Postsynthetic modification is a promising tool for introducing multifunctional properties in metal organic frameworks (MOFs). The effects of postsynthetic metal addition/exchange in a barium-based MOF have been well examined toward their magnetic and electrical properties: The rattling motion of the extra framework organic cation is, responsible for the ferroelectric behavior. The strong magnetic frustration in Tb@l is found to arise from the nearly triangular arrangement of :Tb3+ ions in its secondary building unit along the chain direction.