Hydrogen-Bonded Supramolecular Architectures Based on Tris

Article pubs.acs.org/crystal

Hydrogen-Bonded Supramolecular Architectures Based on Tris(Hydranilato)Metallate(III) (M = Fe, Cr) Metallotectons Matteo Atzori,†,‡ Luciano Marchiò,§ Rodolphe Clérac,∥,⊥ Angela Serpe,† Paola Deplano,† Narcis Avarvari,‡ and Maria Laura Mercuri*,† †

Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, S.S. 554 − Bivio per Sestu, I09042 Monserrato (Cagliari), Italy ‡ Laboratoire MOLTECH-Anjou UMR 6200, UFR Sciences, CNRS, Université d’Angers, Bât. K, 2 Bd. Lavoisier, 49045 Angers, France § Dipartimento di Chimica, Università di Parma, Parco Area delle Scienze 17A, I-43124 Parma, Italy ∥ CNRS, CRPP, UPR 8641, F-33600 Pessac, France ⊥ Univ. Bordeaux, CRPP, UPR 8641, F-33600 Pessac, France S Supporting Information *

ABSTRACT: Here we report on the synthesis and characterization of two isostructural mononuclear complexes of formula [(Ph)4P]3[M(H2An)3]·6H2O (M = Fe(III) (1) or Cr(III) (2); H2An = H2C6O42− = dianion of 3,6-dihydroxy-1,4-benzoquinone (DHBQ)) as suitable metallotectons for the preparation of H-bonded supramolecular architectures. The crystal structure of 1 consists of homoleptic tris-chelated octahedral complex anions [Fe(H2An)3]3− surrounded by crystallization water molecules and (Ph)4P+ cations. The metal complexes are involved in an extensive network of moderately strong hydrogen bonds (HBs) between the peripheral oxygen atoms of the ligand and crystallization water molecules. These interactions are responsible for the formation of supramolecular layers that run parallel to the a crystallographic axis, showing an unprecedented H-bonded 2D architecture in the family of the anilato-based H-bonded networks. The supramolecular interactions present in the structure were investigated analyzing the properties of the Hirshfeld surface (HS), which points out the crucial role of the HBs in the construction of the overall supramolecular architecture, whereas the electronic properties of the metal complex were studied by means of DFT calculations. The magnetic susceptibility measurements reveal the expected paramagnetism of the two compounds with quasi-isolated spin centers.

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magnetic networks with guest-tunable magnetism,5 and chiral porous networks with enantioselective catalytic properties6 to appealing materials such as H-bonded π-conjugated assemblies with tailor-made properties for future plastic and nanosized optoelectronic devices.7 One of the most powerful strategies to design such materials is based on using tectons, in particular metallotectons, which are metal complexes able to be involved in well identified intermolecular interactions such as HBs and can therefore serve as building blocks for the rational construction of crystals. The presence of peripheral CO groups play a key role in this context. The advantages of employing such metallotectons to construct supramolecular architectures are several; in particular it is possible to tune the coordination geometry around the metal center, the bonding capability at the complex periphery, and the metallotecton shape by varying the

INTRODUCTION Hydrogen bonds (hereafter HBs) are ideal noncovalent interactions for constructing supramolecular architectures since they are highly selective and directional.1,2 They are formed when a donor (D) with an available acidic hydrogen atom interacts with an acceptor (A) carrying available nonbonding electron lone pairs.1,2 H-bonded self-assemblies offer an attractive tool to obtain supramolecular functional materials with desired physical properties, and H-bonding interactions have been used to control such molecular assemblies during crystallization and thereby to engineer the crystal structures and the physical properties of the resulting molecule-based materials.3 The proper choice of the metal ion and the ligands coordinated to the metal, as well as the ability of the whole complex to be involved in HBs, provide chemists with a flexible and useful strategy for crystal-engineering design of extended networks with versatile physical properties. Such systems range from highly porous metal−organic frameworks with controllable pore sizes and channel properties,1,4 porous © 2014 American Chemical Society

Received: July 30, 2014 Revised: September 4, 2014 Published: September 15, 2014 5938

