Synthesis, properties and Mössbauer spectra of bisaxially co-ordinated iron(II) phthalocyanine low-spin complexes: the first semi-quantitative explanation of the influence of the character of axial ligands on the spectral parameters †

Abstract

A series of bisaxially co-ordinated low-spin iron(II) phthalocyanine complexes (pc)FeL2 with different types of nitrogen bases as axial ligands has been prepared and characterised by electronic, 1H NMR and Mossbauer spectroscopies. The influence of electronic and steric effects of the axial ligands on Mossbauer quadrupole splitting (ΔEQ) and isomer shift (δ), NMR parameters, and metal-to-ligand charge transfer (MLCT) band position are discussed. Mossbauer partial quadrupole splitting (p.q.s.) and partial isomer shift (p.i.s.) parameters for different ligands have been estimated and rationalised with the overall data for (pc)FeL2 and (nx)2FeL2 (nx = nioxime) complexes. A semi-empirical AM1 method and the cone angle concept were used to factorise σ- and π-electronic and steric effects of the ligands. A good correlation between the predicted and experimental MLCT band position of (pc)FeL1L2 complexes, as well as predicted and experimental p.i.s. and p.q.s. values for different ligands, has been observed.