Coordination chemistry of nickel(II) nitrate with superbasic guanidines as studied by electrospray mass spectrometry

The coordination chemistry of nickel(II) nitrate with four guanidines bearing heteroatom-containing alkyl sidechains is investigated by means of electrospray ionization mass spectrometry of dilute methanolic solutions. In contrast to other nitrogen bases, the ESI spectra of the solutions containing superbasic guanidines are dominated by signals due to the protonated nitrogen bases, BH+. Under soft ionization conditions, also several nickel-containing ions are observed which are best described as complexes between the guanidinum ions BH+ with neutral nickel(II) nitrate coordinated via the nitrato ligands in terms of ion pairs. For guanidine derivatives with at least two N,N-dimethylaminopropyl groups in the sidechains, also the formation of genuine amino-nickel complexes is inferred. The pronounced difference between the ions formed upon ESI of aqueous nickel(II) nitrate in the presence of guanidines compared to other, weaker nitrogen bases is ascribed to the high basicity of the guanidines, which renders their protonation much more favored than their possible operation as ligands for the metal center.

The coordination chemistry of nickel(II) nitrate with four guanidines (1–4) bearing heteroatom-containing alkyl sidechains is investigated by means of electrospray ionization mass spectrometry.Figure optionsDownload high-quality image (12 K)Download as PowerPoint slide