Synthesis and X-ray Structure of the Mn^IICl₂ and Mn^IIIF₂ Complexes of <i>N,N</i><i>‘</i>-Dimethyl-2,11-diaza[3,3](2,6)pyridinophane. High-Field Electron Paramagnetic Resonance and Density Funtional Theory Studies of the Mn(III) Complex. Evidence for a Low-Lying Spin Triplet State

Abstract

Two manganese complexes, (py2(NMe)2)MnIICl2 (1) and [(py2(NMe)2)MnIIIF2]+ (2), are here described with the macrocyclic ligand py2(NMe)2 (py2(NMe)2 = N,N'-dimethyl-2,11-diaza[3,3](2,6)pyridinophane). For both, the crystal structure is reported. The UV-visible spectrum of 2 exhibits a very broad near-infrared (NIR) band corresponding to the transition between the two e(g)-type orbitals split by the Jahn-Teller effect. A negative D value of ca. -4 cm(-1) was estimated by high-field and high-frequency electron paramagnetic resonance (HF-EPR) spectroscopy, which was consistent with symmetry considerations. Density functional theory (DFT) calculations on 2 support the 5B1 electronic ground state predicted from the X-ray structure. Moreover, to explain the large value of the D parameter, a spin triplet first excited spin state was postulated to occur at low energy. This was confirmed by the DFT calculations.