title: Quantum tunneling of magnetization in a new [Mn18]2+ single-molecule magnet with s = 13.
abstract: The reaction between 2-(hydroxyethyl)pyridine (hepH) and a 2:1 molar mixture of [Mn3O(O2CMe)6(py)3](ClO4) and [Mn3O(O2CMe)6(py)3](py) in MeCN leads to isolation of [Mn18O14(O2CMe)18(hep)4(hepH)2(H2O)2](ClO4)2 (1) in 10% yield. The complex is 2MnII,16MnIII and consists of a Mn4O6 central unit to either side of which is attached a Mn7O9 unit. Magnetization data collected in the 2.0-4.0 K and 20-50 kG ranges were fit to yield S = 13, g = 1.86, and D = -0.13 cm-1 = -0.19 K, where D is the axial zero-field splitting parameter. AC susceptibility studies in the 0.04-4.0 K range at frequencies up to 996 Hz display out-of-phase (chiM' ') signals, indicative of a single-molecule magnet (SMM). Magnetization vs applied DC field scans exhibit hysteresis at <1.0 K, confirming 1 to be a SMM. DC magnetization decay data were collected on both a microcrystalline sample and a single crystal, and the combined data were used to construct an Arrhenius plot. Between 3.50 and 0.50 K, the relaxation rate is temperature-dependent with an effective barrier to relaxation (Ueff) of 14.8 cm-1 = 21.3 K. Below ca. 0.25 K, the relaxation rate is temperature-independent at 1.3 x 10-8 s-1, indicative of quantum tunneling of magnetization (QTM) between the lowest energy Ms = +/-13 levels of the S = 13 state. Complex 1 is both the largest spin and highest nuclearity SMM to exhibit QTM.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, USA.
authors.forename: Euan K
authors.initials: EK
authors.lastname: Brechin
authors.forename: Colette
authors.initials: C
authors.lastname: Boskovic
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wernsdorfer
authors.forename: Jae
authors.initials: J
authors.lastname: Yoo
authors.forename: Akira
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: E Carolina
authors.initials: EC
authors.lastname: Sañudo
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Concolino
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Ishimoto
authors.forename: David N
authors.initials: DN
authors.lastname: Hendrickson
authors.forename: George
authors.initials: G
authors.lastname: Christou