Synthesis, structures and photophysical properties of polynuclear copper(I) iodide complexes containing phosphine and 4,4′-bipyridine ligands

Polyhedron 27 (2008) 2202–2208

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Synthesis, structures and photophysical properties of polynuclear copper(I) iodide complexes containing phosphine and 4,40 -bipyridine ligands Xin Gan a, Wen-Fu Fu a,c,*, Yong-Yue Lin b, Mei Yuan c, Chi-Ming Che b,*, Shao-Ming Chi a, Hui-Fang Jie Li a, Jian-Hua Chen a, Yong Chen c, Zhong-Yong Zhou d a

College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650092, PR China Department of Chemistry, HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, PR China c Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Peking 100080, PR China d Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Hum, Hong Kong SAR, PR China b

a r t i c l e

i n f o

Article history: Received 14 October 2007 Accepted 22 March 2008 Available online 20 May 2008 Keywords: Copper(I) iodide Mixed ligands Polynuclear complexes Crystal structures Photochemical studies

a b s t r a c t The highly luminescent polynuclear CuI iodide complexes, [(Cu2I2)(4,40 -bipy)(PCy3)2]2  4H2O (1), [(Cu2I2)(4,40 -bipy)(PCy3)2]1 (2), [(Cu2I2)(4,40 -bipy)(dcpm)]1 (3) and [(Cu2I2)(4,40 -bipy)(dppm)]1 (4), were prepared by reacting CuI with tricyclohexylphosphine (PCy3), bis(dicyclohexylphosphino)methane (dcpm) or bis(diphenylphosphino)methane (dppm) and 4,40 -bipyridine (4,40 -bipy), and their structures were determined by X-ray crystal analysis. The reported complexes [CuClPCy3]2 (5) and [CuIPCy3]2 (6) were also prepared for comparison. In solid state, complexes 1–6 display intense long-lived phosphorescence with kmax at 605, 565, 640, 570, 430 and 450 nm at room temperature, and the solid-state emission quantum yields are 0.11, 0.20, 0.29, 0.35, 0.67 and 0.83, respectively. The relatively high-energy emissions of 5 and 6 are attributed to arising from metal-centered MC (3d ? 4s, 4p) excited state, while the low-energy emissions of 1–4 are assigned to a metal-to-ligand charge transfer (d ? p* MLCT) excited state. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Copper(I) complexes of polypyridyl ligands, such as [Cu(diimine)2]+, have been extensively studied for their potential applications in photocatalysis, molecular electronics and materials science [1–4]. The structures of polynuclear CuI complexes formed by the reaction of CuX and phosphine or bulky nitrogen organic base have been described previously [5–11]. All these complexes contain l2 or l3-bridging X atoms, and their structures are dependent upon the phosphine or nitrogen donor auxiliary ligands. The complexes [CuXPCy3]2 (X = Cl, I) are neutral dimeric species, they have been structurally characterized but no photophysical properties have been reported [12]. Recent studies showed that polynuclear CuI complexes containing halide and phosphine ligands have intriguing structures and rich photoluminescent properties [13–15]. Examples of these copper(I) complexes having Cu centers arranged in a tetrahedron with the tetrahedral faces capped by halides are known [16]. There are also examples of polymeric copper(I) com-

* Corresponding authors. Address: College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650092, PR China. E-mail addresses: [email protected] (W.-F. Fu), [email protected] (C.-M. Che). 0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.03.026

