Self-Assembly of Magnesium and Zinc Trimethoxyphenylporphyrin

Oct 13, 2011 - Polymer as Nanospheres and Nanorods. Jagannath Bhuyan and Sabyasachi Sarkar*. Department of Chemistry, Indian Institute of Technology ...
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Self-Assembly of Magnesium and Zinc Trimethoxyphenylporphyrin Polymer as Nanospheres and Nanorods Jagannath Bhuyan and Sabyasachi Sarkar* Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India

bS Supporting Information ABSTRACT: The crystal structures of [Mg(TMPP)] (1) and [Zn(TMPP)] (2) (TMPP = 3,4,5-trimethoxyphenylporphyrin) show that 1 and 2 possess unusual one-dimensional (1D) coordination polymer structure through metal oxygen (oxygen atom from m-methoxy group of adjacent porphyrin) bonds. In 1 and 2, the metal ion is hexacoordinated with the two axially ligated methoxy groups (bonded through oxygen) from the two neighboring porphyrins. In the nano domain, the self-organization of 1 in dichloromethane (DCM) petroleum ether is in a spherical shape. Complex 2 self-organizes as a nanorod in DCM petroleum ether medium. In DCM or in chloroform, such a self-organization process, which is influenced by air bubble formation, transforms the rod to a circular ring. In coordinating solvent like ethanol, the polymer aggregation is terminated in both 1 and 2 to produce relatively large rectangles. The varied ways of self-organization in the nanodomain of these two porphyrins have been discussed.

’ INTRODUCTION Porphyrin nanostructures have broad interest because of their application in electronics, catalysis, and sensors and as a biomimetic model of electron transfer in photosynthesis.1 On the other hand, self-assembled coordination polymers of porphyrin also have diverse applications especially for biomimetic models of electron transfer of photosynthesis.2 There are different methods applicable in forming porphyrin coordination polymers. Among these, axial coordination to the metal of metalloporphyrin through a peripheral coordinating group of metalloporphyrin is interesting. In such a case, the peripheral coordinating group of a metalloporphyrin binds axially to the central metal atom of another adjacent molecule leading to coordination structures.3 The peripheral coordination group of a metalloporphyrin can also act like a ligand to coordinate an external metal ion. The reported self-assembly of metalloporphyrins in the former case involves mainly through nitrogen coordination from the peripheral group, and the metalloporphyrin is restricted to zinc porphyrin.4 However, self-assembled porphyrin nanostructures from such coordination polymers are scarce.5 In this work, we, therefore, describe the synthesis, crystal structures, and the self-assembled properties of [Mg(TMPP)] (1) and [Zn(TMPP)] (2) (TMPP = 3,4,5-trimethoxyphenylporphyrin) from different solvent mixtures when applied with different solid matrices. The crystal structure reveals the present magnesium and zinc porphyrins as 1D coordination polymers. Though 1 and 2 show identical 1D coordination polymeric structures grown from the same solvent mixture, in the nano domain, they display different structures. r 2011 American Chemical Society

’ EXPERIMENTAL SECTION Materials and Methods. Solvents like acetone, dichloromethane, hexane, petroleum ether, and pyrrole were obtained from S. D. FineChem Ltd. and purified and dried before use by standard methods. 3,4,5Trimethoxybenzaldehyde was procured from Sigma-Aldrich and dimethylformamide (DMF) from Thomas Baker. Magnesium acetate and sodium acetate were purchased from CDH (P) Ltd. Physical Measurements. Electronic absorption spectral measurements were carried out with a Perkin-Elmer (Lamda 35) spectrophotometer. Infrared spectra were recorded on a Bruker Vertex 70 FT-IR spectrophotometer as pressed KBr disks in the IR region. Elemental analysis for carbon, hydrogen, and nitrogen was performed with a Perkin-Elmer 2400 microanalyzer. 13C NMR spectroscopic measurements in CD2Cl2 were recorded with JEOL-500 NMR spectrometer. Powder X-ray diffraction (PXRD) data were collected on an XPERTPRO diffractometer using Cu Kα radiation (λ = 1.540 598 Å). X-ray Data Collection and Structure Determination. The crystal used was glued to a glass fiber and mounted on a BRUKER SMART APEX diffractometer. Cell constant was obtained from the least-squares refinement of three-dimensional centroids through the use of CCD recording of narrow ω rotation frames, completing almost allreciprocal space in the stated θ range. The instrument was equipped with a CCD area detector, and data was collected using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å) at low temperature (100 K). All empirical absorption correction was applied using the SADABS program. All data was collected with SMART 5.628 (BRUKER, 2003) Received: August 2, 2011 Revised: September 29, 2011 Published: October 13, 2011 5410

