Anion Influence on the Structure of N,O-Hybrid Pyrazole ZnII, CdII

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Anion Influence on the Structure of N,O-Hybrid Pyrazole ZnII, CdII, and HgII Complexes. Synthesis, Characterization, and Theoretical Studies Miguel Guerrero,† Josefina Pons,*,† Josep Ros,† Mercè Font-Bardia,‡ and Vicenç Branchadell§ †

Departament de Química, Unitat de Química Inorgànica, Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain Cristal·lografía, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franquès s/n, 08028-Barcelona, Spain and Unitat de Difracció de RX, Serveis Científico Tècnics, Universitat de Barcelona, Martí i Franquès s/n, 08028-Barcelona, Spain § Departament de Química, Unitat de Química Física, Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain ‡

S Supporting Information *

ABSTRACT: In this paper we describe the synthesis and characterization of three new complexes of the 1,8-bis(3,5-dimethyl1H-pyrazol-1-yl)-3,6-dioxaoctane ligand (L) with ZnII (1A), CdII (2A), and HgII (3A) ions. The aim of the present study is to investigate the structural effect of the counteranion (Cl− vs ClO4−) on the type and geometry of the structures of the complexes as well as the ligational behavior of the ligand. Depending on the type of the counteranion, the structural studies revealed a variety of modes of bonding (N,N-bidentate/N,O,O,N-tetradentate), coordination geometries (tetrahedral/octahedral), and different nuclearities (monomer/polymer). Moreover, the density functional theory computational study in combination with several experimental techniques as well as the investigation of the extended structures allowed us to understand the role of the different anions in the structure of the complexes.

1. INTRODUCTION Design and synthesis of mono-, di-, and polynuclear metal ion complexes and other supramolecular architectures are a major area of research in supramolecular chemistry, materials chemistry, and crystal engineering.1 The design of these structures is highly influenced by several factors among others, the coordination geometry, the size of the metal, the structural characteristic of the ligand, and the nature of the counteranion. These key factors are essential for the creation of new functional materials with solvent inclusion or gas-adsorption characteristics and special optical, electronic, magnetic, and catalytic properties.2 One smart strategy to construct such assemblies is the use of a metal complex, formed by various combinations of metal ion (node) and organic ligand (bridge), as a supramolecular synthon to form the primary structure. By exploiting the different varieties of coordination geometries around these metal ions, diverse molecular and crystalline architectures of different shapes and sizes may be accessed through coordination bonds © 2012 American Chemical Society

in cooperation with weak noncovalent interactions such as hydrogen-bonding, electrostatic, and hydrophobic forces.3 Group 12 metals (Zn, Cd, and Hg) are particularly promising not only due to interesting luminescent properties4 and broad applications in the biological area,5 but also to their wide variety of coordination numbers and geometries provided by the d10 configuration of the metal center.6 Moreover, inorganic counteranions can be considered as charged ligands and can effectively induce the coordination versatility of the molecular architecture and, therefore, the later physical properties of the supramolecular structure. Particularly, this domain of anion coordination chemistry is a promising area because of its potential applications in anion template assembly, ion-pair recognition, and supramolecular chemistry.7 Regarding the influence of the ligand, it has been well documented in the literature that functional groups of different Received: April 13, 2012 Revised: May 31, 2012 Published: June 7, 2012 3700

