Supramolecular architectures of metal complexes containing 4-sulfobenzoate dianion and 1,2-bis(4-pyridyl)ethane

Polyhedron 53 (2013) 40–47

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Supramolecular architectures of metal complexes containing 4-sulfobenzoate dianion and 1,2-bis(4-pyridyl)ethane Humberto C. Garcia, Renata Diniz, Luiz Fernando C. de Oliveira ⇑ Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Universidade Federal de Juiz de Fora, Campus Universitário s/n, Martelos, Juiz de Fora, MG 36036-900, Brazil

a r t i c l e

i n f o

Article history: Received 28 November 2012 Accepted 17 January 2013 Available online 26 January 2013 Keywords: Supramolecular chemistry X-ray diffraction Raman spectroscopy 1,2-Bis(4-pyridyl)ethane Sulfobenzoate dianion Metal complexes

a b s t r a c t In this work, synthesis, spectroscopic properties (infrared and Raman) and crystal structures of four new supramolecular arrangement named [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1), [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4) have been reported, where bpa is 1,2bis(4-pyridyl)ethane, Hbpa is the protonated bpa species and 4-sb2 is the sulfobenzoate diânion. All  however, only for the complex 1 it compounds crystallize in a triclinic system with space group P1; was observed the coordination between the metal site and the building block 4-sb2, being possible to assign the metal hardness. Despite this observed differentiation, the supramolecular arrangement exhibited a similar disposition of planes present in all structures (distinction of 4-sb2 ligand), showing supramolecular interactions such as hydrogen bonding, p-stacking, C–H  p and electrostatics interactions, all of them responsible for the stability of the synthesized compounds. The vibrational spectra of all the compounds are very similar, in agreement with the crystal data. The Raman spectra have showed important bands to confirm the compound formation at 1637 and 1617 cm1, assigned m(O–C@O) and m(CC)/m(CN) of the 4-sb2 and Hbpa building blocks, respectively, in addition to the disappearance of a major band in the synthesized compounds at 801 cm1, related to the d(COOH) mode. Other very important vibrational markers for the bpa ligand can be seen at ca. 1020 cm1, all of them assigned to the m(ring) for compounds 1 to 4, respectively. The lower value for the m(ring) was observed for compound 1, then suggesting that the coordination by the 4-sb2 building block is important for the weakness of this vibrational mode. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction In the last years, the study of weak interactions known as beyond the molecule has become an very interesting focus of investigation by several research groups, especially in processes involving chemical solid-state [1,2]. The current interest observed in literature is due to not only by the great variety of observed structural arrangements but also to the much known processes of self-assembly and self-organization of higher complexity entities called building blocks [3–5]. Several supramolecular architectures are formed simply by the contribution of non-covalent intermolecular forces such as hydrogen-bonding, p-stacking, electrostatic and van der Waals [6–10]. In many cases these weak interactions may be used as important tools in prevision of complicated array, in the crystal engineering field [11,12]. Under the focus of crystal engineering and solid-state architectures, the prior knowledge of these interactions are of great interest, due to their potential applications in materials with possible properties opto-

⇑ Corresponding author. Tel./fax: +55 (32) 3229 3310. E-mail address: [email protected] (L.F.C. de Olive). 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.01.011

electronics, electrical conductivity, non-linear optical (NLO), magnetism gas storage, catalysis, host–guest complexes and drug delivery systems [13–18]. The use of different building blocks becomes interesting as an alternative to the formation of new supramolecular assemblies, where the presence of distinct coordination species, with different physical and chemical properties, can bring together the characteristics cited above [19,20]. Thereby the organic species 4-sulfobenzoic acid monopotassium salt (4-KHsb) appears as an interesting building block, containing variable coordination modes through the sulfonate and the carboxylate groups, acting asmonodentate, chelating-bidentate, bridging-bidentate, bridging-multidentateas well as in the anionic form (as counter ion) [21,22]. The literature has also shown that 4-KHsb is a good ligand for the construction of coordination polymers with interesting structures, such as inorganic – organic hybrid, formed from systems heterometallic [23]; according to Zheng et al. [24] there can be found thirty different coordination modes for this building block, each one of them described by X-ray crystallography. Another known ligand used in this study is 1,2-bis(4-pyridyl)ethane(bpa), which has been extensively employed as organic building block for the generation of supramolecular networks. It