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Crystal Growth & Design and integrated with the BRUKER SAINT program. The structure was solved using SIR976 and refined using SHELXL-97.7 The space group of the compound was determined based on the lack of systematic absence and intensity statistics. Full matrix least-squares/difference Fourier cycles were performed, which located the non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters. Both the structures 1 and 2 suffered from disordered dichloromethane (DCM) solvent in the lattice, which was not included in the refinement but was taken care of by the SQUEEZE procedure (from PLATON).8 The volumes occupied by the solvent were 780.7 and 782.5 Å3, respectively, and the number of electrons per unit cell deduced by SQUEEZE were 112 and 110, respectively. The details of SQUEEZE results were appended to the crystallographic data file. Scanning Electron Microscopy. The SUPRA 40VP field emission scanning electron microscope (Carl Zeiss NTS GmbH, Oberkochen. Germany) equipped with energy-dispersive X-ray (EDX), in high vacuum mode operated at 10 kV, was used for the visualization of 1 and 2 in high vacuum mode. Four milliliters of petroleum ether was added to a solution of 2 mL of 1 and 2 (in DCM, 10 3 M) and gently stirred; one drop from this mixture was injected onto the surface of brass stub, which was dried in air and finally under vacuum. Sequential gold sputtering was made before taking an image. Atomic Force Microscopy. Atomic force microscopy (AFM) was carried out with a Pico scan model (Molecular imaging, US) in air under ambient conditions at room temperature. A silicon nitride tip (micromesh) was used, and the size of the cantilever tip (radius of curvature) was less than 10 nm. The spring (force) constant of the cantilever was 1 N/m. Images were obtained by the dynamic force mode. This mode involves cantilever oscillation either by an acoustic signal (AAC) or by a magnetic signal (MAC mode), leading to an enhanced resolution and minimal damage to the samples. Samples were prepared by placing a drop of the solution (sample solution was prepared similarly to the SEM sample) on the surface of freshly cleaved highly oriented pyrolytic graphite (HOPG). Transmission Electron Microscopy. The morphology of the nanorod, rectangle, and ring were imaged by using a Tecnai 20 G2 300 kV, STWIN model transmission electron microscope (TEM). TEM analyses were imaged with an acceleration voltage of 200 kV. Samples for imaging were prepared by placing a small drop of the sample solution (samples solutions were prepared according to the procedure given in the synthesis section) on the surface of a carbon-coated copper grid. Fluorescence Microscopy. The fluorescence images of compounds 1and 2 were performed on a Leica inverted microscope (Leica DC200, Leica microscopy system Ltd., CH- 9435, Heerbrugg) equipped with an RS Photometrics Sensys camera, KAF1401E G1.

Synthesis of meso-Tetrakis(3,4,5-trimethoxyphenyl)magnesium Porphyrin [MgTMPP (1)]. A mixture of meso-tetrakis(3,4,5-tri-

methoxyphenyl)porphyrin (500 mg, 0.502 mmol) and Mg(CH3COO)2 3 H2O (700 mg, 3.26 mmol) in 200 mL of DMF was heated at 90 °C for 30 min in a round-bottom flask, then NaHCO3 (80 mg) was added to the mixture, and the final reaction mixture was refluxed for 4 h. The solvent was then removed on a boiling water bath, and the remaining solid residue was dissolved in DCM, filtered, and again evaporated out. The crude compound 1 was finally purified by column chromatography over neutral alumina using 10% acetone dichloromethane mixture. The yield of the pink crystalline product of 1 was 80%. Molecular formula: C57H54N4O12MgCl2. Molecular weight: 1082.25. UV/vis (CH2Cl2) λmax(ε): 428 (402205), 566 (16210), 606 (10725 mol 1 dm3 cm 1). Elemental analysis calcd (%) for C57H54N4O12MgCl2 C 63.26, H 5.03, N 5.18; found C 63.02, H 5.10, N 5.21.

