Synthesis, Structural, Spectroscopic, and Magnetic Characterization of Two-Coordinate Cobalt(II) Aryloxides with Bent or Linear Coordination

Abstract

Treatment of the cobalt(II) amide, [Co{N(SiMe3)2}2]2, with four equivalents of the sterically crowded terphenyl phenols, HOAr(Me6) (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2) or HOAr(iPr4) (Ar(iPr4) = C6H3-2,6(C6H3-2,6-Pr(i)2)2), produced the first well-characterized, monomeric two-coordinate cobalt(II) bisaryloxides, Co(OAr(Me6))2 (1) and Co(OAr(iPr4))2 (2a and 2b), as red solids in good yields with elimination of HN(SiMe3)2. The compounds were characterized by electronic spectroscopy, X-ray crystallography, and direct current magnetization measurements. The O-Co-O interligand angles in 2a and 2b are 180°, whereas the O-Co-O angle in 1 is bent at 130.12(8)° and its cobalt(II) ion has a highly distorted pseudotetrahedral geometry with close interactions to the ipso-carbons of the two flanking aryl rings. The Co-O distances in 1, 2a, and 2b are 1.858(2), 1.841(1), and 1.836(2) Å respectively. Structural refinement revealed that 1, 2a, and 2b have different fractional occupations of the cobalt site in their crystal structures: 1, 95.0%, 2a, 93.5%, and 2b, 84.6%. Correction of the magnetic data for the different cobalt(II) occupancies showed that the magnetization of 2a and 2b was virtually identical. The effective magnetic moments for 1, 2a, and 2b, 5.646(5), 5.754(5), and 5.636(3) μB respectively, were indicative of significant spin-orbit coupling. The differences in magnetic properties between 1 and 2a/2b are attributed to their different cobalt coordination geometries.

Stabilization of a Two‐Coordinate Mononuclear Cobalt(0) Compound

“…It produces a blue color when dissolved in organic solvents, such as THF, toluene, and benzene. 1 H NMR spectrum of 2 showed broad resonances ranging from δ =−2.5 to 10 ppm indicating the paramagnetic7–9 nature of the solution, as was expected. Compound 2 can be further characterized by MS (EI) spectrometry ( m / z (100 %): 629.4; see the Supporting Information).…”

Low‐Coordinate Single‐Ion Magnets by Intercalation of Lanthanides into a Phenol Matrix

“…One hydrogen atom from methyl group of the wing is deprotonated by LnR 3 (thf) 2 , despite of its weak acidity.O fn ote,t his low-coordinate structure is not idealized, as one aromatic ring shows weak interaction with the central Dy III ion (Dy À C: 2.858(7)-3.105 (9) ). [26][27][28][29] In our case the refined occupancyo fr areearth metal ions is 100 %o rn ear to 100 %. Interestingly,a ll the 1Ln complexes and free ligand ArOH are isostructural (Supporting Information, Table S1).…”

“…Thei ntercalation of rare-earth metal ions only induces very small changes in the unit cell volumes (less than 0.5 %), which is avery rare phenomenon concerning the large ionic radii of Ln III ions.Previously,P ower and co-workers reported acompound [Co(OAr) 2 ], where the occupations of Co are 93.5 % and 84.6 %. [26][27][28][29] In our case the refined occupancyo fr areearth metal ions is 100 %o rn ear to 100 %. Thec hemical compositions of 1Ln were confirmed by the elemental analysis and magnetic study.…”

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…These compounds have an S = 3/2 spin ground state and the cobalt centers make a pronounced orbital contribution to the magnetic moment (L = 2), similar to the iso-electronic linear Fe I compounds. Their magnetic behavior exhibited distinct features, which were attributed to the effect of geometrical influences on orbital magnetism [38]. [K(18-crown-6)] (12) slightly bent nr [36] [Ni(6-Mes)2]Br (13) linear Yes 600 4.6  10 -6 11.8 [37] a Maximal temperature at which magnetic hysteresis was observed; b too small to be measured; nr = not reported.…”