Alkaline Ion-Modulated Solid-State Supramolecular Organization in

Article pubs.acs.org/crystal

Alkaline Ion-Modulated Solid-State Supramolecular Organization in Mixed Organic/Metallorganic Compounds Based on 1,1′Ethylenebis(4-aminopyridinium) Cations and Bis(oxamate)cuprate(II) Anions Tamyris T. da Cunha,† Willian X. C. Oliveira,† Carlos B. Pinheiro,‡ Emerson F. Pedroso,⊥ Wallace C. Nunes,§ and Cynthia L. M. Pereira*,† †

Departamento de Química, Instituto de Ciências Exatas and ‡Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil ⊥ Centro Federal de Educaçaõ Tecnológica de Minas Gerais, Av. Amazonas 5253, Belo-Horizonte, Minas Gerais 30421-169, Brazil § Instituto de Física, Universidade Federal Fluminense, Niterói, Rio de Janeiro 24210-346, Brazil S Supporting Information *

ABSTRACT: Three new coordination compounds of formula (edap)2[Cu(opba)]2·4H2O (1), (edap)[{Na2(H2O)4}{Cu2(opba)2}]·2H2O (2), and (edap)[{K2(H2O)2}{Cu2(opba)2}]·3H2O (3) (edap = 1,1′-ethylenebis(4aminopyridinium) and opba = 1,2-phenylenebis(oxamate)) were synthesized through the metathesis reaction involving A2[Cu(opba)] (A = Li+, Na+, and K+) and (edap)Cl2·2H2O. Crystal structures of 1−3 and edap(IO3)2·4H2O compound were elucidated by single crystal X-ray diffraction. Compounds 1− 3 are built up from dinuclear copper(II) entities, {[Cu(opba)]2}4− with an asymmetric bis(monatomic oxygen) bridge resulting from the parallel “out-ofplane” disposition of the planar mononuclear [Cu(opba)]2−. They possess distinct supramolecular arrangements of varying dimensionality (nD with n = 0 (1), 1 (2), and 2 (3)) in the solid state depending on the nature of the coordinated alkaline ion present alongside edap2+ counterions. While the {[Cu(opba)]2}4− building blocks are well-isolated in 1, they form either double chains or corrugated layers due to the coordination of the Na+ or K+ ions in 2 and 3, respectively. Magnetic properties of 1−3 show a very weak antiferromagnetic coupling between the CuII ions through a double monatomic (μ-O) bridge (−J = 1.63(9) (1), 2.29(2) (2), and 1.65(3) cm−1 (3)), the Hamiltonian being defined as H = −(S1·S2) + g βH(S1 + S2).

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INTRODUCTION

The work on the rich supramolecular coordination chemistry of a large family of aromatic polyoxalamide ligands with firstrow transition metal ions allows researchers to get one step further in the rational design of CPs and MOFs of increasing structural and magnetic complexities.7,8 Interesting examples of the supramolecular chemistry are observed in the [Cu(opba)]2− building block (opba = 1,2-phenylenebis(oxamate))9 (Figure 1). Its analogue complexes, which have been studied in the construction of several multimetallic coordination compounds, possess molecular architectures of varying dimensionality. This mononuclear copper(II) precursor is composed by two oxamate donor groups possessing two lone electron pairs on either side of the peripheral oxygen atoms, being able to act as a bis-bidentate ligand toward other metal ions.10 Besides its paramagnetic nature, the stability and the tendency to crystallize in distinct supramolecular architectures are determin-

Understanding the role of intermolecular interactions in a crystal packing is mandatory for their use in the design of new solids with desired structures, which is the essence of crystal engineering.1 Coordination polymers (CPs)2 and metal− organic frameworks (MOFs)3 constitute the best instances involving this subject. The formation of these extended solids is mainly due to the occurrence of moderately strong coordinative bonding, in one or more dimensions, which can be controlled though the self-assembly process.3 Yet different types of relatively weak intermolecular interactions are also responsible for the formation and crystal packing features of CPs, such as π−π stacking,4 hydrogen bonding,5 and van der Waals interactions, which are rather difficult to control. Therefore, the final structure is determined by the interplay of a large number of moderately strong intra- and weak intermolecular interactions, each of which affects the other intimately. Small changes in the molecular structure can therefore result in relevant changes in the crystal structure and vice versa, as illustrated by the supramolecular chemistry concept.6 © 2016 American Chemical Society

Received: October 12, 2015 Revised: December 23, 2015 Published: January 4, 2016 900

