title: What Controls the Sign and Magnitude of Magnetic Anisotropy in Tetrahedral Cobalt(II) Single-Ion Magnets?
abstract: A family of mononuclear tetrahedral cobalt(II) thiourea complexes, [Co(L1)4](NO3)2(1) and [Co(Lx)4](ClO4)2where x = 2 (2), 3 (3), 4 (4) (where L1= thiourea, L2= 1,3-dibutylthiourea, L3= 1,3-phenylethylthiourea, and L4= 1,1,3,3-tetramethylthiourea), has been synthesized using a rationally designed synthetic approach, with the aim of stabilizing an Ising-type magnetic anisotropy (-D). On the basis of direct-current, alternating-current, and hysteresis magnetic measurements and theoretical calculations, we have identified the factors that govern the sign and magnitude of D and ultimately the ability to design a single-ion magnet for a tetrahedral cobalt(II) ion. To better understand the magnetization relaxation dynamics, particularly for complexes 1 and 2, dilution experiments were performed using their diamagnetic analogues, which are characterized by single-crystal X-ray diffraction with the general molecular formulas of [Zn(L1)4](NO3)2(5) and [Zn(L2)4](ClO4)2(6). Interestingly, intermolecular interactions are shown to play a role in quenching the quantum tunneling of magnetization in zero field, as evidenced in the hysteresis loop of 1. Complex 2 exhibits the largest Ueffvalue of 62 cm-1and reveals open hysteresis loops below 4 K. Furthermore, the influence of the hyperfine interaction on the magnetization relaxation dynamics is witnessed in the hysteresis loops, allowing us to determine the electron/nuclear spin S(Co) =3/2/I(Co) =7/2hyperfine coupling constant of 550 MHz, a method ideally suited to determine the hyperfine coupling constant of highly anisotropic metal ions stabilized with large D value, which are otherwise hard to determine by conventional methods such as electron paramagnetic resonance.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, Maharashtra India.
authors.forename: Shefali
authors.initials: S
authors.lastname: Vaidya
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, Maharashtra India.
authors.forename: Subrata
authors.initials: S
authors.lastname: Tewary
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, Maharashtra India.
authors.forename: Saurabh Kumar
authors.initials: SK
authors.lastname: Singh
authors.affiliation: School of Science and the Environment, Chemistry Division, Manchester Metropolitan University , Manchester M15 6HB, U.K.
authors.forename: Stuart K
authors.initials: SK
authors.lastname: Langley
authors.affiliation: School of Chemistry, Monash University , Clayton 3800, Victoria, Australia.
authors.forename: Keith S
authors.initials: KS
authors.lastname: Murray
authors.affiliation: Institut Néel, CNRS and Université Grenoble Alpes , BP 166, 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France.
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Lan
authors.affiliation: Institut Néel, CNRS and Université Grenoble Alpes , BP 166, 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wernsdorfer
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, Maharashtra India.
authors.forename: Gopalan
authors.initials: G
authors.lastname: Rajaraman
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, Maharashtra India.
authors.forename: Maheswaran
authors.initials: M
authors.lastname: Shanmugam