dx.doi.org/10.1021/cg300506c | Cryst. Growth Des. 2012, 12, 3700−3708

Crystal Growth & Design

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Bruker AC-250 MHz spectrometer in D2O solutions, at room temperature. 1D 113Cd{1H} and 199Hg{1H} spectra were recorded on a DPX-360 Bruker spectrometer equipped with a 5 mm broadband probe. All spectra were recorded at 298 K in CD3CN, using a recycle time of 1 s. Spectra were processed with a line broadening of 1 Hz prior to Fourier transformation and externally referenced to aqueous solutions, 0.1 M of Cd(ClO4)2 and 0.1 M of Hg(ClO4)2 in D2O. All chemical shifts values (δ) are given in ppm. Samples of 1,8-bis(3,5dimethyl-1H-pyrazol-1-yl)-3,6-dioxaoctane (L) were prepared as described in the literature.10b 2.3. Synthesis of Complexes [M(L)(ClO4)2] (M = Zn(1), Cd(2), Hg(3)). An absolute ethanol solution (20 mL) of L (0.196 g, 0.64 mmol) was added to an absolute ethanol solution (20 mL) of Zn(ClO4)2 (0.169 g, 0.64 mmol) for 1, Cd(ClO4)2 (0.199 g, 0.64 mmol) for 2, or Hg(ClO4)2 (0.256 g, 0.64 mmol) for 3 and 5 mL of triethyl orthoformate (for dehydration purposes). The resulting solution was allowed to stir for 24 h at room temperature. The solvent was removed in vacuo to yield a white solid in all cases, which was filtered off, washed twice with 5 mL of cool diethyl ether, and dried in a vacuum. Compound 1.Yield. 59% (0.216 g). C16H26Cl2N4O10Zn: Anal. Calc.: C, 33.67; H, 4.59; N, 9.82; Found: C, 33.69; H, 4.76; N, 9.95. Conductivity (Ω−1 cm2 mol−1, 1.12 × 10−3 M in MeOH): 170.1. MS (m/z) (%): 469.1 (100%) [Zn(L)ClO4]+. IR (KBr, cm−1): 3134 ν(C− H)ar, 2970, 2905 ν(C−H)al, 1553 (ν(CC), ν(CN))ar, 1472 (δ(CC), δ(CN))ar, 1103 ν(ClO4), 1045 ν(C−O−C)as. (Polyethylene, cm−1): 493−467 ν(Zn−N, Zn−O). 1H NMR (D2O solution, 250 MHz) δ: 6.03 (s, 2H, CH(pz)), 4.59 (t, 4H, 3J = 5.7 Hz, NpzCH2CH2O), 4.17 (t, 4H, 3J = 5.7 Hz, NpzCH2CH2O), 4.12 (s, 4H, OCH2CH2O), 2.33 (s, 6H, CH3(pz)), 2.12 (s, 6H, CH3(pz)) ppm. 13 C{1H} NMR (D2O solution, 63 MHz,) δ: 151.6 (pz-C), 143.4 (pzC), 108.1 (CH(pz)), 71.8 (OCH2CH2O), 69.6 (NpzCH2CH2O), 47.1 (NpzCH2CH2O), 13.5 (CH3(pz)), 11.7 (CH3(pz)) ppm. Compound 2. Yield. 76% (0.301 g). C16H26Cl2N4O10Cd: Anal. Calc.: C, 31.11; H, 4.24; N, 9.07; Found: C, 31.25; H, 4.18; N, 9.17. Conductivity (Ω−1 cm2 mol−1, 1.07 × 10−3 M in MeOH): 145.8. MS (m/z) (%): 519.1 (100%) [Cd(L)ClO4]+. IR (KBr, cm−1): 3129 ν(C− H)ar, 2952, 2887 ν(C−H)al, 1552 (ν(CC), ν(CN))ar, 1470 (δ(CC), δ(CN))ar, 1120 ν(ClO4), 1034 ν(C−O−C)as. (Polyethylene, cm−1): 489−471 ν(Cd−N, Cd−O). 1H NMR (D2O solution, 250 MHz) δ: 6.05 (s, 2H, CH(pz)), 4.57 (t, 4H, 3J = 4.1 Hz, NpzCH2CH2O), 4.13 (t, 4H, 3J = 4.1 Hz, NpzCH2CH2O), 4.08 (s, 4H, OCH2CH2O), 2.36 (s, 6H, CH3(pz)), 2.30 (s, 6H, CH3(pz)) ppm. 13C{1H} NMR (D2O solution, 63 MHz,) δ: 149.1 (pz-C), 142.3 (pz-C), 105.1 (CH(pz)), 69.8 (OCH2CH2O), 69.4 (NpzCH2CH2O), 47.4 (NpzCH2CH2O), 14.3 (CH3(pz)), 11.6 (CH3(pz)) ppm. 113Cd NMR (D2O solution, 88 MHz) δ: +629 ppm. Compound 3.Yield. 66% (0.298 g). C16H26Cl2N4O10Hg: Anal. Calc.: C, 27.22; H, 3.71; N, 7.94; Found: C, 27.31; H, 3.70; N, 7.85. Conductivity (Ω−1 cm2 mol−1, 1.15 × 10−3 M in MeOH): 175.2. MS (m/z) (%): 507.2 (100%) [Hg(L)ClO4]+. IR (KBr, cm−1): 3113 ν(C− H)ar, 2924, 2902 ν(C−H)al, 1552 (ν(CC), ν(CN))ar, 1424 (δ(CC), δ(CN))ar, 1091 ν(ClO4), 1081 ν(C−O−C)as. (Polyethylene, cm−1): 475−461 ν(Hg−N, Hg−O). 1H NMR (D2O solution, 250 MHz) δ: 6.02 (s, 2H, CH(pz)), 4.54 (t, 4H, 3J = 6.1 Hz, NpzCH2CH2O), 3.84 (t, 4H, 3J = 5.7 Hz, NpzCH2CH2O), 3.59 (s, 4H, OCH2CH2O), 2.37 (s, 6H, CH3(pz)), 2.35 (s, 6H, CH3(pz)) ppm. 13C{1H} NMR (D2O solution, 63 MHz,) δ: 148.9 (pz-C), 142.4 (pz-C), 106.2 (CH(pz)), 71.7 (OCH2CH2O), 71.3 (NpzCH2CH2O), 46.3 (NpzCH2CH2O), 11.9 (CH3(pz)), 11.3 (CH3(pz)) ppm. 199Hg{1H} NMR (CD3CN, 65 MHz) δ: −1142 (s) ppm. 2.4. Crystallography Data. Colorless single crystals suitable for X-ray analyses were grown by slow diffusion of diethyl ether into an ethanol solution of 1 and 2. A prismatic crystal was selected and mounted on a MAR345 diffractometer with an image plate detector. Unit-cell parameters were determined from automatic centering of 443 reflections (3 < θ < 31°) for 1A and 694 reflections (3 < θ < 31°) for 2A and refined by least-squares method. Intensities were collected with graphite monochromatized Mo Kα radiation, using ω/2θ scantechnique. For complex 1A, 15830 reflections were measured in the

electronic nature attached to the organic ligands have an important effect on the structural frameworks. More specifically, nitrogen containing heteroaromatic systems have recently gained substantial interest. In fact, a majority of these heteroaromatic systems have found an important role in pharmaceutical chemistry and their motifs are found in many natural products.8 Pyrazole-type (Pz) heterocyclic ligands represent a class of potential candidates in this respect because they incorporate a nitrogen moiety which can effectively coordinate with metal ions. Furthermore, substitution at carbons adjacent to the nitrogen atoms is a straightforward way to modify the steric environment around the N-donor atoms and any metal ions coordinated to them.9 In our continuous effort to synthesize new coordinated selfassembled networks with derived hybrid ligands,10 we have herein explored the self-assembly and diverse dimensional structure of d10 metal complexes of ZnII, CdII, and HgII with a mixed-donor ligand 1,8-bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6dioxaoctane ligand (L) (Scheme 1) with special emphasis on Scheme 1

the role of the counteranions. In order to get information on intra- and intermolecular interactions between the ligand and the metallic centers, we also carried out a comparative study with previously published coordination assemblies of different Group 12 complexes.10b

