Solvent Effects on the Assembly of [Cu2I2]- or [Cu4I4]-Based

CRYSTAL GROWTH & DESIGN

Solvent Effects on the Assembly of [Cu2I2]- or [Cu4I4]-Based Coordination Polymers: Isolation, Structures, and Luminescent Properties

2008 VOL. 8, NO. 10 3810–3816

Yang Chen,† Hong-Xi Li,† Dong Liu,† Lei-Lei Liu,† Ni-Ya Li,† Huan-Ying Ye,† Yong Zhang,† and Jian-Ping Lang*,†,‡ Key Laboratory of Organic Synthesis of Jiangsu ProVince, School of Chemistry and Chemical Engineering, Suzhou UniVersity, Suzhou 215123, People’s Republic of China, and State Key Laboratory of Coordination Chemistry, Nanjing UniVersity, Nanjing 210093, People’s Republic of China ReceiVed May 3, 2008; ReVised Manuscript ReceiVed June 21, 2008

ABSTRACT: Four [Cu2I2]- or [Cu4I4]-based coordination polymers, [CuI(bpp)]n (1), {[Cu3I3(bpp)3] · 2aniline · MeCN}n (2), {[Cu2I2(bpp)2] · 2aniline}n (3), and [Cu4I4(bpp)2]n (4), were prepared by solvothermal reactions of CuI or Cu2(OH)2CO3 with 1,3-bis(4pyridyl)propane (bpp) in different solvent systems. The preparation of 2 or 3 is involved in the in situ formation of aniline molecules and the reduction of Cu(II) to Cu(I). These compounds were characterized by elemental analysis, IR, and single crystal X-ray diffraction. Compound 1 consists of [Cu2I2] dimeric cores that link the neighboring ones via bpp bridges to form a one-dimensional double-bridged polymeric chain. Compound 2 or 3 has a similar chain structure in which the shape and size of the [Cu2I2(bpp)2]2 cavities that are occupied by MeCN/aniline or aniline solvent molecules are different from those of 1. Compound 4 has an intriguing two-dimensional 4-fold interpenetrated network in which each cubanelike [Cu4I4] core acts as a rare “seesaw”-shaped four-connecting node to interconnect four other equivalent ones via bpp bridges. The results did provide interesting insights into solvent effects on the construction of cluster-based coordination polymers. In addition, the photoluminescent properties of 1-4 in the solid state at ambient temperature were also investigated. Introduction In recent years, the construction of cluster-based coordination oligomers and polymers has received much attention due to not only their intriguing architectures and topologies1 but also their potential applications as functional materials in magnetism, photoluminescence, electric conductivity, adsorption, and heterogeneous catalysis.2 Preparation of such compounds is always affected by many factors such as core structures of the precursors, symmetry of the ligands, and temperatures.3 However, solvent effects on the formation of cluster-based coordination polymers are less explored or mentioned in the literature.4 On the other hand, among many metal salts possessing potential cluster-forming characteristics, copper(I) iodide is known to self-aggregate into rhomboid [Cu2I2] and cubanelike [Cu4I4] cluster cores.5 In different solvent systems, these two cores may act as 2-4-connecting nodes to connect other equivalent ones via some bridging ligands such as 4,4′bipyridine (4,4′-bipy) and 1,3-bis(4-pyridyl)propane (bpp), forming various multidimensional coordination frameworks. For instance, solvothermal reactions of CuI with bpp in mixed toluene/MeCN at 160 °C for 3 days produced a [Cu2I2]-based polymeric cluster {[Cu2I2(bpp)2] · (toluene)}n5c or a [Cu4I4]-based polymer [Cu4I4(bpp)2]n,5b while those of CuI with bpp in the presence of KI in THF/DMF/H2O followed by slow evaporation of solvents afforded another [Cu2I2]-based polymeric cluster [(CuI)4(bpp)4]n [2-fold interpenetrating two-dimensional (2D) (4,4) polycatenane net].5a These results attracted and activated us to consider one more question: Do other solvent systems work for reactions of CuI with bpp in solvothermal conditions? With this question in mind, we attempted solvothermal reactions of CuI with bpp in iodobenzene/MeCN or cyclohexanol/MeCN * To whom correspondence should be addressed. Tel/Fax: +86 512 65880089. E-mail: [email protected]. † Suzhou University. ‡ Nanjing University.

