Communication pubs.acs.org/Organometallics
A Luminescent 3D Organometallic Network Based on Silver Clusters and Star-like Tris(4-ethynylphenyl)amine Bao Li and Tianle Zhang* School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People’s Republic of China S Supporting Information *
ABSTRACT: A star-like tris(4-ethynylphenyl)amine was used as a ligand to link Ag30 and Ag17 cluster units via argentophilic, Ag(I)-ethynide, and Ag-nitrate interactions to construct one 3D organometallic network possessing small cavities. The solid network displays a yellowish-green emission at room temperature.
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n the past decades, silver−ethynide complexes have been extensively studied due to their interesting reactivity and diverse structures. 1,2 These complexes are capable of aggregating to generate high-nuclearity silver clusters,3 chains, or networks2,4 and can also be utilized as building units to construct supramolecules.5 Usually silver−ethynide complexes are emissive, but in some cases the luminescence is quenched by unlimited π−π packing between the conjugated groups.6 Considering the fact that silver(I)−ethynide cluster units possess numerous vacant binding sites, porous networks constructed from silver−ethynide complexes could be potential materials for luminescent sensors. However, to date, porous and luminescent networks have not been developed based on Ag-ethynide cluster units. It is reasonable to utilize a nonplanar, rigid, and extended organic molecule as a ligand to construct porous and luminescent silver−ethynide networks because this ligand could enlarge the distances between Ag cluster units and minimize π−π stacking. Herein a star-like ligand, tris(4ethynylphenyl)amine, is used to construct a 3D silver−ethynide network that possesses small cavities and displays yellowishgreen emission in the solid state. Tris(4-ethynylphenyl)amine reacted with AgNO3 to produce an insoluble organometallic polymer (1), formulated as [N(C4H4−CC)3Ag3]n. This intermediate polymer was then dissolved in a concentrated solution of AgNO3 to afford a clear orange solution, from which network 2 crystallized as deep red plates by slowly diffusing water at 328 K. In its IR spectrum, the strong peak of NO3− (1384 cm−1) indicates that 1 interacts with AgNO3 to generate silver clusters.6 Compound 2 crystallized in the trigonal space group R3̅c (Table S1). In 2, the triangular star-like ligand displays a propeller geometry (Figure 1). Two ethynide groups in this ligand interact with four silver ions in μ4-η2,η1,η1,η1 (C15−C16) and μ4-η2,η2,η1,η1 (C23−C24) modes, respectively. Four Ag ions coordinated to the C15−C16 group are arranged in a © XXXX American Chemical Society
Figure 1. Coordination mode of the ligand in 2.
butterfly geometry, but four Ag ions attached to the C23−C24 group are located as a trigonal pyramid. However, the remaining (C7−C8) only coordinate to three Ag ions in a μ3-η1,η1,η1 binding mode. The lengths of carbon triple bonds are normal, in the range 1.202(15)−1.231(17) Å, and the Ag··· Ag distances are in the range 2.850(2)−3.334(3) Å, indicating the existence of an argentophilic interaction between Ag ions.7 In the solid state, three star-like ligands are arranged as a trigonal cage in 2 (Figure S1a), and the cages are connected through silver(I)−ethynide and an argentophilic interaction to form a 2D organometallic network (Figure S1b and c). It is interesting that six −(CC)Ag4 and six −(CC)Ag3 units aggregate by sharing Ag ions to generate a novel Ag30 cluster unit (Figures 1 and S2) with C3 symmetry, which can be described as a trigon attached by six Ag4 units in a butterfly geometry. The lengths of two edges of this trigon are 2.932(2) (Ag9−Ag9A) and 3.334(3) (Ag9−Ag9C) Å, respectively. Three ligands are linked by three Ag30 units to form a cage Received: April 22, 2015
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DOI: 10.1021/acs.organomet.5b00761 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics
which subsequently are linked by Ag17 cluster units and nitrate anions to generate a 3D porous and luminescent network. Further work on the design and construction of a highly emissive and porous material is in progress.
(Figure S3a), and one Ag30 unit interacts with six cages (Figure S1b), in such a way that a 2D network is constructed. The space-filling model indicates that there is a very small cavity in this cage (Figure S3b). In one layer, there is no π−π stacking between these cages, but the aromatic C−H···phenyl ring and π(phenyl)−π(phenyl) interactions are observed between three ligands in one cage (Figure S4), confirmed by short C19− H19···center(phenyl) (2.826 Å) and C11−C4A (3.354 Å) distances.8 Clearly there is another Ag17 cluster unit capping the top of the cage (Figures 1 and S3a). In the packing diagram (Figures 2a and S3a), it is shown that these Ag17 cluster units together
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00761. Detailed experimental procedures and figures (PDF) X-ray crystal data for 2 (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail (T.-L. Zhang):
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully acknowledge the National Natural Science Foundation of China for financial support (No. 21371064) and the Analytical and Testing Center, Huazhong University of Science and Technology, for spectral measurements.
Figure 2. (a) Packing diagram of 2. (b) Solid-state excitation and emission spectra of 2 at room temperature.
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with NO3− anions (Figures 2a and S5) in 2 actually function as linkers to interact with terminal ethynide groups pointing outward from two neighboring layers and consequently connect the layers to generate a novel 3D organometallic network. This Ag17 cluster unit also displays C3 symmetry if Ag2F···Ag2G is used as a C3 axis (Figure 1), which can be considered to be constituted by three Ag7 cluster subunits via sharing two silver ions (Ag2F and Ag2G). In one Ag7 subunit, Ag1 is shared by two −(CC)Ag4 units, and six silver ions interact with the Ag1 ion only through an argentophilic interaction (Ag···Ag distances: 2.905(2)−3.255(3) Å) (Figure S6). Compound 2 in the solid state displays yellowish-green luminescence at room temperature. The emission band is located in the range 300−800 nm with λmax at 578 nm and two peaks at 417 and 471 nm, respectively, on excitation at 264 nm (Figure 2b). Obviously the emission of 2 is not very different from that of free ligand except that a red-shift of the highest peak occurs (Figure S7), which could originate from ligandcentered excited states. It is reasonable to assign this emission as intraligand n → π* and π → π* transitions perturbed by silver(I)−ligand interactions.9 To get better insight into its photophysical property, the absorption and emission spectra at low temperatures (Figure S8) of 2 were measured in the solid state. The broad absorption band for 2 was located in the range 300−550 nm (Figure S8(a), λmax = 315 nm). Upon lowering the temperature, no obvious shifts were observed for the main peaks of the emission bands, but the intensity increases gradually (Figure S8(b)), suggesting that this emission is phosphorescent,10 which is supported by the large Stokes shift (14445 cm−1) and long emissive lifetime (0.15 ms). In summary, a nonplanar tris(4-ethynylphenyl)amine was utilized as a ligand to synthesize a new luminescent silver− ethynide compound. Structural analysis revealed that there are two unprecedented Ag30 and Ag17 cluster units aggregated from −(CC)Agn (n = 3, 4) units in 2. The Ag30 cluster units connect star-like triethynide ligands through argentophilic and silver−ethynide interactions to generate organometallic layers,
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DOI: 10.1021/acs.organomet.5b00761 Organometallics XXXX, XXX, XXX−XXX