H.C. Garcia et al. / Polyhedron 53 (2013) 40–47

can be used in coordination chemistry as a bidentate bridging ligand, but can also act as a terminal ligand or as a host molecule [25,26]. Furthermore, an important feature is related to the properties of new materials containing bpa, ranging from magnetism, catalysis, adsorption and NLO [27,28]. In the last years, our research group has been involved in the investigation of polycarbonylic compounds used as building blocks in crystal engineering, including oxocarbons and pseudo-oxocarbons [29,30] as well barbiturate ion and aromatic carboxylic acids [31,32]. The main purpose of this investigation is the understanding of the structural and spectroscopic properties of such compounds. In this sense, we report here the synthesis, spectroscopic properties and crystal structures of four new compounds of Mn2+, Co2+, Ni2+ e Zn2+ ions, all of them containing 4-sulfobenzoatediânion (4-sb2) and 1,2-bis(4-pyridyl)ethane (bpa).

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2.3. X-ray crystallography Single crystal X-ray data were collected using an Oxford GEMINI A Ultra diffractometer with Mo Ka (k = 0.71073 Å) for every compound. Data collection, reduction and cell refinement were performed by CrysAlis RED, Oxford diffraction Ltda, Version 1.171.32.38 program [33]. The structures were solved and refined using SHELXL-97 [34].The empirical isotropic extinction parameter x was refined according to the method previously described by Larson [35], and a Multiscan absorption correction was applied [36]. The structures were drawn by ORTEP-3 for windows [37] and Mercury [38] programs. Crystal and structural refinement data for both compounds are displayed in Table 1.

3. Results and discussions 2. Experimental 2.1. Materials and methods All chemicals used in this study were used as purchased without further purification: 4-sulfobenzoic acidmonopotassium salt (C7H5KO5S, 95.0%, Sigma Aldrich), 1,2-bis(4-pyridyl)ethane (C12H12N2, 98.0%, Sigma Aldrich), MnSO4H2O (98.0%, Vetec), CoCl26H2O (99.5%, Sigma Aldrich), NiCl26H2O (97.0%, Vetec) and ZnSO47H2O (99.0%, Vetec). Elemental analyses of C, H and N were performed with a Perkin-Elmer 240 CHN analyser. Thermogravimetric analysis was obtained on a TG-60. All Samples (5–8 mg) was heated at 10 °C/min from room temperature to 900 °C in a dynamic nitrogen atmosphere (flow rate = 50 mL/min). Infrared spectra were obtained using a Bomem MB-102 spectrometer fitted with a CsI beam splitter, with the samples dispersed on KBr disks and the spectral resolution was acquired at 4 cm1. Good signal-tonoise ratios were obtained from the accumulation of 128 spectral scans. Fourier-transform Raman spectroscopy was performed using a Bruker RFS 100 instrument, Nd3+/YAG laser operating at 1064 nm in the near-infrared region and a CCD detector cooled with liquid N2. Good signal-to-noise ratios were obtained from 2000 scans that were accumulated over a period of 30 min with a spectral resolution of 4 cm1. All spectra were obtained at least twice to show reproducibility, and there were no observed changes in band positions or intensities.

2.2. Synthesis The synthetic procedure in general was similar for all complexes: 10 mL of an aqueous solution containing 65.0 mg (0.27 mmol) of 4-sulfobenzoic acid monopotassium salt (4-KHsb) was mixed with 10 mL of an ethanolic solution containing 50.0 mg (0.27 mmol) of 1,2-bis(4-pyridyl)ethane (bpa), resulting in a homogeneous colorless solution; to this solution was added by slow diffusion 5 mL of an aqueous solution containing 0.27 mmol of a metallic ion. After a few days suitable single crystals were obtained and separated by filtration, being colorless for Mn2+ [yield = 32%] and Zn2+ [yield = 42%] complexes, orange for Co2+ [yield = 35%] and green for Ni2+ [yield = 38%]. Elemental analysis: [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1): Calc.: for C, 50.83; H, 4.72; N, 6.24. Found: C, 51.03; H, 4,95; N, 6,02%; [Co(Hbpa)2(H2O)4](4-sb)2 (2): Calc.: for C, 50.61; H, 4.69; N, 6.21. Found: C, 50.10; H, 4,84; N, 5,92%; [Ni(Hbpa)2(H2O)4](4-sb)2 (3): Calc.: for C, 50.62; H, 4.70; N, 6.21. Found: C, 50.35; H, 4,91; N, 5,98%; [Zn(Hbpa)2(H2O)4](4-sb)2 (4):Calc.: C, 50.25; H, 4.66; N, 6.17. Found: C, 51.15; H, 4,73; N, 6.04%.