Synthesis of meso-Tetrakis(3,4,5-trimethoxyphenyl)zinc porphyrin [ZnTMPP (2)]. 3,4,5-Trimethoxybenzaldehyde (1 g, 5.1 mmol)

was dissolved in 50 mL of DMF. Concentrated hydrochloric acid (0.5 mL) was added into it followed by dropwise addition pyrrole (0.35 mL, 5.1 mmol). The mixture was stirred for 1 h and then ∼2.5 equiv

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Figure 1. Molecular structure showing hexa-coordination of central metal of (a) 1 and (b) 2. of zinc chloride was added into it, and the final reaction mixture was refluxed for 5 h. The mixture was then dried on a boiling water bath, and the solid residue was washed with hot water. The crude washed compound 2 was finally purified by column chromatography over neutral alumina using 5% acetone dichloromethane mixture. The yield of the pink crystalline product of 2 was 19%. Molecular formula: C57H54N4O12ZnCl2. Molecular weight 1123.33. UV/vis (CH2Cl2) λmax(ε): 422 (499460), 550 (22678), 588 (6383 mol 1 dm3 cm 1). Elemental analysis calcd (%) for C57H54N4O12ZnCl2 C 60.94, H 5.85, N 4.99; found C 61.02, H 4.98, N 5.07.

’ RESULTS AND DISCUSSION [Mg(TMPP)] (1) (TMPP = 3,4,5-trimethoxyphenylporphyrin) has been synthesized by a slight modification of the method described earlier.9 Its molecular structure10 has an asymmetric unit comprising half of the porphyrin molecule along with a disordered dichloromethane molecule as solvent. The disordered dichloromethane (DCM) solvent in the lattice was not included in the refinement but was taken care of by the SQUEEZE procedure (from PLATON).8 The environment around the central Mg(II) atom is hexa-coordinated with two trans-axial O atoms of the m-methoxy group of two adjacent MgTMPP molecules (Figure 1 a). Interestingly, 1 shows the 1D coordination polymer arrangements (Supporting Information, Figure S2). The existence of preferentially a 1D polymer is important in the present case because the solvent-dependent reversible penta- and hexacoordination motifs resulting in the interchange in 1D and 2D supramolecular designs of a cobalt porphyrin is known.11 In 1, the four Mg N(py) bonds consist of two sets of equal length 2.038(3) and 2.058(3) Å as exists in the opposite pairs. The axial Mg O bond length, 2.409(5) Å, is within the reported Mg O distance (∼2.49).12 So, in 1, the Mg O bond may be treated as a pure coordinate bond. Both O C bonds (O CH3 and O aryl) that are attached to the Mg are significantly longer than the free O C bonds 1.386(4) vs 1.370 and 1.438(5) vs 1.420 Å, which also corroborates strong Mg O interaction. The splitting of the m- and p-methoxy carbon peak along with their downfield shift (with respect to the free base porphyrin) in the 13C NMR spectrum (Figure S1 in Supporting Information) of complex 1 suggests asymmetry in the molecule, which may be due to the interaction between magnesium and oxygen.4a,13 Interesting intermolecular interactions are present among the adjacent 1D coordination polymer of both 1 and 2. Figure S3, Supporting Information, shows such C H 3 3 3 π interactions.14 The meso-aryl rings of 1 are at an unequal orientation with the mmethoxy C H of the adjacent 1D polymers with a distance of (3.23 Å). Each 1D coordination chain is interconnected with the adjacent chain through this C H 3 3 3 π (3.23 Å) interaction. The center to center distance between the adjacent chains in 1 is 14.2 Å. These interconnected 1D coordination chains may be arranged in a 5411

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Figure 2. (a) Stereoview of the crystal structure of 2 approximately through the b axis and (b) packing motifs of 2 showing the interconnected one-dimensional coordination polymer through C H 3 3 3 π interactions. Intermolecular contacts are shown as dotted black lines.