DOI: 10.1021/acs.cgd.5b01453 Cryst. Growth Des. 2016, 16, 900−907

Crystal Growth & Design

Article

on a PerkinElmer 882 spectrophotometer in the range 4000 and 400 cm−1 using dry KBr pellets. Thermogravimetric analysis (TG/DTA) data were collected with a Shimadzu TG/DTA 60 under a nitrogen atmosphere at a heating rate of 10 °C min−1 from room temperature to 750 °C. 1H NMR spectra were obtained at room temperature with a Bruker DPX-200 Advance (200 MHz) spectrometer using deuterium oxide (D2O) as solvent and tetramethylsilane (TMS) as internal reference. Magnetic measurements were performed using a Quantum Design SQUID magnetometer model MPMS-5S. Synthesis of (edap)Cl2·2H2O.21 1,2-Dichloroethane (640 μL, 4.25 mmol) was added to a solution of 4-aminopyridine (0.800 g, 8.50 mmol) in dmf (40 mL). The resulting mixture was refluxed for 24 h and then left to evaporate at 60 °C until dry. The resultant white powder was washed with acetone and diethyl ether. Yield: 1.520g, 62%. 1H NMR (ppm): 7.75 (C−Hring, 4H, dd), 6.75 (C−Hring, 4H, dd), 4.55 (C−H, 4H, s). Anal. Calcd for C12H20Cl2N4O2: C 44.59; H 6.24; N 17.33%. Found: C, 45.14; H, 6.45; N, 17.54%. IR (KBr, cm−1): 3324 (N−H), 3168 (N−H), 1664 (CN), 1544 (CC), 1212 (C− N), 838 (C−H), 510 (C−C). Synthesis of edap(IO3)2·4H2O.21 A similar reaction procedure to that reported above was carried out using 4-aminopyridine (0.800 g, 8.50 mmol), 1,2-dichloroethane (640 μL, 4.25 mmol), and potassium iodate (1.600 g, 4.25 mmol) in dmf (10 mL). The white powder obtained was dissolved in 20 mL of water and left to evaporate at 40 °C. Colorless prismatic crystals, which were suitable for X-ray diffraction experiments, were obtained after 2 days. Yield: 1.139g, 42%. Anal. Calcd for C12H24I2N4O10: C, 22.59; H, 3.79; N, 8.78%. Found: C, 22.80; H, 3.68; N 8.73%. IR (KBr, cm−1): 3326 (N−H), 3168 (N−H), 1662 (CN), 1546 (CC), 1212 (C−N), 838 (C− H), 622(C−C). Syntheses of 1−3. (edap)2[Cu(opba)]2·4H2O (1). Compound 1 was obtained by metathesis reaction with (edap)Cl2·2H2O using either the lithium(I) salt of the copper(II) complex precursor or their tetraalkyl ammonium derivatives (Me4N+, Et4N+, and n-Bu4N+) as starting materials. A mixture of (edap)Cl2·2H2O (0.015 g, 0.052 mmol) in H2O (1.5 mL) was added to another one containing (Bu4N)2[Cu(opba)] (0.040 g, 0.052 mmol) in H2O (2 mL). The solution was left to crystallize at room temperature, and after 2 days, purple needle-shaped crystals suitable for X-ray experiments were obtained. The crystals were filtered and washed with ethanol and diethyl ether. Yield: 0.021 g, 74%. Anal. Calcd for C44H48Cu2N12O16 (1): C, 46.85; H, 4.29; N, 14.90; Cu, 11.27%. Found: C, 46.54; H, 4.21; N, 14.87, Cu, 11.12%. IR (KBr, cm−1): 3328 (O−H), 3165 (N− H), 1645 (COamide), 1613 (COcarboxilate), 1456 (CC), 1209 (C−N), 1194 (C−H), 774 (C−H), 512 (C−C). (edap)[{Na2(H2O)4}{Cu2(opba)2}]·2H2O (2) and (edap)[{K2(H2O)2}{Cu2(opba)2}]·3H2O (3). Compounds 2 and 3 were synthesized according to the same procedure described for compound 1, by using the sodium(I) and potassium(I) salts of the copper(II) complex precursor, respectively, as starting materials in the metathesis reaction with (edap)Cl2·2H2O. Purple needle-shaped single crystals of 2 and 3 with appropriate quality to X-ray experiments were obtained after 2 days of slow evaporation. Amounts used for 2: (edap)Cl2·2H2O (0.0229 g, 0.079 mmol), Na2[Cu(opba)] (0.050 g, 0.079 mmol). Yield: 0.060 g, 86%. Anal. Calcd for C32H36Cu2N8Na2O18 (2): C, 38.68; H, 3.65; N, 11.28; Cu, 12.79%. Found: C, 38.60; H 3.67; N, 11.18; Cu, 13.17%. IR (KBr, cm−1): 3383 (O−H), 3167 (N−H), 1653 (COamide), 1636(C Ocarboxilate), 1609(CN), 1573 (CC), 1469 (CC), 1322(C−N), 1196 (C−H), 765(C−H), 507 (Cu−O). Amounts used for 3: (edap)Cl2·2H2O (0.033 g, 0.11 mmol), K2[Cu(opba)] (0.050 g, 0.11 mmol). Yield: 0.052 g, 87%. Anal. Calcd for C32H34Cu2N8K2O17 (3): C, 38.13; H, 3.40; N, 11.12; Cu, 12.61%. Found: C, 38.19; H, 3.44; N, 11.05; Cu, 12.84%. IR (KBr, cm−1): 3392 (O−H), 3224 (N−H), 1695 (COamide), 1661 (COcarboxilate), 1615 (CN), 1573 (CC), 1469 (CC), 1274 (C−N), 1194 (C−N) 1194 (C−H), 780 (C−H), 512 (Cu−O). X-ray Crystallographic Analysis. Single crystal X-ray diffraction data were collected on an Oxford-Diffraction GEMINI-Ultra diffractometer (LabCri) at 293 K using Mo Kα radiation (λ =

