Palladium difluoride, structure

The crystal structure of palladium difluoride. By X. Barti,ett and R. Maitland, Chemistry Department, King s College, Keweastle upon Tyne, England... 

N. Bartlett and R. Maitland, The Crystal Structure of Palladium Difluoride, Acta Cryst. 11 (1958) 747-748. 

Transition metal difluorides are known mainly for first transition series elements, with palladium and silver difluorides from the second series, and no examples from the third. All these compounds have either the rutile structure, or, for chromium, copper, and silver, a distorted variant, which can be correlated with a Jahn-Teller distortion of the octahedral coordination of the ions. This rutile structure type is associated with smaller cations and, for comparison, although zinc difluoride has the same rutile structure, cadmium and mercury difluorides have the cubic fluorite structure with eight coordination of the cations (12). 

When subjected to high temperatures and pressures, polymorphs have been prepared for some of the difluorides. These all have distorted variants of the fluorite structure, with cubic, or pseudocubic, tetragonal cells. Manganese difluoride has been most studied (28-30) and similar polymorphism reported for cobalt and zinc difluorides (30). Recently, palladium and silver difluorides have been shown to behave in a similar way forming cubic metastable phases (31). In all cases there is a decrease in volume for the structure change. 

All observed X-ray reflexions, were with the exception of the faint lines of palladium metal, indexed on a tetragonal cell of the rutile type. Since only one of the palladium reflexions overlapped with a difluoride reflexion the presence of metal did not interfere with the structure determination. The dimensions of the bi-molecular imit cell are compared below with those given by Ebert. 

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