The Original CoII Heteroscorpionates Revisited: On the EPR of Pseudotetrahedral CoII

Abstract

An examination of the solution spectroscopy of a series of tetrahedral bis-bispyrazolylborate complexes of Co II is presented. This includes a re-examination of the UV/Vis-NIR of the three stable derivatives, Bp 2 Co, Bp 3,5Me 2 Co and (Ph 2 Bp) 2 Co, which showed two transitions previously unobserved, one arising from splitting of the near-infrared d-d transition and one arising from a ligand-based or charge-transfer mechanism; a reevaluation of Δ and B led to values more in line with similar complexes. Frozen solution EPR of the series of complexes suggests all are under the influence of a non-negligible, negative [a]

Electronic Structure of Three-Coordinate FeII and CoII β-Diketiminate Complexes

“…One example where A( 59 Co) was well resolved is a five-coordinate complex with only O-donors (I = 0 ligands), pentakis(2picoline N-oxide)cobalt(II) perchlorate, prepared as a doped powder (<0.1 mol %) in the isomorphous Zn II host. 98 This system exhibits g′ = [5.96, 3.56, 1.91]�thus similar values to CoCl, and a hyperfine structure was resolved in both the g max and g min (g z , g || ) regions corresponding to an average A( 59 99,100 still similar to that for CoCl. The hyperfine coupling for CoCl is also near those measured for low-spin Co II macrocyclic complexes with N 4 coordination.…”

Trispyrazolylborate Complexes: An Advanced Synthesis Experiment Using Paramagnetic NMR, Variable-Temperature NMR, and EPR Spectroscopies

“…The six-coordinate octahedral complex, typically the first to elute from the column, is collected and left to crystallize, open to the air, in a hood for 1 week. While some of the four-coordinate complexes have been well-characterized, complexes of the form MBp 2 show very short shelf lives, even in the solid state (some as short as a few days) . The five-coordinate (MBpTp) congeners have never been reported, owing to substantially shorter lifetimes, disproportionating rapidly to the two homoleptic complexes (MBp 2 and MTp 2 ).…”

“…While some of the four-coordinate complexes have been well-characterized, complexes of the form MBp 2 show very short shelf lives, even in the solid state (some as short as a few days). 22 The five-coordinate (MBpTp) congeners have never been reported, owing to substantially shorter lifetimes, disproportionating rapidly to the two homoleptic complexes (MBp 2 and MTp 2 ). Consequently, we focused the spectroscopic component on the more stable MTp 2 complexes.…”

Chlorocobalt complexes with pyridylethyl-derived diazacycloalkanes

“…The D and g ave values appear to be in the normal ranges; D values for Co II do cover a wide range, from ca À50 to +100 cm À1 (Cruz et al, 2018;Nemec et al, 2016). While Co II g values intrinsically also cover a wide range, applicable values for fitting ZFS data have been observed to be about 2.0-2.4 (Voronkova et al, 1974;Baum et al, 2016;Banci et al, 1980;Martinelli et al, 1989). Both compounds here show a faster drop in T and a distinct kink at temperatures below ca 15 K. These features have been seen in several other Co II systems (Z ˙urowska et al, 2008;Papa ´nkova ´et al, 2010;Boc ˇa et al, 1999;Rajna ´k et al, 2013); however, no definitive accounting for this has been advanced as yet, apart from the not infrequently employed addition of a weak antiferromagnetism mean field term.…”