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Three complexes of Cu(I) cluster with flexible and rigid ligands: Synthesis, characterization and photoluminescent properties
Journal of Solid State Chemistry 225 (2015) 1–7
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Three complexes of Cu(I) cluster with flexible and rigid ligands: Synthesis, characterization and photoluminescent properties Shu Sun a,b, Li-Juan Liu a, Wang-Yang Ma a, Wei-Xia Zhou a, Jun Li a,n, Feng-Xing Zhang a a b
College of Chemistry & Materials Science, Northwest University, Taibai Avenue 229, 710069 Xi’an, China Department of Chemical Engineering, Ordos College of Inner Mongolia University, Inner Mongolia University, Ordos, Inner Mongolia 017000, China
art ic l e i nf o
a b s t r a c t
Article history: Received 15 August 2014 Received in revised form 2 November 2014 Accepted 9 November 2014 Available online 18 November 2014
Three new Cu(I) cluster complexes, viz. [(Cu4I4)(Cu2I2)(dimb)3]n (1; dimb ¼1,4-diimidazol-1-ylbutane), [(Cu3I2)(dimb)(dmtz)]n (2; dmtz ¼3,5-dimethyl-1,2,4-triazole), and [Cu6(mbt)6] (3; mbt ¼2-mercaptobenzothiazole), have been solvothermally synthesized and structurally characterized. In 1, a Cu4I4 cubane core as a 4-connecting node, connects the neighboring nodes either through single dimb or μ2[(Cu2I2)(dimb)2] linkers, affording an undulated 2D (4,4) net. Parallel interpenetration occurs between the adjacent nets and thus the overall 2D-3D network is formed. Complex 2 is constructed by 2D (4,4) topological plane grid layers of AB stacking. The core, a distorted triangular bipyramidal Cu3I2 cluster, is acted as a 4-connecting node and connected with dimb and μ3-dmtz to form the layer. Complex 3 contains a (Cu6S6) core in discrete paddle-wheel molecule, which serves as a 4-connecting node to link equivalent ones via π π interaction, forming 2D (4,4) layers. Solid-state luminescence properties and thermogravimetric analyses of 1, 2 and 3 were investigated. & 2014 Elsevier Inc. All rights reserved.
Keywords: Cu(I) cluster Flexible and rigid ligands Metal–organic complex Photoluminescent
1. Introduction Metal chalcogenides and halides clusters are used as building units for construction of higher dimensional frameworks [1], and for their potential application such as luminescent materials [2–6]. Particular iodocuprate(I) (cuprous iodide aggregates) are of interests in this area due to their wide variety of stereochemical diversity and rich photoluminescent properties [7–12]. Iodide ion, soft Lewis base, binds strongly to soft Lewis acid of cuprous ion, forming different composition [(CuxIy)x y] clusters, which exist in various shapes, and provide the possibility for diverse coordination manners [13–17]. Moreover, compared with the noble and rare earth metals, d10 transition-metal based complexes have been attracted growing attention from an economical point of view as they are abundance on the earth [18]. Wen et al. synthesized 1D inorganic–organic hybrid coordination polymer, the first example of a linear chain formed by trinuclear Cu3I4 units, which exhibits remarkably rich photoluminescent properties [13]. Huang et al. [14], Feng et al. [4,15], and Fu et al. [17] have investigated the [(CuxIy)x y] cluster combined with rigid ligands of benzotriazole, 1,3-N-dimethylbenzotriazolium, 1-N-methylbenzotriazole, 1-N-methyltriazole, 1,2,3-triazole, 1,3-N-diethyltriazolium, 1,4-diazabicyclo[2.2.2]octane almost systematically, obtained
n
Corresponding author. E-mail address: [email protected] (J. Li).
http://dx.doi.org/10.1016/j.jssc.2014.11.014 0022-4596/& 2014 Elsevier Inc. All rights reserved.
the iodocuprate frameworks ranging from 2D to 3D. In particular, Complex [Cu2I2(MBta)] (MBta¼ 1-N-methylbenzotriazole) reported by Huang et al. [14], exibits interestingly perpendicular interpenetration of 2D (4,4) nets. Kang et al. synthesized a new MTN-type cluster-organic framework (COZ-1) containing giant 64512 and 512 cages. It exhibited perfect integration of porosity and photoluminescent properties from both the cluster and the framework in a porous material [17]. Though a number of complexes based on Cu(I) clusters have been obtained, with good thermal stability and strong photoluminescence properties of these compounds are seldom reported [15,19–21]. In this work, we report three complexes of copper(I) cluster with long flexible dimb and rigid mbt as ligands. The former is chosen because it can adopt different conformations according to the geometric needs of the different cluster cores [22–26]. Complex 1 represents the first example of parallel interpenetrating (4,4) frameworks with neutral Cu4I4 clusters as nodes and flexible ligands as rods. Unlike 1, complex 2 has a noninterpenetrating 2D network, in which the dimb and dmtz ligands serve as linkers to connect cationic Cu3I2 clusters giving rise to 2D sheet structures. Because the orbital energies of transition metal are well matched with S, the thiol group thus can be acted as a bridge to connect the adjacent transition metal sites, and delocalize the spin electron density toward them simultaneously. Accordingly, the latter ligand, with aromatic delocalized electron system existed, is highly desirable in terms of luminescent behavior [27–29]. Complexes 1, 2 and 3 show strong photoluminescence at room temperature.
