Synthesis, X-ray structure, polarized optical spectra and DFT theoretical calculations of two new organic-inorganic hybrid fluoromanganates(III): (bpaH2)[MnF4(H2O)2]2 and (bpeH2)[MnF4(H2O)2]2

Abstract

Two new fluoromanganates(III) of 1,2-bis(4-pyridyl)ethane (bpa) and trans-1,2-bis(4-pyridyl)ethylene (bpe), LH2[MnF4(H2O)2]2 (L = bpa or bpe), have been prepared and their structure have been solved by single-crystal X-ray diffraction. The [MnF4(H2O)2]− anion displays an octahedral geometry with a strong Jahn–Teller tetragonal distortion along the H2O–Mn–OH2 axis. The equatorial metal–ligand distances (Mn–F 1.827(1)–1.859(2) Å) are shorter than the axial ones (Mn–O 2.203(2)–2.234(2) Å). Three polarized absorption bands at 22500, 18300 and 14500 cm−1 are observed in the optical spectra of (bpaH2)[MnF4(H2O)2]2. Finally, we present theoretical calculations on the equilibrium bond distances as well as the crystal-field electron structure using density functional methods. The calculated Mn–F bond distances (1.85 Å) are in agreement with the experimental data but the obtained Mn–O distances (2.53–2.56 Å) are higher than the experimental one as ussually found in similar Jahn–Teller distorted systems. The calculated d–d transition energies are compared with experimental energies derived from the optical spectra. The variation of the HOMO energy and transition energies against the Mn–O distance is also shown.