Solid-State Coordinative Behavior of a New Asymmetrical Bis

Article pubs.acs.org/crystal

Solid-State Coordinative Behavior of a New Asymmetrical Bis-hydrazone Ligand Containing Two Different Binding Pockets Sabina Rodríguez-Hermida,† Ana B. Lago,*,† Laura Cañadillas-Delgado,‡,§ Rosa Carballo,† and Ezequiel M. Vázquez-López*,† †

Departamento de Química Inorgánica, Facultade de Química, Universidade de Vigo, E-36310 Vigo, Galicia, Spain Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, E-50009 Zaragoza, Spain § Centro Universitario de la Defensa de Zaragoza, Ctra. Huesca s/n. 50090 Zaragoza, Spain ‡

S Supporting Information *

ABSTRACT: The potentially multidentate (O2N−NO) trianionic bis(bencylhydrazone) derived from 4-hydroxyisophthaldehyde (H3L) ligand has been synthesized and characterized. The coordinative behavior of the ligand has been explored toward different MII salts (M = Co, Ni, Zn, and Cu), and four complexes, of general formula [M(HL)]·solv (2·solv = molecules of water, dmf, or dmso), have been isolated and characterized. Furthermore, the species [M(H2L)2]·solv (M = Co, 1a·solv; M = Ni, 1b·solv; solv = molecules of water and/or dmf), where the ligand is monodeprotonated and tridentate, has also been detected. The structures of H3L, four solvates of {[Cu(HL)]·solv}n (2c·solv), 1a·5H2O, and 1b·H2O·3dmf were determined by single-crystal X-ray diffraction. The effect of weak interactions on the crystal packing has also been analyzed. The thermal stability and the structural dynamics of the 2c·solv systems have also been investigated.

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modified denticity and/or dimensionality.1d In this field, compartmental symmetrical bis-hydrazone ligands with two rather similar binding pockets were shown to yield [n × n] grid complexes with novel properties.1e−j The asymmetric nature of bis-hydrazone ligands might also provide grids or alternative structures, but this aspect has been explored to a lesser extent.1k In this work, we focused our effort on the design and synthesis of a new asymmetrical ligand (H3L) in which two phenyl hydrazone groups are linked by 4-hydroxyisophthaldehyde (Scheme 1). This new rigid polytopic ligand has appealing

INTRODUCTION The coordination chemistry of hydrazone ligands is an intensive area of study, and numerous transition metal complexes of these ligands have been investigated. They form stable complexes with transition metal, lanthanide, as well as main group elements. Some of these complexes have been proven to show potential applications as catalysts, luminescent probes, molecular sensors, and also therapeutic activity. Nevertheless, information about the supramolecular architectures of coordination complexes based on hydrazone ligands is not widely available.1 In the construction of specific metallosupramolecular architectures, the choice of organic ligand is crucial because the coordinative sphere has to be designed for a given metal center (i.e., net node). Ligands with several kinds of denticity are preferred to build nets based on multiple metal centers.1c The dimensionality of the coordination network can be increased by noncovalent interactions like hydrogen bonds, π···π, C−H···π, and/or other van der Waals interactions,2 and such changes affect the final properties of the supramolecular organizations.2i Coordinated metals may modulate the intermolecular interactions as they modify the electronic distribution of the ligand. On the other hand, hydrazones and particularly acyl-hydrazones are very versatile ligands because they can act as neutral or anionic ligands and link metal ions using different coordinative modes. Furthermore, additional coordinating groups or groups capable of establishing different intermolecular interactions may be easily included in these ligands, resulting in © 2013 American Chemical Society

Scheme 1. H3L Ligand

structural properties for metallosupramolecular design and two potential binding pockets that can control the number and array of metal ions, giving the possibility of producing polymetallic complexes. Received: November 7, 2012 Revised: December 14, 2012 Published: January 14, 2013 1193

dx.doi.org/10.1021/cg301628q | Cryst. Growth Des. 2013, 13, 1193−1205

Crystal Growth & Design

Article

under reflux for 2 h, and the resulting solid was filtered off and dried under vacuum over CaCl2/NaOH. All crystallization methods tested with these compounds were unsuccessful. Complex 2a: Yield 0.093 g (78%). Mp > 300 °C. Anal. Calcd for C22H16N4O3Co·H2O: C, 57.28; H, 3.93; N, 12.14%. Found: C, 57.49; H, 4.15; N, 12.09%. IR (KBr): ν (cm−1) = 3432s, 3249m, 3060w (OH−NH), 1608vs (CO), 1560s + 1525m (CN), 1378s (C− Ophenolic), 1301w (C−N), 1176w (C−Oenolic). MS−ESI: m/z (%) = 387 (7) [(H3L) + H]+, 444 (8) [Co(H2L)]+, 830 (100) [{Co(H2L)2} + H]+, 887 (4) [{Co(HL)}2 + H]+, 1216 (12) [{Co(H2L)3} + 2H]+, 1602 (2) [{Co(H2L)4} + 2H]+. Complex 2b: Yield 0.083 g (69.23%). Mp > 300 °C. Anal. Calcd for C22H16N4O3Ni·H2O: C, 57.31; H, 3.93; N, 12.15. Found: C, 57.58; H, 4.06; N, 12.16. IR (KBr): ν (cm−1) = 3430w, 3266w, 3058w (OH− NH), 1606vs (CO), 1562s + 1527m (CN), 1380s (C−Ophenolic), 1303m (C−N), 1174w (C−Oenolic). MS−ESI: m/z (%) = 387 (7) [(H3L)+H]+, 443 (13) [Ni(H2L)]+, 829 (100) [Ni(H2L)2 + H]+, 885 (10) [{Ni(H2L)}2 + H]+, 1215 (12) [Ni(H2L)3 + 2H]+, 1273 (1) [Ni2(H2L)3]+, 1602 (2) [{Ni(H2L)4} + 3H]+. Complex 2d: Yield 0.072 g (57%). Mp > 300 °C. Anal. Calcd for C22H16N4O3Zn·2H2O: C, 54.39; H, 4.15; N, 11.53. Found: C, 54.13; H, 3.87; N, 11.53. 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 11.51 (s, 1H, N6b-H), 8.62 (s, 1H, C5a-H), 8.32 (s, 1H, C5b-H), 7.98 (s, 1H, C2ab-H), 7.94 (m, 4H),7.69 (d, 1H, C3b-H), 7.55 (m, 6H), 7.04 (d, 1H, C1ab-H). IR (KBr): ν (cm−1) = 3430m, 3220m, 3058w (OH− NH), 1610vs (CO), 1570s + 1508s (CN), 1378s (C−Ophenolic), 1286m (C−N), 1178w (C−Oenolic). MS−ESI: m/z (%) = 387 (8) [(H3L) + H]+, 449 (6) [Zn(H2L)]+, 835 (100) [{Zn(H2L)2} + H]+, 899 (4) [{Zn(H2L)}2 + H]+, 1221 (15) [{Zn(H2L)3} + 2H]+, 1287 (2) [Zn2(H2L)3]+, 1609 (2) [{Zn(H2L)4} + 3H]+. {[Cu(HL)]·2H2O}n(2c·2H2O). Compound 2c·2H2O was obtained from two salt precursors [copper(II) acetate and trifluoroborate] using three different synthetic methods. (a) A solution of Cu(AcO)2·H2O (0.052 g, 0.26 mmol) in MeOH (10 mL) was added to a suspension of H3L (0.1 g, 0.26 mmol) in MeOH (20 mL). The suspension was heated under reflux for 2 h. The resulting green solid was filtered off and dried under vacuum over CaCl2/NaOH. Yield: 0.116 g (92.06%). (b) A solution of 4-hydroxyisophthalaldehyde (0.073 g, 0.50 mmol) in MeOH (10 mL) was added to a suspension of Cu(AcO)2·H2O (0.1 g, 0.50 mmol) in MeOH (10 mL). Immediately, a solution of benzoic hydrazide (0.2 g, 1.5 mmol) in MeOH (10 mL) was added. The reaction mixture was stirred at rt for 4 h. The green solid was filtered off and dried under vacuum over CaCl2/NaOH. Yield: 0.212 g (87.61%). (c) To a suspension of the ligand H3L (0.1 g, 0.26 mmol) in MeOH (20 mL) was added 0.065 M aqueous NaOH (4 mL). The resulting yellow solution was added dropwise to a solution of Cu(BF4)2·xH2O (0.061 g, 0.26 mmol) in MeOH (5 mL). During the addition, a green solid was formed, and the resulting suspension was heated under reflux for 2 h. The solid was filtered off and dried under vacuum over CaCl2/NaOH. Yield: 0.072 g (57.22%). Single crystals of 2c·2H2O suitable for X-ray diffraction were obtained by slow evaporation of a solution of the green solid in acetonitrile. The powder X-ray diffraction data for the different synthetic methods were compared to those simulated from the crystal structure (Supporting Information) and showed that the crystals are representative of the bulk materials. Data for 2c·2H2O (method (a)): Mp > 300 °C. Anal. Calcd for C22H16N4O3Cu·2H2O: C, 54.60; H, 4.17; N, 11.58%. Found: C, 54.28; H, 4.04; N, 11.42%. IR (KBr): ν (cm−1) = 3405w, 3220w, 3075w (OH−NH), 1612vs (CO), 1567s + 1502vs (CN), 1380s (C− Ophenolic), 1307w (C−N), 1178w (C−Oenolic). MS−ESI: m/z (%) = 446 (16) [Cu(H2L)]+, 834 (37) [{Cu(H2L)2} + H]+, 895 (100) [{Cu(H2L)}2 + H]+, 1283 (1) [Cu2(H2L)3]+. {[Cu(HL)]·2H2O·2dmf}n (2c·2H2O·2dmf). Agarose gel (1%) with Cu(SO4)2·5H2O was obtained by the same method as described for