plexes having a ‘‘stairstep” configuration [17]. In the case of [(CuI)4(dcpm)2], the peripheral dcpm and iodide ligands bridge each edge of the Cu4 plane to form a Cu4P4I2 core [18]. In general, polynuclear CuI complexes with phosphine and halide ligands have multiple emissive excited states, which were assigned to the excited state with either metal-to-ligand charge-transfer MLCT or ligand-tometal charge-transfer XMCT, or a mixture of halide-to-copper and metal-centered MC charge-transfer parentage [19]. Ford and Vogler had reported detailed studies on the photophysical properties of the tetranuclear cubane CuX clusters with dpmp (dpmp = 2-(diphenylmethyl)pyridine) and Py (Py = pyridine) ligands [20]. The relatively higher energy emissions for the complexes Cu4X4L4 at 440–500 nm were attributed to coming from halide-to-ligand charge-transfer XLCT excited states, whereas the longer wavelength emissions at 570–630 nm were assigned to originate from excited states with mixed XMCT and MC orbital parentages [21]. In this work, we report the structures and spectroscopic properties of the polynuclear CuI complexes, [(Cu2I2)(4,40 -bipy)(PCy3)2]2  4H2O (1), [(Cu2I2)(4,40 bipy)(PCy3)2]1 (2), [(Cu2I2) (4,40 -bipy)(dcpm)]1 (3) and [(Cu2I2) (4,40 -bipy)(dppm)]1 (4). The photophysical properties of the reported complexes [CuClPCy3]2 (5) and [CuIPCy3]2 (6) were also examined for comparison purpose, but their syntheses and crystal structures would not be described in this paper [12].

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2. Experimental The CuX (Aldrich), 4,40 -bipyridine (Aldrich), PCy3 (Strem), dcpm (Strem) and dppm (Aldrich) were used as received. Solvents (HPLC grade) used in the spectroscopic procedure were dried over suitable reagents and distilled under an argon atmosphere immediately prior to use. 2.1. Preparation of [(Cu2I2)(4,40 -bipy)(PCy3)2]2 (1) and [(Cu2I2)(4,40 bipy)(PCy3)2]1 (2) To a suspending solution of CuI (0.095 g, 0.5 mmol) in dichloromethane (15 mL) was added solid 4,40 -bipyridine (0.039 g, 0.25 mmol). The mixture was stirred for 4 h, and then PCy3 (0.14 g, 0.5 mmol) in dichloromethane (5 mL) was added to the yellow suspending solution. The mixture became red immediately and the yellow suspension dissolved gradually. The resulting solution was stirred for another 2 h and then filtered. The reaction mixture was concentrated in vacuum and the crude product was recrystallized from CH2Cl2/diethyl ether to give the orange crystals of complex 1. 0.173 g (63%). 31P NMR (CDCl3): d 51.5. Anal. Calc. C92H148N4P4Cu4I4 (powders): C, 50.33; H, 6.80; N, 2.55. Found: C, 50.28; H, 6.91; N, 2.59%. If the preparation of complex 1 was processed by refluxing in dichloromethane, complex 2 were obtained. 0.195 g (71%). 31P NMR (CDCl3): d 51.7. Anal. Calc. (C46H74N2P2Cu2I2)1: C, 50.33; H, 6.80; N, 2.55. Found: C, 50.42; H, 6.71; N, 2.61%. 2.2. Preparation of [(Cu2I2)(4,40 -bipy)(dcpm)]1 (3) and [(Cu2I2)(4,40 bipy)(dppm)]1 (4) Complex 3 was synthesized by adding excess 4,40 -bipyridine (0.078 g, 0.5 mmol) to a suspending solution of CuI (0.095 g, 0.5 mmol) in dichloromethane (20 mL). The mixture was stirred for 2 h, and dcpm (0.102 g, 0.25 mmol) in dichloromethane (5 mL) was then added to the yellow suspending solution. The mixture became red gradually. The product was separated by filtration, and the crude product was recrystallized from CH2Cl2/CHCl3/ diethyl ether to give the red crystals. 0.137 g (58%). 31P NMR (CDCl3): d 2.8. Anal. Calc. (C35H54N2P2Cu2I2)1: C, 44.45; H, 5.76; N, 2.96. Found: C, 44.51; H, 5.73; N, 3.05%. The orange crystals of

