Organic Templated Cuprous Cyanide Open Frameworks Based on

ARTICLE pubs.acs.org/crystal

Organic Templated Cuprous Cyanide Open Frameworks Based on Cu2(CN)6 Dimer with Strong and Long-Lived Luminescence Ying-Lian Qin, Juan-Juan Hou, Jin Lv, and Xian-Ming Zhang* School of Chemistry & Material Science, Shanxi Normal University, Linfen 041004, P. R. China

bS Supporting Information ABSTRACT: By using environmental friendly K3[Fe(CN)6] as a cyanide source, hydrothermal reactions of CuCl2 and diamines resulted in four Cu2(1,1,2-μ3-CN)2(CN)4 dimer-based organic templated cuprous cyanide open frameworks, namely, [H1.5mepip]2[Cu4(CN)7] (1), [H1.5etpip]2[Cu4(CN)7] (2), [H2me2pip][Cu3(CN)5 ] (3), and [H2dmpa][Cu4(CN)6] (4) (mepip = N-methylpiperazine; etpip = N-ethylpiperazine, me2pip = N,N-dimethylpiperazine, dmpa = 3-dimethylaminopropylamine). Isomorphic 1 and 2 show three-dimensional (3-D) (4,6)connected FeS2-like open frameworks constructed by 4-connected Cu(CN)4 monomers and 6-connected Cu2(CN)6 dimers. Complex 3 shows an unprecedented 3-D (4,6)-connected open framework in which the ratio of 4-connected Cu(CN)4 monomers to 6-connected Cu2(CN)6 dimers is 1:1. Complex 4 shows a 3-D (3,6)connected AgIn2-like open framework constructed by 3-connected Cu(CN)3 monomers and 6-connected Cu2(CN)6 dimers. Different from CuCN/amine coordination polymers, the protonated organic diamines in 1
4 act as templates in the formation of cuprous cyanide open frameworks. Even at ambient temperature, 1, 2, 3, and 4 show strong blue-green photoluminescence related to Cu2(CN)6 dimer, which is mainly assigned to metal-to-ligand charge-transfer (MLCT) by time-dependent density functional theory (TD-DFT) and electronic band structure calculations.

’ INTRODUCTION Open framework inorganic materials have been the focus of intense research since the discovery of zeolite-like aluminum phosphates in the early 1980s by Flanigen and co-workers1 because of their applications as shape-selective catalysis, molecular sieving, gas adsorption, and ion exchange.2 Lately, a remarkable variety of oxide and a few nitride, sulfide, and halide open frameworks have been documented which involve rich compositions as well as structural topologies.3 As a branch of the metal halides, metal cyanides are of interest because cyanide can act as not only a mediator for the magnetic interaction between spin carried metals4 but also a coordinately diverse ligand.5 For example, Prussian blue, the oldest coordination compound formulated [Fe4{Fe(CN)6}3] 3 xH2O, is one of open framework metal cyanides with a puzzling magnetic property, representing a typical R-Po topological coordination polymer built from octahedral metal ions and bifunctional cyanide ligands.6 Another common structural type of open metal cyanides is diamond-like network with formula M(CN)2, which is built from tetrahedral metals and linearly coordinate cyanides.5a,7 In contrast to R-Po and diamond, metal cyanide open frameworks with novel topologies are very rare. This may be explained by the fact that transition metal ions tend to have octahedral or tetrahedral geometry and cyanide is generally ligated in linear mode in reported metal cyanides. It has been shown that various monomers of cuprous cyanide exist such as linear Cu(CN)2, trigonal Cu(CN)3 and tetrahedral Cu(CN)4.8 Besides, it is also known r 2011 American Chemical Society