The four transition metal complexes of general formula [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1) and[M(Hbpa)2(H2O)4](4-sb)2, (where M = Co2+, Ni2+ and Zn2+, respectively complexes 2, 3 and 4) were obtained by slow diffusion of metal aqueous solutions into a solution containing the building blocks 4-sulfobenzoic acid monopotassium salt (4-KHsb) and 1,2-bis(4-pyridyl)ethane (bpa). In all synthesized compounds the analytical data (which can be seen in the Experimental section) suggest the proportion stoichiometry as 1: 2: 2 [M2+:Hbpa+: 4-sb2]. Thermogravimetric curves (TGA and DTA) of compounds 1, 2, 3 and 4 are deposited as Supplementary materials (Figs. S1–S4, respectively). For compound 1 the thermogravimetric analysis show the first weight loss around 108 °C, which can be associated to the exit of four water molecules mols (calcd./exp.: 8.0%/7.8%) by repeating unit. In this weight loss region it can be observed by DTA the presence of three endothermic events occurring consecutively at 89, 108 and 126 °C. In addition, the TG curve displays other weight loss steps above 200 °C, which can be attributed to the thermal decomposition of organic material, where as the residue can be related to the formation of the metallic species (calcd./exp.: 6.1/6.2%). For complexes 2, 3 and 4 the thermogravimetric analyses showed a very similar profile, suggesting the same crystallization arrangement. It can be observed a first mass loss in the 66–83 °C range, which is associated to the exit of two water molecules (calcd./exp.: 4.0/4.1%, 4.0/4.2%) and 3.9/4.3% for complexes 2, 3 and 4, respectively). For the same compounds a second weight loss is observed at ca. 147–174 °C and attributed to the exit of another two water molecules mols by repeating unit (calcd./exp.: 4.0/4.0%, 4.0/4.1% and 3.9/4.6%, for compounds 2, 3 and 4 respectively). All these events are also observed by DTA analysis, with the presence of two endothermic events in this region. Other important information obtained by DTA is observed through an exothermic event around 201, 197 and 206 °C for compounds 2, 3 and 4, respectively, suggesting a new structural rearrangement with energy liberation. Furthermore, all TG curves display other three weight loss steps which can be attributed to thermal decomposition. For the compound 2 the final residue can be identified as the metallic species (calcd./exp.: 6.5/6.6%);however, for compounds 3 and 4 the maximum temperature measurement at 900 °C was not enough for the complete decomposition of the entire sample, leaving a large amount of mass as the residue. The structural arrangements for compounds 1, 2, 3 and 4 were revealed by X-ray single crystal analysis; all compounds crystallize  space group but only comin a triclinic crystal system with P1 pounds 2, 3 and 4 can be considered as isomorphous. The main geometrical parameters and hydrogen bond interactions observed in the compounds 1 to 4 are presented in Table 2, respectively. Fig. 1 displays for compound 1 the repeating unit consisting of neutral blocks, formed by the metallic ion Mn2+ coordinated in a

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Table 1 Crystal data for [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1), [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4). Compound

[Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1)

[Co(Hbpa)2(H2O)4](4-sb)2 (2)

[Ni(Hbpa)2(H2O)4](4-sb)2 (3)

[Zn(Hbpa)2(H2O)4](4-sb)2(4)

Formula Formula weight (g mol1) T (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Crystal size (mm) Dcalc (g cm3) l(Mo Ka) (cm1) Transmission factors (min/max) Reflections measured/unique Observed reflections [Fo2 > 2r(Fo2)] N°. of parameters refined R[Fo > 2r(Fo)] Rint wR[Fo2 > 2r(Fo)2] S RMS peak

