Novel homochiral holodirected three-dimensional lead(II) coordination polymer, [Pb2(μ-bpa)3(μ-NO3)2(NO3)2]n: Spectroscopic, thermal, fluorescence and structural studies

Available online at www.sciencedirect.com

Solid State Sciences 10 (2008) 854e858 www.elsevier.com/locate/ssscie

Novel homochiral holodirected three-dimensional lead(II) coordination polymer, [Pb2(m-bpa)3(m-NO3)2(NO3)2]n: Spectroscopic, thermal, fluorescence and structural studies Alireza Aslani a, Ali Morsali a,*, Matthias Zeller b a

Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14155-4838, Tehran, Islamic Republic of Iran b Department of Chemistry, Youngstown State University, One University Plaza, P.O. Box 44555-3663, Youngstown, OH, USA Received 9 October 2007; received in revised form 26 October 2007; accepted 3 November 2007 Available online 21 November 2007

Abstract A novel homochiral holodirected coordination polymer of lead(II) nitrate with the bridging ligand 1,2-bis(4-pyridyl)ethane (bpa), [Pb2(mbpa)3(m-NO3)2(NO3)2]n (1), has been synthesized and characterized by elemental analysis, FT-IR, thermal analysis and single crystal X-ray diffraction. In 1, the lead(II) ions are doubly bridged by both bpa and nitrate ligands into a chiral infinite three-dimensional polymeric network. There are two different nine- and eight-coordinate geometries around the lead(II) ion in 1, in which the lead(II) ions have a less common holodirected geometry. Solid-state luminescent spectra of compound 1 indicate intense fluorescent emission at ca. 434 nm. Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Lead(II); Coordination polymer; Holodirected; Homochiral

The design and construction of coordination polymers is one of the most active areas of materials research [1,2]. The intense interest in these materials is driven by both their interesting network topologies and potential applications such as catalysis, molecular magnets, sensors, ion exchange, adsorption, and phase separation [3e6]. On the other hand, lead cations form a range of coordination polymers and polynuclear complexes which display interesting structural features as a consequence of the large radius of the ion, its adoption of different coordination numbers and the possible occurrence of a stereo-chemically active lone electron pair [7]. Pb2þ is employed in the present work for several reasons: (1) it has a 6s2 outer electron configuration and a large ion radius, which can lead to interesting topological arrangements [3]; (2) the absence of crystal field stabilization energy effects allows the Pb2þ ion to adopt varied coordination geometries including octahedra, tetrahedra, or

* Corresponding author. E-mail address: [email protected] (A. Morsali). 1293-2558/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2007.11.008

square planar amongst others, which give rise to novel coordination networks [4,5]; and (3) it has interesting photochemical and photophysical properties. To construct new coordination polymers we have chosen lead(II) nitrate as the node and the ligand 1,2-bis(4-pyridyl)ethane (bpa) as the spacer. bpa is known to form polynuclear complexes with transition metals [8] and may also be a good candidate as a bridging ligand for the investigation of the stereo-chemical activity of valence shell electron lone pairs in lead(II). Herein we have successfully obtained an unusual extended three-dimensional holodirected lead(II) polymer [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1) under the branched tube conditions. The title complex was prepared by the branched tube method [9,10]. Reaction between the ligand bpa and lead(II) nitrate by diffusion along a thermal gradient in a methanolic solution (the branched tube method) produced the new lead(II) coordination polymer, [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1), as colourless crystals. The compound is air-stable and highmelting and it is soluble in DMSO. The IR spectrum of the title compound shows absorption bands resulting from the skeletal vibrations of aromatic rings