dx.doi.org/10.1021/cg501143z | Cryst. Growth Des. 2014, 14, 5938−5948

Crystal Growth & Design

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metal, its oxidation state, or the organic ligands.8 The combination of paramagnetic metals and π-electron systems, which can be easily reduced into a radical form such as quinoid rings or their closed-shell relatives, quinones, versatile redoxactive ligands, has been shown to be particularly successful. For instance, the larger homologues of the negatively charged metal−oxalate complexes [M(C2O4)4]4− (M = Zr(IV) or U(IV); C2O42− = oxalate), which have been successfully used to prepare heterometallic coordination polymers showing porosity9 or magnetic properties,10 namely, [Zr(Cl2An)4]4− and [Zr(H2An)4]4− (Cl2An2− = Cl2C6O42− = chloranilate, H2An2− = H2C6O42− = dianion of 3,6-dihydroxy-1,4-benzoquinone (DHBQ), hereafter hydranilate), have been employed to investigate their HB-acceptor abilities as a function of the distance between coordinated and noncoordinated O atoms, in combination with different HB-donating cations.8 Subtle changes in the ligands can contribute to a fine-tuning of the weaker intermolecular forces, responsible for the molecular packing in the solid state, which in turn may have major effects on the HB network connectivity and dimensionality. In this respect anilato-based complexes11 are of special interest since they show (i) a variety of coordination modes that allow for obtaining polymeric or supramolecular architectures showing different topologies,11,12 (ii) the possibility of introducing different substituents on the ligand moiety that determine different supramolecular noncovalent interactions other than HB, such as halogen bonding or π−π interactions, in the crystal structure,3,13,14 which may influence, in turn, the physical properties of the obtained material,13 (iii) the ability of the ligands to mediate magnetic exchange interactions between metal centers and the possibility of modulating the strength of this interaction,15 and (iv) the capability of an easy reduction process into the radical anionic form.16 These features provide an effective tool for engineering a great variety of new anilatobased materials showing peculiar physical properties.3,15,17 Among them, hydranilate-based molecular building blocks show the highest ability in acting as HB-acceptors compared with the halogenated analogues (chloranilate-, bromanilate-, and iodanilate-based complexes). The crystal packing of these latter is, in fact, dominated by halogen-bonding (XB) interactions due to the presence of the halogen substituents on the quinoid ring, and in particular, the XB interactions between iodanilate-based complexes play a key role in the formation of the supramolecular architecture of the resulting material, being therefore stronger than the HB interactions that could take place in the structure.13 Among the hydranilatobased complexes, some dinuclear17a,18 and n-D (n = 1, 2, 3) polymeric systems12 have been reported, but only a few examples of mononuclear complexes have been obtained so far.10,17c,19 Moreover, to the best of our knowledge, studies on the H-bond-mediated magnetic interactions in anilato-based supramolecular architectures have not been reported yet, although they have been reported for molecular complexes having other types of oxocarbon ligands.20 With this view, we report herein the synthesis, crystal structure, DFT calculations, and magnetic properties of two isostructural mononuclear complexes of general formula [(Ph)4P]3[M(H2An)3]·6H2O (M = Fe(III) (1) or Cr(III) (2)), showing an unprecedented Hbonded supramolecular 2D architecture in the family of the anilato-based H-bonded networks.11 Particular attention has been devoted to the crystal structure description, supported by Hirshfeld surface analysis and DFT calculations, in order to rationalize the HB capabilities of these molecular building units

in terms of electronic charge delocalization compared with their halogenated analogues;13 this, in turn, may be helpful for crystal-engineering design of extended networks with challenging physical properties.

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RESULTS AND DISCUSSION Synthesis. The tris(haloanilato)metallate(III) complexes have been obtained according to the general synthetic strategy reported by some of us13 for the preparation of their tris(haloanilato)metallate(III) (X = Cl, Br, or I; M = Fe or Cr) analogues. An aqueous solution of the trivalent metal ion (M = Fe or Cr) was added dropwise to an aqueous solution of the hydranilate dianion obtained in situ, in a one-pot reaction, as described in detail in the Experimental Section (Scheme 1). Scheme 1. General Reaction Scheme for the Synthesis of [(Ph)4P]3[M(H2An)3] (M = Fe(III) (1) or Cr(III) (2))

Crystal Structure. The crystal structure of 1 consists of the homoleptic tris-chelated complex anions [Fe(H2 An) 3 ]3− surrounded by crystallization water molecules (indicated as O1w−O6w) and (Ph)4P+ cations. The complex exhibits an octahedral geometry with the metal bound by six oxygen atoms from three chelating ligands (Figure 1). According to the metal coordination of three bidentate ligands, the metal complex is chiral, while both Λ and Δ enantiomers are present in the crystal lattice since the space group is centrosymmetric (P1)̅ . The metal−oxygen bond distances, ranging from 1.995(3) to 2.036(2) Å, are in agreement with the high-spin character of FeIII metal ion and are comparable to the reported values for the tris-chelated analogous iron(III) complexes having chloranilate, bromanilate, and iodanilate as ligands.13 The C− O bond distances are influenced by the metal coordination, since the oxygen atoms that are bound to the metal lead to C− O distances that are, on average, 0.06 Å longer than those of the peripheral oxygen atoms (Table 1). The C−O distances are in accordance with the double bond character of the peripheral C−O moieties; thus the hydranilate ligand is likely present in the well-known o-quinone-like resonance structure.11 The metal complexes are arranged in two different types of rectangular lattices having Fe···Fe intermolecular distances of ca. 13.2 Å × 13.7 Å and ca. 13.7 Å × 15.4 Å and are surrounded by several (Ph)4P+ cations and crystallization water molecules. The water molecules establish an extensive network of HBs (Figures 2 and 3) that promotes the formation of supra5939



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Figure 2. View of the molecular structure of 1. Four molecular complexes are indicated showing one of the HB networks running along the a axis. The (Ph)4P+ cations are omitted for clarity. Symmetry codes ′ = −x, −y, −z; ″ = −x, 1 − y, 1 − z; ‴ = x − 1, y, z.

Figure 3. View of the molecular structure of 1. Two molecular complexes of opposite chirality are indicated showing one of the HB networks linking the two complexes. The (Ph)4P+ cations are omitted for clarity. Symmetry codes ′ = −x, −y, −z, ″ = −x; 1 − y; 1 − z.

