Abstract

The synthesis and characterization of Iron(II) complexes [FeCl2(η2-P,N-PPh2Py)2] (1) and [FeCl2(η2-P,P-DPEphos)2] (2), with
PPh2Py and DPEphos ligands, were performed using elemental analysis, ESI-mass, Fourier transform infrared spectra (FTIR),
ultraviolet-visible, 1H and 31P{1H} nuclear magnetic resonance spectroscopy. FTIR measurements predicted cis-isomer to be
the most stable form of complex 1 and trans-isomer to be the most stable form of complex 2. Quantum chemical calculations
using first-principles density functional theory were performed on the two complexes at the B3LYP/LANL2DZ/6-31+G(d,p)
level of theory. Theoretical calculations predicted that the ground state of the complexes would be a quintet spin state. However,
in complex 1, the quintet spin state led to a significant elongation in Fe–P bond length to ~3.55 Å. Thus, a singlet (S = 1/2)
spin state was considered for complex 1 which showed reasonable agreement with calculated geometric parameters. Trans-
configuration of complex 2 was shown to have a higher highest occupied molecular orbital-lowest unoccupied molecular orbital
energy gap (higher stability) than complex 1 which was attributed to the nature of the ligand coordinated to Fe(II) ion.