or reactions of Cu2(OH)2CO3 with bpp in the presence of ammonia in iodobenzene/MeCN, and three [Cu2I2]-based polymeric clusters [CuI(bpp)]n (1), {[Cu3I3(bpp)3] · 2aniline · MeCN}n (2), and {[Cu2I2(bpp)2] · 2aniline}n (3), and one [Cu4I4]-based polymeric cluster, [Cu4I4(bpp)2]n (4), were isolated therefrom. Herein, we report their isolation, crystal structures, and photoluminescent properties. Materials and Methods All chemicals were obtained from commercial sources and used as received. The IR spectra were recorded on a Varian 1000 FT-IR (Scimitar Series) spectrometer as KBr disks (400-4000 cm-1). The elemental analyses for C, H, and N were performed on a Carlo-Erba EA1110 CHNO-S microanalyzer. The emission/excitation spectra were measured on a Varian Cary Eclipse fluorescence spectrophotometer equipped with a continuous Xenon lamp. 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. [CuI(bpp)]n (1). To a Pyrex glass tube (15 cm in length, 7 mm in inner diameter) were added CuI (10 mg, 0.05 mmol), bpp (10 mg, 0.05 mmol), iodobenzene (150 mg, 0.74 mmol), and 2 mL of MeCN. The tube was sealed and heated in an oven at 150 °C for 70 h and then cooled to room temperature at a rate of 5 °C/100 min to form pale yellow needles of 1, which were collected by filtration, washed with MeCN, and dried in air. Yield: 5 mg (23% based on Cu). Anal. calcd for C13H14CuIN2: C, 40.17; H, 3.63; N, 7.21. Found: C, 40.03; H, 3.64; N, 7.17. IR (KBr, cm-1): 3050w, 2939w, 2860w, 1609vs, 1557w, 1498m, 1422s, 1385w, 1221m, 1084w, 1068w, 1013w, 810m, 610w, 571w, 515m. {[Cu3I3(bpp)3] · 2aniline · MeCN}n (2). Compound 2 (yellow block crystals) was prepared as above starting from Cu2(OH)2CO3 (22 mg, 0.1 mmol), bpp (20 mg, 0.1 mmol), iodobenzene (150 mg, 0.74 mmol), 1.5 mL of aqueous ammonia (25%), and 2 mL of MeCN. Yield: 26 mg (57% based on bpp). Anal. calcd for C53H59Cu3I3N9: C, 45.68; H, 4.27; N, 9.05. Found: C, 45.82; H, 4.26; N, 8.99. IR (KBr, cm-1): 3437w, 3342w, 3206w, 3040w, 2941w, 2860w, 2247w, 1609vs, 1556w, 1498m, 1422s, 1283w, 1220m, 1068w, 1012w, 810m, 755w, 695w, 609w, 572w, 510m.

10.1021/cg8004568 CCC: $40.75  2008 American Chemical Society Published on Web 08/13/2008

[Cu2I2]- or [Cu4I4]-Based Coordination Polymers

Crystal Growth & Design, Vol. 8, No. 10, 2008 3811

Table 1. Summary of Crystallographic Data for 1-4 compounds formula FW crystal system space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z T (K) Dcalcd (g 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 ∆Fmax/∆Fmin (e/Å3)

1

2

3

4

C13H14CuIN2 C53H59Cu3I3N9 C38H42Cu2I2N6 C26H28Cu4I4N4 388.71 1393.45 963.68 1158.33 monoclinic triclinic triclinic orthorhombic

The collected data were reduced by the program CrystalClear, and an absorption correction (multiscan) was applied. Measurement of 4 was carried on a CCD-Bruker APEX diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at 293 K. Data reductions and absorption corrections were performed with the SAINT and SADABS software packages. The reflection data for 1-4 were also corrected for Lorentz and polarization effects. The crystal structures of 1-4 were solved by direct methods and refined against F2 by full-matrix least-squares for all independent reflections.6 For 2, the N atom of the each aniline solvent molecule was disordered over two positions, which were isotropically refined with an occupancy factor of 0.48/0.52 for N7/N8 or 0.41/0.59 for N9/ N10. For 4, the N4-containing pyridyl group and C21 were disordered over two sites (C21/C21′, C22/C22′, C23/C23′, C24/C24′, C25/C25′, C26/C26′, and N4/N4′) with an occupancy ratio of 0.54/0.46. The two H atoms on C21′ atoms could not be added properly because of the presence of disorder. All other nonhydrogen atoms were refined anisotropically. 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 1-4 is tabulated in Table 1.

