Nuclear magnetic resonance studies of planar low-spin complexes of cobalt(II) with Schiff bases. N,N'-ethylenebis(salycylideneiminato)cobalt(II) in noncoordinating solvents

Solution and Solid State Properties for Low-Spin Cobalt(II) Dibenzotetramethyltetraaza[14]annulene [(tmtaa)CoII] and the Monopyridine Complex

“…An effective magnetic moment of 2.10 μ B and a ⟨ g ⟩ of 2.42 for (tmtaa)­Co II in a toluene solution were obtained from χ M(P) {μ eff = 2.828√(0.001874 × 295) = 2.10 μ B ; ⟨ g ⟩ = μ eff /√[ S ( S + 1)] = 2.42}. The μ eff and ⟨ g ⟩ for (tmtaa)­Co II in a toluene solution (295 K) are in close agreement with values derived from previously reported EPR spectra for (tmtaa)­Co II in toluene glass (90 K) ( g 1 = 3.83, g 2 = 1.64, and g 3 = 1.79; ⟨ g ⟩ = 2.42) . EPR spectra for (tmtaa)­Co II in toluene glass at 4 K are also in close agreement (Figure S4).…”

“…Whereas spectral and magnetic evidence points to a d yz -based SOMO in (tmtaa)­Co II , prior toluene glass EPR studies of (tmtaa)­Co II in the presence of pyridine give ligand hyperfine coupling with a single 14 N pyridine donor atom, which, along with the g values, conclusively place the unpaired electron in the d z 2 MO associated with a 2 A 1 ground state for (tmtaa)­Co­(py) …”

“…The observation that g zz is larger than g yy provides strong evidence but not proof that the unpaired electron is in the d yz molecular orbital (MO) ( 2 B 2 ground state) . NMR contact shifts for ligand nuclei can assist in the assignment of the unpaired electron MO through observation of the sign and magnitude of the electron–nuclear coupling constants …”

“…The change in the sign of the methine proton’s paramagnetic shift from a large upfield shift for (tmtaa)­Co II to a small downfield shift upon coordination by pyridine in (tmtaa)­Co II (py) is consistent with a change in the unpaired electron MO (Table ). The EPR of (tmtaa)­Co II (py) places the odd electron in the cobalt d z 2 MO that is involved in σ-bonding with pyridine, whereas the odd electron in (tmtaa)­Co II is attributed to the cobalt d yz MO.…”

On the electronic structure of N,N′-ethylenebis(acetylacetonatiminato)Co(II), Co(II)acacen

“…and susceptibility measurements [2][3][4][5], the interpretation of the experimental data was not that clear for the second class of complexes. Two possible groundstates have been proposed, namely a IZA2,yz ) [6,7] and a ]2Ax,z2 ) state [8]. (Symmetry labels with respect to the symmetry group Czv(X ) (cf.…”