MAGNETIC GROUND-STATE AND ITS CONTROL IN PORPHYRIN-BASED MAGNETS

Alternating metalloporphyrin-acceptor systems provide a 'laboratory' f or study of quasi-one-dimensional magnetic phenomena. For example, the ylporphyrinatomanganate(III)][hexacyanobutadiene], [MnOEP][HCBD], com pound is a model alternating classical (spin 2) and quantum (spin 1/2) spin system. While the high temperature susceptibility is well fit to Seiden's model for alternating S = 2 and S = 1/2 chains with antiferr omagnetic exchange J/k(B) = 172 K, and g for [MnOEP] = 1.92, the low t emperature data reveal a transition to a two-dimensional antiferromagn et, followed by a transition to a three-dimensional canted antiferroma gnet The similarly structured yl-porphyrinatomaganate(III)][tetracyano ethenide], [MnTPP][TCNE], also has ferrimagnetic behavior within the c hains, though it has ferromagnetic interactions between the chains. We associate the change in sign of interchain exchange (from antiferroma gnetic to ferromagnetic) with an increase in interchain separation and a change in the interchain exchange pathways. Subtle disorder, the ma gnitude of which depends upon the solvent incorporated within the stru cture, causes cluster glass-like behavior at low temperatures. The rol es of the various constituents of these compounds in determining the f erromagnetic or antiferromagnetic nature of the ground state are discu ssed.