The ligand H3L also has the possibility of changing from the keto to the more conjugated enol form, and this change is always concomitant with a change in properties, particularly photoelectronic properties and valence state.1c In addition, the molecule contains hydrogen-bonding donors and acceptors, thus providing two distinct donor compartments (Scheme 1): a tridentate {NO2} site (pocket I) and a bidentate {NO} site (pocket II). These characteristics suggest great possibilities for metallosupramolecular organization through different weak interactions.3 In this work, we explored the coordinative behavior of H3L toward different MII salts (M = Cu, Co, Ni, and Zn) and analyzed the role of the weak intermolecular interactions in the crystal packing.

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EXPERIMENTAL SECTION

Materials and Physical Measurements. Elemental analyses (C, H, N) were carried out with a Fisons EA-1108 microanalyser. Melting points (mp) were measured with a Gallenkamp MBF-595 apparatus. IR spectra were recorded from KBr discs (4000−400 cm−1) with a Jasco FT/IR-6100 spectrophotometer. 1H NMR spectra were obtained with a Bruker AMX 400 spectrometer. Mass spectra were recorded on a Hewlett-Packard 5989A spectrometer. TGA was performed on a SETSYS Evolution Setaram thermogravimetric analyzer in a flow of N2 with a heating rate of 10 °C min−1. BET experiments were performed at 77K on a Belsorp II Mini apparatus using nitrogen as the probing gas. 2c·2H2O was outgassed at rt, 50, 100, 150, and 200 °C for 12 h prior to the measurement. Synthesis of the Compounds. Synthesis of H3L. A solution of 4-hydroxyisophthaldehyde (0.1 g, 0.68 mmol) in EtOH (10 mL) was added dropwise to a solution of benzoic hydrazide (0.272 g, 2.02 mmol) in EtOH (20 mL). Immediately, 1 drop of HCl was added. The yellow solution was heated under reflux for 2 h, and the resulting white solid was filtered off and dried under vacuum over CaCl2/NaOH for 2 days. Suitable crystals for X-ray diffraction were obtained by slow evaporation of a DMSO solution over 20 days at rt. Yield: 0.150 g (61%). Mp > 300 °C. Anal. Calcd for C22H18N4O3: C, 68.38; H, 4.70; N, 14.50. Found: C, 68.50; H, 4.63; N, 14.22. 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 12.19 (s, 1H, O3a,b-H), 11.79 (s, 1H, N6a,b-H), 11.57 (s, 1H, N6a,b*-H), 8.73 (s, 1H, C5a,b-H), 8.42 (s, 1H, C5a,b*-H), 7.98 (s, 1H, C2a,b-H), 7.94 (m, 4H),7.69 (d, 1H, C3a,b*-H), 7.55 (m, 6H), 7.04 (d, 1H, C1a,b-H). IR (KBr): ν (cm−1) = 3438w, 3234m, 3062w (OH−NH), 1648vs (CO), 1546m (CN), 1348m-w (C−Ophenolic), 1228m (C−N). MS−ESI: m/z (%) = 387 (100) [H3L + H]+. Synthesis of the Complexes. [Co(H2L)2]·5H2O (1a·5H2O). A gel (1%) was prepared by suspending agarose (0.105 g) in H2O (10 mL) and heating the mixture at around 90 °C until complete dissolution occurred. A solution of Co(SO4)2·7H2O (0.036 g, 0.13 mmol) in H2O (2 mL) was added. The resulting solution was poured into a test tube, and, after a few minutes, a gel was obtained. Single crystals of 1a·5H2O were obtained after 4 days by slow diffusion at rt of a solution of the ligand H3L (0.1 g, 0.26 mmol) in DMF (4 mL) into the gel. Insufficient crystals were obtained for elemental analysis or meaningful estimation of yield. IR (KBr): ν (cm−1) = 3446vs (OH−NH), 1647s + 1613s (CO), 1564w (CN), 1384s (C−Ophenolic), 1279w (C−N). [Ni(H2L)2]·H2O·3dmf (1b·H2O·3dmf). This compound was isolated as single crystals by slow evaporation of a DMF/THF solution of 2b. Insufficient crystals were obtained for elemental analysis or meaningful estimation of yield. [Co(HL)]·H2O (2a), [Ni(HL)]·H2O (2b), and [Zn(HL)]·2H2O (2d). Compounds 2a, 2b, and 2d were obtained by following method (a) for the synthesis of 2c, as described below, but using the corresponding metal acetate salt. A solution of the corresponding metal acetate (0.26 mmol) in MeOH (10 mL) was added to a suspension of H3L (0.1 g, 0.26 mmol) in MeOH (20 mL). The suspension was heated 1194



