title: Geometric, electronic and magnetic structures of S = 19/2 and S = 20/2 thiophene-2-carboxylate functionalized Mn12 single molecule magnets.
abstract: The geometric and magnetic structures of two structurally related, but magnetically inequivalent, single molecule magnets (SMMs) have been computationally characterized. The first SMM, with formula [Mn12O12(O2CC4H3S)16(H2O)2](-1) (I), has a half-integer spin (S(I) = 19/2) due to ferrimagnetic ordering. The second SMM, with formula Mn12O12(O2CC4H3S)16(H2O)4 (II), has an integer spin (S(II) = 20/2) and its geometric structure has been computationally predicted. Both SMMs include thiophene-2-carboxylate functional groups for potential use in molecular electronics. To determine structural and electronic differences between both SMMs, spin polarized density functional theory was applied to I and II. Hydrogen bonding of two and four Mn-bound water molecules in I and II, respectively, to thiophene-2-carboxylate oxygen atoms and inner cubane oxygen atoms is essential for structural stabilization of both complexes. The one-electron-reduction of I is concomitant with a structural asymmetry within its cubane whereby two ions, of nominal Mn(4+)(Si = 3/2) character, are inequivalent to the other two and acquire an incipient Mn(3+)(Si = 4/2) character. The geometric asymmetry in I provides an extra, albeit small, contribution to its zero field splitting and anisotropy barrier to spin reversal. Thus, despite its lower spin state, the anisotropy barrier of I is only slightly lower than that of II.
authors.affiliation: Department of Physics and Astronomy, Purdue University, W. Lafayette, IN 47907, USA. jhrodrig@purdue.edu.
authors.forename: Jorge H
authors.initials: JH
authors.lastname: Rodriguez
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ziegler