Figure 1. (top) Picture of the [Fe(H2An)3]3− anion in colored spacefill model, together with crystallization water molecules (light green spacefill mode), and (Ph)4P+ cations. (bottom) ORTEP drawing for the tris(hydranilato)ferrate(III) anionic complex (Λ enantiomer) for 1 with thermal ellipsoids at the 30% probability level.

Table 1. Selected Bond Lengths (Å) for 1 Fe−O(11) Fe−O(21) Fe−O(12) Fe−O(22) Fe−O(13) Fe−O(23) C(11)−O(11) C(21)−O(21) C(41)−O(41) C(51)−O(51)

1.998(3) 1.995(2) 1.997(3) 2.000(3) 2.036(3) 1.990(3) 1.301(5) 1.294(5) 1.228(5) 1.234(5)

C(12)−O(12) C(22)−O(22) C(42)−O(42) C(52)−O(52) C(13)−O(13) C(23)−O(23) C(43)−O(43) C(53)−O(53) C(11)−C(21) C(12)−C(22) C(13)−C(23)

1.298(5) 1.293(5) 1.230(6) 1.231(6) 1.288(6) 1.297(5) 1.227(5) 1.244(5) 1.507(5) 1.508(6) 1.520(6)

Figure 4. View of the crystal packing of 1 highlighting the HB interactions occurring between the water molecules and the metal complexes. The 11 HBs are indicated with colored letters. HB donors and acceptor are also indicated. Symmetry codes are omitted.

molecular layers based on complex anions and water molecules that run parallel to the a crystallographic axis (Figures 4 and 5). In particular, the O3w and O4w water molecules, arranged in a square fashion with two symmetry-related molecules, link together four complex anions by interacting with their peripheral O42 and O51 oxygen atoms, favoring the extension of the layer along the a axis (Figure 2). Moreover, the O5w water molecule exchanges a HB with the O43 oxygen atom of a

symmetry-related complex molecule favoring the extension of the layer along the [011] direction (Figures 3−5). The O1w, O2w, and O6w water molecules do not contribute to the formation of the supramolecular layer, but instead, they form a chain of HBs that runs from the O12 to the O53 oxygen 5940



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Moreover, each one interacts with the quinoid ring of one coordinated H2An2− ligand in a face-to-face alignment and in an almost eclipsed way, with shorter interplanar separation (Figure 6).22

Figure 6. (a) (Ph)4P+ cations inside the hexagonal prism-like cavity where the interplanar distances are highlighted and (b) eclipsed faceto-face arrangement between the quinoid ring of the ligand and the aromatic ring of the cation.

Figure 5. View of the crystal packing of 1 with metal complexes and water molecules in spacefill model highlighting the supramolecular topology.

The hexagonal-like cavity is too small to host a (Ph)4P+, so the other counterions are placed between the 2D supramolecular layers of the structure that are arranged in an alternated disposition (Figure 7).

atoms of [Fe(H2An)3]3− (Figures 3 and 4). On the account of the differences between the interactions established by the water molecules, the HBs can be conveniently divided into three groups, a−d, e−i, and m−n (see Figure 4), and according to the HB donor and acceptor distances, the stronger interaction is exhibited by the a−d system (Table 2). Table 2. Distances (Å) and angles (deg) between the HB Donor and HB Acceptor for the Three Groups of HBs Depicted in Figure 4 HB type

distance

angle

a b c d e f g h i m n

2.756(7) 2.816(6) 2.739(6) 2.685(6) 2.887(5) 2.850(8) 2.860(4) 2.934(6) 2.808(8) 2.901(5) 2.861(4)

164.3(5) 163.0(5) 130.5(5) 159.0(5) 163.0(5) 165.0(5) 172.0(5) 114.4(5) 150.0(5) 150.0(5) 155.0(5)

Figure 7. Two supramolecular layers of the structure of 1 showing the alternated disposition of the layers that precludes the formation of hexagonal channels.

The described HB network between the water molecules and the [Fe(H2An)3]3− complex anions gives rise to a resulting supramolecular architecture showing two types of cavities. One cavity shows a distorted hexagonal symmetry, driven by the presence of metal complexes having opposite absolute configuration (Λ and Δ), and is formed by two complex anions connected through the a, b, and d HB types (Figures 2 and 5). The other cavity show a hexagonal prism-like symmetry and is formed by four metal complexes connected by the m and n HB types along the long side and by the b, c, and d HB types along the short side (Figures 4 and 5). The overall topology of the resulting supramolecular architecture can be described as a 1:1 hybrid between the well-known hexagonal honeycomb and the PtS-related topologies (Figure 5).12a Inside the hexagonal prism-like cavity two symmetry related (Ph)4P+ cations are present. They interact with each other through π···π interplanar interactions with offset, as typically observed in aromatic systems, in a double phenyl embrace.21