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compound 1a·5H2O. Suitable single crystals were grown after 4 days at rt by slow diffusion of a solution of the ligand H3L (0.058 g, 0.15 mmol) in dmf (4 mL) into the gel. IR (KBr): ν (cm−1) = 3430vs, 3241m (OH−NH), 1610vs (CO), 1571s + 1503vs (CN), 1383s (C−Ophenolic), 1305m (C−N), 1176m (C−Oenolic). {[Cu(HL)]·H2O·2dmso}n (2c·H2O·2dmso). Recrystallization of 2c·2H2O from dmso led to the isolation of green crystals suitable for X-ray diffraction after 40 days at rt. IR (KBr): ν (cm−1) = 3430s (OH−NH), 1609vs (CO), 1570vs + 1502vs (CN), 1376s (C−Ophenolic), 1313m (C−N), 1171m (C−Oenolic). {[Cu(HL)]·2dmso}n (2c·2dmso). Recrystallization of 2c·2H2O from dmso produced, after 3 weeks, green crystals suitable for X-ray diffraction. IR (KBr): ν (cm−1) = 3433s, 3196m (OH−NH), 1610vs (CO), 1568m + 1502s (CN), 1377m (C−Ophenolic), 1304w (C−N), 1177w (C−Oenolic). Insufficient crystals were obtained for elemental analysis or meaningful estimation of the yield of 2c·2H2O·2dmf, 2c·H2O·2dmso, and 2c·2dmso. Crystallography. Crystallographic data for 1a·5H2 O and 2c·2dmso were collected on a Bruker Smart 1000 CCD diffractometer at 293 K using graphite monochromated Mo Kα radiation (λ = 0.71073 Å) and were corrected for Lorentz and polarization effects. The frames were integrated with the Bruker SAINT4 software package. Absorption corrections were applied using the program SADABS5 on the data of compounds 1a·5H2O and 2c·2dmso to give max/min transmission factors of 1.000/0.806 and 0.746/0.659, respectively. X-ray diffraction data for single crystals of H3L, 1b·H2O·3dmf, 2c·2H2O, 2c·H2O·2dmso, and 2c·2H2O·2dmf were collected at 100 K in the ESRF synchrotron Spanish BM16-CRG beamline (Grenoble, France). Data were indexed, integrated, and scaled using the HKL2000 program.6 Absorption corrections were not applied. The structures were solved by direct methods using the program SHELXS97.7All non-hydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares calculations on F2 using the program SHELXL97.8 H3L presents crystallographic disorder

imposed by the 2-fold axis. Attempts at anisotropic refinement in the Cc space group were unsuccessful. This crystallographic disorder is undoubtedly responsible for the marked differences in the C−O bond distances of the phenol group. Hydrogen atoms were inserted at calculated positions and constrained with isotropic thermal parameters, except for the hydrogen atoms of the NH group and water molecules. The N−H hydrogen atom was located from difference Fourier maps in 2c·2H2O, 2c·2H2O·2dmf, and 2c·2H2O·2dmso and calculated in H3L, 1a·5H2O, 1b·H2O·3dmf, and 2c·2dmso. The hydrogen atoms of the crystallization water molecules were located and isotropically refined in 2c·2H2O and 2c·2H2O·2dmf, but in 1a·5H2O, 1b·H2O·3dmf, and 2c·2H2O·2dmf the disorder associated with the oxygen atom hindered their localization. The contribution of some water molecules of crystallization in 1a .5H2O and 1b·H2O·3dmf to the diffraction patterns could not be rigorously included in the model and were consequently removed with the SQUEEZE routine of PLATON.9a Drawings were produced with MERCURY9b and ORTEP9c programs, and special computations for the crystal structure discussions were carried out with PLATON.9a Crystal data and structure refinement data are listed in Table 1. The main bond distances and angles are summarized in Table 2. Complete data for the interatomic distances and angles are listed in Tables S1−S7. The structural data have been deposited with the Cambridge Crystallographic Data Centre (CCDC) with the reference numbers included in Table 1. X-ray powder diffraction (XRPD) characterization was performed using a Siemens D-5000 diffractometer with Cu Kα radiation (λ = 1.5418 Å) over the range 5.0−60.0° in steps of 0.20° (2θ) with a count time per step of 5.0 s. The program FULLPROF10 was used to perform profile matching between the powder diffraction data and that calculated from the single-crystal structure of 2c·2H2O (see the Supporting Information). The following parameters were refined in the final run: scale factor, background coefficients, zero-point error, unit cell, and parameters of peak shapes. Thermodiffraction studies were performed using a SIEMENS D-5000 X-ray diffractometer with Co Kα radiation (λ = 1.79091 Å) over the range 6.0−24.037° in steps of 0.014° (2θ) with a count time per step of 2.0s.

Table 1. Crystal and Structure Refinement Data 2c compound formula weight crystal system space group CCDC ref unit cell dimensions a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z λ (Å) T (K) ρcalcd (g cm−3) μ (mm−1) F(000) crystal size (mm3) ind refln (Rint) final R indices [I > 2σ(I)]

H3L

1a·5H2O

·2H2O

1b·H2O·3dmf

·2H2O·2dmf

·2dmso

·H2O·2dmso

385.40 monoclinic C2/c 853 594

957.72 monoclinic C2/c 853 595

1064.79 triclinic P1̅ 853 596

967.92 triclinic P1̅ 853 597

1074.05 triclinic P1̅ 853 598

1052.11 triclinic P1̅ 853 599

622.20 monoclinic P21/c 853 600

19.514(4) 17.533(4) 11.637(2)

16.211(3) 21.047(4) 16.576(4) 107.903(5)

3759.9(13) 8 0.7890 100 1.362 0.094 1608 0.12 × 0.10 × 0.09 4054 (0.039) R1 = 0.0587

5381.5(19) 4 0.7107 293 1.182 0.383 1972 0.19 × 0.12 × 0.12 4713 (0.1110) R1 = 0.0732

9.2330(18) 12.419(3) 18.880(4) 105.73(3) 95.45(3) 94.09(3) 2063.7(7) 2 0.7890 100 1.558 1.102 996 0.10 × 0.10 × 0.09 8983 (0.0570) R1 = 0.0569

10.808(2) 14.539(3) 16.626(3) 111.03(3) 96.96(3) 93.92(3) 2402.8(8) 2 0.7513 100 1.485 0.956 1108 0.11 × 0.09 × 0.08

12.2619(16) 13.8402(18) 15.549(2) 68.296(2) 79.036(2) 89.716(2) 2400.7(3) 2 0.7107 293 1.455 1.035 1084 0.31 × 0.28 × 0.10

12.818(3) 10.705(2) 20.701(4)

109.20(3)

12.840(3) 13.386(3) 18.770(4) 71.71(3) 84.54(3) 62.64(3) 2715.6(14) 2 0.7380 100 1.302 0.424 1116 0.09 × 0.09 × 0.08 7972 (0.0744) R1 = 0.0846

12 485 (0.0504) R1 = 0.0507

10 991 (0.0414) R1 = 0.0648

2825.7(10) 4 0.7513 100 1.463 0.968 1292 0.10 × 0.10 × 0.09 6894 (0.0529) R1 = 0.0637

wR2 = 0.1599

wR2 = 0.1713

wR2 = 0.2097

wR2 = 0.1573

wR2 = 0.1450

wR2 = 0.1600

wR2 = 0.1825

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95.86(3)



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Table 2. Summary of Structural Parameters Observed in the Ligand and Its Metal Complexes (Distances in Å)a,b

2c 1a·0.5H2O

1b·H2O·3dmf

M= M(1)−O(3a)

Co 2.031(3)

Ni 1.996(5) 2.018(5)

M(2)−O(3c) M(1)−N(5a)

2.049(4)

1.991(5) 2.003(5)

H3L

M(2)−N(5c) M(1)−N(5d) M(2)−N(5b) M(1)−O6(a) M(2)−O(6c) M(1)−O6(d) M(2)−O(6b) C6−O6(a,c) C6−O6(b,d) C6−N6(a,c) C6−N6(b,d)

2.119(4)

1.2352(19) 1.222(2) −c

1.246(6)

1.354(2) 1.3607(18) −c

1.340(6)

1.237(7)

1.352(7)

2.081(5) 2.126(4)

1.267(7) 1.245(7) 1.214(9) 1.215(8) 1.347(8) 1.352(7) 1.366(10) 1.356(9)

τd Cu−(SP)e θ (deg)f ω (deg)f

8.89(5) 18.76(6)

13.5(5) 18.8(5)

5.4(4) 6.4(4) 7.2(5) 11.2(5)

·2dmso

·H2O·2dmso

Cu 1.912(2)

·2H2O

Cu 1.9065(15)

·2H2O·2dmf

Cu 1.889(4)(#2)

Cu 1.913(2)

