Bis(nitroxyl) adducts of cobalt and nickel hexafluoroacetylacetonates. Preparation, structures, and magnetic properties of M(F6acac)2(proxyl)2 (M = Co2+, Ni2+)

Abstract

ChemInform Abstract The title adducts (I) are prepared by 1:2 molar reaction of the reactants (no yields given) and characterized by crystal structure analyses (both space group P21/c, Z=2). Magnetic susceptibility data (6-300 K) indicate that antiferromagnetic coupling of ligand and metal free spins yields an S = 1/2 ground state for M: Co and an S = 0 ground state for M: Ni. At higher temp. there is some population of excited states with greater spin multiplicities. Possible orbital interactions that could account for the magnetic behavior are discussed.

Tetrakis(μ-acetato)bis(2-pyridone)dicopper

“…A number of transition metal complexes containing hfa ligands have been characterized crystallographically and the coordination chemistry of/3-diketones has been reviewed (Fackler, 1965;Kawaguchi, 1986). The structure reported here is similar to a recently reported Ni(hfa)2 complex containing nitroxyl radical ligands (Porter, Dickman & Doedens, 1988). (13) (22) 0.0268 (21) Bond lengths (1~) and angles (o) with e.s.d.…”

Radical ligand-containing single-molecule magnets

“…A limitation of these ligands, however, is the poor ability of the weakly Lewis basic N O group to coordinate to a metal center. Nevertheless, enhanced binding of monodentate nitroxides can often be achieved through employment of electron withdrawing groups, such as (1,1,1,5,5,5)-hexafluoroacetylacetonate (hfac) [88][89][90][91][92], halides [93], and halocarboxylate [94,95], as ancillary ligands in order to increase the Lewis acidity of metal ions and generate compounds of the form L n M(L ) 2 (L = nitroxide radical; L = ancillary ligand; n = 1 or 2). The first structurally [88] and magnetically [96] characterized complex of this form, (tempo)Cu(hfac) 2 (tempo = 2,2,6,6-tetramethylpiperidinyl-1-oxyl), comprises a distorted square pyramidal Cu II center with the nitroxyl oxygen atom occupying a basal coordination site.…”

Iron-Mediated Cleavage of Coordinated 1,1,1,5,5,5-Hexafluoropentane-2,4-dione by the 2,2,6,6-Tetramethylpiperidine-1-oxyl Nitroxyl Radical

“…Instead, mixtures were formed containing colorless and red crystalline solids. Single-crystal X-ray analysis of the crystalline products resulted in identification of the organic salt 2,2,6,6-tetramethylpiperidinium trifluoroacetate (1) and a novel Fe 3+ dimer, 2,2,6,6-tetramethylpiperidinium (bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato-O,O′) (2,2,6,6-tetramethylpiperidinium-1-oxo-O)ferrate(III))(µoxo)(bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato-O,O′)(formato-O)ferrate(III)) (2).…”

“…The stable nitroxyl free radical 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) forms adducts with M(hfac) 2 complexes (M 2+ = Mn, Co, VO, Cu; hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionato). − These adducts, which generally exhibit strong magnetic interactions between the nitroxyl unpaired electron and the metal d electrons, can be isolated from organic solvents.

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