Hydrothermal synthesis, crystal structure and optical properties of a 2-D heterometallic iodoplumbate

Inorganic Chemistry Communications 13 (2010) 425–428

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Hydrothermal synthesis, crystal structure and optical properties of a 2-D heterometallic iodoplumbate Hong-Xu Guo a,*, Yong Zhang b, Xi-Zhong Li a, Wen Weng a a b

Department of Chemistry and Environmental Science, Fujian Province University Key Laboratory of Analytical Science, Zhangzhou Normal University, Zhangzhou 363000, PR China Testing and Analysis Center, Suzhou University, Suzhou 215123, PR China

a r t i c l e

i n f o

Article history: Received 28 November 2009 Accepted 11 January 2010 Available online 15 January 2010 Keywords: Heterometallic iodoplumbate Semiconducting property Thermochromic behavior Hydrothermal synthesis Crystal structure

a b s t r a c t A novel two-dimensional heterometallic iodoplumbate, [Pb3I10Cu4(phen)2]n (phen = 1,10-phenanthroline) constructed from [Pb3I10]4 iodoplumbate chains and [Cu2I4(phen)]2 entities has been hydrothermally synthesized and structurally characterized. The solid compound exhibits an intriguing semiconducting property with Eg = 2.62 eV. The thermochromic behavior of the compound has been also studied. Ó 2010 Elsevier B.V. All rights reserved.

Stimulated by the wide range of topological structures and driven by potential applications in electric conductivity, magnetism, ion exchange, film materials and catalysis, the design and preparation of new iodoplumbate hybrid materials have attracted more and more attention in the last decade [1–3]. Among the iodoplumbate hybrid materials reported, two kinds of different template reagents can be classified: organic templates (mainly concentrated on organic amines) and metal–organic complexes. In the former case, the modification of iodoplumbate polymers using organic cationic templates has been well-established. Typical iodoplumbate polymers templated by organic amines include [BuN(CH2CH2)3NBu]3[Pb5I16]4DMF [4], (C9H14N)4 [Pb3I10] [5], (C12H14N2)Pb2I6 [6], (me2pipzH2)2[Pb3I10]4H2O [7], [NH3(CH2)4CH(CH3)NH3][Pb3I10] [8], [Bu3N(CH2)4NBu3]2[Pb3I10] [9]. More recently, the Guo group successfully employed the anionic–cationic co-template into the to yield a new type staircase-like inorganic network ðPb4 I18 Þ10n n of perovskite hybrid structure [10]. While in the latter case, although a number of hybrid materials constructed from iodoplumbate polyanions and transition metal(lanthanide) coordination complexes have been reported, for example the compound [PbCu6I8](PPh3)6 (PPh3 = triphenylphosphine) [11], [Y(DMF)8] [Pb3I9]DMF [12], [Co(phen)3]2[Pb3Cu6I16]C2H5OH [13] and [Zn (C8H23N5)]2 (Pb3I10) [14], and [Ni(opd)2(can)2][Pb4I10] [15], relatively little work has been reported on the 2-D layered hybrid iodoplumbate polymers built up from iodoplumbate anions and metalorganic complexes via a covalent bond linking with the * Corresponding author. Tel.: +86 596 2525017. E-mail address: [email protected] (H.-X. Guo). 1387-7003/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.01.003