C38H42MnN4O14S2 897.84 280.1 triclinic  P1

C38H42CoN4O14S2 901.83 110.00(10) triclinic  P1

C38H42NiN4O14S2 901.59 280.0 triclinic  P1

C38H42ZnN4O14S2 908.29 280.0 triclinic  P1

9.9604(8) 10.6373(8) 11.0079(6) 101.145(6) 96.588(6) 117.146(7) 990.38(15) 1 0.71  0.35  0.11 1.505 0.513 0.807/0.945 8317/4057 3185 288 0.0400 0.0284 0.0944 1.038 0.064

9.7531(3) 10.0176(2) 11.3713(3) 87.760(2) 86.266(2) 64.606(2) 1001.45(5) 1 0.59  0.53  0.25 1.495 0.606 0.706/0.857 44 782/5574 4463 289 0.0479 0.0434 0.1345 1.092 0.118

9.6640(9) 10.0541(7) 11.4854(10) 87.804(7) 85.717(7) 65.549(8) 1013.00(16) 1 0.47  0.26  0.15 1.478 0.655 0.813/0.904 10 581/4141 2523 288 0.0590 0.0477 0.1488 0.975 0.115

9.6813(8) 10.1142(7) 11.4996(8) 87.542(6) 85.504(6) 65.561(7) 1021.91(14) 1 0.76 x 0.56 x 0.21 1.476 0.775 0.599/0.848 8461/4179 3125 288 0.0577 0.0760 0.1561 1.079 0.088

Table 2 Select bond distances (Å), bond angles (°) and hydrogen interactions for [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1), [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4). Bond distance (Å)

[Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1)

M–O1 M–O2 M–O7 M–N1 S1–O2 S1–O3 S1–O4 S1–C17

2.154(2) 2.195(2) 2.283(2) 1.466(2) 1.444(2) 1.441(2) 1.776(2)

Bond distance (Å)

[Co(Hbpa)2(H2O)4](4-sb)2 (2)

[Ni(Hbpa)2(H2O)4](4-sb)2 (3)

[Zn(Hbpa)2(H2O)4](4-sb)2 (4)

2.123(2)

2.065(3)

2.124(3)

2.065(2) 2.135(2) 1.462(2) 1.444(2) 1.463(2) 1.783(2)

2.043(3) 2.095(3) 1.455(3) 1.424(3) 1.440(3) 1.777(3)

2.072(3) 2.148(3) 1.457(3) 1.429(3) 1.442(3) 1.774(4)

180.0

180.0

180.0(2)

89.22(7) 90.78(7)

89.36(13) 90.64(13)

89.91(17) 90.09(17)

2.669(2) 2.591(3)

2.650(4) 2.618(5)

2.660(5) 2.608(5)

Average of bond angles (°) O1–M–O1 180.00(11) O1–M–O2 95.28(7) O1–M–O2 84.72(7) O1–M–O7 O1–M–O7 D  A (Å) O1–H1A  O5 2.851(3) O1–H1A  O3 2.939(3) O1–H1B  O6 2.711(3) N2–H2N  O5 2.591(3) O7–H7A  O4 2.936(4) O7–H7B  O6 2.842(3) C18–H18  O3 2.901(3) O1–H1A  O4 O7–H7A  O2 O7–H7B  O5

2.771(3)

2.862(5)

2.898(6)

2.781(3) 2.705(3) 2.928(2)

2.833(5) 2.710(5) 2.900(4)

2.833(5) 2.720(6) 2.889(5)

D–H  A (°) O1–H1A  O5 O1–H1A  O3 O1–H1A  O4 O1–H1A  O6

176(5) 172(4)

157(5) 177(4)

167(7) 169(5)

143(4) 127(4)

slightly distorted octahedral geometry to two aqua ligands, whereMn–O1distance is 2.154(2) Å, and two building blocks 4-sb2, where Mn–O2distance is 2.195(2) Å, in the equatorial position and two bpa ligands mono protonated (Mn–N1 = 2.283(2) Å) in the axial position. The bpa ligand appears coordinated in a terminal mode, adopting a Trans (T) conformation with N-to-N separation

distances of 9.257(3) Å [39]. It can also be seen that the nitrogen atom N2 of this terminal ligand appears protonated, thus contributing to the neutralization of the neutral block formed. Furthermore, two water molecules of crystallization are completing each repeating unit, which are omitted from Fig. 1 for a better visualization.