complex 4 were prepared following the same procedure as 3 except that dppm was used. 0.154 g (67%). 31P NMR (CDCl3): d 20.8. Anal. Calc. (C35H30N2P2Cu2I2)1: C, 45.62; H, 3.28; N, 3.04. Found: C, 45.54; H, 3.36; N, 3.14%. 2.3. Calculation details All calculations were carried out at the GAUSSIAN 03 package in Virtual Laboratory for Computational Chemistry, CNIC, CAS at the B3LYP level [22,23]. The basis sets which contained in G03 library used for C, P, N and H atoms was 6-31G(d) while effective core potentials with a LanL2DZ basis set of G03 were employed for transition metals. The 6-311G (d) basis set for I, Cl was downloaded from the EMSL basis set library [24]. The contour plots of MOs were obtained with the Gauss View 3.07 program. 2.4. Instrumentation and physical measurements Electronic absorption spectra were recorded at ambient temperature with a HP8453 UV–Vis spectrophotometer. Crystals of suitable size were mounted either on glass fibres or in capillary tubes. X-ray data were collected either on an MAR PSD for 1, a Rigaku Saturn for 2, or a Bruker SMART diffractometer for 3 and 4. Intensity data were collected by x-2h scans technique. The images were interpreted and integrated using program of DENZO [25]. The structures were solved by Direct method (SIR92) or Patterson method (PATTY) and expanded by Fourier method [26]. Structural refinement on F or F2 by full-matrix least square analysis was performed using the SHELXL 97 program [27]. The ORTEP drawings of the structures were displayed with hydrogen atoms omitted for clarity. The unweighted and weighted agreement factors (Rf, Rw) and the goodness of fit are calculated. Crystal data and details on data collection and refinement are summarized in Table 1. Corrected emission spectra were obtained on a Spex Fluorolog2 Model F III A1 fluorescence spectrofluorometer adapted to a right-angle configuration. Filters of suitable bandpass were used to cut off the second harmonic of the monochromatic excitation light source and stray light. Solutions for emission measurements were degassed by at least four freeze–pump–thaw cycles. Lowtemperature (77 K) emission spectra for glass- and solid-state samples were recorded for 5-mm diameter quartz tubes which were

Table 1 Selected crystallographic and data collection parameters for complexes 1–4 Complex

1

2

3

4

Formula M T (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm3) Crystal size (mm) F(0 0 0) Index range (h, k, l) 2hmax (°) Number of unique reflection Rf Rw Goodness-of-fit Residual electron density (e Å3)

C92H156N4P4Cu4I4O4 2267.97 301 triclinic P‰ 10.267(2) 15.135(5) 18.274(3) 73.34(2) 74.83(2) 86.16(2) 2625.5(10) 1 1.434 0.20  0.10  0.07 1156 0, 12; 18, 18; 20, 21 51 8344 0.051 0.065 1.87 1.01, 0.89

C46H74N2P2Cu2I2 1097.89 113 triclinic P‰ 9.992(2) 13.992(3) 17.802(4) 79.044(6) 87.595(6) 83.709(4) 2428.2(9) 2 1.502 0.18  0.16  0.10 1116 13, 13; 19, 19; 24, 24 58.14 12 418 0.034 0.0852 1.035 0.855, 1.988

C70H108Cu4I4N4P4 1891.24 294(2) orthorhombic Pbn21 17.413(5) 19.386(5) 23.367(6) 90 90 90 7888(4) 4 1.593 0.20  0.18  0.14 3776 22, 20; 21, 25; 30, 29 55.2 17 280 0.0536 0.0928 0.998 0.92, 0.82

C70H60Cu4I4N4P4 1842.97 294(2) orthorhombic Pna21 23.859(4) 18.306(3) 17.338(3) 90 90 90 7573(2) 4 1.613 0.20  0.18  0.14 3568 35, 21; 23, 23; 22, 22 55.2 16 788 0.0612 0.1544 1.010 0.939, 0.886

