DOI: 10.1021/cg1001978
Three-Dimensional Photoluminescent Frameworks Constructed from Size-Tunable CuI Clusters
2010, Vol. 10 2047–2049
Ying Zhang,†,‡ Tao Wu,‡ Rui Liu,‡ Tao Dou,† Xianhui Bu,§ and Pingyun Feng*,‡ † The State Key Laboratory of Heavy Oil Processing, China University of Petroleum (Beijing), 102249 Beijing, China, ‡Department of Chemistry, University of California, Riverside, California 92521, and § Department of Chemistry and Biochemistry, California State University, Long Beach, California 90840
Received February 7, 2010; Revised Manuscript Received March 20, 2010
ABSTRACT: Reported here are three 3-D copper iodide frameworks, (Cu4I4)(DABCO)2(solvent)x (1), (Cu6I6)(Cu8I8)(DABCO)5(imidazole) (2), and (Cu2I2)1/2(Cu5I5)(DABCO)2 (3), constructed with DABCO ligands (DABCO=1, 4-diazabicyclo-[2.2.2]-octane) and various neutral CuI clusters. 1, 2, and 3 display an interpenetrating diamond-type net, a 5-connected interpenetrating net, and a (4,6)-connected net, respectively. The variations in Cuþ coordination numbers (2, 3, and 4), cluster types, and framework topologies are achieved by tuning reactant ratios and by employing different mixed solvents. Compound 3 displays chiral symmetry, while compound 2 shows photoluminescence at 298 K. The synthesis of multidimensional coordination polymers is of great current interest because of their structural novelty and potential applications as functional materials.1 An effective strategy commonly used in this area is the building block approach,2 in which, for example, metal carboxylate clusters2b,c or chalcogenide supertetrahedral clusters,2d are used as secondary building units for construction of two- and three-dimensional frameworks. Metal halide clusters, such as cuprous iodide clusters, have been widely studied due to their interesting properties in photochemistry and photophysics.3 However, there are only a few reports about 3-D coordination frameworks constructed from neutral cuprous iodide clusters.4 One early example is a rare chiral triple-interpenetrated quartz net, constructed with the tetrahedrally connected Cu4I4 cluster unit and flexible 1,3-bis(4-pyridyl)propane.4a Through solvothermal reactions of a rather complex mixture containing copper(II) salt, HIO4 3 2H2O, NaClO4 3 H2O, NaHCO3, and C6H12N2 3 6H2O (DABCO) in ethanol, four copper halide frameworks were synthesized and reported.4b Recently, the assembly of cuprous iodide clusters with other metal clusters into a novel three-dimensional framework has also been reported.4c,d Lu et al. reported the synthesis and characterization of a novel example of a hybrid solid consisting of unique six-connected dumbbell-like Cu4I4-O-Cu4I4 clusters and hexanuclear Cu6(datrz)6 rings (datrz = 3,5-diamino-1,2,4-triazole).4c Wang et al. took advantage of the self-assembly of nanometerscale [Cu24I10L12]14þ cages and ball-shaped Keggin clusters to generate a (4,12)-connected three-dimensional framework with photoluminescent and electrochemical properties.4d Here we report three 3-D copper iodide frameworks, (Cu4I4)(DABCO)2(solvent)x (1), (Cu6I6)(Cu8I8)(DABCO)5(imidazole) (2), and chiral (Cu2I2)1/2(Cu5I5)(DABCO)2 (3), constructed with DABCO and various neutral CuI clusters (Figure 1). The crystallographic and structural refinement data for 1, 2, and 3 are listed in the Supporting Information (Table S1). Compounds 1 and 2 were prepared through reactions of CuI and DABCO in the presence of imidazole in the mixed water/ethylene glycol solvents, while compound 3 was synthesized in the mixed DMF and CH3CN solvent (see the Supporting Information). The changes in the CuI/DABCO ratio and the nature of solvents result in great diversity of CuI building units and topological differences among three compounds. A single-crystal X-ray diffraction study performed on 1 revealed the formation of a 2-fold interpenetrating three-dimensional coordination framework. The structure of 1 is constructed
