (see δiso).45

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ASSOCIATED CONTENT

S Supporting Information *

Bonding scheme analysis of the metal−ligand interaction. This material is available free of charge via the Internet at http:// pubs.acs.org.

Figure 5. Comparison between the map representation of the shielding tensor denoting its isotropic (δiso) and zz-components (δzz), for [Ag4L2]2+ (1) and [Ag4(Mes4)].

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Moreover, the δzz component noteworthy exhibits critical differences between both Ag(I) compounds showing values of 4.32 ppm for 1 at the center of the core, which rise up to 22.64 ppm, because of the presence of a increased d10−d10 interaction given by a mild bonding situation in the latter system, which enhances the magnetic response at the center of the array. This fact denotes the presence and importance of a bonding situation in the formation of formally closed-shell arrays showing d10−d10 contacts shorter than the sum of their van der Waals radii.

AUTHOR INFORMATION

Corresponding Author

*Tel: 56 +026618249. E-mail: [email protected]. Website: http://www.amclab.cl. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are thankful for the financial support of FONDECYT Grant 11100027, PROJECT MILLENNIUM No. P07-006-F, 8741



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and UNAB DI-28-12/R. We greatly acknowledge the reviewers for their valuable comments and suggestions.

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