FERROMAGNETISM IN A NEW STRUCTURAL PHASE OF [FE(C(5)ME(5))(2)][TCNQ]

The five integrated-stack charge-transfer salts [M(C(5)Me(5))(2)][TCNQ ] (M=Mn, Cr) and [M(C(5)Me(5))(2)][TCNE] (M=Fe, Mn, Cr) are bulk ferro magnets, whereas [Fe(C(5)Me(5))(2)][TCNQ] was reported to exist as two different phases, a metamagnet and a paramagnet. We now report that w ith careful control of the crystallization conditions, it is possible to isolate a new structural phase of [Fe(C(5)Me(5))(2)][TCNQ] which is a bulk 3-D ferromagnet with T-c = 3.1 K. Thus [Fe(C(5)Me(5))(2)][TCNQ ] is the first example of a single compound giving rise to three disti nctly different magnetic phenomena, a finding that will permit an asse ssment of the subtle structural features that control magnetic orderin g in this class of materials.