Hierarchical Assembly of Antiparallel Homochiral Sheets Formed by

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Hierarchical Assembly of Antiparallel Homochiral Sheets Formed by Hydrogen-Bonded Helixes of a Trapped-Valence CoII/CoIII Complex Ana M. García-Deibe,*,† Matilde Fondo,† Julio Corredoira-Vázquez,† M. Salah El Fallah,‡ and Jesús Sanmartín-Matalobos† †

Departamento de Química Inorgánica, Facultade de Química, Campus Vida, Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Spain ‡ Departament de Química Inorgánica, Facultat de Química, Universitat de Barcelona, E-08028, Barcelona, Spain S Supporting Information *

ABSTRACT: On the basis of selected reagents and reaction conditions, a chiral dinuclear trapped-valence CoII/CoIII complex was conveniently obtained {[Co2(L)(O2CCH2CO2)(H2O)]·EtOH· 1.25H2O, being H3L = 2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine)}. This complex behaves as a compact amphiphile, whose hydrophilic pole attracts ethanol and water solvates. Its crystal packing shows a hierarchical structure controlled by an amphiphatic nature. Molecules of each enantiomer are head-to-tail connected through intermolecular hydrogen bonds to give rise to infinite helixes. These helical chains are stacked in homochiral two-dimensional sheets with hydrophilic pockets, where water and ethanol solvates are trapped. Each layer displays its homoenantiomeric helixes with a parallel orientation, while their mirror helixes, which are alternate, are antiparallelly oriented.

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INTRODUCTION Mixed valence compounds have received considerable attention, not only because of their valence localization/ delocalization character, but also because of those properties derived from their intervalence electronic transitions.1,2 These features can be exploited in many research fields such as magnetism,3,4 electrochromism,5 and/or spintronics.6 In this sense, dinuclear CoII/CoIII complexes could also be potentially interesting, but unfortunately, there are not many examples reported in the literature.7−12 Therefore, new synthetic approaches to obtain these kinds of compounds could improve their knowledge and their subsequent use. Triarmed compartmental ligands of the type shown in the sketch of Figure 1 (X′ = H, CH3; n = 2, 3) have been used by several research groups, including ours, to prepare a wide variety of complexes,10,13−21 and many of them with interesting magnetic properties.10,16−21 Most of these complexes are homodinuclear,10,13−21 with both cations presenting identical valences. In contrast, we have reported the controlled isolation of trapped-valence CoII/CoIII complexes,10 instead of typical homodinuclear CoIII/CoIII compounds,10,16−18 using a convenient control of some simple reaction conditions. This method takes advantage of the asymmetric μ-η1,η2 bridging behavior displayed by ancillary chelating ligands as acetylacetonate or malonate. Because of this asymmetry, the complexes © XXXX American Chemical Society

display two different coordination environments suitable to accommodate two dissimilar valences.10,22 Likewise, we have also used this asymmetric coordination mode to prepare chiral homodinuclear zinc(II)14 and nickel(II)19 complexes with these types of ligands (scheme in Figure 1). Keeping in mind our effective route to CoII/CoIII valencetrapping,10 we have selected a similar Schiff base (X = Br; X′ = H; n = 2 in Figure 1) with new neutral chiral complexes, using dicarboxylates malonate as ancillary ligands. For this occasion, we have included some subtle changes, with the intention of exploring their influence in the crystal packing. This latter aspect is related to some typical structural features of these complexes, in combination with a rather predictable hydrogen bonding scheme in their close proximity.10,14−19 We think that this aspect could be of interest at a supramolecular level, since chiral self-assembly of metallosupramolecular systems and hierarchical processes have attracted great interest,23−25 because of their ability to mimic complex biological processes or because of their applications.26−29 We are presenting here a simple chiral complex (Figure 1) obtained from achiral starting materials, which has also Received: August 26, 2016 Revised: January 2, 2017 Published: January 10, 2017 A