Figure 1. Chemical structures of templating organic cation edap2+ (a) and the metallorganic building block [Cu(opba)]2− (b).

ing characteristics in the choice of this spin-bearing mononuclear copper(II) complex as a building block. Many salts of the [Cu(opba)]2− precursor with either inorganic or organic counterions, ranging from alkali metal ions to tetraalkyl ammonium derivatives, are described in the literature.11−13 Through a simple metathesis reaction, some examples, such as [Etrad]2[Cu(opba)]2·MeCN·H2O (Etrad+ = 2-(4-N-ethyl-pyridinium)-4,4,5,5-tetramethylimidazoline-1oxyl-3-oxide radical cation)14 and [Ph4P]2[Cu(opba)]2 (Ph4P+ = tetraphenylphosphonium cation),13 were synthesized. This thus increases the knowledge about the diversity of molecular architectures containing the building block [Cu(opba)]2−. This opens a new range of application for this building block and analogue ones with other metal ions replacing copper(II).15,16 It is worth to emphasize that the choice of the counterion plays a key role because it can either add or modulate other physical properties to the resultant compound, such as chirality, electrical conductivity, and magnetism.17−19 In order to understand the influence of templating effects of counterions in the crystallization process, we promote metathesis reactions between (cat)2[Cu(opba)] and (edap)Cl2 salt. Cat+ are either alkaline A+ (A = Li, Na, and K) or tetraalkyl ammonium R4N+ (R = Me4N+, Et4N+, and n-Bu4N+) cations, and edap is the rod-like 1,1′-ethylenebis(4-aminopyridinium) counterion (Figure 1). The choice of edap2+ as an additional templating counterion is justified by its ability to establish both hydrogen bonding and π−π interactions in the solid state due to the presence of the amino substituents in the pyridinium aromatic rings. To the best of our knowledge, only the crystal structures of bromide and tetrafluoroborate compounds of formula (edap)Br220 and (edap) (BF4)221 have been reported up to now, raising the necessity of synthesis and further investigation of physical properties of these compounds, for example, optical properties and magnetism. It is worth noting that aminopyridinium derivatives, such as viologens (1,1′disubstituted 4,4′-bipyridinium), show interesting properties such as redox-activity,22 optical switching,23 and sensing.15,24 Herein, we report on the synthesis, the crystal structures, and the magnetic properties of three new complexes with different supramolecular architectures with the formula (edap)2[Cu(opba)]2·4H2O (1), (edap)[{Na2(H2O)4}{Cu 2(opba) 2}]· 2H2O (2), and (edap)[{K2(H2O)2}{Cu2(opba)2}]·3H2O (3), alongside that of edap(IO3)2·4H2O for comparison.