C2/m

P 1j

P 1j

Ibca

16.283(3) 13.068(3) 8.4025(17)

10.162(2) 11.792(2) 17.655(4) 88.18(3) 88.21(3) 65.00(3) 1916.1(8) 2 291(2) 1.670

15.666(5) 25.131(8) 37.527(13)

1784.6(6) 4 293(2) 1.447

11.410(2) 13.446(3) 19.377(4) 100.08(3) 96.88(3) 107.19(3) 2749.3(12) 2 223(2) 1.681

14775(8) 16 293(2) 2.081

752 2.938

1368 2.877

952 2.756

8625.2 5.635

8361

27030

16860

29582

Results and Discussion

1712

9992

6733

6525

1288

7271

4285

2233

0.0820

0.0584

0.0654

0.0448

Synthesis. Our use of the rarely used solvents like iodobenzene and cyclohexanol was based on the following considerations. First, these uncommon solvents were used to check how they affect the formation and topological structures of CuI/bpp coordination polymers. Second, some organic reactions related to the iodide group in iodobenzene and the hydroxyl group in cyclohexanol were anticipated to take place. Third, the iodide group of iodobenzene may offer iodides for generating Cu/I clusters. Reactions of CuI with bpp in iodobenzene/MeCN under solvothermal conditions led to the formation of the [Cu2I2]based polymeric cluster 1 in 23% yield. However, when a Cu(II) salt, Cu2(OH)2CO3, was employed to react with bpp under the presence of aqueous ammonia (25%) at the same conditions, another [Cu2I2]-based polymeric cluster 2 was produced in 57% yield. In this reaction, the reduction of Cu(II) to Cu(I) and the in situ formation of aniline molecules deserves comments. Some previous reports have shown that under the presence of N-containing ligands Cu(II), salts underwent a redox process under hydro/solvothermal conditions to produce Cu(I) compounds.7 In our case (Scheme 1a), the same thing happened, although the possibility that the iodide (derived from the conversion of iodobenzene to aniline) may reduce Cu(II) may not be ruled out. The resulting Cu(I) may combine with iodides to afford some copper iodide aggregates [CuI]n. Such species were trapped by bpp ligands to give [Cu3I3(bpp)3]n (in the case of 2). On the other hand, amination reactions of aryl halides are important for the synthesis of the N-aryl-containing molecules that are related to pharmaceuticals, agrochemicals, pigments, electronic materials, and natural products.8 As compared with the C-N cross-coupling of electron-poor aryl halides with amines, that of aryl halides bearing electron-rich substituents is not accessed easily under mild conditions.9 In our reaction, under the catalysis of Cu+ ions, iodobenzene may undergo an Ullmann coupling reaction,10 allowing the efficient formation of aniline from iodobenzene and NH3 (Scheme 1b). Because of the presence of such in situ-formed aniline molecules, the solvent system in this reaction was changed, and thus, the resulting [Cu3I3(bpp)3]n crystallized with MeCN and aniline solvent molecules to form crystals of 2. In the case of 3, the same solvothermal conditions were maintained for reactions of CuI with bpp in iodobenzene/MeCN while malonic acid was introduced to adjust the pH value of the solution to form other polymeric clusters. The isolation of 3 and the subsequent X-ray analysis revealed that the change

93.52(3)

0.1926 0.1115 0.1375 0.0554 1.042 1.095 1.108 1.005 1.301/-0.553 0.928/-0.747 0.661/-0.542 0.790/-0.566

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

Scheme 1. Conversion from Cu(II) to Cu(I) and the Transformation from Iodobenzene to Aniline during the Formations of 2 or 3

{[Cu2I2(bpp)2] · 2aniline}n (3). Compound 3 (golden yellow plates) was prepared as above starting from Cu2(OH)2CO3 (22 mg, 0.1 mmol), bpp (20 mg, 0.1 mmol), iodobenzene (150 mg, 0.74 mmol), malonic acid (10 mg, 0.1 mmol), 0.5 mL of 25% ammonia, and 2 mL of MeCN. Yield: 29 mg (61% based on bpp). Anal. calcd for C38H42Cu2I2N6: C, 47.36; H, 4.39; N, 8.72. Found: C, 47.41; H, 4.37; N, 8.68. IR (KBr, cm-1): 3433m, 3341m, 3205w, 3039w, 2942w, 2860w, 1610vs, 1556w, 1498s, 1422s, 1285w, 1219m, 1174w, 1070w, 1012w, 835w, 811w, 755m, 695w, 610w, 571w, 510m. [Cu4I4(bpp)2]n (4). Compound 4 (brown block crystals) was prepared as above starting from CuI (10 mg, 0.05 mmol), bpp (10 mg, 0.05 mmol), cyclohexanol (1 mL), and 2 mL of MeCN. Yield: 4 mg (27% based on Cu). Anal. calcd for C26H28Cu4I4N4: C, 26.96; H, 2.44; N, 4.84. Found: C, 26.89; H, 2.44; N, 4.77. IR (KBr, cm-1): 3051w, 2924m, 2852w, 1612vs, 1556w, 1498m, 1445w, 1423vs, 1385w, 1221m, 1127w, 1065m, 1018m, 960w, 804m, 669w, 616w, 582w, 517m. X-ray Crystallographic Study. The X-ray quality crystals of 1-4 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 Å). These crystals were mounted on glass fibers, and compound 2 was cooled at 223 K in a liquid nitrogen stream. Cell parameters were refined on all observed reflections by using the program Crystalclear (Rigaku and MSc, Ver. 1.3, 2001).