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S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
2. Experimental 2.1. Materials and instrumentation Commercially available reagents were used as received without further purification. Elemental analyses of C, H, N were performed on a Vario EL III analyzer. Infrared spectra were obtained from KBr pellets on a Bruker EQUINOX 55 Fourier transform Infrared spectrometer in the 400 4000 cm–1 region. The powder X-ray diffraction (PXRD) was recorded on a Rigaku D/Max-2500 diffractometer at 40 kV, 100 mA for a Cu-target tube and a graphite monochromator. Thermogravimetric measurements were carried out from room temperature to 1000 1C for 1, 2 and 3 on preweighed samples under nitrogen flow (flow rate of 30 mL min 1) using TA Instruments NETRZSCHSTA 449C simultaneous TGA–DSC with a heating rate of 10 1C min 1. Fluorescence spectra were recorded on a Hitachi F-4500 spectrophotometer at room temperature. 2.1.1. Synthesis of [(Cu4I4)(Cu2I2)(dimb)3]n (1) CuI (0.038 g, 0.20 mmol) was dissolved in 6 mL aqueous solution of KI (0.747 g, 4.50 mmol). While stirring, a solution of dimb (0.152 g, 0.80 mmol) in CH3OH (2 mL) was added. The solution was stirred to give a pale precipitate, and then this heterogeneous mixture was placed in a 25 mL Teflon-lined stainless steel reactor and heated at 120 1C for 72 h. Yellow rod-like crystals suitable for X-ray crystal analyses were isolated in 28% yield (based on Cu), which are stable in air and insoluble in water and common organic solvents. Elemental analysis for 1: C30H42N12Cu6I6 (Mr¼ 1713.44). Calcd: H 2.47, C 21.03, N 9.81%. Found: H 2.50, C 21.06, N 9.79%. IR data (KBr, cm 1): 3448(s), 3116(s), 2947(w), 1630(m), 1527(m), 1446(m), 1230(m), 1095(s), 947(w), 847(w), 750(s), 661(s), 627(w). 2.1.2. Synthesis of [(Cu3I2)(dimb)(dmtz)]n (2) A mixture of CuI (0.038 g, 0.20 mmol), dimb (0.038 g, 0.20 mmol), anhydrous CH3OH (2 mL) and acetonitrile (6 mL), was stirred, and then sealed in a 25 mL Teflon-lined stainless steel reactor, kept under autogenous pressure at 90 1C for 72 h. Pale yellow needle-like crystals suitable for X-ray crystal analyses were isolated in 45% yield (based on Cu), which are stable in air and insoluble in water and common organic solvents. Elemental analysis for 2: C14H20N7Cu3I2 (Mr¼730.79). Calcd: H 2.76, C 23.01, N 13.42%. Found: H 2.71, C 22.85, N 13.52%. IR data (KBr, cm 1): 3450(m), 3120(s), 2933(m), 2864(w), 1612(w), 1519(s), 1488(m), 1464(m), 1419(s), 1375(m), 1274(m), 1234(s), 1107(s), 1086(s), 823(s), 750(s), 652(s), 627(m). 2.1.3. Synthesis of [Cu6(mbt)6] (3) A mixture of CuI (0.038 mg, 0.2 mmol), Hmbt (0.034 g, 0.20 mmol), acetonitrile (8 mL) and 0.5 mL ammonia was stirred at room temperature. Immediately, a yellow precipitate appeared and then was transferred into a 25 mL Teflon-lined reactor and kept under autogenous pressure at 160 1C for 96 h. Brown block crystals, stable in air and insoluble in water and common organic solvents, were isolated in 79% yield (based on Cu). Elemental analysis for 3: C42H24N6S12Cu6 (Mr¼1378.63). Calcd: H 1.75, C 36.59, N 6.10%. Found: H 1.78, C 36.33, N 6.15%. IR data (KBr, cm 1): 3429(w), 3066(w), 1452(m), 1402(s), 1313(w), 1280(w), 1244(m), 1080(m), 1007(s), 750(s), 721(m), 694(m). 2.2. Crystal structure determination Diffraction data of 1, 2 and 3 were collected on a Bruker SMART diffractometer with graphite monochromated Mo Kα radiation (λ ¼0.71073 Å) in φ and ω scan modes at 296 K. Absorption correction was applied by using the SADABS program [30]. The
Table 1 Crystallographic data and structure refinement parameters for 1, 2, and 3. Complex
1
2
3
Empirical formula Mr (g mol 1) Crystal system Space group Temperature (K) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm 3) μ (mm 1) F (0 0 0) θ range (deg) Data/restraints/parameters Goodness-of-fit R1a [I4 2σ(I)] wR2a (all data) Residuals (e Å 3)
C30H42Cu6I6N12 1713.40 Monoclinic C2/c 296(2) 25.568(4) 11.3313(18) 16.156(3) 90 100.503(3) 90 4602.3(13) 8 2.473 6.785 3192 1.97–25.50 4067/23/244 1.067 0.0392 0.1137 1.547, 1.310
C14H20Cu3I2N7 730.79 Monoclinic C2/c 296(2) 21.456(4) 8.1045(15) 15.222(3) 90 127.130(2) 90 2110.3(6) 4 2.300 5.935 1384 2.78–25.16 1867/12/120 1.096 0.0360 0.1023 0.694, 1.131
C42H24Cu6S12N6 1378.63 Triclinic P-1 296(2) 7.6786(7) 13.3192(13) 13.8392(19) 115.714(2) 98.183(2) 103.0350(10) 1194.9(2) 1 1.916 3.187 684 2.98–25.05 4165/0/298 1.029 0.0301 0.0670 0.299, 0.278
a
R1 ¼∑||Fo| |Fc||/∑|Fo|; wR2 ¼ [∑w(F2o F2c )2/∑w(F2o)2]1/2.
structure was solved by direct methods and successive Fourier difference syntheses(SHELXS-97), anisotropic thermal parameters for all nonhydrogen atoms were refined by full-matrix leastsquares procedure on F2 (SHELXTL-97) [31,32]. Hydrogen atoms were placed in geometrically calculated positions. Crystal data and details of refinements for complexes are summarized in Table 1. Selected bonds distances and angles are listed in Table 2. [CCDC number 970732, 970733 and 972636].
3. Results and discussion 3.1. Crystal structure of 1 Complex 1 is a 3D coordination polymer constructed from Cu4I4 cubane cores, Cu2I2 rhomboid clusters and dimb ligands. In a Cu4I4 unit, each Cu(I) cation connects three neighboring μ3-I anions, forming a 4-connecting Cu4I4 tetracapped tetrahedron cluster (Fig. 1, upper right), and uses a coordination sphere pointing outward of the tetrahedron to bond dimb ligand via nitrogen atom. Two coordination sites of it connect two other Cu4I4 clusters through merely single dimb ligands. The bond distances of the Cu–I and Cu–N bonds are 2.6104(10) –2.7969(13) Å and 2.003(6) – 2.015(6) Å, respectively. Cu3 and Cu3A (symmetry code: xþ 1/2, yþ 1/2, z) are bridged by μ2-I anions giving rise to a rhomboid Cu2I2 cluster with two dimb ligands (Fig. 1, upper left), meanwhile a longer chain as linker, μ2-[(Cu2I2)(dimb)2], is formed, which connects another two Cu4I4 clusters via nitrogen atoms of the dimb ligands. In Cu4I4 clusters, the spatial arrangement of distorted tetrahedron with Cu Cu distances of 2.701, 2.711 and 2.868 Å is adopted by the Cu(I) ions (Fig. 1, top). The Cu Cu distances are less than or approximately equal to the sum of the van der Waals separations (van der Waals radii for Cu, 1.43 Å) [33,34]. Such a result indicates the existence of the weak Cu Cu interactions. Those of Cu2I2 are 2.469 Å, particularly, shorter than that of Cu4I4. In complex 1, Cu4I4 clusters are linked by single dimb ligands and μ2-[(Cu2I2)(dimb)2] lingkers to form a substructure of highly undulated 2D net (Fig. 2a, b), in which the dihedral angle φ between adjacent folds is 70.8341 (Fig. 2a). The 2D net contains a (Cu4I4)4{μ2[(Cu2I2)(dimb)2]}2(dimb)2 window of 30.717 16.156 Å, which is so
S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
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Table 2 Selected bond lengths(Å) and angles(1) for complexes 1, 2, and 3a. [(Cu4I4)(Cu2I2)(dimb)3]n (1) Cu(1)…Cu(2) Cu(2)…Cu(2)#1 Cu(2)–N(5) Cu(1)–I(2) Cu(2)–I(2) Cu(3)–I(3)#2 I(1)–Cu(1)–I(2) I(1)–Cu(2)–I(2) I(3)–Cu(3)–I(3)#2
2.7127(13) 2.868(2) 2.003(6) 2.7581(11) 2.7223(12) 2.5663(12) 117.81(4) 116.51(4) 122.44(4)
[(Cu3I2)(dimb)(dmtz)]n (2) Cu(1)…Cu(2) Cu(1)–I(1)#2 Cu(2)–I(1) I(1)–Cu(1)–I(1)#2 N(1)–Cu(1)–N(2) [Cu6(mbt)6] (3) Cu(1)–S(4)#1 Cu(2)–S(4) S(4)#1–Cu(1)–S(6) a
Cu(1)…Cu(1)#1 Cu(3)…Cu(3)#2 Cu(3)–N(4) Cu(1)–I(2)#1 Cu(2)–I(1)#1
2.7041(18) 2.4680(18) 1.939(6) 2.6104(10) 2.6348(11)
Cu(1)…Cu(2)#1 Cu(1)–N(1) Cu(1)–I(1) Cu(2)–I(1) Cu(3)–I(3)
2.7017(13) 2.015(6) 2.7231(12) 2.7969(13) 2.5600(12)
I(1)–Cu(1)–I(2)#1 I(1)–Cu(2)–I(1)#1
111.98(4) 107.33(4)
I(2)–Cu(1)–I(2)#1 I(1)#1–Cu(2)–I(2)
109.57(4) 111.25(4)
2.8392(13) 3.0907(12) 2.5281(7) 96.53(3) 151.4(2)
Cu(1)#2…Cu(2) Cu(1)–N(1) Cu(2)–I(1)#2 I(1)–Cu(1)–N(1) I(1)–Cu(2)–N(3)#1
2.8392(13) 1.906(5) 2.5281(7) 106.89(16) 115.97(2)
Cu(1)–I(1) Cu(1)–N(2) Cu(2)–N(3)#1 I(1)–Cu(1)–N(2) I(1)#2–Cu(2)–N(3)#1
3.0001(11) 1.928(5) 1.980(7) 94.22(15) 115.97(2)
2.2457(10) 2.2470(9) 117.41(4)
Cu(1)–S(6) Cu(3)–S(2)#1 S(2)–Cu(2)–S(4)
2.2488(10) 2.2559(10) 117.65(3)
Cu(2)–S(2) Cu(3)–S(6) S(2)#1–Cu(3)–S(6)
2.2556(10) 2.2491(10) 117.80(4)
Symmetry transformations used to generate equivalent atoms: 1. #1 x, y, z þ1/2; #2 xþ 1/2, yþ 1/2, z. 2. #1 x, y, z; #2 x, y, z þ 1/2; 3. #1 x, y, z.