In order to have a more complete description of the environment enveloping the [Fe(H2An)3]3− anion and to better characterize the various interactions from a qualitative point of view, we investigated the properties of the Hirshfeld surface (HS) for [Fe(H2An)3]3−. As previously described, the complex anion is surrounded by different (Ph)4P+ cations and by water molecules responsible for the formation of supramolecular layers. The strongest interactions exhibited by the [Fe(H2An)3]3− complex are those involving the water molecules, in agreement with the presence of moderately strong HBs. Moreover, the complex anion exchanges different types of contacts with the surrounding (Ph)4P+ cations, and these can be categorized as follows: (1) π···π, between one H2An2− ligand and a phenyl ring of the cation, (2) C−H···π, between a C−H of a phenyl ring of the cation and the carbon 5941



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atom of one H2An2− ligand that is linked to the hydrogen atom (according to DFT calculations (vide inf ra) this carbon atom is characterized by a partial negative charge, which favors the interaction with the phenyl residue), and (3) C−H···O, between the C−H of the phenyl rings of the cation and the peripheral oxygen atoms of H2An2− ligands. All these interactions are visualized as red spots on the HS that correspond to the mapping of dnorm on the HS (Figure 8).

Figure 9. Fingerprint plots for 1 highlighting the major interactions occurring between the complex anion and the surrounding environment, water molecules, and (Ph)4P+ cations. IN and OUT refer to atoms or fragments belonging to the [Fe(H2An)3]3− anion or the surrounding molecules, respectively. The fingerprint plot of the indicated interaction is depicted as a coloured area, which is overlaid the full fingerprint plot (in gray).

DFT Calculations. DFT calculations were performed to gain insight into the electronic structures of the [Fe(H2An)]3− and [Cr(H2An)]3− complexes, as well as to characterize the spin and charge distribution of the metal centers and to compare the electronic properties of the free and coordinated H2An2− ligand.23 According to the presence of six oxygen atoms in the coordination sphere of the metals and in agreement with magnetic data (vide inf ra), the calculations were performed in the high spin states for the two complexes (S = 5/2 and S = 3/2 for [Fe(H2An)]3− and [Cr(H2An)]3−, respectively). Two different computational schemes were employed in order to represent the atomic charges in the six anionic complexes, namely, Mulliken and NPA (natural population analysis), to provide a more complete description of the charge distribution on the different structural fragments.24 In the isolated ligand, it is evident that the negative charge is localized on the four oxygen atoms. There is also a significant negative charge accumulation on the carbon atom linked to hydrogen, whereas the remaining carbon atoms and the hydrogen atoms present a positive charge. This charge distribution is qualitatively similar to both Mulliken and NPA schemes (Figure 10). The NPA charges in [Fe(H2An)]3− and [Cr(H2An)]3− predict that when the ligands are coordinated to the metal centers, there is a slight negative charge depletion on the two peripheral oxygen atoms (−0.65) compared with the free ligand (−0.72). The oxygen atoms involved into the metal coordination do not exhibit any charge variation in [Fe(H2An)]3−, but in [Cr(H2An)]3−, they exhibit a slight charge depletion (−0.65). As far as the Mulliken analysis is concerned, upon complexation, there is significant charge depletion for all oxygen atoms, which is more marked for the oxygen atoms bound to the metal centers: the charges are −0.11 in [Fe(H2An)]3− and −0.32 in [Cr(H2An)]3− (Figure 11).

Figure 8. View of the dnorm mapped on the Hirshfeld surface (blue) for the complex anion [Fe(H2An)3]3−: (top) view of the interactions occurring through the HB network; (bottom) view of the interactions occurring with the (Ph)4P+ cations.

It can be appreciated how the HBs are particularly important for the construction of the overall supramolecular arrangement. A more detailed depiction of the interaction exchanged by the [Fe(H2An)3]3− complex and the surrounding moieties can be obtained by the fingerprint plots (Figure 9), confirming the importance of the HBs as the strongest type of interaction in the crystal packing. This is evidenced by the presence of a pronounced cusp for the OIN···HOUT interaction. PXRD measurements performed on a microcrystalline sample of 2 clearly show that the Cr(III) complex is isostructural to its Fe(III) analogue (1) (Supporting Information, Figure S1). Therefore, the crystal packing of 2 can be considered the same as 1 except for small deviations in the bond distances related to the coordination to the different metal center. 5942



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Figure 10. Mulliken (green) and NPA (blue) charges for H2An2− (B3LYP/6-31+G(d)).

Figure 12. Electrostatic potential mapped on the isodensity surface for [Fe(H2An)3]3− and [Cr(H2An)3]3− (B3LYP/6-31+G(d)-lanl2dz). Color codes thresholds are red −0.3, yellow −0.25, green −0.20, and blue −0.15.

