S-Based Semiconductors

Oct 6, 2009 - Synopsis. Solvothermal reactions of CuI with 4,4′-dipyridyl disulfide (dpds) and oxalic acid in toluene and acetonitrile at 150 °C at...
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DOI: 10.1021/cg9007608

Solvothermal Stepwise Formation of Cu/I/S-Based Semiconductors from a Three-Dimensional Net to One-Dimensional Chains

2009, Vol. 9 4963–4968

Yang Chen,†,‡ Zi-Ou Wang,§ Zhi-Gang Ren,† Hong-Xi Li,† Duan-Xiu Li,† Dong Liu,† Yong Zhang,† and Jian-Ping Lang*,†,‡ †

College of Chemistry, Chemical Engineering and Materials Science, Suzhou University, Suzhou 215123, P. R. China, ‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 210032, P. R. China, and §College of Electronics and Information Engineering, Suzhou University, Suzhou 215021, P. R. China Received July 4, 2009; Revised Manuscript Received September 20, 2009

ABSTRACT: Solvothermal reactions of CuI with 4,40 -dipyridyl disulfide (dpds) and oxalic acid in toluene and acetonitrile at three different time periods gave rise to three Cu/I/S-based coordination polymers, [Cu6(μ-4-SpyH)4I6]n (1), {[Cu2(μ-I)(μ-4SpyH)3]I}n (2), and [Cu5(μ-4-SpyH)7(μ-I)I4]n (3). The preparation of 1-3 was involved in the in situ formation of the zwitterionic pyridium-4-thiolate (4-SpyH) molecule from the S-S cleavage of the dpds ligand. These compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRPD), and single crystal X-ray diffraction. Compound 1 contains an adamantine-type [Cu6S4] core that links the neighboring ones via double iodide bridges to form a three-dimensional (3D) diamond-like net. Compound 2 has a one-dimensional (1D) cationic {[Cu2(μ-I)(μ-4SpyH)3]n}nþ polymeric chain with disordered iodides embedded between chains. Compound 3 contains the [Cu5(μ-I)I4(μ-4SpyH)7] species that is interconnected with its neighboring ones through two μ-4-SpyH ligands to form a 1D neutral chain. The formation of 1-3 provided an interesting example that different coordination polymers could be produced from the same components under solvothermal conditions at different time periods. In addition, optical absorption and electric conductivity experiments revealed that 1-3 exhibited good semiconducting performances.

Introduction In the past few decades, preparation of the low-dimensional crystalline semiconductor materials has attracted much interest due to their highly tunable structures1 and their potential applications in optoelectronic devices.2,3 There are many synthetic strategies for the assembly of such low-dimensional nanostructures. One recent method is the segmentation of bulk semiconductors into low-dimensional coordination polymers using special organic ligands. For example, treatment of group II metal chalcogenide semiconductors with organic amines at solvothermal conditions led to the formation of a family of the II-VI system-based low-dimensional coordination polymers. These nanostructures exhibited a strong quantum confinement effect relative to the band gap of the parent semiconductors.3,4 CuI is another kind of common semiconductor.5 However, construction of low-dimensional coordination polymers with better semiconductor properties based on CuI has not been reported so far. We have recently been interested in the construction of CuIbased coordination polymers using solvothermal methods. It was found that the bulk CuI could be segmented into pieces by using 1,3-bis(4-pyridyl)propane (bpp).6 Encouraged by this result and being aware that some CuBr/ET-based (ET = bis(ethylenedithio)tetrathiafulvalene) coordination polymers showed excellent semiconducting behavior,7 we attempted to employ some sulfur-containing ligands such as 4,40 -dipyridyl disulfide (dpds) to break down the three-dimensional (3D) framework of CuI to prepare Cu/I/S-based semiconductors. When CuI was treated with dpds under solvothermal condi-

tions, it was found that the S-S bond of dpds was cleaved to form in situ the zwitterionic pyridium-4-thiolate (4-SpyH),8 which was further inserted into the framework of CuI.9 During the whole reaction, intriguing step-by-step conversions from CuI to a 3D coordination polymer [Cu6(μ-4SpyH)4I6]n (1) to a one-dimensional (1D) cationic chain polymer {[Cu2(μ-I)(μ-4-SpyH)3]I}n (2) to a 1D chain polymer [Cu5(μ-4-SpyH)7(μ-I)I4]n (3) were observed. We herein report their isolation, structural characterization, and semiconducting properties. Materials and Methods

*To whom correspondence should be addressed. Fax/Tel: Int. code þ86 512 65880089; e-mail: [email protected] (J.-P.L.).

