Solid‐State NMR and EXAFS Spectroscopic Characterization of Polycrystalline Copper(I) O,O′‐Dialkyldithiophosphate Cluster Compounds: Formation of Copper(I) O,O′‐Diisobutyldithiophosphate Compounds on the Surface of Synthetic Chalcocite

Abstract

A number of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy. The structural relationship of these compounds is discussed. The polycrystalline copper(I) O,O'-diisobutyldithiophosphate cluster compounds, [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6], were also characterized by using 31P CP/MAS NMR (CP = cross polarization, MAS = magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shift tensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR spectra of the polycrystalline copper(I) cluster compounds, are presented. The adsorption mechanism of the potassium O,O'-diisobutyldithiophosphate collector, K[S2P(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6] compounds.

The Advantages of EPR Spectroscopy in Exploring Diamagnetic Metal Ion Binding and Transfer Mechanisms in Biological Systems

“…The binding of diamagnetic metal ions, such as Zn(II), Mg(II), Cu(I) and Ag(I), to proteins, has been mostly studied by nuclear magnetic resonance (NMR) and X-ray absorbance fine structure (EXAFS) spectroscopy, techniques that can provide information on the metal coordination site at the molecular level, specifically those atoms and residues involved in metal binding [12][13][14][15][16]. While electron paramagnetic resonance (EPR) spectroscopy cannot provide information on residues directly involved in the coordination of diamagnetic metal ions, it can, however, probe the dynamics and conformational changes in a biomolecule in solution upon metal ion binding, thereby providing important structural and functional information on the biomolecule as a function of metal coordination.…”

Solid-State 65Cu and 31P NMR Spectroscopy of Bis(triphenylphosphine) Copper Species

“…However, for samples with Cu sites in nonspherical environments, MAS is not typically an option (since the large quadrupolar interactions cannot even be partially averaged) and time-consuming, static (stationary sample) wide-line NMR experiments are commonly applied. 22,[31][32][33][34][35] Recently, there have been a number of reports of rapid acquisition of broad NMR spectra of half-integer quadrupolar nuclei through the combination of several techniques. First, NMR powder patterns that extend beyond typical excitation bandwidth (i.e., so-called ultra-wideline (UW) NMR spectra) can be acquired using frequency-stepped or "piecewise" acquisition of subspectra, which are Fourier transformed, and then coadded to produce the total spectrum.…”

“…Solid-state copper NMR experiments for many spherically symmetric sites have been conducted under conditions of magic-angle spinning (MAS), in which the effects of copper chemical shielding anisotropy (CSA) are completely averaged, leaving behind the partially averaged second-order quadrupolar pattern. However, for samples with Cu sites in nonspherical environments, MAS is not typically an option (since the large quadrupolar interactions cannot even be partially averaged) and time-consuming, static (stationary sample) wide-line NMR experiments are commonly applied. ,− …”

Solid-State63Cu and65Cu NMR Spectroscopy of Inorganic and Organometallic Copper(I) Complexes

“…This is unfortunate, since copper NMR would enhance the currently limited understanding of structure, dynamics, and reactivity at copper(I) sites for many important inorganic materials, organometallic molecules, and biological systems. − Solid-state copper NMR has largely been applied to Cu sites of high spherical symmetry with reduced electric field gradients (EFGs) and correspondingly small quadrupolar interactions. − For materials with increasingly spherically asymmetric copper sites, time-consuming wide-line static NMR experiments (i.e., stationary NMR samples) tend to be the norm. For instance, Bastow and co-workers have used static 63 Cu NMR experiments to investigate the structural evolution of copper-containing alloys at various temperatures, , and Antzukin et al have applied static 65 Cu NMR experiments to probe copper environments in a series of copper(I) dialkyl-dithiophosphate clusters. − Given the enormous success of NMR of metals for structural characterization, it would greatly benefit chemists, structural biologists, and materials scientists alike to be able to routinely use solid-state copper NMR for characterizing the electronic structure and bonding at Cu(I) sites in systems such as copper proteins, − amyloid fibrils and related peptides, − zeolites, organometallic copper complexes, and a wide array of materials where the Cu oxidation state varies or multiple oxidation states simultaneously exist, such as in high-temperature superconductors. − …”