Characterization of the Structural and Electronic Properties of Spin-Coupled Dinuclear Copper(II) Centers by Proton NMR Spectroscopy

Abstract

The 1H NMR spectra of a series of well-characterized μ-phenoxo and μ-alkoxo spin-coupled dicopper(II) complexes have been investigated. The complexes studied were [Cu2(BPMP)(OH)]2+ (1) (BPMP = 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol), [Cu2(CH3HXTA)(OH)]2- (2) (CH3HXTA = N,N ‘-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-carboxymethylglycine), [Cu2(m-XYL)(OH)]2+ (3) (m-XYL = 2,6-bis[[bis(2-pyridylethyl)amino]methyl]phenol), and [Cu2(TBHP)(OAc)]2+ (4) (TBHP = N,N,N ‘,N ‘-tetrakis[(2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane). The magnetic interactions of these complexes range from strongly antiferromagnetically to weakly ferromagnetically coupled. Both one- and two-dimensional (COSY) 1H NMR methods were used to facilitate the assignment of the hyperfine shifted 1H NMR signals of each complex. COSY experiments provide clear cross signals for resonances \u3c200 Hz wide. These data have facilitated the assignment of the hyperfine shifted 1H NMR signals and have verified that the solid state structures exist in solution for each system studied. Assuming a paramagnetic dipolar relaxation mechanism, the crystallographically determined Cu−H distance (r) is proportional to T11/6. All calculated Cu−H distances for 1−4 are within ca. 20% of the Cu−H distances derived from X-ray crystallography. These data indicate that a paramagnetic dipolar relaxation mechanism is the dominant proton relaxation pathway for spin-coupled dicopper(II) centers. Our results indicate that 1H NMR spectroscopy is an excellent tool with which to probe the solution structures of spin-coupled dicopper(II) centers in model complexes as well as biological systems

A non-canonical metal center drives activity of the Sediminispirochaeta smaragdinae metallo-β- lactamase SPS-1

“…Three solvent-exchangeable peaks can be assigned to histidine residues bound to high spin Co(II), and other resonances, by comparison to spectra of Co(II)-MβLs, can be assigned to cysteine and aspartate residues. The broader peaks observed in the NMR spectra of Co(II)-substituted SPS-1, as compared to those in the spectra of Co(II)-substituted NDM-1, suggest a slower T1e for the unpaired electrons on Co(II) and Co(II) ions that are at best weakly spin-coupled (35,36). The lack of spin coupling is clearly observed in the parallel mode EPR spectra of Co(II)-substituted SPS-1.…”

A new diaza‐18‐crown‐6 ligand containing two quinolin‐8‐ylmethyl side arms: Crystal structures and characterization of the ligand, the protonated ligand and its mononuclear barium(II) and dinuclear copper(II) complexes

“…These data indicate that the hydroxo bridged complex is present in the solution as well as the solid state. Due to this coupling, 1 H nmr signals for Cu 2 L(µ-OH) 3+ can be observed [48]. If the 6…”

μ‐η1:η1‐N,N'‐Imidazolidine‐Bridged Dicopper(II/III) Complexes of a New Dinucleating μ‐Bis(tetradentate) Schiff Base Ligand: Synthesis, Structural Characterization, 1H NMR Spectroscopy, and Magnetic Coupling

“…[50] Construction of a library of compounds along with their NMR properties is beneficial in the context of bioinorganic modeling of naturally occurring metallo-enzymes. 250-MHz 1 H NMR spectroscopic data of complex 1 were collected in [D 4 ]methanol at room temperature.…”