All chemicals and reagents were obtained from commercial sources and used as received. The elemental analyses for C, H, N, and S were performed on a Carlo-Erba CHNO-S microanalyzer. The IR spectra were recorded on a Varian 1000 FT-IR spectrometer as KBr disks (4000-400 cm-1). Thermal analysis was performed with a Perkin_Elmer TGA-7 thermogravimetric analyzer at a heating rate of 10 °C/min and a flow rate of 100 cm3/min (N2). Solid-state UV-vis-NIR spectra were measured with a Shimadzu UV-3150 spectrometer at room temperature in the range 200-2000 nm. XRPD were performed using a PANalytical X’Pert PRO MPD system (PW3040/60). For the electric conductivity measurements, the conductive adhesive was used to fix the two ends of a single crystal, which were further connected with two conducting probes. This device was put on a thermostatic stage, and the conductivity along the fixed direction (Figure S9, Supporting Information) was measured by using an Agilent 4156C semiconductor parameter analyzer and Vector MX-1100B Prober. Caution! The sealed Pyrex glass tubes containing starting materials and solvents may be explosive. At all times, great care must be taken when handling these glass tubes. [Cu6(μ-4-SpyH)4I6]n (1). To a Pyrex glass tube (15 cm in length, 7 mm in inner diameter) was loaded CuI (19 mg, 0.10 mmol), 4,40 dipyridyl disulfide (11 mg, 0.05 mmol), oxalic acid (13 mg,

r 2009 American Chemical Society

Published on Web 10/06/2009

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Table 1. Summary of Crystallographic Data for 1-3 compound

1

2

3

formula FW crystal system space group a (A˚) b (A˚) c (A˚) V (A˚3) Z T (K) Dcalc (g 3 cm-3) F(000) μ (Mo KR, mm-1) total no. of reflns. no. of unique reflns. no. of obsd. reflns. Ra (I > 2.00σ (I)) wRb GOFc ΔFmax/ΔFmin (e/A˚3)

C10H10N2S2Cu3I3 793.69 tetragonal I41/a 15.782(2) 15.782(2) 13.624(3) 3393.4(10) 8 293(2) 3.107 2896 9.419 12717 1518 1409 0.0369 0.0759 1.072 0.828/-0.886

C15H15N3S3Cu2I2 714.41 orthorhombic Cmcm 30.764(6) 16.095(3) 10.559(2) 5228.3(17) 8 223(2) 1.815 2704 4.232 12036 3159 2836 0.0837 0.2578 1.015 2.175/-1.106

C35H35N7S7Cu5I5 1730.44 orthorhombic Pccn 10.005(2) 19.344(4) 25.704(5) 4974.7(17) 4 293(2) 2.310 3264 5.535 44828 4549 4147 0.0452 0.0918 1.046 0.863/-0.749

)

)

a R = Σ Fo|-|Fc /Σ|Fo|. b wR = {Σw(Fo2 - Fc2)2/Σw(Fo2)2}1/2. c GOF = {Σ[w((Fo2 - Fc2)2)/(n - p)}1/2, where n = number of reflections and p = total numbers of parameters refined.

0.10 mmol), toluene (0.5 mL), and acetonitrile (1.5 mL). The tube was then sealed and heated in an oven at 150 °C for 10 h to form dark octahedral crystals of 1, which were collected by filtration, washed with acetonitrile, and dried in air. Yield: 20 mg (76% based on CuI). Anal. Calcd for C10H10N2S2Cu3I3: C, 15.13; H, 1.27; N, 3.53; S, 8.08%. Found: C, 15.34; H, 1.26; N, 3.39; S, 8.33%. IR (KBr, cm-1): 3168w, 3098w, 3040w, 2915w, 1603s, 1586m, 1568m, 1464s, 1385w, 1196w, 1099m, 995w, 777w, 711w, 473w, 426w. {[Cu2(μ-I)(μ-4-SpyH)3]I}n (2). Dark red plates of 2 were prepared by a similar method used in the synthesis of 1 except that the reaction time was prolonged to 70 h. Yield: 3 mg (13% based on dpds) along with red needles of 3 (9 mg, 36% based on dpds). The two components were separated manually under microscope. Anal. Calcd for C15H15N3S3Cu2I2 (2): C, 25.22; H, 2.12; N, 5.88; S, 13.47%. Found: C, 24.81; H, 2.07; N, 5.78; S, 12.98%. IR (KBr, cm-1): 3203m, 3101m, 3064m, 3043m, 2921w, 1610s, 1571m, 1464s, 1385w, 1237w, 1195w, 1147w, 1110m, 1079w, 999w, 767w, 717m, 471w, 426w. Anal. Found for C35H35N7S7Cu5I5 (3): C, 24.41; H, 2.03; N, 5.57; S, 13.09%. [Cu5(μ-4-SpyH)7(μ-I)I4]n (3). Red needles of 3 were prepared by a similar method used in the synthesis of 2 except that another 70 h heating process was employed. Yield: 16 mg (65% based on dpds). Anal. Calcd for C35H35N7S7Cu5I5 (3): C, 24.29; H, 2.04; N, 5.67; S, 12.97%. Found: C, 24.47; H, 2.05; N, 5.61; S, 13.14%. IR (KBr, cm-1): 3166w, 3100w, 3020w, 2914w, 2852w, 2817w, 1607s, 1569m, 1463s, 1385w, 1286w, 1234w, 1195w, 1148w, 1108m, 996m, 808w, 770w, 714w, 475w, 431w. X-ray Crystallographic Study. Single crystals of 1-3 were obtained directly from the above preparations. Diffraction intensities of 1-3 were collected on a Rigaku Mercury CCD X-ray diffractometer (Mo KR, λ = 0.71073 A˚). The crystals were mounted at the top of a glass fiber at 293 K for 1 and 3, and 223 K for 2 in a stream of gaseous nitrogen. Cell parameters were refined on all observed reflections by using the program Crystalclear (Rigaku and MSc, Ver. 1.3, 2001). The collected data were reduced by the program CrystalClear, and an absorption correction (multiscan) was applied. The reflection data were also corrected for Lorentz and polarization effects. The crystal structures of 1-3 were solved by direct methods and refined on F2 by full-matrix least-squares techniques with SHELXTL-97 program.10 For 1, one copper atom in the asymmetric unit was disordered over two positions with an occupancy factor of 0.52/0.48 for Cu1/Cu10 . In an asymmetric unit of 2, there was half an iodide that was split into 16 sites with the sum of their occupancy factors being 0.5. All non-hydrogen atoms except those disordered iodides were refined anisotropically, while all hydrogen atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms. A summary

of the key crystallographic information for 1-3 was tabulated in Table 1. Selected bond lengths and angles for 1-3 are listed in Table 2.

Results and Discussion Synthesis and Characterization. Solvothermal reaction of CuI with dpds and oxalic acid (molar ratio = 2:1:2) in toluene/acetonitrile at 150 °C for 10 h followed by a standard workup produced dark-red octahedral crystals of 1 in 76% yield (Figure S4, Supporting Information). When the solution of 1 was continuously heated at the same conditions for another 60 h, a similar workup produced a mixture containing dark-red plates of 2 (13% yield) and red needles of 3 (36% yield) (Figure S4, Supporting Information), which were manually separated under a microscope (Figure S5, Supporting Information). At this stage, we did not know which one was first converted from 1 or whether 3 was converted from 2. With a further prolonged heating time (70 h), 2 could not be isolated and only red needles of 3 were formed in 65% yield (Figure S4, Supporting Information). Because of the relatively low yield of 2, it is difficult to say that 2 was converted into 3. Intriguingly, if the dpds ligand in the aforementioned reaction was replaced by 4-mercapto pyridine (4-HSpy), we first isolated black-red blocks of 1 (60% yield). Extending the reaction time only resulted in the formation of 3 (61% yield). Furthermore, pure 2 (crystals) did not afford 3 under similar solvothermal conditions. Also compound 3 could not be generated from pure 1 þ 2 under the analogous conditions. Because 2 or 3 was not isolated in 100% yield, the role of the starting materials in the formation of 2 or 3 could not be ruled out. It is possible that 2 and 3 are indeed secondary or tertiary products, but their formation relationship is unclear at this point. Under the solvothermal conditions, the topological structures of metal coordination polymers were affected by many factors such as pH value,11 temperature,12 solvent,6,13 cation,14 anion,15 neutral molecule template,16 and stoichiometry.17 However, the stepwise formation of different topological structures in different time periods is less explored and only a limited number of examples are involved in the formation of two different compounds.18 To our knowledge, the formation of 1-3

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Table 2. Selected Bond Lengths (A˚) and Angles (deg) for 1-3a Complex 1 Cu(1)-S(1) Cu(1)-I(1D) Cu(2)-S(1B) Cu(2)-I(2)

2.337(8) 2.608(8) 2.273(3) 2.532(2)

Cu(1)-S(1C) Cu(1)-I(1) Cu(2)-S(1) S(1)-Cu(1A)

2.350(7) 2.870(8) 2.303(3) 2.350(7)

S(1)-Cu(1)-S(1C) S(1C)-Cu(1)-I(1D) S(1C)-Cu(1)-I(1) S(1B)-Cu(2)-S(1) S(1)-Cu(2)-I(2) S(1)-Cu(2)-I(1A)

100.1(3) 109.6(3) 114.6(3) 115.51(12) 113.76(10) 112.19(10)

S(1)-Cu(1)-I(1D) S(1)-Cu(1)-I(1) I(1D)-Cu(1)-I(1) S(1B)-Cu(2)-I(2) S(1B)-Cu(2)-I(1A) I(2)-Cu(2)-I(1A)

127.5(4) 102.9(3) 102.6(2) 114.83(10) 102.11(9) 95.97(7)

Complex 2 Cu(1)-S(1B) Cu(1)-S(1) Cu(1) 3 3 3 Cu(1A)

2.305(3) 2.402(3) 2.706(3)

Cu(1)-S(2) Cu(1) 3 3 3 Cu(1B) Cu(1)-I(1)

2.316(3) 2.638(3) 2.7677(17)

S(1B)-Cu(1)-S(2) S(2)-Cu(1)-S(1) S(1B)-Cu(1)-I(1) S(1)-Cu(1)-I(1) Cu(1B)-S(1)-Cu(1)

123.76(13) 109.33(11) 99.14(8) 101.72(8) 68.13(9)

S(1B)-Cu(1)-S(1) Cu(1B) 3 3 3 Cu(1) 3 3 3 Cu(1A) S(2)-Cu(1)-I(1) Cu(1)-I(1)-Cu(1A) Cu(1A)-S(2)-Cu(1)

110.29(9) 167.31(6) 110.01(8) 58.52(6) 71.48(12)

Complex 3 Cu(1)-S(3) Cu(1)-S(2) Cu(2)-S(2) Cu(2)-S(2A) Cu(3)-S(1) Cu(3)-I(2)

2.3249(17) 2.3328(17) 2.3113(17) 2.3113(17) 2.3399(18) 2.6227(10)

Cu(1)-S(4) Cu(1)-S(1) Cu(2)-I(1) Cu(2)-I(1A) Cu(3)-S(3B) Cu(3)-I(3)

2.3260(11) 2.3758(17) 2.7191(9) 2.7191(9) 2.3635(18) 2.6875(11)

S(3)-Cu(1)-S(4) S(4)-Cu(1)-S(2) S(4)-Cu(1)-S(1) S(2A)-Cu(2)-S(2) S(2)-Cu(2)-I(1A) S(1)-Cu(3)-S(3B) S(3B)-Cu(3)-I(2) S(3B)-Cu(3)-I(3) Cu(3B)-I(2)-Cu(3) Cu(2)-S(2)-Cu(1) Cu(1)-S(4)-Cu(1A)