that cyanide sometimes can coordinate in 1,1,2-μ3 mode to a pair of tetrahedral Cu(I) centers to give a Cu2(1,1,2-μ3-CN)2(CN)4 dimer that can act as a 6-connected building unit.9 Therefore, one may expect that the combination of Cu(CN)n (n = 2
4) monomers and Cu2(1,1,2-μ3-CN)2(CN)4 dimers can generate rich cuprous cyanide frameworks, which possibly will be an effective and powerful synthetic strategy for metal cyanide open frameworks with novel topologies.10 Furthermore, cuprous cyanides, especially Cu2(1,1,2-μ3-CN)2(CN)4 dimers, have revealed to be long-lived and highly luminescent materials with abundant optical transitions even at ambient temperature.11 Accordingly, we deem that the exploration of Cu2(1,1,2-μ3-CN)2(CN)4 dimer-based cuprous cyanide open frameworks would lead to a variety of novel luminescent and porous materials. On the other hand, organic amines have been incorporated into open framework materials, which usually act as template occupied structural voids and are well-isolated from the inorganic skeleton.12 In contrast, in the CuCN/amine system, organic amines generally act as linkers to give cuprous cyanide coordination polymers,13
16 and they scarcely function as templates to form cuprous cyanide open frameworks.10,17 Organic-templated cuprous cyanide open frameworks almost are a virgin land waiting for exploration. We noted that majority of cuprous cyanide Received: March 22, 2011 Revised: April 20, 2011 Published: May 16, 2011 3101

dx.doi.org/10.1021/cg200362c | Cryst. Growth Des. 2011, 11, 3101–3108

Crystal Growth & Design coordination polymers are prepared by using KCN or CuCN as cyanide source which not only is toxic but also gives a problem to grow suitable crystals for X-ray single crystal analysis due to rapid crystallization. It is well-known that the formation of cuprous cyanide open frameworks is kinetically controlled and highly sensitive to reaction parameters such as starting materials.18 Compared with traditional cyanide sources of KCN and CuCN, K3[Fe(CN)6] can slowly release cyanide upon heat treatment. Thus, replacement of traditional cyanide sources by environmental friendly K3[Fe(CN)6] may produce some novel cuprous cyanide open frameworks. Besides, slow release of cyanide from K3[Fe(CN)6] could generate large crystals suitable for X-ray single crystal structural analysis. In the work, K3[Fe(CN)6], Cu(II) salts and organic diamines are chosen as starting materials to construct luminescent cuprous cyanide open frameworks by in situ release cyanide method, and herein we present four novel compounds, namely, [H1.5mepip]2[Cu4(CN)7] (1), [H1.5etpip]2[Cu4(CN)7] (2), [H2me2pip][Cu3(CN)5] (3) and [H2dmpa][Cu4(CN)6] (4) (mepip = N-methylpiperazine; etpip = N-ethylpiperazine, me2pip = N,N-dimethylpiperazine, dmpa = 3-dimethyl-aminnopropylamine), all of which are organic templated cuprous cyanide open frameworks constructed by Cu2(CN)6 dimers and Cu(CN)3/Cu(CN)4 monomers. Isomorphic 1 and 2 show (4,6)-connected FeS2-like open frameworks and 3 exhibits an unprecedented 3-D (4,4,6)-connected open framework while 4 has a (3,6)-connected AgIn2-like open network. All compounds show long-lived and strong blue-green photoluminescence even at ambient temperature, which is mainly assigned to metal-to-ligand charge-transfer (MLCT) by time-dependent density functional theory (TD-DFT) and electronic band structure calculations.

’ EXPERIMENTAL SECTION Materials and Physical Measurements. All chemicals were analytically pure from commercial sources and used without further purification. Elemental analyses were performed on a Vario EL-II analyzer. Infrared spectra were obtained in KBr pellets on a PerkinElmer Spectrum BX FT-IR spectrometer in the range 400
4000 cm
1. X-ray powder diffraction (XRPD) data were recorded in a Bruker D8 ADVANCE diffractometer. Photoluminescence was performed on an Edinburgh FLS920 luminescence spectrometer. Thermal analyses were carried out in air atmosphere using SETARAM LABSYS equipment with a heating rate of 10 °C/min. Syntheses. [H1.5mepip]2[Cu4(CN)7] (1). A mixture of CuC12 3 2 H2O (0.051 g, 0.30 mmol), K3[Fe(CN)6] (0.099 g, 0.30 mmol), and Nmepip (0.045 g, 0.45 mmol) in a molar ratio of 1.0:1.0:1.5 and H2O (7 mL) was sealed in a 15-mL Teflon-lined stainless container and heated to 160 °C for 7 days. After it was cooled to room temperature and subjected to filtration, colorless plate crystals of 1 in yield of 32% were recovered. Anal. calcd for C17H27Cu4N11 (1): C, 31.92; H, 4.25, N, 24.07. Found: C, 31.68; H, 4.37, N, 23.79. IR (KBr, cm
1): 2095s, 2070s, 1447s, 1379s, 1115m, 1013m, 970m, 3068w, 842w, 578w. [H1.5etpip]2[Cu4(CN)7] (2). The synthetic procedure of 2 is similar to that of 1 except for N-etpip (0.051 g, 0.45 mmol) instead of N-mepip, colorless plate crystals of 2 in a yield of 36% were recovered. Anal. Calcd for C19H32Cu4N11 (2): C, 34.13; H, 4.82; N, 23.04. Found: C, 33.85; H, 4.92; N, 22.90. IR (KBr, cm
1): 2097s, 2070s, 1370s, 1454s, 1002m, 1110m, 973m, 3070w, 844w, 585w. [H2me2pip][Cu3(CN)5] (3). Colorless block crystals of 3 were obtained in the yield of 35% by a similar procedure at 140 °C when N,Nme2pip was used as template. Anal. Calcd for C11H16Cu3N7 (3): C, 30.24; H, 3.69; N, 22.44. Found: C, 30.05; H, 3.92; N, 22.50. IR

