Synthesis and characterization of metal complexes of methylene bridged hexadentate tetraanionic ligands

Abstract

The flexibly-bridged tetraanionic hexadentate ligands (LH₄), methylenbis(salicylaldehyde-<i>o</i>-hydroxybenzylamine) [CH₂(H₂sal-OHYBA)₂] and methylenebis(salicylaldehyde <i>–o-</i>aminobenzylalcohol) [CH₂(H₂sal-OABA)₂] react with acetates of copper(II), nickel(II), cobalt(II), dioxouranium(VI) to give the corresponding metal complexes of formula [Cu₂L], [Ni₂L.4H₂O), [Co₂L.4H₂O] and [(UO₂)₂L.2CH₃OH], respectively. Reaction of these ligands with [MO₂(acac)₂](M=Mo, W) in refluxing methanol affords [(MO₂)₂L.nCH₃OH] (n=0 or 2). Thermogravimetric analyses confirm the coordination of H₂O/CH₃OH in complexes.¹H NMR spectral data of molybdenum, tungsten and uranium complexes suggest coordination of the ligands through deprotonated phenolic/enolic oxygen and azomethine nitrogen atoms. Electronic spectral data suggest square planar structure for copper complexes while an octahedral structure for other complexes.