ELSEVIER Synthetic Metals 85 (1997) 1695-1700 Long-range magnetic order in the quasi-HI metalloporphyrin family of molecule-based magnets* C. M. Wynn”, M. A. Girtu”, K-I. Sugiurab, E. J. Brandonb, J. L. Mansonb, Joel S. Mille?, A. J. Epstein”’ “Department of Physics, The Ohio State University, Columbus, OH 43210-1106, USA bDepartment of Chemistry, Universiry of Utah, Salt Lake City, UT 84112, USA ‘Department of Chemistry, The Ohio State University, Columbus, OH 43210-1106, USA Abstract The unusual magnetic properties of various members of the quasi-1D manganese-porphyrin family are reviewed. Typical members of the family consist of spin S = 2 Mn”‘porphyrin ions alternating with trans-&-bonded spin s = l/2 acceptors [C,(CN),]’ or [C,(CN),]-. All members exhibit ID behavior at high temperatures as evidenced by their similarities to predictions for mixed quantum- classical ferrimagnetic chains. Below approximately SO K, deviations from one-dimensionality are observed due to the effects of interchain interactions. The competition between interchain exchange, single-ion anisotropy, and dipolar interactions are considered when examining the remarkable differences in the low temperature magnetic states of the various compounds. Keywords: Magnetic measurements, Magnetic phase transitions I. Introduction The manipulation of the magnetic ground state of new materials has been the object of an ever-increasing amount of experimental research because of the potential for new fundamental science and a variety of useful technological applications. Molecule-based magnets provide many advantages over traditional atomic-based systems including the flexibility of synthetic chemistry and enhanced processability. The metalloporphyrin electron-transfer family represents an important class of molecule-based magnetsLz3 This quasi-1D family consists of extended linear chains comprised of (S = 2) Mn”‘porphyrin cations alternating with trans-,&-bonded (s = l/2) anions TCNB or HCBD’ (TCNE = tetracyanoethylene, HCBD = hexacyanobutadiene). In recent years, many new members of this family have been synthesized and structurally characterized. Small structural differences among the members are observed to produce significant changes in the bulk properties, leading to a variety of different magnetic phenomena. This family presents an opportunity to probe the physics of one-dimensional systems in order to better understand the relationship between the microscopic and the bulk behavior. In particular, the effects of disorder, the creation of a spontaneous moment and the factors influencing the ordering temperature can be examined. * This work supported in ptis by the DOE under Grant Nos. DE-FGOZ86BR45271 and DE-FG03-93ER45504, and by the NSF under Grant No. CHE9320478. This paper presents an overview of the family while highlighting some of the more interesting members. Parameters influencing the magnetic state and their relative importance, including the intra- and interchain exchange (Ji,,, and J,,,,,), dipole interactions, single-ion anisotropy (SIA) and disorder are discussed. 2. Experimental Structural characterization of the various members was performed using single-crystal X-ray diffraction and has been reported elsewhere. ‘, ’ The dc magnetic data was recorded using a Quantum Design MPMS-5 SQUID magnetometer. The dc susceptibility is the ratio of the magnetization, M, and field, H, xdc = M/H (assuming a linear response of M on H). The ac susceptibility was measured with a Lake Shore ac susceptometer model 7225 using various ac driving frequencies and amplitudes. A lock-in amplifier allowed phase sensitive detection such that both the in-phase (x’) and out-of-phase (x”) susceptibilities were measured. Powder samples were sealed in quartz sample holders in an argon environment to avoid exposure to air. The diamagnetism of the sample holders was measured in situ. All susceptibilities have been corrected for both core diamagnetism and sample holder diamagnetism. 0379-6779/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved PII 80379-6779(96)04553-5