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EXPERIMENTAL SECTION

Materials and Methods. The building blocks of the general formula (cat)2[Cu(opba)] (cat = Me4N+, Et4N+, n-Bu4N+, Li+, Na+, and K+) were prepared according to literature methods.11 Chemicals and solvents used were of analytical grade and used as received. Physical Techniques. Elemental analyses (C, H, and N) were performed using a PerkinElmer 2400 analyzer, and the atomic absorption for Cu was carried out with a Hitachi Z-8200 polarized atomic absorption spectrophotometer. Infrared spectra were recorded 901



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Table 1. Crystallographic Data for Compounds 1−3

a

compound

edap(IO3)2·4H2O

1

2

3

empirical formula formula weight/g mol−1 crystal shape size/mm color crystal system space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z λ/Å T/K μ/mm−1 Dcalcd/g cm−3 theta range/deg goodness-of-fit R1 factor alla wR2b F(000)

C12H20N4O10I2 638.15 prismatic 0.59 × 0.47 × 0.32 colorless orthorhombic Pbca 17.524 (4) 6.6020 (13) 17.571 (4) 90 90 90 20328 (7) 4 0.71073 293 3.15 2.085 2.3−29.5 0.81 0.024 0.059 1240

C44H56Cu2N12O20 1200.08 plate 0.62 × 0.17 × 0.02 purple triclinic P1̅ 7.112 (5) 12.399 (5) 15.422 (5) 113.011 (5) 92.504 (5) 92.626 (5) 1247.5 (11) 1 1.54180 150 1.85 1.597 3.1−66.6 1.04 0.041 0.103 622

C32H36Cu2N8Na2O18 993.75 prismatic 0.73 × 0.24 × 0.12 purple triclinic P1̅ 7.058 (5) 11.113 (8) 13.257 (8) 71.726 (5) 79.610 (5) 74.172 (5) 945 (11) 1 1.54180 150 1.24 1.746 3.5−66.7 1.00 0.048 0.133 508

C32H34Cu2N8K2O17 1007.95 prismatic 0.23 × 0.18 × 0.11 purple monoclinic C2/c 7.057 (5) 25.764 (5) 20.525 (5) 90.000 (5) 93.429 (5) 90.000 (5) 3725 (3) 4 1.54180 150 4.21 1.797 3.4−66.1 1.02 0.052 0.118 2056

R1 = Σ∥Fo| − |Fc∥/Σ|Fo. bR2 = [Σ{w(Fo2 − Fc2)2}/Σ{w(Fo2)2}]1/2.

0.71073 Å) for edap(IO3)2·4H2O and at 150 K using Cu Kα radiation (λ = 1.5418 Å) for 1−3. Data integration, scaling of the reflections, and analytical absorption corrections were performed using CRYSALIS suite.25 Final unit cell parameters were based on the fitting of all reflections positions. Space group identification was done with XPREP26 and structure solution was carried out by direct methods using SIR-92.27 Refinements were performed using SHELXL2013 based on F2 through full-matrix least-squares routine.26 All non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms bonded to C and N atoms were located in difference maps and refined as fixed contributions according to the riding model.28 For organic moieties C−H = 0.97 Å and Uiso(H) = 1.5Ueq(C) for methyl groups C−H = 0.97 Å and Uiso(H) = 1.2Ueq(C) for methylene groups and aromatic carbon and protonated nitrogen atoms and finally N−H = 0.90 Å and Uiso(H) = 1.5Ueq(N) for ammonium group. Table 1 shows a summary of the crystal data collected, experimental details, and refinement results for edap(IO3)2· 4H2O and compounds 1−3. Crystallographic data for the structures have been deposited at the Cambridge Crystallographic Data Centre with CCDC reference numbers 1423484 (edap(IO3)2·4H2O), 1423486 (1), 1423487 (2) and 1423485 (3).

maintained in all further compounds 1−3 (see discussion below). Figure 2b shows the crystal packing of the 4aminopyridinium rings; iodate anions are intercalated between the edap2+ cations as well as the crystallization water molecules. The anions and cations are further linked through hydrogen bonds involving the terminal NH2 groups from edap2+ and the oxygen atoms from iodate (see Table S1, Supporting Information). The mean distance between the NH2 groups from neighboring molecules is 3.23(9) Å, while that between the nitrogen atoms from the same pyridine rings is 3.37(9) Å. These distances are compatible with π−π stacking interactions between the nonhybridized p orbital of nitrogen atom from NH2 groups and aromatic systems. edap2+ and [Cu(opba)]2− Structures. Structural elucidation of the salt products obtained by the metathesis reactions between edap2+ and [Cu(opba)]2− by single crystal X-ray diffraction showed that this structure is related to the cation utilized. Metathesis reaction using either Li+ or R4N+ (R = Me, Et, and n-Bu) as starting cations led to the formation of a compound of the formula (edap)2[Cu(opba)2]2·4H2O (1). On the other hand, coordination compounds of formula (edap)Na2[Cu(opba)]2·6H2O (2) and (edap)K2[Cu(opba)]2·5H2O (3) were obtained when using Na+ and K+ as starting cations, respectively. Hence, the metathesis reaction proved to be completely efficient for 1, with only one counterion being present in the resulting complex, while it was only partially achieved for both 2 and 3, leading to the occurrence of two different cations in the same complex. (edap)2[Cu(opba)2]2·4H2O (1). The structure of 1 is composed by dicopper(II) anionic entities, {[Cu(opba)]2}4−, and edap2+ counterions, together with water molecules of crystallization (Figure 3). In 1, the Cu2+ is pentacoordinated with two nitrogen (N1 and N2) and two oxygen (O1 and O4) atoms arising from two