[M(I2An)3]3− complexes, in which there is a certain positive charge localization on the iodine atoms and a negative charge localization of the corresponding C−I carbon atom.13 According to these charges, the [M(I2An)3]3− (M = Fe or Cr) were involved in a series of halogen bonds with adjacent molecules largely responsible for the supramolecular arrangement in the crystal lattice. On the other hand, in the crystal structure of [Fe(H2An)]3−, the hydrogen atoms of the ligands are not involved in any appreciable interaction with the surrounding environment, but they may play a role in favoring the electron delocalization toward the peripheral oxygen atoms of the ligands that act, in turn, as suitable HB-acceptors compared with the halogenated homologues. The spin distribution on the metal for the iron and chromium complexes is approximately 4 and 3, respectively, pointing to a localized nature of the spin on the chromium centers but to a less localized spin distribution in the iron complexes (Table 3). This is also evidenced by inspecting the shape of total spin density, which for the iron complexes is markedly distributed over the six oxygen atoms of the coordination sphere (Figure 13). Vibrational Spectroscopy. The infrared spectra of 1 and 2 show, in the 3700−3100 cm−1 range, a broad and asymmetric band centered at ca. 3415 cm−1, ascribed to the several ν(O− H) vibrational modes of the crystallization water molecules present in the structures. In the 3100−2900 cm−1 region, the typical ν(C−H) vibrational modes of the (Ph)4P+ cation are

Figure 11. Mulliken (green) and NPA (blue) charges for [Fe(H2An)3]3− and [Cr(H2An)3]3− (B3LYP/6-31+G(d)-lanl2dz).

It should be highlighted that in both models the carbon atom linked to the hydrogen presents a considerable negative charge (i.e., −0.47, NPA). A thorough depiction of the charge distribution can be obtained by visualizing the electrostatic potential (EP) of the complex molecules. The isodensity surfaces mapped with the EP are shown in Figure 12. The oxygen atoms are regions where there is a marked negative charge accumulation, followed by the C−H carbon atom, whereas the hydrogen atoms and the metal are the main source of the positive charge. From a comparison with the homologous series of complexes [M(Cl 2 An) 3 ] 3− , [M(Br2An)3]3−, and [M(I2An)3]3− (M = Fe or Cr), the present compounds exhibit a charge distribution similar to the 5943



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Table 3. Mulliken Spin Densities and Mulliken and NPA Charges on Metal Centers Together with the Expectation Values of the ⟨S2⟩ operator for [Fe(H2An)]3− and [Cr(H2An)]3− 3−

[Fe(H2An)] [Cr(H2An)]3− a

Mulliken spin density

Mulliken charges

NPA spin density

NPA charges

⟨S2⟩

4.181 3.006

−1.812 −0.697

4.032 2.866

1.802 1.337

8.759 (8.750)a 3.773 (3.750)a

Values in parentheses are after annihilation of the first spin contaminant.

ν(C−C) + ν(C−O) + δ(C−H) combination band, whereas the band centered at ca. 1245 cm−1 can be related to the ν(C−O) + δ(C−H) + Ringdef. combination band of the ligand.26 It is noteworthy that in the 650−400 cm−1 region the spectra of the two metal complexes show some differences. Except for the vibrational mode associated with the (Ph)4P+ cation centered at ca. 527 cm−1, three bands at ca. 560, 500, and 483 cm−1 are present for 1 and four bands at ca. 590, 578, 506, and 483 cm−1 are observed for 2 (Supporting Information, Figure S3). These bands, which are not present in the ligand and counterion spectra, can be related to vibrational modes involving M−O bonds. Magnetic Measurements. The temperature dependence of the magnetic susceptibility for 1 is shown in Figure 14 as a

Figure 13. Spin density for [Fe(H2An)3]3− and [Cr(H2An)3]3− (B3LYP/6-31+G(d)-lanl2dz). Colors blue and red refer to α- and βspin density, respectively (isosurface plot at 0.0008 esu Å−3). Figure 14. Temperature dependence of χT product at 1000 Oe (where χ is the molar magnetic susceptibility equal to M/H per mole of Fe(III) complex) between 1.85 and 300 K for a polycrystalline sample of 1. The solid line is the best fit obtained using a Curie−Weiss law. Inset shows field dependence of the magnetization for 1 between 1.85 and 8 K at magnetic fields between 0 and 7 T. The solid line is the best fit obtained using S = 5/2 Brillouin function.

present, along with the ν(C−H) vibration of the ligand (3093 cm−1), which is not shifted with respect to the protonated ligand.25,26 A comparison between the spectra of 1 and 2 in the 1700−650 cm−1 range (Supporting Information, Figure S2), where the same vibrational bands with similar shape and relative intensity are observed, suggests the same chemical environment and therefore the same coordination geometry for both Fe(III) and Cr(III) complexes, in agreement with PXRD results. The band centered at ca. 1600 cm−1 might be assigned to the ν(CO) vibrational mode for the uncoordinated CO groups of the ligands; a downshift of this band with respect to the free ligand (1647 cm−1)25 is observed, and it can be attributed to a weakened double bond character of these terminal groups due to the coordination with the metal ion, in agreement with structural data. The strong and broad band centered at ca. 1535 cm−1 can be assigned to a ν(CC) + ν(CO) combination band and the observed significant downshift (1611 cm−1 for the free ligand26) could be related, also in this case, to the coordination effect. The strong and broad band centered at ca. 1375 cm−1 may be assigned to the

χT versus T plot. The χT value at room temperature of ca. 4.5 cm3 K mol−1 is close to the expected value (4.375 cm3 K mol−1) for isolated high spin Fe(III) centers (S = 5/2, g = 2). This value remain constant down to ca. 20 K, then the χT product decreases slightly to 4.3 cm3 K mol−1 at 1.85 K. The observed behavior in the high temperature region (T > 20 K) is typical of magnetically isolated S = 5/2 ions, whereas the observed decrease at low temperature is likely due to weak antiferromagnetic interactions between the isotropic Fe(III) magnetic sites. On the basis of the crystal structure (vide supra) that highlights the presence of short contacts in many different directions, the magnetic data have been modeled in the frame 5944