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Fig. 1. ORTEP view of the [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1) crystal structure. Ellipsoids are drawn at the 50% probability level, except for hydrogen atoms which are represented by circles of arbitrary radius.The crystallization water molecules are omitted for clarity. Symmetry code: (i) 1  x, 1  y, z.

Fig. 2. Supramolecular arrangement of theobserved planesfor [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1)compound: (a) showing the building blocks coordination and supramolecular interactions, and (b) showing the supramolecular disposition of the observed planes.

The bi-dimensional supramolecular arrangement of compound 1can be seen in Fig. 2. Through Fig. 2a, along the ac diagonal, it can be observed the presence of hydrogen bonds, which are classified as medium. These interactionsare better displayed between the 4-sb2 and hbpa building blocks of the distinct neutral units, presenting interaction distance of O5  N2 = 2.591(3) Å. Other important interactions to be considered in the supramolecular arrangement can be seen along the c-axis, occurring between the aromatic rings of the nitrogen ligand bpa, more precisely the rings which have the protonated nitrogen N2; such interactions, the socalled p-stacking [40], present centroid–centroid interaction distance of 3.735(2) Å, and interactions of C–H  p type between aromatic rings of 4-sb2 building blocks and the hydrogen atoms of hbpa ligand, with interaction distance of 3.499(2) Å. Fig. 2b exhibits the tri-dimensional arrangement of compound 1, where the planes are forming a parallelogram with manganese ions located on the vertices and their planes perpendicular to the ab plane. The interaction between these planes occurs through hydrogen bonds between water molecules (both the coordination and crystallization water molecules) and carboxylate/sulfonate groups of the sb2 building blocks. These supramolecular interactions (Fig. S5) can be described as graph set networks [41] named C 21 ð20ÞR42 ð12ÞR32 ð22ÞR22 ð10Þ, where basically the symbols C and R

are related to an infinite chain and ring set, respectively, whereas the numbers indicate the quantities of donor (subscript) and acceptor (superscript) moieties in each set. For compounds 2, 3 and 4, Fig. 3 shows the repeating unit, formed by two distinct building blocks:a cationic block consisting of a metal ion covalently bonded to four aqua ligands, and two terminal bpa ligands, giving rise to a slightly distorted octahedral geometry. The average distances of the M–O and M–N1 bonds are 2.094(2) and 2.135(2) Å for compound 2, 2.054(3) and 2.095(3) Å for compound 3 and 2.098(3) and 2.148(3) Å for compound 4, respectively. It is straightforward to note that bpa ligand adopts a Trans (T) conformation with N-to-N separation distances of 9.246(2), 9.230(3) and 9.204(2) Å for the compounds 2, 3 and 4, respectively. The terminal nitrogen atom N2 of this ligand appears protonated, thereby preventing the formation of a coordination polymer and originating the cationic unit of [M(Hbpa)2 (H2O)4]4+ general formula. To neutralize this cationic building block it can be seen two anionic blocks, acting as counter ions and formed by 4-sb2 moiety. It is important to note that4-sb2 is not coordinated to the metal ions, thus being structurally different from compound 1. The supramolecular arrangement of the complexes 2, 3 and 4 can be observed across Fig. 4. Fig. 4a displays the formation of

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Fig. 3. ORTEP view of the [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4) crystal structure. Ellipsoids are drawn at the 50% probability level, except for hydrogen atoms which are represented by circles of arbitrary radius. Symmetry code: (i) 1  x, y, 1  z.

