摘要:
Rhodium–tetranuclear complexes as building blocks for the construction of coordination polymers: chiroselectivity in the formation of [ClCuRh4(µ-PyS2)2(cod)4]n (H2PyS2 = 2,6-dimercaptopyridine) Miguel A. Casado, Jesús J. Pérez-Torrente, Andrew J. Edwards, Luis A. Oro,* Miguel A. Ciriano* and Fernando J. Lahoz Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C., 50009-Zaragoza, Spain. E-mails: oro@posta.unizar.es; mciriano@posta.unizar.es Received 14th June 2000, Accepted 7th July 2000, Published 19th July 2000 The reaction of the complex [Rh4(µ-PyS2)2(cod)4], containing two juxtaposed coordination donor sites, with CuCl creates the coordination polymer [ClCuRh4(µ-PyS2)2(cod)4]n. This polymeric structure results from the self-assembly of alternating rhodium tetranuclear complexes and CuCl as linking units, and shows zigzag chains containing exclusively homochiral tetranuclear building blocks.Monoclinic P21/n 9.9690(10) 16.300(3) 27.737(5) 92.42(2) 44503.1(12) 2.261 293(2) 0.0580 3747 0.152 0.995 Introduction Self-assembly phenomena through metal coordination have shown remarkable potential in the construction of solid-state architectures.1 Moreover, the design of metalloorganic polymeric networks based on organometallic and coordination compounds is a topic of current interest and the control of the self-assembly of coordination polymers presents an interesting challenge.2 Coordination polymers have been typically obtained by simple mixing of metal cations and polydentate ligands, the dimensionality and topology being predominantly controlled by the coordination preferences of the metal centre and the structure of the bridging ligand.3 The formation of extended solids by the assembly of metal complexes could be a powerful synthetic method for the design of new materials if the appropriate linkers are used.4 For example, the rod-shaped dicyanoargentate(I) complex can bridge additional metal centres linked to secondary ligands to produce multidimensional coordination polymers.5 Mononuclear transition metal isocyanide complexes carrying cyano groups in peripheral sites are also effective building blocks for coordination polymers.6 In the same way, dinuclear [{(CH2)n(PPh2)2}Au2]2+ complexes have been assembled using rigid-rod ligands such as trans-1,2- bis(4-pyridyl)ethylene.7 We envisaged the formation of molecular networks from polynuclear complexes as building blocks, assuming that the polynuclear entities have available coordination donor sites oriented in a divergent fashion to be glued by further metal atoms.In this context, we decided to explore the chemistry of the chiral tetranuclear complex [Rh4(µ-PyS2)2(cod)4] (1), which contains four d8 rhodium centres supported by two 2,6-pyridinedithiolate (PyS22–) ligands8 and two juxtaposed donor sites at the peripheral sulfur atoms prone to bind suitable metal centres, making thus possible the controlled construction of heterometallic coordination polymers.The viability of this new approach is shown in the present paper by the formation of a one-dimensional Rh–Cu heteronuclear coordination polymer, which additionally shows the self-organisation of homochiral tetrarhodium units in the chains. DOI: 10.1039/b004750n Results The reaction of [Rh4(µ-PyS2)2(cod)4] (1) with an excess of CuCl in dichloromethane at room temperature gives a dark red solution from which compound 2 is isolated as an orange solid.