A. Aslani et al. / Solid State Sciences 10 (2008) 854e858

855

Fig. 1. An ORTEP plot showing the repeating units of [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1), showing conformers TT and TG of bpa ligands. Ellipsoids are at the 30% ˚ ]: N(1)ePb(1) 2.696(4), N(2)ePb(1)#1 2.706(4), N(3)ePb(1) 2.519(4), N(4)ePb(2) 2.667(4), N(5)ePb(2) 2.668(4), probability level. Selected bond lengths [A N(6)ePb(2)#2 2.725(5), O(1)ePb(1) 2.587(4), O(2)ePb(1) 2.627(4), O(6)ePb(2) 2.639(3), O(7)ePb(2) 2.749(4). Selected bond angles [ ]: N(3)ePb(1)eO(1) 81.03(13), N(3)ePb(1)eO(2) 75.69(14), O(1)ePb(1)eO(2) 49.18(11), N(3)ePb(1)eN(1) 87.97(14), O(1)ePb(1)eN(1) 122.56(13), O(2)ePb(1)eN(1) 73.43(12), N(3)-Pb(1)eN(2)#3 77.45(14), O(1)-Pb(1)-N(2)#3 72.58(12), O(2)ePb(1)eN(2)#3 118.39(13), O(6)ePb(2)eN(4) 76.46(12), O(6)ePb(2)eN(5) 80.72(13), N(4)ePb(2)eN(5) 80.14(14), O(6)ePb(2)eN(6)#4 160.93(12), N(4)ePb(2)eN(6)#4 101.58(14), N(5)ePb(2)eN(6)#4 80.26(14), O(6)ePb(2)eO(10) 89.64(13), N(4)ePb(2)eO(10) 146.01(14), N(5)ePb(2)eO(10) 66.95(13), N(6)#4ePb(2)eO(10) 81.63(14), O(6)ePb(2)eO(4) 47.56(11), N(4)ePb(2)eO(4) 75.94(13), N(5)ePb(2)eO(4) 126.53(13), N(6)#4ePb(2)eO(4) 151.03(13), O(10)ePb(2)eO(4) 116.82(12), O(6)ePb(2)eO(7) 120.57(12), N(4)ePb(2)eO(7) 74.55(12), N(5)ePb(2)eO(7) 140.77(13), N(6)#4ePb(2)eO(7) 76.13(13), O(10)ePb(2)eO(7) 137.65(13), O(4)ePb(2)eO(7) 75.43(11). #1: x, y, z þ 1; #2: x, y1/2, z; #3: x, y, z1 #4 x, y þ 1/2.

in the 1400e1600 cm1 range. The relatively weak absorption bands at around 3010 cm1 is due to the CeH modes of the aromatic rings. Bands in the region 550e1070 cm1 can be assigned to the bending vibration of the CeH groups in or out of the aromatic plane, and to ring deformation absorptions of the pyridine moieties of the bpa ligands [11]. The n(NO3) signals are found at ca. 1392 cm1. Determination of the structure of [Pb2(m-bpa)3(m-NO3)2 (NO3)2]n (1) by X-ray crystallography [12] showed the

Fig. 2. The crystal packing in [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1) showing the three-dimensional coordination polymer.

complex to be a three-dimensional polymeric network in the solid state (Figs. 1e4). The coordination polymer displays two distinct molecular moieties within the structure so that each can exhibit a bpa ligand with a different conformation. The primary difference between them lies in the torsion angles of C(py)eCeCe C(py) in the bpa ligand, which are 74.35 , 173.29 and 178.32 , respectively. These different torsion angles of the pyridyl groups in turn cause a variation in bond lengths and angles around the lead ions in the two molecular moieties. There are three previously observed conformations of the flexible bpa ligand: TT, TG or GG (Chart 1) with quite different N-to-N distances [8,13,14]. The TT conformation has been fairly widely encountered and such structures tend to pack efficiently, whereas the GG or TG conformations are quite rare in the context of coordination polymers [13,14]. In the title compound, self-assembly leads to the inclusion of two bpa conformers, two of the TT type with N-to-N distances of ˚ (Fig. 1) and one in the TG conformation 9.282 and 9.308 A ˚ (Fig. 1). with an N-to-N distance of 7.043 A There are two distinctly different types of PbII ions in 1: a Pb(1)N3O6 sphere with a coordination number of nine (Fig. 3a) and a Pb(2)N3O5 sphere with a coordination number of eight (Fig. 3b). The stereo-chemical activity of the lone pair in divalent lead compounds is interesting and has extensively been reported in Refs. [15e18]. For the structure described here,

856

A. Aslani et al. / Solid State Sciences 10 (2008) 854e858

Fig. 3. Schematic representation of the PbII environments with no hole in the coordination sphere of [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1). #1: x, y, z þ 1.

coordination around the lead atoms is holodirected and the arrangement of the ‘‘bpa’’ ligand and nitrate anions does not suggest any gap or hole in coordination geometry around the metal, indicating that the lone pair of electrons on lead(II) is sterically inactive. The spontaneous aggregation of ‘‘bpa’’ and nitrate bridging ligands along with the high coordination number may cause the gap to disappear and the geometry of the coordination sphere of Pb2þ, Pb(1) and Pb(2) in this compound to be of the holodirected type.

Fig. 4. A view of the homochiral helix generated from the bpa ligand with the TG conformation.