2. EXPERIMENTAL SECTION 2.1. Chemical Risks. Although no problem was encountered in all our experiments, transition metal perchlorates are potentially explosive and should be handled in small quantities. 2.2. Materials and Methods. Elemental analyses (C, H, and N) were carried out by the staff of Chemical Analyses Service of the Universitat Autònoma de Barcelona on a Eurovector 3011 instrument. Conductivity measurements were performed at room temperature (r.t.) in 10−3 M methanol solutions, employing a CyberScan CON 500 (Euthech instrument) conductimeter. Infrared spectra were run on a Perkin-Elmer FT spectrophotometer, series 2000 cm−1 as KBr pellets or polyethylene films in the range 4000−150 cm−1. Electrospray mass spectra were obtained with an Esquire 3000 ion trap mass spectrometer from Bruker Daltonics. 1H, 13C{1H} NMR, DEPT, COSY, HSQC, and NOESY spectra were recorded on a NMR-FT 3701



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range 2.58 ≤ θ ≤ 32.57, 4549 of which were nonequivalent by symmetry (Rint(on I) = 0.066). 2385 reflections were assumed as observed applying the condition I ≥ 2σ(I) while for complex 2A, 16256 reflections were measured in the range 2.65 ≤ θ ≤ 27.79, 5060 of which were nonequivalent by symmetry (Rint(on I) = 0.043). 4785 reflections were assumed as observed applying the condition I ≥ 2σ(I). Lorentz-polarization and absorption corrections were made. The structures were solved by Direct methods, using the SHELXS computer program (SHELXS-97) and refined by full matrix leastsquares method with SHELXL-9711 computer program using 15830 reflections for 1A and 16256 reflections for 2A (very negative intensities were not assumed). The function minimized was Σw||FO|2 − |FC|2 |2, where w = [σ2(I) + (0.0469P)2 + 0.0821P]−1 for 1A and w = [σ2(I) + (0.0852P)2 + 2.4555P)2]−1 for 2A and P = (|FO|2 + 2|FC| 2)/3. For complex 1A, 13 H atoms were computed and refined, using a riding model, with an isotropic temperature factor equal to 1.2 times the equivalent temperature factor of the atom which are linked and 2 H atoms were located for a difference synthesis with an isotropic temperature factor equal to 1.2 times the equivalent temperature factor of the atom which are linked. For complex 2A, 2 H atoms were calculated and refined with an isotropic temperature factor equal to 1.2 times the equivalent temperature factor of the atom which are linked and 26 H atoms were computed and refined, using a riding model, with an isotropic temperature factor equal to 1.2 times the equivalent temperature factor of the atom which are linked. The final R(F) factor and Rw(F2) values as well as the number of parameters refined and other details concerning the refinement of the crystal structure are gathered in Table 1.

2.5. Computational Details. All calculations have been done with the Gaussian-09 program.12 All structures have been optimized using the M0613 density functional with a 6-31+G(d,p) basis set for nonmetal atoms. For metals, the Stuttgart relativistic effective core potentials (SDD)14 have been used with a a triple-ζ basis set for the valence orbitals. The number core electrons are 10 (Zn) and 28 (Cd). All structures have been fully characterized as energy minima though the calculation of vibrational frequencies. Single point calculations in ethanol solution have been done using the SMD method.15 The reported Gibbs energies have been computed from energies computed in solution and from zero point and thermal energies and entropies computed in the gas phase. Wiberg bond indexes16 have been computed using natural bond orbitals.17