† Compound [ClCuRh4(µ-PyS2)2(cod)4]n (2) is a non-conductor in chloroform and the analytical figures are consistent with the stoichiometric formula [ClCuRh4(µ-PyS2)2(cod)4]. Slow diffusion of n-hexane into a dichloromethane solution gave orange crystals of 2, and the structure was determined by single crystal X-ray analysis (see Table 1).Table 1 Crystal data for 2·0.5C6H14·0.665CH2Cl2a Crystal system Space group a/Å b/Å c/Å /° ZV/Å3 µ/mm–1 T/K R1 Reflections with I . (I) wR2 GOF a The structure was solved by Patterson and Fourier techniques (SHELXS-97); refinement was carried out with anisotropic displacement parameters for all non-hydrogen non-disordered atoms. Two spatial regions of heavily disordered solvent were identified and modelled with partially occupied dichloromethane and hexane molecules (more details in supporting information). Hydrogen atoms of the metallic complex were included in calculated positions and refined riding on carbon atoms. Click here for full crystallographic data (CCDC no. 1350/29).CrystEngComm, 2000, 23The compound [ClCuRh4(µ-PyS2)2(cod)4]n (2) is an infinite coordination polymer resulting from the self-assembly of alternating [Rh4(µ-PyS2)2(cod)4] (1) complexes and CuCl as linking units. The independent unit (Fig. 1) propagates along a screw twofold axis to form chain arrangements constituted of homochiral tetranuclear building blocks (see below). Each CuCl unit is bonded to two tetranuclear rhodium complexes through the outer sulfur atoms of the framework resulting in a trigonal-planar coordination for the copper ion. Accordingly, each tetranuclear rhodium complex is bonded to two CuCl molecules that are directed away from the bulky 1,5-cyclooctadiene ligands on the neighbouring rhodium atoms (Fig.2). The interaction of complex 1 with CuCl produces no significant structural changes within the framework of the tetranuclear building block although a modification of the rhodium–rhodium distances is observed. Thus, a shortening of the internal intermetallic distance, Rh(2)···Rh(4), from 3.9210(6) Å in 1 to Fig. 1 Asymmetric unit of the polymer [ClCuRh4(µ-PyS2)2(cod)4]n (2) with indication of the labelling scheme used. Selected bond lengths (Å) and angles (°): Rh(1)–S(1) 2.384(3), Rh(1)–S(4) 2.383(3), Rh(1)–C(cod) 2.153(6), Rh(2)–S(2) 2.380(3), Rh(2)–N(2) 2.079(9), Rh(2)–C(cod) 2.149(6), Rh(3)–S(3) 2.385(3), Rh(3)–S(2) 2.400(3), Rh(3)–C(cod) 2.152(6), Rh(4)–S(4) 2.371(3), Rh(4)–N(1) 2.099(9), Rh(4)–C(cod) 2.131(6), Cu–Cl 2.279(4), Cu–S(1) 2.288(4), Cu–S(3') 2.277(3), S(1)– Rh(1)–S(4) 98.25(10), S(2)–Rh(2)–N(2) 87.4(3), S(2)–Rh(3)–S(3) 97.81(10), S(4)–Rh(4)–N(1) 87.6(3), Cl–Cu–S(1) 113.67(15), Cl–Cu–S(3') 117.93(15), S(1)–Cu–S(3') 128.36(13) (symmetry transformation for primed atom: 1/2 – x, 1/2 – y, 1/2 – z).Click on image or here for a 3D representation. Fig. 2 View of a portion of the two homochiral infinite chains of [ClCuRh4(µ-PyS2)2(cod)4]n (2) showing the packing complementarity and the enantiomeric relationship of both polymeric structures (crystallographic b axis across; chirality for the sulfur atoms is indicated as a subscript). Colour codes are: sulfur (yellow), chlorine (green), nitrogen (blue), rhodium (pink), copper (dark grey), and carbon (grey).Click on image or here for a 3D representation. 2 3.682(14) Å in 2, together with a lengthening of the external Rh···Rh separations from 3.1435(5) Å in 1 to 3.263(12) Å (mean value) in 2 have been detected. Both 2,6-pyridinedithiolate ligands in 2 are bonded to the five metal atoms acting as an eight-electron donor. Thus, both sulfur atoms of the PyS 2– ligands are coordinated in a µ2-fashion, one to two rhodium atoms and the other to a third rhodium and to the copper atoms, the pyridinic nitrogen being bonded to the fourth rhodium centre (Fig. 1). Each rhodium centre completes its coordination environment linked to the two olefinic bonds of a 1,5-cyclooctadiene molecule maintaining a reasonable square-planar geometry.The more striking feature of the solid state structure of [ClCuRh4(µ-PyS2)2(cod)4]n (2) concerns the chiroselectivity observed in the formation of the polymeric chain. The tetranuclear compound [Rh4(µ-PyS2)2(cod)4] (1) possesses a stereogenic (C2) S,RS)–(1) and (SS,SS)–(1) since both sulfur atoms µ2-coordinated