3812 Crystal Growth & Design, Vol. 8, No. 10, 2008

Chen et al.

Figure 1. (a) View of a section of the 1D double chain of 1 extending along the b-axis. (b) View of a portion of the 1D double chain of 2 extending along the [321] direction. (c) View of a part of the 1D double chain of 3 extending along the [111] direction. All H atoms were omitted for clarity. Atom color code: Cu, turquoise; I, pink; N, blue; and C, light gray. Symmetry codes for 1: (A) -x, -y + 1, -z + 1; (B) x, -y + 1, z; (C) -x, y, -z + 1; (D) x, -y, z; (E) -x, -y, -z + 1; (F) -x, y + 1, -z + 1; and (G) x, y + 1, z. Symmetry codes for 2: (A) -x + 3, -y + 1, -z + 1; and (B) -x, -y - 1, -z. Symmetry codes for 3: (A) x - 1, y + 1, z; and (B) x + 1, y - 1, z.

of pH did not result in the formation of a new structure. However, the shape and size of the [Cu2I2(bpp)]2 cavities in 3 were somewhat changed, and each cavity was occupied by the same aniline solvent molecules. As discussed later in this paper, compounds 1-3 have a similar double-chain structure, but there are MeCN/aniline (2) or aniline (3) molecules in the [Cu2I2(bpp)]2 cavities of the chain of 2 or 3. It seems that 1 could be converted into 2 or 3 if crystals of 1 were immersed in MeCN/aniline or aniline. When crystals of 1 were immersed into MeCN/aniline or aniline for up to 1 week, the IR spectrum and X-ray analysis revealed that its structure was always retained. Furthermore, the conversion between 2 and 3 was also proved unsuccessful when crystals of 2 were immersed into pure aniline or crystals of 3 were immersed into pure MeCN. The reason for these results is that the 1D chains of 1-3 have a staggered stacking in their crystals, which may prevent the solvent molecules from moving in or out of the [Cu2I2(bpp)]2 cavities freely (Figures S2, S5, and S8 of the Supporting Information). Intriguingly, when cyclohexanol was used instead of iodobenzene, analogous reactions of CuI with bpp under the same solvothermal conditions afforded 4 in 27% yield. We employed cyclohexanol in this reaction based on the following considerations. One is that it combines with MeCN to constitute another solvent system. The other is to explore whether the 1D chain similar to those of 1-3 is changed if formed. In fact, the structure of 4 is quite different from those of 1-3, which is mainly due to the driving force of solvent effects. The relatively low yields of 1 and 4 may be due to the fact that CuI has low solubility in either iodobenzene/MeCN or cyclohexanol/MeCN. Solid 1-4 are stable toward air and moisture and are insoluble in common organic solvents such as MeOH, THF, CH2Cl2, acetone, toluene, DMF, and DMSO. The elemental analysis was

consistent with the chemical formulas of 1-4. The identities of 1-4 were further confirmed by X-ray crystallography. Crystal Structures of 1-3. Compound 1 crystallizes in the monoclinic space group C2/m and the asymmetric unit of 1 consists of one-fourth of [Cu2I2(bpp)2] species. Compounds 2 and 3 crystallize in the triclinic space group P 1j and the asymmetric unit of 2 contains half of the [Cu2I2(bpp)2]3 species and one MeCN and two aniline solvent molecules while that of 3 consists of one [Cu2I2(bpp)2] species and two aniline solvent molecules. Figure 1 shows the structures of 1-3, and the selected bond lengths and angles for 1-3 are compared in Table 2. Compounds 1-3 contain rhombiod Cu2I2 cluster cores that are linked by two pairs of bpp bridges, forming a 1D double chain structure extending along the b-axis (1) (Figure 1a), the [321] direction (2) (Figure 1b), or the [111] direction (3) (Figure 1c). In the [Cu2I2] core, each Cu(I) center is coordinated by two I atoms and two N atoms of bpp, forming a slightly distorted tetrahedral geometry. The mean Cu · · · Cu contact [2.7657(17) Å] of 3 is slightly shorter than that of [Cu2I2L4] [L ) 3-methylpridine, 2.781(4) Å]11c but longer than those of 1 [2.713(4) Å] and 2 [2.6958(16) Å] and other complexes containing tetrahdrally coordinated Cu(I) such as [Cu2I2L4] [L ) pyridine, 2.698(2) Å; L ) 3,5-dimethylpridine, 2.687(2) Å].11a,b The mean Cu-I and Cu-N bond lengths of 1-3 are normal relative to those of [Cu2I2L4] (L ) pyridine; 3,5-dimethylpridine; L ) 3-methylpridine).11 It is worth noting that the bpp ligands in 1-3 exhibit different conformations (Scheme 2) with different N-to-N distances (Scheme 2). In 1, each bpp ligand shows a trans-trans conformation (Scheme 2a and Figure 1a) with a N1-to-N1D distance of 9.686 Å and the dihedral angle between the pyridyl rings of

