High?spin square planar iron(II) alkali metal siloxide complexes – influence of the alkali metal and reactivity towards O 2 and NO

Complexes [L2Fe][Li(DME)]2, 1(DME), {[L2Fe][Na2(DME)3]}?, 2(DME) and [L2Fe][K(DME)2]2, 3(DME) were synthesized by deprotonation of LH2 (LH2=O(SiPh2OH)2) with the respective alkali metal tert-butoxides followed recrystallization from DME. It turned out that upon crossing over Li+ via Na+ to K+ counterions structures high-spin iron(II) complexes are increasingly distorted a square planar towards tetrahedral structure so represents borderline case, as indicated ?-values. The distortions also reflected in Mössbauer spectra through quadrupole splittings. compounds behave inert contact O atom transfer reagents but react rapidly dioxygen. reaction rates too high be determined even stopped-flow measurements quantitatively, qualitatively it emerged increase Li Na K. Using NO an O2 surrogate adduct S = 3/2 ground state was isolated where is coordinated end-on binding mode, formally NO? ligand, significantly weakened bond.