Mononuclear nickel(II) and copper(II) complexes, namely, (C6H9N2)2[Ni(ntaH)2] (1), (C5H7N2)2[Cu(mal)2(H2O)2] (2), and (C5H7N2)4[Ni(mal)2(H2O)2](NO3)2 (3) [ntaH3 = nitrilotriacetic acid; C6H8N2H = protonated 2-amino-4-picoline; malH2 = malonic acid; C5H7N2 = protonated 2-aminopyridine] have been synthesized in water and their crystal structures have been determined by single crystal X-ray diffraction. In all the complexes, robust bimolecular cyclic hydrogen bonding R22(8) motifs are observed between the protonated heteroaromatic N-rings and the metal-carboxylate complexes. Moreover, the aromatic molecules are engaged in carbonyl···π and anion···π interactions with the noncoordinated carbonyl moieties of the metal complexes and with a nitrate ion respectively, giving rise to remarkable carbonyl···π/π···π/carbonyl···π and carbonyl···π/π···π/π···anion interactions having sandwich type topologies. In 1 and 3, the carbonyl···π interactions are one of the weak forces responsible for the stabilization of the fina...