[Cu2I2]- or [Cu4I4]-Based Coordination Polymers

Crystal Growth & Design, Vol. 8, No. 10, 2008 3813

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1-3a

Scheme 2. Possible Conformations of the bpp Ligand

complex 1 I(1)-Cu(1) Cu(1)-N(1B) Cu(1) · · · Cu(1A) Cu(1)-I(1)-Cu(1A) N(1B)-Cu(1)-I(1) N(1B)-Cu(1)-I(1A) I(1)-Cu(1)-I(1A)

2.620(2) 2.066(9) 2.713(4) 61.31(8) 108.7(2) 105.3(2) 118.69(8)

I(1)-Cu(1A) Cu(1)-N(1)

2.700(2) 2.066(9)

N(1B)-Cu(1)-N(1) N(1)-Cu(1)-I(1) N(1)-Cu(1)-I(1A)

109.9(5) 108.7(2) 105.3(2)

complex 2 Cu(1)-I(1) Cu(2)-I(1) Cu(3)-I(3) Cu(1)-N(1) Cu(2)-N(3) Cu(3)-N(2) Cu(1) · · · Cu(2) I(2)-Cu(1)-I(1) N(1)-Cu(1)-I(1) N(1)-Cu(1)-I(2) I(1)-Cu(2)-I(2) N(3)-Cu(2)-I(1) N(6A)-Cu(2)-I(1) I(3B)-Cu(3)-I(3) N(2)-Cu(3)-N(4B) N(2)-Cu(3)-I(3B) Cu(2)-I(1)-Cu(1) Cu(3B)-I(3)-Cu(3)

2.6902(12) 2.6526(12) 2.6648(12) 2.057(6) 2.044(6) 2.049(5) 2.6844(14) 119.16(4) 103.63(16) 107.78(16) 119.19(4) 107.60(17) 107.79(16) 118.40(4) 107.2(2) 109.97(16) 60.32(3) 61.60(4)

Cu(1)-I(2) Cu(2)-I(2) Cu(3)-I(3B) Cu(1)-N(5) Cu(2)-N(6A) Cu(3)-N(4B) Cu(3) · · · Cu(3B) N(5)-Cu(1)-N(1) N(5)-Cu(1)-I(1) N(5)-Cu(1)-I(2) N(3)-Cu(2)-N(6A) N(6A)-Cu(2)-I(2) N(3)-Cu(2)-I(2) N(4B)-Cu(3)--I(3B) N(2)-Cu(3)-I(3) N(4B)-Cu(3)-I(3) Cu(1)-I(2)-Cu(2)

2.6443(12) 2.6812(12) 2.6219(12) 2.056(6) 2.049(6) 2.063(6) 2.7072(18) 109.9(2) 104.09(16) 111.82(17) 115.1(2) 101.31(16) 106.15(17) 108.28(17) 105.39(16) 107.09(18) 60.53(3)

complex 3 Cu(1)-I(1) Cu(2)-I(2) Cu(1)-N(2A) Cu(2)-N(4B) Cu(1) · · · Cu(2) N(2A)-Cu(1)-N(1) N(1)-Cu(1)-I(1) N(1)-Cu(1)-I(2) N(4B)-Cu(2)-N(3) N(3)-Cu(2)-I(2) N(3)-Cu(2)-I(1) Cu(2)-I(1)-Cu(1)

2.6667(13) 2.6310(13) 2.060(7) 2.059(7) 2.7657(17) 106.0(3) 103.10(18) 110.1(2) 104.6(3) 105.7(2) 109.4(2) 62.67(4)

Cu(1)-I(2) Cu(2)-I(1) Cu(1)-N(1) Cu(2)-N(3)

2.6681(14) 2.6512(14) 2.065(6) 2.073(6)

N(2A)-Cu(1)-I(1) N(2A)-Cu(1)-I(2) I(1)-Cu(1)-I(2) N(4B)-Cu(2)-I(2) N(4B)-Cu(2)-I(1) I(2)-Cu(2)-I(1) Cu(2)-I(2)-Cu(1)

110.37(19) 110.4(2) 116.27(5) 108.69(19) 109.3(2) 118.14(5) 62.92(4)

a Symmetry codes for 1: (A) -x, -y + 1, - z + 1; and (B) x, -y + 1, z. Symmetry codes for 2: (A) -x + 3, -y + 1, -z + 1; and (B) -x, -y - 1, -z. Symmetry codes for 3: (A) x - 1, y + 1, z; and (B) x + 1, y - 1, z.

67.967°. In 2, the three bpp ligands in an asymmetric unit are not uniform, which assume two different conformations (Figure 1b). The two bpp ligands bearing a N1/N2 pair and a N5/N6 pair adopt a trans-gauche conformation (Scheme 2b) with N-to-N distances of 9.049 and 8.694 Å, and with the dihedral angles between the pyridyl rings 60.637 and 60.225°, respectively. The third bpp ligand carrying N3/N4 pair exhibits the trans-trans conformation (Scheme 2a) with an N-to-N distance of 9.511 Å and the dihedral angle between the pyridyl rings of

74.033°. For 3, the two bpp ligands in an asymmetric unit assume a trans-gauche conformation (Scheme 2b and Figure 1c) with N-to-N distances of 8.644 (N1/N2 pair) and 8.635 Å (N3/N4 pair), and the dihedral angles between the pyridyl rings of 71.980 (N1/N2 pair) and 74.132° (N3/N4 pair), respectively.12 Because of the different conformations of the bpp ligands, the [Cu2I2(bpp)]2 metallomacrocycles in 1-3 show somewhat different shapes and sizes with different cross-section areas (Scheme 3). On the basis of the distances of closest methylenes of two bpp ligands and two [Cu2I2] cluster fragments, the [Cu2I2(bpp)]2 metallomacrocycle (with a pair of bpp ligands carrying the same trans-trans conformations) in 1 has an approximate cross-section dimension of 6.868 × 13.068 Å2, which produces the total potential solvent accessible voids of ca. 275 Å3 per unit cell (Figure 1a and Scheme 3a).13 For 2, two types of the [Cu2I2(bpp)]2 metallomacrocycles exist. One has a couple of bpp ligands carrying the same trans-gauche conformations (Scheme 3b), while the other has a pair of trans-trans and trans-gauche conformations (Scheme 3c). The cavity for the former is occupied by two aniline solvent molecules (Figure 1b), and its size is roughly calculated to be 7.419 × 11.795 Å2. Intriguingly, the void for the latter is located by one MeCN and one aniline solvent molecules, and its dimension is ca. 6.868 × 13.068 Å2. For 3, the [Cu2I2(bpp)]2 metallomacrocycle (with a pair of bpp ligands carrying the same trans-gauche conformations) is occupied by two aniline molecules (Figure 1c) and has cross-section dimensions of ca. 7.981 × 11.876 Å2 (Scheme 3b). Another interesting thing that should be mentioned is that there are relatively strong C-H · · · π interactions and hydrogenbonding interactions in the crystals of 1-3. For 1, each 1D chain is held together via C-H · · · π interactions (see Figure S1 of the Supporting Information, H · · · pyridyl centroid 3 Å),14 forming a 2D H-bound network extending along the bc plane. In the case of 2, each aniline molecule is fixed with its adjacent iodine atom via N-H · · · I hydrogen-bonding interactions (H · · · I, 3.105-3.344 Å; N-H · · · I, 150.59-154.97°), and each acetonitrile molecule interacted with its adjacent bpp ligand via C-H · · · N hydrogen-bonding interaction (H · · · N, 2.879 Å; C-H · · · N, 160.39°) (Figure S3 of the Supporting Information). In addition, each 1D chain connect with each other via C-H · · · π interactions (H · · · pyridyl centroid 2.664-3.387 Å) to form a

Scheme 3. Three Types of [Cu2I2(bpp)]2 Metallomacrocycles

3814 Crystal Growth & Design, Vol. 8, No. 10, 2008

Chen et al. Table 3. Selected Bond Lengths (Å) and Angles (deg) for 4a Cu(1)-N(1) Cu(1)-I(3) Cu(1)-I(1) Cu(1)-I(2) Cu(2) · · · Cu(4) Cu(2) · · · Cu(3) Cu(2)-I(1) Cu(3)-I(3) Cu(3)-I(4) Cu(4)-N(4B) Cu(4)-I(4) N(1)-Cu(1)-I(3) I(3)-Cu(1)-I(1) I(3)-Cu(1)-I(2) N(2A)-Cu(2)-I(4) I(4)-Cu(2)-I(2) I(4)-Cu(2)-I(1) N(3)-Cu(3)-I(3) I(3)-Cu(3)-I(4) I(3)-Cu(3)-I(2) N(4B)-Cu(4)-I(1) I(1)-Cu(4)-I(4) I(1)-Cu(4)-I(3) a

