Location of H Atoms Using X-Ray Data

In the introductory section of this article we will, out of convenience, take the liberty of using a few examples from our own experience to illustrate some of the methods that can be used to locate H atoms with x-ray data. 

The earliest attempts at determining the structures of transition metal complexes involved an indirect approach, in which H atom positions are inferred from the geometry of the remainder of the molecule. This technique is still heavily used today. 

Clues are usually derived from unusual distances and angles, or from the particular orientation of the other ligands in the complex. In the structure determinations of HPtBr(PEt3)2 HMn(CO)s 10), for example, a gap (or hole ) in the coordination sphere around the metal atom was interpreted to be a result of the steric influence of the missing H atom. 

Direct Location ofHA toms Using X-Ray Data 

It is becoming increasingly common these days to find H atoms directly using X-ray diffraction methods. Success is not always guaranteed, but one s chances are generally better for hydride complexes of first row transition metals, as opposed to those of the heavier transition elements. 

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