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(KBr, cm
1): 2097s, 2070s, 1370s, 1454s, 1002m, 1110m, 973m, 3070w, 844w, 585w. [H2dmpa][Cu4(CN)6] (4). A mixture of CuC12 3 2H2O (0.068 g, 0.4 mmol), K3[Fe(CN)6] (0.099 g, 0.30 mmol), and dmpa (0.071 g, 0.70 mmol) in a molar ratio of 1.33:1.0:2.33 and H2O (7 mL) was sealed in a 15-mL Teflon-lined stainless container and heated to 160 °C for 7 days. After it was cooled to room temperature and subjected to filtration, yellow prism crystals of 4 in a yield of 45% were recovered. Anal. calcd for C11H14Cu4N8 (4): C, 25.78; H, 2.75; N, 21.86. Found: C, 25.89; H, 3.28; N, 22.04. IR (KBr, cm
1): 2110s, 2076s, 1686s, 1323m, 3447w, 1158w, 1002w, 447w. Crystallographic Studies. X-ray single-crystal diffraction data for 1
3 at 298(2) K and 4 at 140(2) K were collected on a Bruker SMART APEX CCD diffractometer using Mo KR radiation (λ = 0.71073 Å). The program SAINT was used for integration of the diffraction profiles, and the program SADABS was used for absorption correction. All the structures were solved by direct methods using the SHELXS program of the SHELXTL package and refined by full-matrix least-squares methods with SHELXTL.19 All non-hydrogen atoms were refined with anisotropic thermal parameters. The hydrogen atoms of organic groups were generated theoretically onto the specific carbon and nitrogen atoms, and refined isotropically with fixed thermal factors. For 4, organic H2dmpa cations were refined by using a model of trimethyl-propylamine because of the disorder and difficulty in distinguishing 3-methyl and 3-amino. Further details for structural analysis are summarized in Table 1. Selected bond lengths and bond angles are shown in Table S1, Supporting Information. Calculation Details. TD-DFT calculations were performed by using B3LYP20 functional. The LANL2DZ basis sets were employed for Cu. The initial ground-state geometries of dimeric [Cu2(CN)6]4
, trinuclear [Cu3(CN)9]6
, and [Cu3(CN)8]5
directly obtained from the X-ray crystal structures as well as a modified neutral dimer model [Cu2(CN)2(HCN)4] with D2h symmetry have been used for calculations with the Gaussian 03 software package.21 The dimensional plots of molecular configurations and orbitals were generated with the GaussView program.22 To make a comparison with the TD-DFT results, the electronic band structure along with density of states (DOS) for anionic cuprous cyanide frameworks was calculated by DFT using the crystallographic data with the CASTEP code, which uses a plane wave basis set for the valence electrons and norm-conserving pseudopotential for the core electrons.23 The number of plane waves included in the basis was determined by a cutoff energy Ec of 550 eV. Pseudoatomic calculations were performed for C-2s22p2, N-2s22p3, and Cu-3d104s1. The parameters used in the calculations and convergence criteria were set by the default values of the CASTEP code, for example, reciprocal space pseudopotentials representations and eigen-energy convergence tolerance 1.0  10
5 eV.

