Ligand field parameters and the ground state of Fe(II) phthalocyanine.

A judicious analysis of previously published experimental data leads one to conclude that the ground state of iron(II) phthalocyanine is an orbitally degenerate spin triplet a(1g)(2) e(g)(↑↓↑) b(2g)(↑) ((3)Eg). The ligand field parameters, in relation to Racah's C, are approximately as follows: B20∕C = 0.84, B40∕C = 0.0074. The uniqueness of this result is demonstrated by means of a special diagram in the B20∕C - B40∕C plane (under additional conditions that B44∕B40 = 35∕3 and B∕C = 0.227). The system is in a strong-ligand-field regime, which enables the use of single-determinant techniques corrected for correlations within the 3d shell of Fe.