Determination of bond lengths from extended X-ray absorption fine structure in cobalt(III)-oxo cubane-like clusters

Abstract

The extended X-ray absorption fine structure (EXAFS) at the K-edge of cobalt has been studied in two cobalt complexes having Co(III)-oxo cubane-like clusters of the type Co4O4(O2CR)4L4 where R is CH3 and L is pyridine (py) in one of the complex and ammonia (NH3) in the other complex. The spectra have been recorded at BL-9 scanning EXAFS beamline at the 2.5-GeV INDUS-2 Synchrotron, RRCAT, Indore, India. The positions of EXAFS maxima and minima have been reported. Using this data, the bond length has been determined by simple bond determination methods, viz., Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The normalized EXAFS spectra have been Fourier transformed and the value of the bond length has also been determined from the position of the first peak in the Fourier transform. This distance is the phase-uncorrected bond length. LSS method also gives such bond length. The results obtained from Fourier transform and LSS methods have been found to be comparable to each other. For the pyridine complex, the value obtained from Levy's method has been found to be in agreement with the available crystallographic value.