Magnetic and Optical Studies on an S = 6 Ground-State Cluster [Cr₁₂O₉(OH)₃(O₂CCMe₃)₁₅]:  Determination of, and the Relationship Between, Single-Ion and Cluster Spin Hamiltonian Parameters

Abstract

The dodecametallic Cr(III) cluster [Cr(12)O(9)(OH)(3)(O(2)CCMe(3))(15)] has a ground spin state of S = 6 characterized by the spin Hamiltonian parameters g(ZZ)() = 1.965, g(XX)() = g(YY)() = 1.960, D(S=)()(6) = +0.088 cm(-)(1), and E(S=)()(6) = 0 (where D and E are the axial and rhombic zero-field splitting parameters, respectively) as determined by multifrequency EPR spectroscopy and magnetization studies. Micro-SQUID magnetization studies reveal steps due to the fine structure of the ground state, with the spacing between the steps in excellent agreement with the D(S=)()(6) value determined by EPR. Analysis of high-resolution optical data (MCD) allows us to determine the single-ion g values and D value (= -1.035 cm(-)(1)) of the constituent Cr(III) ions directly. A vector coupling analysis demonstrates that the cluster ZFS is almost entirely due to the single-ion component. Thus, the relative orientations of the local and cluster magnetic axes can lead to a cluster ZFS of opposite sign to the single-ion value, even when this is the only significant contribution.

A Nonanuclear Iron(II) Single‐Molecule Magnet

“…Large S values arise from ferromagnetic or competing antiferromagnetic exchange, and there are many competing contributions to D such as single-ion ZFS, anisotropic and dipolar exchange, and relative orientations of the single ions and the cluster magnetic axes. [13] Herein we report the first member of a new class of iron(ii)-based SMMs obtained by a rational synthetic route: [Fe 9 = the dianion of 2-salicylidene-amino-1-ethanol). [14] Iron SMMs are of considerable interest, because it is known [15] that the nuclear spin of the transition metal in a polynuclear SMM affects the rate of QTM (Mn has a nuclear spin of I = 5/2, whereas 56 Fe has I = 0).…”

Encouraging Chromium(III) Ions to Form Larger Clusters: Syntheses, Structures, Magnetic Properties and Theoretical Studies of Di‐ and Octametallic Cr Clusters

“…In conclusion, the reactions between CrCl 2 and the tripodal ligands H 3 X-ray Crystallography: Data were collected with either Bruker SMART APEX CCD (1) or Oxford Diffraction Crysalis CCD diffractometers (2, 3) at 100(2) K using Mo-K α radiation (λ = 0.71073 Å). Both structures were solved by direct methods and refined (on F 2 for all reflections) using SHELXTL.…”

“…The results are shown in the Table 5. In Figure 7 is displayed a spin density map of the most stable configuration, SD 3 . A more detailed description of this study is able in the Supporting Information.…”

“…[2] An interesting aspect of this chemistry is that homometallic Cr clusters all contain bridging carboxylates, the majority have topologies that are based on either cubes or wheels, and most are characterised by S = 0 spin ground states. The exceptions to this are a Cr 12 centred-pentacapped trigonal prism with S = 6, [3] a ferromagnetic Cr 10 wheel, [2] and a tetrametallic cluster with S = 6. [4] Theoretical calculations based on density functional theory of magnetic exchange coupling constants (J) in binuclear and polynuclear transition-metal complexes have gained much attention recently because these methods have proven to give good numerical estimates of J values as well as providing insight into the electronic structure of the molecule of interest.…”

“…+ or the heating of the Cr III salt in the presence of a carboxylic acid. For example, the use of a combination of CrF 3 and pivalic acid leads to a family of clusters based on wheels, [1] as does the solvothermal heating of [Cr 3 O(O 2 CR) 6 (H 2 O) 3 ] + in alcohol. [2] An interesting aspect of this chemistry is that homometallic Cr clusters all contain bridging carboxylates, the majority have topologies that are based on either cubes or wheels, and most are characterised by S = 0 spin ground states.…”