Using analysis of the magnetization data in the α-a n dβ-phase of copper phthalocyanine (CuPc) samples, the electronic state of Cu and exchange interactions are reported. After verifying the crystal structure of the powder samples using x-ray diffraction, the temperature dependence (2 K to 250 K) of the magnetization M of both samples was measured in magnetic field H = 1 kOe and isothermally at 2 K and 5 K in H up to 90 kOe. The data were analyzed first using the modified Curie-Weiss law, χ = χ

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... o + C/( T + θ), showing good fit for T > 4K and yielding θ = 2.3K( 0 . 2K )f o rα-CuPc (β-CuPc) and spin S = ½characteristic of Cu 2+ . The data were next fitted to the Bonner-Fisher model for S =1/2 antiferromagnetic Heisenberg chain showing excellent fit to all the M vs. T data and yielding the Cu 2+ -Cu 2+ exchange constant J/k B =3.4 K ( 0.4 K) the for α-CuPc (β-CuPc). The isothermal data of M vs. H is analyzed taking exchange coupling into account. The large difference in the magnitudes of J/k B for the two phases is discussed in terms of the differences in their crystal structures.