EPR studies on halogen-bridged one-dimensional Pt(II)-Pt(IV) mixed-valence complexes, Pt(en)₂X(ClO₄)₂

Abstract

The platinum(III) state in single crystals of Pt(en)2X(ClO4)2 (X=Cl, Br and I) has been detected by EPR. The values of g/sub /// and gperpendicular to have been determined to be 1.956 and 2.299 respectively for X=Cl, 1.980 and 2.276 respectively for X=Br, and 1.962 and 2.253 respectively for X=I at 295K. Hyperfine splitting was observed below 150K in X=Cl. Its intensity ratio with the magnetic field perpendicular to the b axis shows that the two adjacent platinum ions with total nuclear spin I=0, 1/2 and 1 contribute to the hyperfine structure with the following values assigned to A:A/sub ///=610 and Aperpendicular to =379, in units of 10-4 cm-1 at 77K. As for X=Br and I, the signal remains unsplit being a broad line with width 200 G down to 4.2K. Above 100K, line narrowing was observed with activation energies 5.9 and 8.5 meV respectively. The spin concentrations were determined to be of the order of 1020 mol-1 for all salts at 295K. The electrical conduction mechanism in these chain complexes are suggested to be based on EPR and optical absorption data.