Abstract: Coordination compounds of nickel(II) and copper(II) 1,5-naphthalenedisulfonates with nicotinamides, [Ni(L)2(H2O)4](Nds) · 3H2O (I) and [Cu(L)2(H2O)4](Nds) (II) (L = nicotinamide, NC5H4C(O)NH2, Nds2 = doubly deprotonated 1,5-naphthaledisulfonate anion, C10H6(SO3)2 2-, were synthesized and studied by IR and diffuse reflectance spectroscopy. The crystal structures of I and II were determined by X-ray diffraction (CIF files CCDC nos. 1863367 (I) and 1863368 (II)). In both structures, the Ni and Cu atoms are coordinated by two nitrogen atoms of two monodentate L ligands and by four oxygen atoms of water molecules. The coordination polyhedron of Ni in I is a slightly distorted octahedron and that of Cu in II is a tetragonal (4 + 2) bipyramid extended due to the Jahn–Teller effect, with the O(H2O) atoms in the axial positions. The [M(L)2(H2O)4]2+ complex cations, the Nds2– anions, and water molecules of crystallization in II are combined by a branched network of hydrogen bonds. © 2019, Pleiades Publishing, Ltd.