DOI: 10.1021/cg900476m
Two Iodoargentate Hybrid Coordination Polymers Induced by Transition-Metal Complexes: Structures and Properties
2010, Vol. 10 1068–1073
Hao-Hong Li,† Zhi-Rong Chen,*,† Ling-Guo Sun,† Zhao-Xun Lian,‡ Xiao-Bo Chen,† Jun-Bo Li,† and Jun-Qian Li† †
College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian, 350002, P. R. China, and ‡School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang, 453003, P. R. China Received April 30, 2009; Revised Manuscript Received December 4, 2009
ABSTRACT: Two iodoargentate hybrid solids {[Ni(2,20 -bipy)(THF)2(H2O)2](Ag10I12) 3 2DMF}n (1) and {[Cu(2,20 -bipy)3](Ag5I7)}n (2) (THF=tetrahydrofuran, DMF=N,N0 -dimethyl formamide, 2,20 -bipy =2,20 -bipyridine) have been synthesized in a polar organic solvent, whose one-dimensional iodoargentate polymers are induced by second entrapped metal-organic complexes. In 1, the [Ag5I6]nn- chain exhibits a columnar structure based on an Ag5I6 quasi-pentagram building block. In 2, the zigzag chain [Ag5I7]n2n- is constructed from an Ag6I11 building block. Two compounds exhibit intriguing semiconducting properties with Eg = 2.74 and 2.80 eV. As indicated by density functional theory calculations, the observed strong photoluminescence in 1 arises from band-edge transitions. Introduction Inorganic-organic hybrids have attracted considerable attention for the significance of discovering new materials such as display and storage devices,1 which provides a great motivation for research on metal-halide-based hybrids. Among metal-halide-based hybrids, silver halide hybrids are one of the most attractive for not only their versatile coordination modes but also their potential applications in various fields.2 So far, for silver halide hybrids, much attention has been paid to coordination polymers with variable dimensions and topologies modified by organic templates.3 Recently, hybrid compounds incorporating novel templates have emerged, and these new templates include transition-metal (tm) complexes4 and bifunctional organic cations.4 In particular, the second metal-organic subunits can generally serve two roles: (a) bridging linkers that link inorganic moieties to higher dimensional structures through either direct bonding5 or π-π interactions of the organic ligands;6 (b) cations occupying the void spaces shaped by inorganic units.7 The latter type hybrids are of special importance because the second metal-organic complex provides not only charge compensation for the inorganic substructure but also a rigid framework for controlling the inorganic microstructure.1 This idea can also be introduced into the iodoargentate system. A great diversity of interesting structures and exciting properties can be expected if a second metal-organic subunit is introduced into the iodoargentate network. But due to the preference of formation of isolated M(amine)mnþ complexes for metal ions in the presence of strongly chelating amines, it is difficult to probe the condition under which the second metal complexes are incorporated into the iodoargentate polymers. So work in this field is still in its infancy. To our best knowledge, so far, reports about hybrid bimetallic halide materials incorporating transition metal complexes are still rare.7 At present, we are extending our previous work by introducing a heterometal together with organic ligands; we consider that *To whom correspondence should be addressed. E-mail: zrchen@ fzu.edu.cn. pubs.acs.org/crystal
Published on Web 02/04/2010