3. RESULTS AND DISCUSSION 3.1. Synthesis and General Characterization of Complexes. The synthetic procedure for the preparation of the 1,8-bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6-dioxaoctane ligand (L) has been previously reported by our group.10b The reaction of L with M(ClO4)2 (M = ZnII, CdII, or HgII) in absolute ethanol for 2 h with a 1:1 M/L molar ratio yields the ionic complexes [M(L)](ClO4)2 [M = ZnII (1A), CdII (2A), HgII (3A)]. Several techniques were used for the characterization of all the complexes: elemental analysis, mass spectrometry, conductivity measurements, IR and 1D/2D NMR spectroscopies. In addition, a full 3D structure determination for compounds 1A and 2A was performed. Unfortunately, in the case of compound 3A no suitable single crystals could be obtained. The elemental analyses for complexes 1A−3A are consistent with the formula [M(L)(ClO4)2] [M = ZnII (1A), CdII (2A), and HgII (3A)]. The positive ionization spectra (ESI+-MS) of compounds 1A−3A give a peak attributable to [M(L)ClO4]+. Molecular peaks of the cations are observed with the same isotope distribution as the theoretical ones. As an example, ESI+-MS spectra of complex 1A for fragment [Zn(L)ClO4]+ and its theoretical isotopic distribution are presented in Figure 1. Conductivity values in methanol for complexes 1A and 3A are in agreement with the presence of 1:2 electrolyte compounds, since the reported values (170.1−175.2 Ω−1 cm2 mol−1) are between 160 and 220 Ω−1 cm2 mol−1.18 However, for complex 2A (M = Cd), the conductivity value (145.8 Ω−1 cm2 mol−1) is slightly lower, and it is found between 1:1 (80− 115 Ω−1 cm2 mol−1) and 1:2 (160−220 Ω−1 cm2 mol−1) electrolyte compounds, indicating a certain kind of coordination to the metallic center. Taking the crystal structure obtained in solid state (section 3.2), this conductivity value could signify some sort of coordination of the ClO4− anion to the Cd atom. Comparison of the IR bands of the free pyrazole ligand (the most characteristic bands are those attributable to the pyrazolyl and ether groups) and its complexes revealed that the ligand is coordinated to the metallic center. This is mainly because the ν(CC), ν(CN), and ν(C−O−C)as stretching bands increase upon complexation.10b,19 Moreover, the presence of the perchlorato anions is confirmed by the v(ClO4) stretching band between 1120 and 1091 cm−1.19b The IR spectra of complexes 1A−3A in the 600−100 cm−1 region were also studied. The presence of bands between 493 and 461 cm−1 for all complexes, assigned to ν(M-N) and ν(M-O), confirms the coordination of the Npz and the ether group of the ligand to the metallic center.20 3.2. Crystal Structures of Complexes 1A and 2A. Through crystallization from a diethyl ether solution, colorless

Table 1. Crystallographic Data for 1A and 2A 1A (ZnII) molecular formula formula weight temperature (K) wavelength (Å) system, space group unit cell dimensions a (Å) b (Å) c (Å) β (°) U (Å 3) Z Dcalc (g cm−3) μ (mm−1) F(000) crystal size (mm3) hkl ranges 2θ range (°) reflections collected/unique/ [Rint] completeness to θ (%) absorption correction data/restraints/ parameters goodness-of-fit on F2 final R indices [I > 2σ(I)] R indices (all data) largest diff peak and hole (e Å −3)

2A (CdII)

C16H30Cl2N4O12Zn 606.71 293(2) 0.71073 monoclinic, C2/c

C16H28Cl2N4O11Cd 635.72 293(2) 0.71073 monoclinic, P21/c

17.111 (14) 9.427 (5) 17.606 (12) 113.37 (4) 2607 (3) 4 1.546 1.210 1256 0.09 × 0.07 × 0.07 −25 ≤ h ≤ 25, −14 ≤ k ≤ 14, −24 ≤ l ≤ 25 2.58−32.57 15830/4549 [R(int) = 0.0664]

10.267 (3) 14.302 (3) 17.097 (4) 95.02 (2) 2500.9 (11) 4 1.688 1.147 1288 0.2 × 0.1 × 0.1 −13 ≤ h ≤ 13, −16 ≤ k ≤ 18, −22 ≤ l ≤ 22 2.65−27.79 16256/5060 [R(int) = 0.0432]

99.0% (θ = 25.00°)

99.3% (θ = 25.00°)

empirical

none

4549/3/201

5060/5/318

1.094

1.202

R1 = 0.0659, wR2 = 0.1221

R1 = 0.0538, wR2 = 0.1417

R1 = 0.1529, wR2 = 0.1468 0.375 and −0.358

R1 = 0.0595, wR2 = 0.1494 0.980 and −0.912

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Figure 1. ESI+-MS spectra in methanol of fragment (a) [Zn(L)ClO4]+ and (b) its theoretical isotopic distribution.

monocrystals for complexes 1A and 2A (suitable for X-ray diffraction) were obtained. Selected bond lengths, bond angles, parameters refined, and other details concerning the refinement of the crystal structures 1A and 2A are listed in Tables 1 and 2. Table 2. Selected Bond Lengths (Å) and Bond Angles (°) for 1A and 2A M−N(1) M−N(1′) M−O(1) M−O(1′) M−O(2) M−O(2′) N(1′)−M−N(1) N(1′)−M−O(1′) N(1)−M−O(1′) O(1′)−M−O(1) O(1′)−M−O(2) O(1)−M−O(2) N(1′)−M−O(1) N(1)−M−O(1) N(1′)−M−O(2) N(1)−M−O(2) O(2)−M−O(2′)

1A (ZnII)

2A (CdII)

2.069(3) 2.069(3) 2.171(3) 2.171(3) 2.182(2) 2.182(2) 110.72(16) 100.32(11) 86.56(11) 167.97(14) 92.10(10) 78.21(9) 86.56(11) 100.32(11) 156.66(10) 89.54(11) 73.64(12)

2.242(4) 2.245(3) 2.318(3) 2.407(4) 2.357(3) 2.372(3) 123.19(13) 86.97(12) 88.25(13) 173.16(14) 100.00(13) 80.86(13) 88.91(14) 98.58(15) 149.05(13) 87.35(12) 68.22(11)

Figure 2. ORTEP diagram of complex 1A showing an atom labeling scheme. 50% probability amplitude displacement ellipsoids are shown. Hydrogen atoms are omitted for clarity.

