New cobalt (II) complexes of general formula [Co(L) (NO3) (H2O)2]·NO3 (L = methyl 2-(pyridine-2yl-methylene) hydrazinecarboxylate, C8H9N3O2 (2-PYMC) (1) and ethyl 2-(pyridine-2yl-methylene) hydrazinecarboxylate, C9H11N3O2 (2-PYEC) (2), have been synthesized and characterized by elemental analysis, UV–vis, IR, and photoluminescence measurements. The crystal structures of 1 and 2 reveal the presence of CoN2O5 pentagonal-bipyramidal coordination polyhedra in each complex: the basal plane consists of an N, N, O-tridentate 2-PYMC/2-PYEC ligand and a chelating nitrate anion and the axial sites are occupied by water molecules. The crystal structures are consolidated by O–H⋯O and C–H⋯O hydrogen bonds. © 2019 Elsevier B.V.