The design and construction of coordination polymers from preformed metal clusters, [1] such as metal carboxylate clusters [2] and chalcogenide supertetrahedral clusters, [3] to produce new materials with unique properties have been the focus of recent research interest. However, given the impor-tance of cuprous iodide clusters in photochemistry and photophysics, [4] as well as their considerable variety of structural forms not encountered for other iodometalates, [5] it is surprising that relatively little progress has been made in using them as building blocks for the fabrication of multidimensional coordination frameworks. [6] On the other hand, polyoxometalates (POMs), [7, 8] as a unique class of metaloxide clusters, have many properties that make them attractive for applications in catalysis, biology, magnetism, optics, and medicine. [9] Impressive studies on linking of these welldefined metal-oxygen building blocks to generate giant discrete clusters and related extended structures have been performed. [10, 11] However, up to now no reports have been made on the combination of these two interesting fields to prepare high-dimensional cluster-based compounds, although POM chemistry has touched an almost unprecedented number of other fields of chemistry. [9b] Such composite materials present the opportunity to generate high-dimensional nanoscopic assemblies from even larger multinanounits and also have vast potential for use in materials science by incorporation of their own physical and chemical properties.
Among the many different types of POMs, we chose the Keggin heteropolyanions, as they are the most widely recognized and thoroughly studied. Furthermore, we used the N-heterocyclic ligand 4-[3-(1H-1,2,4-triazol-1-yl)propyl]-4H-1,2,4-triazole (L, see the Supporting Information) for our synthetic strategy because 1) its clawlike donor atoms and bent coordination geometry offer the possibility of incorporating more metal atoms into high-nuclearity clusters, and 2) ligands containing a large number of N atoms could partially reduce Mo VI to Mo V , [12] whereby the surface charge density of the polyanion is increased and the surface oxygen atoms are activated to facilitate formation of high-dimensional covalent networks. Herein we report the synthesis, structure, and luminescent and electrochemical properties of an unprecedented (4,12)-connected 3D network, namely, (NH 4 )[Cu 24 I 10 L 12 ][PMo V 2 Mo VI 10 O 40 ] 3 (1), assembled by covalent connection of nanometer-scale [Cu 24 I 10 L 12 ] 14+ cages and ball-shaped Keggin anions.
Crystals of 1 were obtained by hydrothermal reaction of CuI, H 3 PMo 12 O 40 , NH 4 Cl, and L. Single-crystal X-ray analysis of 1 [13] showed the presence of two different nanocluster subunits (see the Supporting Information). One is the familiar Keggin cluster anion [PMo V 2 Mo VI 10 O 40 ] 5ร (ca. 10.5 in diameter), which consists of four internally edge sharing triads (Mo 3 O 13 ) that share corners with each other and are disposed tetrahedrally around a central T d atom (Figure 1 c). Valence-sum calculations based on bond lengths established that the Mo centers are in + 5/ + 6 oxidation states (see the Supporting Information). The assignment of the oxidation state is also consistent with the charge requirement of the anion and the UV/Vis spectrum. [14] The other subunit is an unprecedented, highly symmetrical [Cu 24 I 10 L 12 ] 14+ cluster (Figure 1 a) built up of a tetrahedral Cu 12 I 10 N 12 core and twelve supporting copper(I) atoms (Figure 1 b). As shown in Figure 1 d, the linking mode of the Cu 12 I 10 N 12 core is very similar to that of the Keggin ion, that is, four Cu 3 I 4 N 3 triad clusters that result from the association of three edge-sharing CuI 3 N tetrahedra share corners to gen-