’ RESULTS AND DISCUSSION Description of Crystal Structures. [H1.5mepip]2[Cu4(CN)7] (1) and [H1.5etpip]2[Cu4(CN)7] (2). Complexes 1 and 2 are

isostructural except for the organic templated cations, and thus only the structure of 1 is described herein in detail. Compound 1 crystallizes in orthorhombic space group Pnnm, and the asymmetric unit contains two crystallographically independent Cu(I) centers, three and half cyanides, and half protonated H1.5mepip cation as shown in Figure 1a. All atoms except for C(1), N(1), C(5), and C(6) localize in special positions. The indistinguishable C(3) and N(3) atoms occupy the same sites and have a site occupancy of 0.25; Cu(1), Cu(2), C(2), and N(2) atoms are within the crystallographic mirror and thus have site occupancies of 0.5. The charge balance requires that mepip exists in protonated 3102

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Table 1. Crystal Data and Structure Refinement Parameters for Compounds 1
4 compound

a

1

2

3

4

formula

C17H27Cu4N11

C19H32Cu4N11

C11H16Cu3N7

C11H14Cu4N8

fw

639.66

668.72

436.93

512.46

crystal system

orthorhombic

orthorhombic

orthorhombic

orthorhombic

space group

Pnnm

Pnnm

Pnma

Pbcn

a (Å)

11.211(3)

11.361(7)

16.3232(16)

14.4440(18)

b (Å)

12.244(3)

12.393(8)

8.7492(9)

12.5254(15)

c (Å)

8.541(2)

8.440(6)

10.9207(11)

13.3074(16)

R (°) β (°)

90 90

90 90

90 90

90 90 90

γ (°)

90

90

90

V (Å3)

1172.4(5)

1188.3(14)

1559.6(3)

2407.5(5)

Z

2

2

4

4

Fcalc (g cm
3)

1.812

1.869

1.861

1.414

μ (mm
1)

3.608

3.564

4.056

3.491

F(000)

644

678

872

1008

size (mm) reflections

0.15  0.03  0.02 6004/1358

0.18  0.10  0.04 5778/1358

0.21  0.14  0.13 7693/1808

0.22  0.14  0.12 15435/2614 0.6794/0.5139

Tmax/Tmin

0.9313/0.6137

0.8706/0.5663

0.6207/0.4830

data/parameters

1358/0/85

1358/0/88

1808/0/112

2614/20/100

S

1.179

1.261

1.066

1.184

R1a

0.0479/0.1134

0.0345, 0.1037

0.0586, 0.1579

0.0861, 0.2363

wR2b

0.0527/0.1163

0.0447, 0.1212

0.0699, 0.1647

0.0912, 0.2539

ΔFmax/ΔFmin(e A
3)

0.809/
0.447

1.477/
1.352

3.113/
0.832

2.420/
2.218

R1 = ∑||Fo|
|Fc||/∑|Fo|. b wR2 = [∑[w(Fo2
Fc2)2]/∑[w(Fo2)2]]1/2.

H1.5mepip form. The Cu(1) has tetrahedral geometry, coordinated by two μ3-cyanide carbon atoms and two μ2-cyanide nitrogen atoms. The Cu(1)
X (XdC or N) bonds are in the range of 1.961(4)
2.128(5) Å, and the X
Cu(1)
X angles are between 107.84(13)
116.6(2)°. The Cu(2) also adopts a tetrahedral geometry, coordinated by N(2), C(1), and C(1E) atoms as well as indistinguishable C(3)/N(3) atom. The Cu(2)
X (XdC or N) bonds are in the range of 1.991(4)
2.042(4) Å, and the X
Cu(2)
X angles are in the range of 108.98(12)
109.9(2)°. The six-membered ring of H1.5mepip exists in chair configuration. The cyanides are coordinated to Cu(I) atoms in μ2-C,N and μ3-C,C,N modes. In 1, two Cu(1)(CN)4 tetrahedra are fused via two μ3-CN carbon atoms into a Cu2(CN)6 dimer. The Cu(1) 3 3 3 Cu(1d) distance in the Cu2(CN)6 dimer is 2.48 Å, which is close to Cu 3 3 3 Cu distances in documented Cu2(μ3-CN)2 dimers.9 Each Cu(1)2(CN)6 dimer is linked to six Cu(2)(CN)4 monomers, while each Cu(2)(CN)4 monomer is connected to three Cu(1)2(CN)6 dimers and one Cu(2)(CN)4 monomer (Figure 1b). The node ratio of 4-connected monomers to 6-connected dimers is 2:1, which results in three-dimensional (3D) (4,6)-connected FeS2-like open frameworks with a short Schl€afli symbol {4.55}2{42.58.62.83} (Scheme 1a).24 Within the host framework of [Cu4(CN)7]3
, there are two types of channels: one is hexagonal with 18-atoms along the b-axis (Figure 1c) and the other is irregular with 15atoms along the c-axis (Figure S1, Supporting Information). The channels are filled by protonation H1.5mepip cations which act as templates for charge-compensation and space-filling. The usage of etpip instead of mepip as a template leads to the formation of isomorphic 2 (Figure S2, Supporting Information). It should be noted that Cu
C/N bond lengths in 2 are a little longer than