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placed inside a liquid nitrogen bath contained in a quartz optical Dewa flask. Measurement of emission quantum yields of powdered samples involves determining the diffuse reflectance of complexes 1–6 relative to KBr at the excitation wavelength [28]. The measured results were corrected according to the relative response of the detector as a function of wavelength. Emission lifetimes of solid or solution samples were performed with a Quanta Ray DCR-3 Nd-YAG laser with pulse-width of 8 ns and excitation wavelength of 266 nm (fourth harmonic). Emission signals were collected at right angles to the excitation pulse by a Hamamatsu R928 photomultiplier tube and recorded on a Tektronix model 2430 digital oscilloscope. 3. Results and discussion 3.1. Description of the structures The photophysical properties of CuX complexes with phosphine and/or bulky nitrogen organic base ligands have received considerable interest over the past decades. The complexes [(Cu2I2)(4,40 -bipy)(PCy3)2]2  4H2O (1) and [(Cu2I2)(4,40 -bipy)(PCy3)2]1 (2) were both obtained by reacting CuI with tricyclohexylphosphine and 4,40 -bipyridine in stoichiometric ratio of 1:1:0.5 in dichloromethane solutions. When the reaction was conducted at room temperature, 1

was isolated with two water molecules of crystallization. In contrast, the 1-D complex 2 was obtained from the reaction in refluxing dichloromethane solution. Their structures have been determined by X-ray crystal analysis. Perspective views of the molecules are depicted in Figs. 1 and 2, and their bond lengths and angles are given in Table 2. The asymmetric unit of complex 1 consists of half the molecule and the whole molecule is generated by inversion, as shown in Fig. 1. Complex 1 contains a 22-membered ring, and can be viewed as two [CuIPCy3]2 fragments connected by two bridging 4,40 -bipyridine ligands. In contrast, 2 consists of [(Cu2I2)(PCy3)2] subunits bridged by 4,40 -bipyridine ligands into an infinite chain, being similar to that of [(Cu2I2)(4,40 -bipy)(PPh3)2]1 [29]. The Cu atoms of 1 and 2 have a distorted tetrahedral configuration. The distortion from tetrahedral geometry is evidenced by the wider P–Cu–N angle (123.2(2)°) and the narrower I–Cu–N (101.6(2)°), I–Cu–I (103.17(4)°) ones for 1, and P–Cu–N (119.40(7)°), I–Cu–N (102.03(7)°) and I–Cu–I (105.14 (2)°) ones for 2. Both complexes exhibit symmetric CuI2Cu core. The average Cu–I bond lengths of 2.727 Å for 1, and 2.680 Å for 2 are slightly longer than those of 2.573 Å in 6. The average Cu–I–Cu angles in both 1 (72.48°) and 2 (77.00°) are slightly larger than that of 6 (70.97°). Complex 1 has a Cu  Cu distance of 3.224(2) Å, whereas different Cu  Cu distances of 3.267(0) and 3.404(1) Å are found in 2. We note that the two pyridyl rings of 4,40 -bipyridine in 2 are twisted with a dihedral angle of 27.6°, while the 4,40 -bipyridine in 1 is almost coplanar.

Fig. 1. Perspective view of [(Cu2I2)(4,40 -bipy)(PCy3)2]2 (30% probability ellipsoids).

Fig. 2. Perspective view of [(Cu2I2)(4,40 -bipy)(PCy3)2]1 (30% probability ellipsoids).

X. Gan et al. / Polyhedron 27 (2008) 2202–2208 Table 2 Selected bond lengths and bond angles of 1–4 Complex 1 Cu(1)–I(1) Cu(1)–P(1) Cu(1)–I(1)–Cu(2) I(1)–Cu(1)–N(1)

2.778(1) 2.237(2) 71.77(4) 101.6(2)

Cu(2)–I(1) Cu(1)–N(1) I(1)–Cu(1)–I(2) I(1)–Cu(1)–P(1)

2.722(1) 2.079(7) 103.17(4) 108.66 (7)

