Two-dimensional square-grid iron(ii) coordination polymers showing anion-dependent spin crossover behavior |
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| Authors: | Jong Won Shin Ah Rim Jeong Jong Hwa Jeong Hikaru Zenno Shinya Hayami Kil Sik Min |
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| Institution: | Department of Chemistry, Kyungpook National University, Daegu 41566 Republic of Korea.; Department of Chemistry, Kumamoto University, Kumamoto 860-8555 Japan ; Department of Chemistry Education, Kyungpook National University, Daegu 41566 Republic of Korea, |
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| Abstract: | Two Fe(ii)-based coordination polymers Fe(tpmd)2(NCS)2]·5.5H2O (1) and Fe(tpmd)2(NCSe)2]·7H2O (2) with the framework of square-grid type have been assembled from FeSO4·7H2O, N,N,N′,N′-tetrakis(pyridin-4-yl)methanediamine (tpmd), and KNCS/KNCSe in methanol and characterized. By utilizing two pyridine groups of a tpmd ligand, 1 and 2 are formed in two-dimensional layered structures through coordination of octahedral iron(ii) ions with the tpmd to NCS−/NCSe− ligands in which they have a supramolecular isomorphous conformation. 1 shows a paramagnetic behavior between 2 and 300 K, while 2 exhibits two-step spin crossover (ca. 145 and 50 K) in the temperature range due to the coordination of NCSe− ligands. At 300 K 2 is fully high-spin state. However, at 100 K 2 becomes ca. 50% high spin and 50% low spin iron(ii) ions, which is verified by magnetic moments. In the structural analysis of 2 at 100 K, two different layers are observed with different bond distances around iron(ii) ions in which the layers are stacked alternately.Two-dimensional Fe-based coordination polymers with square-grid shapes were prepared by self-assembly and exhibited an interesting spin crossover behavior depending on the coordinated counter ions. |
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