exception of the compound (Nd2DMF12IN2)(Pb8I20)]n (HIN = isonicotinic acid) [16]. Heterometallic iodoplumbate, especially containing Cu sites, was demonstrated an important hybrid because of its diverse coordination geometry and possible semiconductor features [13]. Although a variety of iodoplumbate hybrid compounds structuredirected by different templates mentioned above have been extensively studied, to the best of our knowledge, the compounds containing a metal other than Pb, templated by CuI system coordination complexes serving as covalent linkers have not been observed. Herein we report on the synthesis [17], crystal structure and optical properties of a new heterometallic iodoplumbate, [Pb3I10Cu4(phen)2]n (1). The single-crystal X-ray analysis revealed that the structure of 1 is composed of 1-D iodoplumbate chain constructed from [Pb3 I10]4 polyanions building blocks and [Cu2I4(phen)] complex units [18]. As shown in Fig. 1, in the polyanion ½Pb3 I10 4n n , the two crystallographically independent Pb atoms are situated in a distorted octahedral coordination environment. The Pb(1)I6 features highly distorted octahedral symmetry, in which the six different PbI bond lengths are in the range of 3.177(1)3.395(2) Å, and the IPbI bond angles between cis ligands vary from 74.85(4) to 88.00(4)° and trans angles from 115.62(4) to 158.56(3)°. The PbI bond distances in the Pb(2)I6 octahedron in the compound 1 are quite uniform (from 3.136(1) to 3.245(1) Å), with the average value of 3.190 Å, which is similar to that of the reported compound (C8H4I2S)20.5(PbI6)H2O [19]. The Pb(1)I6 and Pb(1A)I6 (symmetry code A: x + 3, y, z) octahedra connect in an edge-shared fashion to form dimer subunit {Pb2I6} with the PbPb separation of

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Fig. 1. Fragment of the polymeric anion structure of ½Pb3 I10 4n . n

5.326 Å, which in turn are linked together through a Pb(2)I6 octahedron via three common edges to construct a rare 1-D iodoplumbate chain. Thus the 1-D chain can also be described as follows: the adjacent two dinuclear subunits {Pb2I6} link Pb(2)I6 octahedron via

Fig. 2. Structure of binuclear unit [Cu2I4(phen)]2, the C atoms of phen have been omitted for clarity.

edge-sharing to form a pentamer subunit, in which the Pb(2) occupies the inversion centre between the two dinuclear subunits

Fig. 4. Diffuse reflectance data for compound 1(black), polycrystalline CuI (red) and polycrystalline PbI2 (blue). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3. View of the 2-D layered structure of the compound 1 in the ab plane, the phen C atoms have been omitted for clarity.

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Fig. 5. Thermochromism of compound 1. The dark-brown color (a) changes to bright orange (b) upon cooling to liquid-nitrogen temperature. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

{Pb2I6}, then each pentamer subunits connect together alternatively through a Pb(2)I6 octahedron to construct a rare inorganic iodoplumbate chain along the a axis. Thus the 1-D chain ½Pb3 I10 n4n in compound 1 is significantly different from the reported compounds based on [Pb3I10]4 subunits, and is also unusual in the iodoplumbate chemistry. The [Cu2I4(phen)] dinuclear coordination unit in the compound 1 consists of one fairly regular CuI4 and one distorted CuI2N2 tetrahedron, in which the two Cu atoms share two bridging I atoms, as shown in Fig. 2. Each Cu atom has tetrahedral coordination, in which the Cu(1) is coordinated to two I atoms and two N atoms from one phen ligand, while the Cu(2) is bound to four I atoms. The CuI bond lengths are in the range of 2.584(2)2.680(2) Å, which is close to that found in bulk CuI, 2.63 Å, and the two CuN bond distances are 2.066(9) and 2.081(10) Å. The distance of the two Cu sites in the dinuclear subunit is 2.659(2) Å, indicating there exists an obvious CuCu metal bond, which is longer than that of the compound [Cu2I2(tpt)]n (2.547 Å) and shorter than that of the compound [Cu3I3(tpt)]n (2.782 Å) [20]. An important feature of the solid compound 1 is its neutral 2-D layer network, which can be conceptually described as resulting from the condensation of [Pb3I10]4 chains and [Cu2I4(phen)]2 entities, as shown in Fig. 3. As a consequence of two building units mentioned above, the iodide ligands in the compound 1 act as two different linking modes defined by their connectivity to Pb and(or) Cu sites, that is, (i) triply bridging mode (I(1) and I(2) linking two Cu atons and one Pb atom; I(3) linking three Pb atoms; and I(5) linking two Pb atoms and one Cu atom); and (ii) doubly bridging mode (I(4) linking one Cu and one Pb). Compared with the similar compound [Co(phen)3]2[Pb3Cu6I16]C2H5OH [13], reported by Burns etc., which contains a Pb3Cu6I16 net made up of linked Pb3I16 and Cu6I11 clusters, while the [Co(phen)3]2+ serve as counter ions separated in the layers, the compound 1 has a striking feature, that is, the transitionmetal complex [Cu2I4(phen)] acts as bridging linkage to construct a layer-like hybrid structure. To the best of our knowledge, the compound 1 represents a rare 2-D iodoplumbate hybrid complex constructed from Pb/I skeleton polyanions and transitionmetal complex via covalent bonding, which maybe, but in the same field, one iodostannate has been reported by the Krautscheid group [21]. Thermogravimetric analysis (TGA) of compound 1 (See Fig. S1), carried out under N2 with a heating of 10 °C min1, showed a visible weight loss of 14.98% in the temperature range 110256 °C, corresponding to the release of organic phen molecules (calculated value of 14.38%). Finally, compound 1 has been completely decomposed to PbI2, which melts at ca. 405 °C. Optical absorption spectra reveal the presence of an obvious optical gap of 2.62 eV for compound 1, consistent with its brown color, as shown in Fig. 4, which suggests the complex may be a po-