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RESULTS AND DISCUSSION edap(IO3)2·4H2O Crystal Structure. In this work, the structure of the cation selected to perform the metathesis reactions was elucidated by the single crystal X-ray diffraction technique. Single crystals of edap(IO3)2·4H2O were obtained during the synthesis of the edap2+ cation from the 4aminopyridine and 1,2-dichloroethane reactants in the presence of potassium iodate. The structure consists of two 4aminopyridinium rings connected through an ethylene spacer (Figure 2a). Only half of the molecule is present at the asymmetric unit the other half being generated by the symmetry operation (i) = −x, 1 − y, −z. In this compound, the rod-like edap2+ cation has an anti-conformation with respect to the central −CH2CH2− spacer, which was 902



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atom in 1 is lifted by 0.11(1) Å from the mean basal plane toward the apical O1i atom. This gives rise to the well-known “out-of-plane” dinuclear {[Cu(opba)]2}4− entity29 possessing a parallel displaced disposition of the two mononuclear [Cu(opba)]2− planar fragments (Figure 3). Within the Cu2(μ-O)2 core of 1, intramolecular Cu···Cu distance through the asymmetric bis(monatomic oxygen) double bridge is 3.420 Å. This value is smaller than previously reported by Unamuno et al. for an analogue of formula (dhdppz)Na2(C14H12N2){[Cu(opba)]2}·4H2O (4) (dhdppz2+ = 6,7-dihydrodi-pyrido[1,2a:22,12-c]pyrazinium cation) (Cu····Cu = 3.560 Å).29 The values of the Cu1−O1−Cu1i (α) and O1−Cu1i−O1i (β) bridging angles (α = 96.1(1)° and β = 83.9(1)°) (Figure 3) and those of the Cu−O1i (R = 1.967(4) Å) and Cu−O1 (R′ = 2.592(2) Å) bond distances within the Cu2O2 core are similar to those reported for Na2(C14H12N2){[Cu(opba)]2}·4H2O (α = 95.4°, β = 84.6(1)°, R = 2.788(4) Å, and R′ = 1.967(1) Å).29 The view from the crystallographic b axis of the crystal packing of 1 revealed that dinuclear units are isolated from each other because of the presence of the bulky organic edap2+ counterions, so that they dispose themselves within the a × c plane creating a rectangular framework that surrounds the dinuclear units (Figure 4a). Therefore, one of the edap2+ cations packs in a weak face-to-face π−π stacking interactions with the aromatic benzene ring from the tetraanionic dicopper(II) units (centroid−centroid distance ∼3.70 Å), whereas the other edap2+ cation shows very weak edge-toface π−π stacking interaction with the phenyl rings. According to the view from the crystallographic a axis (Figure 4b), the edap2+ cations alternate along the crystallographic c axis because of supramolecular interactions. (edap)[{Na2(H2O)4}{Cu2(opba)2}]·2H2O (2) and (edap)[{K2(H2O)2}{Cu2(opba)2}]·3H2O (3). The structures of 2 and 3 consist of dicopper(II) anionic entities, {[Cu(opba)]2}4−, and coordinated by Na+ (2) and K+ (3) ions, together with edap2+ counterions and water molecules (coordinating and noncoordinating) (Figures 5−8). The molecular structure of “out-of-plane” anionic dinuclear entities of 2 and 3 (Figures 5 and 7, respectively) are very similar to that of 1, but their crystal packing is completely different (Figure 6) due to the presence of the additional Na+ (2) or K+ (3) ions (since the metathesis reaction was not complete). The copper atom in 2 and 3 are lifted by 0.13 Å (2) and 0.05 (3) from the mean basal plane composed by the atoms N1, N2, O1, and O4 toward the apical donor, which is occupied by the atom O1i from the adjacent centrosymmetrically related [Cu(opba)]2− unit (Cu···Cui = 3.378(1) (2) and 4.303(1) Å (3); symmetry code (i) = −x, 2 − y, −z in both crystal structures). Within the Cu2O2 core of 2 and 3, the apical Cu1− O1i bond distances (R′ = 2.616(1) (2) and 2.910(3) Å (3)) are slightly larger than that of 1, whereas the Cu1−O1−Cu1i bridging angles (α = 93.7(7) (2) and 94.1(1)° (3)) are remarkably smaller. The sodium atom Na1 in 2 possesses a distorted octahedral geometry involving atoms O5, O6, O2ii, and O3ii (symmetry code (ii): x, −1 + y, z) from the oxamate groups of two adjacent {[Cu(opba)]2}4− entities in equatorial positions and atoms O7 and O8 from the coordinated water molecules in axial positions. Consequently, a supramolecular double chain running along the crystallographically c axis is formed by the coordinative interactions among Na+ cations and dinuclear {[Cu(opba)]2}4− anions in 2 (Figure 6a). The space between each double chain is occupied by crystallization solvent