from Cu4I4 cubane units corner-connected by DABCO organic ligands. In a Cu4I4 cubane unit (Figure1b), each Cu(I) cation connects three neighboring iodide anions and uses a coordination sphere pointing outward of the cube to bond a DABCO ligand. The bond distances of the Cu-I and Cu-N bonds are 2.6585(3)2.6972(3) A˚ and 2.102(2)-2.131(2) A˚, respectively. If the Cu4I4 cubane building block is assigned as a node and the DABCO ligand as a linker, compound 1 displays a diamond-like net (Figure S1 in the Supporting Information). A similar example of 2-fold diamond-like networks is zinc cyanide.5 Compound 2 is an interpenetrating 5-connected network containing Cu6I6 and Cu8I8 building units. The Cu6I6 cluster is composed of five tetrahedrally coordinated Cu atoms and one three-coordinated Cu atom in a trigonal pyramidal geometry (Figure 1d). The hexanuclear Cu6I6 cluster is rare in the CuI system, and until now only a few compounds with a Cu6I6 cluster have been reported.4b,6 Usually, the “hexagonal” prism-shaped Cu6I6 cluster is constructed by the combination of two sixmembered Cu3I3 units through bonding between six iodine anions with six tetrahedrally coordinated copper(I) atoms. The Cu6I6 cluster reported here is an unusual example of the Cu6X6 “hexagonal” prismatic cluster with one Cu atom in a trigonal pyramidal geometry. Each of the other five Cu atoms in the Cu6I6 cluster is coordinated to three iodide atoms and a nitrogen atom from DABCO, and thus, every Cu6I6 cluster becomes a fiveconnected node. The Cu8I8 cluster is constructed by linking two Cu4I4 clusters together through two Cu-I bonds. There are three types of Cu(I) cations in the Cu8I8 cluster. One type of Cu atom is coordinated to four iodide atoms. The second type of Cu atom is coordinated to three iodide atoms and one nitrogen atom from DABCO. The third type of Cu atom is also coordinated to three iodide atoms and one nitrogen atom (from terminal imidazole). Overall, each Cu8I8 building unit is coordinated to five DABCO molecules and one terminal imidazole, again serving as the 5-connected node (Figure 1e), just like the Cu6I6 cluster. Each Cu6I6 cluster connects to four Cu8I8 building units (vice versa) through four DABCOs, forming a two-dimensional square gridlike sheet of (4,4) topology (Figure 2a). Then, the last coordination site of each Cu6I6 cluster in one sheet joins one Cu8I8 cluster in the neighboring sheet through one DABCO linker, which results in a 3-D extended architecture in compound 2 (Figure 2b and c). If the Cu6I6 and Cu8I8 building blocks are assigned as nodes and the DABCO ligand as a linker, compound 2 displays an interpenetrating 5-connected network (Figure 2d).
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Zhang et al.
Figure 1. Various neutral CuI clusters and their connectivity: (a) Cu2I2; (b) Cu4I4; (c) Cu5I5; (d) Cu6I6; (e) Cu8I8. Color code: Cu, green; I, pink.
Figure 3. Compound 3: (a) array of Cu2I2 and Cu5I5 in the ab plane; (b) view along the c-axis direction; (c) view along the b-axis direction; (d) (4,6)-connected network. Color code: Cu2I2, pink; Cu5I5, green; DABCO, blue.
Figure 2. Compound 2: (a) two-dimensional square gridlike sheet of Cu6I6 and Cu8I8 clusters; (b) view along the a-axis direction; (c) view along the b-axis direction; (d) 2-fold interpenetrated 5-connected network. Color code: Cu6I6, green; Cu8I8, red; DABCO, blue; imidazole, cyan.
