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

Treatment
of the cobalt­(II) amide, [Co­{N­(SiMe3)2}2]2, with four equivalents of the sterically crowded
terphenyl phenols, HOArMe6 (ArMe6 = C6H3-2,6­(C6H2-2,4,6-Me3)2) or HOAriPr4 (AriPr4 = C6H3-2,6­(C6H3-2,6-Pri2)2), produced the
first well-characterized, monomeric two-coordinate cobalt­(II) bisaryloxides,
Co­(OArMe6)2 (1) and
Co­(OAriPr4)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.