DOI: 10.1021/acs.cgd.6b01269 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Supporting Information). This has also facilitated a full characterization, including single-crystal X-ray diffraction and magnetic studies in the solid state (see Supporting Information). It must be mentioned that, as occurred before,10 no reaction with terephthalic acid occurred under these conditions. By contrast, the use of succinic acid has leaded to obtain Co2L(O2CC2H4CO2)·3H2O·3MeOH. Although ES-MS points to a dinuclear nature, we cannot corroborate its similarity to [Co2(L)(O2CCH2CO2)(H2O)]. Unfortunately, and despite multiple attempts and efforts to obtain single crystals, we have not succeeded, and consequently, its crystal structure cannot be discussed and compared here. With regard to the ES mass spectrum of [Co2(L)(O2CCH2CO2)(H2O)]·EtOH·1.25H2O, this shows a maximum intensity peak at 909.9 m/z. The isotopic profile of this peak is very similar to that calculated for a [Co2L(O2CCH2CO2H)]+ fragment. This behavior indicates that the ancillary malonate ligand remains coordinated to the metal ions in solution, while the more labile water molecule is not already present. However, the structure of the neutral complex in solution appears quite similar to that found in the solid state (Figure 1). Single Crystal X-ray Diffraction Studies for [Co2(L)(O2CCH2CO2)(H2O)]·EtOH·1.25H2O. It could be determined that the asymmetric unit of this compound contains one of the enantiomers of the dinuclear cobalt complex, in combination with some solvated water and ethanol molecules. Some of these solvates are present with some disorder. As expected,10,14−19 the heptadentate Schiff base is acting as trianionic, with its central phenolate-O atom (O103) forming a μ2-bridge. Both equivalent O,N,N,O + O,N,N,O donor sets display symmetric Δ-cisβ and Λ-cisβ configurations, with respect to their corresponding edges,34 but they only display a seesaw-shaped geometry around each metal ion. Therefore, in order to achieve hexacoordination, cobalt ions complete their pseudo-octahedral chromophores by means of a terminal water molecule and a malonate dianion, which also provides neutrality. As intended, this malonate anion is asymmetrically coordinated, with a μ2-η2:η1-O,O mode. In joint, both two cobalt ions are triply bridged by the imidazolidine NCN chain, and by a double O-bridge. This spatial arrangement leads to form a four-membered Co2O2 metallacycle (Figure 2), with an intramolecular Co11···Co12 separation of only ca. 3.08 Å. Despite both cobalt ions display pseudo-octahedral N2O4 coordination polyhedra (Figure 2), the pseudo-octahedron around Co11 is less regular, and 73 nm3 bigger than that around Co11. These differences, and the bi- and trideprotonated nature of the two anionic ligands present in this neutral complex, lead us to think that both cobalt ions exhibit +II and +III oxidation states. This conclusion is reinforced not only by comparison of the geometric parameters around the cobalt ions, with others found in the literature for cobalt(II) and (III) in mixed-valence complexes,7−12,35−38 but also by the values of their bond valence sums (BVS),39,40 which are 2.33 and 3.75, for Co11 and Co12, respectively. The conformational change in the chromophores can be ascribed to both the change in the charge on the cobalt ions, and the spin change between high-spin CoII and low-spin CoIII. Therefore, the complex shows a clearly localized mixed-valence nature in the solid state, and the distinct difference in bond

Figure 1. Ellipsoid representation of the enantiomer S-[CoII/III2(L)(O 2 CCH 2 CO 2 )(H 2O)], along with some solvates with high occupation sites. Intramolecular H-bonds and those involving the latter solvates are highlighted. S refers to the configuration of the methanetriyl C atom (C120), while in this enantiomer N103 and N104 display R and S configurations, respectively. A scheme for related tri-armed ligands has been also included.