the introduction of a second metal will modify the properties of hybrid materials. Herein, we report the structures and properties of two hybrid compounds templated by transitionmetal complexes: {[Ni(2,20 -bipy)(THF)2(H2O)2](Ag10I12) 3 2DMF}n (1) and {[Cu(2,20 -bipy)3](Ag5I7)}n (2) (THF=tetrahydrofuran, DMF=N,N0 -dimethyl formamide, 2,20 -bipy = 2,20 -bipyridine). Experimental Section General Remarks. All chemicals were of reagent grade quality obtained from commercial sources and used without further purification. C, H, N analyses were carried out with a Vario EL III element analyzer. Heavy elemental analyses were determined on an Ultima2 inductively coupled plasma (ICP) spectrometer. IR spectra were recorded on a Nicolet Co. Magna-IR 750 spectrometer with a KBr pellet in the 4000-400 cm-1 region. Photoluminescence measurements were carried out on an Edinburgh ELS920 fluorescence spectrometer. Optical diffuse reflectance spectra were measured on a PE Lambda 35 UV-vis spectrophotometer equipped with an integrating sphere at 293 K, and a BaSO4 plate was used as reference. Synthesis of {[Ni(2,20 -bipy)(THF)2(H2O)2](Ag10I12) 3 2DMF}n (1). A solution reaction of AgI, NaI, Ni(NO3)2 3 6H2O,2,20 -bipyrine, and HI in DMF/THF mixed solvent gave green block crystals. In a 50 mL triangular flask, Ni(NO3)2 3 6H2O (0.145 g, 0.5 mmol) and 2,20 -bipy(0.234 g, 1.5 mmol) were dissolved in 6 mL of DMF/THF mixed solvent (volume ratio: 1:1) and then the reaction was stirred for 10 min at room temperature and a dark green solution was obtained. In the other triangular flask, AgI (0.234 g, 1.0 mmol) and NaI (0.225 g. 1.5 mmol) were dissolved in 6 mL of DMF/THF mixed solvent and the mixture was stirred until it became clear. The latter solution was dropped into the former slowly under stirring conditions. The resultant mixture was stirring continuously for about 30 min and a dark green liquor was obtained. The pH was adjusted to 5.0 by the addition of 10% HI/DMF solution, and then the solution was filtered. The filtrate was kept at room temperature for five days and then green block single crystals (0.189 g,yield 58.9% based on Ag) were obtained. It is noteworthy that 1 grows in solutions richer in NaI and in an acidic environment with a pH of 5.0; otherwise the crystals will be low-quality or even no product can be obtained. IR (KBr, cm-1): 3278 m, 3090s, 2924 m, 1648s, 1576s, 1605 m, 1484 m, 1441s, 1250 m, 1058 m, 765ss, 654 m, 412w. UVvis: 244 nm, 332 nm. C24H38Ag10I12N4NiO6 (3138.77): calcd. C 8.41, H 1.21, N 1.78, Ni 1.87, Ag 34.36; found C 8.35, H 1.15, N 1.80, Ni 1.83, Ag 34.30. r 2010 American Chemical Society
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Crystal Growth & Design, Vol. 10, No. 3, 2010 Table 2. Selected Bond Lengths [A˚] for 1 and 2
Table 1. Summary of the Crystal Data and Structure Determination for 1 and 2 compound empirical formula formula mass crystal system space group a [A˚] b [A˚] c [A˚] β [°] V [A˚] Z Dc [g/cm3] μ [mm-1] F(000) reflections, total reflections, unique reflections, observed no. of parameters refined R [I > 2σ(I)] Rw [I > 2σ(I)] residual extremes (e/A˚3)
1
2
C24H38Ag10I12N4NiO6 3138.77 monoclinic P2(1)/m 7.9480(16) 19.681(4) 20.365(4) 100.02(3) 3137.1(11) 2 3.323 9.277 2784 23180 7349 (Rint = 0.0273) 6596 251 0.0743 0.1929 2.902, -1.605
C30H24Ag5CuI7N6 1959.75 monoclinic P2(1)2(1)2(1) 13.681(3) 14.016(3) 23.383(5) 90.00 4483.9(15) 4 2.903 7.455 3524 31955 5683 (Rint = 0.0777) 1688 292 0.0412 0.0848 1.459, -1.873
Synthesis of {[Cu(2,20 -bipy)3](Ag5I7)}n (2). The procedure was similar to the synthesis of compound 1, except that Cu(ClO4)2 3 6H2O ((0.185 g, 0.5 mmol) was used instead of Ni(NO3)2 3 6H2O. Yield: 0.121 g, 13.2% based on Ag. IR (cm-1): 1593s, 1579s, 1471 m, 1458w, 759 m, 768 m, 636s, 627 m. C30H24Ag5CuI7N6 (1959.75): calcd. C 18.38, H 1.23, N 4.29, Cu 3.24, Ag 27.52; found C 18.45, H 1.17, N 4.50, Cu 3.20, Ag 27.55. X-ray Crystallography Study. X-ray data on suitable single crystals of 1 and 2 were collected at 293(2) K with a Rigaku Weissenbery IP diffractometer using graphite-monochromated Mo-KR radiation [λ(Mo-KR) = 0.71069 A˚]. The correction of Lp factors and multiscan absorption correction were applied. Both structures were solved by direct method and refined by full-matrix least-squares techniques on F2 using SHELXTL-97.8 All nonhydrogen atoms were treated anisotropically. Hydrogen atoms of C-H were generated geometrically. Crystallographic data and structural refinements for 1 and 2 are summarized in Table 1. Important bond lengths are listed in Table 2. CCDC-697132 (1) and 726173 (2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; Fax: þ44(0)1223-336033; email:
[email protected]).