axis and exits as a pair of enantiomers which can be designed as (R are stereogenic.9 Obviously, both enantiomers are present in the crystal structure of 2 (space group P21/n). However, this structure consists of a packing of alternating polymeric zigzag chains containing exclusively homochiral tetranuclear building blocks, (SS,SS)–(1) in Fig. 1.10 Taking into account that the interconversion of the enantiomers of 1 is not a simple process, the formation of the chiral infinite zigzag chains is a rare example of chiral selection during the self-assembly process.Chiroselective self-assembly of [2 × 2] grid-type inorganic arrays with octahedral metal centres has been recently reported.11 Diastereoselectivity has also been observed in the self-assembly of molecular squares based on palladium and platinum square-planar12 and octahedral molybdenum13 complexes, respectively. On the other hand, a related 2D phenomenon in a supramolecular 3D hydrogen-bonded network derived from diacetylene dicarboxylic acid dihydrate has been noticed.14 The ordered build-up of the polymeric structure suggests that probably the compound [ClCuRh4(µ-PyS2)2(cod)4]n (2) is labile in solution. Moreover, the fragmentation of the polymeric structure in solution becomes evident after the determination of a remarkably low molecular weight (a mean value of 1730 is measured in chloroform).In addition, the aromatic region of the 1H NMR spectrum in [2H6]benzene at room temperature is outstandingly simple and indicative of the presence of two well defined molecular species in solution. It is noticeable that the tetranuclear complex 1 is not observed. On the other hand, the FAB+ mass spectrum also shows key species resulting from the fragmentation of the polymer. These observations suggest that Cl2Cu2–(1) (molar mass = 1323) and ClCu–(1)2 (molar mass = 2351) could be the species resulting from the fragmentation of the polymeric chain in solution.This proposal is substantiated by the following: (i) the alternated combination of both species produce the polymeric chain; (ii) the calculated average molecular weight (1837) compares well, within the experimental error, to the experimentally observed value; and (iii) the 1H NMR is compatible with the presence of both species in a 1 : 1 ratio. The trigonal-planar environment of the copper ion in the ClCu–(1)2 fragment seems to play a significant role in the chiroselectivity observed in the formation of [ClCuRh4(µ-PyS2)2(cod)4]n (2). Thus, while the species Cl2Cu2–(1) possesses a stereogenic (C2) axis and exists as a pair of enantiomers, the species ClCu–(1)2 could exist as three diastereoisomers: the pair of enantiomers ClCu–[(RS,RS)– (1)]2/ClCu–[(SS,SS)–(1)]2 and ClCu–[(RS,RS)–(1)][(SS,SS)–(1)], with C2 and CS symmetries, respectively.The inspection of molecular models suggests that the steric interaction between the bulky 1,5- cyclooctadiene groups and the bridging ligands is notably reduced if ClCu–(1)2 consists of homochiral tetranuclear complexes. As a consequence, the formation of the polymer would encompass the molecular recognition between the following chiral molecularcomponents ClCu-[(RS,RS)-(1)]2/Cl2Cu2–[(RS,RS)–(1)] and ClCu- [(SS,SS)–(1)]2/Cl2Cu2–(SS,SS)–(1)], in agreement with the crystal structure of 2. Regarding the factors controlling the molecular recognition in the self-assembly process it is worthwhile to mention that no close contacts between homochiral chains—in particular no hydrogen bonding involving the chloro ligands—have been observed in the crystal structure of 2.In conclusion, we have shown the ability of tetranuclear rhodium complexes supported by N and S donor ligands to behave as ligands for the construction of heterometallic coordination polymers. Moreover, the growing of the polymeric chains occurs with chiral-selectivity starting from