Open Pentameric Calixarene Nanocage Kongzhao Su, †,‡ Feilong Jiang, † Jinjie Qian, †,‡ Mingyan Wu, † Yanli Gai, †,‡ Jie Pan, †,‡ Daqiang Yuan, † and Maochun Hong* ,† † State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China ‡ University of the Chinese Academy of Sciences, Beijing 100049, China * S Supporting Information ABSTRACT: A novel open helmetlike coordination cage has been synthesized based on Co 4 -calixarene shuttlecock- like secondary building units and in situ generated phosphate anions, where the opening of the cage comprises a large 16-membered ring. The above unprecedented Co 20 nanocage presents the first pentame- ric calixarene coordination compound. Sorption behavior and magnetic properties are also investigated. T he exploration for high-nuclearity transition-metal cage complexes has attracted growing attention because of not only their wonderful architectures 1 but also their widespread applications in encapsulating guest molecules, 2 gas separation and storage, 3 nanoscale catalysts, 4 and so on. 5 A variety of coordination cages with distinct geometries and various sizes have been reported in recent years. 6 However, there are very few reports on the construction of coordination cages using molecular building blocks as large vertices. p-tert-Butylthiacalix[4]arene (H 4 BTC4A; Figure 1a), as an emerging and particular ligand in calixarene chemistry, 7 possesses four hydroxyl groups at the lower rim and four sulfur bridge atoms, which have been documented as good candidates to construct polymetallic complexes. 8 H 4 BTC4A ligands always bond the metals directly by their phenolic oxygen atoms and sulfur bridges. It is also found that one thiacalix[4]arene molecule can bind to four metal ions, simultaneously forming a tetranuclear metal entity acting as an excellent secondary building unit (SBU), which can be bridged by different linkers into high-nuclearity coordination complexes. For example, they can be linked into isolated sandwich-like Co 8 , saddlelike M 12 (M = Co, Ni), wheel-like Co 16 clusters, tetragonal-prismatic Co 32 nanocages, and one-dimensional chains by in situ generated nitrogen-donor ligands, 9 a large metallamacrocycle Co 24 by 1,2,4- triazole molecules, 10 a wavelike belt or Co 16 squares with aromatic dicarboxylates, 11 and a series of calixarene-supported octahedral coordination Co 24 nanocages by 6 Co 4 -TBC4A SBUs with 8 tripodal ternary aromatic carboxylates 12 or 12 1,4- benzenedicarboxylates as linkers. 13 In spite of the fact that calixarenes are facile to construct polymetallic complexes, there are no reports on polymetallic complexes supported by five calixarene molecules. To our best knowledge, all of the reported calixarene-based polymetallic complexes are assembled by mono-, bi-, tri-, tetra-, hexa-, or octameric calixarene units. 14 Our group is particularly interested in the design and synthesis of new solid inorganic-organic hybrid materials based on calixarene. 9a,13,15 In this paper, we present the first pentameric calixarene coordination cage, [Co 20 (BTC4A) 5 ( μ 2 -H 2 O)( μ 3 -OH) 4 (HPO 4 ) 8 ] 2 · 2DMF · 8CH 3 OH (1) (DMF = N,N-dimethylformamide). Herein, the crystal structure, sorption behavior, and magnetic properties of the title compound are presented and discussed. Red block crystals of 1 were obtained under solvothermal reaction by mixing Co(ClO 4 ) 2 ·6H 2 O, H 4 BTC4A, and H 2 PO 3 in a 3:1:2 molar ratio in DMF-CH 3 OH mixed solvents (1:1, v/v) at 160 °C. Powder X-ray diffraction (PXRD) analysis confirms the phase purity of the bulk product (Figure S5 in the Supporting Information, SI). Single-crystal X-ray diffraction analysis shows that Co 4 -TBC4A SBUs are linked by eight HPO 4 2- anions to form an unprecedented open helmet-shaped Co 20 structural motif (Figure 1b). Compound 1 crystallizes in the triclinic system with space group P1̅, featuring a nanosized open coordination cage. The asymmetric unit is large and contains two open Co 20 nanocages and some disordered solvent molecules, whose contribution has been subtracted from the diffraction data by the SQUEEZE command in PLATON 16 (see the SI). Each Co 20 nanocage is constructed from five Co 4 -TBC4A SBUs acting as the metal vertexes and eight HPO 4 2- linkers through a [5 + 8] condensation. Here we only provide one structure of a half- open Co 20 nanocage as a generic description (Figure 1c) because these two thiacalix[4]arene-supported Co 20 cages are structurally analogous and show similarity in their coordination environ- ments. Co1, Co3, and the opening four cobalt (Co8, Co12, Co16, and Co20) ions are five-coordinated in a distorted square- pyramidal coordination geometry with two phenoxyl oxygen atoms, one sulfur atom, and two oxygen atoms from two different HPO 4 2- anions, while the other 14 cobalt sites are six- coordinated in a distorted octahedral geometry with two phenoxyl oxygen atoms, one sulfur atom, and two oxygen atoms from two different HPO 4 2- anions, as well as one other component (μ 2 -H 2 O for Co2 and Co4 and μ 3 -OH for other cobalt cations). It should be noted that phosphates are excellent ligands for making polymetallic complexes because their different anionic forms can adopt various coordination modes. In compound 1, all HPO 4 2- anions are generated by an in situ reaction of H 2 PO 3 and adopt two coordination modes. Four HPO 4 2- anions in the lower part of the helmet bind to four cobalt Received: September 24, 2013 Communication pubs.acs.org/IC © XXXX American Chemical Society A dx.doi.org/10.1021/ic4024184 | Inorg. Chem. XXXX, XXX, XXX-XXX