facilitated a well-defined valence-trapping. Interestingly, some motifs of its crystal packing are reminiscent of some aspects of the secondary and tertiary structure of proteins. These features are related to its helical chaining, and its amphipathic behavior,30 which is also related to the complicated helix− helix packing.31,32

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RESULTS AND DISCUSSION With the intention of preparing some new Co II /Co III complexes, we have employed again our previous synthetic method,11 where acidity is a key factor. In that previous study, we used an unsubstituted ligand (X and X′ = H; n = 2 in Figure 1), combined with acetylacetonate, and malonic or terephthalic acids (H2A), as ancillary ligands. On that occasion, we used different molar ratios to obtain mixed-valence complexes of the types [Co2L′(O2CCH2CO2)(MeOH)], [Co2L′(acac)(OH)] and [Co2L′(acac)(HA)]. These last two types of complexes had been obtained after mixing Co(acac)2, H3L, and the dicarboxylic acid in a 4:2:1 molar ratio, with only slightly acid pH. As an inconvenience, they appear cocrystallized, and with some disorder.10 To avoid this complication, in this study, we will only focus our attention on the results obtained when combining cobalt(II) acetylacetonate, H3L, and the corresponding acid in a 2:1:1 molar ratio. This latter molar ratio leads to a lower pH that allows a total deprotonation of the dicarboxylic acids. In this particular case, we have also added some ethanol to the mixture, instead of using only methanol, or this latter mixed with acetonitrile.10 The synthetic procedure described in the Experimental Section has allowed us to obtain the chiral neutral complex [Co2(L)(O2CCH2CO2)(H2O)]·EtOH·1.25H2O (Figure 1). Hence, and as expected, the aerial oxidation suffered by the starting cobalt(II) salt was only partial and easily controlled. This has allowed the straightforward isolation of the complex with high purity, as its X-ray powder diffractogram shows (see B



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Figure 3. Homochiral H-bonded Λ and Δhelical chains, containing only S and R enantiomers of the complex, respectively. Backbone C atoms of the malonate dianion, O and H atoms involved in H-bonds have been space-filled, other atoms are represented as sticks, and other H atoms have been omitted. Both chains have been here represented as mirror images, with a parallel orientation of their heads and tails. Crystallographic 21 screw axes parallel to b have been included to appreciate the pitch of these helixes.

Figure 2. Balls and sticks representation of the pseudo-octahedral coordination polyhedron for the C(R),N(R,S), or simply, the R enantiomer. The imidazolidine NCN bridge, as well as the whole malonate ligand are represented for an easier understanding of the asymmetry, as well as of the triple bridge between the cobalt ions. H atoms have been omitted for clarity. A table with equivalent Co−N and Co−O distances has been included for an easier comparison.

respect to the central arm (Figure 3). This different degree of opening is typical of those chromophores holding asymmetrically chelated ligands.10,14,16,19 Hydrogen Bonding Scheme and Secondary Structure. As we were interested in the propagation of H-bonds,15 and bearing in mind the structures found for other cobalt complexes with this kind of ligand,10,16 we have decided to use a mixture of ethanol and methanol, instead of using only methanol. This decision was based not only on a less coordinating ability of ethanol, if compared to methanol, but also on its more hygroscopic nature. This choice could appear as a subtle difference, but it was not trivial at all. The use of only methanol to prepare another trapped-valence complex10 had led to its coordination to the cobalt(II) ion. Consequently, formation of classic H-bonds was much more restricted, since methanol only allowed one intramolecular H-bond acting as the donor, while the malonate ligand was the corresponding acceptor.43 In contrast, the presence of some water in the medium has been crucial for the present crystal packing. Thus, the coordinated water molecules act as a double H-donor, intraand intermolecular, while the chelated malonate behaves as a double H-acceptor, for intra- and intermolecular H-bonds as well.43 Consequently, a linear head-to-tail propagation of O− H···O bonds occurs between neighboring molecules of the complex. The anti disposition of the donor water molecules, with respect to the carboxylate acceptor, leads to form a simple spiral (Figure 3). Even though enantiomers are typically interacting between them in racemic crystals, this one-dimensional chaining only occurs between identical molecules. As a result, each complex unit is only connected to other two identical enantiomers. These interactions generate a secondary structure of infinite homochiral helical chains (Figure 3), along the 21 screw axes of the crystal, which are parallel to b. In this case, Λ or M helixes are only formed by S enantiomers, while the Δ or P helixes only contain R enantiomers of the complex. In order to appreciate