2.024(9) 2.6603(18) 2.6633(15) 2.7146(16) 2.653(2) 2.6755(18) 2.7169(15) 2.6574(17) 2.6645(17) 1.877(10) 2.6951(18) 101.8(3) 113.75(6) 114.00(5) 103.8(3) 112.91(5) 114.74(6) 105.9(3) 115.61(6) 112.99(5) 113.8(6) 114.69(6) 110.64(6)

Cu(1) · · · Cu(3) Cu(1) · · · Cu(2) Cu(1) · · · Cu(4) Cu(2)-N(2A) Cu(2)-I(4) Cu(2)-I(2) Cu(3)-N(3) Cu(3) · · · Cu(4) Cu(3)-I(2) Cu(4)-I(1) Cu(4)-I(3) N(1)-Cu(1)-I(1) N(1)-Cu(1)-I(2) I(1)-Cu(1)-I(2) N(2A)-Cu(2)-I(2) N(2A)-Cu(2)-I(1) I(2)-Cu(2)-I(1) N(3)-Cu(3)-I(4) N(3)-Cu(3)-I(2) I(4)-Cu(3)-I(2) N(4B)-Cu(4)-I(4) N(4B)-Cu(4)-I(3) I(4)-Cu(4)-I(3)

2.6554(19) 2.6629(17) 2.681(2) 2.035(8) 2.6705(17) 2.6929(15) 2.004(9) 2.6599(19) 2.7485(17) 2.6936(16) 2.7280(18) 109.2(3) 103.4(3) 113.36(5) 107.8(3) 104.2(3) 112.34(5) 108.5(3) 101.2(3) 111.34(5) 101.6(5) 103.0(5) 112.29(6)

Symmetry codes: (A) x - 1, y, z; and (B) x, y - 1/2, -z.

Figure 3. View of the 4-fold interpenetration in 4 looking down the a-axis.

Figure 2. (a) Perspective view of the cubanelike [Cu4I4(bpp)4] fragment of 4. See Figure 1 for the color codes; hydrogen atoms were omitted for clarity. Symmetry codes: (A) x - 1, y, z; and (B) x, y - 1/2, -z. (b) View of the interactions of a central [Cu4I4] core via four bpp bridges in 4. (c) View of one 2D layer structure of 4 extending along the ab plane.

Figure 4. Excitation (dashed line) and emission (solid line) spectra of 1-4 in the solid state at ambient temperature.

2D H-bound network (Figure S4 of the Supporting Information).14 For 3, aniline guests also interact with the [Cu2I2] cluster fragment through N-H · · · I hydrogen-bonding interaction (H · · · I,

