Polynuclear platinum complexes deriving from squaric acid

Abstract The squarate ion (C 4 O 4 ) 2− does not substitute for chlorine in K 2 [PtCl 4 ] or in (NH 3 ) 2 PtCl 2 but it reacts with the ‘ cis -dichlorodiammine hydrolysis products’ to yield two complexes. The first one ( 1 ) can be described from the results of an X-ray diffraction study as a tetranuclear chain of platinum atoms bridged by squaric anions. The second one ( II ) is an amorphous blue compound with the platinum atom in a formal oxidation state of 2.5. A structure involving dinuclear entities is proposed for II on the basis of XPS, EPR and LAXS analysis. Oxidation of I by nitric acid in the presence of X − (X − Cl − or Br − ) generates products IV and V involving an oxidation of 3.0 for platinum. Considering the whole set of complexes derived from squaric acid points to significant similitudes with the ‘amide platinum blues’.