Figure 2. (a) Representation of the cationic and anionic units of edap(IO3)2·4H2O with atom labeling scheme (symmetry code: (i) = −x, 1 − y, −z). Ellipsoids are drawn at 50% of probability levels. Hydrogen atoms and water molecules were omitted for the sake of clarity. (b) View of the crystal packing of edap(IO3)2·4H2O along the crystallographic b-axis. Hydrogen atoms were omitted for the sake of clarity. Color code: carbon (gray), nitrogen (blue), oxygen (red), iodine (purple).

Figure 3. View of the anionic dinuclear entity {[Cu(opba)]2}4− of 1 with atom and angle labeling scheme (symmetry code (i) = 1 − x, −y, 2 − z). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms were omitted for the sake of clarity.

oxamate groups in basal plane. Deviations from planarity of those basal atoms (N1, N2, O1, and O4) are less than 0.02 Å. The square-pyramidal coordination sphere of the Cu2+ ion is completed by an apical oxygen atom (O1i) from the centrosymmetrically related [Cu(opba)]2− unit. The copper 903



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Figure 4. Views of the crystal packing of 1 along the crystallographic b (a) and a axes (b), respectively. Metallorganic anions and the organic cations are represented in stick and space-filling models, respectively. Hydrogen atoms were omitted for the sake of clarity. Nitrogen atoms are in light blue, carbon atoms in gray, and oxygen atoms are in red.

Figure 5. Representation of the anionic dinuclear entity {[Cu(opba)]2}4− of 2 showing coordinated Na+ ions with the atom labeling scheme. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms were omitted for the sake of clarity (symmetry codes: (i) = −x, 2 − y, −z; (ii) = x, 1 + y, z).

Figure 6. (a) View of a fragment of the double chain of 2. Green and purple spheres of arbitrary radii represent copper and sodium atoms, respectively. (b) and (c) Crystal packing views of parallel array of double chains of 2 along the crystallographic a axis including either the crystallization water molecules or the edap2+ cations, respectively. For the sake of clarity, hydrogen atoms were omitted. Carbon atoms are in gray and nitrogen atoms are in blue in the space-filling model.

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3.84 Å and dihedral angles between their mean planes of 2.60(8)°). The two crystallographic independent potassium atoms in 3 present different geometries. Potassium(I) atom K1 is in a distorted trigonal prismatic geometry composed by the oxygen atoms O5, O5ii, O2i, O2iii from the opba ligand and O7, O7ii from the water molecules. Potassium K2 atom is octacoordinated in a distorted square antiprism geometry also composed by the free carbonyl oxygen atoms O1i, O1iii, O2i, O2iii, O5, O5ii from the opba ligand and the atoms O7, O7ii from bridging water molecules (Figure 7). The coordination geometry of the potassium atoms is determinant for the observed crystal packing of 3, which consists of dinuclear {[Cu(opba)]2}4− anions connected by the coordinated K+ ions resulting in a parallel array of corrugated layers growing in a × c plane (Figure 8a). The interplanar separation along the crystallographically b axis is enough to accommodate the crystallization water molecules and the edap2+ counterions (Figure 8, panels b and c, respectively). Parallel-displaced π−π stacking interactions occur between pyridinium rings from the edap2+ counterions and aromatic benzene rings from the opba ligands (pyridinium centroid−benzene centroid distance of 3.57(1) Å). Magnetic Properties. The magnetic properties of 1−3 in the form of the χMT versus T plots (χM being the molar magnetic susceptibility per dinuclear unit) were investigated in the temperature range of 2.0−300 K (Figure 9). They exhibited χMT values at room temperature equal to 0.78 (1), 0.81 (2),

Figure 7. Crystal structure of the anionic dinuclear entity {[Cu(opba)]2}4− of 3 showing the coordinated K+ ions with atom labeling scheme. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms were omitted for the sake of clarity (symmetry codes: (i) = −x + 1/2, −y + 1/2, − z; (ii) = −x, y, −z + 1/2; (iii) = x + 1/2, −y + 1/2, z + 1/2).

