Hydrothermal synthesis and structure of three novel open-framework lanthanide sulfate–oxalates Li Li a,b , Ranbo Yu c , Dan Wang a, ⁎, Xiaoyong Lai a , Dan Mao a , Mei Yang a a State Key Laboratory of Multi-Phase & Complex Systems, Institute of Processing Engineering, Chinese Academy of Sciences, Beijing 100190, PR China b Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China c Department of physical chemistry, University of Science and Technology Beijing, Beijing 100086, PR China abstract article info Article history: Received 28 January 2010 Accepted 2 April 2010 Available online 12 April 2010 Keywords: Hydrothermal synthesis Inorganic–organic hybrid material Open-framework Crystal structure Three novel hybrid open-framework lanthanide sulfate–oxalates, {[NH 4 ][Ln(H 2 O)(SO 4 )(C 2 O 4 )]} n [Ln = Y (I), La (II), Sm (III)] have been synthesized via hydrothermal reaction, and characterized by single crystal X-ray diffraction, powder X-ray diffraction, infrared spectrophotometry, thermal gravimetric analysis and fluorescence analysis. These three compounds were isostructural, and all crystallized into the monoclinic system with space group of P2 1 / n. In their structures, LnO 8 dodecahedra, SO 4 tetrahedral and C 2 O 4 groups are linked to give rise to a three-dimensional open-framework, which contains two kinds of 12-membered ring channel systems running along the a and b axis, respectively. © 2010 Elsevier B.V. All rights reserved. Crystal engineering of inorganic open-framework materials has attracted considerable interests due to their fascinating structural diversity and potential applications [1]. A variety of inorganic frameworks mostly involving with silicate [2] and phosphate [3] tetrahedral anionic moieties have been well reported. Nowadays, great researches are devoted to the design and synthesis of new inorganic framework materials with different compositions and structures. While SO 4 ions and PO 4 ions have different charges, they are of similar size and shape. It can also be effectively used to construct materials with new topological structures and interesting properties [4]. The lanthanide centers have high and variable coordination numbers and a wide variety of coordination environ- ments compared with other transition metals. Therefore, it is possible to lead to unusual topological frameworks [5]. Work reported on lanthanide sulfate mainly focused on inorganic hydrates and species of whose structures containing alkali metal, or ammonium ions, or organic amines template [6,7]. Selection of multidentate ligands as spacers to link multiple lanthanide ions as nodes under suitable reaction conditions has been proved to be a powerful methodology, and important progress has been achieved [8]. However, it is still a challenge for preparing lanthanide sulfate using the organic compo- nent as ligand directly coordinated to the lanthanide sulfate scaffolding to form the organic–inorganic hybrid materials. Oxalic acid has been well reported to build up a 3D metal-organic framework [9,10]. Herein, the three-dimensional open-framework lanthanide sulfate–oxalates {[NH 4 ][Ln(H 2 O)(SO 4 )(C 2 O 4 )]} n were reported and the synthesis, structure, and fluorescent properties of these lantha- nide sulfate–oxalates were discussed. Colorless columnar crystals of compound I were obtained by heating a mixture of Y 2 O 3 ,H 2 SO 4 , (NH 4 ) 2 SO 4 , oxalic acid, H 2 O and ethanol in the molar ratio of 1:8:4:2:833:74 at 160 °C for 3 days. Syntheses of compounds II and III were similar to that of compound I, except that La 2 O 3 and Sm 2 O 3 were used to replace Y 2 O 3 respectively. Crystallographic analysis reveals that all the three compounds are isostructural [11–13]. Therefore, only the crystal structure of compound I is described in detail. The single crystal X-ray diffraction study of the compound showed that the framework structure is made up of YO 8 dodecahedra, SO 4 tetrahedra and oxalate groups (Fig. 1). Each oxalate group links two Y ions in a bidentate mode, showing a zigzag chain along b axis (Fig. 2a). The sulfate groups adopting η 3 , μ 3 -tridentate coordinated mode connect with YO 8 dodecahedra at three vertices, with the fourth one being a free terminal oxygen, to form a one-dimensional chain along the a axis as shown in Fig. 2b. The inorganic [Y 2 (O–S–O) 2 ] chain is further linked via oxalate groups to produce an open-framework structure with one-dimensional chan- nels running along the a and b axes, respectively. Those along the a axis have a 12-membered window (six YO 8 , two SO 4 and four C 2 O 4 ) with a diagonal of 12.6 Å as shown in Fig. 3a. The channel systems along the b axis also have a 12-membered window (six YO 8 , four SO 4 and two C 2 O 4 )(Fig. 3b). It has a pore opening of 7.2 Å × 4.0 Å. The pore is generated by the removal of free ammonium molecules, and the void volumes are 49.9% (I), 53.1% (II) and 56.1% (III) respectively as estimated by PLATON [14]. The ammonium cations are located in the 12-membered windows to balance the framework's negative charge. The Y 3+ ions are eight-coordinate and described as a dodecahe- dron: three oxygen atoms from three SO 4 2- with distances in the range Inorganic Chemistry Communications 13 (2010) 831–833 ⁎ Corresponding author. Tel./fax: + 86 10 62631141. E-mail address: danwang@home.ipe.ac.cn (D. Wang). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.04.004 Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche