Macrocycle Containing Phosphonate-Bridged Trinuclear Subunits

Apr 28, 2014 - magnets. Two broad strategies are in vogue for the assembly of polynuclear complexes. The first of these called the serendipity method ...
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A 30-Membered Nonanuclear Cobalt(II) Macrocycle Containing Phosphonate-Bridged Trinuclear Subunits Dipankar Sahoo,† Ramakirushnan Suriyanarayanan,‡ and Vadapalli Chandrasekhar*,†,§ †

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India Department of Chemistry, University of the Free State, P. O. Box 339, Bloemfontein 9300, South Africa § National Institute of Science Education and Research, Institute of Physics Campus, Sachivalaya Marg, Sainik School Road, Bhubaneshwar 751005, Orissa, India ‡

S Supporting Information *

ABSTRACT: The reaction of Co(ClO4)2·6H2O with (trichloromethyl)phosphonic acid and 3,5-dimethyl-1H-pyrazole in a 3:1:6 ratio in the presence of triethylamine afforded [Co9(3,5-DMPz)12(3,5-DMPzH)6(Cl3CPO3)3](toluene)7 (1). The latter contains three trinuclear (Co3) subunits which are linked to each other by three bridging phosphonate ligands affording a 30-membered macrocycle. 1 contains an equilateral triangle comprising the phosphorus atoms of the bridging phosphonate groups. In solution, 1 breaks down into the trinuclear subunits as detected by electrospray ionization mass spectrometry.

P

Scheme 1. Synthesis of 1

olynuclear complexes have received a lot of attention in recent years because of a variety of reasons.1 These include

Chart 1. Schematic Representation of [P(S){N(Me)NCHC6H4-o-O}3]2Co3

the challenges in their synthesis, interest in their structural features, and the properties of some of these compounds.1 For example, many polynuclear 3d,2 3d/4f,3 and 4f4 complexes have been shown to be extremely useful in the field of molecular magnets. Two broad strategies are in vogue for the assembly of polynuclear complexes. The first of these called the serendipity method utilizes polyfunctional ligands containing diverse coordination sites.5 In most cases this approach leads to compounds whose composition and structure cannot be predicted a priori.6 On the other hand a number of novel assemblies which could not have been designed otherwise have been prepared by using this method.6 We ourselves have profitably employed this approach to prepare polynuclear complexes, containing diverse transition metal ions, whose nuclearity and structure could be varied significantly by altering the reaction conditions.7 The second synthetic methodology relies on a precise design of the ligand and therefore allows the assembly of complexes of specific nuclearity and structure.8 Utilizing this approach, we have designed a phosphorus supported ligand, P(S)[N(Me)NCH-C6H4-o-OH]3, which in its reactions with divalent metal ions affords trinuclear © XXXX American Chemical Society

complexes such as [P(S){N(Me)NCH-C6H4-o-O}3]2Co3 (Chart 1).9 Modification of this ligand to (S)P[N(Me)N CH-C6H3-2-OH-3-OMe]3 allowed the preparation of heterometallic (3d/4f) trinuclear complexes such as [{(S)P[N(Me)NCH-C 6 H 3 -2-O-3-OMe] 3 } 2 Co 2 Ln]ClO 4 ·2CHCl 3 ·4H 2 O Received: March 15, 2014 Revised: April 16, 2014

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Information. 1 is a nonanuclear-Co(II) molecular aggregate, [Co9(3,5-DMPz)12(3,5-DMPzH)6(Cl3CPO3)2](toluene)7 (Figures 1 and 2). It is a 30-membered macrocycle containing three identical trinuclear motifs [Co3(3,5-DMPz)4(3,5-DMPzH)2] that are connected to each other by three [Cl3CPO3]2− ligands bridging in 2.110 coordination mode (Harris Notation13) (Chart 2). Each of the three subunits of the macrocycle are identical and contain three cobalt centers and six pyrazole ligands (of these, four are deprotonated while two are neutral). Adjacent cobalt centers are bridged by a pair of deprotonated pyrazole units (η1,η1 coordination) generating a Co2N4 sixmembered ring (Figure 2). Pyrazole or hydrazine bridged Co(II) polynuclear systems have been reported by other groups, but in most of the cases Co(II) is hexacoordinate in an octahedral geometry.14 Two adjacent Co2N4 rings join together at the central Co(II) ions, and the intersection of the planes formed by the atom of each ring make a dihedral angle of ∼111° (Supporting Information). The 30-membered macrocycle contains within it six 6-membered Co2N4 rings (Figure 2). All the cobalt centers are tetracoordinate in a tetrahedral geometry. While the central Co(II) possesses a 4N coordination environment (all from deprotonated pyrazole ligands), the two terminal Co(II) atoms possess a 3N,1O coordination mode involving two deprotonated pyrazole ligands, one neutral pyrazole ligand and one oxygen atom from a bridging phosphonate ligand. The average Co−N (deprotonated pyrazole) distance of 1.97 Å is slightly less than that of the average Co−N (neutral pyrazole) distance of 2.05 Å. Within the trinuclear motif the three Co(II) atoms are arranged in a nearly linear manner (Figure 2b) (Co1---Co2, 3.6 Å; Co2---Co3, 3.6 Å; Co1---Co2, 7.2 Å; Co1---Co2---Co3, 172°). A comparison of the structural parameters within the trinuclear motif in the current instance with that found by us previously in discrete trinuclear complexes is presented in the Supporting Information. The trinuclear motifs of 1 are interconnected through the phosphonate ligands which bridge the terminal Co(II) centers (Figure 1). Interestingly, the phosphorus atoms of the bridging phosphonate groups occupy the vertices of an equilateral triangle (Figure 3). In order to assess the structural integrity of 1 in solution we carried out its electrospray ionization mass spectrometry (ESIMS) in acetonitrile under positive ion conditions. It has been found that 1 fragments under these conditions to its trinuclear repetitive unit (Supporting Information). The supramolecular architecture of 1 consists of macrocyclic layers with ab type packing and a supramolecular channel. The molecule is surrounded by a large number of toluene molecules (Supporting Information).

