Crystal-Structures And Magnetic-Properties Of (M-Pyridinium-Nitronyl-Nitroxide)+Center-Dot-X- - Possible Spin-1 Kagome Antiferromagnet

Crystal structures and magnetic properties of m-N-methylpyridinium nitronyl nitroxide (abbreviated as m-MPYNN+) salts were studied. m-MPYNN+. ClO4-.(1/3)(acetone) is found to crystallize into the trigonal P3c1 space group, where the m-MPYNN+ molecules exist as a dimer and the dimer units form a 2-D triangular lattice. Temperature dependence of the magnetic susceptibility can be well interpreted in terms of a strong ferromagnetic intradimer interaction J(1) forming a triplet state and a weak antiferromagnetic interdimer interaction J(2). There is a possibility that this spin system can be characterized as a spin-1 Kagome antiferromagnet at very low temperatures. m-MPYNN+ makes salts with various anions, I-, Cl-, BF4-, ClO4- etc. and their mixtures. In an isostructural solid-solution system, m-MPYNN+.(ClO4-)(x) . l-(1-x).(1/3)(acetone) (0 less than or equal to x less than or equal to 1), J(2) quickly weakens with increasing the ratio of the ClO4- ion, in contrast to little dependence of J(1).