Fig. 1. The coordination environments of Cu(I) ion (bottom), and Cu4I4, Cu2I2 cluster (top) in 1.
large that allows simultaneously catenated by the other two ones (orange and plum windows) in the adjacent nets (Fig. 3a). Therefore, each highly undulated 2D net is simultaneously penetrated by the two nearest neighbouring ones. The interpenetrating nets have parallel mean planes and are coincident, and thus an overall 2D3D framework is produced (Fig. 2b). To better understand the structure of 1, the topological analysis approach is employed. If the Cu4I4 clusters and dimb/μ2-[(Cu2I2)(dimb)2] are assigned as 4-connected nodes and rods, respectively, the substructure displays a parallel interpenetrating 2D-3D nets (Fig. 3b and c). The high degree of entanglement is due to: (i) the large enough windows of the net; (ii) the highly undulated nature of the single (4,4) net. 3.2. Crystal structure of 2 In complex 2, the dmtz ligands are present, it should be generated from the in situ reaction of acetonitrile under the solvothermal conditions, and the possible reaction mechanism may proposed Scheme 1 [35–51]. The structure of 2 is constructed from [Cu3I2] þ clusters linked by mixed dmtz anions and dimb ligands. In [Cu3I2] þ cluster, weak Cu Cu interactions is exhibited due to the fact that the isosceles triangular arrangement with two equicrural Cu Cu distances of 2.839 Å and a bottom of 3.223 Å is adopted by the Cu(I) ions (Fig. 4, left). The Cu(I) ions are bridged by μ3-I anion on the either side of the triangle giving rise to a distorted triangular bipyramidal [Cu3I2] þ cluster (Fig. 4, left),
Fig. 2. (a) The dihedral angle φ in the net, (b) perspective views of the undulated 2D (4,4) net, (c) 2D-3D parallel interpenetration in the structure of 1.
in which Cu(I) features distorted triangular and tetrahedral coordination geometry. Furthermore, the triangular Cu2 connects N3 atom of μ3-dmtz linking another [Cu3I2] þ cluster, while the
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16.562 8.104 Å (Fig. 4, right). The bond distances of the Cu–I and Cu–N bonds are 2.5281(7) –3.0907(12) Å and 1.906(5) – 1.980(7) Å, respectively. Different from 1, although the (4,4) grids in 2 also have large windows, these grids are not undulated but are planar. The layers are further stacked in an ABAB sequence along the [1 0 1] direction, which is visualized by the translucent blue plane (Fig. 5a), and the short average plane-to-plane separations are 3.950 Å (Fig. 5b). 3.3. Crystal structure of 3 Complex 3 is a discrete paddle-wheel molecule, which is neutral and composed of six Cu(I) cations bridged by six tridentate mbt monoanions, forming (Cu6S6) core (Fig. 6). Each of the Cu (I) ions is three-coordinated by one nitrogen atom and two thiolate sulfur atoms from three mbt ligands, forming a distorted trigonal CuNS2 geometry. In other words, each mbt ligand serves as a tridentate ligand to connect three Cu(I) ions by using its thiolate sulfur atom as a μ2 linker to connect two ones, and its nitrogen atom to coordinate the third one. The six copper atoms forms a distorted octahedron with Cu Cu distances in the range of 3.002–3.100 Å, which are larger than the sum of the van der Waals separations [33,34]. The mbt is a rigid and aromatic delocalized electron system, and its coordination geometry is different from dimb or dmtz. As a result, the complex 3 can not exhibit 2D or 3D framework formed by covalent bonds. Nonetheless, the infinite offset face-to-face π π interactions of benzene rings of mbts are present, through which the discretely paddle-wheel molecules extend 2D planar networks (Fig. 7). The distances between two centers of benzene rings are 3.933, 4.126 Å, but the distances of π π interactions between benzene faces are 3.450, 3.504 Å, and the degrees of offset, θ, are 28.6941, 31.8701, respectively (Fig. 7). In complexes, it is found that many planar aromatic moieties tend to be stacked with an interplanar separation in the range 3.3–3.6 Å, and most examples with the degrees of offset lie between 101 and 451 [52– 56]. Furthermore, the 2D networks are stacked along the [1 0 0] direction in parallel, and the large average plane-to-plane separations are 7.220 Å (Fig. 8). 3.4. Powder X-ray diffraction Fig. 3. (a) A view of catenation of windows, (b) and (c) Schematic representation of 2D-3D parallel interpenetration of highly undulating 2D networks of 1 viewed from different directions.
The experimental and simulated X-ray powder diffraction patterns of complexes 1, 2 and 3 are in good agreement with each other, proving the phase purity of the as-synthesized products. The difference in reflection intensity is probably caused by the preferred orientation effect in the powder sample (Fig. S1 of the Supporting information). 3.5. Thermal property
Scheme 1. Possible formation mechanisms of 3,5-dimethyl-4H-1,2,4-triazole from acetonitrile.
tetrahedral Cu1 and Cu1A are simultaneously bridged by the μ3-dmtz via N2, N2A ( x, y, zþ 1/2), and bonded by N1, N1A from dimb ligands linking other two [Cu3I2] þ clusters via nitrogen atoms. As a result, a 2D (4,4) topological planar grid layer is formed, which contains (Cu3I2)4(μ3-dmtz)2(dimb)2 windows of
Thermogravimetric Analysis of 1, 2 and 3 was carried out in nitrogen atmospheres to investigate their thermal stabilities. TGA profiles for complexes 1, 2 and 3 are shown in Fig. S2, Supporting information. As can be seen in the figure, a stable state can be maintained for Complex 1 below 350 1C. However, with the temperature increased, two obvious weight loss steps can be observed. The first weight loss of 28.35% in the range of 350– 450 1C, which should correspond to a large proportion of dimb decomposition. The second weight loss of 48.67% between 450 and 830 1C should be attributed to a fraction of dimb and CuI volatilization. Similar to 1, complex 2 has two weight loss steps. The first weight loss of 35.05% in the range of 250–456 1C corresponds to the most of decomposition of organic ligands. The second weight loss appeared between 500 and 880 1C, which could be ascribed to the decomposition of organic ligands and the
S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
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Fig. 4. The coordination environments of Cu(I) ion (left), and 2D (4,4) grid (right) in 2. (symmetrically generated).