molecules and also by edap2+ counterions (Figure 6, panels b and c, respectively). Anionic dicopper(II) entities and the edap2+ counterions in 2 are associated through parallel displaced π−π interactions between the aminopyridinium rings from the edap2+ and the aromatic benzene rings from the opba ligand (centroid-centroid distances of approximately

Figure 8. (a) View of a fragment of the corrugated layer of 3. Green and purple spheres of arbitrary radii represent copper and potassium atoms, respectively. Crystal packing views of the parallel array of corrugated layers of 3 along the crystallographic a axis in the absence (b) and including (c) either the crystallization water molecules or the edap2+ counterions in the given order. Hydrogen atoms were omitted for the sake of clarity. Carbon and nitrogen atoms from the organic counterions are represented in purple and yellow spheres in the space-filling model respectively, whereas anionic dicopper(II) units and the water molecules are in green and red, sequentially. 905



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of each square pyramidal copper(II) ion (“magnetic orbitals”) due to the parallel “out-of-plane” disposition of the metal basal planes.29 A correlation between the J values and the Cu−Oap−Cu bridging angle (α) and/or the Cu−Oap bond distance (R′) has been originally discussed by Chiari et al.31 for carboxylatebridged dicopper(II) complexes containing a double asymmetric monatomic bridge with one short Cu−Oeq and one long Cu−Oap bond distance (Table 2). They reported that, for an α Table 2. Selected Structural and Magnetic Data for 1−4 and Related Carboxylate-Bridged Dinuclear Copper(II) Complexes Containing a Double Asymmetric Monoatomic Bridge

and 0.83 cm3 K mol−1 (3), which are close to those expected for two noninteracting copper(II) ions based on the spin only approximation considering g = 2.0 and SCu = 1/2(χMT = 0.38 cm3 K mol−1 per copper(II) ion). For all compounds, the χMT versus T curves are very similar; i.e., χMT remains constant from room temperature to ca. 50 K, when a slight decrease started to reach χMT values of 0.51 (1), 0.40 (2), and 0.55 cm3 K mol−1 (3) at 2.0 K. This common magnetic behavior for 1−3 indicates the presence of weak intramolecular antiferromagnetic interactions between the two copper(II) ions within the Cu2O2 core, the intermolecular magnetic interactions through the diamagnetic Na+ and K+ in 2 and 3, respectively, being thus negligible. Magnetic susceptibility data of 1−3 were analyzed through the phenomenological spin Hamiltonian proposed by Heisenberg−Dirac-Van Vleck (eq 1) for an isolated pair of isotropic metal ions.30 H = − J(S1·S2) + gβH(S1 + S2)

R′b/Å

αc/o

Jd/cm−1

ref

1

2.592(2)

96.1(1)

−1.63

2

2.616(1)

93.7(7)

−2.29

3

2.911(1)

94.1(1)

−1.65

(dhdppz)Na2[Cu(opba)]2· 4H2O (4) {[CuL1(MeCO2)]2} {[CuL2(MeCO2)]2} {[CuL3(MeCO2)]2} {[Cu(PhCONHCH2CO2) (H2O)2]2}·2H2O {[Cu(bpca)]2(H2opba)}2· 6H2O

2.788(4)

94.5(1)

−0.80

this work this work this work 4

2.655(4) 2.577(2) 2.490(1) 2.37(1)

96.3(5) 96.1(1) 95.34(5) 107.0(5)

−1.84 −1.51 −0.25 −2.15

2.669(2)

102.81(7)

−2.36

compounda

Figure 9. Temperature dependence of χMT products for 1 (○), 2 (□), and 3 (△) at H = 500 Oe. Solid lines represent the best-fit curves (see text).

31 31 32 31, 33, 34 35

a

Ligand abbreviations: HL1 = N-(5-Bromosalicylicidene)-N-methylpropane-1,3-diamine, HL2 = N-methyl-N′-(5-nitrosalicylidene)-propane-1,3-diamine, HL3 = 7-amino-4-methyl-5-aza-3-hepten-2-one, Hbpca = bis(2-pyridylcarbonyl)amide, dhdppz2+ = 6,7-dihydrodipyrido[1,2-a:22,12-c]pyrazinium, and H 4 opba = N,N′-1,2phenylenebis(oxamic) acid. bCu−Oap−Cu bridging angle. cCu−Oap bond distance. dMagnetic coupling parameter in eq 1.

