The cis- and trans-effects in carbonyl complexes of bis(dimethylglyoximato) iron(II)

Abstract

Mössbauer spectra of the complexes [Fe(Hdmg)₂L₂] and [Fe(Hdmg)₂L(CO)](H₂dmg = dimethylglyoxime, L = pyridine or 1-methylimidazole) have been measured between 4.2 and 295 K, and in applied magnetic fields at 4.2 K. Changes in isomer shifts and quadrupole splittings on carbonylation are similar to those observed in haemochromes. In all four complexes studied the principal component V_zz of the electric field gradient is positive, and the asymmetry parameter η > 0.5. Replacement of an axial amine by CO is shown to result in perturbations of the iron–nitrogen bonding both cis and trans to the site of substitution.