Fig. 6. The coordination environments of Cu(I) ion and (Cu6S6) core in 3.
3.6. Photoluminescent property
Fig. 5. (a) Topological illustration of the ABAB sequence stacking along the [1 0 1] direction, representing the 2D grid structure of 2, (b) viewed along the a-axis (orange: A sheet, blue: B sheet). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
volatilization of CuI. While for the complex 3, a mass loss of 57.59% occurred between 240 and 490 1C, indicating the decomposition of organic ligands only according to the calculation result of their theoretical weight loss. The thermal stability of these complexes are better than those of normal Cu(I) cluster based ones given in the earlier reports [6,15,19–21], which makes them potential candidates for practical application.
The photoluminescent properties for 1, 2 and 3 were investigated in the solid state at room temperature. The results are summarized in Table 3 and in Fig. 9. Upon excitation of complex 1 at λmax, ex ¼320 nm, an intense orange luminescence appeared at λmax, em ¼612 nm (Table 3, Fig. S3), which agree with the previous literature [17]. The low energy (LE) emission decayed with a lifetime is in the microsecond regime (Table 3, Fig. S4), revealing that the emission is phosphorescent, most likely associated with a spin-forbidden transition. According to the previous reports about the polynuclear Cu(I) clusters and their decay lifetimes, the emission of 1 can be tentatively attributed to the triplet clustercentered (3CC) excited state which combine halide-to-ligand (XMCT) and metal-centered (d–s) components [57–60]. Hexanuclear complex 3 displays a quite intense near-infrared (NIR) emission (typically between 700 and 900 nm) [61,62] at λmax, em ¼ 792 nm, which should also be involved in 3(d–s/LMCT) excited
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Table 3 Excitation and emission data of complexes 1, 2 and 3. Complex λmax, ex (nm)
λmax, em (nm)
τ1
τ2
χ2
Suggested origin
1 2
612 440 467 610 792
3.66 μs 0.99 ns 0.93 ns 0.87 ns 5.54 μs
14.65 μs 6.42 ns 5.86 ns 27.11 ns 9.24 μs
1.005 1.298 1.258 1.101 1.102
3
3
320 370 370 370 370
(d–s/XMCT) (MLCT/XLCT) (MLCT/XLCT) 1 (d–s/XMCT) 3 (d–s/LMCT) 1 1
Fig. 9. Emission spectra of complexes 1, 2 and 3 in solid state at room temperature.
Fig. 7. The infinite offset face-to-face π π interactions of benzene rings of mbts.
behavior of the two bands (Table 3, Fig S6 and S7). In contrast, LE and HE emissions are independent, apparently. It is worthy to mention that multiple emissions of complexes are extremely rare at room temperature [66], and the emission of 2 which almost covers the full visible range, makes it a potential candidate for practical application as a white-light emission device. In addition, complexes 1, 2 and 3 exhibit large Stokes shift between the excitation and the emission maxima should attributed to strong distortion between the ground- and excited-state geometries.
4. Conclusions
Fig. 8. 2D planar networks are constructed by discrete molecules via the π π interactions.
state [6,63,64]. To the best of our knowledge, the NIR emission is a sparse phenomenon in d10 transition-metal complexes [6,64–66]. The emission behavior of complex 2 is quite distinct from those of 1 and 3. At ambient temperature three emissions can be detected, a LE band at λmax, em ¼610 nm and the other two HE bands at λmax, em ¼440, 467 nm (Fig. S5). The emissions should be tentatively assigned to singlet excited states since their lifetime are in the nanosecond regime. In analogy to 1 and 3, we assume that the LE emission of 2 originates from 1(d–s/XMCT). Two HE emissions are occurred on 2, accordingly, the excited states of 1 (MLCT/XLCT) thus can be proposed. Notably, the approximate lifetimes of the two HE emissions indicate the relatively coupled
In summary, three new Cu(I) clusters complexes have been synthesized under solvothermal conditions. Complex 1 exhibits 2D-3D two-fold parallel interpenetrating structure. Despite the vast number of interpenetrating networks now reported, we believe that 1 represents the first example of two-fold 2D-3D parallel interpenetrating networks with neutral Cu4I4 clusters as nodes and flexible ligands as rods. 2 is constructed from 2D (4,4) topological grid layers by AB stacking. 3 contains a (Cu6S6) core in discrete paddle-wheel molecule, via π π interaction forming a 2D (4,4) layers. Moreover, complexes 1, 2 and 3 show strong photoluminescence at room temperature. The results indicate that 1 and 3 possess excellent phosphorescence properties, while 2 shows triple emissions with fluorescence property, which are likely to be potential luminescent or photochemical materials.
Acknowledgments The authors gratefully acknowledged the financial supports from the National Natural Science Foundation of China (Grant no. 20971103 and 21271148).
S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jssc.2014.11.014. References [1] P. Feng, X. Bu, N. Zheng, Acc. Chem. Res. 38 (2005) 293. [2] N.F. Zheng, X.H. Bu, H. Vu, P.Y. Feng, Angew. Chem. Int. Ed. 44 (2005) 5299. [3] Y. Chen, Z. Yang, C.X. Guo, C.Y. Ni, H.X. Li, Z.G. Ren, J.P. Lang, CrystEngComm 13 (2011) 243. [4] Y. Zhang, T. Wu, R. Liu, T. Dou, X.H. Bu, P.Y. Feng, Cryst. Growth Des. 10 (2010) 2047. [5] Kylie M. Henline, Charles Wang, Robert D. Pike, Cryst. Growth Des. 14 (2014) 1449. [6] X.-C. Shan, F.-L. Jiang, D.-Q. Yuan, M.-Y. Wu, S.-Q. Zhang, M.-C. Hong, Dalton Trans. 41 (2012) 9411. [7] J.A. Rusanova, K.V. Domasevitch, O.Y. Vassilyeva, V.N. Kokozay, E.B. Rusanov, S.G. Nedelko, O.V. Chukova, B. Ahrens, P.R. Raithby, J. Chem. Soc. Dalton Trans. (2000) 2175. [8] S. Haddad, R.D. Willett, Inorg. Chem. 40 (2001) 809. [9] R.D. Willett, J.R. Jeitler, B. Twamley, Inorg. Chem. 40 (2001) 6502. [10] J.D. Martin, J. Yang, A.M. Dattelbaum, Chem. Mater. 13 (2001) 392. [11] J.-J. Hou, S.-L. Li, C.-R. Li, X.-M. Zhang, Dalton Trans. 39 (2010) 2701. [12] Q. Hou, J.-N. Xua, J.-H. Yu, T.-G. Wang, Q.-F. Yang, J.-Q. Xua, J. Solid State Chem. 183 (2010) 1561. [13] J.-K. Cheng, Y.-G. Yao, J. Zhang, Z.-J. Li, Z.-W. Cai, X.-Y. Zhang, Z.-N. Chen, Y.-B. Chen, Y. Kang, Y.-Y. Qin, Y.-H. Wen, J. Am. Chem. Soc. 126 (2004) 7796. [14] T. Wu, M. Li, D. Li, X.