those in 1, which may be due to the larger size of the etpip template. The structure and formula of 1 are reminiscent of [{NH2(CH2CH2)2NCH2CH2NH2}2H][Cu4(CN)7] (10 )10e and [NH3(CH2)5NH3]3[Cu8(CN)14] (100 )10b and {(CH3)4N[Cu(H2O)(NH3)4][Cu4(CN)7]}n (1000 )17b because all of them display 3D anionic [Cu4(CN)7]3
open frameworks constructed by Cu2(CN)6 dimers and Cu(CN)4 monomers. Although 1, 10 , 100 , and 1000 have the same ratio of Cu2(CN)6 dimers to Cu(CN)4 monomers, their open frameworks are quite different. 10 shows 3D (4,6)-connected binodal fsh-like open framework with short Schl€afli symbol {43.63}2{46.66.83}, 100 shows 3D (4,4,6)-connected trinodal net with short Schl€afli symbol {4.53.62}{43.52.6}{44.54.64.7.82}, and 1000 shows 3D (4,6)-connected binodal open framework with short Schl€afli symbol (42.53.6)2(44.54.64.83). Different from 10 , 100 , and 1000 , the topology of compound 1 is binodal FeS2-like net. [H2me2pip][Cu3(CN)5] (3). Compound 3 crystallizes in orthorhombic space group Pnnm and the asymmetric unit contains three crystallographically independent Cu(I) centers, five cyanides and half doubly protonated H2me2pip cation as shown in Figure 2a. All atoms except for C(7) and C(8) localize in the special positions with a site occupancy of 0.5. All copper atoms show tetrahedral coordination geometry. The Cu(1) tetrahedron consists of N(1), N(2), C(4A)/N(4A) and C(4B)/N(4B) from two μ-cyanides and two μ3-cyanides. The Cu(1)
C/N bonds are in the range of 1.997(5)
2.011(6) Å, the X
Cu(1)
X (XdC, N) bond angles are in the range of 108.00(19)
112.20(3)°. The Cu(2) is coordinated by C(2), C(1C), N(5)/C(5), and C(5D)/N(5D) from two μ-cyanides and two μ3-cyanides. The Cu(2)
C/N bonds are in the range of 1.994(6)
2.052(7) Å, and the X
Cu(2)
X bond angles are in 3103

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Scheme 1. Schematic Representation of (a) 4,6-Connected FeS2-like Net in 1, (b) 4,4,6-Connected Trinodal Net in 3 and (c) 3,6-Connected AgIn2-like Net in 4

Figure 1. (a) The coordination environments of copper atoms and organic mepip cation, (b) the 6-connected Cu(1)2(CN)6 dimer and 4-connected Cu(2)(CN)4 monomer, and (c) 3D open anionic framework [Cu4(CN)7]3
along the b-axis showing channels filled by organic H1.5mepip cation in 1.

the range of 109.10(2)
113.9(4)°. The coordination geometry of Cu(3) is similar to Cu(2) but more distorted. The Cu(3)
C/ N bonds are in the range of 1.935(6)
2.312(8) Å, and the X
Cu(3)
X bond angles are in the range of 105.40(19)
129.0(4)°. The Cu(2)
C(1)
N(1) and Cu(3)
C(1)
N(1) angles are 162.2(8)° and 126.2(7)°, which indicates that μ3-C,C, N cyanide coordinates to Cu(2) and Cu(3) atom in an asymmetric fashion. The Cu(2) 3 3 3 Cu(3) distance in Cu2(CN)6 dimer is 2.5255(15) Å, which is a little longer than that in 1 and 2. Compared with 1 and 2, the 1:1 ratio of 6-connected Cu2(CN)6 dimer to 4-connected Cu(CN)4 monomer generates 3D (4,4,6)-connected trinodal open framework in 3. The short Schl€afli symbol is {43.53}{4.55}{45.56.63.7} (Scheme 1b), which is not enumerated in RCSR and topos. The microporous anionic open framework is filled by protonated H2me2pip cations which act as charge-compensator and space-filler. Within the open framework of 3, there are two-dimensional (2D) channels: one is hexagonal and has 18-atoms along the a-axis somewhat similar to that in 1 and 2 (Figure 2b) and the other is asymmetric with 15-atoms along the b-axis (Figure S3, Supporting Information). The structure and formula of 3 are reminiscent of {[Cu(H2O)(NH3)4][Cu3(CN)5] 3 H2O}n (30 ),17b because both have 3D