Complex 1 crystallizes in the monoclinic and chiral space group P21 and has a three-dimensional structure with an M (left-handed) configuration. Interestingly, the bpa ligand displays two different conformations in each [Pb2(m-bpa)3(mNO3)2(NO3)2]n section, which is important for the formation of an infinite chiral structure. Three two different conformers of bpa ligands bridge three Pb atoms, with the Pb/Pb separa˚ , respectively. tion being 14.43, 14.40 and 10.05A The two bridging bpa ligands with TT conformation form a two-dimensional motif that is grown into a three-dimensional network by bridging with the bpa ligand with the TG conformation to form a helix (Fig. 3). However, the singlestranded infinite helices are of the same M handedness and are intertwined to form a chiral infinite three-dimensional structure (Fig. 2). In conclusion, the compound reported here is an interesting example of a homochiral infinite three-dimensional coordination polymer based on an achiral ligand. The adjacent chiral double helices are of the same chirality and are packed in a parallel fashion, leading to a homochiral solid. The thermal stability of compound 1 has been determined on a single crystalline sample between 0 and 700  C in an air atmosphere by thermogravimetric (TG) and differential thermal analyses (DTA) (Fig. 5). For compound 1, TGA shows that chemical decomposition starts at about 197  C and ends at 490  C with the weight loss of 64.20%; the remaining weight corresponds to PbO. The DTA curve displays four distinct endothermic peaks at 235, 270, 430 and 450  C as well as an exothermic peak at 480  C. Solid-state photoluminescent spectra of compound 1 were recorded at room temperature. Excited at 383 nm, compound 1 shows one broad emission spectrum centered at 434 nm (Fig. 6). These fluorescent emissions can be tentatively assigned to the intraligand fluorescence emission as similar

A. Aslani et al. / Solid State Sciences 10 (2008) 854e858

857

N H

H

H

N

H

H

H

H

H H N

H

H

H

N N GG

N

TG

TT

Chart 1. Schematic representation of the conformational isomers of the bpa ligand.

Complete bond lengths and angles, co-ordinates and displacement parameters have been deposited at Cambridge Crystallography Data Centre. Supplementary data are available from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK on request, quoting the deposition number 662248.

15

120 TG

80

5

60

0

40

-5

20

-10

0 0

200

400

600

t(°C)

Weight of loss(%)

10

DTA

100

Acknowledgements The authors acknowledge financial support by Tarbiat Modares University. The Smart Apex diffractometer was funded by NSF grant 0087210, by Ohio Board of Regents grant CAP491, and by YSU.

-15 800

Temperature(°C)

References

Fig. 5. Thermal behaviour of [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1).

Intensity (a.u.)

emissions at 430 nm upon the same excitation can also be observed for the free bpa ligand [19]. In summary, the structure of [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1) is highly interesting as it represents a new, rarely observed three-dimensional framework with two Pb atoms in different environments and also contains stereo-chemically ‘inactive’ electron lone pair. Also the compound exhibits three different bpa ligands with two different conformational isomers, and it is, to our best knowledge, first lead(II) homochiral coordination polymer. 100 90 80 70 60 50 40 30 20 10 0 400

420

440

460

480

500

520

Wavelength (nm) Fig. 6. Solid-state fluorescence spectra for compound [Pb2(m-bpa)3(m-NO3)2(NO3)2]n (1) at room temperature, lexc ¼ 383 nm.

[1] S. Kitagawa, R. Kitaura, S.-i. Noro, Angew. Chem. Int. Ed. 43 (2004) 2334. [2] H. Li, M. Eddaoudi, T.L. Groy, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8571. [3] W. Shi, X.-Y. Chen, B. Zhao, A. Yu, H.-B. Song, P. Cheng, H.-G. Wang, D.-Z. Liao, S.-P. Yan, Inorg. Chem. 45 (2006) 3949. [4] J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim, Nature 404 (2000) 982. [5] S. Mondal, M. Mukherjee, S. Chakraborty, A.K. Mukherjee, Cryst. Growth Des. 6 (2006) 940. [6] R.-Q. Fang, X.-M. Zhang, Inorg. Chem. 45 (2006) 4801. [7] J. Parr, Polyhedron 16 (1997) 551. [8] C.-Y. Sun, L.-C. Li, L.-P. Jin, Polyhedron 25 (2006) 3017. [9] J.M. Harrowfield, H. Miyamae, B.W. Skelton, A.A. Soudi, A.H. White, Aust. J. Chem. 49 (1996) 1165. [10] bpa (0.184 g, 1 mmol) was placed in one arm of a branched tube and lead(II) nitrate (0.361 g, 1 mmol) in the other. Methanol was carefully added to fill both arms, then the tube was sealed and the ligand-containing arm was immersed in a bath at 60  C, while the other was kept at ambient temperature. After 5 days, white crystals were deposited in the cooler arm which was filtered off, washed with acetone and methanol and air dried. Yield: 45%. decomp. p. ¼ 196  C. Anal. Calcd. for C36H36N10O12Pb2 (%): C, 35.55; H, 2.96; N, 11.52; found: C, 35.35; H, 2.25; N, 11.60. IR (cm1) selected bonds: 526 (m), 820 (s), 996 (s), 1065 (m), 1215 (m), 1392 (vs), 1416 (m), 1593 (vs), 2900 (w), 3010 (w). [11] J.G. Contreras, C.J. Diz, J. Coord. Chem. 16 (1997) 245. [12] X-ray crystallographic data were collected at 100(2) K using a Bruker AXS SMART APEX CCD diffractometer. The intensity data were collected within the range of 1.46e28.28 using graphite monochromated ˚ ). Accurate unit cell parameters and Mo Ka radiation (l ¼ 0.71073 A the orientation matrix for data collection were obtained from leastsquares refinements using the programs Smart [Bruker Advanced X-ray

