X-ray structure analysis, electronic and vibrational circular dichroism of chiral-at-metal dioxidovanadium(V) complexes with amino acids derived Schiff base ligands

Schiff Base Ligands Derived from l‐Histidine Methyl Ester: Characterization, Racemization, and Dimerization of Their Transition‐Metal Complexes

“…Interestingly, the above complexes show slow racemization of the ligand, as confirmed by circular dichroism spectroscopy. Racemic Ni II complexes of [Ni(HL Me )(H 2 L Me )](PF 6 or Cl) (rac-6PF 6 or rac-6Cl) are isolated and their crystal structures are confirmed by X-ray diffraction analysis. In the case where Co(OAc) 2 is used as the metal(II) salt, a new ligand dimerization reaction takes place to afford a complex of [Co(H 2 Schiff bases, thus prepared, might act as multidentate ligands, stabilizing multioxidation states and a specific coordination geometry of the metal center.…”

“…Recrystallization from a methanol solution of the crude product by vapor diffusion of iPr 2 O affords green crystals (S-6PF 6 ) suitable for X-ray diffraction study. The PF 6 salt crystallizes in an orthorhombic space group P2 1 2 1 2 1 with Z = 8, indicating that there are two crystallographically independent Ni II complex cations and two PF 6 anions in an asymmetric unit. Both Ni II complex cations (S-6 + ) have a similar molecular structure to those of S-1 + and S-3 + (Figure 3a).…”

“…We assume that one of the two tridentate ligands has a phenol form (S-H 2 L Me ) and the other has a monoanionic phenolato form (S-HL Me ) -. Thus, the complex S-6PF 6 can be formulated as a Ni II complex [Ni(S-HL Me )(S-H 2 L Me )]PF 6 .…”

“…When a similar reaction mixture of NiCl 2 ·6H 2 O and S-H 2 L Me (without KPF 6 ) in methanol is allowed to stand for several days, green block crystals with a different anion (rac-6Cl) are deposited by vapor diffusion of iPr 2 O. The crystals of rac-6Cl are insoluble in acetonitrile, unlike those of S-6PF 6 . The single-crystal X-ray diffraction study indicates that this compound also contains a doubly hydrogen-bonded dimer of {[Ni(HL Me )(H 2 L Me )] 2 } 2+ (6 + ), similar to the abovementioned S-6PF 6 , but the space group of rac-6Cl is found to be a centrosymmetric Pbca.…”

“…The ligand precursor derived from l ‐histidine ( S ‐H 2 his) and salicylaldehyde, ( S )‐2‐[(2‐hydroxylbenzylidene)amino]‐3‐(1 H ‐imidazol‐4‐yl)propanoic acid ( S ‐H 3 L), is an interesting multidentate ligand having four different kinds of potential donor groups, but it is, therefore, difficult to control the coordination modes on complexation to a certain metal ion. So far, a few V, Cu, Mo, and U complexes with the S ‐H 3 L anion have been reported, but no systematic study on the coordination properties of this ligand has been reported. Here, we reveal the functionality of histidine complexes originating from the coordination of the imidazole group.…”