1.916(2) 1.932(3)

1.9043(13) 1.9253(16)

1.879(4) 1.928(4)(#2)

1.934(2)

1.921(3) 2.465(3) 2.495(3)(#1) 1.937(2)

1.9388(15) 2.3812(17) 2.5297(17)(#3) 1.9365(15)

1.924(5) 2.423(5) 2.483(5) 1.930(4)(#2)

2.291(2) 1.931(2)

1.950(2) 1.980(2) 1.958(2)(#2) 1.290(4) 1.283(4) 1.248(4) 1.250(4) 1.320(4) 1.330(4) 1.339(4) 1.335(4) 0.05 0.03 −0.143(1) +0.155(1) 3.3(2) 12.5(2) 6.5(2)

1.9351(13) 1.9750(14) 1.9905(14)(#3) 1.288(2) 1.295(2) 1.248(2) 1.244(2) 1.329(2) 1.319(2) 1.343(2) 1.345(2) 0.21 0.12 −0.1723(7) −0.1484(7) 20.3(1) 11.8(1) 3.8(1) 6.0(1)

1.932(4) 1.995(4)(#1) 1.983(4) 1.293(7) 1.281(7) 1.244(6) 1.242(7) 1.316(7) 1.327(7) 1.342(7) 1.319(7) 0.27 0.29 +0.177(2) −0.169(2) 31.7(3) 30.2(3) 13.6(4) 16.0(3)

2.031(2) 1.301(3) 1.253(3) 1.313(3) 1.336(4) 0.28 +0.254(1) 5.6(1) 8.7(1)

a

Details of the structural data of all compounds are included in Tables S1−S6. bSymmetry code to be applied to the coordinate of the coordinate atom: #1, x − 1, y, z; #2, x + 1, y, z; #3, 2 − x, −1/2 + y, 1/2 − z. cAtom−atom (a,c) distances = atom−atom (b,c) distances. dTrigonal distortion following Addison et al.25 eDistance from the metal atom to the basal plane. fAngles defined in the attached scheme.

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RESULTS AND DISCUSSION Synthesis and Spectroscopic Characterization. H3L was easily prepared through the condensation of 4-hydroxyisophthaldehyde and benzoic hydrazide in ethanol.11 The new Schiff base was obtained in good yield and was stable in air and soluble in dmf and dmso. In general, compounds 2a−d (Scheme 2) were isolated from reactions carried out under reflux in methanol with a 1:1 metal/ ligand ratio using the corresponding metal acetate as precursor. A special effort was made to crystallize all of the compounds, but this was not possible for 2a, 2b, and 2d. The result of a PXRD analysis of the synthesized 2b product closely matched the simulated patterns generated from the single-crystal diffraction data of 2c·2H2O (Supporting Information). Unfortunately, 2a and 2d had not enough crystallography quality to be compared. Single crystals of 1a·5H2O and 2c·2H2O·2dmf were obtained by slow diffusion using the agarose−gelatin gel technique and the metal sulfate as the precursor (see the Experimental Section). Although these compounds generally have poor solubility, single crystals of compounds 2c·2H2O·2dmso, 2c·2dmso, and 1b·H2O·3dmf were obtained from dmso solutions of compound

2c·2H2O and dmf/thf solution of 2b, respectively. The solids isolated from the reaction of the ligand with Co2+/Ni2+ salts under conditions similar to those used in the gel experiments (dmf/H2O as solvent, H3L:Co2+/Ni2+ stoichiometry relation 2:1) show IR bands attributable to the free ligand and complex 2a/2b. The three different synthetic methods of obtaining compound 2c (see the Experimental Section) represent evidence for the stability of this compound. Interestingly, this compound can also be obtained by the copper template effect on the aldehyde and hydrazide reaction.12 Single crystals of the dihydrate complex were obtained from an acetonitrile solution. The low solubility of compounds 2 is probably responsible for the high yield observed, whereas complexes 1a·5H2O and 1b·H2O·3dmf were obtained in poor yield due to the inherent limitations of the gel synthesis and crystallization techniques. Unfortunately, attempts to obtain bulk samples of these compounds were unsuccessful. Nevertheless, the agreement between the X-ray single-crystal structures included in this work (in addition to the IR characterization of 1a) and the 1196



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Scheme 2

Table 3. Significant IR Bands for the Ligand and Its Complexes amide I ν(CO)

amide II ν(CN)

ν(C−O)phenolic

amide III ν(C−N)

1546m 1564w

1348m-w 1384s

1288m 1279w

·H2O

1648vs 1647s 1613s 1608vs

1378s

1301w

1176w

2b

·H2O

1606vs

1380s

1303m

1174w

2c

·2H2O

1612vs

1380s

1307w

1178w

·2H2O·2dmf

1610vs

1383s

1305m

1176m

·2dmso

1610vs

1377m

1304w

1177w

·H2O·2dmso

1609vs

1376s

1313m

1171m

·H2O

1610vs

1560s 1525m 1562s 1527m 1567s 1502vs 1571s 1503vs 1568m 1502s 1570vs 1502vs 1570s 1508s

1378s

1286m

1178w

compound H3L 1a

·5H2O

2a

2d

ν(C−O)enolic

The structurally significant IR bands for the free ligand and its complexes are listed in Table 3. The analysis of the spectra was centered on the set of bands in the 1650−1250 cm−1 region. The free ligand exhibits IR bands at 3438−3062 cm−1 due to ν(O−H/N−H), at 1648 cm−1 attributed to ν(CO) (amide I), and the corresponding amide II (CN) and III (C−N) bands at 1546 and 1288 cm−1, respectively.13 The IR spectra of the different solids containing 2c show a shift of the amide I band to around 1610 cm−1, which suggests the involvement of the carbonyl groups in the coordination. Other important variations are the presence of two bands at around 1570 and 1500 cm−1, which are attributed to amide II

reported hydrazine/semicarbazone analogues (Table S10) confirms the correctness of the corresponding models. The compounds 2 were characterized by elemental analysis, mass spectrometry (ESI), infrared, and NMR spectroscopy of the diamagnetic compounds (H3L and 2d). The 1H NMR spectrum in DMSO-d6 of the zinc complex (2d) shows one signal in the range 10−12.5 ppm, and this is attributed to the N(6b)−H proton. The electroneutrality and the 1H NMR spectra of the compound indicate the dianionic character of the ligand, suggesting tridentate behavior through the O(3a), N(5a), and O(6a) atoms of pocket I (see the Supporting Information) 1197



