Determination of metal-metal distances: significance and accuracy

Nature utilises a variety of metal clusters as catalytic centers. Some of t hem make use of two or more metals in the catalytic site. The variation of metal-metal distances plays an important role in several processes like cha rge transfer and weakening of bonds. X-ray absorption spectroscopy can dete rmine these metal-metal distances in several states (crystal, solution or a morphous). However sometimes backscattering from light elements hides the m etal-metal contribution to the fine structure. Here we point out significan ce and accuracy of metal-metal distances in a model system. Therefore a num ber of different refinement protocols are applied to the data. These protoc ols will be discussed focusing on the significance and accuracy of the meta l-metal distances extracted from the data.