109.79(6) 96.74(7) 112.18(6) 111.40(9) 107.31(4) 96.94(6) 114.54(5) 114.38(5) 90.19(5) 125.48(8) 143.55(11)

S(3)-Cu(1)-S(2) S(3)-Cu(1)-S(1) S(2)-Cu(1)-S(1) S(2A)-Cu(2)-I(1A) I(1A)-Cu(2)-I(1) S(1)-Cu(3)-I(2) S(1)-Cu(3)-I(3) I(2)-Cu(3)-I(3) Cu(3)-S(1)-Cu(1) Cu(1)-S(3)-Cu(3B)

122.78(6) 100.56(6) 115.08(6) 110.37(4) 110.10(5) 114.47(5) 115.39(5) 101.88(3) 119.13(7) 134.35(8)

a Symmetry codes for 1: A: 1/4 - x, -1/4 þ y, 5/4 - z; B: -x, 1/2 - y, z; C: 1/4 þ x, 1/4 - y, 5/4 - z; D: -x, 1 - y, 1 - z. Symmetry codes for 2: A: x, y, 1/ 2 - z; B: x, 1 - y, 1 - z. Symmetry codes for 3: A: 3/2 - x, 1/2 - y, þ z; B: 5/2 - x, 1/2 - y, þ z.

using the same components under the three time periods is unprecedented. Compounds 1-3 are stable toward air and moisture. Complex 1 is not soluble in common organic solvents, while 2 and 3 could slightly dissolve in DMF and DMSO. The elemental analysis was consistent with the chemical formula of the three compounds. According to the thermogravimetric analysis (Figure S7, Supporting Information), they could maintain their structural framework below 200 °C. When the temperature rises, a series of decomposition steps commence by loss of the 4-SpyH and 2I, and the decomposition of residual species is assumed to be copper metal according to X-ray fluorescence analysis. The identities of 1-3 were further confirmed by X-ray crystallography. Crystal Structure of 1. Complex 1 crystallizes in the tetragonal space group I41/a and the asymmetric unit contains one-quarter of the [Cu6(μ-4-SpyH)4I6] molecule. This molecule has an adamantine-type Cu6S4 core (Figure 1a). The four equatorial Cu(I) atoms (Cu1, Cu1A, Cu1B, Cu1C) are tetrahedrally coordinated by two μ-I atoms and two S atoms from the two 4-SpyH ligands while the two apical Cu(I) centers are trigonally coordinated by one terminal iodide and two sulfur atoms from one 4-SpyH ligand. The

Cu-S bond lengths (2.273(8)-2.350(8) A˚) in 1 are longer than those of its chloride analogue [Cu6(4-SpyH)4Cl6] (2.229(3)-2.265(4) A˚).19 Its Cu 3 3 3 Cu separations (3.141(5)-3.894(5) A˚) are longer than those of [Cu4I4(bpp)2]n (2.653(2)-2.681(2) A˚).6 Each [Cu6S4] core works as a tetrahedral 4-connecting node to link with other equivalent ones through four pairs of iodide bridges coordinated at equatorial Cu(I) (Figure 1b), forming a 3D diamond-like net (Figure 1c,d). One Cu-I distance (2.870(8) A˚) in each Cu2I2 rhomb is much longer than that of the other (2.608(8) A˚). All these results implied that this 3D net may not be robust enough to survive at solvothermal conditions and may be disassociated into other more stable species if the time of this reaction is deliberately prolonged. Crystal Structure of 2. Compound 2 crystallizes in the orthorhombic space group Cmcm and the asymmetric unit consists of half a [Cu2(μ-I)(μ-4-SpyH)3]þ cation and a set of disordered iodides. In this cation, each Cu(I) is tetrahedrally coordinated by one μ-I and three S atoms from three different 4-SpyH ligands (Figure 2). Two Cu atoms are bridged by one μ-I and one μ-4-SpyH, forming a Cu2IS ring. The ring is puckered slightly with a dihedral angle of ca. 28° around the Cu 3 3 3 Cu vector, which may lead to the existence

