Determination of the Distributions of the Spin-Hamiltonian Parameters in Spin Triangles: A Combined Magnetic Susceptometry and Electron Paramagnetic Resonance Spectroscopic Study of the Highly Symmetric [Cr3O(PhCOO)6(py)3](ClO4)·0.5py

Abstract

Magnetic susceptibility and X-band electron paramagnetic resonance (EPR) studies have been carried out on the highly symmetric [Cr₃O(PhCOO)₆(py)₃](ClO₄)·0.5py (1; py = pyridine), whose cation exhibits a D_{3 h} crystallographically imposed molecular symmetry. While magnetic susceptibility data can be interpreted with an equilateral magnetic model described by the effective multispin Hamiltonian Ĥ = -2 J(Ŝ₁·Ŝ₂ + Ŝ₂·Ŝ₃ + Ŝ₃·Ŝ₁), EPR data require an isosceles model described by the multispin Hamiltonian Ĥ = -2 J( Ŝ₁· Ŝ₂ + Ŝ₂· Ŝ₃) - 2 J' Ŝ₃· Ŝ₁, where Δ J = J - J' ≠ 0. Moreover, EPR data reveal the interplay of antisymmetric exchange (or Dzyaloshinskii-Moriya) interactions, described by a 2G(Ŝ₁ × Ŝ₂ + Ŝ₂ × Ŝ₃ + Ŝ₃ × Ŝ₁) term, which induce significant anisotropy to the S_T = ¹/₂ ground state of 1, as well as an important broadening of the g_⊥ resonance ( g strain). Through careful analysis of these data and in conjunction with neutron scattering data, this g strain can be deconvoluted into distributions of the individual spin-Hamiltonian parameters Δ J and |G|. This method of analysis provides simultaneous estimates of the central values and distribution profiles of the spin-Hamiltonian parameters, which are shown not to be described by monodisperse values.