anionic [Cu3(CN)5]2
open frameworks constructed by Cu2(CN)6 dimers and Cu(CN)4 monomers. Investigation indicates that 30 has 3D (4,6)-connected binodal open frameworks with a short Schl€afli symbol (43.53)2(45.56.63.7). [H2dmpa][Cu4(CN)6] (4). Compound 4 crystallizes in the orthorhombic space group Pbcn and the asymmetric unit contains two crystallographically independent Cu(I) centers, three cyanides, and half protonated H2dmpa cations as shown in Figure 3a. The atoms of C(3), N(3), C(4), and N(4) localize in the special positions with a site occupancy of 0.5. The Cu(1) 3104

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Figure 2. (a) The coordination environments of copper atoms, and (b) 3D open anionic framework [Cu3(CN)5]2
showing the channels filled by organic H2me2pip cation in 3.

has tetrahedral geometry, coordinated by C(1A), C(1B), N(2), and C(4)/N(4) atoms. The Cu(1)
C bond lengths are 1.969(8) and 2.112(9) Å, and the Cu(1)
N bond length is 1.967(8)Å. The X
Cu(1)
X bond angles are in the range of 107.0(3)
112.3(4)°. The Cu(2) atom shows a trigonal environment, coordinated by one C(2), N(1), and C(3)/N(3) atoms. The Cu(2)
C bond length is 1.910(8) Å; the Cu(2)
N bond length is 1.929(7) Å. The X
Cu(2)
X bond angles are 115.1(3)
122.7(3)°. Complex 4 is constructed by Cu2(CN)6 dimer and Cu(CN)3 monomer SBUs and shows an unusual 3D (3,6)connected AgIn2-like open network with a short Schl€afli symbol {53}2{54.68.83} (Scheme 1c). It should be noted that 4 is formed by 3-connected monomers, different from 4-connected monomers in 1
3. Compound 4 contains 2D layered [Cu4(CN)5]
motifs which are formed by fusion of [Cu5(CN)5] rings (Figure 3b). These layers are further linked by disordered cyanides to form a 3D microporous framework with two types of channels along the a- and b-axis: one is rectangular (Figure 3c) and the other is trapezoidal (Figure S4, Supporting Information). EA, TG, and charge balance indicate that the channels are filled with protonated H2dmpa cations. However, due to high disorder and difficulty in distinguishing 3-methyl and 3-amino, organic H2dmpa cations were refined by using a model of trimethylpropylamine. Only three (3,6)-connected 3D cuprous cyanide open frameworks have been documented, which include [NH2(iPr)2][Cu2(CN)3] (40 ), [NH2(Pr)2][Cu2(CN)3] (400 ), and [NH2(secBu)2][Cu2(CN)3] (4000 ) (NH2(iPr)2 = diisopropylamine, NH2(Pr)2 = dipropylamine, NH2(secBu)2 = disec-butylamine).10a

Figure 3. (a) The coordination environments of copper atoms, (b) 2D [Cu4(CN)5]
layer constructed by fusion of [Cu5(CN)5] rings and (c) 3D microporous [Cu4(CN)6]2
framework formed by linkage of [Cu4(CN)5]
layers via cyanide groups in 4.

