The magnetic behavior of Mn(SCN)2(CH3OH)2 in single-crystal form has been studied, and the crystal structure has also been determined. The system is monoclinic, C2/c, Z=4 with a=14.467(5), b=5.927(2), c=10.979(3), and 2=93.19(3)°. Manganese ions, of distorted octahedral coordination, are coupled together into quasi-two-dimensional arrays by bridging thiocyanate groups, and also by some hydrogen bonding. Potential interlayer-superexchange pathways are substantially less efficient, though probably not insignificant either. The magnetic properties seem consistent with the structural features. The single-crystal susceptibility exhibits uniaxial anisotropy in the paramagnetic regime, with a* somewhat larger than bc. A broad maximum appears at 12.6(4) K in b and c, and a sharper maximum at 10.5 K in a*. An antiferromagnetic transition at 10.5(2) K is also apparent in the b- and c-axis susceptibilities, and below this temperature substantial anisotropies appear. A weak ferromagnetic moment develops along the b axis below 10.5 K, and from the magnitude of the spontaneous moment along this axis it is deduced that the spins are canted 0.20°from the c axis toward b. A possible spin-reorientation transition at 3.75 K is also apparent. High-temperature series-expansion fits to the susceptibilities suggest that a two-dimensional Heisenberg model is appropriate, but that interlayer exchange cannot be neglected; derived parameters are J/k=-0.70(3) K and J/k=-0.16(2) K. The anisotropy observed in the paramagnetic regime suggests that a rather strong single-ion anisotropy of the form D[S Sz2(S+1)/3], with D/k=0.29(2) K, is also present. The results are compared with various theoretical predictions for two-dimensional and three-dimensional models, and it appears that the system is more or less intermediate between these two lattice dimensionalities. The canting that is observed is almost certainly due to site-inequivalent single-ion anisotropy rather than to antisymmetric exchange. A detailed consideration of intralayer- and interlayer-superexchange pathways is also presented, and rather satisfactorily accounts for the observed differences in exchange interactions between this system and the analogous ethanol compound. © 1990 The American Physical Society.
