The Effect of Axial Pyridine Ligands on the Charge Transfer Bands of trans-Bis(dimethylglyoximato)Cobalt(III) and -Iron(II) Complexes

Abstract

The electronic absorption spectra of [CoIII(dmgH)2B2]+ and [FeII(dmgH)2B2] (dmgH=dimethylglyoximate monoanion and B=pyridine derivatives) are inspected with respect to the effect of the axial pyridine ligands on the charge-transfer bands of the complexes. The characteristic bands observed in the 275–305 mμ region for the Co(III) complexes and in the 485–555 mμ region for the Fe(II) complexes, which have been assigned to a metal→oxime charge-transfer band, are shifted to shorter wavelengths with a decrease in the basicity of the pyridine derivatives. The results have been discussed by taking into account the π-interaction of the dπ(dxz, dyz) orbital of the central metal ion with the empty π-orbitals of both the dimethylglyoximate and the pyridine derivatives. It is suggested that the π-interaction is stronger in the Fe(II) complexes than in the Co(III) complexes, while the σ-bond is stronger in the latter. The infrared spectral evidence that the C=N stretching frequency is dependent on the axial pyridine derivatives, and that it is observed at a lower frequency in the Fe(II) than in the Co(III) complexes, is consistent with the above results.

X-ray structural studies of some group VIII compounds with catalytic implications / by Douglas Allen Sullivan.

“…This holds true in C£Co(H2drag) (dmg) (clan) where the N-0 distances appear to be different. The N (21) -0 (21) o and N(22)-0(22) distances of 1.348(6) and 1.359(6) A in the diprotonated dmg are longer than the N (12) -0(12) and N(ll)o 0(11) distances of 1.329(6) and 1.337 (6) A in the dianionic dmg. Using the significance test described by Cruickshank and Robertson the N (21) -0(21) distance is possibly longer than the N (12) -0(12) with a t^value of 2.2 4 and the N(22)-0(22) bond is significantly longer than the N (11) -0(11) bond with a t value of 2.59.…”

“…The N (21) -0 (21) o and N(22)-0(22) distances of 1.348(6) and 1.359(6) A in the diprotonated dmg are longer than the N (12) -0(12) and N(ll)o 0(11) distances of 1.329(6) and 1.337 (6) A in the dianionic dmg. Using the significance test described by Cruickshank and Robertson the N (21) -0(21) distance is possibly longer than the N (12) -0(12) with a t^value of 2.2 4 and the N(22)-0(22) bond is significantly longer than the N (11) -0(11) bond with a t value of 2.59. Also, in [Co (Hdmg) 2 (clan) 2] C£ the o N(12)-0(12) bond of 1.362 3A is significantly longer than o the N (11) -0(11) bond of 1.340(3) A, v/here the bridging hydrogen atom is bonded to 0(12).…”

Coenzyme B12 model studies: Equilibrium constants for the pH-dependent axial ligation of benzyl(aquo)cobaloxime by various N- and S-donor ligands

“…The charge-transfer spectra of the trans[RCo(DH) 2 L] complexes show bands at about 33,000 cm -1 due to intra ligand π-π* transition of the coordinated DH, bands occurring at 27,500 cm -1 are assigned to the imidazole to Co(III) (LMCT) and those at 33,000 cm -1 are due to the dπ (Co(III)) → π* (DH) (MLCT) transition. The σ DH to σ * Co(III) (LMCT) is marked by the intense short wavelength bands of alkyl(ligand)cobaloximes 30 . The data presented in table 2 show the 1 H NMR chemical shifts of benzyl(aquo)cobaloximes and benzyl (ligand)cobaloximes.…”

Metallomacrocycles as ligands: synthesis and characterisation of aluminium-bridged bisglyoximato complexes of palladium and iron

“…The band at 548 nm (5a-Fe) is consistent with a d-π* charge transfer, as previously assigned. 54,55,58 The observed shift to higher energy is likely due to an increase in the energy of the glyoxime π* orbital due to more direct interactions with d orbitals.…”