Although 4 and the above three compounds have similar monomers and dimers, topological analyses reveal that they are significantly different open frameworks. 40 shows a pyr-like open framework with a short Schl€afli symbol {63}2{612.83}; 400 shows a rtl-like open framework with a short Schl€afli symbol{4.62}2{42.610.83}; 4000 has an unenumerated net with a short Schl€afli symbol {63}6{66.86.102.12}. In addition, the anionic formula of 4 is also reminiscent of {(CH3OH2)2[Cu2(CN)3]}n (40000 )17b which only contains 6-connecting Cu2(CN)2 dimers and shows 3D R-Po-like open framework. Syntheses Chemistry. Temperature and Template Effect. It is well-known that the construction of open frameworks under hydrothermal conditions is easily affected by physical or chemical factors, and a slight change such as the structural character of organic template, coordination nature of metal, solvent and reaction temperature may result in different products.25,26 Compounds 1
4 were hydrothermally obtained by treatment of CuCl2 and K3[Fe(CN)6] in the presence of organic diamines, which display new organically templated cuprous cyanide open 3105

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Figure 5. Electron-density distribution of the lowest unoccupied and highest occupied frontier orbitals calculated for the neutral dimer model [Cu2(CN)2(HCN)4] with D2h symmetry.

Figure 4. Solid-state excitation and emission spectra of 1
4.

frameworks. It is found that template, temperature, and ratio of starting materials play important roles in the formation of products. To be mentioned, under similar conditions by using different diamine templates (mepip or etpip), isostructural 1 and 2 are synthesized, which have 3D (4,6)-connected FeS2-like open frameworks. However, when me2pip instead of mepip or etpip was used, similar reactions did not obtain a crystalline product. With a decrease of reaction temperature from 160 to 140 °C, 3D (4,4,6)-connected trinodal open framework 3 with an unenumerated topology was obtained. It means that temperature plays an important role in the assembly fashion of building blocks. Besides, the size of channels of 3 is larger than that of 1, which may be influenced by the me2pip template. For 4, when chain-like alkanediammonium (dmpa) was used in place of N-heterocyclic diamines, a similar reaction resulted in a 3D (3,6)-connected AgIn2-like open network. The square channel of 4 is constructed from 2D sheets linked by symmetry-related disordered cyanide groups, and the size of channel is the largest among the compounds 1
4. This may be caused by other factors such as steric hindrance of templates and coordination preference of different nodes. Thermal Analyses. TG/DTA analyses for 1
4 in air at the heating rate of 10 °C min
1 were performed to examine thermal stabilities (Figure S5, Supporting Information). Phase purity of the bulk materials was confirmed by comparison of recorded X-ray powder diffraction patterns with those calculated by singlecrystal X-ray diffraction data (Figure S6, Supporting Information). Compounds 1 and 2 have similar thermal stabilities, which show an endothermic peak ca. 255 °C and an exothermic peak ca. 470 °C. The first weight loss of 33.3% in the range of 170
285 °C corresponds to removal of protonated H1.5mepip cation (calc. 32.0%), which is followed by decomposing of the framework. In the temperature range of 285
780 °C, the continuous removal of cyanides possibly forms an intermediate of copper as indicated by empirical composition (40.01%, calc. 39.7%). The red wire-like metal observed in controlled experiment also supports formation of intermediate copper in this step. The intermediate of copper is slowly oxidized in air upon further heating and the stable residue is not formed up to 900 °C. Compound 3 shows an endothermic peak ca. 270 °C and an exothermic peak ca. 415 °C. The first weight loss of about 28.5% in the temperature range of 170
290 °C is in agreement with the removal of H2me2pip cations (calc. 26.6%), which is also followed

