Magneto-Structural Correlations in a 1,3,2-Dithiazolyl Radical Crystal, BBDTA⋅GaBr₄: Structure and Magnetic Properties of its Three Polymorphs

We investigate the preparation, crystal growth, crystal structure, and magnetic properties of the three polymorphs (alpha, beta, and gamma) of an organic magnet, BBDTA(= benzo[1,2-d:4,5-d'] bis[1,3,2]dithiazole) x GaBr(4), which is an S-1/2 system. In the alpha phase, BBDTA(+) units form a square-planar lattice, and show canted antiferromagnetism with a magnetic coupling constant J/k(B) of -18 K and a canting angle of 0.15 degrees below 15.5 K. The beta phase is composed of a ferromagnetic regular chain with a J/k(B) value of +4.5 K and a strong antiferromagnetic chain with J/k(B) = -99 K, and shows ferromagnetic ordering in spins of purely the ferromagnetic chain below 0.4 K. The gamma phase is isostructural with gamma-BBDTA x GaCl(4), which is an organic ferromagnet below 7.0 K, and possesses antiferromagnetic interactions of J/k(B) = -60 K between BBDTA(+) cations, and shows no magnetic ordering until 2 K. The magnetic properties of these phases are quite sensitive to the molecular alignment in the crystals.