Abstract
The structural features of the ammoniated (NH3)K3C60 fulleride are studied by synchrotron X-ray powder diffraction as a function of pressure to 6.7 GPa. A superstructure appears at 1 GPa as a result of orientational ordering of both the C60 and K+-NH3 units (orthorhombic symmetry, space group Fddd). The pressure evolution of the lattice constants reveals a highly compressible, strongly anisotropic structure. The centre-to-centre interfullerene separations of 10.40 Åin the basal plane are comparable to those in the superconducting cubic analogue, RbCs2C60 and evidently sufficiently short to drive the system superconducting, despite its low crystal symmetry.