A similar net type has been reported in a totally different structure containing C-methylcalix[4]resorcinarene and the linker molecule bis(4-pyridylmethylidyne)hydrazine (bpmh).7 Compound 3 contains Cu2I2 and Cu5I5 building units, as shown in Figure 1. The dimeric Cu2I2 acts as a pseudosquare planar node with two Cu atoms coordinated to four iodide atoms from four separate Cu5I5 building units (Figure 1a). Interestingly, the Cu5I5 building unit contains four tetrahedrally coordinated Cu atoms and one peculiar two-coordinated Cu atom. This peculiar Cu atom is almost linearly coordinated to two iodide atoms with an I-Cu-I angle of 175.3(2)° and a very short Cu-I bond length of 2.5311(6) A˚. The other four Cu atoms are respectively coordinated to three iodide atoms and a nitrogen atom from DABCO, creating four points of connectivity to other clusters. The two additional points of connectivity of Cu5I5 come from two iodide atoms connecting two Cu2I2 clusters through the Cu-I bonds (Figure 1c). Except for the unusually short Cu-I bonds involving bicoordinated Cu(I), all other Cu-I and Cu-N bond distances are in the normal range of 2.615(1)-2.821(2) A˚ and 2.059(8)-2.061(8) A˚. Neutral Cu5I5 building units are very rare. Wu et al. reported one Cu5I5 cluster, in which all Cu atoms are tetrahedrally coordinated.6a The connection between Cu5I5 and Cu2I2 building units according to the above-mentioned modes forms (4,4)-type layers
Figure 4. Emission and excitation spectra of compound 2: (left) excitation spectrum (λmax = 379 nm); (right) emission spectrum (λmax = 600 nm).
(Figure 3a). Between the two neighboring layers, the Cu5I5 building units are connected by DABCO linkers. Specifically, each Cu5I5 building unit in one layer links with four Cu5I5 building units in the neighboring layer by four DABCOs (Figures 3b and c), thus generating the 3D framework of compound 3. If the Cu2I2 and Cu5I5 building blocks are respectively assigned as a four-connected node and a six-connected node, the overall 3D framework of compound 3 displays a (4,6)-connected net (Figure 3d). Although there exist other examples of (4,6)connected nets,8 the (4,6)-connected net reported here is unique. Among these three compounds, only 2 was obtained as a single phase, as confirmed by powder X-ray diffraction (Figure S2 in the Supporting Information). The IR spectra of 2 are provided in the Supporting Information (Figure S3). Similar to other Cu-I cluster compounds,4b compound 2 shows photoluminescence at room temperature in the solid state. The spectrum displays a single excitation peak with a maximum at 379 nm that leads to a yellow emission centered at 600 nm (Figure 4). The mechanism of the photoluminescence is expected to be similar to that of other Cu-I clusters.4b Thermal analysis performed in air from 30 to 1000 °C (Figure S4 in the Supporting Information) shows that compound 2 is stable up to ca. 230 °C. The initial weight loss of the compound before 230 °C is likely due to the loss of ethylene glycol guest molecules. In the range 230-530 °C, the second and third steps of weight loss likely correspond to the decomposition of DABCO and imidazole ligands and the sublimation of iodine.
Communication
Crystal Growth & Design, Vol. 10, No. 5, 2010
In summary, described here are three 3-D copper iodide frameworks constructed from DABCO linker and various neutral CuI clusters including peculiar Cu5I5 and Cu6I6 clusters, which demonstrates the structural diversity of high-nuclear CuI cluster-based architectures. The results clearly show that structural features such as the coordination of Cu(I) ions, the type of clusters, and their interconnectivity are sensitively dependent on the synthetic conditions. These results suggest that further syntheses under other synthesis conditions can lead to many more novel neutral CuI clusters and 3-D copper iodide frameworks that may have unique structures and potentially useful properties.
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Acknowledgment. We acknowledge the support of this work by the NSF (P.F., X.B.) and DOE (P.F.). (5)
Supporting Information Available: Crystal structure information (CIF) and more experimental details and data (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.
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