Structural Studies of Partially Oxidized One-dimensional Bis(oxalato)-platinate Salts Containing Bivalent Cations: Ni0.84[Pt(C2O4)2]·6H2O

Fundamental structure, kF and 2kF satellite reflections, and electrical properties of Ni0.84[Pt(C2O4)2]·6H2O (Ni–OP) were determined. Complex Ni–OP crystallizes in the orthorhombic space group Pccn with cell parameters of a=14.296(2), b=16.387(3), and c=5.671(1) A and Z=4. Ni–OP is essentially isostructural with Mg–OP (Mg0.82[Pt(C2O4)2]·5.3H2O) and Co–OP (Co0.83[Pt(C2O4)2]·6H2O). The space group of Mg–OP and Co–OP is Cccm. Owing to the change in the space group, there are two independent Pt chains in Ni–OP. X-Ray studies of M–OP (M=Co, Ni) show that there exist strong kF satellite spots and weak 2kF spots. One M2+ cation is vacant per period of the lattice modulation wave of the platinum chain, λ2kF. The periodic cation defect induces the kF modulation waves. The 2kF waves do not have a Peierls origin but are induced by the kF modulation wave. A second order phase transition is observed at about 305 K above which the 2kF spots disappear.