Spin state of two mononuclear iron(II) complexes of a tridentate bis(imino) pyridine N-donor ligand: Experimental and theoretical investigations
Abstract
Investigations on the spin states of octahedral Fe(II) complexes have received special attention due to their clear discrimination in the spin states of the d-orbitals. As a means to further understand the factors that influence the spin-crossover (SCO) phenomenon in Fe(II) systems, we herein report two mononuclear Fe(II) complexes, [FeL2] (ClO4)(2).2CH(3)OH [1] and [FeL2](BF4)(2).CH3CN.CH3OH [2], derived from a novel N(3)-donor Schiff base ligand, 2,6-bis[(3-methylbenzylimino)methyl]pyridine [L] with varying counteranion and the diamagnetic [ZnL2](BF4)2 congener for a comparative investigation.
The complexes have been synthesized and characterized by electrospray-ionization mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopy, single-crystal X-ray diffraction (XRD) and magnetic susceptibility studies. Structural and magnetic investigations reveal that both [1] and [2] show Fe--N6 distorted octahedral geometry and are locked in the diamagnetic LS state throughout the entire explored temperature range from 1.8 to 400 K.
The LS state of [FeL2](2+) is also confirmed by comparing the experimentally found structural parameters, NMR chemical shifts and excitation energies in the visible region with density functional theory (DFT) calculations.