Crystal structures and magnetic properties of (m-pyridinium nitronyl nitroxide)+·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−·(13)(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 trinagular lattice. Temperature dependence of the magnetic susceptibility can be well interpreted in terms of a strong ferromagnetic intradimer interaction J1 forming a triplet state and a weak antiferromagnetic interdimer interaction J2. 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(13)(acetone) (0≤x≤1), J2 quickly weakens with increasing the ratio of the ClO4- ion, in contrast to little dependence of J1.