layer structure. The layered structure of complex 1 is shown in Figure S3 of Supporting Information. Similar to 1, its corresponding zinc analogue 2, which was synthesized by a one-pot synthetic procedure,15 also crystallizes in the monoclinic system with space group C2/c.16 The asymmetric unit of complex 2 also consists of half of the porphyrin molecule along with half of a dichloromethane solvent. As shown in Figures 1b and 2, here also the central Zn(II) atom is hexacoordinated with two trans-axial O atoms of the m-methoxy group of two adjacent ZnTMPP molecules. The 1D coordination structure is produced by forming hexa-coordinated Zn using O atoms of m-methoxy groups of two adjacent porphyrins similar to 1. Interestingly the zinc oxygen coordination is through mmethoxy oxygen, while it is through p-methoxy in the case of CoTMPP.11 Such coordination structures with zinc oxygen bonds from the peripheral tetraphenyl moiety are limited.4 The Zn N(py) bonds of 2 are almost equal in length (2.038(3) 2.058(3) Å). The axial Zn O bond length is 2.519(5) Å, within the range of a six-coordinated Zn O bond.4 The lengthening of O C bonds (O CH3 and O-phenyl, 1.438(5) and 1.386 (4) Å for O C bond of oxygen no. 3) that are attached to zinc compared with the free O C bonds (1.420(5) and 1.370 (4) Å for O C bond of oxygen no 1), similar to 1, also indicate zinc oxygen interaction. So the Zn O bond can be considered as a pure coordination bond. Each coordination polymer chain of 2 is weakly interconnected with adjacent polymer chains through C H 3 3 3 π (3.20 Å) interactions of the m-methoxy group and meso-phenyl ring and concomitantly formed layer structures as shown in Figure 2b. Although X-ray crystallographic analysis indicates that 1 is a hexa-coordinated 1D coordination polymer (1D geometrical motif), its self-assembly in the nano domain is as a nanosphere. The assembly of 1(3  10 4 M) from DCM and petroleum ether mixture when placed on a brass stub and after immediate evaporation, subjected to scanning electron microscopy (SEM), shows nanospherical (3D geometrical motif) shape in assorted sizes from 200 to 500 nm in diameter (Figure 3). The size of these nanospheres show wide distribution from 200 nm to 1 μm with more than half in the 400 600 nm range (Figure 3b). The higher resolution SEM images along with their corresponding energydispersive X-ray (EDX) spectrum of the nanosphere is shown in Figure S4 of Supporting Information. Further in HPOG matrix, the atomic force microscopy (AFM) clearly shows its spherical shape with the height of the spheres around 200 nm and with the average diameter 300 nm. At 10 4 M concentration, 1 exists as a monomer with some interaction, but during the nucleation stage, a high diffusion flux of monomers into the diffusion layer forms

Figure 3. (a) SEM images of nanospheres, (b) particle size distribution histogram of the nanospheres, (c) AFM images of nanospheres on HOPG, and (d) optical fluorescence image of the nanospheres on a glass plate.

the favored 1D (rodlike) structure on the highest energy surface, but as the monomer concentration drops, low diffusion flux induces an equidirectional growth of the nanocrystals forming nanospheres (3D). A similar type of 0D growth of Cd Se nanocrystals (quantum dots) is known.17 Such self-organized and well-defined structures result spontaneously from the component of the systems at room temperature. Such assembly appears to be of general interest for polymer and macromolecular chemistry where the spherical shape is achieved based on the principle of minimizing the surface area. Such spherical assembly is reminiscent of the spherical shape adopted by native chlorophyll a.18 Once we succeeded in observing the nanosphere shape for 1, we extended our search for a similar shape for 2 also. A drop of 2 (10 4 M, DCM and petroleum ether mixture) was placed on a brass stub, and when the drop was dried, it was analyzed by scanning electron microscopy (SEM). The SEM micrograph showed assorted nanorods instead of nanospheres of diameter 100 nm to 1.4 μm, and the diameter distribution histogram clearly indicates that 52% of the nanorods are within the range 100 400 nm (Figure 4a and Figure S6 of Supporting Information). It is known that the morphology of nanoparticles can be changed due to the kinetics and thermodynamics of selfassembly during nanoparticle formation, which depends on the different solubility in solvent molecules and the difference in their viscosities. But in the same solvent mixture different structures for two metals are interesting. We anticipate that such difference may be due to the varied amount of π π interactions and metal oxygen interactions of these two porphyrins in the nanoenvironment. Transmission electron microscopy (TEM) on a carboncoated copper grid of 2 from the same solvent mixture also revealed rodlike structures with almost 20 nm diameters (Figure 5a). The EDX spectrum of the nanorod clearly shows the presence of all the atoms present in 2 (Figure S5 in the Supporting Information). Formation of an ordered array of mesoscopic structures in moist solvents with density higher than water on polymer surfaces is known due to the formation of air 5412

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Figure 4. (a) SEM image of the nanorods, inset higher magnification SEM image, (b) optical fluorescence image of the rods on glass plate, (c) SEM image of the rectangle, inset higher magnification SEM image, (d) optical fluorescence image of the rectangles on a glass plate, (e, f) SEM images of rings at low and high magnification, respectively.

