Nuclear magnetic resonance studies of multinuclear chromium assemblies

Aminopyridine complexes of Cr(III) basic carboxylates as potential polymer precursors: Synthesis, characterization, and crystal structure of [Cr3O(propionate)6(X-aminopyridine)3]+ (X = 3 or 4)

“…The chromium centers in these trinuclear assemblies are antiferromagnetically coupled, resulting in a reduction of the magnetic moment per Cr(III) ion; thus, the paramagnetic shifts and broadening of the resonances should be slightly reduced in comparison to NMR spectra of mononuclear Cr(III) complexes. Additionally, as the unpaired electrons of the chromic centers are in the t 2g orbitals, directed at the pi system so of the ligands and not along the sigma bonds, only pbased pathways for delocalization of the unpaired spin density from the metal ion to the ligands is expected to be significant, as observed previously for basic chromic carboxylates [13,[49][50][51].…”

“…Thus, NMR spectra of Cr(III) complexes display greatly broadened and shifted resonances, particularly for the atoms of aromatic ligands where the half-occupied t 2g orbitals are oriented at the pi clouds of the ligands, such that knowledge of the structure of the complex is often required to interpret the spectra, rather than the reverse. Yet, paramagnetic 1 H, 2 H, and 13 C NMR have been demonstrated to be of utility in characterizing Cr(III) carboxylate assemblies [13,[49][50][51].…”

Structural and magnetic studies on mono- and polynuclear chromium ascorbate complexes

“…technique has recently been successfully applied to paramagnetic Cu II - [39] and Cr III -ascorbates [10,28] as for the oxo-centered polynuclear chromium carboxylates [40][41]. 1 H-n.m.r.…”

Examination of the molecular nature of low-molecular-mass chromium(III) ions in isolated osteoarthritic knee-joint synovial fluid

“…Although the electronic relaxation time of the isolated Cr(III) ion is relatively long (approximately 10 À8 s, a phenomenon expected to give rise to prohibitively broad lines) in view of hyperfine coupling to 1 H nuclei, 1 H NMR resonances in spectra acquired on solutions of biomolecules treated with this agent do not exhibit this behaviour, since previous studies of Cr III (acac) 3 [45,46], Cr III -benzoate, Cr III -pyridine [47] and Cr III -pyridinecarboxylate complexes [48] have demonstrated the detectability of paramagnetically shifted and broadened signals. Additionally, the redox reaction between CrO 2À 4 and cytochrome c 7 , resulting in a Cr(III)-fully oxidized protein adduct, has been monitored via the hyperfine coupling between the metal ionÕs unpaired electrons and the proteinÕs 1 H nuclei, the paramagnetic line-broadening effects observed for the latter yielding valuable structural information regarding the chromium ion binding-site [49].…”