-C. Huang, Cryst. Growth Des. 8 (2008) 568. [15] Y. Zhang, T. Wu, R. Liu, T. Dou, X.H. Bu, P.H. Feng, Cryst. Growth Des. 11 (2011) 29. [16] J. Song, Y.J. Hou, L.F. Zhang, Y.L. Fu, CrystEngComm 13 (2011) 3750. [17] Y. Kang, F. Wang, J. Zhang, X.h. Bu, J. Am. Chem. Soc. 134 (2012) 17881. [18] A. Barbieri, G. Accorsi, N. Armaroli, Chem. Commun. (2008) 2185. [19] M.H. Bi, G.H. Li, Y.C. Zou, Z. Shi, S.H. Feng, Inorg. Chem. 46 (2007) 604. [20] M.H. Bi, G.H. Li, J. Hua, Y.L. Liu, X.M. Liu, Y.W. Hu, Z. Shi, S.H. Feng, Cryst. Growth Des. 7 (2007) 2066. [21] M.H. Bi, G.H. Li, J. Hua, X.M. Liu, Y.W. Hu, Z. Shi, S.H. Feng, CrystEngComm 9 (2007) 984. [22] L. Carlucci, G. Ciani, M. Moret, D.M. Proserpio, S. Rizzato, Angew. Chem. Int. Ed. 39 (2000) 1506. [23] X.H. Bu, W.F. Hou, M. Du, W. Chen, R.H. Zhang, Cryst. Growth Des. 2 (2002) 303. [24] L. Carlucci, G. Ciani, D.M. Proserpio, Chem. Commun. (2004) 380. [25] J. Zhang, Y.B. Chen, S.M. Chen, Z.J. Li, J.K. Cheng, Y.G. Yao, Inorg. Chem. 45 (2006) 3161. [26] X.-G. Liu, L.-Y. Wang, X. Zhu, B.-L. Li, Y. Zhang, Cryst. Growth Des. 9 (2009) 3997. [27] S.-C. Chen, R.-M. Yu, Z.-G. Zhao, S.-M. Chen, Q.-S. Zhang, X.-Y. Wu, F. Wang, C.-Z. Lu, Cryst. Growth Des. 10 (2010) 1155. [28] S. Delgado, P.J.S. Miguel, J.L. Priego, R. Jimenez-Aparicio, C.J. Gomez-Garcia, F. Zamora, Inorg. Chem. 47 (2008) 9128. [29] S.S. Alexandre, J.M. Soler, P.J.S. Miguel, R.W. Nunes, F. Yndurain, J. GomezHerrero, F. Zamora, Appl. Phys. Lett. 90 (2007) 193107.
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Three complexes of Cu(I) cluster with flexible and rigid ligands: Synthesis, characterization and photoluminescent properties Shu Sun a,b, Li-Juan Liu a, Wang-Yang Ma a, Wei-Xia Zhou a, Jun Li a,n, Feng-Xing Zhang a a b
College of Chemistry & Materials Science, Northwest University, Taibai Avenue 229, 710069 Xi’an, China Department of Chemical Engineering, Ordos College of Inner Mongolia University, Inner Mongolia University, Ordos, Inner Mongolia 017000, China
art ic l e i nf o
a b s t r a c t
Article history: Received 15 August 2014 Received in revised form 2 November 2014 Accepted 9 November 2014 Available online 18 November 2014
Three new Cu(I) cluster complexes, viz. [(Cu4I4)(Cu2I2)(dimb)3]n (1; dimb ¼1,4-diimidazol-1-ylbutane), [(Cu3I2)(dimb)(dmtz)]n (2; dmtz ¼3,5-dimethyl-1,2,4-triazole), and [Cu6(mbt)6] (3; mbt ¼2-mercaptobenzothiazole), have been solvothermally synthesized and structurally characterized. In 1, a Cu4I4 cubane core as a 4-connecting node, connects the neighboring nodes either through single dimb or μ2[(Cu2I2)(dimb)2] linkers, affording an undulated 2D (4,4) net. Parallel interpenetration occurs between the adjacent nets and thus the overall 2D-3D network is formed. Complex 2 is constructed by 2D (4,4) topological plane grid layers of AB stacking. The core, a distorted triangular bipyramidal Cu3I2 cluster, is acted as a 4-connecting node and connected with dimb and μ3-dmtz to form the layer. Complex 3 contains a (Cu6S6) core in discrete paddle-wheel molecule, which serves as a 4-connecting node to link equivalent ones via π π interaction, forming 2D (4,4) layers. Solid-state luminescence properties and thermogravimetric analyses of 1, 2 and 3 were investigated. & 2014 Elsevier Inc. All rights reserved.
Keywords: Cu(I) cluster Flexible and rigid ligands Metal–organic complex Photoluminescent
1. Introduction Metal chalcogenides and halides clusters are used as building units for construction of higher dimensional frameworks [1], and for their potential application such as luminescent materials [2–6]. Particular iodocuprate(I) (cuprous iodide aggregates) are of interests in this area due to their wide variety of stereochemical diversity and rich photoluminescent properties [7–12]. Iodide ion, soft Lewis base, binds strongly to soft Lewis acid of cuprous ion, forming different composition [(CuxIy)x y] clusters, which exist in various shapes, and provide the possibility for diverse coordination manners [13–17]. Moreover, compared with the noble and rare earth metals, d10 transition-metal based complexes have been attracted growing attention from an economical point of view as they are abundance on the earth [18]. Wen et al. synthesized 1D inorganic–organic hybrid coordination polymer, the first example of a linear chain formed by trinuclear Cu3I4 units, which exhibits remarkably rich photoluminescent properties [13]. Huang et al. [14], Feng et al. [4,15], and Fu et al. [17] have investigated the [(CuxIy)x y] cluster combined with rigid ligands of benzotriazole, 1,3-N-dimethylbenzotriazolium, 1-N-methylbenzotriazole, 1-N-methyltriazole, 1,2,3-triazole, 1,3-N-diethyltriazolium, 1,4-diazabicyclo[2.2.2]octane almost systematically, obtained
n
Corresponding author. E-mail address: [email protected] (J. Li).
http://dx.doi.org/10.1016/j.jssc.2014.11.014 0022-4596/& 2014 Elsevier Inc. All rights reserved.
the iodocuprate frameworks ranging from 2D to 3D. In particular, Complex [Cu2I2(MBta)] (MBta¼ 1-N-methylbenzotriazole) reported by Huang et al. [14], exibits interestingly perpendicular interpenetration of 2D (4,4) nets. Kang et al. synthesized a new MTN-type cluster-organic framework (COZ-1) containing giant 64512 and 512 cages. It exhibited perfect integration of porosity and photoluminescent properties from both the cluster and the framework in a porous material [17]. Though a number of complexes based on Cu(I) clusters have been obtained, with good thermal stability and strong photoluminescence properties of these compounds are seldom reported [15,19–21]. In this work, we report three complexes of copper(I) cluster with long flexible dimb and rigid mbt as ligands. The former is chosen because it can adopt different conformations according to the geometric needs of the different cluster cores [22–26]. Complex 1 represents the first example of parallel interpenetrating (4,4) frameworks with neutral Cu4I4 clusters as nodes and flexible ligands as rods. Unlike 1, complex 2 has a noninterpenetrating 2D network, in which the dimb and dmtz ligands serve as linkers to connect cationic Cu3I2 clusters giving rise to 2D sheet structures. Because the orbital energies of transition metal are well matched with S, the thiol group thus can be acted as a bridge to connect the adjacent transition metal sites, and delocalize the spin electron density toward them simultaneously. Accordingly, the latter ligand, with aromatic delocalized electron system existed, is highly desirable in terms of luminescent behavior [27–29]. Complexes 1, 2 and 3 show strong photoluminescence at room temperature.
