We report on neutron powder-diffraction experiments, inelastic incoherent neutron-scattering experiments, and density-functional calculations on dynamics, order and disorder properties of and . From refinement of structure at 10 and 302 K, we found an almost ideal tetrahedral geometry of ions (difference between shortest and longest interatomic distances is less than 4% for B-D bond, and less than 3% for D-D bond), close to the calculated geometry. A quantitative agreement was found between experimental and calculated anisotropic temperature factors of individual atoms. For phonon energies , the phonon density of states of in the low-temperature phase depends quadratically on the phonon energy while for the high-temperature phase a linear dependence is observed, revealing a high lattice anharmonicity in the high-temperature phase. Moreover, an increased phonon density of states at low energies in the high-temperature phase compared to the low-temperature phase give a direct evidence for disorder in the high-temperature phase of of the hydrogen sublattice which can originate from orientational disorder of units. Potential energy landscape for rotation of indicates that fairly localized minima and barriers higher than 0.6 eV exist in the low-temperature phase, i.e., ordered ions. The high-temperature structure shows shallow barriers of without distinct energy minima, i.e., orientation of a single unit cannot be precisely defined. This corroborates the large thermal displacements observed in diffraction studies and high disorder of ions deduced from experimental partial phonon density of states in the high-temperature phase.