by decomposition of framework. The continuous loss of cyanides in the range of 290
556 °C gives an unstable intermediate of elemental copper (44.8%, calc. 43.6%) that is slowly oxidized in air upon further heating. Compared with 1
3, 4 only shows an exothermic peak at 450 °C and the weight loss in the range of 170
573 °C corresponds to removal of H2dmpa cations and cyanide groups. Residue at 573 °C (48.5%, calc. 49.4%) is in agreement with the theoretical value of elemental copper that slowly oxidizes in air upon further heating. Photoluminescence. The room temperature emission spectra of powdered 1
4 are shown in Figure 4. As can be seen, all of these complexes display a very strong blue-green emission band at 483, 472, 500, and 511 nm upon photoexcitation at 319, 326, 338, and 320 nm, respectively. The lifetimes of the emission bands for 1
4 were measured to be 17.46, 16.46, 16.95, and 10.66 μs, respectively, suggesting some character of phosphorescence. A number of possible assignments for the excited states include ligand centerd π f π* transitions (LC), metal clustercentered transitions (CC), metal-to-ligand (MLCT) charge transfer, and single metal centered 3d f (4p, 4s) (MC) transitions.27 Transitions of the LC type may be ruled out since cyanide has a large band gap. Because 1
4 contain dimers with short Cu 3 3 3 Cu distances, the transitions of CC nature cannot be completely ruled out.14,16 TD-DFT calculations have been used to theoretically predict optical spectra and function as an assistant method helps to qualitatively analyze the luminescent origin of the complexes,28 in which the selection of molecular models is crucial. In order to understand the emission mechanism of the compounds, we have made TD-DFT calculations by using different model complexes. Initially, the isolated dimeric [Cu2(CN)6]4
, trinuclear [Cu3(CN)9]6
, and [Cu3(CN)8]5
ground-state building blocks with high negative charges adapted from the X-ray data have been used as models for calculations at the B3LYP level, and the keyword Pop = Reg was added into the calculation to analyze the molecular orbitals (Figure S7, Supporting Information). The results indicate that all transitions in dimeric [Cu2(CN)6]4
, trinuclear [Cu3(CN)9]6
, and [Cu3(CN)8]5
complexes are qualitatively dominated by copper-to-cyanide charge transfer. However, the energy gaps of 1.5
1.7 eV in these models are significantly lower than those in their excitation spectra, which indicates that these [Cu2(CN)6]4
, [Cu3(CN)9]6
, and [Cu3(CN)8]5
model complexes are less reasonable. In fact, the local charges in dimeric and trimeric units in the infinite frameworks of 1
4 should be much lower than those in model complexes, which is mainly responsible for the inconformity between calculated and experimental energy gaps. In order to decrease the 3106

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Crystal Growth & Design

ARTICLE

π* orbitals of peripheral cyanides (Figure 5). The energy gap is 3.60 eV (343 nm), which is close to experimental values of 319
338 nm. In order to further assign the emissions, DFT calculation of the electronic band structure of anionic frameworks of 1 and 3 along with density of states has been carried out with the CASTEP code. The results indicate that, in both compounds, the top of valence bands (VBs) are mostly formed by Cu-3d state mixing with a small amount of cyanide-2p states, while the bottom of the conduction bands (CBs) are almost a contribution from cyanide2p states mixing with a small amount of Cu-4p states (Figures 6 and S8). The calculated energy gaps for 1 and 3 are 2.94 and 3.02 eV, respectively. On the basis of the above various calculations, strong bluegreen photoluminescence of four complexes can be assigned as mainly originating from copper-to-cyanide charge-transfer, which is consistent with the previous reports on CuCN compounds. 29 For example, emission peaks at 432 nm for [Me4N][Cu3(CN)2Br2], 544 nm for [Me4N]2[Cu4(CN)5Cl],9b and 468 nm for {[CuII(NH3)4(H2O)](H2O)[CuI3(CN)5]}n29d were assigned to be the copper-(I) center to the unoccupied π* orbital of cyanide ligand.

’ CONCLUSIONS We have successfully obtained four new organically templated 3D cuprous cyanide open frameworks under hydrothermal condition by using environmentally friendly K3[Fe(CN)6] as cyanide source. Three new topologies of cuprous cyanide openframework have been extended by combining of dimeric Cu2(CN)6 and monomeric Cu(CN)3/Cu(CN)4 building blocks. Strong blue-green phosphorescent emissions are observed even at ambient temperature. Time-dependent density functional theory and electronic band structure calculations indicate the excited electronic states of 1
4 are mainly originated from metalto-ligand charge-transfer transitions. ’ ASSOCIATED CONTENT Supporting Information. Additional figures, TG/DTA, XPRD, cyano-bridged copper dimer interactions in 1
4, frontier orbitals calculated for the Cu2(CN)64
, Cu3(CN)96
, and Cu3(CN)85
units, energy band structures and density of states, and crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

bS

’ AUTHOR INFORMATION Corresponding Author

*Fax: Int. code: þ86 357 2051402; e-mail: zhangxm@ dns.sxnu.edu.cn. Figure 6. Energy band structures and density of states (total and partial) of 1. Energy bands are shown only between
3.0 and 4.5 eV for clarity, and the Fermi level is set at 0 eV.

inconformity, we also made a related TD-DFT calculation by using a modified neutral dimer model [Cu2(CN)2(HCN)4] with D2h symmetry. The results show that the lowest singlet excitation in this model is dominated by the HOMO f LUMO transition, in which HOMO is composed of d orbitals of Cu(I) and π orbitals of central cyanides, while LUMO mainly consists of

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