Synthetic Metals, 19 (1987) 781-785 7 81 MAGNETIC TRANSITIONS IN A MOLECULAR METAL WITH EMBEDDED LOCAL MOMENTS: Cu(pc)l MICHAEL Y. OGAWA, SHARON M. PALMER, JENS MARTINSEN, JUDITH L. BRIAN M. HOFFMAN and JAMES A. IBERS Department of Chemistry and Materials Research Center, Northwestern University, Evanston, IL 60201 (U.S.A.) SOONCHIL LEE, MICHAEL YUDKOWSKY and WILLIAM P. HALPERIN Department of Physics and Astronomy and Materials Research Center, Northwestern University, Evanston, IL 60201 (U.S.A.) STANTON, ABSTRACT We discuss the low temperature magnetic properties of (phthalocyaninato)- copper(ll) iodide (Cu(pc)l). This molecular metal contains conductive stacks that incorporate a one-dlmenslonal array of local Cu+2 moments strongly coupled to conduction electrons. Below 20K, the EPR g-value of the coupled spln system increases anomalously and at 8K the EPR signal broadens abruptly and becomes unobservable. Anomalies in the proton NMR spin-lattice relaxation times are observed at the transition temperature. Preliminary EPR experiments conducted on a newly synthesized series of materials, CuxNil_x(PC)l, indicate the existence of a slmllar low temperature transition in the presence of various concentrations of local moments. INTRODUCTION The metallophthalocyanlnes, M(pc), are ideal buildlng blocks for con- structing highly conducting molecular crystals. Partial oxldatlon of these metallomacroeycle complexes results in the formation of an isolonlc and isostructural family of molecular conductors that displays a variety of Interesting properties [I-4]. These compounds, havlng the stolchlometry M(pc)l, exist as metal-over-metal stacks of metallomacrocycles surrounded by channels contalnlng linear chains of trliodlde anlons. A full description of the structure of a typical M(pc)l conductor is glven in reference Is. An advantage of studying metallomacrocycle-based molecular conductors is that the chemical flexibility of these molecules allows for the possibility of incorporating paramagnetlc metal centers directly into the conductive frame- 0379-6779/87/$3.50 © Elsevier Sequoia/Printed in The Netherlands