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Figure 1. (a) View of the [Cu6(μ-4-SpyH)4I6] structure of 1 with a labeling scheme. (b) View of the interactions of a Cu6S4 core with four equivalent ones via four pairs of iodides in 1. All pyridyl groups are omitted for clarity. (c) View of part of the 3D diamond net of 1. Each red dot represents a [Cu6(μ-4-SpyH)4I6] subunit. (d) Cell packing diagram of 3 looking down along the c axis. All H atoms have been omitted for clarity. Atom color codes: Cu turquoise; I pink; S yellow; N blue; C black. Symmetry codes: A: 1/4 - x, -1/4 þ y, 5/4 - z; B: - x, 1/2 - y, z; C: 1/4 þ x, 1/4 - y, 5/4 - z; D: - x, 1 - y, 1 - z; E: 1/4 þ x, 3/4 - y, 1/4 þ z; F: x, -1/2 þ y, 1 - z; G: 1/4 - x, -3/4 þ y, 1/4 þ z.

of relatively short Cu 3 3 3 Cu contacts (Table 2). The Cu 3 3 3 Cu contacts range from 2.638(3) A˚ to 2.706(3) A˚, which are shorter than those of 1, implying existence of weak Cu 3 3 3 Cu interactions. Such a core further connects with its neighboring ones through two pairs of μ-4-SpyH ligands to form a 1D cationic chain. The two counter iodides are imbedded among the chains (Figure S2, Supporting Information). The thickness of one chain is ca. 0.4 nm, and the intervals between the adjacent chains are ca. 0.48 nm (b direction) and ca. 0.96 nm (a direction). In addition, each pyridyl group of the 4-SpyH ligand is approximately parallel to its adjacent ones with the centroid-to-centroid distance ranging from 3.551 A˚ to 3.668 A˚, indicating typical π-π stacking interactions. Crystal Structure of 3. Compound 3 crystallizes in the orthorhombic space group Pccn and the asymmetric unit contains half of a [Cu5(μ-I)I4(μ-4-SpyH)7] molecule. Cu2, S4, C18, and N4 locate at a crystallographic mirror, while a

2-fold axis runs through the I2 (Figure 3). Each [Cu5(μ-I)I4(μ-4-SpyH)7] molecule may be viewed as having a [Cu4(μ-I)I2(μ-4-SpyH)5]þ fragment and [CuI2(μ-4-SpyH)2]- fragment, which are linked by one μ-4-SpyH ligand. The resulting [Cu5(μ-I)I4(μ-4-SpyH)7] species is interconnected with its neighboring ones through a couple of μ-4-SpyH ligands to form a 1D chain extending along the a axis. All Cu(I) centers adopt a tetrahedral coordination geometry, coordinated by four S atoms from four μ-4-SpyH ligands (Cu1), or by two S atoms from two μ-4-SpyH ligands and two terminal iodides (Cu2), or by two S atoms from two μ-4-SpyH ligands and one terminal and bridging iodides (Cu3). The mean Cu-S bond length (2.3357(17) A˚) resembles those of 1 and 2 (Table 2). The Cu 3 3 3 Cu separations range from 4.066 to 4.419 A˚, which are much longer than those of 1 and 2, thereby eliminating any copper-copper interactions. The thickness of each chain is ca. 0.8 nm, and the smallest interval between the adjacent chains is ca. 0.48 nm. Furthermore, these 1D

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Figure 2. View of the 1D cationic chain of 2 extending along the c axis. Brown and green dashed lines represent Cu 3 3 3 Cu and π-π interactions, respectively. See Figure 1 for color code; hydrogen atoms were omitted for clarity. Symmetry codes: A: x, y, 1/2 - z; B: x, 1 - y, 1 - z; C: x, 1 - y, -1/2 þ z.