value higher than 94°, an antiferromagnetic coupling can be expected, which should increase with the augmentation of α value due to the overlap between the magnetic orbitals when deviations from the parallel disposition of the metal basal planes become greater. In addition, the Cu−Oap distances should also play a role in the magnetic properties interpretation. An increase in the apical bond distance implies a decrease of the overlap between the magnetic orbitals, thus reducing the magnitude of the antiferromagnetic coupling. Therefore, for instance, the trend observed for the calculated magnetic coupling parameter in 1−3 (this work) and (C14H12N2)Na2 [Cu(opba)]2·4H2O (4)29 [−J = 0.80 (4) < 1.63(9) (1) < 1.65(3) cm−1 (3) < 2.29(2) cm−1 (2)] does not directly correlate with the variation of the Cu−Oap−Cu bridging angles [α = 93.7(7) (2) < 94.1(1) (3) < 94.5(1) (4) < 96.1(1)° (1)] or the Cu−Oap bond distances [R′ = 2.592(2) (1) < 2.616(1) (2) < 2.788(4) (4) < 2.910(3) Å (3)].

(1)

with Si (i = 1 and 2) being the spin operator for each CuII ion (Si = SCu = 1/2), J the magnetic coupling parameter, and g the isotropic Landé factor of the CuII ions. In this case, the equation derived from the Hamiltonian is known as the Bleaney−Bowers30 eq (eq 2): 2Ng 2β 2 (3 + e−J / kT )−1 (2) kT where N is the Avogadro constant, β is the Bohr′ magneton, and k is the Boltzmann constant. The least-squares fits of the experimental data for 1−3 gave −J = 1.63(9) (1), 2.29(2) (2), and 1.65(3) cm−1 (3) and g = 2.03(1) (1), 2.08(1) (2), and 2.10 (1) (3), with R = 1.27 × 10−5 (1), 3.18 × 10−5 (2), and 2.17 × 10−5 (3) (R being the agreement factor between experimental and theoretical values defined as ∑[(χMT)exp − (χMT)calcd]2/∑[(χMT)exp]2). The theoretical curves for 1−3 match precisely the experimental ones (solid lines in Figure 9). The small −J values found for 1−3 reflect the occurrence of a weak antiferromagnetic coupling between the copper(II) ions within the Cu2(μ-O)2 bridging unit, as reported previously for the related complex of formula (dhdppz)Na2[Cu(opba)]2· 4H2O (4) (dhdppz2+ = 6,7-dihydrodi-pyrido[1,2-a:22,12-c]pyrazinium cation).29 This is an expected because of the poor overlap between dx2−y2 orbitals containing the unpaired electron χM =

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CONCLUSION In the present work, we report a systematic magnetostructural study on a novel series of mixed organic/metallorganic compounds based on the rod-like 1,1′-ethylenebis(4-aminopyridinium) (edap) cation and the well-known 1,2phenylenebis(oxamate) (opba)-cuprate(II) anion and prepared through a straightforward metathesis reaction from the corresponding alkaline ion salts in aqueous solution. The 906



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metathesis reaction was complete for the lithium(I) derivative leading to the compound 1, while it was only partial for the sodium(I) and potassium(I) derivatives resulting in the coordination compounds 2 and 3. Compounds 1−3 present the same “out-of-plane” dicopper(II) basic structural unit formed by the parallel displaced arrangement of two mononuclear [Cu(opba)]2− planar fragments. The alkaline ion-mediated solid-state aggregation of these dinuclear {[Cu(opba)]2}4− building blocks renders sodium(I)−copper(II) double chains and potassium(I)−copper(II) corrugated layers in 2 and 3, in the given order. Despite the distinct supramolecular organization of 1−3 in the solid state, they show a common magnetic behavior with small variations in the weak intramolecular antiferromagnetic coupling depending on the structural dimensions of the Cu2O2 bridging core.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01453. A table containing the geometry hydrogen bonds present in the crystal packing of compound edap(IO3)2·4H2O (PDF) Accession Codes

CCDC 1423484−1423487 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 [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

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Conselho Nacional de ́ Desenvolvimento Cientifico e Tecnológico (CNPq), Fundaçaõ de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), and Coordenaçaõ de Aperfeiçoamento de Pessoal de Nı ́vel Superior (CAPES). T.T.C. and C.L.M.P. thank A. M. Moreira for all X-ray powder diffraction measurements and Prof. Miguel Julve and Dr. Rafael Ruiz-Garcı ́a from Universitat de València, Spain, for fruitful discussions. W.C.N. is grateful to FAPESP (09/54082-2) for the use of Squid-UFSCAR.

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Alkaline Ion-Modulated Solid-State Supramolecular Organization in

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