lengths identifies it as a valence-trapped Robin-Day class I complex.1,41 The same conclusion can be also extracted from the magnetic study of this complex. In fact, its behavior can be fully interpreted in terms of an isolated high-spin octahedral cobalt(II) ion. The results obtained also suggest a weak crystalfield and quite small reduction orbital (see Supporting Information for more details of the magnetic studies). The difference between both coordination spheres appears basically associated with the asymmetric coordination of the dianionic malonate ligand, which is chelating the cobalt(III) ion, while it is only monocoordinated to the cobalt(II) ion. The chelation of malonate or acetylacetonate to the most oxidized metal ion has also been observed for other trapped-valence complexes10,22 and could be useful to design other complexes of this nature. Likewise, these imidazolidine-containing ligands appear as adequate M−O−M angles for ferromagnetic coupling,42 as well as short intermetallic distances.10,14−19,42 In this case, the Co···Co distance is short, if compared with most of mixed-valence cobalt complexes.7,11,12,35−38 Hence, a combination of this type of ligand, with adequate ancillary ligands as malonate and acetylacetonate, with controlled reaction conditions could be adequate to obtain new trappedvalence complexes with short intervalence distances. This asymmetric coordination of the malonate also leads to chirality, and as a result, the Schiff base displays three stereocenters in its central imidazolidine ring: the methanetriyl C atom and both N atoms. The racemate so obtained could be described as C(R),N(R,S) and C(S),N(S,R) enantiomers, but to simplify, it could be simply described as R and S, only alluding to the configuration of the central asymmetric C atom. In the solid state, additional asymmetry is also provided by the different conformations adopted by the two ethylene chains (Figures 1 and 3). This flexibility allows the salicylaldimine lateral branches to display a different degree of opening with C



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the Δ and Λ helixes with more clarity, we have represented both helixes as mirror images in Figure 3. Arbitrarily, we have considered the malonate anion as the head, while the coordinated water has been considered as the tail. The pitch of these helixes is ca. 13.8 Å long and contains two whole complex units. The spatial disposition adopted by the ligand after coordination, where O101 and O102 are very accessible, allows an easy connection of both terminal phenol atoms to a solvated molecule through two classic H-bonds,43 while this solvate can be connected to other molecules as well (Figures 1 and 4).10,14−19 In this case study, the predictable presence of a

phobic sides are also helically alternate (Figure 5, top left). Along the helical axis, these helixes display a pseudorhomboidal

Figure 5. Two space filled views, parallel and perpendicular to b, of the Λ(S)-helix, (top) showing the rhomboidal spool-like appearance along the screw axis, and the alternate positioning of the hydrophilic and hydrophobic poles (schematized as red dots (when they can be directly observed), and pink (when they are oriented towards the opposite side). The same colors are used to represent the helixes along the screw axis when they are stacked (bottom). The grey color corresponds to more hydrophobic parts.