Results and Discussion Structural Description. Structure of {[Ni(2,20 -bipy)(THF)2(H2O)2](Ag10I12) 3 2DMF}n (1). According to structural analysis, the crystal structure of 1 exhibits a one-dimensional (1-D) structure constructed from metal-organic fragments [Ni(2,20 -bipy)(THF)2(H2O)2]2þ and [Ag5I6]nn- 1-D chains in combination with each other by electrostatic force. The [Ni(2,20 -bipy)(THF)2(H2O)2]2þ units are discrete, and the inorganic moiety [Ag5I6]nn- is a 1-D polymer. In other words, this structure is a 1-D polymeric anion accompanied by discrete cations. The 1-D inorganic framework of 1 takes on a columnar configuration based on complicated bridging iodine and Ag 3 3 3 Ag interactions. As shown in Figure 1a, the basic structural unit of 1 is a Ag5I6 quasi-pentagram building block in which each silver atom has an I4 donor set and pseudotetrahedral geometry when the Ag 3 3 3 Ag interactions are not taken into account. Ag5I6 building block presents as a quasi-pentagram along the c axis; it is not a planar configuration but a net-sling with I(3) located at the bottom of the
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Compound 1a Ag(1)-I(1) Ag(1)-I(3) Ag(2)-I(2) Ag(2)-I(4) Ag(3)-I(2) Ag(3)-I(6) Ag(4)-I(3) Ag(4)-I(4) Ag(5)-I(5) Ag(5)-I(6) Ag(6)-I(5) Ag(6)-I(7) Ag(1)-Ag(2) Ag(3)-Ag(3)#1 Ag(6)-Ag(5) Ni(1)-O(1) Ni(1)-O(2) Ni(1)-N(1)
2.852(3) 2.913(2) 2.855(2) 2.8254(19) 2.881(2) 2.808(2) 2.9882(19) 2.829(2) 2.985(2) 2.837(2) 2.981(3) 2.8240(18) 3.198(2) 3.143(3) 3.237(2) 2.077(14) 2.34(4) 2.084(13)
Ag(1)-I(2) Ag(1)-I(2)#1 Ag(2)-I(3) Ag(2)-I(6)#2 Ag(3)-I(5) Ag(3)-I(1)#4 Ag(4)-I(8) Ag(4)-I(7)#2 Ag(5)-I(4) Ag(5)-I(7) Ag(6)-I(8) Ag(6)-I(7)#1 Ag(2)-Ag(4) Ag(3)-Ag(5) Ag(6)-Ag(5)#1 Ni(1)-O(1)#1 Ni(1)-O(3) Ni(1)-N(1)#1
2.8460(15) 2.8460(15) 2.9645(17) 2.8667(19) 2.956(2) 2.822(2) 2.8182(19) 2.858(2) 2.836(2) 2.812(2) 2.869(3) 2.8240(18) 3.151(2) 3.338(3) 3.237(2) 2.077(14) 2.054(17) 2.084(13)
Compound 2b Ag(1)-I(1) Ag(1)-I(3) Ag(2)-I(1) Ag(2)-I(6) Ag(3)-I(1) Ag(3)-I(2)#2 Ag(4)-I(1) Ag(4)-I(2)#2 Ag(5)-I(1) Ag(5)-I(5) Ag(1)-Ag(2) Ag(1)-Ag(4)#1 Ag(2)-Ag(4) Ag(3)-Ag(5) Cu(1)-N(1) Cu(1)-N(3) Cu(1)-N(5)
2.934(3) 2.783(4) 3.036(4) 2.781(4) 2.913(4) 2.883(4) 3.054(5) 2.818(4) 3.146(4) 2.797(4) 3.286(5) 3.143(5) 3.147(5) 3.168(5) 1.98(2) 2.06(3) 2.01(3)
Ag(1)-I(2) Ag(1)-I(4) Ag(2)-I(3) Ag(2)-I(7) Ag(3)-I(5) Ag(3)-I(3)#2 Ag(4)-I(6) Ag(4)-I(4)#2 Ag(5)-I(4) Ag(5)-I(7) Ag(1)-Ag(3)#1 Ag(1)-Ag(5) Ag(3)-Ag(1)#2 Ag(4)-Ag(1)#2 Cu(1)-N(2) Cu(1)-N(4) Cu(1)-N(6)
2.940(4) 2.808(4) 2.926(4) 2.794(4) 2.762(4) 2.965(4) 2.718(4) 2.910(4) 2.864(4) 2.767(4) 3.130(5) 3.378(5) 3.130(5) 3.143(5) 2.28(3) 2.05(2) 2.32(3)
Symmetry codes: #1 x, -y þ 3/2, z; #2 x - 1, y, z; #3 x - 1, -y þ 3/2, z; #4 x þ 1, y, z. b Symmetry codes: #1 -x þ 2, y þ 1/2, -z þ 1/2; #2 -x þ 2, y - 1/2, -z þ 1/2. a
net-sling. In the Ag5I6 building block, strong Ag 3 3 3 Ag interactions could be found, upon which a nearly planar Ag5 pentagon forms. The deviation from least-squares planes of the Ag5 pentagon is less than 0.0101 A˚, suggesting a planar nature. The Ag 3 3 3 Ag distances in the Ag5I6 building block are 3.151(1), 3.198(6), 3.465(3) A˚, respectively, indicating that the pentagon is unequilateral. These four Ag 3 3 3 Ag distances in the Ag5I6 building block are slightly longer than metallic silver (2.88 A˚) but shorter than the van der Waals radius sum of silver (3.44 A˚)9 and could be treated as chemical bonds except Ag(4)-Ag(4)#1 (#1 x, -y þ 3/2, z). Adjacent Ag5I6 building blocks are linked via μ3-I-Ag bonds to exhibit a columnar structure (Figure 1b). Along a-axis, a decagon could be observed due to cross-linkage of