The tetratertiary phosphine tris-(o-diphenylphosphinophenyl)phosphine, QP, forms iron(II) complexes [FeX(QP)]+(X = Cl, Br, and I) which are pentaco-ordinate, have µeff. values of about 3 B.M., and have been assigned trigonal bipyramidal structure, and also [FeX2(QP)](X = NCS and CN) which are hexaco-ordinate and diamagnetic.