spool-like shape that allows a rather compact packing, with the hydrophilic sides of the complexes oriented toward both longer sides (Figure 5, top right). This close proximity of the helixes is also observed in the packing of protein alpha helixes, where amphipathicity plays a key role.31,32 Likewise this distribution of polarity is well suited for membrane binding, and consequently binding amphipathic helices are involved in membrane remodeling machineries and vesicular transport.30 This compact arrangement contrasts with those broad hydrophilic pockets previously observed for another complex with this type of ligand.15 Thus, this packing only gives rise to small voids, where the polar guests (water and ethanol) are occluded (Figure 6). The polar cavities are so close that they appear as a narrow groove with a hydrophilic zigzag, or as a polar zip fastener. In contrast, the bottom of these cavities is hydrophobic, so the apolar hydrocarbon tail of the ethanol solvates is oriented toward hydrophobic parts of a neighboring helix (Figure 6). Hydrophobic interactions are also important in the protein helix packing, as in four helix bundles.31−33 All the helixes stacked as described in Figures 5 and 6 are of the same handedness, and therefore they form a homochiral two-dimensional (2-D) layer. Furthermore, in each one of these layers all the helixes display the same orientation, since all their heads and tails are unvaryingly equivalently oriented (Figure 7). Hence, using some terminology typical of the protein packing,31−33 we can say that in this homochiral 2-D ensemble or sheet, the helixes are parallelly oriented. Obviously, the other enantiomer is forming the same architecture, but of course, as a mirror image. So, both homoenantiomeric layers are alternate, but their directions are antiparallel (Figure 7). Consequently, when we observe the crystal unit perpendicularly to b (the screw axial direction), we can see parallel sheets of helixes with the same handedness, and parallel to b, alternating with antiparallely oriented sheets formed by helixes with opposite handedness (Figure 7). This

Figure 4. (Top) Space filling views of the neutral complex S[CoII/III2(L)(O2CCH2CO2)(H2O)] with a 180° rotation, to show the patently different polarity of both sides: (right) hydrophobic and (left) hydrophilic. (Bottom) The same views including all the solvates. The ethanol molecule is disordered on two sites. Two water molecules with residual occupation sites have been also included (Br brown, C gray, Co dark blue, H white, N blue, O red).

solvate near the terminal phenolate groups corresponds to a water molecule (O1w). At the same time, this water molecule is H-bonded to an ethanol solvate, which is disordered on two different sites (75% and 25%). In addition, this latter solvate appears to be connected to water molecules with residual occupations (Figure 4). Amphiphatic Character: Tertiary Structure. The role of the central imidazolidine ring is of crucial importance in different aspects as (i) predisposing to dinuclearity;10,14−20,42 (ii) favoring the coordination of additional ligands;10,14−19 and (iii) once the Schiff base is coordinated, behaving as a compact amphiphile (Figure 4). With respect to the amphipathic character, on one hand, the envelope conformation displayed by the saturated heterocycle, in joint with the two contiguous ethylene chains, and the three salicylidene rings are practically hydrophobic (Figure 4), even in the presence of the three Br atoms. On the other hand, the presence of the phenol groups attached to the three pendants, and sited at the opposite side of this heterocycle, is am actual hydrophilic zone (Figure 4). This amphipathic behavior are crucial for the crystal packing, and only the hydrophilic groups are closely connected to the polar solvates (water and ethanol) via classic H-bonds.43 With the formation of the H-bonded homochiral helixes of [CoII/III2(L)(O2CCH2CO2)(H2O)], the hydrophilic and hydroD



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Figure 6. Three Λ(S) H-bonded helical chains (along the c axis), as represented in Figure 2, showing the hydrophilic groove between them, and which is filled by water and ethanol solvates (O atoms pink, C atoms light blue and gray). For a better understanding, a scheme has been included above.