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deprotonation of the −OH group in its coordination compounds. The C(6)−N(6) and C(6)−O(6) bond distances have typical values for the ketonic resonance form (Table S1) in H3L. Hydrogen-bonding synthon interaction allows the formation of six- and seven-membered rings, and, consequently, each molecule stacks with four adjacent ones to form angles of 61.33°. The hydroxyl group also participates as an acceptor in an intermolecular interaction with −CH groups of benzene rings as donors. As a result of these interactions, the molecules are arranged in the manner shown in Figure 2 (bottom). There are also π−π stacking interactions involving central and terminal aromatic rings, with a centroid−centroid distance of 3.73 Å and an angle of 7.74° between the planes formed by the rings. Structural Studies of Monomer Compounds, 1. Selected structural parameters are listed in Table 2, and the coordination environment of the cobalt atom in compound 1a·5H2O is shown in Figure 3. Both compounds are neutral mononuclear complexes in which the two ligands are monodeprotonated and crystallized as solvated compounds. Compound 1a·5H2O crystallized in the centrosymmetric space group C2/c with the metal atom lying in an e Wyckoff position; therefore, the 2-fold axis generates two symmetrically equivalent ligand molecules. In 1b·H2O·3dmf, the nickel atom occupies a general position in the triclinic space group P1.̅ The metal is N2O4 hexa-coordinated by the hydrazone N(5a) and O(6a) atoms and the O(3a) atom belonging to the deprotonated hydroxyl group of each ligand. The metal atom is in a distorted octahedral environment with M−N and M−O distances in the expected range for such coordination bonds.1d However, the Co−Ohydrazone distance is longer than the Co−Ohydroxyl distance. The configuration around the metal(II) ion can be described by the index [OC-6-22],16 and the nitrogen atoms are located in trans positions. The orientation of the two ligands around the metal cation is almost perpendicular: 86° in 1a·5H2O (see inset in Figure 3) and 84° in 1b·H2O·3dmf. The monodeprotonated ligand acts as a tridentate chelate system using pocket I (Scheme 1). As far as the ligand moiety is concerned, the main differences with respect to the free ligand structure are the slight distortion of the aromatic rings and the values of the angles between the planes defined by these three rings, 13.5(5)°/18.8(5)° for the cobalt complex and 5.4(4)°/ 6.4(4)°/7.2(5)°/11.2(5)° for the nickel complex, which are the highest values found in the complexes with this ligand (vide inf ra). In both complexes 1, there are no significant differences in the bond distances [C(6)−O(6) and C(6)−N(6)] in comparison to those in the free ligand, meaning that the predominance of the keto form is present in both carboxamide groups. Despite that the supramolecular organization is different in both compounds, the hydrogen-bonding synthon observed in the free ligand is present in all pockets. Pocket II is involved in these hydrogen bonds with deprotonated hydroxyl group (O3a) as the acceptor in 1a·5H2O and with an oxygen atom belonging to dmf molecule in 1b·H2O·3dmf. Otherwise, coordinated pocket I is involved in synthon hydrogen bonds with deprotonated hydroxyl group (O3a) (Figure 4, bottom) and carbonyl (O6d) (Figure 4, bottom) as acceptors in 1b·H2O·3dmf, whereas it is involved in hydrogen-bond interaction with water molecule in 1a·5H2O (Table 4). The monomers in 1a·5H2O are connected to give rise to a double chain along the c axis. The planarity of the ligand means that this double chain is arranged in an X-shaped cross-like

modes and a shift in the amide III band to higher frequencies than in the free ligand. Both effects are attributed to deprotonation of the enol−imine tautomer of one pocket.14 In contrast to the above, the IR spectrum of compound 1a·5H2O displays two bands at 1647 and 1613 cm−1, which are attributed to two different carbonyl groups. The highest frequency band is probably due to the uncoordinated pocket observed in the crystal structure (see the Supporting Information). Comparison of the IR spectra of compounds 2a, 2b, and 2d, for which it was not possible to determine X-ray structures, with those of 1a·5H2O and 2c·solv leads to the conclusion that the ligand in the three former compounds use both pockets to coordinate the corresponding metal (Table 3 and the Supporting Information). In addition, the spectra of solvato complexes 2c display absorption bands due to the solvent molecules present in the corresponding framework: one ν(CO) band at 1659 cm−1 due to dmf in 2c·H2O·2dmf and ν (SO) bands at 1027 and 1035 cm−1 due to dmso molecules in 2c·2dmso and 2c·H2O·2dmso, respectively. Structural Studies. Crystal and Molecular Structures of the Ligand H3L. The molecular structure of H3L is represented in Figure 1 together with the atom numbering scheme. Selected

Figure 1. Molecular structure of H3L showing the two alternative positions of the phenol−OH group in the crystal structure (top). The atomic numbering is shown. Representation of the synthon responsible for the supramolecular arrangements in the structures of the ligand in its complexes (bottom).

bond distances and angles are listed in Table 2. The compound crystallizes in the C2/c space group, and the two central atoms of the molecule (C1a and C2a) are located in a 2-fold axis (Wyckoff position e). In this way, the asymmetric unit contains two half crystallographically independent molecules, and the oxygen phenol atom (O3) and the corresponding hydrogen atom are distributed over two symmetrically equivalent positions, thus giving a fixed occupancy factor of 50. The molecule is around 20 Å long and is nearly planar due to the presence of three clearly planar segments. This flatness is reflected in the value of the angle between the planes defined for these three rings of 8.89(5)°/18.76(6)° (Table 2). This planarity is also presented in all coordination compounds (vide infra). There is an intramolecular H-bond involving the O(3)−H hydroxyl group as the donor and the N(5) of hydrazone group (Table 4), which leads to a highly stabilized six-membered ring.15 This strong intramolecular H-bond is broken by the 1198



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Table 4. Main Intra- and Intermolecular Hydrogen Interactions (Å/deg)a D−H···A H3L O(3)−H···N(5) N(6)−H(6)···O(6)#1 C(5)−H(5)···O(6)#1 C(12)−H(12)···O(6)#1 C(11)−H(11)···O(3)#2 1a·5H2O N(6a)−H(6a)···O(1w) C(12a)−H(12a)···O(1w) N(6b)−H(6b)···O(3a)#3 C(12b)−H(12b)···O(3a)#3 C(5b)−H(5b)···O(3a)#3 O(2w)−O(6b)#4 O(3w)−(O6b)#4 1b·H2O·3dmf N(6a)−H(6a)···O(6d)#5 C(5a)−H(5a)···O(6d)#5 C(12a)−H(12a)···O(6d)#5 N(6b)−H(6b)···O(3d) C(5b)−H(5b)···O(3d) C(12b)−H(12b)···O(3d) N(6c)−H(6c)···O(3a)#6 N(6d)−H(6d)···O(4d)#7 C(5d)−H(5d)···O(4d)#7 C(12d)−H(12d)···O(4d)#7 2c·2H2O O(1w)−H(11W)···N(6a)#8 O(3w)−H(32W)···N(6c)#9

d(D−H) d(H···A)

d(D···A)

∠(DHA)

0.84 0.88 0.93 0.93 0.93

1.78 2.08 2.33 2.55 2.49

2.511(3) 2.9182(18) 3.151(2) 3.447(2) 3.099(3)

144.8 158.5 147 163 123

0.86 0.93 0.86 0.93 0.93

2.01 2.44 2.31 2.51 2.87

2.852(6) 3.301(17) 3.129(6) 3.438(18) 3.616(6) 2.863(6) 2.823(7)

167.6 154 159.2 174 138.4

0.88 0.95 0.95 0.88 0.95 0.95 0.88 0.88 0.95 0.95

1.93 2.46 2.48 2.00 2.40 2.27 1.93 2.04 2.47 2.39

2.784(7) 3.251(9) 3.405(9) 2.826(13) 3.197(13) 3.205(13) 2.718(7) 2.862(10) 3.230(12) 3.330(15)

162.0 141 163 156.0 141 169 147.6 155.0 137 168

0.79(5) 0.99(5)

2.61(5) 2.08(5)

3.296(4) 3.050(4)

D−H···A 2c·2H2O O(3w)−H(31W)···O(2W)#10 O(2w)−H(21W)···O(3c)#9 O(2w)−H(21W)···N(6a)#11 N(6b)−H(6b)···O(1W)#12 C(5b)−H(5b)···O(1W)#12 C(12b)−H(12b)···O(1W)#12 N(6d)−H(6d)···O(3W)#13 C(5d)−H(5d)···O(3W)#13 C(12d)−H(12d)···O(3W)#13 2c·2H2O·2dmf N(6b)−H(6nb)···O(1s) C(5b)−H(5b)···O(1s) C(12b)−H(12b)···O(1s) N(6d)−H(6nd)···O(2s)#7 O(1w)···O(3c) O(2w)···N(6a) 2c·2dmso N(6b)−H(6b)···O(1)#14 C(5b)−H(5b)···O(1)#14 C(12b)−H(12b)···O(1)#14 N(6d)−H(6d)···O(2) C(5d)−H(5d)···O(2) C(12d)−H(12d)···O(2) 2c·H2O·2dmso N(6b)−H(6n)···O(1W)#15 C(5b)−H(5b)···O(1w)#15 C(12b)−H(12b)···O(1w)#15