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because a Curie−Weiss model, used for 1, does not reproduce the experimental data. On the other hand, S = 3/2 models considering magnetic anisotropy were not more successful. Therefore, in the absence of an accurate crystal structure, it is only possible to speculate on the origin of this magnetic behavior that might find its origin, for example, in some kind of charge transfer between the Cr metal ions and the hydranilate ligands.

of the mean-field approximation using the well-known Curie− Weiss law. This model satisfactorily reproduces the magnetic properties of compound 1 in the whole temperature range, with g = 2.03(5) and zJ/kB = −20 mK. The magnitude of the intercomplex magnetic interactions of the order of a few millikelvins falls well in the range expected for dipolar magnetic interactions, but this observation does not rule out the possibility to have extremely small coupling also mediated by HB interactions. The field dependence of the magnetization below 8 K supports the S = 5/2 ground spin state of the Fe(III) ions for 1 since a Brillouin function for an S = 5/2 spin state reproduces well the experimental data with g = 2.06(3) (Inset in Figure 14). Thus, compound 1 presents a high spin configuration for the Fe(III) ions with a S = 5/2 ground spin state and shows a typical paramagnetic behavior of quasiisolated ions. The thermal variation of the magnetic susceptibility per mole of Cr(III) complex expressed as χT for compound 2 is shown in Figure 15. The χT value at room temperature of ca. 2.0 cm3

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CONCLUSIONS Two new isostructural anionic mononuclear complexes, obtained by reacting the hydranilate anion with the Fe(III) and Cr(III) paramagnetic metal ions, were reported along with their crystal structure, DFT calculations, Hirshfeld surface analysis, and magnetic properties. Their crystal structures are dominated by an extensive network of moderately strong HBs between the peripheral oxygen atoms of the ligands and crystallization water molecules. These interactions are responsible, as clearly shown by the analysis of the Hirshfeld surface, for the formation of supramolecular layers showing an unprecedented H-bonded 2D architecture in the family of anilato-based H-bonded networks. DFT theoretical calculations were employed to demonstrate the key role of the H substituent on the hydranilato ligand in modulating the electron density of the whole complex and favoring the electron delocalization toward the peripheral oxygen atoms of the ligands, compared with the other components of the family of halogenated tris-chelated anilato-based complexes;13 these peripheral oxygen atoms act, in turn, as suitable HB-acceptors in the observed supramolecular architecture. The magnetic properties of 2 are intriguing and might find their origin in some kind of charge transfer between the Cr metal ions and the hydranilate ligands, while those of compound 1 show a typical paramagnetic behavior of quasi-isolated spin centers. These observations do not rule out the possibility to have extremely small magnetic coupling also mediated by HB interactions. Furthermore, the combined structural/theoretical analysis reported herein enlarges the general knowledge on the supramolecular interactions shown by the anilato-based metallotectons and provides an effective tool for designing and engineering the supramolecular architectures of new anilatobased materials showing peculiar physical properties. Currently, as perspective, the combination of these anionic metallotectons with HB-donating cations or size-tunable cationic metallotectons is of special interest for obtaining porous coordination polymers or porous magnetic networks with guest-tunable magnetism.

Figure 15. Temperature dependence of χT product at 1000 Oe (where χ is the molar magnetic susceptibility equal to M/H per mole of Fe(III) complex) between 1.85 and 300 K for a polycrystalline sample of 2. Inset shows field dependence of the magnetization for 2 between 1.85 and 8 K at magnetic fields between 0 and 7 T.

K mol−1 is close to the expected values (1.875 cm3 K mol−1) for isolated Cr(III) magnetic centers (S = 3/2, g = 2). This value slowly decreases to reach 1.4 cm3 K mol−1 at ca. 1.85 K with a more marked decrease below 120 K. The observed behavior in the high temperature region is typical of magnetically isolated S = 3/2 ions, whereas the observed decrease below 120 K is not usually seen for Cr(III) complexes with an S = 3/2 ground state.13 The field dependence of the magnetization (inset Figure 15) is indeed not compatible with an S = 3/2 spin state with a magnetization of about 2.5μB at 1.85 K under 7 T, much lower than the expected 3μB. Moreover these experimental data cannot be modeled by a simple S = 3/2 Brillouin function with reasonable g factor. The magnetic behavior of 2 is not well understood at this point because none of the magnetic models tried were able to reproduce both χT versus T and M vs H data. The decrease of the χT product at low temperature is incompatible with the presence of magnetic interactions between magnetic centers