Figure 7. (Top) H-bonded helical chains (as represented in Figure 2), along the a axis, with a scheme below to show their antiparallel disposition. (Bottom) Helixes along the b axis showing the hydrophilic groove between them, which is actually filled by water and ethanol guests. A scheme show the antiparallel stacking of homochiral helixes.

alternate distribution of homochiral helical sheets is rather uncommon, since alternation of enantiomers occurs typically in the three directions,44−46 but its antiparallelism is even more uncommon.47,48 As all the hydrophilic parts are positioned toward the interior part of the homochiral sheets of helixes, interactions between alternate antiparallel sheets are weak interactions. Among them, weak π−π stacking between antiparallel sheets, through the 5Br-salicylidene residues, including some C−H···Br interactions, and some hydrophobic contacts, contribute to maintain the packing of these antiparallel layers (Figures 5 and 7, bottom). In the case of proteins, apart from H-bonding, both hydrophobic and hydrophilic interactions collaborate to their hierarchical structure, and particularly for helix−helix packing.31−33 This fact is patent for simple motifs as four-helix bundles or for more complicated barrels and sandwiches.

Likewise, many of the antiparallel domains consist of two sheets packed against each other, with hydrophobic side chains forming their interface. Bearing in mind that side chains of a βstrand point alternately to opposite sides of a sheet, this means that such structures will tend to have a sequence of alternating hydrophobic and polar residues.31−33 This motif also appears in this structure, but as helixes display a perfect alternation of hydrophobic and hydrophilic with turns of 180°, their packing is strictly parallel, and no torsion is observed between consecutive helixes.47,48

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CONCLUSIONS Simple and achiral starting materials, with controlled reaction conditions allow the isolation of neutral molecules of the complex rac-[CoII/III2(L)(O2CCH2CO2)(H2O)]. The valenceE



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73%), mp >300 °C. Found: C, 37.9; H, 3.9; N, 4.9. C34H44Br3Co2N4O13 (1070.91) requires: C, 38.0; H, 4.1; N, 5.2%. MS (ES): m/z 810.8 (100%) [Co2L]+2. IR (KBr, ν/cm−1): 1636 (C N), 3421 (H2O). Crystallographic Measurements. Crystals of [Co 2 L(O2CCH2CO2)(H2O)]·EtOH·1.25H2O were obtained as detailed above. Selected crystal data and some details of refinements are given in Supporting Information (Table S1). Diffraction data were collected at 100 K, using a Bruker AXS ApexII-CCD area detector diffractometer, employing graphite monochromated Mo−Kα radiation (λ = 0.71073 Å). Data were corrected for Lorentz and polarization effects. Multiscan absorption corrections were applied using SADABS.49 The structure was solved by standard direct methods employing SHELXS and refined by Fourier techniques based on F2 using SHELXL-2014.50 Non-hydrogen atoms were anisotropically refined. Hydrogen atoms of organic groups were included at geometrically calculated positions, with thermal parameters derived from the parent atoms. H atoms corresponding to the coordinated water molecule were located on Fourier maps, and then thermal parameters were included as dependent on the parent atoms. Final difference Fourier maps were flat, after assigning two punctual electronic densities as water molecules with residual occupation sites (0.15 and 0.10).

trapping is evidenced by the differences found for Co−N and Co−O bond distances for both cobalt ions in its crystal structure, while its BVS analysis provides values of 2.33 and 3.75. Magnetic studies demonstrate that the complex behaves as an isolated high-spin cobalt(II) ion. This complex possesses two interesting and expected features: (i) chirality and (ii) an amphiphatic character. The combination of both characteristics, with the use of convenient ligands and solvents, leads to an outstanding supramolecular behavior, with a hierarchical packing, in the solid state, with four levels. In this way, its secondary level results from the head-to-tail chaining, via classic O−H···O bonds of each enantiomer of the complex into homochiral helixes. As in protein helix−helix packing, the amphiphatic character influences the tertiary level. Thus, homochiral helixes form 2D layers of helixes with identical handedness, which intercalate ethanol and water guests between them in polar voids. Each homoenantiomeric layer displays a parallel disposition of its helixes, while the alternate layers of each enantiomer are antiparallely oriented.