Fig. 4. Supramolecular arrangement of theobserved plane for [Co(Hbpa)2(H2O)4](4-sb)2(2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4) compounds: (a) showing the building blocks coordination and supramolecular interactions, and (b) showing the hydrogen-bonding 2D network, responsible for the supramolecular interaction between planes.

planes which are perpendicular to the ab plane; such planes are originated by the cationic and anionic building blocks, which were previously discussed. The interactions of these blocks occur through hydrogen bonds along the ac diagonal between the carboxylate group of sb2 building block and the protonated terminal nitrogen of the Hbpa moiety, presenting interaction distance O5  N2 of 2.591(3), 2.618(5) and 2.608(5) Å for compounds 2, 3 and 4, respectively. Other supramolecular interactions present in these compounds can be observed along the c axis, with the presence of p-stacking interactions between the aromatic rings of the protonated Hbpa, where it can be seen a centroid–centroid distance of 3.678(2) Å. It can also be seen a C–H  p interaction, appearing between the aromatic rings of the 4-sb2 and the hydrogen atoms from the Hbpa, with bond distance of 3.736(3) Å. An interesting fact observed for compounds 2, 3 and 4 is that the special arrangement of their planes can also be seen in a similar way to the discussed before for compound 1 (Fig. 2b). However, some differences can be observed through the interaction between the

planes, for compounds 2, 3 and 4 occurs between the carboxylate group of the 4-sb2 building block and coordination water molecules. These supramolecular interactions can be observed in Fig. 4b, presenting the graph set representation [41] as N ¼ C 22 ð8ÞR12 ð6ÞR44 ð16Þ. An interesting comparison between the synthesized compounds is the behavior of the 4-sb2 ligand, which is coordinated to the metal center in compound 1, whereas it appears not coordinated in compounds 2, 3 and 4. A reasonable explanation for this observed fact can be given through the principle of Pearson [42] involving hard and soft acids and bases.In this sense, manganese ion is considered by Pearson as a hard acid (small and poorly polarizable), whereas Co2+, Ni2+ and Zn2+ions are intermediary acid. Thus the coordination observed in compound 1 can be explained by the fact that the Mn2+ ion and 4-sb2 building block, classified as hard acid and hard base respectively, do not favor the coordination of the other metal ions used in this work, and considered intermediate hardness.

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In an attempt to explain the preference for compound 1 coordination via the sulfonic group, instead of the carboxylate group, the steric effect associated with intermolecular forces present in the building block 4-sb2 can be considered the main responsible for the observed phenomenon. The coordination by sulfonic group favors the formation of intermolecular forces such as p-stacking, C– H  p and hydrogen bonds, through the approach of the aromatic rings from bpa and 4-sb2 building blocks, besides the formation of a crystalline solid system presenting a small volume. If the coordination occurs through carboxylate group, probably the sulfonic group prevents the approximation of the aromatic rings from the building blocks used in the synthesis, due to their biggest occupied volume, then promoting the formation of a crystalline array of large volume, and consequently less stable. In this sense, Fig. 4a shows clearly for compounds 2, 3 and 4 that the approach of the 4-sb2 building block to the metallic site occurs through sulfonic group, even there is no coordination, resulting in a more stable structure and with a small volume, as previously discussed. The vibrational spectra of all the investigated ligands and complexes are displayed in Figs. 5 and 6 (infrared absorption and Raman scattering, respectively). It is important to note that all spectra are very similar and in agreement with the crystal data. The main vibrational modes are summarized in Table 3, as well as the tentative assignment based on similar chemical systems [43–46]. The infrared spectrum (Fig. 5) of 4-sulfobenzoic acid monopotassium salt displays a very broad band in the 3600–3300 cm1 region, which has been assigned to the OH stretching mode m(OH) present both in carboxylic acid groups and/or water molecules. An important band marker for the salt can be observed at 1726 cm1, assigned to the m(C@O)mode from carboxylic groups; this same vibrational mode appears shifted to a lower wave number when the carboxylate group is deprotonated observed, due to the extended electronic delocalization which is responsible by the new stretching mode of the O–C@O bond. Moreover, this band at 1726 cm1can be used to corroborate that the formation of monoprotic acid salt occurs through the exit of a hydrogen atom, which was present in the sulfonic acid group –SO3H structure, indicating that the sulfonic group can be seen as more acidic than the carboxylic group in the molecule. Other two bands of medium and high intensity from this building block can be observed at 1406 and

Fig. 5. Infrared spectra of [Mn(Hbpa)2(H2O)2(4-sb)2].2H2O (1), [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4); for comparison purposes the spectra of the precursors (4-KHsb and bpa) are also displayed.

45

Fig. 6. Raman spectra of [Mn(Hbpa)2(H2O)2(4-sb)2]2H2O (1), [Co(Hbpa)2(H2O)4](4sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4); for comparison purposes the spectra of the precursors (4-KHsb and bpa) are also displayed.