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EXPERIMENTAL SECTION

Synthesis. [(Ph)4P]3[Fe(H2An)3]·6H2O (1). An aqueous solution (10 mL) of FeCl3 (195 mg, 1.2 mmol) was added dropwise to an aqueous solution (250 mL) of H2H2An (500 mg, 3.6 mmol), NaOH (286 mg, 7.2 mmol), and (Ph)4PBr (1.50 g, 3.6 mmol). After ca. 30 min at 30 °C, 1 precipitates slowly as a brown lacquer-like solid, partially soluble in water. The mixture was allowed to cool to room temperature, and the mother liquor was separated. The precipitate was vigorously washed with clean boiling water, and the resulting mixture was ultrasonicated. A red-brown microcrystalline solid was obtained by washing the lacquer-like solid several times with fresh boiling water. The solution was filtered and washed with cold water, and the precipitate was recrystallized in a MeOH/H2O (9:1) mixture to give 1 as red shiny crystals suitable for an X-ray analysis. Yield 40%. Elemental Anal. Calcd for C90H78FeP3O18: C, 67.72; H, 4.92. Found: C, 67.28; H, 4.44. FT-IR (υ̅max/cm−1, KBr pellets): 3415(s), 3058(w), 5945



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diffractometer, Mo Kα, λ = 0.71073 Å. The unit cell parameters were obtained using 60 ω-frames of 0.5° width and scanned from three different zones of reciprocal lattice. The intensity data were integrated from several series of exposures frames (0.3° width) covering the sphere of reciprocal space.27 An absorption correction was applied using the program SADABS28 with minimum and maximum transmission factors of 0.798 and 1.000. The structure was solved by direct methods (SIR200429) and refined on F2 with full-matrix leastsquares (SHELXL201330), using the Wingx software package.31 Nonhydrogen atoms were refined anisotropically. The hydrogen atoms of the water molecules of crystallization could be located from the difference Fourier map, and they were refined with distance and angle restraints. The remaining hydrogen atoms were placed at their calculated positions. Graphical material was prepared with Mercury 3.332 program. CCDC 1004935 contains the supplementary crystallographic data for this paper. Powder X-ray Crystallography. Wide-angle X-ray diffraction (WAXRD) patterns on microcrystalline powder samples were recorded on a Panalytical Empyrean diffractometer equipped with a graphite monochromator on the diffracted beam and a X’Celerator linear detector. The scans were collected within the range 5−40° (2θ) using Cu Kα radiation. The simulated patterns were generated from the atomic coordinates of the single-crystal structure solutions using the program Mercury 3.3 (copyright CCDC, http://www.ccdc.cam.ac. uk/mercury/) using a fwhm (full width at half-maximum) of 0.15 and a 2θ step of 0.05. Hirshfeld Surface Analysis. The Hirshfeld surface (HS) properties were investigated in order to have a thorough description of interactions occurring between the complex anion [Fe(H2An)3]3− and the surrounding environment.33 The HS defines the volume of space in a crystal where the sum of the electron density of spherical atom for the molecule (promolecule) exceeds that for the crystal (procrystal). In particular, the HS contains a region of space where the promolecule electron density is greater than that of the surrounding molecules. Various properties of the HS can be computed and visualized, in particular de and di, which represent the distance from a point on the surface to the nearest nucleus outside or inside the surface, respectively. The dnorm is the normalized contact distance and is defined by taking into account de and di and the van der Waals radii of the atoms:

2928(w), 1629(w), 1604(m), 1586(w), 1535(vs), 1484(w), 1437(m), 1370(s), 1247(s), 1188(w), 1164(w), 1108(s), 1027(w), 996(m), 829(m), 814(m), 758(m), 723(m), 690(m), 660(w), 560(m), 527(m), 483(w). ESI-MS, m/z found (calcd) = 1147.91 (1148.18) [[(Ph)4P]2[Fe(H2An)3]]−; 809.64 (810.05) [[(Ph)4P][Fe(H2An)3]H]−; 404.43 (404.53) [[(Ph)4P][Fe(H2An)3]]2−; 156.66 (156.64) [[Fe(H2An)3]]3−. [(Ph)4P]3[Cr(H2An)3]·6H2O (2). An aqueous solution (20 mL) of CrCl3·6H2O (330 mg, 1.2 mmol) was added dropwise to an aqueous solution (250 mL) of H2H2An (500 mg, 3.6 mmol), NaOH (286 mg, 7.2 mmol), and (Ph)4PBr (1.50 g, 3.6 mmol). After ca. 30 min at reflux temperature, 2 precipitates as a red-brown lacquer-like solid, partially soluble in water. The mixture was allowed to cool to room temperature, and the mother liquor was separated. The precipitate was dissolved in the minimum amount of methanol, and then 150 mL of boiling water was slowly added to the methanolic solution. A redbrown microcrystalline solid was obtained by removing the residual methanol by rota-evaporation. The solution was filtered and washed with cold water, and the precipitate was recrystallized in a MeOH/ H2O (9:1) mixture to give 2 as red shiny crystals. Crystals of 2 were also obtained by slow cooling of the mother liquor. Yield 30%. Elemental Anal. Calcd for C90H78CrP3O18: C, 67.88; H, 4.94. Found: C, 67.36; H, 4.25. FT-IR (νmax/cm−1, KBr pellets): 3416(s), 3058(w), 2928(w), 1627(w), 1602(m), 1535(vs), 1484(w), 1437(m), 1377(s), 1245(s), 1188(w), 1164(w), 1108(s), 1027(w), 996(m), 835(m), 812(m), 758(m), 723(m), 690(m), 664(w), 578(m), 527(m), 482(w). ESI-MS, m/z Found (Calcd) = 1143.88 (1144.19) [[(Ph)4P]2[Cr(H2An)3]]−; 804.67 (805.06) [[(Ph)4P][Cr(H2An)3]-H]−; 402.35 (402.53) [[(Ph) 4 P][Cr(H 2 An) 3 ]] 2− ; 155.28 (155.31) [[Cr(H2An)3]]3−. Characterization. FT-IR spectra were performed on KBr pellets with a Bruker Equinox 55 spectrophotometer. C, H, N analyses were performed with a Thermo Electron Analyzer CHNS Flash 2000. ESIMS spectra were performed with a Bruker Esquire 3000 Ionic Trap (TOF analyzer) in negative mode. Single Crystal X-ray Crystallography. A summary of data collection and structure refinement for 1 is reported in Table 4. Single crystal data were collected with a Bruker Smart Breeze area detector