146(5) 167(4)

d(D−H) d(H···A)

d(D···A)

∠(DHA)

0.86(2) 0.95(6) 0.92(6) 0.88 0.95 0.95 0.88 0.95 0.95

1.86(2) 1.87(6) 1.95(6) 2.02 2.42 2.48 2.06 2.30 2.55

2.713(4) 2.810(4) 2.846(4) 2.872(4) 3.247(5) 3.408(5) 2.887(4) 3.150(5) 3.483 (5)

169(5) 170(5) 163(5) 162.1 145 166 156.7 148 166

0.93(4) 0.93 0.93 0.92(3)

1.93(4) 2.55 2.31 1.93(3)

2.835(2) 3.326(3) 3.219(3) 2.809(2) 2.798(2) 2.932(2)

163(3) 141 167 160(3)

0.86 0.93 0.93 0.86 0.93 0.93

1.95 2.47 2.45 1.98 2.48 2.43

2.781(6) 3.248(8) 3.300(10) 2.808(7) 3.265(8) 3.298(10)

0.83(4) 0.93 0.93

1.97(4) 2.48 2.52

2.790(3) 3.265(4) 3.325(5)

163.6 142 153 161.9 142 156 168(4) 142 145

Symmetry equivalence: (#1) 1/2 − x, 3/2 − y, 1 − z; (#2) x, 1 + y, 1 + z; (#3) x, 1 − y, −1/2 + z; (#4) x + 1/2, y − 1/2, z; (#5) −x + 2, −y + 2, −z + 1; (#6) x, y + 1, z; (#7) x + 1, y, z − 1; (#8) x + 1, y, z; (#9) x − 1, y, z; (#10) −x + 1, 1 − y, −z + 2; (#11) −x + 1, 1 − y, −z + 1; (#12) −x, −y + 2, −z + 2; (#13) 2 − x, −y, 1 − z; (#14) x, 1/2 − y, 1/2 + z; (#15) x, −1 + y, z. a

Figure 2. Crystal association of the molecules of H3L showing details of the N−H···O and C−H···O intermolecular interactions (bottom, left) and angle between the molecules (top, right). Space filling representation of the final 3D organization in the ca plane.

large slippage angles rule out any meaningful π-stacking interactions.17 In 1a·5H2O, the crystallographically independent crystallization water molecules are associated by Ow···Ow hydrogen

disposition normal to the ab plane (Figure 4). Surprisingly, there are no significant π-stacking interactions between the multiple rings despite the parallel disposition of the planar ligands. The long centroid−centroid distances (>4.7 Å) with 1199



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molecules (three for asymmetric unit according to SQUEEZE9a calculations) are hosted. A calculation using PLATON9a gave a potential solvent area of 1160 Å3 per unit cell volume of 5370.6 Å3, 22% of the total crystal volume.21 The value of Kitaigorodskii index22 is 57% when the solvent (except disordered water molecules) is included and 49% when water molecules are omitted. If all of the solvent water molecules are omitted from the calculation, the solvent area obtained is 2002 Å3 or 37% of the total crystal volume. Structural Studies of Solvates (2c·solv). Selected structural parameters are listed in Table 2. The coordination environment of the copper atom is represented in Figure 6; the atom numbering scheme used for solvates 2c·2H2O, 2c·2H2O·2dmf, 2c·2dmso, and 2c·H2O·2dmso is included in Scheme 3. Compounds 2c can be considered as pseudopolymorphs.17,23 Compounds 2c·2H2O, 2c·2H2O·2dmf, and 2c·2dmso crystallize in the triclinic space group P1,̅ and 2c·H2O·2dmso crystallizes in the monoclinic space group P21/c. All four crystal structures are based on a 1D neutral chain (Figure 6) with different solvents of crystallization (Tables S4−S7 include structural parameters and pictures of the asymmetric units for all solvates). In these compounds, the ligand HL2− bridges two metal centers by using both binding pockets, and, consequently, it acts as a tri- and bidentate dianionic ligand. Each copper atom lies in a pentacoordinate sphere (O3N2). The Addison parameter24 τ (values in the range 0.03−0.29) (Table 2) for each copper(II) suggests that the coordination sphere around the copper atom can be described as a square pyramidal geometry, with three oxygen (Ophenolate and two Ocarbonyl) atoms and one nitrogen imino atom in the basal positions and a hydrazinic N(5) atom in the apical position, with a Cu−N(5) distance in the range 2.391−2.530 Å. The copper atoms deviate slightly from the plane defined by the four atoms in the basal positions, with deviations between 0.254 Å (2c·H2O·2dmso) and 0.143 Å (2c·2H2O). Each HL2− ligand adopts a μ2-bridging mode connecting the copper centers along the a axis and forming zigzag chains. The orientation of the two different ligands around the metal center forms angles close to 76°, that is, greater than the value observed in the distribution based on hydrogen bonding in the free ligand (vide supra) but far from the near orthogonality in compounds 1a·5H2O and 1b·H2O·3dmf. The electroneutrality demands the bideprotonation of the ligand. Our model considers that the hydrazinic −NH group in pocket I (Scheme 1) is also deprotonated, and thus the ligand acts simultaneously as tridentate and dianionic. Pocket II of the same ligand is coordinated to another metal center in a bidentade chelate fashion without deprotonation. In this way, coordination of the ligand to copper cations involves the formation of two new five-membered chelate rings and one sixmembered chelate ring. The rms deviation of the least-squares planes defined by coordinated and metal atoms (Table S8) indicates that these new rings are almost planar. This coordinative behavior of the ligand leads to the main differences with respect to the structure of free ligand and compounds 1a·5H2O and 1b·H2O·3dmf. In the carboxamide group of pocket I, the bond distances C(6)−O(6) are longer and C(6)−N(6) are shorter than in the free ligand and compounds 1a·5H2O and 1b·H2O·3dmf (Table 2). The geometry of the ligand HL2− changes substantially upon coordination to the metal: the Ccarbonyl−N bonds, with an average distance decreasing to 1.319 Å in 2c·2H2O·2dmf, show some double

Figure 3. Structure of [Co(H2L)2]·5H2O (1a·5H2O) showing details of the planarity and angle between the two ligands.

Figure 4. NH···O and CH···O interactions between adjacent monomers in 1a·5H2O (top) and 1b·H2O·3dmf (bottom). Different representations of the 1D chain formed in 1a·5H2O with two monomers in a space filling representation.

bonds in a tape of four-membered rings that share one water molecule, thus giving rise to a 1D arrangement that can be defined as T4(0)A(0).18 The O···O distances are in the range 2.725−2.882 Å, that is, similar to those found in other waterassociated cobalt complexes.19 The water molecules are selfassembled into undulating chains that form an angle of 81.7° between the planes defined by the two different water squares. Moderate hydrogen bonds, which involve the water molecules as donors and the hydrazone oxygen [O2w−O(6b)#1 = 2.863(6) and O3w−(O6b)#1 = 2.823(7) Å, #1 = x + 1/2, y − 1/2, z] from pocket II as the acceptor, anchor the water tapes to the metal−organic framework to form the final 3D supramolecular arrangement (Figure 5).20 The system of hydrogen bonds involves an implicit juxtaposition of water molecules and the organic molecules. The resulting 3D architecture of 1a·5H2O can be described as being based on square grids formed by water clusters and metal−organic fragments in the ab plane. It is noteworthy that, within the 3D supramolecular structure, there are 1D parallelogramlike channels along the c axis with an effective cavity size of ca. 12.13 Å × 10.08 Å (Figure 5) where some disordered water 1200



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Figure 5. View of the 3D supramolecular structure in 1a·5H2O showing a fragment of the hydrogen-bonded tape of water molecules and their disposition in the final arrangement. Top, right: metal−organic organization in the final 3D structure [d(O1W−O3W) = 2.868(6), d(O1W−O4W) = 2.742(7), d(O2W−O4W) = 2.909(8), d(O4W−O5W) = 2.733(8) Å].