Ag5I6 building blocks (Figure 1c). It is worth mentioning that Ag-μ5-I(3), I(5) distances (average length: 2.9681(9) A˚) are much longer than those between Ag and peripheral I, so I(1) could be treated as an inclusion ion; that is, Ag5I6 unit could depicted as Ag5I5@I. Consequently, with I(3) and I(5) absence from the [Ag5I6]nn- columnar chain, a nanotube with a diameter of 9.079(5) A˚ could be observed (Figure 1d). In the [Ni(2,20 -bipy)(THF)2(H2O)2]2þ fragment, Ni adopts octahedron coordination geometry with two O atoms of water occupying an axial position and other four coordinated atoms from 2,20 -bipy and THF located at the equator
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Figure 1. (a) Diagram of Ag5I6 building block; (b) view of the 1-D tube-like chain structure of [Ag5I6]nn- along the b-axis; (c) decagon diagram of [Ag5I6]nn- chain along the c-axis; (d) nanotube structure of silver iodide.
Figure 2. Packing diagram of 1 showing metal-organic cations contained in the caves formed by the inorganic framework.
plane. This octahedron is highly distorted with one axial Ni-O distance being as long as 2.34(4) A˚, which is led by a Jahn-Teller effect and this bond could also treated as a semibond. In 1, transition metal complex cations occupy the void spaces shaped by inorganic units, which could be classified as type b as described in the introduction. DMF molecules also stack in the crystal and stabilize the whole structure. A particularly obvious feature of the polymeric structure is the charge-balanced cations [Ni(2,20 -bipy)(THF)2(H2O)2]2þ trapped within the cavity of the threedimensional cavities, which act as the nut-bolt of the tube-like
combination (Figure 2). It is worth noting that the formation of the 1-D Ag/I columnar chain is a good illustration of a template effect of the transition metal complex. Its formation may be achieved by the synergistic interaction between the silver iodide and the second metal-organic subunit. Structure of {[Cu(2,20 -bipy)3](Ag5I7)}n (2). The crystal structure of 2 also presents a 1-D [Ag5I7]n2n- zigzag chain built upon [Cu(2,20 -bipy)3]2þ fragments (Figure 3a). Although 2 has the same chemical formula of [Ag5I7]n2- with {[Et3N(CH2)6NEt3][Ag5I7]}n,3a its basic structure differs greatly. As shown in Figure 3b, the basic structural unit of 2 is Ag6I11 building block in which each silver adopts a tetrahedral geometry. The Ag6I11 building block could be described as edge-sharing of six AgI4 tetrahedra. The nestlike structure (Ag5I5 unit with I(1) located at the bottom of the nest) in this Ag6I11 building block is similar with that in {[Et3N(CH2)6NEt3][Ag5I7]}n.3a In the Ag6I11 building block, strong Ag 3 3 3 Ag interactions could also be found, upon which a boat-like Ag6 hexagon is shaped (Figure 3b). The Ag 3 3 3 Ag distances are 3.130(5), 3.143(5), 3.286(5), 3.378(5), 3.147(5), 3.143(5) A˚, indicating that the hexagon is unequilateral. If the ligands are eliminated, a unique Ag chain based on argentophilicity interaction could be obtained. Adjacent Ag6I11 building blocks link with each other via μ3-I(2), I(3), I(4), μ5-I(1), and Ag 3 3 3 Ag interactions shaped by Ag(1)Ag(2) (3.286(5) A˚), Ag(1)-Ag(5) (3.378(5) A˚) to give a substructure unit Ag10I18 (Figure 3c). And ultimately, the extended [Ag5I7]n2n- zigzag chain along the b axis is generated from the trans-edge-face of the Ag10I18 subunit via the
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Figure 3. (a) View of the 1-D zigzag chain structure of [Ag5I7]n2n- along the b-axis; (b) diagram of the Ag6I11 building block; (c) structure of the Ag10I18 substructure unit.
