Paramagnetic Anisotropy, Low Temperature Magnetization, and Electronic Structure of Iron(II) Phthalocyanine

Magnetic anisotropy, magnetization, and average magnetic susceptibility have been measured for iron (II) phthalocyanine. The anisotropy was measured from the room temperature to about 90°K, the average susceptibility from 296 to 1.57°K, and the magnetization was measured at 1.57°K for field strengths between 1100 and 15 000 Oe. The results are interpreted in terms of a ${}^3{B}_{\text{2g}}$ ground state with a zero‐field splitting parameter $\text{D\hspace{0.17em}=\hspace{0.17em}64}{\mathrm{cm}}^{\text{−1}},\mathrm{and}{g}_{\Vert }{\mathrm{\hspace{0.17em}=\hspace{0.17em}g}}_{\perp }\text{\hspace{0.17em}=\hspace{0.17em}2.74}$ . Iron (II) phthalocyanine is an unusual example in which a large magnetic anisotropy arises entirely from the zero‐field splitting. The danger inherent in the existing method of evaluation of ligand‐field parameters from the average magnetic susceptibility data has been highlighted, and the advantages of magnetic anisotropy studies in deducing the ligand‐field parameters and the electronic structures are discussed. A change of about 70° of the “setting angle” between 290 and 90°K is observed in this crystal when measured with $b$ axis vertical. It is shown that this change is not indicative of a change in the ligand‐field parameters with temperature, as generally assumed previously, but depends on the temperature dependence of the ratio of principal susceptibilities.