A particularly noteworthy structural feature of 2c·2H2O, 2c·2H2O·2dmf, and 2c·2dmso is that one terminal phenyl ring from a neighboring ligand points toward the center of the fivemembered copper chelate ring of pocket I (Figure 7). This kind of intermolecular π−π (planar chelate ring) interaction suggests the presence of certain metalloaromaticity in such planar chelate rings.26 This intermolecular interaction is not observed in 2c·H2O·2dmso (Figure 8). Analysis of short ring interactions was carried out with the program PLATON,9a and relevant structural parameters are listed in Table S9. In cases where this interaction is observed, the centroid−centroid distance is very similar (dc−c in the range of 3.44−3.65 Å), and α and the slipping angles β and γ have reasonably low values (see caption for Table S9). On the other hand, there are no reasonable π-stacking interactions between the other aromatic rings, as observed in compounds 1a·5H2O and 1b·H2O·3dmf. In any case, the crystallization solvent molecules are by far the most influential factor in the supramolecular organization. The noncoordinated water molecules in 2c·2H2O·2dmf are associated by Ow···Ow hydrogen bonds in a four-membered tetramer with an almost square geometry (Figure 9, top). The Ow···Ow distances are 2.826(3) and 2.825(2) Å. The water clusters are also associated with dmf solvent molecules by means of C−H···Ow interactions. In the same way, dmso and water molecules in 2c·H2O·2dmso are associated by means of different kinds of interactions (Figure 9, bottom). The volume occupied by the solvents and their stabilizing effect on the network are also evident in the corresponding values of the Kitaigorodskii packing index:22 63%, 55%, 46%, and 54% when the solvent is omitted, and 70%, 69%, 68%, and 65% when the solvent is included in 2c·2H2O, 2c·2H2O·2dmf, 2c·2dmso, and 2c·H2O·2dmso, respectively. A calculation using PLATON9a led to variable potential solvent areas per unit cell volume from 175 Å3 in 2c·2H2O to 1082 Å3 in 2c·H2O·2dmso, with these values representing 9% and 38% of the total crystal volume in 2c·2H2O and 2c·H2O·2dmso, respectively. Solvates 2c·2H2O·2dmf and 2c·2dmso have similar values, with solvent areas per unit cell

Figure 6. Structure of the 1D chain [Cu(HL)]·solv (2c·solv). Right: The copper atom environment with the corresponding labeling scheme. Note the formation of the three chelate rings.

Scheme 3

bond character; the CcarbonylO distances, with an average value increasing to 1.295 Å in 2c·2H2O·2dmf, suggest a single bond; and the N−N and C−N distances are moderately elongated. These findings suggest the predominance of the enol resonance form with charges delocalized along the conjugated arms. This effect has also been observed in other complexes.25 On the other hand, the CcarbonylO and Ccarbonyl−N bond distances in pocket II are 1.248(2) and 1.343(2) Å (in 2c·2H2O·2dmf), respectively, and these values are very similar to those in the same pocket in compounds 1a·5H2O and 1b·H2O·3dmf and in the free ligand. The undeprotonated N−H group in pocket II is used to trap different solvent molecules by means of the synthon hydrogenbonds system (Table 4). The oxygen atoms belonging to dmf, water, or dmso solvent molecules are the hydrogen-bond acceptors in these interactions. 1201



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Figure 7. Intermolecular “benzyl−metal chelate ring” interactions and arrangement of the two chains in different planes.

Figure 8. Packing in the 2c solvates (a, 2c·2H2O; b, 2c·2H2O·2dmf; c, 2c·2dmso; and d, 2c·H2O·2dmso) showing the variations of the π−π stacking interaction between the phenyl and chelate groups (green, 2c chains; red, water molecules; blue, dimethylformamide molecules; yellow, dimethylsulfoxide molecules). In 2c·H2O·2dmso (d), the solvent molecules block access to the chelate rings and hinder this interaction.

volume of approximately 26% (618 Å3) and 22% (534 Å3) after removing solvent molecules from the model. Changes in the bond distances and angles within the copper-ligand 1D chain are negligible, with the most marked differences being those related to the intermolecular π−π (planar chelate ring/phenyl group) interactions (Table S8). When the net hosts bigger molecules, this interaction is broken, as is the case for 2c·H2O·2dmso. Taking into account these findings, it is clear that the [Cu(HL)]n (2c) framework possesses some flexibility and the pore surface of the polymeric compound can be readily tailored by different guest molecules. In this way, the solvents that fill the cavities of the networks can act as a template in the formation of the metallosupramolecular compounds. Structural Dynamics and Thermal Stability (2c·solv). 2c can be considering as a soft, flexible, and dynamic framework, which transforms under the influence of external stimuli such as temperature or guest molecules.

This transformation is reversible with the temperature, water molecules, and dmf or dmso solvent molecules. This expansion is reversible, and crystallinity is maintained throughout. The expansion and contraction of the structure may be controlled by the presence of guest molecules. The thermogravimetric analysis of 2c·2H2O shows two weight losses of 5% (calcd 7%) below 60 °C corresponding to the loss of the occlude water molecules, and the next weight loss corresponds to the decomposition of the phase at 300 °C. Variable-temperature powder X-ray diffraction studies, performed at up to 350 °C under atmospheric pressure, show that structural changes clearly occur upon dehydration, to produce finally the dehydrated phase above 60 °C. Interestingly, dehydrated phase shows high crystallinity, and this structural transformation with the temperature can be repeated in several cycles without apparent degradation (Figure 10). To achieve the expulsion of water molecules and to obtain dehydrated phase, freshly ground sample 2c·2H2O was heated 1202



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molecules. Thermal analysis shows a first step between rt and 200 °C with a weight loss in the range of 4−10% in dmf solvates forms, and with a weight loss in the range of 10−24% in dmso solvate forms. The last weight loss occurred at 300 °C when the material begins to decompose in all of the cases. The highest values of solvent weight loss are obtained when dehydrated phase is used. In this case, water molecules are cosorbed as is proven by the step weight loss that takes place before 120 °C in both dmf and dmso solvates. Despite the different values of weight loss, XRPD pattern of solvate materials does not show significant differences between them. Whereas XRPD analysis of dmso solvates closely matched the simulated pattern generated from the single crystal diffraction data of 2c·2dmso, XRPD analysis of dmf solvates shows the same structural change, but they do not match the simulated pattern of solvated 2c·2H2O·2dmf. A reversible transformation to the crystalline guest-free phase is achieved in dmf/dmso solvates when the samples are heated at 280 °C. The desolvated samples are characterized by IR and XRPD analysis showing the change of the frameworks to the dehydrated form 2c (Supporting Information). The sorption of dmf and dmso is likely controlled by synthon host−guest interactions, and their structures may show extreme flexibility in the solid state, as we could see in the structural study of the different pseudopolymorphs. Unit cell is expanded with respect to the hydrated phase (with a variation of almost 30% of the potential solvent area) with dmso and dmf, but, with dmso, water can also be cosorbed changing to a monoclinic space group unit cell (2c·H2O·2dmso). The driving force for this conversion is likely the presence of free oxygen atoms capable to form part of the acceptors of the hydrogen-bonding synthon system responsible for the supramolecular arrangements. The interaction of the compound with organic molecules is important, because many materials show selective uptake of guest molecules, which is highly desirable for use in the separation or purification of organics.27 Selective guests that fit the shape with the suitable interactions to form the synthon responsible for the supramolecular arrangements in these pseudopolymorphs are required. In this sense, solvated and desolvated materials were treated with another different organic molecule such as urea, thiourea, acetone, aniline, dimethylacetamide, benzaldehyde, and acetophenone, but in any case they were not detected into the lattice. Further studies aimed at understanding the selective flexibility of 2c are underway.

