Iron(III)–Oxo Cluster Chemistry with Dimethylarsinate Ligands: Structures, Magnetic Properties, and Computational Studies

Abstract

A program has been initiated to develop FeIII/oxo cluster chemistry with the “pseudocarboxylate” ligand dimethylarsinate (Me2AsO2 –) for comparison with the well investigated FeIII/oxo/carboxylate cluster area. The synthesis and characterization of three polynuclear FeIII ­complexes are reported, [Fe12­O4(O2CtBu)8­(O2As­Me2)17(H2O)3]­Cl3 (1), Na2[Fe12­Na2O4­(O2AsMe2)20­(NO3)6­(Me2As­O2H)2­(H2O)4]­(NO3)6 (2), and [Fe3­(O2As­Me2)6­(Me2As­O2H)2­(hqn)2]­(NO3) (3), where hqnH is 8-hydroxyquinoline. The Fe12 core of 1 is a type never previously encountered in FeIII carboxylate chemistry, consisting of two Fe6 units each of which comprises two {Fe3(μ3-O2–)} units bridged by three Me2AsO2 – groups and linked into an Fe12 loop structure by two anti–anti η1:η1:μ Me2AsO2 – groups, a bridging mode extremely rare with carboxylates. 2 also consists of two Fe6 units, differing in their ligation from those in 1, and this time linked together into a linear structure by a central {Na2(NO3)2} bridging unit. 3 is a linear Fe3 complex with no monatomic bridges between FeIII ions, a very rare situation in FeIII chemistry with any ligands and unprecedented in Fe carboxylate chemistry. The distinct differences observed in arsinate vs carboxylate ligation modes are rationalized largely based on the greater basicity of the former vs the latter. Variable-temperature dc and ac magnetic susceptibility data reveal all Fe2 pairwise interactions to be antiferromagnetic. For 1 and 2, the different J ij couplings were estimated by use of a magnetostructural correlation for high nuclearity FeIII–oxo clusters and by density functional theory calculations using broken symmetry methods, allowing identification of their relative spin vector alignments and thus rationalization of their S = 0 ground states. The J ij values were then used as input values to give excellent fits of the experimental χM T vs T data. For 3, the fits of the experimental χM T vs T data to the Van Vleck equation or with PHI gave a very weak J 12 = −0.8(1) cm–1 (H = −2JŜ i ·Ŝ j convention) between adjacent FeIII ions and an S = 5/2 ground state. These initial FeIII arsinate complexes also provide structural parameters that help validate literature assignments of arsinate binding modes to iron oxide/hydroxide minerals as part of environmental concerns of using arsenic-containing herbicides in agriculture.

Validation of the Green’s Function Approximation for the Calculation of Magnetic Exchange Couplings

“…The polynuclear set consists of five homonuclear Fe III , Ni II , and Cr III complexes (Figure ). Two of the Fe complexes are taken from a recent study by Lee et al: a (+1 charge) Fe 3 (CCDC refcode: MALSOL) and a (+3 charge) Fe 6 complex (CCDC refcode: MALSEB). Note that the full structure contains two of these Fe 6 subunits.…”

“…This method is popular in the quantum chemistry community and has several flavors, depending on the assumptions made for this mapping. ,− For the simple case of two centers, where the high-spin (HS) and broken-symmetry (BS) solutions can be easily determined by density functional theory (DFT) methods in most cases, one can derive the well-known spin-projected BS expression where E BS and E HS are the energies for the BS and HS solutions, respectively, and S A and S B are the nominal total spin quantum numbers for each center . This expression can be straightforwardly generalized to the multi-center case. , We refer the reader to the pioneering work of Noodleman and the widely available literature regarding methods based on energy differences to extract magnetic exchange couplings from DFT calculations. ,, Another approach has been proposed that deserves to be highlighted. Using the spin-flip time-dependent DFT, Mayhall et al derived a method for mapping single spin-flip energies into the spectrum of an effective Hamiltonian that can be used to extract the exchange couplings. , …”

“…27 This expression can be straightforwardly generalized to the multi-center case. 31,32 We refer the reader to the pioneering work of Noodleman 27 and the widely available literature regarding methods based on energy differences to extract magnetic exchange couplings from DFT calculations. 17,18,30 Another approach has been proposed that deserves to be highlighted.…”

Dimerization of [FeIII(bpy)3]3+ in Aqueous Solutions: Elucidating a Mechanism Based on Historical Proposals, Electrochemical Data, and Computational Free Energy Analysis

“…At 1.0 V versus SHE, the [Fe(bpy) 3 ] 3+/2+ redox couple, with all earth-abundant elements, has one of the highest accessible reduction potentials for near-neutral pH aqueous electrochemical energy storage. 30 species undergoes hydrolysis and ultimately dimerizes into a binuclear oxo-bridged complex, a moiety common to Fe III species, 31,32 according to 33, (2)…”

A new hexanuclear Fe(iii) nanocluster: synthesis, structure, magnetic properties, and efficient activity as a precatalyst in water oxidation

“…[1][2][3][4] The Lewis acidity and high charge of a metal ion such as Fe III provide good support to produce oxo bridges from water that induce strong Fe III exchange interactions. 5,6 In addition, the high-spin Fe III (S = 5/2) ions, which are antiferromagnetically coupled, can produce spin frustration effects from competing for exchange interactions, and may yield single-molecule magnets (SMMs). 7,8 SMMs are those molecules that show a superparamagnetic behavior in the absence of an external magnetic field.…”