858

A. Aslani et al. / Solid State Sciences 10 (2008) 854e858

Solutions SMART for WNT/2000 (Version 5.628), Bruker AXS Inc., Madison, Wisconsin, USA, 1997e2002] and Saint [Bruker Advanced X-ray Solutions SAINT (Version 6.45), Bruker AXS Inc., Madison, Wisconsin, USA, 1997e2003)]. The structure has been solved by direct methods and refined by full-matrix least-squares techniques on F2 using SHELXTL [Bruker Advanced X-ray Solutions SHELXTL (Version 6.14), Bruker AXS Inc., Madison, Wisconsin, USA, 2003]. Crystal data: formula, C36H36N10O12Pb2; Mr 1215.15 g/mol; monoclinic system, space ˚, b¼ group P21; a ¼ 9.2307(8), b ¼ 15.4834(13), c ¼ 14.4266(12)A ˚ 3; Dc ¼ 2.023 Mg/m3 (Z ¼ 2); F(000) ¼ 104.676(2) , V ¼ 1994.6(3)A 1164; total number reflections 15 854; unique reflections 9256; Rint 0.0247; absorption coefficient 8.505 mm1; Largest diff. peak, hole ˚ 3; R(wR) ¼ 0.0259 (0.0543) with I > 2s(I ); R(wR) ¼ 3.280, 0.971 e A 0.0276 (0.0550) for all data. [13] L. Carlucci, G. Ciani, D.M. Proserpio, S. Rizzato, Cryst. Eng. Commun. 4 (2002) 121. [14] F.M. Tabellion, S.R. Seidel, A.M. Arif, P.J. Stang, J. Am. Chem. Soc. 123 (2001) 11982. [15] C. Janiak, Dalton Trans. (2003) 2781.

[16] L. Shimoni-Livny, J.P. Glusker, C.W. Bock, Inorg. Chem. 37 (1998) 1853. [17] J.M. Harrowfield, H. Miyamae, B.W. Skelton, A.A. Soudi, A.H. White, Aust. J. Chem. 49 (1996) 1111 and references cited therein. [18] (a) A. Morsali, M. Payeghader, S.S. Monfared, M. Moradi, J. Coord. Chem. 56 (2003) 761; (b) A. Morsali, X.-M. Chen, J. Coord. Chem. 57 (2004) 1233; (c) A. Morsali, A.R. Mahjoub, M.J. Soltanian, P.E. Pour, Z. Naturforsch. 60b (2005) 300; (d) Y.J. Shi, Y. Xu, Y. Zhang, B. Huang, D.R. Zhu, C.M. Jin, H.G. Zhu, Z. Yu, X.T. Chen, X.Z. You, Chem. Lett. (2001) 678; (e) A. Morsali, A.R. Mahjoub, Chem. Lett. (2004) 64; (f) A. Morsali, A.R. Mahjoub, Polyhedron 23 (2004) 2427; (g) J.-X. Yuan, M.-L. Hu, A. Morsali, Inorg. Chem. Commun. 9 (2006) 277; (h) A. Morsali, A.R. Mahjoub, Solid State Sci. 7 (2005) 1429; (i) H.-P. Xiao, A. Morsali, Helv. Chim. Acta 88 (2005) 2543; (j) A. Morsali, A. Ramazani, Z. Anorg, Z. Anorg. Allg. Chem. 631 (2005) 1759. [19] G. Mahmoudi, A. Morsali, L.-G. Zho, Polyhedron 26 (2007) 2885.