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bubbles.19 In chloroform medium, such nanorod self-organization concomitantly coupled with the formation of air bubbles led to transformation of the rod to a ring shape (Figure 4e,f and Figure S8 of Supporting Information). When one drop of 10 4 M solution of 2 in chloroform was placed on a carbon-coated copper grid and analyzed by TEM it showed beautiful rings (Figure 5c). When the same copper grid after pasting on a brass stub by carbon tape was analyzed by SEM, it revealed similar ringshaped structures (Figure 4e,f). At this stage, such structures may be related to the zinc oxygen coordination, and therefore we checked its aggregation in a coordinating solvent like ethanol. In ethanol, it formed rectangles of assorted width, 600 nm to 2.3 μm with several micrometers (1 20) length (Figure 4c and Figure S6b of Supporting Information). Here ethanol coordinates as an axial ligand preventing the formation of the Zn O ( OCH3) bond concomitantly changing the morphology to rectangles. We could not get good diffraction-quality crystals in ethanol medium to verify the crystal structure of ZnTMPP, but it is well-known that alcohol coordinates with zinc porphyrin easily. The zinc oxygen (from the peripheral methoxy group) interaction is important to decide the aggregation, which is disrupted under a coordinating solvent like ethanol to form discrete molecules with ethanol coordination. The 13C NMR data show the retention of such a zinc methoxy association in a noncoordinating solvent like DCM (Figure S1b, Supporting Information). The crystal structure confirms the presence of such a zinc methoxy interaction in the solid state as was found with 13C NMR. This shows the conservation of the structural aggregation in solution similar to that present in the solid state.

’ CONCLUSION The crystal structures of [Mg(TMPP)] (1) and [Zn(TMPP)] (2) (TMPP = 3,4,5-trimethoxyphenylporphyrin) show one-dimensional (1D) coordination polymer structures through metal oxygen (oxygen atom from m-methoxy group of adjacent porphyrin) bonds. These polymers are produced by forming hexa-coordinated metal (Mg and Zn) using O atoms of m-methoxy groups of two adjacent cofacial porphyrins. This TMPP ligand has a strong ability to form beautiful self-assembled multiporphyrin arrays, which is of interest in relation to several biological light-harvesting complexes. In the nano domain, the selforganization of 1 in dichloromethane petroleum ether results in spherical shape, but 2 self-organizes as nanorods. In a coordinating solvent like ethanol, 1 and 2 aggregate as rectangles. The detailed photophysical studies of these varied forms and shapes are in progress. ’ ASSOCIATED CONTENT

bS

Supporting Information. The synthetic procedures, 13C NMR spectra of free ligand TMPP, 1, and 2, EDX analysis, diameter distribution histograms of 1 and 2 at different states, and X-ray structural data of 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Figure 5. TEM images of (a) the nanorod, (b) the rectangle, and (c) the ring.

