Enhancing the Magnetic Anisotropy of Linear Cr(II) Chain Compounds Using Heavy Metal Substitutions

• Published in: Inorganic chemistry 2016-07, Vol.55 (13), p.6376-6383
• Main Authors: Christian, Jonathan H, Brogden, David W, Bindra, Jasleen K, Kinyon, Jared S, van Tol, Johan, Wang, Jingfang, Berry, John F, Dalal, Naresh S
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.5b02545

Magnetic properties of the series of three linear, trimetallic chain compounds Cr2Cr­(dpa)4Cl2, 1, Mo2Cr­(dpa)4Cl2, 2, and W2Cr­(dpa)4Cl2, 3 (dpa = 2,2′-dipyridylamido), have been studied using variable-temperature dc and ac magnetometry and high-frequency EPR spectroscopy. All three compounds possess an S = 2 electronic ground state arising from the terminal Cr2+ ion, which exhibits slow magnetic relaxation under an applied magnetic field, as evidenced by ac magnetic susceptibility and magnetization measurements. The slow relaxation stems from the existence of an easy-axis magnetic anisotropy, which is bolstered by the axial symmetry of the compounds and has been quantified through rigorous high-frequency EPR measurements. The magnitude of D in these compounds increases when heavier ions are substituted into the trimetallic chain; thus D = −1.640, −2.187, and −3.617 cm–1 for Cr2Cr­(dpa)4Cl2, Mo2Cr­(dpa)4Cl2, and W2Cr­(dpa)4Cl2, respectively. Additionally, the D value measured for W2Cr­(dpa)4Cl2 is the largest yet reported for a high-spin Cr2+ system. While earlier studies have demonstrated that ligands containing heavy atoms can enhance magnetic anisotropy, this is the first report of this phenomenon using heavy metal atoms as “ligands”.