Complex 2 #1 x, y, z + 2 Cu(1)–I(1) 2.6613(6) Cu(1)–P(1) 2.2285(9) Cu(2)–I(2)#2 2.6442(7) Cu(2)–P(2) 2.2287(9) N(1)–Cu(1)–P(1) 119.40(7) N(1)–Cu(1)–I(1)#1 102.96(7) I(1)–Cu(1)–N(1) 102.03(7) N(2)–Cu(2)–P(2) 114.09(7) P(2)–Cu(2)–I(2)#2 111.02(2) P(2)–Cu(2)–I(2) 121.19(3) Cu(1)–I(1)–Cu(1)#1 74.860(16)

#2 x + 2, y, z + 1 Cu(1)–I(1)#1 Cu(1)–N(1) Cu(2)–I(2) Cu(2)–N(2) I(1)–Cu(1)–I(1)#1 P(1)–Cu(1)–I(1)#1 I(1)–Cu(1)–P(1) N(2)–Cu(2)–I(2)#2 N(2)–Cu(2)–I(2) I(2)#2–Cu(2)–I(2) Cu(2)#2–I(2)–Cu(2)

2.7119(7) 2.054(2) 2.6993(6) 2.058(2) 105.14(2) 107.64(2) 117.93(7) 109.93(7) 98.35(7) 100.87(2) 79.13(2)

Complex 3 Cu(1)  Cu(2) Cu(1)–I(1) Cu(1)–P(1) Cu(1)–I(1)–Cu(2) N(1)–Cu(1)–P(1) P(1)–Cu(1)–Cu(2) Cu(2)–Cu(1)–I(2)

2.7110(9) 2.6917(9) 2.203(1) 60.45(2) 123.37(8) 95.31(3) 60.59(3)

Cu(3)  Cu(4) Cu(1)–I(2) Cu(1)–N(1) N(1)–Cu(1)–I(1) N(1)–Cu(1)–Cu(2) I(1)–Cu(1)–Cu(2) P(1)–Cu(1)–I(1)

2.7240(9) 2.761(1) 2.044(3) 100.99(7) 141.31(8) 59.82(3) 112.89(3)

Complex 4 Cu(1)  Cu(2) I(1)–Cu(1) Cu(1)–N(1) Cu(1)–I(1)–Cu(2) N(1)–Cu(1)–I(1) I(1)–Cu(1)–I(2)

2.7827(7) 2.5971(6) 2.042(3) 61.18 (2) 106.29(7) 105.37(2)

Cu(3)  Cu(4) I(2)–Cu(1) Cu(1)–P(1) N(1)–Cu(1)–P(1) P(1)–Cu(1)–I(1) I(1)–Cu(1)–Cu(2)

2.7706(7) 2.7490(6) 2.226(1) 114.16(8) 118.24(3) 63.96(2)

The preparation of [(Cu2I2)(4,40 -bipy)(dcpm)]1 (3) and [(Cu2I2)(4,40 -bipy)(dppm)]1 (4) are similar to that of 1 except that the PCy3 ligand is replaced by bridging dcpm or dppm ligand. Perspective views of 3 and 4 are depicted in Figs. 3 and 4, respectively. Selected bond lengths and angles of the complexes are listed in Table 2. The structures of 3 and 4 consist of 1-D [–Cu(P^P) (l2-I)2Cu(4,40 -bipy–)] zig-zag chains. The [–Cu(P^P)(l2-I)2Cu(4,40 -bipy–)] unit as the building block contains two 6-membered rings with bridging biphosphine and iodide lignds, and a distorted square –Cu(l2-I)2Cu– unit with torsion