O(ether) distances (2.182(3) Å) are significantly longer than the Zn−N distances (2.069(3) Å). If the crystal structure of 1A is compared with that of [ZnCl2(L)]n (1B),10b one can observe the influence of the coordination capacities of the different counterions (Scheme 1). The Cl− anion has a strong coordination ability, and a tetrahedral complex with L acting in a NN-bridge bidentate mode can be obtained (1B). On the other hand, the ClO4− anion has a weaker coordination ability and the hybrid pyrazole ligand can further coordinate to the ZnII centers to form an octahedral complex (1A) with L acting as a NOON-equatorial tetradentate ligand. Contrary to what we found for complex 1A, the structure of complex 2A (M = CdII) consists of discrete monomeric units ([Cd(H2O)(ClO4)(L)]+) where one perclorate anion remains coordinated (Figure 3). The cadmium atom is coordinated to one oxygen atom of a perchlorate anion, one water molecule, two cis pyrazolic nitrogen atoms, and two cis ether oxygen atoms. Once again, the L ligand is coordinated to the metal center via a κ4 NOON-bonding mode and forms two sixmembered rings and one five-membered ring. The metal center, which adopts distorted octahedral coordination geometry, presents bond angles between 68.22° and 173.16°. These angles once again significantly deviate from 90° or 180°,

The structure of complex 1A (M = ZnII) consists of discrete monomeric units [Zn(H2O)2(L)]2+ and two perchlorate anions (Figure 2). The zinc atom is coordinated to two trans water molecules, two cis pyrazolic nitrogen atoms, and two cis ether oxygen atoms. The L ligand in complex 1A is coordinated to the metal centers in a κ4 NOON-bonding mode. The L ligand chelates the center metal atoms through the pyrazolic nitrogen atoms and the ether oxygen atoms forming two six-membered rings and one five-membered ring. The metal center, which adopts a distorted octahedral coordination geometry, shows bond angles between 73.64° and 167.97°. These angles significantly deviate from 90° or 180°, presumably due to the restrictions induced by the chelation of the tetradentate L ligand. The [Zn(Npz)2O4] core has been reported in 11 complexes in the literature, seven of them corresponding to the [Zn(Npz)2O2(H2O)2] core.14 As shown in Table 2, the Zn− 3703



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second most stable structure is only 0.5 kcal mol−1 higher in Gibbs energy. To further study the effect of the counterions, we have also investigated the ClO4−/H2O exchange between the connected species [M(ClO4)2(L)], [M(H2O)(ClO4)(L)]+, and [M(H2O)2(L)]2+. The reaction Gibbs energies corresponding to the first exchange are 3.1 (M = Zn) and 3.8 (M = Cd) kcal mol−1, whereas for the second exchange the values are −1.3 (M = Zn) and −1.7 (M = Cd) kcal mol−1. This clearly indicated that the difference between ZnII and CdII complexes in the two exchanges is only 0.7 and 0.4 kcal mol−1, respectively. The difference in relative Gibbs energies between the complexes shown in Table 3 are generally larger due to the existence of additional interactions with the second coordination sphere ligands (water and/or perchlorate) (Figure 4). Figure 3. ORTEP diagram of complex 2A showing an atom labeling scheme. 50% probability amplitude displacement ellipsoids are shown. Hydrogen atoms are omitted for clarity.

presumably due to the restrictions induced by the chelation of the tetradentate L ligand. The [Cd(Npz)2O4] core has been reported for nine complexes in the literature,21 whereas the [Cd(Npz)O3(H2O)] core is present only in three complexes.22 As seen in Table 2, the Cd−O(ether) distances (2.318(3), 2.407(2) Å) are significantly longer than the Cd−N distances (2.242(4), 2.245(3) Å). Crystal structures of complexes 2A and [CdCl2(L)] (2B)10b show that in both cases the metal center adopts octahedral coordination geometry. However, it is clear that the nature of the counterions plays a very important role in the final structure. When the Cl− anion is present (2B), L adopts a NOON-meridional tetradentate mode, whereas L acts as NOON-equatorial tetradentate mode when the ClO4− anion is present. The single-crystal X-ray diffraction studies have confirmed the structural diversity of L (from NN-bridge bidentate to NOON-equatorial/axial tetradentate mode) depending on the type of the counteranion. 3.3. Computational Studies. To better understand the structural differences in the crystals under the present study, we have carried out theoretical calculations for complexes 1A, 1B, 2A, and 2B and studied the role of the different anions (Cl− vs ClO4−). We have optimized the geometries of [M(ClO4)2(L)], [M(H2O)(ClO4)(L)]+, and [M(H2O)2(L)]2+ species (M = ZnII, CdII) and their interactions with water molecules and perchlorate anions in a second coordination sphere. Table 3 shows the relative Gibbs energies of complexes with the same stoichiometry. Cartesian coordinates of all computed structures can be found as Supporting Information. The most stable structures for ZnII and CdII complexes correspond to [Zn(H2O)2(L)]2+···(ClO4−)2 and [Cd(H2O)(ClO4)(L)]+···(H2O)(ClO4−), respectively. This is in good agreement with the observed crystal structures (Figures 2 and 3, respectively). However, for the CdII complex (2A), the

Figure 4. Optimized geometries of several Zn and Cd complexes. Selected interatomic distances in Å. Nonpolar hydrogen atoms have been omitted for clarity.

