Hydrothermal Crystal Growth, Structures and Thermal Properties of Co(II)-4,4¢-bipyridine-Based Coordination Polymeric Materials Sanchai Luachan, 1 Chaveng Pakawatchai, 2 and Apinpus Rujiwatra 3,4 Submitted November 9, 2006; Accepted February 24, 2007 Hydrothermal synthetic parameters were studied and optimized for the preparation of new coordination polymeric materials based on Co(II) and 4,4¢-bipy. A new polymeric compound, [Co 2 (H 2 O) 2 (OH) 2 (4,4¢-bipy) 8 ](NO 3 ) 2 Æ2(4,4¢-bipy) 10(H 2 O) (1), was prepared and structurally characterized by single crystal experiment. The framework of (1) is made up of two different one-dimensional substructures, i.e., the neutral chain A and positively charged chain B, both of which share the same nodes and node linkers. This is rarely found, especially from a one-pot crystal growth technique. Two other crystals were also identified, i.e., [Co(SO 4 )(H 2 O) 3 (4,4¢- bipy)]Æ2(H 2 O), and K 2 Co(H 2 O) 6 (SO 4 ) 2 . The optimization of synthetic parameters apparently favors the formation of different polymeric structures, and this can be experimentally fine tuned. The influences of these parameters on phase formation, purity and crystal growth are discussed. The complicated thermogravimetric property of the new compound is also reported. KEY WORDS: hydrothermal crystal growth; crystal structure; thermal behavior; coordination polymer; cobalt; 4,4¢-bipyridine 1. INTRODUCTION Among various materials playing an important role in modern materials research, inorganic–organic hybrid frameworks or so-called coordination poly- meric materials have attracted worldwide attention [1–3]. The prime motivations are due to their inherent potential for various applications, e.g., in catalysis, separation, gas storage, sensing, ion exchange, and magnetism, with superiority over other corresponding conventional materials [4–8]. The strategies adopted in the preparation of these polymeric materials have mostly been based on conventional solution techniques using organic solvents. In 1997, Laudise introduced the hydrothermal synthesis technique [9]. This technique has proved to be an effective approach in the prepa- ration and crystal growth of many important solids, e.g., microporous crystals, complex oxide ceramics and magnetic materials [10, 11]. The fast kinetics of nucleation and crystal growth under hydrothermal conditions, however, generally lead to crystals of poor quality, which then hinders the achievement of struc- tural information, particularly of new materials, due to the fact that the detailed structure of these generally insoluble polymeric materials can only be determined by single crystal X-ray diffraction. The disadvantages hence hamper the success in using hydrothermal synthesis in preparing new coordination polymeric materials with a full understanding of their structures [12]. Thermodynamic and kinetic parameters under 1 Department of Physics, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand. 2 Department of Chemistry, Faculty of Science, Prince of Songkla University, Songkhla, 90110, Thailand. 3 Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand. 4 To whom correspondence should be addressed. E-mail: apinpus@gmail.com Journal of Inorganic and Organometallic Polymers and Materials, Vol. 17, No. 3, September 2007 (Ó 2007) DOI: 10.1007/s10904-007-9145-0 561 1574-1443/07/0900-0561/0 Ó 2007 Springer Science+Business Media, LLC