an equimolecular mixture of two enantiomeric tetranuclear complexes. As distinctive molecular architectures are expected to be formed with different metal ions as linkers, further studies concerning both the scope of the synthetic strategy, the chemical behaviour and the physical properties are in progress. Acknowledgement Financial support from DGICYT (Projects PB95-221-C1 and PB94-1186) and fellowships from Diputación General de Aragón and the EU Human Capital and Mobility Programme (to M.A. Casado and A. J. Edwards, respectively) are gratefully acknowledged. References 1 J.-M. Lehn, Supramolecular Chemistry. Concepts and Perspectives, VCH, Weinheim, 1995; C. Provent and A. F. Williams, in Transition Metals in Supramolecular Chemistry, ed. J. P. Sauvage, Wiley, Chichester, 1999, ch. 4. 2 R. Robson, in Comprehensive Supramolecular Chemistry, ed. J. L. Atwood, J. E. D. Davis, D. D. Macnicol and F. Vögtl, Pergamon, Oxford, 1996, vol. 6, p. 733; R. Robson, B. F. Abrahams, S. R. Batten, R. W. Gable, B. F. Hoskins and J. Liu, Supramolecular Architecture, American Chemical Society, Washington, DC, 1992, ch.19. 3 A. J. Blake, N. R. Champness, P. Hubberstey, W.-S. Li, M. A. Withersby and M. Schröder, Coord. Chem. Rev., 1999, 183, 117; K. Biradha, C. Seward and M. J. Zaworotko, Angew. Chem., Int. Ed., 1999, 38, 9492; M. J. Zaworotko, Angew. Chem., Int. Ed., 1998, 37, 1211; G. Mislin, E. Graft, M. W. Hosseini, A. De Cian, N. Kyritsakas and J. Fischer, Chem. Commun., 1998, 2545; D. Fortin, M. Drouin and P. D. Harvey, J. Am. Chem. Soc., 1998, 120, 5351; C. Kaes, M. W. Hosseini, C. E. F. Rickard, B. W. Skelton and A. H. White, Angew. Chem., Int. Ed., 1998, 37, 920. 4 O.-S. Jung and C. G. Pierpont, J. Am. Chem. Soc., 1994, 116, 2229. 5 T. Soma, T. K. Miyamoto and T. Iwamoto, Chem. Lett., 1997, 319; T.Soma and T. Iwamoto, Inorg. Chem., 1996, 35, 1849. 6 A. Mayr and L.-F. Mao, Inorg. Chem., 1998, 37, 5776; L.-F. Mao and A. Mayr, Inorg. Chem., 1996, 35, 3183. 7 M. J. Irwin, J. J. Vittal, G. P. A. Yap and R. J. Puddephatt, J. Am. Chem. Soc., 1996, 118, 13101. 8 J. J. Pérez-Torrente, M. A. Casado, M. A. Ciriano, F. J. Lahoz and L.A. Oro, Inorg. Chem., 1996, 35, 1782. 9 Priority numbers have been assigned according to the standard sequence rule developed for carbon compounds (CIP rules), see A. von Zelewsky, Stereochemistry of Coordination Compounds, Wiley, Chichester, 1996. 10 The two peripheral sulfur atoms also become chiral centres on coordination to the CuCl linkers. All the sulfur atoms in the tetranuclear building blocks in a chain possess the same 11 D. M. Bassani, J. -M. Lehn, K. Fromm and D. Fenske, Angew. 12 P. J. Stang and B. Olenyuk, Angew. Chem., Int. Ed. Engl., 13 A.-K. Duhme, S. C. Davis and D. L. Hughes, Inorg. Chem., configuration (SS,SS, SS,SS)–1 in Fig. 1. Chem., Int. Ed., 1998, 37, 2364. 1996, 35, 732. 1998, 37, 5380. 14 J. D. Dunitz, Chem. Eur. J., 1998, 4, 745. Footnote † Preparations: [ClCuRh4(µ-PyS2)2(cod)4]n (2). CuCl (0.066 g, 0.132 mmol) was added to a solution of [Rh4(µ-PyS2)2(cod)4] (1) (0.075g, 0.066 mmol) in dichloromethane (15 ml). The resulting dark red solution was stirred at room temperature for 3 h and then filtered through celite. Concentration of the solution under vacuum and slow addition of diethyl ether resulted in obtaining the compound as an orange solid. Yield: 0.059 g (80%). Anal. calc. for C42H54ClCuN2Rh4S4: C, 41.15; H, 4.44; N, 2.28. Found: C, 41.02; H, 4.73; N, 2.26. MS (FAB+, CH2Cl2): m/z 1289 [ClCu2– (1)]+(5%), 1227 [ClCu–(1)]+ (12%), 1189 [Cu–(1)]+ (25%), 1126 (1)+ (81%). 1H NMR (C6D6, 293 K, aromatic region): 8.40 (d, 2H), 7.90 (d, 2H), 6.90 (m, 4H), 6.80 (d, 2H), 6.55 (d, 2H), 6.40 (m, 2H), 6.30 (t, 2H), 6.05 (t) (PyS22– ligands). CrystEngComm © The Royal Society of Chemistry 2000
ISSN:1466-8033
DOI:10.1039/b004750n
出版商:RSC
年代:2000
数据来源: RSC