2
S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
2. Experimental 2.1. Materials and instrumentation Commercially available reagents were used as received without further purification. Elemental analyses of C, H, N were performed on a Vario EL III analyzer. Infrared spectra were obtained from KBr pellets on a Bruker EQUINOX 55 Fourier transform Infrared spectrometer in the 400 4000 cm–1 region. The powder X-ray diffraction (PXRD) was recorded on a Rigaku D/Max-2500 diffractometer at 40 kV, 100 mA for a Cu-target tube and a graphite monochromator. Thermogravimetric measurements were carried out from room temperature to 1000 1C for 1, 2 and 3 on preweighed samples under nitrogen flow (flow rate of 30 mL min 1) using TA Instruments NETRZSCHSTA 449C simultaneous TGA–DSC with a heating rate of 10 1C min 1. Fluorescence spectra were recorded on a Hitachi F-4500 spectrophotometer at room temperature. 2.1.1. Synthesis of [(Cu4I4)(Cu2I2)(dimb)3]n (1) CuI (0.038 g, 0.20 mmol) was dissolved in 6 mL aqueous solution of KI (0.747 g, 4.50 mmol). While stirring, a solution of dimb (0.152 g, 0.80 mmol) in CH3OH (2 mL) was added. The solution was stirred to give a pale precipitate, and then this heterogeneous mixture was placed in a 25 mL Teflon-lined stainless steel reactor and heated at 120 1C for 72 h. Yellow rod-like crystals suitable for X-ray crystal analyses were isolated in 28% yield (based on Cu), which are stable in air and insoluble in water and common organic solvents. Elemental analysis for 1: C30H42N12Cu6I6 (Mr¼ 1713.44). Calcd: H 2.47, C 21.03, N 9.81%. Found: H 2.50, C 21.06, N 9.79%. IR data (KBr, cm 1): 3448(s), 3116(s), 2947(w), 1630(m), 1527(m), 1446(m), 1230(m), 1095(s), 947(w), 847(w), 750(s), 661(s), 627(w). 2.1.2. Synthesis of [(Cu3I2)(dimb)(dmtz)]n (2) A mixture of CuI (0.038 g, 0.20 mmol), dimb (0.038 g, 0.20 mmol), anhydrous CH3OH (2 mL) and acetonitrile (6 mL), was stirred, and then sealed in a 25 mL Teflon-lined stainless steel reactor, kept under autogenous pressure at 90 1C for 72 h. Pale yellow needle-like crystals suitable for X-ray crystal analyses were isolated in 45% yield (based on Cu), which are stable in air and insoluble in water and common organic solvents. Elemental analysis for 2: C14H20N7Cu3I2 (Mr¼730.79). Calcd: H 2.76, C 23.01, N 13.42%. Found: H 2.71, C 22.85, N 13.52%. IR data (KBr, cm 1): 3450(m), 3120(s), 2933(m), 2864(w), 1612(w), 1519(s), 1488(m), 1464(m), 1419(s), 1375(m), 1274(m), 1234(s), 1107(s), 1086(s), 823(s), 750(s), 652(s), 627(m). 2.1.3. Synthesis of [Cu6(mbt)6] (3) A mixture of CuI (0.038 mg, 0.2 mmol), Hmbt (0.034 g, 0.20 mmol), acetonitrile (8 mL) and 0.5 mL ammonia was stirred at room temperature. Immediately, a yellow precipitate appeared and then was transferred into a 25 mL Teflon-lined reactor and kept under autogenous pressure at 160 1C for 96 h. Brown block crystals, stable in air and insoluble in water and common organic solvents, were isolated in 79% yield (based on Cu). Elemental analysis for 3: C42H24N6S12Cu6 (Mr¼1378.63). Calcd: H 1.75, C 36.59, N 6.10%. Found: H 1.78, C 36.33, N 6.15%. IR data (KBr, cm 1): 3429(w), 3066(w), 1452(m), 1402(s), 1313(w), 1280(w), 1244(m), 1080(m), 1007(s), 750(s), 721(m), 694(m). 2.2. Crystal structure determination Diffraction data of 1, 2 and 3 were collected on a Bruker SMART diffractometer with graphite monochromated Mo Kα radiation (λ ¼0.71073 Å) in φ and ω scan modes at 296 K. Absorption correction was applied by using the SADABS program [30]. The
Table 1 Crystallographic data and structure refinement parameters for 1, 2, and 3. Complex
1
2
3
Empirical formula Mr (g mol 1) Crystal system Space group Temperature (K) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm 3) μ (mm 1) F (0 0 0) θ range (deg) Data/restraints/parameters Goodness-of-fit R1a [I4 2σ(I)] wR2a (all data) Residuals (e Å 3)
C30H42Cu6I6N12 1713.40 Monoclinic C2/c 296(2) 25.568(4) 11.3313(18) 16.156(3) 90 100.503(3) 90 4602.3(13) 8 2.473 6.785 3192 1.97–25.50 4067/23/244 1.067 0.0392 0.1137 1.547, 1.310
C14H20Cu3I2N7 730.79 Monoclinic C2/c 296(2) 21.456(4) 8.1045(15) 15.222(3) 90 127.130(2) 90 2110.3(6) 4 2.300 5.935 1384 2.78–25.16 1867/12/120 1.096 0.0360 0.1023 0.694, 1.131
C42H24Cu6S12N6 1378.63 Triclinic P-1 296(2) 7.6786(7) 13.3192(13) 13.8392(19) 115.714(2) 98.183(2) 103.0350(10) 1194.9(2) 1 1.916 3.187 684 2.98–25.05 4165/0/298 1.029 0.0301 0.0670 0.299, 0.278
a
R1 ¼∑||Fo| |Fc||/∑|Fo|; wR2 ¼ [∑w(F2o F2c )2/∑w(F2o)2]1/2.
structure was solved by direct methods and successive Fourier difference syntheses(SHELXS-97), anisotropic thermal parameters for all nonhydrogen atoms were refined by full-matrix leastsquares procedure on F2 (SHELXTL-97) [31,32]. Hydrogen atoms were placed in geometrically calculated positions. Crystal data and details of refinements for complexes are summarized in Table 1. Selected bonds distances and angles are listed in Table 2. [CCDC number 970732, 970733 and 972636].
