Morphology-Selective Formation and Morphology-Dependent Gas-Adsorption Properties of Coordination Polymer Particles By Hee Jung Lee, Won Cho, Soyoung Jung, and Moonhyun Oh* Coordination polymers are very useful materials in catalysis, optics, recognition, and separation. [1] In particular, there is an enormous interest in the storage of gas molecules, that is, H 2 , CO 2 ,C 2 H 2 , etc. [2] Although the vast majority of coordination polymer materials, including metal–organic frameworks (MOFs), are focused on macroscaled crystalline products, for structural studies based on single-crystal X-ray analysis, we and others have recently reported the synthetic strategies for the preparation of nano- and microsized coordination polymer particles (CPPs). [3,4] In contrast to bulk coordination polymers, CPPs have consider- able potential for use in innovative applications, such as imaging probes and heterogeneous catalysts. [3] Furthermore, CPPs also provide the opportunity for the fine tuning of materials, to achieve the properties desired. [4a,b] On the other hand, manipulation of the chemical and physical properties of metal or semiconductor particles through morphology control is a well-known strategy. [5] However, no research related to morphology-dependent proper- ties in CPPs has been performed. Herein, we report the selective formation of CPPs with diverse shapes from the same basic building blocks. We also demonstrate that the gas-sorption properties of CPPs, despite their identical chemical composi- tions, vary according to the morphology of the particles. A carboxyl-functionalized ligand (H 2 L ¼ 2,6-bis[(4-carboxy- anilino)carbonyl]pyridine, Fig. 1a) was synthesized according to the literature [6] with slight modifications. Subsequently, CPPs were prepared by the following solvothermal reactions. H 2 L, In(NO 3 ) 3  xH 2 O, imidazole, and CH 3 CO 2 H were combined in dimethylformamide (DMF), and the resulting solution was heated at 80 8C for 10 min. After this time, the precipitated products were cooled to room temperature, collected by centrifugation, and rinsed several times with DMF and methanol. The morphology of the resulting products was characterized by field-emission scanning electron microscopy (SEM), optical microscopy (OM), and fluorescence microscopy (FM), as shown in Figure 1b. The images reveal the formation of elongated hexagonal particles (CPP-6), with an average width and length of 1.52 and 3.00 mm, respectively. Infrared spectroscopy was used to confirm the creation of coordination polymers, as evidenced by a shift in CO stretching frequency of the carboxylate group to 1605 cm 1 . This value can be compared to that of 1688 cm 1 for the uncoordinated precursor H 2 L. The chemical composition of CPP-6 was determined by energy-dispersive X-ray (EDX, Supporting Information) spectroscopy and elemental analysis (EA). As shown in the inset of Figure 1b, CPP-6 is fluorescent in the blue region of the spectrum, due to ligand-to-metal charge-transfer (LMCT) of the coordination polymer. [7] In contrast, the free ligand does not emit and luminescence in this range. SEM and OM images of products generated in the presence of 100 mL of acetonitrile under otherwise identical reaction conditions reveal the selective formation of ellipsoidal particles (CPP-7, Fig. 2a), rather than elongated hexagons (CPP-6). The ellipsoidal-shaped CPPs have an average width and length of 1.33 and 3.40 mm, respectively. By increasing the amount of acetonitrile to 200 mL, while maintaining other reaction condi- tions, rod-shaped particles (CPP-8) were discriminatively gener- ated, with an average width and length of 0.62 and 4.16 mm, respectively, as characterized by SEM and OM (Fig. 2b). Interestingly, despite the variety of morphologies, all particles COMMUNICATION www.advmat.de [*] Prof. M. Oh, H. J. Lee, W. Cho, S. Jung Department of Chemistry, Yonsei University 134 Shinchon-dong, Seodaemun-gu Seoul 120-749 (Korea) E-mail: moh@yonsei.ac.kr DOI: 10.1002/adma.200802485 Figure 1. a) Organic precursor H 2 L, used for the preparation of CPP-6, -7, and -8. b) SEM (left, inset is the high-magnification SEM image), OM (right), and FM (right inset) images of the elongated hexagons CPP-6. 674 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2009, 21, 674–677