Transforming abundant thermal energy into electrical energy is an essential and sustainable solution to meet the rapidly growing global energy demand. In this communication, we report an electrical poling-free molecular complex [Zn(bpy)3](ClO4)2·H2O (1) with an appreciable pyroelectric coefficient value of 25 μC m-2 K-1. This allowed us to harvest waste heat energy using a pyroelectric nanogenerator (PyG) device of 1, a relatively unexplored area for molecular complexes.