Application of multiwavelength anomalous diffraction (MAD) analysis on single crystals has been used to provide insight into redox delocalization on homometallic clusters[1]. This synchrotron-based technique is sensitive to the ligand environment and charge distribution in a site-specific manner and can address an individual metal site’s role in the overall chemistry of a metal cluster. We have investigated two tetracopper(I) complexes, [Cu4(µ4-S)(µ2-dppm)4]2+ (1, dppm = bis(diphenylphosphino)methane)[2] and [Cu4(µ4-S)(µ2-dppa)4]2+ (2, dppa = bis(diphenylphosphino)amine)[3] which are structurally related to CuZ active site of nitrous oxide reductase. MAD data for 1 and 2 were rigorously analyzed by collecting calibration data on various literature compounds. MAD study of 2 has identified a more Lewis acidic Cu site within the formally homovalent, homometallic tetracopper cluster that has been shown to convert N2O to N2 and H2O[4]. In hand with the DFT calculations, a more polarized Cu-Cu edge was determined to participate in N2O activation. In support of this finding, complex 1’s lack of reactivity towards N2O was found to be in accord with the MAD analysis and DFT calculations carried out.

Multiwavelength anomalous diffraction (MAD) analysis on enzyme-mimicking multi-nuclear tetracopper complexes

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