Chart 2. Coordination Mode of the Phosphonate Ligand, [Cl3CPO3]2−a

a

Harris notation13 has been used.

Figure 1. Molecular structure of 1 (solvent molecules and some H atoms have been deleted for clarity).

(Ln = Dy, Gd, Tb, Ho, Er) (Supporting Information), which was shown to be a single-molecule magnet.10 With this family of ligands, always precisely, linear trinuclear complexes were obtained. On the other hand using organophosphonates/ ancillary nitrogen ligands we were able to modulate the nuclearity of the complexes, prompting us to explore this methodology further.11 Accordingly, herein, we report the synthesis and structural characterization of a novel nonanuclear 30-membered macrocycle, [Co9(3,5-DMPz)12(3,5-DMPzH)6(Cl3CPO3)3](toluene)7 (1) [3,5-DMPzH = 3,5-dimethyl-1Hpyrazole].12 The latter contains three linear trinuclear Co3 motifs which are linked to each other by three bridging phosphonate ligands (Figure 1). The reaction of Co(ClO4)2·6H2O with (trichloromethyl)phosphonic acid using 3,5-dimethyl-1H-pyrazole as the ancillary ligand in a 3:1:6 ratio in the presence of triethylamine, as a hydrogen chloride scavenger, in acetonitrile, at room temperature, afforded a solid which upon crystallization gave shining violet crystals of 1 (Scheme 1). The molecular structure of 1 was determined by X-ray crystallography. Details of the data collection and refinement parameters for 1 have been provided in the Supporting



ASSOCIATED CONTENT

S Supporting Information *

Experimental section, crystallographic information file (CIF), crystal data and structure refinement parameters of 1, tables of bond distances (Å) and bond angles (°), coordination environments around metal centers, Figures S1−S3, Charts S1−S2, and Tables S1−S3. This material is available free of charge via the Internet at http://pubs.acs.org.



AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. Phone: (+91) 512-2597259. Fax: (+91) 521-259-0007/7436. B