Table 4. Summary of X-ray Crystallographic Data for 1 empirical formula formula wt color, habit cryst size, mm3 cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z T, K ρ (calc), Mg/m3 μ, mm−1 θ range, deg no. reflns/unique GOF R1a wR2a

dnorm =

C90H78FeO18P3 1596.28 red, plate 0.32 × 0.10 × 0.03 triclinic P1̅ 13.704(3) 17.106(4) 19.923(5) 77.007(4) 84.696(5) 64.123(4) 4094(2) 2 293(2) 1.295 0.312 1.4−25.7 46987/15587 1.010 0.0606 0.1241

d i − rivdW rivdW

+

de − revdW revdW

Mapping dnorm on the HS gives a clear-cut and thorough picture of the interactions occurring between adjacent molecules or molecular fragments that are shorter than the van der Waals radii sum (visualized as red spots on the HS). In addition, 2D diagrams reporting the correlation between de and di (fingerprint plots) are particularly useful to highlight the types of interactions that occurs between molecular fragments. The HS surface and its properties were calculated with CrystalExplorer 3.0.34 Computational Details. Density functional theory calculations were performed on the isolated anion H2An2− and on the complex anions [Fe(H2An)]3− and [Cr(H2An)]3−. The molecular geometry of the complexes and of the H2An 2− ligand were optimized starting from the experimental X-ray geometry of [Fe(H2An)]3−. The B3LYP35,36 hybrid density functional and the LANL2DZ basis set with Hay and Wadt effective core potential (ECP)37,38 for iron and the 6-31+G(d) basis set39,40 for the C, O, and H atoms were employed. Single point calculations were performed at the same level of theory used for the geometry optimizations. Natural bond orbital analysis and natural atomic charges were obtained from the natural population analysis (NPA) performed with the NBO 3.1 program41 incorporated in the Gaussian03 package. Spin density and electrostatic potential diagrams were generated with the Gabedit42 program. All the calculations have been performed with the Gaussian 03 program suite43 Magnetic Measurements. The magnetic susceptibility measurements were obtained with the use of MPMS-XL Quantum Design SQUID magnetometer that works between 1.8 and 400 K for dc

a R1 = ∑||F o | − |F c ||/∑|F o |; wR2 = [∑[w(F o 2 − F c 2 ) 2 ]/ ∑[w(Fo2)2]]1/2; w = 1/[σ2(Fo2) + (aP)2 + bP], where P = [max(Fo2,0) + 2Fc2]/3.

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applied fields ranging from −7 to 7 T. Measurements were performed on a polycrystalline sample of 11.64 and 13.63 mg for 1 and 2, respectively, introduced in a polyethylene sample holder (3 × 0.5 × 0.02 cm3). M vs H measurements have been performed at 100 K to check for the presence of ferromagnetic impurities, which have been found absent. The magnetic data were corrected for the sample holder and the diamagnetic contribution. Powder XRD (PXRD) measurements have been performed on the same microcrystalline samples that were measured in the SQUID. They show experimental patterns that correspond to the simulated X-ray patterns obtained from the single crystal X-ray structures, confirming that the solved structure is representative of the entire measured sample. PXRD data are reported in the Supporting Information (Figure S4).

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ASSOCIATED CONTENT

S Supporting Information *

Additional figures, FT-IR spectra, PXRD patterns, and crystallographic information in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic information has been deposited with Cambridge Crystallographic Data Centre as CCDC 1004935. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: (+39)0706754486. Tel: (+39) 0706754486. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Dr. Danilo Loche (Dip. Scienze Chimiche e Geologiche, Università di Cagliari) is acknowledged for PXRD measurements. Dr. Ingrid Freuze (Lab. Moltech Anjou, Université d’Angers) is acknowledged for ESI-MS analyses. This work was supported in Italy by Regione Autonoma della Sardegna, L.R. 78-2007, Bando 2009, CRP-17453 Project “Nano Materiali Multifunzionali per Applicazioni nell’Elettronica Molecolare”, Fondazione Banco di Sardegna, and INSTM. The work in France was supported by the CNRS, the Région Aquitaine, the ANR, the University of Bordeaux, and the University of Angers.

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REFERENCES

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Hydrogen-Bonded Supramolecular Architectures Based on Tris

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