Figure 9. Association of the solvent molecules in 2c·2H2O·2dmf (top) and 2c·H2O·2dmso (bottom). Space filling representation of the final 3D supramolecular architecture showing the different shapes of the voids.

Figure 10. Graphical scheme of the solvation/desolvation process in 2c derivatives. Variable-temperature X-ray powder diffraction of 2c·2H2O with a phase transition at around 60 °C.

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CONCLUSIONS In the present work, we have designed, synthesized, and characterized a new ligand, the bis(benzylhydrazone) of 4-hydroxyisophthaldehyde (H3L). This new rigid and almost planar polytopic asymmetric ligand reacted with different metal salts and allowed the isolation of the compounds [M(HL)]·solv [M = Cu(II), Co(II), Ni(II), and Zn(II)] containing bideprotonated ligand. The use of Co(SO4)2·7H2O in the agarose gel technique or the crystallization of [Ni(HL)]·H2O from dmf/thf led to the monomers [Co(H2L)2]·5H2O (1a·5H2O) and [Ni(H2L)2]· H2O·3dmf (1b·H2O·3dmf), in which the ligand is in the monodeprotonated keto form. The use of different synthesis conditions with copper(II) salts or crystallization from solvents such as dmf or dmso yielded the same 1D polymeric chains of [Cu(HL)] units (2c). This result

in an oven at 75 °C for 4 days. The desolvation of the sample was confirmed by the weight loss, TGA, and the X-ray powder diffraction (XRPD) proved the change of the framework in the desolvated material. Upon exposure of the dehydrated phase to moist air, it reverts to the crystalline hydrated form. The XRPD pattern and the thermogravimetric study show the total reversibility of this process. Different BET measurements showed nonpermanent porosity in the hydrated and dehydrated forms. Nevertheless, on leaving hydrated and dehydrated phases in a chamber with dmso or dmf at rt, they reverted to different crystalline solvate forms. The thermogravimetric (TG) curves shows similar weight loss behavior for both compounds (Figures S9−S11). The first weight loss is assigned to the loss of trapped solvent 1203



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beamline BM16 (Dr. A. Labrador, Dr. F. J. M. Casado, and Dr. E. Fraga) are thanked for their help. Dr. Franck Millange is thanked for his assistance in BET and thermal diffractometric measurements. Financial support from Xunta de Galicia (Spain) is gratefully acknowledged (research project 10TMT314002PR). A. B. L. thanks the Xunta de Galicia for a postdoctoral contract under the “Ángeles Alvariño” Program.

suggests a dynamic behavior of the ligand H3L and its Ni(II) and Co(II) complexes. The structural results show that the combination of the H3L ligand with different metal centers allows the isolation of two kind of compounds, monomers [M(H2L)2] (1) and coordination polymers [M(HL)] (2). The M(II)/H3L system seems to present a dynamic behavior where monomers (1a·5H2O, 1b·H2O·3dmf) are kinetic compounds of the thermodynamic stable polymers (2a−d). Formation of monomers (1) could be detected when Co(II) and Ni(II) metals centers were used. 1a·5H2O was obtained from a slow diffusion, whereas 1b·H2O·3dmf was crystallized from a solution of the polymeric 2b. Nevertheless, coordination polymers solvates were obtained from recrystallization in different solvents of the copper(II) complex 2c and from a agarose-gel diffusion of the reagents (i.e., copper(II) acetate and the ligand H3L). This fact is likely due to the different coordination sphere requirement of the metal center jointly with the different denticity of the ligand pockets. Co(II) and Ni(II) with high tendency to hexacoordination favor the formation of 3 + 3 coordination spheres of monomeric compounds in 1a and 1b against the 3 + 2 coordination (not necessarily pentacoordinated) in the polymeric structures, 2, based on the bridge HL2−. It is noteworthy the role of the hydrazinic −NH group, which remains undeprotonated in the complexes, and the C−H groups in the supramolecular organization of ligand and complexes as well as in the link of solvent to the network. Both groups form two rings (Figure 1, bottom) by means of N−H···O interactions and two C−H···O interactions with the Cphenyl and Chydrazone groups (Table 4), where the O atoms belong to solvent molecules (water, dmf, or dmso), hydroxyl, or carbonyl group of neighbor molecules. 2c is a stable framework from which four different solvates were obtained as crystals. These findings suggest flexible behavior of the network in 2c. The absence of permanent porosity in the desolvated material (BET experiments) in contrast to its ability to adsorb solvents (water/DMSO/DMF) in the vapor phase at rt confirmed this hypothesis.

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ASSOCIATED CONTENT

S Supporting Information *

IR and NMR spectra, PXRD studies for the complexes, complete structural data tables from single-crystal X-ray structures, and results of the studies of the solvation−desolvation processes in 2c. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (A.B.L.); [email protected] (E.M.V.-L.). Notes

The authors declare no competing financial interest. Dedication

This work is dedicated to our dear friend and colleague Professor Alfonso Castiñeiras (Universidade de Santiago de Compostela, Galicia, Spain) on the occasion of his retirement.

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ACKNOWLEDGMENTS We thank the Spanish BM16 beamline facility at the ESRF (Grenoble, France) for provision of synchrotron radiation beam time under projects 16-01-747 and 16-01-769. Staff members of 1204



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(16) Connelly, N. G.; Damhus, T.; Hartshorn, R. M.; Hutton, A. T. Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005; RSC Publising Cambridge, UK, 2005. (17) Monfared, H. H.; Chamayou, A.-C.; Khajeh, S.; Janiak, C. CrystEngComm 2010, 12, 3526 and references cited therein. (18) Infantes, L.; Motherwell, S. CrystEngComm 2002, 4, 454. (19) Manna, S. C.; Zangrando, E.; Ribas, J.; Chaudhuri, N. R. Eur. J. Inorg. Chem. 2007, 4592. (20) Varughese, S.; Desiraju, G. R. Cryst. Growth Des. 2010, 10, 4184. (21) Xing, Y.-Y.; Lin, J.-G.; Xu, Y.-Y.; Duan, X.-Y.; Li, Y.-Z.; Wang, F.M.; Meng, Q.-J. Inorg. Chem. Commun. 2010, 13, 514. (22) Kitaigorodskii, A. I. Molecular Crystals and Molecules; Academia Press: New York, 1973. (23) Robin, A. Y.; Fromm, K. M. Coord. Chem. Rev. 2006, 250, 2127. (24) Addison, A. W.; Reedijk, T. N; Ra, J.; Van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349. (25) Barbazán, P.; Carballo, R.; Prieto, I.; Tunes, M.; Vázquez López, E. M. J. Organomet. Chem. 2009, 694, 3102. (26) (a) Masui, H. Coord. Chem. Rev. 2001, 219−221, 957. (b) Castiñeiras, A.; Sicilia-Zafra, A. G.; González-Pérez, J. M.; Choquesillo-Lazarte, D.; Niclós-Gutiérrez, J. Inorg. Chem. 2002, 41, 6956. (c) Carballo, R.; Covelo, B.; Fernández-Hermida, N.; Lago, A. B.; Vázquez-López, E. M. J. Mol. Struct. 2009, 936, 87. (27) Millange, F.; Guillou, N.; Medina, M. E.; Ferey, G.; CarlinSinclair, A.; Golden, K. M; Walton, R. I. Chem. Mater. 2010, 22, 4237.

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Solid-State Coordinative Behavior of a New Asymmetrical Bis

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