Corresponding Author

*E-mail address: abya@iitk,ac.in. 5413

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’ ACKNOWLEDGMENT J.B. acknowledges Doctoral Research Fellowships from the CSIR, New Delhi, and S.S. thanks the DST, New Delhi, for funding the project. ’ REFERENCES (1) (a) Wasielewski, M. R. J. Org. Chem. 2006, 71, 5051–5066. (b) Drain, C. M.; Varotto, A.; Radivojevic, I. Chem. Rev. 2009, 109, 1630–1658. (c) Medforth, C. J.; Wang, Z.; Martin, K. E.; Song, Y.; Jacobsen, J. L.; Shelnutt, J. A. Chem. Commun. 2009, 7261–7277. (d) Gao, Y.; Zhang, X.; Ma, C.; Li, X.; Jiang, J. J. Am. Chem. Soc. 2008, 130, 17044–17052. (e) Wang, Z; Medforth, C. J.; Shelnutt, J. A. J. Am. Chem. Soc. 2004, 126, 15954–15955. (f) Lee, S. J.; Malliakas, C. D.; Kanatzidis, M. G.; Hupp, J. T.; Nguyen, S. T. Adv. Mater. 2008, 20, 3543–3549. (g) Nakanishi, T.; Kojima, T.; Ohkubo, K.; Hasobe T.; Nakayama, K.; Fukuzumi, S. Chem. Mater. 2008, 20, 7492–7500. (h) Borras, A.; Aguirre, M.; Groening, O.; Lopez-Cartes, C.; Groening, P. Chem. Mater. 2008, 20, 7371–7373. (i) Yoon, S. M.; Hwang, I. C.; Kim, K. S.; Choi, H. C. Angew. Chem., Int. Ed. 2009, 48, 2506–2509. (2) (a) Sakamoto, J.; Heijst, J.; Lukin, O.; Schluter, A. D. Angew. Chem., Int. Ed. 2009, 48, 1030–1069. (b) Lipstman, S.; Goldberg, I. Cryst. Growth Des. 2010, 10, 5001–5006. (c) Ptaszek, M.; Yao, Z.; Savithri, D.; Boyle, P. .D.; Lindsey, J. S. Tetrahedron 2007, 63, 12629–12638. (d) Sharma, C. V. K.; Broker, G. A.; Huddleston, J. G.; Baldwin, J. W.; Metzger, R. M.; Rogers, R. D. J. Am. Chem. Soc. 1999, 121, 1137–1144. (e) Muniappan, S.; Lipstman, S.; George, S.; Goldberg, I. Inorg. Chem. 2007, 46, 5544–5554. (f) Karmakar, A.; Goldberg, I. CrystEngComm 2010, 12, 4095–4100. (f) Bhuyan, J.; Sarkar, R.; Sarkar, S. Angew. Chem., Int. Ed. 2011, DOI: 10.1002/anie.201103876. (3) (a) Krupitsky, H.; Stein, Z.; Goldberg, I.; Strouse, C. E. J. Inclusion Phenom. 1994, 18, 177–192. (b) Barkigia, K. M.; Battioni, P.; Riou, V.; Mansuy, D.; Fajer, J. Chem. Commun. 2002, 956–957. (c) Deiters, E.; Bulach, V.; Kyritsakas, N.; Hosseini, M. W. New J. Chem. 2005, 29 1508–1513. (4) (a) Teo, T. L.; Vetrichelvan, M.; Lai, Y. H. Org. Lett. 2003, 5, 4207–4210. (b) Adilov, S.; Thalladi, V. R. Cryst. Growth Des. 2007, 7, 481–484. (5) (a) Wang, Z.; Lybarger, L. E; Wang, W.; Medforth, C. J.; Miller, J. E.; Shelnutt, J. A. Nanotechnology 2008, 19, No. 395604. (b) Heim, D.; Ecija, D.; Seufert, K.; Auwarter, W.; Aurisicchio, C.; Fabbro, C.; Bonifazi, D.; Barth, J. V. J. Am. Chem. Soc. 2010, 132, 6783–6790. (6) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115–119. (7) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Analysis, Release 97-2; University of G€ottingen: G€ottingen, Germany, 1997. (8) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13. (9) (a) Lindsey, J. S.; Woodford, J. N. Inorg. Chem. 1995, 34 1063–1069. (b) Zhang, J.; Zhang, P.; Zhang, Z.; Wei, X. J. Phys. Chem. A 2009, 113, 5367–5374. (10) Detailed synthesis, see Supporting Information. Crystallographic data for 1: C57H54Cl2N4O12Mg, Mr = 1082.25, 0.10  0.06  0.04 mm3, monoclinic, a = 15.491(5), b = 25.283(5), c = 14.293(5) Å, α = 90.000°, β = 108.877(7)°, γ = 90.000°, V = 5297(3) Å3, space group C2/c, Z = 4, λ(Mo Kα) = 0.71073 Å, T = 100(2) K, 14679 reflections, 5185 unique. After SQUEEZE, R1 = 0.0743, ωR2 = 0.2048. (11) Maji, S.; Kumar, A.; Pal, K.; Sarkar, S. Inorg. Chem. 2005, 44, 7277–7279. (12) (a) Bock, C. W.; Kaufman, A.; Glusker, J. P. Inorg. Chem. 1994, 33, 419–427. (b) Dove, A. P.; Gibson, V. C.; Marshall, E. L; White, A. J. P.; Williams, D. J. Dalton Trans. 2004, 570–578. (13) Saleh, R. Y.; Straub, D. K. Inorg. Chim. Acta 1989, 156, 9–11. (14) (a) Bhyrappa, P.; Wilson, S. R.; Suslick, K. S. J. Am. Chem. Soc. 1997, 119, 8492–8502. (b) Hunter, R.; Haueisen, R. H.; Irving, A. Angew. Chem., Int. Ed. 1994, 33, 566–568. (c) Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441–449.

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