This computational information is in good agreement with our previously described results. This therefore confirms the significant effect of the counterion (perchlorate or chloride) on the structure of Cd(L) complexes. To further rationalize this effect, we have also optimized the structures of cis- and trans[CdCl2(L)] complexes. Surprisingly, the trans complex (where L acts a NOON-equatorial tetradentate ligand) is the most stable one (by 2.0 kcal mol−1) in disagreement with the crystal structure obtained for 2B.10b

Table 3. Relative Gibbs Energiesa of Zn(L) and Cd(L) Complexes with Water and Perchlorate in Ethanol Solution

a

M(L) complexes

M = Zn

M = Cd

M(ClO4)2(L)···(H2O)2 [M(H2O)(ClO4)(L)]+···(ClO4−)(H2O) [M(H2O)2(L)]2+···(ClO4−)2

1.2 3.5 0.0

2.5 0.0 0.5

Relative to the most stable one. In kcal mol−1. 3704



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The relative strengths of the Cd−Cl and Cd−OClO3 bonds were also investigated. The computed Wiberg bond indexes are 0.5 and 0.15, respectively. These values are consistent with corresponding bond dissociation energies [CdX2(L)] → [Cd(L)]2+ + 2 X− (X = Cl−, ClO4−), which are 32.5 and 21.2 kcal mol−1, respectively. 3.4. Extended Structures. Intermolecular forces have considerable current interest because of their relationship to materials science.23 To shed some light on the effective role of the counterions in our complexes, we have studied the extended structures of compounds 1A and 2A in the solid state. The control of the assembly of matter with sufficient certainty and precision to allow preparation of materials and molecular assemblies with far more sophisticated and tunable properties and functions than are currently accessible has been put forward in the past decade because of its potential application in optical, electronic, and/or magnetic areas.24 In order to better understand how molecular building blocks could assemble into predesigned structures, we have studied in detail how noncovalent intermolecular interactions compete or complement each other in the assembly process.25 All the bonding parameters of these complexes are listed in Table 4.

We have also optimized the geometries of meridional and equatorial [Cd(L)]2+ complexes. Both isomers are nearly isoenergetic (their Gibbs energy difference is only 0.03 kcal mol−1), so that the different stabilities of cis- and trans[CdCl2(L)] is due to the interaction with the chloride ligands (Figure 5). Nevertheless, the computed dipole moments found

Table 4. Bonding Interactions O−H···O and C−H···O Parameters of Complexes 1A and 2A complex

D−H···A

H···A (Å)

D···A (Å)

D−H···A (deg)

1A (ZnII)

O(1)−H(1O)···O (3) O(1)− H(1AO)···O(6) C(5)− H(5C)···O(6′) C(6)−H(6B)···O(4) O(11)− H(11D)···O(8) O(11)− H(11C)···O(7) C(15)− H(15A)···O(9) C(8)−H(8A)···O(4) C(3)−H(2)···O(5)

2.042(25)

2.296(14)

174(3)

2.083(25)

2.924(14)

157(3)

2.592(26)

3.290(17)

123(2)

2.497(26) 1.927(26)

3.187(17) 2.838(19)

141(2) 174(3)

1.935(32)

2.853(12)

175(6)

2.574(31)

3.530(11)

175(5)

2.654(29) 2.610(29)

3.607(15) 3.373(15)

167(4) 140(5)

2A (CdII)

Figure 5. Optimized geometries of several Zn and Cd complexes. Selected interatomic distances in Å. Nonpolar hydrogen atoms have been omitted for clarity.

Intermolecular hydrogen bonding interactions were observed in 1A, and they are believed to be responsible for the arrangement of molecules in their crystal packing. As shown in Figure 7 and Table 4, Cl−O···H−O intermolecular hydrogen bonds are observed between the perchlorate anion and the coordination water molecules (2.042(25) Å, 2.083(25) Å, and 174(3)°, 157(3)°, respectively). In addition, C−H···O intermolecular hydrogen contacts are found between the H atoms (group CH3 and CH2) and the oxygen moiety of the other perchlorate anion (Table 4). It is noteworthy to mention that no π−π stacking interactions between the pyrazole rings were found in the crystal packing of 1A. In the crystal packing of 2A, four Cl−O···H−O intermolecular hydrogen bonds between the noncoordinated perchlorate anion and the coordination water molecules (1.927(26) Å, 1.935(32) Å, and 174(3)°, 175(6)°, respectively) were observed. Interestingly, the noncoordinated perchlorate anions form a supramolecular dimeric structure as shown in Figure 8a) and Table 4. As in 1A, C−H···O intermolecular hydrogen contacts were found between the H atoms (group CH3 and CH2) and the oxygen moiety of the other perchlorate

for cis- and trans-[CdCl2(L)] complexes are 17.6 and 4.2 D, respectively (Figure 6), indicating that the large polarity of the cis-[CdCl2(L)] complex favors intermolecular interactions and finally leads to the experimentally observed crystal structure.

Figure 6. Optimized structures and dipole moments of cis- and trans[CdCl2(L)] complexes. Selected interatomic distances in Å. 3705



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Figure 8. View in complex 2A of the intermolecular O−H···O and C− H···O bonding interactions for a) noncoordinated and b) coordinated perchlorate anions. All the bonding interactions are indicated with dashed lines. Hydrogen atoms are omitted for clarity.

