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We study the electronic structure and magnetic interactions inmethylamine-intercalated orthorhombic alkali-doped fullerene (CH3NH2)K3C60within the density functional theory. As in the simpler ammonia intercalatedcompound (NH3)K3C60, the orthorhombic crystal-field anisotropy \Delta lifts thet1u triple degeneracy at the \Gamma point and drives the system deep into theMott-insulating phase. However, the computed \Delta and conduction electronbandwidth W cannot alone account for the abnormally low experimental N\'eeltemperature, T_N = 11 K of the methylamine compound, compared to the muchhigher value T_N = 40 K of the ammonia one. Significant interactions betweenCH3NH2 and C60^{3-} are responsible for the stabilization of particularpseudo-Jahn-Teller fullerene-cage distortions and the ensuing low-spin S = 1/2state. These interactions also seem to affect the magnetic properties, asinterfullerene exchange interactions depend on the relative orientation ofpseudo-Jahn-Teller distortions of neighboring C60^{3-} molecules. For theferro-orientational order of CH3NH2-K^+ groups we find an apparent reduceddimensionality in magnetic exchange interactions, which may explain thesuppressed N\'eel temperature. The disorder in exchange interactions caused byorientational disorder of CH3NH2-K^+ groups could further contribute to thissuppression.

Orthorhombic fulleride (CH3NH2)K3C60 close to Mott-Hubbard instability: Ab initio study