Figure 5. Solid-state emission spectrum of 1 at room temperature.
Figure 4. Packing diagram of 2 showing [Cu(2,20 -bipy)3]2þ fragments (red polyhedron) contained in the caves formed by inorganic chains (green polyhedron).
μ3-I(2), I(3), I(4), and Ag(1)-Ag(3)#1 (3.130(5) A˚), Ag(1)Ag(4)#1 (3.143(5) A˚, #1: -x þ 2, y þ 1/2, -z þ 1/2). In the [Cu(2,20 -bipy)3]2þ fragment, Cu adopts octahedron coordination geometry with N(1), N(3), N(4), and N(5) locating equator plane. The charge-balanced cations [Cu(2,20 -bipy)3]2þ are trapped within the cavity of the two-dimensional cavities (Figure 4). Fluorescent and Optical Adsorption Spectrum. As shown in Figure 5, compound 1 exhibits a strong photoluminescent emission band at 447 nm and relative peak photoluminescent emission shoulder peaks at 518, 542 nm upon photoexcitation at 250 nm. According to the results for similar silver(I)
halides,3a,10 the emission peak at 447 nm can be assigned to the mixture of LMCT (I to Ag) and metal-centered (ds/dp) states modified by Ag-Ag interactions within [(Ag5I6)]nnchains. No fluorescence can been found for 2, which might be attributed to the presence of a fluorescent quenching reagent (Cu2þ ion) in the lattice. The absorption edges for 1 and 2 are of about 2.74 and 2.80 eV, showing that the present compounds belong to semiconductors (Figure s1 in Supporting Information, the values of Eg were obtained with the use of a straightforward extrapolation method),11 which indicate a 0.07 and 0.01 eV red shift of the absorption edges compared with the measured value of 2.81 eV for bulk β-AgI12 and slightly larger than that of polymeric iodoplumbate modified by transition metal complexes ({[M(en)2][Pb2I6]}, M = Ni, Zn, Fe, Mn, from 2.45 to 2.62 eV).13 For 1, the photoluminescent emission band 447 nm is close to the energy gap of 2.74 eV (452 nm) obtained from the optical absorption data (Figure s1 in Supporting Information). To understand the structure-property relationship, an electronic band-structure calculation with the density function theory method14 is
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dispersion of the calculated ε2(ω) spectra, which appears at 3.45 eV. Compared with that of bulk β-AgI (3.88 eV), it exhibits a 0.43 eV shift. Therefore, the first-absorption peaks of 1 can be attributed as the charge transfer within the inorganic iodoargentate network. The [Ni(2,20 -bipy)(THF)2(H2O)2]2þ cation results in the formation of an interesting columnar iodoargentate chain, which only exhibits a perturbation effect on the adsorption of inorganic iodoargentate moiety but does not directly participate in the optical transition. In addition, the observed blue shift can be explained with the quantum confinement effect (QCE).16 Conclusions In summary, two iodoargentate polymers induced by second entrapped metal-organic complexes have been structurally investigated. Both compounds exhibit a semiconductor nature judging from their optical band gaps, and interesting fluorescence properties can be observed in 1. Explorations of the incorporation of some other functional metals into the Ag/I system, such as magnetic Mn2þ, Co2þ, or luminescent Ln3þ (Ln = rare earth metal) are still ongoing. Acknowledgment. We acknowledge support of this research by National Natural Science Foundation of China (NOS: 20901017), Innovation Fund for Young Scientist of Fujian Province (2007F3049), specialized research fund for the doctoral program of higher education of China (20093514120003), and Sci & Tech Promotion Foundation of Fuzhou University (2009-XQ-08). Supporting Information Available: Optical adsorption spectra and calculated imaginary parts ε2(ω) of dielectric functions for 1 are available free of charge via the Internet at http://pubs.acs.org/. Figure 6. PDOS (partial density of states) of (a) [(Ag5I6)]nn- (b) and [(Ag5I7)]nn- chains.
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