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Magnetic couplings in spin frustrated Fe disklike clusters Jordan Joshua Phillips, Juan E. Peralta, and George Christou J. Chem. Theory Comput., Just Accepted Manuscript • Publication Date (Web): 12 Nov 2013 Downloaded from http://pubs.acs.org on November 14, 2013
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Journal of Chemical Theory and Computation
Magnetic couplings in spin frustrated FeIII 7 disklike clusters Jordan J. Phillips,† Juan E. Peralta,∗,‡,† and George Christou¶ Science of Advanced Materials, Central Michigan University, Mt. Pleasant, Michigan 48859, USA, Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48859, USA, and Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA E-mail:
[email protected] Abstract Using a methodology based on noncollinear coupled-perturbed density functional theory [J. Chem. Phys. 2013, 138, 174115] we calculate the magnetic exchange coupling parameters in a recently synthesized set of FeIII 7 disklike clusters [Inorg. Chem. 2011, 50, 3849-3851] to explain the unusually high ground-state spin found in the experiments. We show that the calculated exchange interactions for the new series of FeIII 7 disks present strikingly different trends compared to prior FeIII 7 disks. These differences are attributed to variations in the bridging ligands and the consequent structural changes in the complexes. The impact of these differences on the experimental groundstate spin of these complexes is rationalized using a simple classical spin model system and the calculated magnetic exchange couplings. ∗
To whom correspondence should be addressed Science of Advanced Materials, Central Michigan University ‡ Department of Physics, Central Michigan University ¶ Department of Chemistry, University of Florida †
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Introduction
Transition metal complexes featuring a large number of unpaired metal d electrons are of growing interest for applications such as spintronics 1 and magnetic memory storage. 2 One area of interest is the design of novel molecular magnets featuring high ground-state spins Stot by tuning the different magnetic interactions through motivated structural perturbations. Disklike clusters such as Mn7 3,4 and Fe7 5–7 have attracted attention since they can feature a rich variety of spin ground-states depending on the particular competition between different J interactions and spin-frustration effects. 8 Recently, a set of FeIII 7 disklike clusters with a six-pointed star topology were prepared by one of us (GC), 9 given by [Fe7 O3 (OMe)3− (heen)3 Cl4.5 (MeOH)(H2 O)1.5 ]Cl1.25 [FeCl4 ]1/4 (shown in Scheme 1 as complex 2), and [Fe7 O3 (OH)3 Cl(paeo)6 ](Cl)(ClO4 )4 (shown in Scheme 1 as complex 3), that feature an unusually large experimentally observed ground-state spin of Stot = 15/2 and 21/2 respectively. Except a recently reported Stot = 21/2 disk prepared by Kizas et al., 10 typically 5–7 FeIII 7 disks with antiferromagnetic interactions yield low-spin ground-states of Stot = 5/2.
To gain insight into the origin of this unusually large spin, in this work we determine the magnetic interactions that take place in complexes 2 and 3 using Kohn-Sham density functional theory (KS-DFT) 11 calculations. For comparison we also consider a prior studied 6 FeIII 7 disklike cluster (Fe7 O3 (O2 CR9 (mda)3 (H2 O)3 ; shown in Scheme 1 as complex 1) with
ground-state spin of Stot = 5/2. For clarity, the Heisenberg-Dirac 12,13 spin Hamiltonian convention we will be employing is given by
ˆ HD = − H
X
ˆi · S ˆj . Jij S
(1)
i