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Figure 2. (a) Thirty-membered Co9N24P3O6 macrocycle (all the C, H and some O atoms have been deleted for clarity. (b) The trinuclear unit, [Co3(3,5-DMPz)4(3,5DMPzH)2] of the macrocycle. Selected bond distances (in Å) and bond angles (in deg.): Co1−N2, 2.061(15); Co1−N3, 1.997(12); Co1−N6, 1.951(12); Co1−O1, 1.948(11); Co2−N9, 1.974(13); Co2−N4, 1.967(11); Co2−N5, 1.961(12); Co2−N7, 1.980(13); Co3− N11, 2.055(15); Co3−N10, 1.961(12); Co3−N8, 1.949(14); Co3−O4, 1.925(12); O1−Co1−N2, 104.2(5); N6−Co1−N2, 115.2(5); N6−Co1− N3, 109.2(5); O1−Co1−N3, 114.1(5); O1−Co1−N6, 107.5(5); N3−Co1−N2, 106.7(5); N4−Co2−N9, 113.8(5); N5−Co2−N4, 109.3(5); N4− Co2−N7, 101.9(5); N5−Co2−N9, 103.7(5); N9−Co2−N7, 110.1(5); N5−Co2−N7, 118.5(5); O4−Co3−N10, 109.3(5); N8−Co3−N11, 113.1(5); N8−Co3−N10, 108.6(5); O4−Co3−N11, 104.7(5); O4−Co3−N8, 113.9(5); N10−Co3−N11, 106.9(6). Inorg. Chem. 2014, 53, 1662. (c) Lamouchi, M.; Jeanneau, E.; Novitchi, G.; Luneau, D.; Brioude, A.; Desroches, C. Inorg. Chem. 2014, 53, 63. (d) Mukherjee, G.; Biradha, K. Cryst. Growth Des. 2014, 14, 419. (e) Han, S.-D.; Zhao, J.-P.; Chen, Y.-Q.; Liu, S.-J.; Miao, X.-H.; Hu, T.L.; Bu, X.-H. Cryst. Growth Des. 2014, 14, 2. (f) Beavers, C. M.; Prosvirin, A. V.; Cashion, J. D.; Dunbar, K. R.; Richards, A. F. Inorg. Chem. 2013, 52, 7817. (g) Clearfield, A.; Demadis, K. Metal Phosphonate Chemistry; RSC: Cambridge, U.K., 2012. (h) Zhang, P.; Guo, Y.-N.; Tang, J. Coord. Chem. Rev. 2013, 257, 1728. (i) Perry, J. J., IV; Kravtsov, V. C.; Zaworotko, M. J.; Larsen, R. W. Cryst. Growth Des. 2011, 11, 3183. (j) Layfield, R. A. Organometallics 2014, 33, 1084. (2) (a) Tsai, H.-L.; Schake, A. R.; Wang, S.; Vincent, J. B.; Folting, K.; Gatteschi, D.; Christou, G.; Hendrickso, D. N. J. Am. Chem. Soc. 1993, 115, 1804. (b) Chandrasekhar, V.; Dey, A.; Mota, A. J.; Colacio, E. Inorg. Chem. 2013, 52, 4554. (c) Murrie, M. Chem. Soc. Rev. 2010, 39, 1986. (d) Vallejo, J.; Castro, I.; Ruiz-Garcia, R.; Cano, J.; Julve, M.; Lloret, F.; Munno, G. D.; Wernsdorfer, W.; Pardo, E. J. Am. Chem. Soc. 2012, 134, 15704. (e) Zadrozny, J. M.; Liu, J.; Piro, N. A.; Chang, C. J.; Hill, S.; Long, J. R. Chem. Commun. 2012, 48, 3927. (f) Klinke, F. J.; Das, A.; Demeshko, S.; Dechert, S.; Meyer, F. Inorg. Chem. 2014, 53, 2976−2982. (g) Lampropoulos, C.; Redler, G.; Data, S.; Abboud, K. A.; Hill, S.; Christou, G. Inorg. Chem. 2010, 49, 1325. (h) Taguchi, T.; Wernsdorfer, W.; Abboud, K. A.; Christou, G. Inorg. Chem. 2010, 49, 199. (3) (a) Mondal, K. C.; Sundt, A.; Lan, Y.; Kostakis, G. E.; Waldmann, O.; Ungur, L.; Chibotaru, L. F.; Anson, C. E.; Powell, A. K. Angew. Chem., Int. Ed. 2012, 51, 7550. (b) Chandrasekhar, V.; Bag, P.; Speldrich, M.; van Leusen, J.; Kögerler, P. Inorg. Chem. 2013, 52, 5035. (c) Chandrasekhar, V.; Dey, A.; Das, S.; Rouzières, M.; Clérac, R. Inorg. Chem. 2013, 52, 2588. (d) Chandrasekhar, V.; Bag, P.; Kroener, W.; Gieb, K.; Müller, P. Inorg. Chem. 2013, 52, 13078. (e) Mossin, S.; Tran, B. L.; Adhikari, D.; Pink, M.; Heinemann, F. W.; Sutter, J.; Szilagyi, R. K.; Meyer, K.; Mindiola, D. J. J. Am. Chem. Soc. 2012, 134, 13651. (f) Prasad, T. K.; Poneti, G.; Sorace, L.; Rodriguez-Douton, M. J.; Barra, A. L.; Neugebauer, P.; Costantino, L.; Sessoli, R.; Cornia, A. Dalton Trans. 2012, 41, 8368. (g) Petit, S.; Neugebauer, P.; Pilet, G.; Chastanet, G.; Barra, A. L.; Antunes, A. B.; Wernsdorfer, W.; Luneau, D. Inorg. Chem. 2012, 51, 6645. (h) Colacio, E.; Ruiz, J.; Mota, A. J.; Palacios, M. A.; Cremades, E.; Ruiz, E.; White, F. J.; Brechin, E. K.

Figure 3. An equilateral triangle containing phosphorus corner atoms, in 1.

Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS We thank the Department of Science and Technology, India, and the Council of Scientific and Industrial Research, India, for financial support. V.C. is thankful to the Department of Science and Technology for a J. C. Bose fellowship. D.S. thanks the Council of Scientific and Industrial Research, India, for a Senior Research Fellowship.



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