Investigation of vanadium(iii) and vanadium(iv) compounds supported by the linear diaminebis(phenolate) ligands: correlation between structures and magnetic properties

Abstract

A family of oxidovanadium(IV) compounds containing linear diaminebis(phenolate (salans) L^1–5 ligands (L¹ = [MeNCH₂CH₂NMe(CH₂-4-CMe₂CH₂CMe₃-C₆H₃O)₂]²⁻; L² = [MeNCH₂CH₂NMe(CH₂-4-CH₃-C₆H₃O)₂]²⁻; L³ = [MeNCH₂CH₂NMe(CH₂-4-Cl-C₆H₃O)₂]²⁻; L⁴ = {MeNCH₂CH₂NMe[CH₂-4,6-(CH₃)₂-C₆H₂O]₂}²⁻; and L⁵ = {MeNCH₂CH₂NMe[CH₂-4,6-(Br)₂-C₆H₂O]₂}²⁻) and non-oxidovanadium(III) with L^2,4 and acac ligands has been prepared and characterized by chemical and physical techniques. Reactions of [VO(acac)₂] with ligand precursors H₂L^2,4 in toluene or hexane afforded vanadium(III) compounds [V(L-κ⁴ONNO)(acac)] (1, L²; 2, L⁴), while the use of acetonitrile or ethanol led to the formation of dimeric oxidovanadium(IV) [(VO)₂(μ-L-κ⁴ONNO)₂] (3, L¹; 4, L²; 5, L³) and monomeric [VO(L-κ⁴ONNO)] (6, L⁴, 7, L⁵) compounds. As shown by X-ray crystallography, compounds 1 and 2 are monomeric, in which the chelating ligands afford octahedral cis-α geometry at the vanadium center. In the dimeric structures of 3–5, the six-coordinate vanadium centers are bridged via two oxygen atoms of the L^1–3 ligands while the L^4,5 ligands generate square pyramidal structures of the monomeric 6 and 7 compounds. HFEPR studies allowed the determination of the spin Hamiltonian parameters of the S = 1 spin state of the monomeric V(III) and dimeric V(IV), and S = ½ in monomeric V(IV) compounds. Magnetic measurements of 3–5 indicated weak ferromagnetic metal–metal exchange interactions. A reaction course for the deoxygenation and reduction of vanadyl-salan compounds is proposed.