Synthesis, Crystal Structure, and High-Precision High-Frequency and -Field Electron Paramagnetic Resonance Investigation of a Manganese(III) Complex:  [Mn(dbm)₂(py)₂](ClO₄)

Abstract

The complex [Mn(dbm)(2)(py)(2)](ClO(4)) (dbm = anion of 1,3-diphenyl-1,3-propanedione (dibenzoylmethane), py = pyridine) was synthesized and characterized by X-ray crystallography. It has tetragonally distorted geometry with the axial positions occupied by the py ligands and the equatorial positions by the dbm ligands. This mononuclear complex of high-spin Mn(III) (3d(4), S = 2) was studied by high-frequency and -field electron paramagnetic resonance (HFEPR) both as a solid powder and in frozen dichloromethane solution. Very high quality HFEPR spectra were recorded over a wide range of frequencies. The complete dataset of resonant magnetic fields versus transition energies was analyzed using automated fitting software. This analysis yielded the following spin Hamiltonian parameters (energies in cm(-1)): D = -4.504(2), E = -0.425(1), B(4)(0) = -1.8(4) x 10(-4), B(4)(2) = 7(3) x 10(-4), B(4)(4) = 48(4) x 10(-4), g(x) = 1.993(1), g(y) = 1.994(1), and g(z) = 1.983(1), where the B(4)(n) values represent fourth-order zero-field splitting terms that are generally very difficult to extract, even from single-crystal measurements. The results here demonstrate the applicability of HFEPR at high-precision measurements, even for powder samples. The zero-field splitting parameters determined here for [Mn(dbm)(2)(py)(2)](+) are placed into the context of those determined for other mononuclear complexes of Mn(III).

Slow Magnetic Relaxation in Mononuclear Octahedral Manganese(III) Complexes with Dibenzoylmethanide Ligands

“…Hydrogen atoms on organic ligands were set in calculated positions and generated by the riding model. The structures of complexes 1 [17,33] and 3 [18] were previously reported, but we recollected the data on our own samples to confirm their structures. CCDC-1017697 (for 2), -1018575 (for 3), and 1018576 (for 1) contain the supplementary crystallographic data for this paper.…”

“…[29] [Mn(dbm , 2; L = py, 3) were prepared according to a modified method of Aromi et al, which was originally used to prepare 3. [18] Elemental analyses were performed with an Elementar Vario ELIII elemental analyzer. The powder XRD patterns were measured at room temperature with a Bruker D8 Advance X-ray diffractometer.…”

“…It is clear that good agreement was achieved between the experimental and the simulated data for χ M T vs. T ( Figure 2) and M vs. H curves at various temperatures ( Figure 3). It should be noted that 1 and 3 have been studied by Gatteschi et al [17] and Aromi et al [18] by using high-frequency and -field (HF) EPR spectroscopy, respectively. Evidently, the D and E values obtained here are consistent with the values determined by HFEPR (D = -4.35 cm -1 , E = 0.28 cm -1 for 1; D = -4.5 cm -1 , E = -0.4 cm -1 for 3).…”

Redox Chemistry of a Dimanganese(II,III) Complex with an Unsymmetric Ligand: Water Binding, Deprotonation and Accumulative Light‐Induced Oxidation

“…By inclusion of the last term in Equation (1), the following parameters were obtained: J = 10.9 Ϯ 0.3 cm -1 and D 3 = 3.35 cm -1 (Model 2 in Table 2). The relatively large and positive zero-field parameter D 3 reflects to some degree the coordination geometry of the [32] …”

“…[32] The solution was transferred to EPR tubes and the samples were immediately frozen in an ethanol/dry ice bath (T = 198 K) and then frozen at 77 K. All sample mixing and handling took place under dim red light and inert atmosphere, and care was taken to minimise the interval between mixing and freezing of the samples (mix-freeze time Ͻ 1 min). Laser flashes from a frequency doubled Spectra Physics DCR 3G Nd:YAG laser at 5 Hz and 532 nm (6 ns pulse width, about 250 mJ flash -1 ) were given at room temperature to the prethawed EPR samples.…”