[Cu2I2]- or [Cu4I4]-Based Coordination Polymers

3.137 Å; N-H · · · I, 177.44°) (Figure S6 of the Supporting Information). Like 1 and 2, each 1D chain is held together via C-H · · · π interactions (see Figure S7 of the Supporting Information, H · · · pyridyl centroid 2.915-3.214 Å),14 thereby generating another 2D H-bound layer structure extending along the [112] plane (Figure S7 of the Supporting Information). Crystal Structure of 4. Compound 4 crystallizes in the orthorhombic space group Ibca, and the asymmetric unit of 4 contains one independent [Cu4I4(bpp)2] molecule. Figure 2 shows the structure of 4, and the selected bond lengths and angles for 4 are listed in Table 3. As shown in Figure 2a, this molecule has a distorted cubanelike [Cu4I4] core structure, which closely resembles those of its isomer [Cu4I4(bpp)2]n and [Cu4I4(phpy)4] (phpy ) 4-phenylpyridine).15 Each copper(I) atom adopts a distorted tetrahedral coordination geometry. The Cu-I and Cu-N bond lengths are comparable to those of 1-3. The Cu · · · Cu separations range from 2.653(2) to 2.681(2) Å, which are shorter than those of 1-3 but are comparable to those found in other [Cu4I4L4] clusters (L ) nitrogen-containing ligand).15 All of the bpp ligands exhibit trans-trans formation with N-to-N distances of 9.599 (N1/N2 pair) and 9.527 Å (N3/ N4 pair) and dihedral angles between the pyridyl rings of 63.158 (N1/N2 pair) and 89.511° (N3/N4 pair), respectively. Topologically, each cubanelike [Cu4I4] cluster core works as a rare “seesaw”-shaped four-connecting node (Figure 2b) linked by a pair of bpp ligands to form a 1D linear [Cu4I4(bpp)]n chain extending along the a-axis. Such a chain is further interconnected by another pair of bpp ligands to form a unique 2D (4,4) wavelike network extended along the ab plane (Figure 2c). Within the layer, each rectangle mesh has an approximate size of 15.666 Å × 15.928 Å, which is large enough to make interpenetration of layers. In fact, each single net interpenetrates three other identical ones, resulting in a quadruply interpenetrated net (Figure 3.) Although interpenetrating 2D coordination framework with Cu(II) and bpp ligands16a-c and 4-fold interpenetrating 3D network with Cu(II) and 4,4′-bipy16d are known, compound 4, to our knowledge, is the first example of a 4-fold interpenetrating 2D network with Cu(I) and bpp ligands. There are C-H · · · π interactions (H · · · pyridyl centroid 3.297 Å) (Figure S8 of the Supporting Information) within each layer due to such an interpenetration.14 No evident interactions are found between the adjacent 2D layers. It is interesting to make a structural comparison between 4 and its isomer.5b The latter compound has a [Cu4I4] core that serves a tetrahedral fourconnecting node. The resulting 3D net is an unique chiral tripleinterpenetrated, quartz net with vertex symbol 64.82. Photoluminescent Properties. The photoluminescent properties of 1-4 in the solid state at room temperature have been investigated. The excitation and emission maxima (λmaxex and λmaxem) are shown in Figure 4. For 1-3, upon excitation at 344, 333, and 335 nm, they exhibited strong photoluminescence with emission maxima at ca. 507, 502, and 492 nm, respectively, which is similar to that of the dimeric complex [Cu2I2(py)4] (py ) pyridine) with λmaxem ) 517 nm at 294 K.17a These emissions may be assigned to be cluster-centered (CC*) transition and halide-to-ligand charge-transfer (XLCT).17b,c It should be noted that blue shift occurred in the fluorescent spectra from 1 to 3. The reason for this phenomenon is probably due to the fact that the N-H · · · I hydrogen-bonding interaction between aniline molecules and [Cu2I2] cluster cores may reduce the electron density of iodine ion, which decreases the efficiency of XLCT. For 4, excitation at 333 nm produced an intense yellow emission with a peak maximum at 569 nm, which might be assigned as a combination of a CC* excited state containing

Crystal Growth & Design, Vol. 8, No. 10, 2008 3815

mixed halide-to-metal charge-transfer (XMCT) and d-s transitions by Cu(I)-Cu(I) interactions of 4.15,18 Conclusions In the work reported here, we demonstrated our efforts to explore the solvent effects on the assembly of [Cu2I2]- or [Cu4I4]-based coordination polymers. Compounds 1-4 were prepared from solvothermal reactions of CuI or Cu2(OH)2CO3 with bpp in the prearranged solvent systems or in the systems consisting of prearranged solvents and the in situ-formed solvents. The conversion of iodobenzene to aniline in the formation of 2 or 3 under solvothermal conditions is unprecedented. It is also unique that relative to those of 1, the shape and size of the [Cu2I2(bpp)]2 metallomacrocycles of 2 or 3 are changed because of inclusion of MeCN or in situ-formed aniline molecules into their cavities. In addition, inclusion of different solvent molecules into the cavities of the [Cu2I2(bpp)]2 metallomacrocycles of 2 and 3 made their emission maxima blueshifted relative to that of 1. These results indicate that solvent effects could place great impact on the construction of [CuI]xbased coordination polymers as well as their photophysical and photochemical properties. Further studies on solvothermal reactions of CuI with other linkers such as 2,4,6-tri(4-pyridyl)1,3,5-triazine and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin in other solvent systems are underway in this laboratory. Acknowledgment. This work was supported by the National Natural Science Foundation of China (20525101), the Specialized Research Fund for the Doctoral Program of Higher Education (20050285004), the State Key Laboratory of Coordination Chemistry of Nanjing University, and “SooChow Scholar” Program and Program for Innovative Research Team of Suzhou University. We thank Prof. Guo-Xin Jin of Fudan University in China for X-ray measurement of 4. We are also grateful to the reviewers for their helpful suggestions. Supporting Information Available: Crystal structural data for 1-4 in CIF format and figures giving a crystal packing diagram of 1-4 in pdf format. This material is available free of charge via the Internet at http://pubs.acs.org.

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CG8004568