Electronic Structure of the Tris(ethylenediamine)manganese(II) Ion. Circular and Linear Dichroism and Electron Paramagnetic Resonance Spectra of Mn(en)3(NO3)
The electronic structure of the tris(ethylenediamine)manganese(II) ion has been investigated by measurement of the orthoaxial linear dichroism (LD), axial absorption, axial circular dichroism (CD), and electron paramagnetic resonance (EPR) spectra of manganese-doped Zn(en)3(NO3)2 single crystals. Cotton effects associated with the spin-forbidden ligand field transitions to states derived from 4T2g(G) ((4Eg, A1g)(G)) and 4T2g(D) are observed in the CD spectra at 1.98, 2.36, and 2.65 μm-1, respectively, all with the same sign of ΔЄ in a given crystal. These transitions, as well as the lower quartet level 4Tlg(G) (1.50 μm-1), not observed in the CD spectra, are also observed in the LD and axial absorption spectra. The sharp band assigned to the (4Eg, 4A2,)(G) transitions reveals four distinct components at 2, 357 ± 0.005, 2.370 ± 0.001, 2,385 ± 0.0005, and 2.395 ± 0.001 μm-1 in the absorption spectra. Only the first two of these are prominent in the CD spectra and they are assigned to the origins of the 4Eg(G) and 4Alg(G) transitions, respectively. The ligand field parameters deduced are Dq = 0.108, B = 0.0860, and C = 0.301 μm-1. The EPR data yield g1, = 2.004 ± 0.005 and g- = 2.021 ± 0.005 and A = 77 ± 1, D = +197 ± 10, and (a - F) = (+15 ± 10) × 10-4 cm-1. The magnitude and sign of D correlate with the magnitude of the trigonal splitting deduced from the electronic spectrum and the trigonally compressed geometry revealed in the crystal structure of the nickel analogue. © 1978, American Chemical Society. All rights reserved.
Palmer, RA; Yang, MCL; Hempel, JC
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