Coordination of Imidazoles by Cu(II) and Zn(II) as Studied by NMR Relaxometry, EPR, far-FTIR Vibrational Spectroscopy and Ab Initio Calculations: Effect of Methyl Substitution

Abstract

Synthetic imidazole ligands are typically substituted at the N(1) ((1)-Im) position while natural imidazole ligands are substituted at the C(4) ((4)-Im) position. To outline the difference in coordination properties, the methyl-substituted imidazoles Me(4)-Im and Me(1)-Im were complexed with CuCl(2) and ZnCl(2) and investigated by NMR relaxometry, electron paramagnetic resonance, far-Fourier transform IR vibrational spectroscopy, and ab initio calculations. Me(4)-Im, Me(1)-Im, and Im in excess form the usual tetragonal D(4h) [CuL(4)X(2)] complexes with CuCl(2) whereas the methylated imidazoles form pseudotetrahedral C(2v) complexes instead of the usual octahedral O(h) [ZnIm(6)](2+) complex. All imidazoles display a high degree of covalence in the M-L σ- and π-bonds and the π-interaction strength affects the relative energies of complexation. Opportunities to tailor complexes by the chemical properties of the substituents are envisaged due to the role of the inductive and hyperconjugative effects, rather than position.

Synthesis and structure of Zn(II) and Cu(II) complexes derived from 2-(aminomethyl)benzimidazole and glycine

“…Likewise, the H 2 O rocking vibration at 842 cm −1 was observed. The existence of Zn-N and Zn-Cl bonds was confirmed with absorptions at 491 and 283 cm −1 , respectively [43][44][45][46]. In contrast, the Raman spectrum of 3 showed the ν a (COO) vibration at 1592 cm −1 and ν(Cu-Cl) at 242 cm −1 , respectively.…”

Encapsulation of actives for sustained release

“…The solvent is subsequently removed resulting in a porous material with excellent control of the pore size. [108][109][110] Transition metal ions, such as Cu 2+ and Zn 2+ , are very common, and di-and tricarboxylates, such as o-, m-and p-phthalic acid, unsaturated short aliphatic diacids, benzene-1,3,5-tricarboxylic acid and multidentate azole ligands, [111][112][113][114][115] are examples of popular organic linker molecules. The solvothermal synthesis yields a crystalline material with a very good control of the pore size.…”

Changes in the NMR characteristics of 3,6‐di‐tert‐butylquinone on formation of paramagnetic complexes

“…Characteristic features of intramolecular exchange of semiquinolate cobalt complex were revealed . The nature of metal–ligand bonding in complexes of unsubstituted imidazole with Cu(II) and Zn(II) was studied in detail . Intramolecular chemical exchange in some complexes of 18‐membered macrocyclic polyethers with paramagnetic lanthanide cations were successfully investigated .…”