1250 cm1, assigned to the S@O and COOH stretching modes, respectively. The Raman spectrum of 4-KHsb shows three important bands for characterization, at 1720, 1608 and 801 cm1, referring to the m(COOH), m(CC) and d(COOH) modes. For the free bpa ligand the infrared spectrum has shown very characteristic bands, such as the ones at 1597 and 991 cm1, assigned to the m(CC)/m(CN) and m(ring) of the pyridyl ring portion, respectively. The Raman spectrum has also shown these same bands at 1598 and 995 cm1, in addition to an intense feature at 1216 cm1, assigned to the d(CH) mode. In terms of the coordination chemistry analysis, the bands from the bpa ligand concerning m(CC)/m(CN) and m(ring) modes mentioned above are very important for the confirmation of this building block attached to metallic ion. Experimental observations have shown that such bands appear shifted to higher wave numbers when the ligand is directly coordinated to the metal ion [32,46]. For compounds 1 to 4 the infrared spectra exhibita broad band between 3500 and 3200 cm1, assigned to the m(OH) mode from H2O molecules; this observation is been based on the fact that all spectra present an intense band at 1637 cm1, assigned to the asymmetrical m(O–C@O)mode of 4-KHsb, originated after the carboxylic group deprotonation. Other important band observed for every compound can be seen at 1393 cm1assigned to the carboxylate group symmetrical m(O–C@O) mode. Two other strong bands are observed at 1009 and 1030 cm1, assigned to the symmetrical and asymmetrical m(SO3) respectively. The presence of bpa can be confirmed by the bands at 1612–1620 cm1 region for complexes 1 to 4, and assigned to the m(CC)/m(CN) mode. When comparing these bands with the one for the free ligand (occurring at 1597 cm1), it can be observed that for all complexes there is a shift to higher wavenumbers, then supporting the bpa coordination to the metal ion, which causes a strengthening of the chemical bond and a consequent increase in the bond order, mainly due to the participation of non-bonding electrons in the chemical bond. The Raman spectra of compounds 1 to 4 can be seen in Fig. 6; it can observed for all the four synthesized compounds the presence of a set of intense bands in the 3100–2800 cm1 region, assigned to m(CH) modes of aliphatic and aromatic groups present in the bpa and 4-sb2 building blocks. It is straightforward to note these bands are observed only in the Raman spectra, since in the infrared spectrum this region is overlapped by the presence of water molecules present in the structure. Another two important Raman

46

H.C. Garcia et al. / Polyhedron 53 (2013) 40–47

Table 3 Raman (R) and infrared (IR) wavenumbers (in cm1) and tentative assignment of the most important bands observed for [Mn(Hbpa)2(H2O)2(4-sb)2H2O (1), [Co(Hbpa)2(H2O)4](4sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4). 4-KHsb IR

