Two-dimensional square-grid iron() coordination polymers showing anion-dependent spin crossover behavior

• Published in: RSC advances 2020-01, Vol.1 (9), p.54-549
• Main Authors: Shin, Jong Won, Jeong, Ah Rim, Jeong, Jong Hwa, Zenno, Hikaru, Hayami, Shinya, Min, Kil Sik
• Format: Article
• Language: English
• Subjects: Chemistry; Coordination polymers; Crossovers; Crystallography; Electron spin; Iron sulfates; Ligands; Magnetic moments; Structural analysis
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c9ra09782a

Two Fe( ii )-based coordination polymers [Fe(tpmd) 2 (NCS) 2 ]·5.5H 2 O ( 1 ) and [Fe(tpmd) 2 (NCSe) 2 ]·7H 2 O ( 2 ) with the framework of square-grid type have been assembled from FeSO 4 ·7H 2 O, 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.