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angles being 36.25(2)° and 41.75(2)° in 3 and 4, respectively (Fig. 4). In contrast, for 4 there are two crystallographically non-equivalent chains. The Cu  Cu distances in 3 (2.7110 Å) and 4 (2.7706 Å) are slightly shorter than that in 6 (2.8925 Å), while the Cu–I–Cu bond angles are 59.91(2)° for 3 and 61.41(2)° for 4. The coordination geometry of the CuI center in 4 is much close to tetrahedron with bond angles varying from 104.91(7)° to 114.16(8)°, whereas those angles of 3 vary from 100.99(7)° to 123.37(8)°. The two pyridyl rings of bridging 4,40 -bipy ligand are twisted with dihedral angles being 29.3(4)° and 26.3(4)° for 3 and 4, respectively. 3.2. Electronic absorption spectra The UV–Vis absorption spectral data for 1–6 in acetonitrile or dichloromethane solutions are summarized in Table 3 and the absorption spectra are depicted in Fig. 5. For 5 and 6, the electronic absorption spectra in dichloromethane show high-energy absorption peaks at 233 nm with tails extending to ca. 320 nm. A definitive assignment of the UV absorption is difficult due to the strong absorption of the ligands. However, density functional theory (DFT) calculation showed HOMO–LUMO gaps are 223.5 and 235.7 nm for 5 and 6, respectively. This is consistent with the experimental results described as MC (metal-centered) transition (Fig. 6). The DFT investigations of complexes 2–4 containing bipy ligand show that the character of the HOMO is dominated by metal orbitals with iodide contribution, whereas the LUMO is mainly localized on the pyridyl rings and displays p* character (Fig. 6). The energy gaps were calculated for 2–4, being 337, 392 and 397 nm, respectively. The calculated wavelength nicely correlates with the presence of the broad absorption bands measured at 350–390 nm in dichloromethane solutions of 1–4. Thereby, the low-energy absorptions are assigned to a MLCT (CuI ? 4,40 -bipyridine) transition. Complexes 5 and 6 have vacant coordination site at CuI, allowing for substrate-binding reactions. As depicted in Fig. 5, the absorption bands of 5 and 6 in acetonitrile solutions are red-shifted from 260 and 270 nm in dichloromethane to 275 and 286 nm, respectively, indicating the coordination of CH3CN to CuI centers. Furthermore, this absorption band around 360 nm of 1 and 2 in dichloromethane is not present in acetonitrile solutions (3 and 4 being sparely soluble). Indeed, the similarity of the absorption spectra for complexes 1, 2, 5 and 6 in acetonitrile solutions suggests that the substitution of 4,40 -bipyridine by CH3CN solvent molecule occurs in the case of 1 and 2.

Fig. 3. Perspective view of [(Cu2I2)(4,40 -bipy)(dcpm)]1 (30% probability ellipsoids).

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Fig. 4. Perspective view of [(Cu2I2)(4,40 -bipy)(dppm)]1 (30% probability ellipsoids).

3.3. Emission spectra Upon excitation at 330 nm, 1–6 exhibit intense photoluminescence with kmax at 605, 565, 640, 570, 430 and 450 nm and the measured emission quantum yields are 0.11, 0.20, 0.29, 0.35, 0.67 and 0.83 in the solid state at room temperature, respectively (Figs. 7 and 8). The high solid-state emission quantum yields of 5 and 6 suggest that the [CuXPCy3]2 solids can be useful as blue light emitting materials. The spectral data are summarized in Table 3. The emissions have lifetimes on the microsecond timescale, implying that these emissions originate from triplet excited state. We propose that the relative high-energy emissions for 5 and 6 originate from metal-centered 3d ? (4s, 4p) triple excited state, and the low-energy emissions for 1, 2, 3 and 4 are from the triplet-parentage MLCT excited state, assignment of

the latter is based on the results of DFT calculations and the fact that the emission maxima for 1–4 are red-shifted from that of 6 [30]. The solid state of complexes 1 and 2 at 77 K exhibits intense luminescences at 640 and 580 nm which are ascribed to phosphorescence derived from the 3MLCT state. Whereas complex 6 displays two intense emission bands centered at 455 and 395 nm in solid state at 77 K, which are similar to the solid emissions of the reported [(CuI)4(pyridine)4], [(CuI)3(dcpm)2], and [(CuI)4(dcpm)2] complexes at 77 K [18,31]. In butyronitrile glassy solution at 77 K, both of 5 and 6 exhibit two emission bands at 400, 480 nm and 390, 480 nm, respectively. The low-energy emission centered at 480 nm is tentatively attributed to solvent exciplex formation. All complexes are non-emissive in dichoromethane or acetonitrile solutions.

Table 3 Spectroscopic and photophysical properties of complexes 1–6 complex

Medium (T/K)

kabs (nm) (e [dm3 mol1 cm1])

kem (nm)/i (ls)

1

CH2Cl2 (298) CH3CN (298) Glass (77)a Solid (298) Solid (77)

232 (80 492), 269 (sh) (18 933), 363 (sh) (2077) 242 (93 620), 267 (sh) (15 769)

Non-emissive Non-emissive 545/41.8 605/1.8 640/3.8

CH2Cl2 (298) CH3CN (298) Glass (77)a Solid (298) Solid (77)

232 (51 287), 267 (sh) (13 238), 355 (sh) (2755) 244 (55 100), 270 (sh) (6230)

3

CH2Cl2 (298) Solid (298)

236 (21 458), 385 (sh) (1196)

Non-emissive 640/1.3

0.29

4

CH2Cl2 (298) Solid (298)

270 (sh) (13 502), 365 (321)

Non-emissive 570/2.6

0.35

5

CH2Cl2 (298) CH3CN (298) Glass (77)a Solid (298) Solid (77)

234 (13 403), 260 (sh) (270) 226 (19 822), 275 (sh) (849)

Non-emissive Non-emissive 400/22.8, 480 (sh)/53.2 430/37.3 430/57.4

CH2Cl2 (298) CH3CN (298) Glass (77)a Solid (298) Solid (77)

233 (17 063), 270 (sh) (2053) 244 (31 288), 286 (sh) (571)

2

6

a

Solvent: butyronitrile; sh = shoulder.

Non-emissive Non-emissive 550/50.1 565/2.2 580/81.1

Non-emissive Non-emissive 390/55.7, 480/86.0 450/3.9 395/7.8, 455/4.8

/em

0.11

0.20

0.67

0.83

X. Gan et al. / Polyhedron 27 (2008) 2202–2208

Fig. 5. UV–Vis spectra of [(Cu2I2)(4,40 -bipy)(PCy3)2]2 (dot line), [CuClPCy3]2 (solid line) and [CuIPCy3]2 (dashed dot line) in dichloromethane solution at room temperature. Inset: complexes [(Cu2I2)(4,40 -bipy)(PCy3)2]1 (dot line) 5 (solid line) and 6 (dashed dot line) in acetonitrile.

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Fig. 7. Room-temperature solid-state emission spectra of [(Cu2I2)(4,40 -bipy)(PCy3)2]2 (dot line), [(Cu2I2)(4,40 -bipy)(PCy3)2]1 (dashed dot dot line), [CuClPCy3]2 (solid line) and [CuIPCy3]2 (dashed dot line) with excitation at 330 nm.

Fig. 8. Room-temperature solid-state emission spectra of [(Cu2I2)(4,40 -bipy)(dcpm)]1 (solid line) and [(Cu2I2)(4,40 -bipy)(dppm)]1 (4) (dashed line) with excitation at 330 nm.

4. Conclusion In this work, we obtained four new polynuclear CuI complexes by reacting CuI with 4,40 -bipyridine and tricyclohexylphosphine, bis(dicyclohexylphosphino)methane or bis(diphenylphosphino)methane. Their crystal structures and photophysical properties have been examined. Also, we have examined the spectroscopic properties of the related [CuClPCy3]2 and [CuIPCy3]2 complexes. All of the complexes exhibit intense phosphorescent emissions with kem varying 430–640 nm in solid state at room temperature. These emissions were attributed to arising from metal-centered MC (3d ? 4s, 4p) excited state for 5 and 6, and a triplet-parentage MLCT (CuI ? 4,40 -bipyridine) excited state for 1–4. The successful preparation of these CuI complexes with relatively high emission quantum yields in solid state provides great potential for light emitting materials. Acknowledgement

Fig. 6. Plots of the relevant HOMOs and LUMOs for complexes 2–6.

The work was supported by the National Basic Research Program of China (973 program 2005CCA06800, 2007CB613304), the

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