bpa R

IR

Mn (1) R

IR

Co (2) R

IR

736 m

561 w 642 w 739 s

Ni (3) R

IR

741 m

561 m 642 m 739 s

Zn (4) R

IR

744 m

565 w 638 m 743 w

Tentative assignment R

548 vs 559 636 708 766

w vs vs m

563 w 634 m

638 m 734 m

742 m

801 s 830 vs

833 m 862 w

856 m 991 m 1009 1032 1105 1173

vs vs s vs

1227 sh 1250 vs

1006 1033 1102 1170 1187

w w m m m

873 m 995 vs

878 w 1016 s 1013 1034 1115 1175

s s m vs

1216 s

1257 m

829 m 865 w

1035 1114 1178 1216

s s m m

1250 vs 1393 s

1247 w 1394 m

1612 s

1614 s 1596 vs 1637 m

829 m 875 w 1023 s

1009 1030 1113 1171

s s m vs

1240 vs 1257 vs 1394 s

1114 s 1176 w 1216 m

1392 m

1009 1032 1113 1173

vs s s vs

1236 vs 1257 vs 1393 vs

831 m 879 w 1025 s 1009 sh 1114 s 1176 w 1214 m

875 w 1023 s 1012 s 1038 s 1184 s

1114 s 1178 w 1216 m

1230 vs 1392 m

1398 vs

1392 m

1406 m 1414 s 1597 vs

1598 s

1608 vs 1637 m 1726 vs

1637 m

1617 s 1594 vs 1637 m

1508 m 1620 s 1637 m

1617 s 1596 vs 1635

1720 vs 2924 s 3054 vs 3069 s 3087 s

a

1508 m 1612 s

1508 w 1616 s 1637sh 1717 m

1617 s 1594 vs 1637 s

2917 m

2908 m

2906 m

2908 m

3073 vs

3073 vs

3073 vs

3073 vs

do.p.(CH)+dwagg(CH2) do.p(OH)+ do.p(CH) do.p(CC) di.p(CC) do.p(OH) do.p(COOH) do.p(CH) di.p(CH) do.p(CH)

mring mas(SO3) mas(SO3) mas(SO3) di.p(CH) ms(SO3) m(COOH) m(O–C@O) m(S@O) mring + do.p(CH) m(CC)/m(CN) m(CC) ms(O–C@O) ms(CO) m(CH2) m(CH) m(CH) m(CH)

Abbreviations: vs very strong; s, strong; m, medium; w, weak; i.p., in-plane; o.p., out-of-plane; sh, shouder; br, broad.

features are observed at 1637 and 1392 cm1, referring to the carboxylate group stretching mode (asymmetrical and symmetrical m(O–C@O)) of the 4-sb2 building block. Additionally the formation of the carboxylate group can be seen for all compounds by the disappearance of an intense band at 801 cm1 in the 4-KHsb spectrum, assigned d(COOH). Moreover, the presence of an intense band at 1594 cm1, referring to a weakening of the stretching mode m(CC) of structure, is also related to the presence of 4KHsb.Two intense bands at 1617 and 1023 cm1, assigned to the m(CC)/m(CN) and m(ring) modes, respectively, are due to the presence of bpa in the supramolecular arrangement; such bands appear shifted to higher wavenumbers, when compared to the free ligand (at 1598 and 995 cm1, respectively), thus confirming the coordination, also evidenced by X-ray diffraction. However, the smallest shift for the m(ring) was observed for compound 1 (occurring at 1016 cm1), which can be understood as the coordination is responsible for the weakening the bonds of the 4-sb2 building block. 4. Conclusions In summary this work presents the synthesis, the spectroscopic (infrared and Raman) and structural investigation of four novel supramolecular compounds named as [Mn(Hbpa)2(H2O)2(4-sb)2] 2H2O (1), [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4). For all structures the same  were observed. crystalline system (triclinic) and space group (P1) However, the coordination mode verified for compound 1 is different, which can be explained using the Pearson concepts for acid/ base hardness and softness. The intriguing is that even presenting different coordination geometries, the supramolecular arrangements of the compounds are very similar, when analyzing the planes and spatial disposition of their atoms, showing supramolecular interactions such as hydrogen bonds, p-stacking and C–H  p. The vibrational spectra of the synthesized compounds are also very

similar, presenting a good agreement with the X-ray diffraction data, supporting the idea as an additional tool for the coordination chemistry of such systems, mainly based on the analysis of some band markers, which appear shifted after coordination. The success obtained in the synthesis and characterization of the four new supramolecular compounds described here demonstrates that the use of multifunctional organic ligands, containing different coordination groups such as nitrogen atoms, sulfonate and carboxylate groups, emerges as a powerful tool for obtaining new and interesting supramolecular arrangements. Acknowledgements Authors thank CNPq, CAPES, FAPEMIG (PRONEX 04370/10, CEXAPQ-00617) and FINEP (PROINFRA 1124/06) for financial support and also LabCri (Departamento de Física – UFMG) for the X-ray facilities. Appendix A. Supplementary material CCDC 900059, 900058, 900060 and 900061 contains the supplementary crystallographic data for 1, 2, 3, and 4. 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 e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.poly.2013.01.011. References [1] H.-P. Zhou, X.-P. Gan, X.-L. Li, Z.-D. Liu, W.-Q. Geng, F.-X. Zhou, Cryst. Growth Des. 10 (2010) 1767. [2] S. Thakurta, J. Chakraborty, G. Rosair, R.J. Butcher, S. Mitra, Inorg. Chim. Acta 362 (2009) 2828.

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