Alkali metal imidazolates are important compounds, serving as intermediates in organic synthesis and additives in alkali ion electrolytes. However, their solid-state structures and thermal behaviors remain largely unexplored. In this study, we present the synthesis, structural analysis, and thermal characterization of lithium and sodium benzimidazolate (bim-). The crystal structures of these microcrystalline materials, determined by 3D electron diffraction, reveal closely related layered coordination networks. In these structures, 4-fold N-coordinated alkali ions are bridged in two dimensions by bim- linkers, with the networks’ surfaces decorated by the phenyl rings of the bim- linkers, stacking atop one another in the solid state. Differential scanning calorimetry combined with variable temperature X-ray powder diffraction indicates that both materials melt above 450 °C. Additionally, Na(bim) undergoes a displacive phase transition from an ordered α-phase to a highly disordered β-phase before melting. Structural variations, primarily attributable to the differing ionic radii of Li+ and Na+, result in distinct coordination environments of the alkali metal ions and varying orientations of the bim- linkers. These differences lead to markedly distinct thermal behaviors: Li(bim) exhibits positive thermal expansion along all crystal axes, whereas Na(bim) switches from area negative thermal expansion (NTE) to linear NTE during the α → β phase transition.