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EXPERIMENTAL SECTION

ASSOCIATED CONTENT

S Supporting Information *

All solvents, salicylaldehyde, triethylenetetramine, malonic acid, cobalt(II) acetate tetrahydrate, and cobalt(II) acetylacetonate are commercially available and were used without further purification. Physical Measurements. Elemental analysis of C, H, and N was performed on a Carlo Erba EA 1108 analyzer. An IR spectrum was recorded as KBr pellets on a FT-IR Mattson Instruments 202Q spectrophotometer in the range 4000−600 cm−1. Electrospray mass spectrum of rac-[CoII/III2(L)(O2CCH2CO2)(H2O)]·EtOH·H2O was recorded on a Hewlett-Packard LC/MS spectrometer, using methanol as solvent. Magnetic susceptibility measurements for a crushed crystalline sample of the complex were carried out at the Unitat de Mesures Magnètiques of the Universitat de Barcelona with a Quantum Design SQUID MPMS-XL susceptometer, working in the range 2− 300 K under magnetic fields of 300 G (2−30 K) and 5000 G (30−300 K) and at 2 K from 0 to 50000 G. Diamagnetic corrections were estimated from Pascal’s Tables. The agreement factor is based on the function R = Σ(χMTexp − χMTcal)2/Σ(χMTexp)2. Synthesis. 2-(5-Bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine, H3L, was prepared following a procedure previously described and satisfactorily characterized by elemental analysis, mass spectrometry, IR and 1H NMR spectroscopy.19 [Co2L(O2CCH2CO2)(H2O)]·EtOH·1.25H2O: To a methanol/ ethanol (20:10 mL) solution of Co(acac)2 (0.22 g, 0.86 mmol), H3L (0.3 g, 0.43 mmol) was added. The mixture was stirred for 10 min until a perfect brown solution was obtained. Malonic acid (0.044 g, 0.43 mmol) was added to the resultant solution, and the mixture (pH = 4.8) was refluxed for 3 h and then filtered in order to eliminate any possible impurity. Slow evaporation of the filtered solution allowed the formation of brown crystals, which were suitable for X-ray diffraction and magnetic studies. These crystals were filtered and dried in air. Elemental analysis of the crystalline sample is in agreement with the proposed stoichiometry, and its powder X-ray diffraction (PXRD) is in full agreement with that of the single crystal structure solved (0.22 g, 51%), mp >300 °C. Found: C, 37.9; H, 3.5; N, 5.5. C32H36.5Br3Co2N4O10.25 (998.74) requires: C, 38.4; H, 3.6; N, 5.6%. MS (ES): m/z 909.9 (100%) [Co2L(O2CCH2CO2H)]+. IR (KBr, ν/ cm−1): 1635 (CN), 3400 (H2O). Co2L(O2C(CH2)2CO2)·3H2O·3MeOH: To a methanol/ethanol (20:10 mL) solution of Co(acac)2 (0.22 g, 0.86 mmol), H3L (0.20 g, 0.43 mmol) was added. The mixture was stirred for 10 min until a perfect brown solution was obtained. Succinic acid (0.051 g, 0.43 mmol) was added to this brown solution. The resulting acid mixture (pH = 5.98) was refluxed, and after 3 h was filtered. Several attempts of crystallization only led to dark brown powdery samples (0.34 g,

This material is also available free of charge via the Internet at The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01269. Powder and single crystal X-ray diffraction data, with crystal parameters; details of the magnetic studies (PDF) Accession Codes

CCDC 1501024 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 34 881814237. Fax 34 981597525. E-mail: ana.garcia. [email protected]. Web: http://www.usc.es/gl/investigacion/ grupos/suprametal/index.html. ORCID

Ana M. García-Deibe: 0000-0001-9127-0740 Matilde Fondo: 0000-0002-7535-946X Author Contributions

The manuscript was written through contributions of all authors. Funding

Authors thank the Spanish Ministerio de Ciencia e Innovación (MICINN) for financial support (Project Nos. CTQ201456312-P and CTQ2015-63614-P). Notes

The authors declare no competing financial interest.

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REFERENCES

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