Figure 3. View of the 1D chain of 3 extending along the a axis. See Figure 1 for color code; hydrogen atoms were omitted for clarity. Symmetry code: A: 3/2 - x, 1/2 - y, þ z; B: 5/2 - x, 1/2 - y, þ z; C: -1 þ x, þ y, þ z.

Cu/S/I chains are interconnected by the N3-H3 3 3 3 S1 hydrogen bonding interactions (N3 3 3 3 S1 = 3.222(6) A˚, N3-H3 3 3 3 S1 = 161.9°, symmetry code: 2 - x, 1/2 þ y, 1/2 - z) into a 2D layer network (Figure S3, Supporting Information). Electric Properties. Optical diffuse-reflection spectra of crystalline solids 1-3 were measured at room temperature. The absorption (R/S) data were calculated from the reflectance using the Kubelka-Munk function.20 The energy band gaps (Eonset) obtained by extrapolation of the linear portion of the absorption edges were estimated to be 1.69 eV (1), 2.10 eV (2), and 2.13 eV (3) (Figure S8, Supporting Information), which are in-between the band gap of Cu2S (1.2 eV)9a and the band gap of CuI (3.1 eV)5e as expected. This suggests that the introduction of thiolates into the framework of CuI may make the resulting polymers carry semiconductor characteristics of CuI and Cu2S. The in situ resulting 4-SpyH ligands may also provide significant electronic interactions with Cu(I) centers.21 It is worth noting that the band gaps of 2 and 3 are blue-shifted by ∼0.4 eV with respect to that of the bulk 1, which may be ascribed to the quantum confinement effect3,4 due to the extremely small length scale of the thickness of the Cu/I/S single atomic monochain in the hybrid structures of 2 and 3 (0.4-0.8 nm). To further explore the semiconducting properties of 1-3, we measured the conductivity of their single crystals in variable temperatures. The flowing directions of current in single crystals 1-3 have been presented in Figure S9, Supporting Information. As shown in Figure 4, from 293 to 443 K, the electrical conductivities of their single crystals increased exponentially from 1.97  10-7 S 3 m-1 to

Figure 4. Temperature dependence of the electrical conductivity of the single crystals of 1-3.

6.32  10-5 S 3 m-1 (1), from 6.84  10-6 S 3 m-1 to 3.96  10-4 S 3 m-1 (2), and from 2.74  10-7 S 3 m-1 to 2.43  10-5 S 3 m-1 (3), showing a typical semiconducting behavior. The conductivity of 2 is better than those of 1 and 3, which may be ascribed to the fact that the density of states or effective mass of 2 is larger than those of 1 and 3.22 The increase of the conductivity of 2 with temperature is faster that those of 1 and 3, which indicates that its intrinsic carriers can be excited by heat more easily than those of 1 and 3.22 In addition, the disordered counter iodides and the weak Cu 3 3 3 Cu interactions in the crystal of 2 may also contribute to its increase in conductivity.

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Conclusions In the present work, we have demonstrated a unique solvothermal stepwise formation from CuI to a 3D coordination polymer 1, a 1D cationic chain polymer 2, and a 1D chain polymer 3 under the presence of dpds and oxalic acid. Optical absorption and electric conductivity experiments revealed that 1-3 exhibited good semiconducting performances. The band gaps of the two 1D nanostructures (2 and 3) showed a large blue shift relative to that of 1 due to the strong quantum confinement effect. It is anticipated that the aforementioned synthetic methodology may be applied to prepare a new type of Cu/S/I-based hybrid semiconductors and other low-dimensional crystalline nanostructure quantum dots. Studies on these aspects are under way in our laboratory. Acknowledgment. This work was supported by the National Natural Science Foundation of China (20525101 and 20871088), the State Key Laboratory of Organometallic Chemistry of Shanghai Institute of Organic Chemistry (08-25), the Qin-Lan Project, and “SooChow Scholar” Program and Program for Innovative Research Team of Suzhou University. We are grateful to the reviewers and the editor for their helpful suggestions and comments. Supporting Information Available: CIF and crystallographic data, syntheses, structural figures, crystal photos, XRPD and TGA analyses, optical absorption spectra of 1-3. These materials are available free of charge via the Internet at http://pubs.acs.org.

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