3. Results and discussion 3.1. Crystal structure of 1 Complex 1 is a 3D coordination polymer constructed from Cu4I4 cubane cores, Cu2I2 rhomboid clusters and dimb ligands. In a Cu4I4 unit, each Cu(I) cation connects three neighboring μ3-I anions, forming a 4-connecting Cu4I4 tetracapped tetrahedron cluster (Fig. 1, upper right), and uses a coordination sphere pointing outward of the tetrahedron to bond dimb ligand via nitrogen atom. Two coordination sites of it connect two other Cu4I4 clusters through merely single dimb ligands. The bond distances of the Cu–I and Cu–N bonds are 2.6104(10) –2.7969(13) Å and 2.003(6) – 2.015(6) Å, respectively. Cu3 and Cu3A (symmetry code: xþ 1/2, yþ 1/2, z) are bridged by μ2-I anions giving rise to a rhomboid Cu2I2 cluster with two dimb ligands (Fig. 1, upper left), meanwhile a longer chain as linker, μ2-[(Cu2I2)(dimb)2], is formed, which connects another two Cu4I4 clusters via nitrogen atoms of the dimb ligands. In Cu4I4 clusters, the spatial arrangement of distorted tetrahedron with Cu Cu distances of 2.701, 2.711 and 2.868 Å is adopted by the Cu(I) ions (Fig. 1, top). The Cu Cu distances are less than or approximately equal to the sum of the van der Waals separations (van der Waals radii for Cu, 1.43 Å) [33,34]. Such a result indicates the existence of the weak Cu Cu interactions. Those of Cu2I2 are 2.469 Å, particularly, shorter than that of Cu4I4. In complex 1, Cu4I4 clusters are linked by single dimb ligands and μ2-[(Cu2I2)(dimb)2] lingkers to form a substructure of highly undulated 2D net (Fig. 2a, b), in which the dihedral angle φ between adjacent folds is 70.8341 (Fig. 2a). The 2D net contains a (Cu4I4)4{μ2[(Cu2I2)(dimb)2]}2(dimb)2 window of 30.717 16.156 Å, which is so
S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
3
Table 2 Selected bond lengths(Å) and angles(1) for complexes 1, 2, and 3a. [(Cu4I4)(Cu2I2)(dimb)3]n (1) Cu(1)…Cu(2) Cu(2)…Cu(2)#1 Cu(2)–N(5) Cu(1)–I(2) Cu(2)–I(2) Cu(3)–I(3)#2 I(1)–Cu(1)–I(2) I(1)–Cu(2)–I(2) I(3)–Cu(3)–I(3)#2
2.7127(13) 2.868(2) 2.003(6) 2.7581(11) 2.7223(12) 2.5663(12) 117.81(4) 116.51(4) 122.44(4)
[(Cu3I2)(dimb)(dmtz)]n (2) Cu(1)…Cu(2) Cu(1)–I(1)#2 Cu(2)–I(1) I(1)–Cu(1)–I(1)#2 N(1)–Cu(1)–N(2) [Cu6(mbt)6] (3) Cu(1)–S(4)#1 Cu(2)–S(4) S(4)#1–Cu(1)–S(6) a
Cu(1)…Cu(1)#1 Cu(3)…Cu(3)#2 Cu(3)–N(4) Cu(1)–I(2)#1 Cu(2)–I(1)#1
2.7041(18) 2.4680(18) 1.939(6) 2.6104(10) 2.6348(11)
Cu(1)…Cu(2)#1 Cu(1)–N(1) Cu(1)–I(1) Cu(2)–I(1) Cu(3)–I(3)
2.7017(13) 2.015(6) 2.7231(12) 2.7969(13) 2.5600(12)
I(1)–Cu(1)–I(2)#1 I(1)–Cu(2)–I(1)#1
111.98(4) 107.33(4)
I(2)–Cu(1)–I(2)#1 I(1)#1–Cu(2)–I(2)
109.57(4) 111.25(4)
2.8392(13) 3.0907(12) 2.5281(7) 96.53(3) 151.4(2)
Cu(1)#2…Cu(2) Cu(1)–N(1) Cu(2)–I(1)#2 I(1)–Cu(1)–N(1) I(1)–Cu(2)–N(3)#1
2.8392(13) 1.906(5) 2.5281(7) 106.89(16) 115.97(2)
Cu(1)–I(1) Cu(1)–N(2) Cu(2)–N(3)#1 I(1)–Cu(1)–N(2) I(1)#2–Cu(2)–N(3)#1
3.0001(11) 1.928(5) 1.980(7) 94.22(15) 115.97(2)
2.2457(10) 2.2470(9) 117.41(4)
Cu(1)–S(6) Cu(3)–S(2)#1 S(2)–Cu(2)–S(4)
2.2488(10) 2.2559(10) 117.65(3)
Cu(2)–S(2) Cu(3)–S(6) S(2)#1–Cu(3)–S(6)
2.2556(10) 2.2491(10) 117.80(4)
Symmetry transformations used to generate equivalent atoms: 1. #1 x, y, z þ1/2; #2 xþ 1/2, yþ 1/2, z. 2. #1 x, y, z; #2 x, y, z þ 1/2; 3. #1 x, y, z.
Fig. 1. The coordination environments of Cu(I) ion (bottom), and Cu4I4, Cu2I2 cluster (top) in 1.
large that allows simultaneously catenated by the other two ones (orange and plum windows) in the adjacent nets (Fig. 3a). Therefore, each highly undulated 2D net is simultaneously penetrated by the two nearest neighbouring ones. The interpenetrating nets have parallel mean planes and are coincident, and thus an overall 2D3D framework is produced (Fig. 2b). To better understand the structure of 1, the topological analysis approach is employed. If the Cu4I4 clusters and dimb/μ2-[(Cu2I2)(dimb)2] are assigned as 4-connected nodes and rods, respectively, the substructure displays a parallel interpenetrating 2D-3D nets (Fig. 3b and c). The high degree of entanglement is due to: (i) the large enough windows of the net; (ii) the highly undulated nature of the single (4,4) net. 3.2. Crystal structure of 2 In complex 2, the dmtz ligands are present, it should be generated from the in situ reaction of acetonitrile under the solvothermal conditions, and the possible reaction mechanism may proposed Scheme 1 [35–51]. The structure of 2 is constructed from [Cu3I2] þ clusters linked by mixed dmtz anions and dimb ligands. In [Cu3I2] þ cluster, weak Cu Cu interactions is exhibited due to the fact that the isosceles triangular arrangement with two equicrural Cu Cu distances of 2.839 Å and a bottom of 3.223 Å is adopted by the Cu(I) ions (Fig. 4, left). The Cu(I) ions are bridged by μ3-I anion on the either side of the triangle giving rise to a distorted triangular bipyramidal [Cu3I2] þ cluster (Fig. 4, left),
Fig. 2. (a) The dihedral angle φ in the net, (b) perspective views of the undulated 2D (4,4) net, (c) 2D-3D parallel interpenetration in the structure of 1.
in which Cu(I) features distorted triangular and tetrahedral coordination geometry. Furthermore, the triangular Cu2 connects N3 atom of μ3-dmtz linking another [Cu3I2] þ cluster, while the
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16.562 8.104 Å (Fig. 4, right). The bond distances of the Cu–I and Cu–N bonds are 2.5281(7) –3.0907(12) Å and 1.906(5) – 1.980(7) Å, respectively. Different from 1, although the (4,4) grids in 2 also have large windows, these grids are not undulated but are planar. The layers are further stacked in an ABAB sequence along the [1 0 1] direction, which is visualized by the translucent blue plane (Fig. 5a), and the short average plane-to-plane separations are 3.950 Å (Fig. 5b). 3.3. Crystal structure of 3 Complex 3 is a discrete paddle-wheel molecule, which is neutral and composed of six Cu(I) cations bridged by six tridentate mbt monoanions, forming (Cu6S6) core (Fig. 6). Each of the Cu (I) ions is three-coordinated by one nitrogen atom and two thiolate sulfur atoms from three mbt ligands, forming a distorted trigonal CuNS2 geometry. In other words, each mbt ligand serves as a tridentate ligand to connect three Cu(I) ions by using its thiolate sulfur atom as a μ2 linker to connect two ones, and its nitrogen atom to coordinate the third one. The six copper atoms forms a distorted octahedron with Cu Cu distances in the range of 3.002–3.100 Å, which are larger than the sum of the van der Waals separations [33,34]. The mbt is a rigid and aromatic delocalized electron system, and its coordination geometry is different from dimb or dmtz. As a result, the complex 3 can not exhibit 2D or 3D framework formed by covalent bonds. Nonetheless, the infinite offset face-to-face π π interactions of benzene rings of mbts are present, through which the discretely paddle-wheel molecules extend 2D planar networks (Fig. 7). The distances between two centers of benzene rings are 3.933, 4.126 Å, but the distances of π π interactions between benzene faces are 3.450, 3.504 Å, and the degrees of offset, θ, are 28.6941, 31.8701, respectively (Fig. 7). In complexes, it is found that many planar aromatic moieties tend to be stacked with an interplanar separation in the range 3.3–3.6 Å, and most examples with the degrees of offset lie between 101 and 451 [52– 56]. Furthermore, the 2D networks are stacked along the [1 0 0] direction in parallel, and the large average plane-to-plane separations are 7.220 Å (Fig. 8). 3.4. Powder X-ray diffraction Fig. 3. (a) A view of catenation of windows, (b) and (c) Schematic representation of 2D-3D parallel interpenetration of highly undulating 2D networks of 1 viewed from different directions.
