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Abstract:
Three ion pair complexes,
[4-R-benzylpyridinium][bis(maleodinitriledithiolato)platinum(III)]
(abbreviated as [RBzPy]-[Pt(mnt)(2)]; R = Cl (1), Br (2), or NO2 (3)),
have been synthesized. The cations and anions stack into well-separated
columns in the solid state, and the Pt(III) ions form a 1-D zigzag
chain within a [Pt(mnt)(2)](-) column through Pt...S, S...S, and
Pt...S...Pt interactions. The chain is uniform in 1 and 2, while it
alternates in 3. Unusual magnetic phase transitions from paramagnetism
to diamagnetism were observed in these three complexes at similar to275
K for 1, similar to269 K for 2, and similar to184 K for 3. These phase
transitions were also found in DSC measurements for 1 and 2. The
overall magnetic behaviors for 1-3 indicate the presence of
antiferromagnetic exchange interactions in the high-temperature phase
and spin-gapped systems in the low-temperature phase. Below 50 K, 2
exhibits weak ferromagnetism. The spontaneous moments are nearly
repressed by a field of 1.0 T. The crystal structure of 2 at 173 K
reveals that there are two crystallographically independent
[Pt(mnt)(2)](-) entries in an asymmetric unit. These two
crystallographically independent [Pt(mnt)(2)](-) entries satisfy the
spin-canting condition, and the EPR spectra measured at room
temperature exhibit anisotropic character. Therefore, the weak
ferromagnetic behavior in the low-temperature region for 2 can be
attributed to the spin-canting phenomenon.