tential wide-gap semiconductor. This value is intermediate to that of CuI (2.92 eV) and PbI2 (2.30 eV). The gradual slopes of the optical absorption edge for 1 is indicative of the existence of indirect transitions [22], which is similar to that of the Bi/I/Ag(Cu) heterometallic compounds [23]. The principal optical absorption of 1 is likely originates from the charge-transfer excitations mainly from the valence band of the polyanions [Pb3I10]4 to the conduction band of the binuclear copper centers, which is similar to that of the 1-D 2 compound ½Bi2 Ag2 I2 10 n or 2  D complex ½Bi4 Ag2 I16 n [23a]. Thermochromic behavior, as an interesting temperature-dependent thermochromic atmosphere, in halometallates is well demonstrated recently by the Loye group [13,24]. Similarly, compound 1 is a thermochromic material, that is, it changes from dark-brown (298 K) to bright orange (123 K) upon cooling to liquid-nitrogen temperature, where images of a crystal at room and liquid nitrogen temperature are shown in Fig. 5. Such atmosphere can be attributed the shifts in the band edge caused by the lattice contraction during cooling [24]. In summary, we have successfully synthesized a new 2-D heterometallic iodometallate with thermochromic behavior containand [Cu2I4(phen)] binuclear units ing 1-D polyanion ½Pb3 I10 4n n serving as covalent linkage, that exhibits an intriguing semiconducting property with Eg = 2.62 eV. It represents a rare heterometallic iodometallate with copperhalide complexes as a bridging coligand. Acknowledgements This work was supported by the Natural Science Foundations of Fujian Province (No. 2008J0172) and the National Natural Science Foundations of China (No. 20705031). Appendix A. Supplementary material CCDC 749481 contains the supplementary crystallographic data for 1. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2010. 01.003. References [1] (a) C.R. Kagan, D.B. Mitzi, C.C. Dimitrakopoulos, Science 286 (1999) 945; (b) P.J. Hagrman, D. Hagrman, J. Zubieta, Angew. Chem., Int. Ed. 38 (1999) 2638; (c) A.M. Guloy, Z.J. Tang, P.B. Miranda, V.I. Srdanov, Adv. Mater. 13 (2001) 833; (d) L.M. Wu, X.T. Wu, L. Chen, Coord. Chem. Rev. 253 (2009) 2787; (e) X.H. Zhu, M. Meicier, P. Frere, P. Blanchard, J. Roncali, M. Allan, C. Pasquier, A. Riou, Inorg. Chem. 42 (2003) 5330;

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