The experimental and simulated X-ray powder diffraction patterns of complexes 1, 2 and 3 are in good agreement with each other, proving the phase purity of the as-synthesized products. The difference in reflection intensity is probably caused by the preferred orientation effect in the powder sample (Fig. S1 of the Supporting information). 3.5. Thermal property
Scheme 1. Possible formation mechanisms of 3,5-dimethyl-4H-1,2,4-triazole from acetonitrile.
tetrahedral Cu1 and Cu1A are simultaneously bridged by the μ3-dmtz via N2, N2A ( x, y, zþ 1/2), and bonded by N1, N1A from dimb ligands linking other two [Cu3I2] þ clusters via nitrogen atoms. As a result, a 2D (4,4) topological planar grid layer is formed, which contains (Cu3I2)4(μ3-dmtz)2(dimb)2 windows of
Thermogravimetric Analysis of 1, 2 and 3 was carried out in nitrogen atmospheres to investigate their thermal stabilities. TGA profiles for complexes 1, 2 and 3 are shown in Fig. S2, Supporting information. As can be seen in the figure, a stable state can be maintained for Complex 1 below 350 1C. However, with the temperature increased, two obvious weight loss steps can be observed. The first weight loss of 28.35% in the range of 350– 450 1C, which should correspond to a large proportion of dimb decomposition. The second weight loss of 48.67% between 450 and 830 1C should be attributed to a fraction of dimb and CuI volatilization. Similar to 1, complex 2 has two weight loss steps. The first weight loss of 35.05% in the range of 250–456 1C corresponds to the most of decomposition of organic ligands. The second weight loss appeared between 500 and 880 1C, which could be ascribed to the decomposition of organic ligands and the
S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
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Fig. 4. The coordination environments of Cu(I) ion (left), and 2D (4,4) grid (right) in 2. (symmetrically generated).
Fig. 6. The coordination environments of Cu(I) ion and (Cu6S6) core in 3.
3.6. Photoluminescent property
Fig. 5. (a) Topological illustration of the ABAB sequence stacking along the [1 0 1] direction, representing the 2D grid structure of 2, (b) viewed along the a-axis (orange: A sheet, blue: B sheet). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
volatilization of CuI. While for the complex 3, a mass loss of 57.59% occurred between 240 and 490 1C, indicating the decomposition of organic ligands only according to the calculation result of their theoretical weight loss. The thermal stability of these complexes are better than those of normal Cu(I) cluster based ones given in the earlier reports [6,15,19–21], which makes them potential candidates for practical application.
The photoluminescent properties for 1, 2 and 3 were investigated in the solid state at room temperature. The results are summarized in Table 3 and in Fig. 9. Upon excitation of complex 1 at λmax, ex ¼320 nm, an intense orange luminescence appeared at λmax, em ¼612 nm (Table 3, Fig. S3), which agree with the previous literature [17]. The low energy (LE) emission decayed with a lifetime is in the microsecond regime (Table 3, Fig. S4), revealing that the emission is phosphorescent, most likely associated with a spin-forbidden transition. According to the previous reports about the polynuclear Cu(I) clusters and their decay lifetimes, the emission of 1 can be tentatively attributed to the triplet clustercentered (3CC) excited state which combine halide-to-ligand (XMCT) and metal-centered (d–s) components [57–60]. Hexanuclear complex 3 displays a quite intense near-infrared (NIR) emission (typically between 700 and 900 nm) [61,62] at λmax, em ¼ 792 nm, which should also be involved in 3(d–s/LMCT) excited
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S. Sun et al. / Journal of Solid State Chemistry 225 (2015) 1–7
Table 3 Excitation and emission data of complexes 1, 2 and 3. Complex λmax, ex (nm)
λmax, em (nm)
τ1
τ2
χ2
Suggested origin
1 2
612 440 467 610 792
3.66 μs 0.99 ns 0.93 ns 0.87 ns 5.54 μs
14.65 μs 6.42 ns 5.86 ns 27.11 ns 9.24 μs
1.005 1.298 1.258 1.101 1.102
3
3
320 370 370 370 370
(d–s/XMCT) (MLCT/XLCT) (MLCT/XLCT) 1 (d–s/XMCT) 3 (d–s/LMCT) 1 1
Fig. 9. Emission spectra of complexes 1, 2 and 3 in solid state at room temperature.
Fig. 7. The infinite offset face-to-face π π interactions of benzene rings of mbts.
behavior of the two bands (Table 3, Fig S6 and S7). In contrast, LE and HE emissions are independent, apparently. It is worthy to mention that multiple emissions of complexes are extremely rare at room temperature [66], and the emission of 2 which almost covers the full visible range, makes it a potential candidate for practical application as a white-light emission device. In addition, complexes 1, 2 and 3 exhibit large Stokes shift between the excitation and the emission maxima should attributed to strong distortion between the ground- and excited-state geometries.
4. Conclusions
Fig. 8. 2D planar networks are constructed by discrete molecules via the π π interactions.
state [6,63,64]. To the best of our knowledge, the NIR emission is a sparse phenomenon in d10 transition-metal complexes [6,64–66]. The emission behavior of complex 2 is quite distinct from those of 1 and 3. At ambient temperature three emissions can be detected, a LE band at λmax, em ¼610 nm and the other two HE bands at λmax, em ¼440, 467 nm (Fig. S5). The emissions should be tentatively assigned to singlet excited states since their lifetime are in the nanosecond regime. In analogy to 1 and 3, we assume that the LE emission of 2 originates from 1(d–s/XMCT). Two HE emissions are occurred on 2, accordingly, the excited states of 1 (MLCT/XLCT) thus can be proposed. Notably, the approximate lifetimes of the two HE emissions indicate the relatively coupled
In summary, three new Cu(I) clusters complexes have been synthesized under solvothermal conditions. Complex 1 exhibits 2D-3D two-fold parallel interpenetrating structure. Despite the vast number of interpenetrating networks now reported, we believe that 1 represents the first example of two-fold 2D-3D parallel interpenetrating networks with neutral Cu4I4 clusters as nodes and flexible ligands as rods. 2 is constructed from 2D (4,4) topological grid layers by AB stacking. 3 contains a (Cu6S6) core in discrete paddle-wheel molecule, via π π interaction forming a 2D (4,4) layers. Moreover, complexes 1, 2 and 3 show strong photoluminescence at room temperature. The results indicate that 1 and 3 possess excellent phosphorescence properties, while 2 shows triple emissions with fluorescence property, which are likely to be potential luminescent or photochemical materials.
Acknowledgments The authors gratefully acknowledged the financial supports from the National Natural Science Foundation of China (Grant no. 20971103 and 21271148).
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