Cyano-Bridged 4 f ± 3d Coordination Polymers with a Unique Two-Dimensional Topological Architecture and Unusual Magnetic Behavior

Cyano-Bridged 4 f ± 3d Coordination Polymers with a Unique Two-Dimensional Topological Architecture and Unusual Magnetic Behavior

** Bao-Qing Ma, Song Gao,* Gang Su, and GuangXian Xu

State Key Laboratory of Rare Earth Materials Chemistry and Applications PKU-HKU Joint Laboratory on Rare Earth Materials and Bioinorganic Chemistry Peking University, Beijing 100871 (P. R. China) Fax: (‡86) 10-6275-1708

Department of Physics, Graduate School at Beijing University of Science and Technology of China CAS, P.O. Box 3908, Beijing 100039 (P. R. China)

Received: July 26, 2000 [Z15532]

Cyano-bridged dimetallic hybrid Prussian Blue one- to three-dimensional (1D ± 3D) coordination polymers based on [M(CN)6] 3ÿ (M ˆ Fe, Cr, Mn) have attracted great attention because of their rich and interesting structures and magnetic behavior.[1] These studies were mainly focused on transition metals. In principle, it would be possible to enhance the coercive field by the introduction of paramagnetic lanthanide ions because these possess rather large and anisotropic magnetic moments. However, the magnetism, rarely investigated, for known cyano-bridged lanthanide / transition metal complexes such as ion pairs, dinuclear, trinuclear, tetranuclear, and one-dimensional chains,[2], does not seem exciting, since the couplings between the lanthanide and transition metals are very weak, because of the effective shielding of the 4f electrons by the outer-shell electrons. However, the 3D polymer [SmFe(CN)6]´4H2O, with strong anisotropic coercive field, exhibits a long-range ferrimagnetic ordering below 3.5 K, and that [TbCr(CN)6]´4H2O has the highest known Curie temperature (TC ˆ 11.7 K) for 4 f ± 3d molecule-based magnets.[3] This implies that increasing the number of dimensions may enhance and improve bulk magnetic properties. Our strategy for the rational synthesis of a high-dimensional network is to use a suitable combination of cyanide groups and other bridging ligands. Here, 2,2'-bipyrimidine (bpym) was selected, in preference to 4,4'-bipyridine and pyrazine, because it is more capable of transmitting magnetic interactions[4] and its bis(chelating) coordination modes facilitate connection between lanthanide ions. Unexpectedly, two novel coordination polymers [NdM(bpym)(H2O)4- (CN)6]´3H2O (M ˆ Fe (1), Co (2)) were obtained, which have a unique 2D topological architecture, and exhibit unusual magnetic behavior.