Figure 7. View of the two-dimensional ordering of complex 1A generated by intermolecular O−H···O and C−H···O bonding interactions. All the bonding interactions are indicated with dashed lines. Hydrogen atoms are omitted for clarity.

explained by the different coordination modes of L with ZnII in 1B (κ2 NN) that in 1A (κ4 NOON) (Figure 2). NMR of the naturally occurring spin 1/2 isotopes of CdII and HgII is possible, enabling their use as probes for protein active sites. It was possible to record 113Cd{1H} NMR (for complex 2A) and 199Hg{1H} NMR (for complex 3A) spectra in CD3CN at 298 K. In the case of 2A, the spectrum shows only one broad band at +629 ppm indicating the presence of a single hexacoordinated complex in solution.26 The 199Hg{1H} NMR chemical shift of −1142 ppm in 3A (in CD3CN, relative to HgII perchlorate) is characteristic of mercury perchlorate complexes and suggests a similar coordination environment as in 2A (hexacoordinated complex).27 This value is in good agreement with some analogous Hg complexes and indicates that only one mercuric species is present in solution.27b In both complexes, coordination of the nitrogen/oxygen atoms with the metallic center tends to provide a greater deshielding effect than that of the typical thiolate sulfur atoms. This suggests significant back-donation by the metal ions.28 In the case of the HgII complex (3A), the back-donation of π electron density is presumably less important than that in the CdII complex (2A) due to the poor overlap of the metal d orbital with ligand orbitals.29 These 113Cd and 199Hg NMR data are less common in the literature.30 Therefore, determining the behavior and structure of ZnII, CdII, and HgII complexes with N,O-heteroatom-containing ligands in solution will expand the number of known coordination complexes. Moreover, it can be useful for a better understanding of not only the coordination

anion (Table 4). Moreover, in 2A the aromatic pyrazole acts as former H-contacts between the aromatic hydrogen atoms and their neighboring perchlorate oxygen atoms (Figure 8b). Regarding the effect of the counteranion, we have previously observed that in 1B [ZnCl2(L)]) the bonding interactions C− H···O (2.565(12) Å) between the CH3 groups and the oxygen atom of the ether group of L form a 2D zigzag network.10b Nonetheless, in the crystal structure of complexes 1A, 2A, and 2B the oxygen atom of the ether group does not play any role in this kind of interaction, probably due to its direct participation in the coordination to the metallic center. 3.5. NMR Studies. Metal ion binding to L with the perchlorate salts of divalent zinc triad metals was studied in solution using NMR spectroscopy. The 1H NMR spectra (D2O) for all the complexes exhibit the typical roof pattern of the ethylene protons of the NpzCH2CH2O chain: two triplets (δ(1H) (ppm) = 4.59, 4.17 (1A); 4.57, 4.13 (2A) and 4.54, 3.84 (3A) with values of 3JH−H (5.7 − 6.1 Hz). The proton chemical shifts of the complexes were generally downfield to that of the free ligand, a commonly observed result due to a sigma donation to the metal cation. However, if we compare the 1H NMR spectra of Zn complexes, 1A with ClO4− anion and 1B with Cl− anion, we can observe that for complex 1B the ethylene protons of OCH2CH2O and NpzCH2CH2O chains of L appear at lower fields and as broad bands. The presence of these bands may be 3706



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modes of Cd/HgII complexes in biological systems but also ZnII complexes by comparison with their Cd/HgII analogues.31

2341. (b) Fleischer, H.; Dienes, Y.; Mathiasch, B.; Schmitt, V.; Schollmeyer, D. Inorg. Chem. 2005, 44, 8087−8096. (7) (a) Wu, Z. S.; Hsu, J. T.; Hsieh, C. C.; Horng, Y. C. Chem. Commun. 2012, 48 (28), 3436−3438. (b) Wei, S.; Li, X.; Yang, Z.; Lan, J.; Gao, G.; Xue, Y.; You, J. Chem. Sci. 2012, 3 (2), 359−363. (c) Reed, C. A. Acc. Chem. Res. 1998, 31, 133−139. (8) Martinez, R.; Chacon-Garcia, L. Curr. Med. Chem. 2005, 12, 127− 151. (9) (a) Zats, G. M.; Arora, H.; Lavi, R.; Yufit, D.; Benisvy, L. Dalton Trans. 2011, 40 (41), 10889−10896. (b) Pettinari, C.; Pettinari, R. Coord. Chem. Rev. 2005, 249, 525−543. (10) (a) Guerrero, M.; Pons, J.; Branchadell, V.; Parella, T.; Solans, X.; Font-Bardía, M.; Ros, J. Inorg. Chem. 2008, 47, 11084−11094. (b) Guerrero, M.; Pons, J.; Parella, T.; Font-Bardía, M.; Calvet, T.; Ros, J. Inorg. Chem. 2009, 48, 8736−8750. (c) Guerrero, M.; Pons, J.; Font-Bardia, M.; Calvet, T.; Ros, J. Polyhedron 2010, 29, 1083−1087. (d) Guerrero, M.; Pons, J.; Font-Bardia, M.; Calvet, T.; Ros, J. Aust. J. Chem. 2010, 63, 958−964. (e) Guerrero, M.; Pons, J.; Ros, J. J. Organomet. Chem. 2010, 695, 1957−1960. (f) Guerrero, M.; GarcíaAntón, J.; Tristany, M.; Pons, J.; Ros, J.; Philippot, K.; Chaudret, B.; Lecante, P. Langmuir 2010, 26, 15532−15540. (g) Guerrero, M.; Pons, J.; Ros, J.; Font-Bardia, M.; Vallcorba, O.; Rius, J.; Branchadell, V.; Merkoçi, A. CrystEngComm 2011, 13, 6457−6470. (11) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (12) Frisch, G. W.; Trucks, H. B.; Schlegel, G. E.; Scuseria, M. A.; Robb, J. R.; Cheeseman, G.; Scalmani, V.; Barone, B.; Mennucci, G. A.; Petersson, H.; Nakatsuji, M.; Caricato, X.; Li, H. P.; Hratchian, A. F.; Izmaylov, J.; Bloino, G.; Zheng, J. L.; Sonnenberg, M.; Hada, M.; Ehara, K.; Toyota, R.; Fukuda, J.; Hasegawa, M.; Ishida, T.; Nakajima, Y.; Honda, O.; Kitao, H.; Nakai, T.; Vreven, J. A.; Montgomery, Jr. J. E.; Peralta, F.; Ogliaro, M.; Bearpark, J. J.; Heyd, E.; Brothers, K. N.; Kudin, V. N.; Staroverov, R.; Kobayashi, J.; Normand, K.; Raghavachari, A.; Rendell, J. C.; Burant, S. S.; Iyengar, J.; Tomasi, M.; Cossi, N.; Rega, J. M.; Millam, M.; Klene, J. E.; Knox, J. B.; Cross, V.; Bakken, C.; Adamo, J.; Jaramillo, R.; Gomperts, R. E.; Stratmann, O.; Yazyev, A. J.; Austin, R.; Cammi, C.; Pomelli, J. W.; Ochterski, R. L.; Martin, K.; Morokuma, V. G.; Zakrzewski, G. A.; Voth, P.; Salvador, J. J.; Dannenberg, S.; Dapprich, A. D.; Daniels, Ö .; Farkas, J. B.; Foresman, J. V.; Ortiz, J.; Cioslowski, D. J.; Fox Gaussian 09, Revision B.01; Gaussian, Inc.: Wallingford, CT, 2009. (13) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241. (14) (a) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987, 86, 866−872. (b) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (15) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2009, 113, 6378−6396. (16) Wiberg, K. B. Tetrahedron 1968, 24, 1083−1096. (17) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899−926. (18) (a) Thompson, L. K.; Lee, F. L.; Gabe, E. J. Inorg. Chem. 1988, 27, 39−46. (b) Geary, W. J. Coord. Chem. Rev. 1971, 7, 81−122. (19) (a) Pretsh, E.; Clerc, T.; Seibl, J.; Simon, W. Tables of Determination of Organic Compounds. 13C NMR, 1H NMR, IR, MS, UV/Vis, Chemical Laboratory Practice; Springer-Verlag: Berlin, 1989. (b) Williams, D. H.; Fleming, I. Spectroscopic Methods in Organic Chemistry; McGraw-Hill: London, 1995. (20) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds; John Wiley and Sons: New York, 1986. (21) Allen, F. A. Acta Crystallogr. 2002, B58, 380−388. (22) (a) Hänggi, G.; Schmalle, H.; Dubler, E. Inorg. Chem. 1988, 27, 3131−3137. (b) Hänggi, G.; Schmalle, H.; Dubler, E. Acta Crystallogr., Sect. C 1994, 50, 380−388. (c) Breller, S.; Haghin, A.; Botle, M.; Bats, J. W.; Wagner, M.; Wjene, H. Inorg. Chim. Acta 2006, 359, 1559− 1572. (23) (a) Belser, K.; Slenters, T. V.; Pfumbidzai, C.; Upert, G.; Mirolo, L.; Fromm, K. M.; Wennemers, H. Angew. Chem., Int. Ed. 2009, 48, 3661−3664. (b) Doonan, J.; Tranchemontagne, D. J.; Glover, T. G.; Hunt, J. R.; Yaghi, O. M. Nat. Chem. 2010, 2, 235−238.

4. CONCLUSIONS In the present study, we have demonstrated that the nature of the counteranion (Cl− vs ClO4−) clearly influences the type and geometry of the ZnII, CdII, and HgII complexes as well as the ligational behavior of the 1,8-bis(3,5-dimethyl-1H-pyrazol-1yl)-3,6-dioxaoctane ligand (L). In the reported structural comparison of L, it is reflected a variety of modes of bonding (bidentate/tetradentate) as well as various geometries (tetrahedral/octahedral) depending on the type of the counteranion. The above results point toward the fact that the different counteranions have a direct influence on the coordinative abilities of the hybrid pyrazol ligand showing high flexibility as well as high versatility of L.

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ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic files in CIF format for the structure determinations of 1A and 2A, and Cartesian coordinates of all computed structures. This information is available free of charge via the Internet at http://pubs.acs.org. CCDC 875948 and 875949 contain the supplementary crystallographic data for complex 1A and 2A. These data can be obtained free of charge via: http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223−336−033; or email: [email protected].

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AUTHOR INFORMATION

Corresponding Author

*Fax: 34-93 581 31 01. E-mail: Josefi[email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Spanish Ministry of Science and Innovation (CTQ201015408), Generalitat de Catalunya (2009SGR-733, XRQTC, and a grant to Miguel Guerrero). Computer time from Centre de Supercomputació de Catalunya (CESCA) is gratefully acknowledged.

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REFERENCES

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Anion Influence on the Structure of N,O-Hybrid Pyrazole ZnII, CdII

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