JOURNAL OF MAGNETIC RESONANCE 37, 217-222 (1980) Magnetic Susceptibility and EPR Changes Caused by Grinding of Samples K. M. MORE AND G. R. EATON Department of Chemistry, University of Denver, Denver, Colorado 80208 AND S. S. EATON Degartment of Chemistry, University of Colorado at Denver, Denver, Colorado 80202 Received June 4, 1979 EPR signals were observed in four metal-free porphyrins. The intensity of the EPR signal increased upon grinding the sample, and then decreased upon evacuation of the sample. The lineshape of the EPR signal and the magnetic susceptibility of seven copper porphyrins changed when the samples were ground. INTRODUCTION Many years ago it was observed that metal-free phthalocyanines and certain complexes of phthalocyanines with metals which are diamagnetic in their common oxidation states gave EPR signals (1). Recent comment on these results attributed them to “partial oxidation or impurities” (2). It was also observed that the process of powdering graphite resulted in the generation of EPR signals (3). We now report the observation of EPR signals in metal-free porphyrins and changes in the EPR signals and magnetic susceptibility of copper porphyrins upon grinding of the sample. EXPERIMENTAL EPR spectra were run on a Varian E-9 EPR spectrometer interfaced to a Varian 620L computer as previously described (4). All spectra on solid samples were run in the same 4-mm quartz tube using 10 to 20 mg of sample. The tube was designed to position the sample at the center of the cavity. Magnetic susceptibilities were measured at four field strengths on a Bruker Faraday balance with l-kg sensitivity. HgCo(SCN)4 was used as the susceptibility standard (5). Based on measurements of the magnetic susceptibilities of three free porphyrins a value of -700 x iOe6 was used as the diamagnetic correction for H2TPP. The temperature-independent paramagnetism of Cu(I1) was assumed to be 60x 10e6 (4). The porphyrins and metalloporphyrins were prepared by standard methods (6) as part of another study. All compounds studied were purified by chromatography on alumina or silica gel 217 0022-2364/80/020!217-06$02.00/0 Copyright @I IYSO by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain